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snake_dizzy/viewtopicphpt4402.txt | [ ](./index.php?sid=fcc51776967bd876dfb289ced6b6e848 "Board index")
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## [ Crotalus (or any other snake) self envenomation)
](./viewtopic.php?t=4402&sid=fcc51776967bd876dfb289ced6b6e848)
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7 posts • Page **1** of **1**
[ ADCIII
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**Posts:** [ 100 ](./search.php?author_id=1160&sr=posts&sid=fcc51776967bd876dfb289ced6b6e848)
**Joined:** August 26th, 2010, 10:56 am
### [ Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=52678&sid=fcc51776967bd876dfb289ced6b6e848#p52678)
* [ __ Quote ](./posting.php?mode=quote&p=52678&sid=fcc51776967bd876dfb289ced6b6e848 "Reply with quote")
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by **[ ADCIII
](./memberlist.php?mode=viewprofile&u=1160&sid=fcc51776967bd876dfb289ced6b6e848)
** » February 14th, 2011, 11:04 am
Are there any documented cases of snakes biting themselves to cause their own
deaths? I was witness to two possible cases of self envenomation. One was a
tigris which was caught by hand, placed in a capture sack, hung on the
collectors belt, and when the sack was opened one half hour later, was dead.
The second was a gravid willardi which was captured by tongs with virtually
the same result. I had dismissed the remarks that "they bit themselves" to
other circumstances that could have happened, but now have the question that
maybe this might have been true. Are Crotalus immune to their own venom? Have
any studies been done on this ? I am sorry if this topic has been gone over
before, but I am a relatively new member to NAFTA. Thanks, Art
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[ Chris Smith
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**Posts:** [ 2291 ](./search.php?author_id=307&sr=posts&sid=fcc51776967bd876dfb289ced6b6e848)
**Joined:** June 7th, 2010, 9:13 pm
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### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=52687&sid=fcc51776967bd876dfb289ced6b6e848#p52687)
* [ __ Quote ](./posting.php?mode=quote&p=52687&sid=fcc51776967bd876dfb289ced6b6e848 "Reply with quote")
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by **[ Chris Smith
](./memberlist.php?mode=viewprofile&u=307&sid=fcc51776967bd876dfb289ced6b6e848)
** » February 14th, 2011, 11:49 am
I cannot comment on whether or not they are immune to their own venom, but it
is certainly possible that a fang puncture wound alone to the right area
(lung, heart, etc...) could cause death. I have personally seen venomous
snakes bite themselves and live a full life, but getting envenomated directly
into an organ might be enough to kill a snake (even if it is normally immune
to the venom).
Hopefully someone with more knowledge will chime in.
-Chris
P.s. I am pretty sure Crotalus willardi are protected across their range ( [
USFWS
](https://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=C01S)
). Collecting is a no-no!!
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[ ADCIII
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**Posts:** [ 100 ](./search.php?author_id=1160&sr=posts&sid=fcc51776967bd876dfb289ced6b6e848)
**Joined:** August 26th, 2010, 10:56 am
### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=52733&sid=fcc51776967bd876dfb289ced6b6e848#p52733)
* [ __ Quote ](./posting.php?mode=quote&p=52733&sid=fcc51776967bd876dfb289ced6b6e848 "Reply with quote")
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by **[ ADCIII
](./memberlist.php?mode=viewprofile&u=1160&sid=fcc51776967bd876dfb289ced6b6e848)
** » February 14th, 2011, 3:41 pm
> P.s. I am pretty sure Crotalus willardi are protected across their range ( [
> USFWS
> ](https://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=C01S)
> ). Collecting is a no-no!!
The specimen was collected well before the ban. In 1963 I Believe.
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[ VICtort
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**Joined:** July 2nd, 2010, 6:48 pm
**Location:** AZ.
### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=53934&sid=fcc51776967bd876dfb289ced6b6e848#p53934)
* [ __ Quote ](./posting.php?mode=quote&p=53934&sid=fcc51776967bd876dfb289ced6b6e848 "Reply with quote")
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by **[ VICtort
](./memberlist.php?mode=viewprofile&u=850&sid=fcc51776967bd876dfb289ced6b6e848)
** » February 19th, 2011, 8:15 pm
In a somewhat related incident, I was caring for a captive group of _C.
oreganus_ (C.v. oreganus at the time...). These three year olds were very
agressive feeders, and I dropped in a mouse which was quickly envenomated by
no. 1 and released. Another snake, apparently stimulated by the scent and
feeding response, struck and bit the original no. 1 biting snake in the head
and quickly released. I could see a distinct swelling bump, and a droplet of
dark blood on no. 1's head, just behind dorsal and posterior to the eye. No. 1
did not eat the mouse, but seemed to retire to a corner and the mouse was
consumed by no. 2 snake. No. 1 seemed just fine the next day and fed, and
lived to a ripe old age, apparently no long term effect from the venom (if
any...). For sure, it was bit and had at least mechanical damage from a fang,
as evidenced by the blood droplet and slight but dintinct swelling nodule. I
would guess self induced bites may be fairly common, given how excited some
species get when feeding (i.e. cottonmouths, cantils, etc.), and they probably
have evolved some resistance to venoms...? Vic
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[ ADCIII
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**Posts:** [ 100 ](./search.php?author_id=1160&sr=posts&sid=fcc51776967bd876dfb289ced6b6e848)
**Joined:** August 26th, 2010, 10:56 am
### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=53988&sid=fcc51776967bd876dfb289ced6b6e848#p53988)
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by **[ ADCIII
](./memberlist.php?mode=viewprofile&u=1160&sid=fcc51776967bd876dfb289ced6b6e848)
** » February 20th, 2011, 9:54 am
Vic, Very interesting, that indicates it was an intended bite rather than a
dry one, and that there were no lasting complications. Thanks, Art
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[ hellihooks
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### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=53989&sid=fcc51776967bd876dfb289ced6b6e848#p53989)
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by **[ hellihooks
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** » February 20th, 2011, 9:59 am
I had a helli bite a ruber... the ruber suffered significant tissue necrosis
at the site, and ended up dying.  Jim
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### [ Re: Crotalus (or any other snake) self envenomation)
](./viewtopic.php?p=54807&sid=fcc51776967bd876dfb289ced6b6e848#p54807)
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by **[ Jeremy Westerman
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** » February 23rd, 2011, 3:28 pm
A friend of mine lost a cobra to a self inflicted bite but it was prolonged
and infected, certainly not the venom.
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| biology | 46835 | https://no.wikipedia.org/wiki/Color%20Line | Color Line | Color Line er et norsk fergeselskap, eid av Color Group ASA, som i hovedsak driver kombinerte passasjer-/bilferger fra Norge til Sverige, Danmark og Tyskland. Selskapet ble etablert i 1990, men overtatte og oppkjøpte virksomheter kan føre sin historie mer enn 100 år tilbake i tid. Selskapet har ca. 2 300 ansatte i fire land, av disse er over 2 000 ombord på skipene. Selskapet disponerer fem skip.
Historie
Color Line ble dannet av Jahre Line og Norway Line 1991 og har de senere år overtatt selskaper og linjer som kan trekke sin historie tilbake til 1872, da en ferjeforbindelse mellom Kristiansand og Frederikshavn i Danmark ble startet, etter at Frederikshavn hadde fått jernbaneforbindelse året før. Det første skipet i ruten var DS «Frithjof». Fra 1879 ble ruten drevet av Det Stavangerske Dampskibsselskab, men i 1887 kom Christiania Kyst-Dampskibsselskab med et underbud og fikk driften; de satte inn DS «Nyland». Overfarten tok 11 timer og ruten var svært attraktiv da det var korresponderende tog videre til kontinentet. Fra 1895 satte man også inn DS «Harald Haarfager», de to fartøyene betjente ruten til selskapets konkurs i 1899. Et nytt selskap ble opprettet for å drive ruten videre, A/S Christianssands Dampskibsselskab (senere KDS) tok over begge fartøyene. I 1903 ble DS «Jylland» satt inn i ruten, og i 1912 ble DS «Nyland» erstattet av DS «Skagen». Selskapet ble i 1968 solgt til Fred. Olsen & Co..
I 1961 kom også linjer fra Oslo, drevet av Jahre Line med ferger til Kiel i Tyskland.
Dagens Color Line
Color Line ble etablert i 1990 med utgangspunkt i de to Kosmos-selskapene Jahre Line og Norway Line. Samme år ble også ferjeaktivitetene i Fred. Olsen Lines overtatt.
I 1996 solgte Olav Nils Sunde selskapet Larvik Line AS i konsernet Larvik Scandi Line ASA i mot aksjer i Color Line, Larvik Line AS hadde ferjetrafikken Larvik – Frederikshavn. I 1999 solgte Olav Nils Sunde hele Larvik Scandi Line ASA og det resterende firmaet Scandi Line AS som hadde ferjetrafikken Sandefjord – Strömstad. Samtidig ble Olav Nils Sunde konsernsjef i Color Line. Etter overtagelsen opprettet Color Line AS datterselskapet Color Scandi Line AS som hadde ansvaret for driften og skipene på strekningen Sandefjord-Strømstad som varte frem til 2001 da den ble slått sammen med Color Line AS.
I tillegg til selskapets hovedområde som er fergedrift, drives et hotell i Skagen, Danmark. Hovedaksjonær i Color Group er Olav Nils Sunde.
I 2007 transporterte selskapet 4 279 868 passasjerer. De nye «cruisefergene» MS «Color Fantasy» og MS «Color Magic» ble satt i drift i 2004 og 2007. MS «Color Magic» er verdens største kombinerte passasjer- og roll on/roll off ferge med sine 75 156 BRT og en kapasitet på 2812 passasjerer.
Den 13. mars 2008 gikk jomfruturen for MS SuperSpeed 1, som trafikkerer ruten Kristiansand – Hirtshals. Skipet tilbakelegger strekningen på 3t 15min. Med skipet «Silvia Ana», som i en årrekke har gått i trafikk mellom Kristiansand og Danmark i sommerhalvåret, var overfartstiden kun 2,5 timer. På grunn av økte drivstoffpriser valgte Color Line imidlertid å ta dette skipet ut av drift – og heller satse på en mellomting mellom de to tidligere transportløsningene «Christian IV» og «Silvia Ana». Fjord Line trafikkerer også overfarten Kristiansand-Hirtshals i sommersesongen med et hurtiggående skip. MS «SuperSpeed 1» har ikke lugarer, men forholdsvis store butikkarealer, to restauranter og én bar. Søsterskipet MS «SuperSpeed 2» ble satt inn på ruten Larvik – Hirtshals i juni 2008.
Nedleggelse og oppsigelser
21. november 2007, samtidig som at det ble kjent at Color Festival var solgt, ble det også kjent at ruten Bergen – Stavanger – Hirtshals ble lagt ned da MS «Prinsesse Ragnhild» skulle flyttes over til Oslo og trafikkere ruten Oslo – Hirtshals.
22. april 2008 kom Color Line med en pressemelding; den gikk ut på at den tradisjonsrike ruta mellom Oslo og Hirtshals skulle legges ned med virkning fra 6. mai samme år. MS «Prinsesse Ragnhild» ble i oktober samme år solgt til Celebration Cruise Holdings, Nassau, Bahamas, og opererer som cruiseskip i Karibia.
Selskapets linjer og skip
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Skip som ikke lenger er i trafikk for selskapet
Flåtefornyelse
Color Line gjennomførte i perioden 2004–2008 et omfattende fornyelsesprogram for til sammen 7,5 milliarder kroner med de to cruiseskipene MS «Color Fantasy» og MS «Color Magic», og de to nye hurtiggående SuperSpeed-skipene.
Høsten 2007 solgte selskapet skip for over en milliard kroner.
Alle skipene ble solgt med gevinst i forhold til bokført verdi.
Color Line solgte 22. januar 2007 M/S «Kronprins Harald» til Irish Ferries for 43,6 millioner euro. 19. oktober 2007 ble M/S «Peter Wessel» solgt til MSC (Meditteranean Shipping Company) for 25 millioner euro. 12. november 2007 ble FF «Silvia Ana» solgt til Buquesbus for 16 millioner amerikanske dollar og 21. november 2007, var salget av M/S «Color Festival» til Corsica Ferries for 49 millioner euro et faktum. MS «Prinsesse Ragnhild» ble 3. november 2008 solgt til Celebration Cruise Holdings for ca. 180 millioner kroner.
Color Line bestilte nytt hybridskip i 2017 med 4 MWh batteri, til å seile i 2019.
Trivia
Under Alta-konflikten ble et av Jahre Lines skip chartret av politiet og brukt som flytende hotell for de om lag 800 politifolkene som voktet utbyggingen.
På amerikansk-engelsk er color line en betegnelse på «raseskille».<ref>[https://www.collinsdictionary.com/dictionary/english/color-line#:~:text=A%20color%20line%20is%20the,exist%20between%20different%20racial%20groups. «Color line», Collins dictionary]</ref> Selskapet fikk kritikk for ikke å ha gjort «hjemmeleksen» da det valgte navnet.
Se også
MS «Color Magic»
MS «Color Fantasy»
Referanser
Litteratur
Bruce Peter; Color Line - and the development of Norwegian international Ferry services since 1825'' Ferry Publications 2020 ISBN 978-1-911268-39-0
Eksterne lenker
Larvik-Frederikshavnferjens fartøy, bilder - fra «Fakta om Fartyg»
Næringsliv i Oslo
Norske reiseselskaper
Selskaper etablert i 1990 | norwegian_bokmål | 0.936037 |
kissing_natural_human_activity/Kiss.txt | A kiss is the touch or pressing of one's lips against another person or an object. Cultural connotations of kissing vary widely. Depending on the culture and context, a kiss can express sentiments of love, passion, romance, sexual attraction, sexual activity, sexual arousal, affection, respect, greeting, peace, and good luck, among many others. In some situations, a kiss is a ritual, formal or symbolic gesture indicating devotion, respect, or a sacramental. The word came from Old English cyssan ("to kiss"), in turn from coss ("a kiss").
History[edit]
Anthropologists disagree on whether kissing is an instinctual or learned behaviour. Those who believe kissing to be an instinctual behaviour cite similar behaviours in other animals such as bonobos, which are known to kiss after fighting - possibly to restore peace. Others believe that it is a learned behaviour, having evolved from activities such as suckling or premastication in early human cultures passed on to modern humans. Another theory posits that the practice originated in males during the paleolithic era tasting the saliva of females to test their health in order to determine whether they would make a good partner for procreation. The fact that not all human cultures kiss is used as an argument against kissing being an instinctual behaviour in humans; only around 90% of the human population is believed to practice kissing.
The earliest reference to kissing-like behavior comes from the Vedas, Sanskrit scriptures that informed Hinduism, Buddhism, and Jainism, around 3,500 years ago, according to Vaughn Bryant, an anthropologist at Texas A&M University who specialized in the history of the kiss. However, recent studies challenge the belief that kissing originated in South Asia around 1500 BCE, arguing that there is no single point of origin in historical times. Figurines have been found that indicate kissing may have been practiced in prehistory. It’s been suggested that Neandertals and humans kissed. Evidence from ancient Mesopotamia and Egypt suggests that kissing was documented as early as 2500 BCE. Kissing was present in both romantic and familial contexts in ancient Mesopotamia, but it was subject to social regulation, and public display of the sexual aspect of kissing was discouraged. Kissing also had a role in rituals. The act of kissing may have unintentionally facilitated the transmission of orally transmitted microorganisms, potentially leading to disease. Advances in ancient DNA extraction have revealed pathogen genomes in human remains, including those transmitted through saliva. The shift in dominant lineages of the herpes simplex virus 1 (HSV-1) during the Bronze Age implies that cultural practices like romantic-sexual kissing could have contributed to its transmission. Ancient Mesopotamian medical texts mention a disease called bu'shanu, which may have been related to HSV-1 infection. While kissing itself was not directly associated with disease transmission in Mesopotamia, certain cultural and religious factors governed its practice.
Both lip and tongue kissing are mentioned in Sumerian poetry:
My lips are too small, they know not to kiss.
My precious sweet, lying by my heart,one by one "tonguemaking," one by one.
When my sweet precious, my heart, had lain down too,each of them in turn kissing with the tongue, each in turn.
Kissing is described in the surviving ancient Egyptian love poetry from the New Kingdom, found on papyri excavated at Deir el-Medina:
Finally I will drink life from your lips and wake up from this ever lasting sleep.
The wisdom of the earth in a kiss and everything else in your eyes.
I kiss her before everyone that they all may see my love.
And when her lips are pressed to mine I am made drunk and need not wine.When we kiss, and her warm lips half open,I fly cloud-high without beer!
His kisses on my lips, my breast, my hair......Come! Come! Come! And kiss me when I die,For life, compelling life, is in thy breath;And at that kiss, though in the tomb I lie,I will arise and break the bands of Death.
The earliest reference to kissing in the Old Testament is in Genesis 27:26, when Jacob deceives his father to obtain his blessing:
And his father Isaac said unto him, Come near now, and kiss me, my son.
Genesis 29:11 features the first man-woman kiss in the Bible, when Jacob flees from Esau and goes to the house of his uncle Laban:
And Jacob kissed Rachel, and lifted up his voice, and wept.
Much later, there is the oft-quoted verse from Song of Songs 1:2:
May he kiss me with the kisses of his mouth,for your love is better than wine.
In Cyropaedia (370 BC), Xenophon wrote about the Persian custom of kissing in the lips upon departure while narrating the departure of Cyrus the Great (c. 600 BC) as a boy from his Median kinsmen. According to Herodotus (5th century BC), when two Persians meet, the greeting formula expresses their equal or inequal status. They do not speak; rather, equals kiss each other on the mouth, and in the case where one is a little inferior to the other, the kiss is given on the cheek.
During the later Classical period, affectionate mouth-to-mouth kissing was first described in the Hindu epic the Mahabharata.
Anthropologist Vaughn Bryant argues kissing spread from India to Europe after Alexander the Great conquered parts of Punjab in northern India in 326 BCE.
The Romans were passionate about kissing and talked about several types of kissing. Kissing the hand or cheek was called an osculum. Kissing on the lips with mouth closed was called a basium, which was used between relatives. A kiss of passion was called a suavium.
A fresco from Pompeii showing the kiss of a Roman couple
Kissing was not always an indication of eros, or love, but also could show respect and rank as it was used in Medieval Europe.
The study of kissing started sometime in the nineteenth century and is called philematology, which has been studied by people including Cesare Lombroso, Ernest Crawley, Charles Darwin, Edward Burnett Tylor and modern scholars such as Elaine Hatfield.
Types[edit]
Kristoffer Nyrop identified a number of types of kisses, including kisses of love, affection, peace, respect, and friendship. He notes, however, that the categories are somewhat contrived and overlapping, and some cultures have more kinds, including the French with twenty and the Germans with thirty.
Expression of affection[edit]
Kissing another person's lips has become a common expression of affection or warm greeting in many cultures worldwide. Yet in certain cultures, kissing was introduced only through European settlement, before which it was not a routine occurrence. Such cultures include certain indigenous peoples of Australia, the Tahitians, and many tribes in Africa.
A kiss can also be used to express feelings without an erotic element but can be nonetheless "far deeper and more lasting", writes Nyrop. He adds that such kisses can be expression of love "in the widest and most comprehensive meaning of the word, bringing a message of loyal affection, gratitude, compassion, sympathy, intense joy, and profound sorrow."
Nyrop writes that the most common example is the "intense feeling which knits parents to their offspring", but he adds that kisses of affection are not only common between parents and children, but also between other members of the same family, which can include those outside the immediate family circle, "everywhere where deep affection unites people." The tradition is written of in the Bible, as when Esau met Jacob after a long separation, he ran towards him, fell on his neck, and kissed him (Genesis 33:4), Moses greeted his father-in-law and kissed him (Exodus 18:7), and Orpah kissed her mother-in-law before leaving her (Ruth 1:14). The family kiss was traditional with the Romans and kisses of affection are often mentioned by the early Greeks, as when Odysseus, on reaching his home, meets his faithful shepherds.
Affection can be a cause of kissing "in all ages in grave and solemn moments," notes Nyrop, "not only among those who love each other, but also as an expression of profound gratitude. When the Apostle Paul took leave of the elders of the congregation at Ephesus, "they all wept sore, and fell on Paul's neck and kissed him" (Acts 20:37)." Kisses can also be exchanged between total strangers, as when there is a profound sympathy with or the warmest interest in another person.
Folk poetry has been the source of affectionate kisses where they sometimes played an important part, as when they had the power to cast off spells or to break bonds of witchcraft and sorcery, often restoring a man to his original shape. Nyrop notes the poetical stories of the "redeeming power of the kiss are to be found in the literature of many countries, especially, for example, in the Old French Arthurian romances (Lancelot, Guiglain) in which the princess is changed by evil arts into a dreadful dragon, and can only resume her human shape in the case of a knight being brave enough to kiss her." In the reverse situation, in the tale of "Beauty and the Beast", a transformed prince then told the girl that he had been bewitched by a wicked fairy, and could not be recreated into a man unless a maid fell in love with him and kissed him, despite his ugliness.
A kiss of affection can also take place after death. In Genesis 50:1, it is written that when Jacob was dead, "Joseph fell upon his father's face and wept upon him and kissed him." And it is told of Abu Bakr, Muhammad's first disciple, father-in-law, and successor, that, when the prophet was dead, he went into the latter's tent, uncovered his face, and kissed him. Nyrop writes that "the kiss is the last tender proof of love bestowed on one we have loved, and was believed, in ancient times, to follow mankind to the nether world."
Kissing on the lips can be a physical expression of affection or love between two people in which the sensations of touch, taste, and smell are involved. According to the psychologist Menachem Brayer, although many "mammals, birds, and insects exchange caresses" which appear to be kisses of affection, they are not kisses in the human sense.
Surveys indicate that kissing is the second most common form of physical intimacy among United States adolescents (after holding hands), and that about 85% of 15 to 16-year-old adolescents in the US have experienced it.
Kiss on the lips[edit]
The kiss on the lips can be performed between two friends or family. This move aims to express affection for a friend. Unlike kissing for love, a friendly kiss has no sexual connotation. The kiss on the lips is a practice that can be found in the time of patriarchs (Bible). In Ancient Greece, the kiss on the mouth was used to express a concept of equality between people of the same rank. In the Middle Ages, the kiss of peace was recommended by the Catholic Church. The kiss on the lips was also common among knights. The gesture has again become popular with young people, particularly in England.
Romantic kiss[edit]
A straight couple kissing
In many cultures, it is considered a harmless custom for teenagers to kiss on a date or to engage in kissing games with friends. These games serve as icebreakers at parties and may be some participants' first exposure to sexuality. There are many such games, including truth or dare, seven minutes in heaven (or the variation "two minutes in the closet"), spin the bottle, post office, and wink.
A gay couple kissing
A lesbian couple kissing
The psychologist William Cane notes that kissing in Western society is often a romantic act and describes a few of its attributes:
It's not hard to tell when two people are in love. Maybe they're trying to hide it from the world, still they cannot conceal their inner excitement. Men will give themselves away by a certain excited trembling in the muscles of the lower jaw upon seeing their beloved. Women will often turn pale immediately of seeing their lover and then get slightly red in the face as their sweetheart draws near. This is the effect of physical closeness upon two people who are in love.
Romantic kissing in Western cultures is a fairly recent development and is rarely mentioned even in ancient Greek literature. In the Middle Ages it became a social gesture and was considered a sign of refinement of the upper classes. Other cultures have different definitions and uses of kissing, notes Brayer. In China, for example, a similar expression of affection consists of rubbing one's nose against the cheek of another person. In other Eastern cultures kissing is not common. In South East Asian countries the "sniff kiss" is the most common form of affection and Western mouth to mouth kissing is often reserved for sexual foreplay. In some tribal cultures the "equivalent to 'kiss me' is 'smell me.'"
The kiss can be an important expression of love and erotic emotions. In his book The Kiss and its History, Kristoffer Nyrop describes the kiss of love as an "exultant message of the longing of love, love eternally young, the burning prayer of hot desire, which is born on the lovers' lips, and 'rises,' as Charles Fuster has said, 'up to the blue sky from the green plains,' like a tender, trembling thank-offering." Nyrop adds that the love kiss, "rich in promise, bestows an intoxicating feeling of infinite happiness, courage, and youth, and therefore surpasses all other earthly joys in sublimity." He also compares it to achievements in life: "Thus even the highest work of art, yet, the loftiest reputation, is nothing in comparison with the passionate kiss of a woman one loves."
The power of a kiss is not minimized when he writes that "we all yearn for kisses and we all seek them; it is idle to struggle against this passion. No one can evade the omnipotence of the kiss ..." Kissing, he implies, can lead one to maturity: "It is through kisses that a knowledge of life and happiness first comes to us. Runeberg says that the angels rejoice over the first kiss exchanged by lovers," and can keep one feeling young: "It carries life with it; it even bestows the gift of eternal youth." The importance of the lover's kiss can also be significant, he notes: "In the case of lovers a kiss is everything; that is the reason why a man stakes his all for a kiss," and "man craves for it as his noblest reward."
As a result, kissing as an expression of love is contained in much of literature, old and new. Nyrop gives a vivid example in the classic love story of Daphnis and Chloe. As a reward "Chloe has bestowed a kiss on Daphnis—an innocent young-maid's kiss, but it has on him the effect of an electrical shock":
Ye gods, what are my feelings. Her lips are softer than the rose's leaf, her mouth is sweet as honey, and her kiss inflicts on me more pain than a bee's sting. I have often kissed my kids, I have often kissed my lambs, but never have I known aught like this. My pulse is beating fast, my heart throbs, it is as if I were about to suffocate, yet, nevertheless, I want to have another kiss. Strange, never-suspected pain! Has Chloe, I wonder, drunk some poisonous draught ere she kissed me? How comes it that she herself has not died of it?
Romantic kissing "requires more than simple proximity," notes Cane. It also needs "some degree of intimacy or privacy, ... which is why you'll see lovers stepping to the side of a busy street or sidewalk." Psychologist Wilhelm Reich "lashed out at society" for not giving young lovers enough privacy and making it difficult to be alone. However, Cane describes how many lovers manage to attain romantic privacy despite being in a public setting, as they "lock their minds together" and thereby create an invisible sense of "psychological privacy." He adds, "In this way they can kiss in public even in a crowded plaza and keep it romantic." Nonetheless, when Cane asked people to describe the most romantic places they ever kissed, "their answers almost always referred to this ends-of-the-earth isolation, ... they mentioned an apple orchard, a beach, out in a field looking at the stars, or at a pond in a secluded area ..."
Kiss as ritual[edit]
Kiss on the crucifix in Catholicism
Denis Thatcher, husband of Margaret Thatcher, kissing the hand of Nancy Reagan, wife of former US President Ronald Reagan in 1988
Kissing the Blarney Stone
Throughout history, a kiss has been a ritual, formal, symbolic or social gesture indicating devotion, respect or greeting. It appears as a ritual or symbol of religious devotion. For example, in the case of kissing a temple floor, or a religious book or icon. Besides devotion, a kiss has also indicated subordination or, nowadays, respect.
In modern times the practice continues, as in the case of a bride and groom kissing at the conclusion of a wedding ceremony or national leaders kissing each other in greeting, and in many other situations.
Religion[edit]
A kiss in a religious context is common. In earlier periods of Christianity or Islam, kissing became a ritual gesture, and is still treated as such in certain customs, as when "kissing... relics, or a bishop's ring." In Judaism, the kissing of the Torah scroll, a prayer book, and a prayer shawl is also common. Crawley notes that it was "very significant of the affectionate element in religion" to give so important a part to the kiss as part of its ritual. In the early Church the baptized were kissed by the celebrant after the ceremony, and its use was even extended as a salute to saints and religious heroes, with Crawley adding, "Thus Joseph kissed Jacob, and his disciples kissed Paul. Joseph kissed his dead father, and the custom was retained in our civilization", as the farewell kiss on dead relatives, although certain sects prohibit this today.
A distinctive element in the Christian liturgy was noted by Justin in the 2nd century, now referred to as the "kiss of peace," and once part of the rite in the primitive Mass. Conybeare has stated that this act originated within the ancient Hebrew synagogue, and Philo, the ancient Jewish philosopher called it a "kiss of harmony", where, as Crawley explains, "the Word of God brings hostile things together in concord and the kiss of love." Saint Cyril also writes, "this kiss is the sign that our souls are united, and that we banish all remembrance of injury."
Kiss of peace[edit]
Nyrop notes that the kiss of peace was used as an expression of deep, spiritual devotion in the early Christian Church. Christ said, for instance, "Peace be with you, my peace I give you," and the members of Christ's Church gave each other peace symbolically through a kiss. St Paul repeatedly speaks of the "holy kiss," and, in his Epistle to the Romans, writes: "Salute one another with an holy kiss" and his first Epistle to the Thessalonians (1 Thessalonians 5:26), he says: "Greet all the brethren with an holy kiss."
The kiss of peace was also used in secular festivities. During the Middle Ages, for example, Nyrop points out that it was the custom to "seal the reconciliation and pacification of enemies by a kiss." Even knights gave each other the kiss of peace before proceeding to the combat, and forgave one another all real or imaginary wrongs. The holy kiss was also found in the ritual of the Church on solemn occasions, such as baptism, marriage, confession, ordination, or obsequies. However, toward the end of the Middle Ages the kiss of peace disappears as the official token of reconciliation.
Kiss of respect[edit]
Man kissing the ground after a long sea voyage (as part of a reenactment of the first landing of English settlers in Virginia in 1607)
The kiss of respect is of ancient origin, notes Nyrop. He writes that "from the remotest times we find it applied to all that is holy, noble, and worshipful—to the gods, their statues, temples, and altars, as well as to kings and emperors; out of reverence, people even kissed the ground, and both sun and moon were greeted with kisses."
He notes some examples, as "when the prophet Hosea laments over the idolatry of the children of Israel, he says that they make molten images of calves and kiss them" (Hosea 13:2). In classical times similar homage was often paid to the gods, and people were known to kiss the hands, knees, feet, and the mouths, of their idols. Cicero writes that the lips and beard of the famous statue of Hercules at Agrigentum were worn away by the kisses of devotees.
People kissed the cross with the image of Jesus, and such kissing of the cross is always considered a holy act. In many countries it is required, on taking an oath, as the highest assertion that the witness would be speaking the truth. Nyrop notes that "as a last act of charity, the image of the Redeemer is handed to the dying or death-condemned to be kissed." Kissing the cross brings blessing and happiness; people kiss the image of Mary and the pictures and statues of saints—not only their pictures, "but even their relics are kissed," notes Nyrop. "They make both soul and body whole." There are legends innumerable of sick people regaining their health by kissing relics, he points out.
The kiss of respect has also represented a mark of fealty, humility and reverence. Its use in ancient times was widespread, and Nyrop gives examples: "people threw themselves down on the ground before their rulers, kissed their footprints, literally 'licked the dust,' as it is termed." "Nearly everywhere, wheresoever an inferior meets a superior, we observe the kiss of respect. The Roman slaves kissed the hands of their masters; pupils and soldiers those of their teachers and captains respectively." People also kissed the earth for joy on returning to their native land after a lengthened absence, as when Agamemnon returned from the Trojan War.
Kiss of friendship[edit]
The kiss is also commonly used in American and European culture as a salutation between friends or acquaintances. The friendly kiss until recent times usually occurred only between ladies, but today it is also common between men and women, especially if there is a great difference in age. According to Nyrop, up until the 20th century, "it seldom or never takes place between men, with the exception, however, of royal personages," although he notes that in former times the "friendly kiss was very common with us between man and man as well as between persons of opposite sexes." In guilds, for example, it was customary for the members to greet each other "with hearty handshakes and smacking kisses," and, on the conclusion of a meal, people thanked and kissed both their hosts and hostesses.
Cultural significance[edit]
In approximately 10% of the world population, kissing does not take place, for a variety of reasons, including that they find it dirty or because of superstitious reasons. For example, in parts of Sudan it is believed that the mouth is the portal to the soul, so they do not want to invite death or have their spirit taken. Psychology professor Elaine Hatfield noted that "kissing was far from universal and even seen as improper by many societies." Despite kissing being widespread, in some parts of the world it is still taboo to kiss publicly and is often banned in films or in other media.
As a theme in art[edit]
Romeo and Juliet by Sir Frank Dicksee (1884)
Jean-Honoré Fragonard The Stolen Kiss (1786)
The Kiss by Francesco Hayez (1859)
Psyche Revived by Cupid's Kiss by Antonio Canova
Le Baiser ("The Kiss") by Auguste Rodin (1882)
The Last Kiss (1931 film)
South Asia[edit]
On-screen lip-kissing was not a regular occurrence in Bollywood until the 1990s, although it has been present from the time of the inception of Bollywood. This can appear contradictory since the culture of kissing is believed to have originated and spread from India.
Middle East[edit]
There are also taboos as to whom one can kiss in some Muslim-majority societies governed by religious law. In the Islamic Republic of Iran, a man who kisses or touches a woman who is not his wife or relative can be punished such as getting whipped up to 100 times or even go to jail.
Research from May 2023 found texts from ancient people in Mesopotamia that indicates that kissing was a well-established practice 4500 years ago. According to Dr Troels Pank Arbøll, one of the authors of this study:
"In ancient Mesopotamia, which is the name for the early human cultures that existed between the Euphrates and Tigris rivers in present-day Iraq and Syria, people wrote in cuneiform script on clay tablets. Many thousands of these clay tablets have survived to this day, and they contain clear examples that kissing was considered a part of romantic intimacy in ancient times, just as kissing could be part of friendships and family members' relations."
East Asia[edit]
Donald Richie comments that in Japan, as in China, although kissing took place in erotic situations, in public "the kiss was invisible", and the "touching of the lips never became the culturally encoded action it has for so long been in Europe and America." The early Edison film, The Widow Jones – the May Irwin-John Rice Kiss (1896), created a sensation when it was shown in Tokyo, and people crowded to view the enormity. Likewise, Rodin's sculpture The Kiss was not displayed in Japan until after the Pacific War. Also, in the 1900s, Manchu tribes along the Amur River regarded public kissing between adults with revulsion. In a similar situation in Chinese tradition, when Chinese men saw Western women kissing men in public, they thought the women were prostitutes.
Contemporary practices[edit]
Princess Madeleine of Sweden and Christopher O'Neill kiss each other after their wedding, 2013.
In modern Western culture, kissing on the lips is commonly an expression of affection or a warm greeting. When lips are pressed together for an extended period, usually accompanied with an embrace, it is an expression of romantic and sexual desire. The practice of kissing with an open mouth, to allow the other to suck their lips or move their tongue into their mouth, is called French kissing. "Making out" is often an adolescent's first experience of their sexuality and games which involve kissing, such as spin the bottle, facilitate the experience. People may kiss children on the forehead to comfort them or the cheek or lips to show affection.
In modern Eastern culture, the etiquette vary depending on the region. In West Asia, kissing on the lips between both men and women is a common form of greeting. In South and Eastern Asia, it might often be a greeting between women, however, between men, it is unusual. Kissing a baby on the cheeks is a common form of affection. Most kisses between men and women are on the cheeks and not on the lips unless they are romantically involved. And sexual forms of kissing between lovers encompass the whole range of global practices.
Kissing in films[edit]
The first romantic kiss on screen was in American silent films in 1896, beginning with the film The Kiss. The kiss lasted 18 seconds and caused many to rail against decadence in the new medium of silent film. Writer Louis Black writes that "it was the United States that brought kissing out of the Dark Ages." However, it met with severe disapproval by defenders of public morality, especially in New York. One critic proclaimed that "it is absolutely disgusting. Such things call for police interference."
Rock Hudson and Julie Andrews kissing in film Darling Lili (1970)
Young moviegoers began emulating romantic stars on the screen, such as Ronald Colman and Rudolph Valentino, the latter known for ending his passionate scenes with a kiss. Valentino also began his romantic scenes with women by kissing her hand, traveling up her arm, and then kissing her on the back of her neck. Actresses were often turned into stars based on their screen portrayals of passion. Actresses like Nazimova, Pola Negri, Vilma Bánky and Greta Garbo, became screen idols as a result.
Eventually, the film industry began to adopt the dictates of the Production Code established in 1934, overseen by Will Hays and influenced by Christian religious leaders in America. According to the new code, "Excessive and lustful kissing, lustful embraces, suggestive postures and gestures, are not to be shown." As a result, kissing scenes were shortened, with scenes cut away, leaving the imagination of the viewer to take over. Under the code, actors kissing had to keep their feet on the ground and had to be either standing or sitting.
The heyday of romantic kissing on the screen took place in the early sound era, during the Golden Age of Hollywood in the 1930s and 1940s. Body language began to be used to supplement romantic scenes, especially with the eyes, a talent that added to Greta Garbo's fame. Author Lana Citron writes that "men were perceived as the kissers and women the receivers. Should the roles ever be reversed, women were regarded as vamps . . ." According to Citron, Mae West and Anna May Wong were the only Hollywood actresses never to have been kissed on screen. Among the films rated for having the most romantic kisses are Gone with the Wind, From Here to Eternity, Casablanca, and To Have and Have Not.
Sociologist Eva Illouz notes that surveys taken in 1935 showed that "love was the most important theme represented in movies. Similar surveys during the 1930s found the 95% of films had romance as one of their plot lines, what film critics called "the romantic formula."
In early Japanese films, kissing and sexual expression were controversial. In 1931, a director slipped a kissing scene past the censor (who was a friend), but when the film opened in a downtown Tokyo theater, the screening was stopped and the film confiscated. During the American occupation of Japan, in 1946, an American censor required a film to include a kissing scene. One scholar says that the censor suggested "we believe that even Japanese do something like kissing when they love each other. Why don't you include that in your films?" Americans encouraged such scenes to force the Japanese to express publicly actions and feelings that had been considered strictly private. Since Pearl Harbor, Americans had felt that the Japanese were "sneaky", claiming that "if Japanese kissed in private, they should do it in public too."
Non-sexual kisses[edit]
People kissing in this sketch by reporter and artist Marguerite Martyn of a New Year's Eve celebration in 1914
In some Western cultures, it is considered good luck to kiss someone on Christmas or on New Year's Eve, especially beneath a sprig of mistletoe. Newlyweds usually kiss at the end of a wedding ceremony.
Female friends and relations and close acquaintances commonly offer reciprocal kisses on the cheek as a greeting or farewell.
Where cheek kissing is used, in some countries a single kiss is the custom, while in others a kiss on each cheek is the norm, or even three or four kisses on alternating cheeks. In the United States, an air kiss is becoming more common. This involves kissing in the air near the cheek, with the cheeks touching or not. After a first date, it is common for the couple to give each other a quick kiss on the cheek (or lips where that is the norm) on parting, to indicate that a good time was had and perhaps to indicate an interest in another meeting.
A symbolic kiss is frequent in Western cultures. A kiss can be "blown" to another by kissing the fingertips and then blowing the fingertips, pointing them in the direction of the recipient. This is used to convey affection, usually when parting or when the partners are physically distant but can view each other. Blown kisses are also used when a person wishes to convey affection to a large crowd or audience. The term flying kiss is used in India to describe a blown kiss. In written correspondence a kiss has been represented by the letter "X" since at least 1763. A stage or screen kiss may be performed by actually kissing, or faked by using the thumbs as a barrier for the lips and turning so the audience is unable to fully see the act.
Some literature suggests that a significant percentage of humanity does not kiss. It has been claimed that in Sub-Saharan African, Asiatic, Polynesian and possibly in some Native American cultures, kissing was relatively unimportant until European colonization. Historically however, the culture of kissing is thought to have begun and spread from the Eastern World, specifically India.
With the Andamanese, kissing was only used as a sign of affection towards children and had no sexual undertones.
In traditional Islamic cultures, kissing is not permitted between a man and woman who are not married or closely related by blood or marriage. A kiss on the cheek is a very common form of greeting among members of the same sex in most Islamic countries, much like the Southern European pattern.
Legality of public kissing[edit]
This section needs expansion. You can help by adding to it. (March 2017)
In 2007, two people were fined and jailed for a month after kissing and hugging in public in Dubai.
In India, public display of affection is a criminal offence under Section 294 of the Indian Penal Code, 1860 with a punishment of imprisonment of up to three months, or a fine, or both. This law was used by police to prosecute couples engaging in intimate acts, such as kissing in public. However, in a number of landmark cases, the higher courts dismissed assertions that kissing in public is obscene.
In religion[edit]
The Taking of Christ by Caravaggio (c. 1602) depicts Judas betraying Jesus with a kiss as a signal to arrest Jesus.
Kissing was a custom during the Biblical period mentioned in the Genesis 27:26, when Isaac kissed his son Jacob. The kiss is used in numerous other contexts in the Bible: the kiss of homage, in Esther 5:2; of subjection, in 1 Samuel 10:1; of reconciliation, in 2 Samuel 14:33; of valediction, in Ruth 1:14; of approbation, in Psalms 2:12; of humble gratitude, in Luke 7:38; of welcome, in Exodus 18:7; of love and joy, in Genesis 20:11. There are also spiritual kisses, as in Song of Songs 1:2; sensual kisses, as in Proverbs 7:13; and hypocritical kisses, as in 2 Samuel 15:5. It was customary to kiss the mouth in biblical times, and also the beard, which is still practiced in Arab culture. Kissing the hand is not biblical, according to Tabor. The kiss of peace was an apostolic custom, and continues to be one of the rites in the Eucharistic services of Roman Catholics.
In the Roman Catholic Order of Mass, the bishop or priest celebrant bows and kisses the altar, reverencing it, upon arriving at the altar during the entrance procession before Mass and upon leaving at the recessional at the closing of Mass; if a deacon is assisting, he bows low before the altar but does not kiss it.
Among primitive cultures, it was usual to throw kisses to the sun and to the moon, as well as to the images of the gods. Kissing the hand is first heard of among the Persians. According to Tabor, the kiss of homage—the character of which is not indicated in the Bible—was probably upon the forehead, and was expressive of high respect.
This woodcut of the practice of kissing the pope's toe is from Passionary of the Christ and Antichrist by Lucas Cranach the Elder.
In Ancient Rome and some modern Pagan beliefs, worshipers, when passing the statue or image of a god or goddess, will kiss their hand and wave it towards the deity (adoration).
The holy kiss or kiss of peace is a traditional part of most Christian liturgies, though often replaced with an embrace or handshake today in Western cultures.
In the gospels of Matthew and Mark (Luke and John omit this),Judas betrayed Jesus with a kiss: an instance of a kiss tainted with betrayal. This is the basis of the term "the kiss of Judas".
Catholics will kiss rosary beads as a part of prayer, or kiss their hand after making the sign of the cross. It is also common to kiss the wounds on a crucifix, or any other image of Christ's Passion.
Pope John Paul II would kiss the ground on arrival in a new country.
Visitors to the pope traditionally kiss his foot.
Catholics traditionally kiss the ring of a cardinal or bishop.
Catholics traditionally kiss the hand of a priest.
Eastern Orthodox and Eastern Catholic Christians often kiss the icons around the church on entering; they will also kiss the cross and/or the priest's hand in certain other customs in the church, such as confession or receiving a blessing.
Local lore in Ireland suggests that kissing the Blarney Stone will bring the gift of the gab.
Jews will kiss the Western Wall of the Holy Temple in Jerusalem, and other religious articles during prayer such as the Torah, usually by touching their hand, Tallis, or Siddur (prayerbook) to the Torah and then kissing it. Jewish law prohibits kissing members of the opposite sex, except for spouses and certain close relatives. See Negiah.
Muslims may kiss the Black Stone during Hajj (pilgrimage to Mecca). Many Muslims also kiss shrines of Ahlulbayt and Sufis.
Biology and evolution[edit]
Black-tailed prairie dogs "kissing." Prairie dogs use a nuzzle of this variety to greet their relatives.
Within the natural world of other animals, there are numerous analogies to kissing, notes Crawley, such as "the billing of birds, the cataglottism of pigeons and the antennal play of some insects." Even among mammals such as the dog, cat and bear, similar behavior is noted.
Anthropologists have not reached a conclusion as to whether kissing is learned or a behavior from instinct. It may be related to grooming behavior also seen between other animals, or arising as a result of mothers premasticating food for their children. Non-human primates also exhibit kissing behavior. Dogs, cats, birds and other animals display licking, nuzzling, and grooming behavior among themselves, and also towards humans or other species. This is sometimes interpreted by observers as a type of kissing.
Kissing in humans is postulated to have evolved from the direct mouth-to-mouth regurgitation of food (kiss-feeding) from parent to offspring or male to female (courtship feeding) and has been observed in numerous mammals. The similarity in the methods between kiss-feeding and deep human kisses (e.g. French kiss) is quite pronounced; in the former, the tongue is used to push food from the mouth of the mother to the child with the child receiving both the mother's food and tongue in sucking movements, and the latter is the same but forgoes the premasticated food. In fact, through observations across various species and cultures, it can be confirmed that the act of kissing and premastication has most likely evolved from the similar relationship-based feeding behaviours.
Physiology[edit]
Kissing is a complex behavior that requires significant muscular coordination involving a total of 34 facial muscles and 112 postural muscles. The most important muscle involved is the orbicularis oris muscle, which is used to pucker the lips and informally known as the kissing muscle. In the case of the French kiss, the tongue is also an important component. Lips have many nerve endings which make them sensitive to touch and bite.
Health benefits[edit]
Kissing stimulates the production of hormones responsible for a good mood: oxytocin, which releases the feeling of love and strengthens the bond with the partner, endorphins – hormones responsible for the feeling of happiness –, and dopamine, which stimulates the pleasure center in the brain.
Affection in general has stress-reducing effects. Kissing in particular has been studied in a controlled experiment and it was found that increasing the frequency of kissing in marital and cohabiting relationships results in a reduction of perceived stress, an increase in relationship satisfaction, and a lowering of cholesterol levels.
Disease transmission[edit]
Kissing on the lips can result in the transmission of some diseases, including infectious mononucleosis (known as the "kissing disease") and herpes simplex when the infectious viruses are present in saliva. Research indicates that contraction of HIV via kissing is extremely unlikely, although there was a documented case in 1997 of an HIV infection by kissing. Both the woman and infected man had gum disease, so transmission was through the man's blood, not through saliva.
See also[edit]
Human sexuality portal
Eskimo kissing
Hand-kissing
Hugs and kisses
International Kissing Day
Kissing games
Kissing traditions
Kissing booth | biology | 13453 | https://da.wikipedia.org/wiki/Parforhold | Parforhold | Et parforhold er et længerevarende kærlighedsforhold og mellemmenneskeligt forhold mellem 2 mennesker som kan bo eller som ikke bor sammen.
Efter to år får et parforhold betydning i visse juridiske anliggender.
Se også:
Arrangeret ægteskab
Bryllup
Charme
Familie
Flirte
Forelskelse
Forførelse
Hengivenhed
Hvedebrødsdage
Jalousi
Kærlighed
Monogami
Polygami
Separeret
Sex
Skilsmisse
Tabu
Ægteskab
Eksterne henvisninger
Seksualitet og følelser er en guide til kærlighedslivets veje og vildveje Forord af Pernille Aalund: Åbent brev til en ny mand.
How Much Is Too Much? Or Not Enough? By Carmen Sutra Citat: "...I've received countless letters from men AND women detailing the pain of either constant rejection from their partner or disappointment in the frequency of lovemaking...."
Where Has The Love Gone Citat: "...When sexual intimacy starts to disappear in a relationship, many couples fall into a trap that I call the standoff. In a standoff situation, neither partner is honestly communicating their needs with one another...."
What Is Romantic Love (forelskelse) Anyway? Citat: "...No wonder so many pre-marital couples think they don't need counseling to aid in communication..."
January 13 2005, iol: Experts shed light on battle of the sexes Citat: "..."Conversation has differing functions for the two sexes, conditioned by their cultural background," Dirk Zimmer, professor of psychotherapy at the University of Tuebingen..."
Love. Is it worth the hassle? Citat: "...Falling in love, says Peck, is really a regression to that stage of babyhood...Now there is a choice: either the relationship ends or, as Peck puts it, 'they initiate the work of real loving' (Peck 88)..."
Familie
Kærlighedsforhold | danish | 0.805184 |
kissing_natural_human_activity/Air_kiss.txt | An air kiss, blown kiss, or thrown kiss is a ritual or social gesture whose meaning is basically the same as that of many forms of kissing. The air kiss is a pretence of kissing: the lips are pursed as if kissing, but without actually touching the other person's body. Sometimes, the air kiss includes touching cheek-to-cheek. Also, the gesture may be accompanied by the mwah sound. The onomatopoeic word mwah (a representation of the sound of a kiss) has entered Webster's dictionary.
The character block Unicode 1F618 provides the "emoji face throwing a kiss 😘" to computer screens.
Western culture[edit]
Francesco Totti blowing a kiss at UEFA Euro 2000
A symbolic kiss is frequent in Western cultures. A kiss can be "blown" to another by kissing the fingertips and then blowing the fingertips, pointing them in the direction of the recipient. This is used to convey affection, usually when parting or when the partners are physically distant but can view each other. Blown kisses are also used when a person wishes to convey affection to a large crowd or audience. The term flying kiss is used in India to describe a blown kiss.
North America[edit]
In North America and most western countries influenced by North America, air kisses are sometimes associated with glamour models and other celebrities. It is a modified cheek kiss, involving kissing in the air near the cheek, with the cheeks touching the lips or not.
Southeast Asia[edit]
In Indonesia, and Malaysia, it is common to air-kiss an elder's hand as a traditional form of respectful greeting. Instead of pursing one's lips, the younger person exhaling through his nose softly on the hand before drawing the hand to the younger person's forehead.
In the Philippines, elder relatives traditionally kiss a younger relative's cheek in this same way, by exhaling gently through the nose when the younger relative's cheek is brought close.
See also[edit]
Air guitar
Air quotes | biology | 207941 | https://no.wikipedia.org/wiki/Foggy%20Dew | Foggy Dew | «Foggy Dew» (eller «The Foggy Dew») er navnet på flere ballader.
Foggy, Foggy Dew
Den eldste versjonen, som også kalles «Foggy, Foggy Dew», er en sorgfull ballade om en ung elsker. Den ble publisert i England omkring 1815, men for de fleste er den kjent gjennom Burl Ives' versjon fra 1940-årene. Ives hevdet at sangen hadde sitt opphav i Amerika i kolonitiden, men det er ikke noen støtte for dette i kildene. Han ble engang arrestert i Mona i Utah for å synge den offentlig, ettersom myndighetene mente den var uanstendig.
Musikken er en versjon fra slutten av det 18. eller begynnelsen av det 19. århundre av «When I First Came to Court» fra 1689.
When I was a bachelor, I liv'd all alone
I worked at the weaver's trade
And the only, only thing that I did that was wrong
Was to woo a fair young maid.
I wooed her in the wintertime
Part of the summer, too
And the only, only thing that I did that was wrong
Was to keep her from the foggy, foggy dew.
One night she knelt close by my side
When I was fast asleep.
She threw her arms around my neck
And she began to weep.
She wept, she cried, she tore her hair
Ah, me! What could I do?
So all night long I held her in my arms
Just to keep her from the foggy foggy dew.
Again I am a bachelor, I live with my son
We work at the weaver's trade.
And every single time I look into his eyes
He reminds me of that fair young maid.
He reminds me of the wintertime
Part of the summer, too,
And the many, many times that I held her in my arms
Just to keep her from the foggy, foggy, dew.
En irsk versjon av sangen begynner med linjene:
When I was a bachelor, airy and young, I followed the roving trade,
And the only harm that ever I did was courting a servant maid.
I courted her all summer long, and part of the winter, too
And many's the time I rode my love all over the foggy dew.'Axel Schiøtz, tenor Herm D. Koppel piano akk. spilte den inn i København 7. mai 1951. Den ble utgitt på 78-platene His Master's Voice X 8009 og på His Master's Voice A.L. 3204. Arrangør var Benjamin Britten.
Irsk sørgevise
«Foggy Dew» er også en sørgevise fra Irland, av ukjent datering. Teksten nedenfor er hentet fra 1931-utgaven av The Home and Community Songbook.
Oh, a wan cloud was drawn o'er the dim weeping dawn
As to Shannon's side I return'd at last,
And the heart in my breast for the girl I lov'd best
Was beating, ah, beating, how loud and fast!
While the doubts and the fears of the long aching years
Seem'd mingling their voices with the moaning flood:
Till full in my path, like a wild water wraith,
My true love's shadow lamenting stood.
But the sudden sun kiss'd the cold, cruel mist
Into dancing show'rs of diamond dew,
And the dark flowing stream laugh'd back to his beam,
And the lark soared aloft in the blue;
While no phantom of night but a form of delight
Ran with arms outspread to her darling boy,
And the girl I love best on my wild throbbing breast
Hid her thousand treasures with cry of joy.
Påskeopprøret
En annen sang ved navn «Foggy Dew», også kjent som «Down the Glen», som kanskje har blitt den best kjente for mange, handler om påskeopprøret i Irland i 1916. Den er attribuert til Charles O'Neill. Det finnes ikke beviser for noen av attribueringene.
Teksten finnes i en rekke versjoner, og fremføres ofte i forkortet versjon. De fleste av de større irske folkemusikkgruppene har spilt den inn, som The Clancy Brothers and Tommy Makem, The Dubliners, The Chieftains (med Sinéad O'Connor som vokalist), Shane MacGowan, The Battering Ram, og Wolfe Tones.
As down the glen one Easter morn to a city fair rode I
There Armed lines of marching men in squadrons passed me by
No pipe did hum nor battle drum did sound its dread tattoo
But the Angelus bell o'er the Liffey's swell rang out through the foggy dew
Right proudly high over Dublin Town they hung out the flag of war Twas better to die 'neath an Irish sky than at Suvla or Sud-El-Bar
And from the plains of Royal Meath strong men came hurrying through
While Britannia's Huns, with their long range guns sailed in through the foggy dew
'T'was England bade our wild geese go, that "small nations might be free";
Their lonely graves are by Suvla's waves or the fringe of the great North Sea.
Oh, had they died by Pearse's side or fought with Cathal Brugha
Their graves we'd keep where the Fenians sleep, 'neath the shroud of the foggy dew.
Oh the night fell black, and the rifles' crack made perfidious Albion reel
In the leaden rain, seven tongues of flame did shine o'er the lines of steel
By each shining blade a prayer was said, that to Ireland her sons be true
But when morning broke, still the war flag shook out its folds the foggy dew
Oh the bravest fell, and the requiem bell rang mournfully and clear
For those who died that Eastertide in the spring time of the year
And the world did gaze, in deep amaze, at those fearless men, but few,
Who bore the fight that freedom's light might shine through the foggy dew
As back through the glen I rode again and my heart with grief was sore
For I parted then with valiant men whom I never shall see more
But to and fro in my dreams I go and I kneel and pray for you,
For slavery fled, O glorious dead, when you fell in the foggy dew.
Referanser
Irske sanger
Britiske sanger | norwegian_bokmål | 1.193555 |
kissing_natural_human_activity/Cheek_kissing.txt |
Cheek kissing is a ritual or social kissing gesture to indicate friendship, family relationship, perform a greeting, to confer congratulations, to comfort someone, or to show respect.
Cheek kissing is very common in the Middle East, the Mediterranean, Southern, Central and Eastern Europe, the Low Countries, the Horn of Africa, Central America and South America. In other countries, including the U.S. and Japan, cheek kissing is common as well at an international meeting between heads of state and First Ladies or members of royal and the Imperial families.
Depending on the local culture, cheek kissing may be considered appropriate among family members as well as friends and acquaintances: a man and a woman, two women, or two men. The last has different degrees of familiarity.
In Eastern Europe, male–female and female–female cheek kissing is a standard greeting among friends, while male–male cheek kisses are less common. Eastern European communist leaders often greeted each other with a socialist fraternal kiss on public and state occasions.
In a cheek kiss, both persons lean forward and either lightly touch cheek with cheek or lip with cheek. Generally the gesture is repeated with the other cheek, or more, alternating cheeks. Depending on country and situation, the number of kisses range from one to four. Hand-shaking or hugging may also take place.
Cheek kissing is used in many cultures with slightly varying meaning and gesture. For example, cheek kissing may or may not be associated with a hug. The appropriate social context for use can vary greatly from one country to the other, though the gesture might look similar.
In cultures and situations where cheek kissing is the social norm, the failure or refusal to give or accept a kiss is commonly taken as an indicator of antipathy between the people, and to dispel such an implication and avoid giving offense may require an explanation, such as the person has a contagious disease such as a cold.
Europe[edit]
Southern Europe[edit]
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Cheek kissing is a standard greeting throughout Southern Europe between friends or acquaintances, but less common in professional settings. In general, men and women will kiss the opposite sex, and women will kiss women. Men kissing men varies depending on the country and even on the family, in some countries (like Italy) men will kiss men; in others only men of the same family would consider kissing.
Greece is an example of a country where cheek kissing highly depends on the region and the type of event. For example, in most parts of Crete, it is common between a man and a woman who are friends, but is very uncommon between men unless they are very close relatives. In Athens it is commonplace for men to kiss women and women to kiss other women on the cheek when meeting or departing. It is uncommon between strangers of any sex, and it may be considered offensive otherwise. It is standard for children and parents, children and grandparents etc., and in its "formal" form it will be two kisses, one on each cheek. It may be a standard formal form of greeting in special events such as weddings.
However, in Portugal and Spain, usually, women kiss both men and women, and men only kiss women (so, two men rarely kiss). In Portuguese families men rarely kiss men (except between brothers or father and son); the handshake is the most common salutation between them. However, men kissing may occur in Spain as well particularly when congratulating close friends or relatives. Cheek to cheek and the kiss in the air are also very popular. Hugging is common between men and men and women and women; when the other is from the opposite sex, a kiss may be added.
In Italy (especially southern and central Italy) it is common for men to kiss men, especially relatives or friends.
In most Southern European countries, kissing is initiated by leaning to the left side and joining the right cheeks and if there's a second kiss, changing to the left cheeks. In some cases (e.g. some parts of Italy) the process is the opposite, you first lean to the right, join the left cheeks and then switch to the right cheeks.
Southeastern Europe[edit]
In the former Yugoslavia, cheek kissing is also very commonplace, with your ethnicity being ascertainable by the number of kisses on each cheek. Typically, Croats and Bosniaks will kiss once on each cheek, for two total kisses, whereas Serbs will kiss once, but three times as a traditional greeting, typically starting at the right cheek. In Serbia and Montenegro, it is also common for men to kiss each other on the cheek three times as a form of greeting, usually for people they have not encountered in a while, or during the celebrations (wedding, birthday, New Year, religious celebrations, etc.).
In Bulgaria cheek kissing is practiced to a far lesser extent compared to ex-Yugoslavia and is usually seen only between very close relatives or sometimes between close female friends. Kissing is usually performed by people of the opposite sex and between two women. Men kissing is rare even between close friends and is usually considered unnatural and awkward. Male relatives are more likely to initiate kissing if there is a significant age gap, such as between uncles and nephews, or if both men are elderly.
In Romania, cheek kissing is commonly used as a greeting between a man and a woman or two women, once on each cheek. Men usually prefer handshakes among themselves, though sometimes close male relatives may also practice cheek kissing.
In Albania, cheek kissing is used as a greeting between the opposite sex and also the same sex. The cheek is kissed from left to right on each cheek. Males usually slightly bump their heads or just touch their cheeks (no kissing) so to masculinize the act. Females practice the usual left to right cheek kissing. Albanian old women often kiss four times, so two times on each cheek.
Western Europe[edit]
"La bise" redirects here. For other uses, see Bise (disambiguation).
Number of kisses in FranceCheek given for first kiss in France
French president Charles de Gaulle kisses Argentine president Arturo Illia in 1964.
In France, cheek kissing is called "faire la bise". A popular French joke states that you may recognize the city you are in by counting the number of cheek kisses, as it varies across the country. It is very common, in the southern parts of France, even between males, be they relatives or friends, whereas in the north (Langue-d'oïl France), it is less usual for two unrelated males to perform ′la bise′. (See Kissing traditions#Greetings.) The custom came under scrutiny during the H1N1 epidemic of 2009.
In the Netherlands and Belgium, cheek kissing is a common greeting between relatives and friends (in the Netherlands slightly more so in the south). Generally speaking, women will kiss both women and men, while men will kiss women but refrain from kissing other men, instead preferring to shake hands with strangers. In the Netherlands usually three kisses are exchanged, mostly for birthdays. The same number of kisses is found in Switzerland and Luxembourg. In the Flanders, one kiss is exchanged as a greeting, and three to celebrate (e.g., a birthday). In Wallonia, the custom is usually one or three kisses, and is also common between men who are friends.
In northern European countries such as Sweden and Germany, hugs are preferred to kisses, though also rare. It is customary in many regions to only have kisses between women and women, but not men and women, who tend to shake hands.
Although cheek kissing is not as widely practiced in the United Kingdom or Ireland as in other parts of Europe, it is still common and increasing. Generally, a kiss on one cheek is common, while a kiss on each cheek is also practiced by some depending on relation or reason. It is mostly used as a greeting and/or a farewell, but can also be offered as a congratulation or as a general declaration of friendship or love. Cheek kissing is acceptable between parents and children, family members (though not often two adult males), couples, two female friends or a male friend and a female friend. Cheek kissing between two men who are not a couple is unusual but socially acceptable if both men are happy to take part. Cheek kissing is associated with the middle and upper classes, as they are more influenced by French culture. This behaviour was traditionally seen as a French practice.
Asia[edit]
Southeast Asia[edit]
In the Philippines, cheek kissing or beso (also beso-beso, from the Spanish for "kiss") is a common greeting. The Philippine cheek kiss is a cheek-to-cheek kiss, not a lips-to-cheek kiss. The cheek kiss is usually made once (right cheek to right cheek), either between two women, or between a woman and a man. Amongst the upper classes, it is a common greeting among adults who are friends, while for the rest of the population, however, the gesture is generally reserved for relatives. Filipinos who are introduced to each other for the first time do not cheek kiss unless they are related.
In certain communities in Indonesia, notably the Manado or Minahasa people, kissing on the cheeks (twice) is normal among relatives, including males.
In parts of Central, South, and East Asia with predominantly Buddhist or Hindu cultures, or in cultures heavily influenced by these two religions, cheek kissing is largely uncommon and may be considered offensive, although its instances are now growing.
Middle East[edit]
Lebanese singer Fares Karam responds to his audience request to kissing Rita Harb after receiving Hazmieh festival award on July 20, 2012. Harb described it later as a "Brotherly Kissing" and gave him the best wish.
Cheek kissing in the Arab world is relatively common, between friends and relatives. Cheek kissing between males is very common. However, cheek kissing between a male and female is usually considered inappropriate, unless within the same family; e.g. brother and sister, or if they are a married couple. Some exceptions to this are liberal areas within cities in some of the more liberal Arab countries such as Lebanon, Syria, Jordan and Tunisia, where cheek kissing is a common greeting between unrelated males and females in most communities. The Lebanese custom has become the norm for non-Lebanese in Lebanese-dominated communities of the Arab diaspora. Normally in Lebanon, the typical number of kisses is three: one on the left cheek, then right, and then left between relatives. In other countries, it is typically two kisses with one on each cheek.
Cheek kissing in Turkey is also widely accepted in greetings. Male to male cheek kissing is considered normal in almost every occasion, but very rarely for men who are introduced for the first time. Some men hit each other's head on the side instead of cheek kissing, possibly as an attempt to masculinize the action. Cheek kissing between women is also very common, but it is also very rare for women who are introduced for the first time. A man and a woman could cheek kiss each other for greeting without sexual connotations only if they are good friends or depending on the circle, the setting, and the location like in big cities.
Cheek kissing in Iran is relatively common between friends and family. Cheek kissing between individuals of the same sex is considered normal. However, cheek kissing between male and female in public is considered to be inappropriate, but it may occur among some youth Iranians.
In 2014, Leila Hatami, a famous Iranian actress, kissed the president of Cannes Gilles Jacob on the red carpet. Responses ranged from criticism by the Iranian government to support from Iranian opposition parties. Former president of Iran Mahmoud Ahmadinejad kissed the mother of former President of Venezuela Hugo Chávez at his funeral.
Americas[edit]
United States and Canada[edit]
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A father kissing the cheek of his daughter
In the United States and Canada, the cheek kiss may involve one or both cheeks. According to the March 8, 2004 edition of Time magazine, "a single [kiss] is [an] acceptable [greeting] in the United States, but it's mostly a big-city phenomenon." Occasionally, cheek kissing is a romantic gesture.
Cheek kissing of young children by adults of both sexes is perhaps the most common cheek kiss in North America. Typically, it is a short, perfunctory greeting, and is most often done by relatives.
Giving someone a kiss on the cheek is also a common occurrence between loving couples.
Cheek kissing between adults, when it occurs at all, is most often done between two people who know each other well, such as between relatives or close friends. In this case, a short hug (generally only upper-body contact) or handshake may accompany the kiss. Likewise, hugs are common but not required. A hug alone may also suffice in both of these situations, and is much more common. Particularly in the southeastern United States (Southern), elderly women may be cheek kissed by younger men as a gesture of affection and respect.
In Quebec, cheek kissing is referred to in the vernacular (Québécois) as un bec ("donner un bec") or la bise ("faire la bise"). Whether francophone or other, people of the opposite sex often kiss once on each cheek. Cheek kissing between women is also very common, although men will often refrain. Two people introduced by a mutual friend may also give each other un bec.
Immigrant groups tend to have their own norms for cheek kissing, usually carried over from their native country. In Miami, Florida, an area heavily influenced by Latin American and European immigrants, kissing hello on the cheek is the social norm.
Latin America[edit]
In Latin America, cheek kissing is a universal form of greeting between a man and a woman or two women. In some countries, such as Argentina, Chile and Uruguay, men will kiss on the cheek as a greeting.
It is not necessary to know a person well or be intimate with them to kiss them on the cheek. When introduced to someone new by a mutual acquaintance in social settings, it is customary to greet him or her with a cheek kiss if the person being introduced to them is a member of the opposite sex or if a woman is introduced to another woman. If the person is a complete stranger, i.e. self-introductions, no kissing is done. A cheek kiss may be accompanied by a hug or another sign of physical affection. In business settings, the cheek kiss is not always standard upon introduction, but once a relationship is established, it is common practice.
As with other regions, cheek kissing may be lips-to-cheek or cheek-to-cheek with a kiss in the air, the latter being more common.
As in Southern Europe, in Argentina, Chile and Uruguay men kissing men is common but it varies depending on the region, occasion and even on the family. In Argentina and Uruguay it is common (almost standard) between male friends to kiss "a la italiana", e.g. football players kiss each other to congratulate or to greet. In Chile, one cheek kiss is given between male friends (specially young men) and male relatives (despite age and relationship), although sometimes it can be between acquaintances.
In Ecuador it is normal that two male family members greet with a kiss, especially between father and son or grandfather and grandson.
Africa[edit]
Cheek kissing is common in the Horn of Africa, which includes Djibouti, Eritrea, Ethiopia, and Somalia, and is also present in countries within the Arab world, but is largely uncommon in most areas south of the Sahara. In South Africa, cheek kisses are usually found among male and female friends, with handshakes or hugs usually being preferable among other people.
Oceania[edit]
In Australia and New Zealand, cheek kissing is usually present among close friends, with handshakes or hugs usually being preferable. In New Zealand, Māori people may also traditionally use the hongi for greetings.
See also[edit]
Society portal
Wikimedia Commons has media related to Cheek kissing.
Greeting habits
Hug
Hand-kissing
Kiss of peace
Paschal greeting
Public display of affection
Salute
Socialist fraternal kiss | biology | 477938 | https://sv.wikipedia.org/wiki/Swinging | Swinging | Swinging (engelska ordet swing betyder gunga) är en livsstil som innebär deltagande i sexuella aktiviteter där fler än en partner är inblandade. En deltagare i swinging kallas swinger. Termen partnerbyte används också, speciellt om deltagarna är etablerade par.
Swinging är inte begränsat till partners av motsatt kön. Det finns utrymme för särskilt kvinnor att leva ut en bisexualitet, medan det för män generellt inte är sett som lika vanligt. Personer som endast utforskar sin bisexuella sida i swingerssammanhang kan benämnas "partybi".
Swinging-aktiviteter
Swinging kan inkludera följande aktiviteter:
Exhibitionism: Att låta andra se på när man utför en sexuell handling.
Voyeurism: Att titta på när andra utför en sexuell handling.
Partnerbyte: Att ett par som har en sexuell relation tillfälligt byter sexuell partner med ett annat par som har en sexuell relation. Det kan vara allt från kyssar, smekningar och oralsex till fullbordade samlag.
Gruppsex: En sexuell aktivitet där fler än två personer är inblandade.
Soft swinging: Kyssar, smekningar och ofta oralsex räknas som detta.
Hustrubyte: Innebär att en man lånar ut sin hustru till en man som är på besök hos honom, oftast mot att mannen får låna den andras hustru i gengäld. Det går också att säga att hustrun byter ut sin man mot en annan man.
Mötesplatser
Swingersklubbar
Swingersklubbar eller sexklubbar är klubbar där swingers träffas för att umgås och ha sex. Swingersklubbar finns över hela världen och på flera ställen i Sverige. Swingersklubbar dit man går parvis kvinna-man kallas parklubbar, men de flesta har idag så kallade mixkvällar då både singlar och par är välkomna. För att få komma in på en klubb krävs oftast medlemskap.
Swingersfester
Swingersfester liknar swingersklubbar men har, som namnet antyder, mer karaktär av privat fest. Vanligast är att man går dit parvis i ett kvinna-man-förhållande, men vissa swingersfester kan även vara öppna för singlar.
Nakenbad
Nakenbad fungerar ibland som mötesplatser för swingers och det händer att man har sex på avskild plats utomhus, i anslutning till badet.
Subgrupper
Key party
Key party, eller nyckelpartyn, är en swinging-företeelse från 50- och 70-talet, där slumpen bestämmer vem som ska gå hem med vem. Alla representanter för ena könet lägger sina hus- eller bilnycklar i en skål och det andra könet drar en slumpmässig nyckel. Lustkammaren arrangerar fester runt om i landet i mer organiserad form.
Dogging
Dogging är en ursprungligen brittisk benämning för sorts swinging med olika varianter av sex utomhus eller i parkerade bilar inför ögonen på okända och ibland även med dem. Sedan en tid tillbaka finns företeelsen även i Sverige. Ordet "dogging" kommer till synes från dem som påstår att de bara skall "gå ut med hunden", men egentligen är ute efter något annat. Runt omkring i Europa finns det ett antal kända så kallade dogging-platser, som besöks av människor när mörkret faller, för att de då kan ägna sig åt voyeurism och exhibitionism eller delta i gruppsex.
Cuckolding
Cuckolding är när ena partnern i förhållandet (oftast kvinnan) har en eller flera älskare och den andra partnern (x) är undergiven och kanske till och med hjälper till med förberedelserna, valet av älskare och att anordna träffar mellan kvinnan och älskaren/älskarna.
(x) lever i fullständig trohet gentemot sin kvinna/man och njuter dessutom av att veta om att partnern har andra älskare och till och med av att titta på. Detta kan dock avvika och kvinnan agerar även i vissa fall ensam och mannen kan ev. få vetskap om aktiviteter i efterhand. I förekommande fall kan kvinnan komma hem med älskarens sperma i slidan varpå mannen ger oralsex till kvinnan och konsumerar älskarens säd, kallat "Cuckold cleanup". Nämnda "Cleanup" förekommer även i direkt anslutning till älskarens sädesavgång och/eller när älskaren lämnat rummet.
Det handlar alltså inte om otrohet eller att kvinnan/mannen går bakom ryggen på sin man/kvinna, utan om ett spel där kvinnan/mannen av olika anledningar och med den andres vetskap har andra älskare.
Cuckolding behöver inte innebära sexuell förnedring, utan kan utgöra en möjlighet att leva ut en fantasi, uppfylla en önskan, eller en sexuell upplevelse som normalt inte kan erhållas inom de normala gränserna i en relation.
Hot Wife
I ett cuckold-förhållande (se nedan) där kvinnan har andra älskare med sin mans samtycke benämns kvinnan Hot Wife.
En variant av Hot Wife-fenomenet är när två män turas om att tillfredsställa den enes kvinna och där till exempel den andra mannen tar över omedelbart, så snart den första mannens orgasm har uppnåtts. Således återhämtar sig en man medan den andra är aktiv och kvinnan har kontinuerligt saml
Stag / Vixen
En stag-vixen-relation innebär en variant av cuckolding, men helt utan inslag av förnedring. Relationen innebär att kvinnan i relationen (vixen) är emotionellt trogen sin man (stag), men sexuellt tillgänglig för andra män. Mannen i relationen kan vara delaktig eller enbart ha kännedom om sin vixens andra relationer.
En vixen markerar ofta sin tillgänglighet för andra män genom att bära en fotlänk.
Bastuklubbar
Swingersklubbar kan för homosexuella män finns ibland i form av bastuklubbar. I Sverige förbjöds dessa 1987, via den så kallade bastuklubbslagen i ett försök att minska spridningen av aids, men förbudet hävdes 1 juli 2004.
Referenser
Sexuella relationer | swedish | 0.861416 |
kissing_natural_human_activity/French_kiss.txt | A French kiss, also known as cataglottism or a tongue kiss, is an amorous kiss in which the participants' tongues extend to touch each other's lips or tongue. A kiss with the tongue stimulates the partner's lips, tongue and mouth, which are sensitive to the touch and induce sexual arousal. The sensation when two tongues touch—also known as tongue touching—has been proven to stimulate endorphin release and reduce acute stress levels. Extended French kissing may be part of making out. The term originated at the beginning of the 20th century, in America and Great Britain, as the French had acquired a reputation for more adventurous and passionate sex practices.
French kissing may be a mode for disease transmission, particularly if there are open wounds.
Description[edit]
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A French kiss is an amorous kiss in which the participants' tongues extend to touch each other's lips or tongue. A tongue kiss stimulates the partner's lips, tongue and mouth, which are sensitive to the touch and induce sexual arousal, as the oral zone is one of the principal erogenous zones of the body. The implication is of a slow, passionate kiss which is considered intimate, romantic, erotic or sexual. French kissing is often described as "first base", and is used by many as an indicator of what stage a relationship has reached. Extended French kissing may be part of making out.
History[edit]
Open-mouth kissing is alluded to in Sanskrit texts from 1500 BCE, and the Kama Sutra from the 3rd century mentions kissing inside of mouths.
Etymology[edit]
A French kiss is so called because at the beginning of the 20th century, in the English-speaking world, the French had acquired a reputation for more adventurous and passionate sex practices. It originated in America and Great Britain. In France, it is referred to as un baiser amoureux ("a lover's kiss") or un baiser avec la langue ("a kiss with the tongue"), and was previously known as un baiser Florentin ("a Florentine kiss"). The Petit Robert 2014 French dictionary, released in 2013, added the French verb "se galocher," slang for kissing with tongues. The informal English term "frenching" also means French kissing, as does the Quebec French term "frencher".
Disease risks[edit]
A study showed that French kissing can carry moderate risk of HPV. However, a professor calls kissing a low-risk activity that should be safe from HPV. The possibility of contracting HIV from French kissing is extremely low as transmission would require open wounds. Centers for Disease Control and Prevention considers transmission of Hepatitis B via French kissing to be an unlikely mode of infection. However, deep kissing that involves the exchange of large amounts of saliva might result in infection if there are cuts or abrasions in the mouth of the infected person, especially if they have a high viral load. Occasionally, syphilis can be passed through prolonged French kissing, but this usually requires contact with an active lesion. French kissing is an unlikely mode of transmission of infection by gonorrhea.
In other species[edit]
As of 2019, bonobos are the only species, other than humans, to have been observed engaging in tongue kissing.
See also[edit]
Human sexual activity
Oral sex
Anilingus
Cunnilingus
Fellatio
Socialist fraternal kiss | biology | 16017 | https://no.wikipedia.org/wiki/Lingua%20franca | Lingua franca | Lingua franca (uttales lingva franka; italiensk, bokstavelig «frankisk språk») var opprinnelig en betegnelse for et blandingsspråk eller fellesspråk,<ref>«fellesspråk», NAOB</ref> som oppsto i korsfarertiden (middelalderen) rundt om i Middelhavet. Det har siden blitt en generell betegnelse for kommunikasjon mellom personer som ikke har et felles morsmål, og derfor bruker et tredjespråk som er adskilt fra begges språk, eksempelvis fransk som diplomatspråk.
Ulike former for lingua franca har utviklet seg rundt om i verden i menneskehetens historie, tidvis av kommersielle hensyn (såkalte «handelsspråk»), men også av kulturelle, religiøse, diplomatiske og administrativ bekvemmelighet, og som et virkemiddel for å utveksle informasjon mellom vitenskapsfolk og andre lærde av forskjellige nasjonaliteter.Gordin, Michael D. (2015): Scientific Babel: How Science Was Done Before and After Global English. Chicago, Illinois: University of Chicago Press. ISBN 9780226000299. Et verdensspråk er idéen bak et global lingua franca. Et av de mest utstrakt praktiserte språket og hurtigst spredte verdensspråket i dag er engelsk. Det har over 980 000 000 bruker som første- og andrespråk verden over.
Karaktertrekk
Lingua franca er et funksjonelt eller praktisk begrep, uavhengig av lingvistisk historie eller språklig struktur. Pidgin- og kreolspråk har ofte funksjon som lingua francas. Hvor morsmålet er benyttet som et innfødt språk i et samfunn, er lingua franca benyttet utfor dette samfunnets grenser og som et andrespråk for kommunikasjon mellom grupper. Lingua franca fungerer som et fellesspråk for grupper som ikke deler samme morsmål, for eksempel kiswahili i Sentral- og Øst-Afrika, og engelsk som er innfødt språk Storbritannia, men er benyttet som lingua franca på Filippinene og i India. Russisk, mandarin (kinesisk), arabisk, spansk, portugisisk, og fransk fungerer med tilsvarende hensikt som lingua francas i mange områder.
Etymologi
Begrepet «lingua franca» er avledet fra det språk som folk rundt Midtøsten og den østlige delen av Middelhavet benyttet som hovedspråk for handel og diplomati i senmiddelalderen, også under renessansen og fram til 1700-tallet. Til tross for navnet, som bokstavelig betyr «frankisk språk», var det en svært forenklet form for italiensk, fylt opp med spanske, greske, arabiske og tyrkiske ord. På denne tiden dominerte italienere handelen i havnbyene rundt Middelhavet innenfor Det osmanske rike og i arabiske Midtøsten. Selve betegnelsen, som muligens er av arabisk opprinnelse, har sitt opphav tilbake til korsfarertiden, hvor araberne kalte alle europeere for «frankere». Engelske kilder fra 1600-tallet omtalte det også som «bastardspansk».
I betydningen «fellesspråk»
Flere versjoner av lingua franca utviklet seg, blant annet en portugisisk form som ble brukt på portugisiske skip og i landets kolonier. I dag finner man spor etter språket særlig i algirsk slang. Også i britisk engelsk finner man enkelte ord fra lingua franca'', da mange engelske sjømenn gjorde tjeneste på skip hvor man snakket språket.
Funksjonen lingua franca hadde som handelsspråk, har ført til at man også bruker navnet som betegnelse på et fellesspråk i en region med flere språkgrupper, spesielt i forbindelse med uoffisielle språk. Man finner for eksempel hausa i Vest-Afrika, hindi i det meste av India og swahili i Øst-Afrika. Språkformen som er i bruk som lingua franca avviker ofte fra formen som brukes som morsmål, da den påvirkes av de forskjellige morsmålene i regionen. Et lands offisielle språk kan også ha funksjon som lingua franca, men omtales da gjerne nettopp som offisielt språk. Dette er et vanlig fenomen særlig i tidligere kolonier, der kolonimaktens språk brukes i offentlige sammenhenger, mens befolkningen ofte har andre morsmål.
I Europa har flere språk gjort tjeneste som fellesspråk i de øvre samfunnssjikt. Spesielt har latin utmerket seg som akademisk og kirkelig språk gjennom mange århundrer.
Konstruerte språk som esperanto, ido, interlingua og volapük har vært ment å skulle fylle en funksjon som globalt fellesspråk, og er derfor ofte omtalt som kandidater for et globalt lingua franca. Bruken har imidlertid vært begrenset.
Referanser
Språk
Konstruerte språk | norwegian_bokmål | 0.972558 |
kissing_natural_human_activity/Kissing_traditions.txt |
Many societies have traditions which involve kissing. Kissing can indicate joy or be used as part of a greeting. Kissing involves the touching of one's lips to the lips or other body part, such as the cheek, head or hand of another person. Sometimes people often kiss their friends as a way of giving luck or even showing feelings.
Greetings[edit]
See also: Hand-kissing and Cheek kissing
Denis Thatcher, husband of then-Prime Minister of the United Kingdom Margaret Thatcher, greets then-American First Lady Nancy Reagan by kissing her hand, 1988.
In the Western world, a kiss is a common gesture of greeting, and at times a kiss is expected. Throughout all cultures people greet one another as a sign of recognition, affection, friendship and reverence. Depending on the occasion and the culture, a greeting may take the form of a handshake, hug, bow, nod, nose rub, a kiss on the lips with the mouth closed or a kiss or kisses on the cheek. Cheek kissing is most common in Europe and Latin America and has become a standard greeting in Latin Europe.
While cheek kissing is a common greeting in many cultures, each country has a unique way of kissing. In Slovenia, Serbia, North Macedonia, Montenegro, Russia, the Netherlands, Luxembourg, Switzerland, Poland and Lebanon, it is customary to "kiss three times, on alternate cheeks". Italians, Croatians and Hungarians usually kiss twice in a greeting and in Mexico and Belgium only one kiss is necessary. In Ecuador, women kiss on the right cheek only and in Oman it is not unusual for men to kiss one another on the nose after a handshake.
Number of kisses in FranceCheek given for first kiss in France
French culture expects kisses on the cheek in greeting, though the customs differ. Two kisses are most common throughout all of France but, in Provence, three kisses are given and in Nantes, four are exchanged.
Kissing quickly on the lips with the mouth closed is a common greeting in some places of Western culture such as South Africa.
Kissing traditions were often modified during the COVID-19 pandemic to avoid spreading severe illness.
Kissing spots[edit]
Kiss me at the kissing bench[edit]
The Syracuse University senior class of 1912 left behind a stone bench. With this gesture the graduating class hoped "to begin a tradition of graduating classes leaving behind similar gifts that would add to the beauty of the campus." While the bench does enhance the beauty of the Syracuse University quad, the kissing bench has become much more than an ordinary seat. In the 1950s, it was said that if a woman were kissed while sitting on the bench she would "avoid the risk of becoming a spinster." However, in 1970 the tradition was expanded to state that a woman must be kissed on the bench to graduate and marry. Currently the tradition stands that if two people kiss while sitting on the kissing bench they will eventually marry.
Meet me at the kissing post[edit]
The kissing post, supporting Ellis Island's registry room, is a famous column at which millions of US immigrants reunited with family. At the registry room, final stages of the immigration process were completed. Then, as immigrants moved towards the pillar it marked a significant moment in their journey. Processed immigrants would search for family members who were to meet them at the kissing post. The once ordinary post was named the kissing post by staff members at Ellis Island in reaction to the "joyful reunions" and kisses between relatives and loved ones. Not only did immigrants endure the long passage to the United States but upon arriving they underwent a lengthy inspection process. This emotional process included physical exams, medical detentions, Board hearings for unaccompanied women and children and separation from family members. Seeing the kissing post at the end of their journey to America was an emotional conclusion to their experience. The kissing post signifies freedom, reunion and a new beginning.
Kissing the Blarney stone[edit]
Tourist kissing the Blarney Stone
Kissing the Blarney Stone (also called the Stone of Eloquence) is a popular custom in the Castle of Blarney in Ireland. The stone is below the battlements on the parapet, making kissing the stone difficult. Originally, people would be hung by their feet over the parapet and be lowered to reach the stone. However, after a man died from falling, a new system was developed. The person now lies on their back with someone securing their feet, and they lower themselves downward while holding on to iron rails. Then, they can reach the stone that people have kissed for hundreds of years. How this tradition started is unknown, but people who succeed in kissing the stone are said to be given the gift of eloquence. One legend describes an old woman who was rescued from drowning by the king of Munster. She rewarded him by casting a spell on a stone that would give him magical speaking abilities whenever he kissed it. Another story tells of a past ruler of the castle, Dermont McCarthy, who was noted for never giving up his castle to Queen Elizabeth I. McCarthy was expected to give the castle to the Queen as a sign of his loyalty, however, he always seemed to have an excuse to put it off. He was said to have had convincing and eloquent reasons for postponing his gift, thus the Queen began to call it "Blarney talk". The word Blarney now means "the ability to influence and coax with fair words and soft speech without giving offense". This led to the belief that anyone who kissed the stone would receive McCarthy's skill or the "gift of the gab", as locals call it. Many have traveled to become more eloquent including Sir Walter Scott, world leaders, American presidents, and international entertainers. They all come for this promise: kiss the Blarney Stone, and "you’ll never again be lost for words."
Special occasions[edit]
Kissing under the mistletoe[edit]
It is a Christmas custom for a couple who meet under a mistletoe to kiss. Mistletoe is commonly used as a Christmas decoration, though such use was rarely alluded to until the 18th century. The tradition has spread throughout the English-speaking world but is largely unknown in the rest of Europe. It was described in 1820 by American author Washington Irving in his The Sketch Book of Geoffrey Crayon, Gent.:
The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases.
Some claim that the origin of the tradition of kissing under the mistletoe goes back to ancient Norse mythology. According to the myth, a goddess named Frigg had a son named Baldr. When he was born, she made all plants unable to hurt him. Yet she overlooked the mistletoe plant, and a god known for his mischief, Loki, tricked another god into killing Baldr with a spear made of mistletoe. The gods eventually brought Baldr back to life, and Frigg declared that mistletoe would bring love rather than death into the world. People then kissed under the mistletoe to obey the goddess, as well as to remember Baldr's resurrection.
Another theory is that the tradition originated in the ancient Babylonian-Assyrian Empire. Single women apparently stood under mistletoe hung outside the temple for the goddess of beauty and love. They were expected to bond with the first man that approached them - but they did not kiss. Historically, mistletoe was seen as a supernatural, healing plant. It was believed to promote fertility, and its leaves were said to be an aphrodisiac. Mistletoe was once a part of marriage ceremonies for this reason, and was placed under couples' beds for good luck. The tradition later was found in England, when young men would kiss women standing under the mistletoe, and would pluck a berry from the bush after each kiss. After all the berries were gone, it was bad luck to continue kissing under that bush. It is important to remember that during this period a kiss was taken very seriously - it was usually seen as a promise of marriage.
New Year's kiss[edit]
In some Western cultures, it is a custom for people to kiss at the stroke of midnight on New Year's Eve. Some hold the superstition that failing to kiss someone ensures a year of loneliness.
When celebrating at a Scottish Hogmanay party, it is custom to try to give a kiss to everyone in the room after the stroke of midnight "the bells".
Wedding kiss[edit]
Married couple's first kiss
It is a Western custom for a newly married couple to exchange a kiss at the conclusion of their wedding ceremony. Some Christians hold the belief that the kiss symbolizes the exchange of souls between the bride and the groom, fulfilling the scripture that "the two shall become one flesh". However, some trace the tradition to an ancient Roman tradition, whereby the exchange of a kiss signified the completion of a contract. Although the kiss is not a formal requirement of the ceremony, most regard the gesture as a joyful start of the marriage. The most traditional way guests entice the new couple to kiss is by clinking their glasses. An ancient Christian tradition explains that the clinking sound scares the devil away and the couple kisses in his absence. Another tradition is to ring bells placed at the tables by the wedding party. A ring of the bell signals the bride and groom to kiss.
Youth and kissing[edit]
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Kissing songs[edit]
Child and teenage culture includes a number of simple songs about kissing, love and romance, with some revolving around heartbreak and others focussing on enduring love. One of the most famous songs is a children's song often used to tease other children who are thought to feel affection toward each other:
[name] and [name] sitting in a tree
K-I-S-S-I-N-G
First comes love, then comes marriage
Then comes a baby in a baby carriage
Sometimes there are more verses to the song, depending on the particular variation the children know.
Religious kiss[edit]
Kissing in Christianity[edit]
Kissing out of honor, respect, and even forgiveness is a tradition that is incorporated into many Christian denominations. The kissing of icons, painted images of Jesus and the saints, is the primary form of veneration in Orthodox Christianity. Veneration of the holy images is an ancient custom dating back to the 5th and 6th centuries, and is still practiced today in Orthodox Christian worship. Through veneration, Orthodox Christians show reverence for the people and the events depicted in the icon.
Another Christian kissing tradition is known as the "kiss of peace." This tradition is traced to Apostle Paul's instruction for Christians to "greet each other with a holy kiss". (Romans 16:16) Today during the "kiss of peace" ritual members will exchange a handshake, hug, or kiss on the cheek as a sign of mutual forgiveness.
Kissing of feet is an important Christian religious ritual. Feet washing, which precedes the kissing, is a sign of humility and is looked upon as an "act of lowly service, of loving service, and of self-giving service." Jesus washed the feet of his disciples and then commanded them to "wash one another's feet" (John 13:12) with love and humbleness as a service through which one can express "the love of God and the saving, cleansing grace of our savior Jesus Christ to each other." After cleansing, a kiss would be bestowed on the feet as an act of servitude. By performing the actions of the lowliest servant, Jesus demonstrated what kind of servant-based leadership was expected from his disciples.
Judas was said to have betrayed Jesus with a kiss - condemning him to death.
Kissing the pope's ring[edit]
Kissing the Ring of the Fisherman (in Italian, the pescatorio) is a centuries-old Roman Catholic tradition. Each newly elected Pope is given a gold ring with his name in raised lettering and the image of St. Peter in a fishing boat. The title Pope (Latin: papa; from Greek: πάππας pappas, a child's word for father) is an informal name for the bishop of Rome, the first of whom was believed to be the apostle Peter, who was known as one of the "fishers of men" (Mark 1:17). Originally the ring was used to seal documents, historically called papal briefs. However, this custom ended in 1842 when the wax seal was replaced by a stamp. Today, Roman Catholics pay respect to the reigning Pope by kneeling before him and kissing his ring.
Kissing a bishop's ring[edit]
Kissing the hand or ring of a bishop (in Italian, the baciamano) is an ancient custom.
See also[edit]
Kiss
Traditions | biology | 670939 | https://no.wikipedia.org/wiki/Elizabeth%20Barrett%20Browning | Elizabeth Barrett Browning | Elizabeth Barrett Browning (født 6. mars 1806 i Durham, England, Storbritannia, død 29. juni 1861 i Firenze, Toscana, Italia) var en britisk poet.
Bakgrunn og virke
Hennes far, en rik forretningsmann og presbyterianer som hadde tjent en formue på en sukkerplantasje på Jamaica, var nærmest en hustyrann. Familien, som bestod av tolv barn, bodde på en stor eiendom utenfor Durham. Som barn kom hun ut for en rideulykke, hun falt av sin ponny. hun skadet ryggraden og ble siden behandlet som invalid av sin far. Hun hadde ingen egentlige helseproblemer etter ulykken, men ble betraktet som «nervesyk» og fra 1821 ble hun satt på opium av familiens huslege.
Hun var interessert i litteratur, hadde lest Shakespeares samlede verk og de greske og italienske klassikerne. Hun var i prinsippet helt autodidakt, lærde seg latin, gresk og til og med så meget hebraisk att hun kunne lese Det gamle testamentet på originalspråket. Med årene ble hun fascinert av Rousseau, Voltaire og Mary Wollstonecraft Shelley og deres kamp for menneskerettigheter. Hun var også meget interessert i metafysikk. Som nittenåring utga hun en diktsamling og i 1844 kom hennes Poems ut.
Faren gikk på en rekke økonomiske tap på 1830-tallet og flyttet til Wimpole Street i London. På grunn av sin sykdom flyttet hun 1837 sammen med en av sine brødre til Torquay i det sørlige England, der klimaet ble sett på som mer gunstig. Under oppholdet der druknet broren og dette ble en stor sorg for henne. De følgende årene tilbrakte hun sengeliggende, helt isolert i sitt soveværelse.
Tidlig på 1840-tallet begynte hun å lese Robert Brownings poesi og skrev et brev til ham. Browning hadde satt pris på hennes diktsamlinger, særlig The Cry of the Children. De begynte å brevveksle og etterhvert, i mai 1845, fikk Browning lov til å besøke henne. Hun hadde da vært sengeliggende i flere år og hennes hovedmåltid bestod av en «eggetoddy», eggeplommer og litt portvin. Deres første møte ble starten til et dypt vennskap som modnet til kjærlighet. Den «syklige» Elizabeths helse ble merkbart forbedret. Under Brownings oppvartning av henne skrev hun ett av sine mest kjente verk, Sonnets from the Portuguese (utgitt 1847), under påvirkning fra Luís de Camões verk.
Av frykt for hennes tyranniske far giftet de seg i hemmelighet i august 1846 og rømte siden til Italia. Paret bosatte seg i Firenze og deres ekteskap var meget lykkelig. Hun fødte en sønn, Robert, den 9. mars 1849. Hennes far gjorde henne imidlertid arveløs. Faren kunne ikke akseptere at noen av hans døtre ble oppvartet og giftet seg.
I årene i Italia skrev hun flere politiske dikt. Hun engasjerte seg i fattige barns levekår og i Italias frihetskamp og forening. Hun beundret Napoleon III, som ga håp om et forent Italia. I 1851 utgav hun diktsamlingen Casa Guidi Windows, som var oppkalt etter det hus i Firenze der ekteparet bodde, og 1857 blankverset Aurora Leigh.
Hun døde 1861, i sin ektemanns armer.
Noen av hennes mest kjente kjærlighetsdikt er fra Sonnets from the Portuguese, som hun skrev på den tiden Robert Browning i hemmelighet oppvartet henne.
XXXVI:e sonnette:
First time he kissed me, he but only kissed,
The fingers of this hand wherewith I write;,
And, ever since, it grew more clean and white...,
Slow to world-greetings ... quick with its "Oh, list",
When the angels speak. A ring of amethyst, I could not wear here, plainer to my sight,
Than that first kiss. The second passed in height,
The first, and sought to the forehead, and half missed,´
Half falling on the hair, Oh, beyond meed;
That was the chrism of love, which love's own crown,
With sanctifying sweetness, did preceede,
The third upon my lips were folded down,
In perfect purple state; since when indeed,
I have been proud and said, "My love, my own"
XLIII: sonnette:
How do I love thee? Let me count the ways,
I love thee to the depth and breadth and height,
My soul can reach, when feeling out of sight,
For the ends of Being and ideal Grace,
I love thee to the level of every day's,
Most quiet need, by sun and candelight,
I love thee freely, as men strive for Right,
I love thee purely, as they turn from Praise,
I love thee with the passion put to use,
In my old griefs, and with my childhood's faith,
I love thee with a love I seemed to lose,
With my lost saints – I love thee with the breadth,
Smiles, tears, of all my life! – and, if Good choose,
I shall but love thee better after death
Bibliografi
Poems 1844
Sonnets from the Portuguese 1847
Casa Guidi Windows 1851
Aurora Leigh 1857
Film
Elizabeth Barretts voksne liv frem til Italia-reisen har blitt skildret i to amerikanske filmer, begge med tittelen The Barretts of Wimpole Street. I filmen fra 1934 hovedrollen spilt av Norma Shearer og i filmen fra 1951 spilte Jennifer Jones tilsvarende rolle.
Referanser
Eksterne lenker
Engelske lyrikere
Engelskspråklige forfattere
Personer fra City of Durham | norwegian_bokmål | 0.818225 |
cell_membrane_break_apart/Entropic_force.txt |
In physics, an entropic force acting in a system is an emergent phenomenon resulting from the entire system's statistical tendency to increase its entropy, rather than from a particular underlying force on the atomic scale.
Mathematical formulation[edit]
In the canonical ensemble, the entropic force
F
{\displaystyle \mathbf {F} }
associated to a macrostate partition
{
X
}
{\displaystyle \{\mathbf {X} \}}
is given by
F
(
X
0
)
=
T
∇
X
S
(
X
)
|
X
0
,
{\displaystyle \mathbf {F} (\mathbf {X} _{0})=T\nabla _{\mathbf {X} }S(\mathbf {X} )|_{\mathbf {X} _{0}},}
where
T
{\displaystyle T}
is the temperature,
S
(
X
)
{\displaystyle S(\mathbf {X} )}
is the entropy associated to the macrostate
X
{\displaystyle \mathbf {X} }
, and
X
0
{\displaystyle \mathbf {X} _{0}}
is the present macrostate.
Examples[edit]
Pressure of an ideal gas[edit]
The internal energy of an ideal gas depends only on its temperature, and not on the volume of its containing box, so it is not an energy effect that tends to increase the volume of the box as gas pressure does. This implies that the pressure of an ideal gas has an entropic origin.
What is the origin of such an entropic force? The most general answer is that the effect of thermal fluctuations tends to bring a thermodynamic system toward a macroscopic state that corresponds to a maximum in the number of microscopic states (or micro-states) that are compatible with this macroscopic state. In other words, thermal fluctuations tend to bring a system toward its macroscopic state of maximum entropy.
Brownian motion[edit]
The entropic approach to Brownian movement was initially proposed by R. M. Neumann. Neumann derived the entropic force for a particle undergoing three-dimensional Brownian motion using the Boltzmann equation, denoting this force as a diffusional driving force or radial force. In the paper, three example systems are shown to exhibit such a force:
electrostatic system of molten salt,
surface tension and,
elasticity of rubber.
Polymers[edit]
Main article: Ideal chain
A standard example of an entropic force is the elasticity of a freely jointed polymer molecule. For an ideal chain, maximizing its entropy means reducing the distance between its two free ends. Consequently, a force that tends to collapse the chain is exerted by the ideal chain between its two free ends. This entropic force is proportional to the distance between the two ends. The entropic force by a freely jointed chain has a clear mechanical origin and can be computed using constrained Lagrangian dynamics. With regards to biological polymers, there appears to be an intricate link between the entropic force and function. For example, disordered polypeptide segments – in the context of the folded regions of the same polypeptide chain – have been shown to generate an entropic force that has functional implications.
Hydrophobic force[edit]
See also: Hydrophobic effect § Cause
Water drops on the surface of grass
Another example of an entropic force is the hydrophobic force. At room temperature, it partly originates from the loss of entropy by the 3D network of water molecules when they interact with molecules of dissolved substance. Each water molecule is capable of
donating two hydrogen bonds through the two protons,
accepting two more hydrogen bonds through the two sp-hybridized lone pairs.
Therefore, water molecules can form an extended three-dimensional network. Introduction of a non-hydrogen-bonding surface disrupts this network. The water molecules rearrange themselves around the surface, so as to minimize the number of disrupted hydrogen bonds. This is in contrast to hydrogen fluoride (which can accept 3 but donate only 1) or ammonia (which can donate 3 but accept only 1), which mainly form linear chains.
If the introduced surface had an ionic or polar nature, there would be water molecules standing upright on 1 (along the axis of an orbital for ionic bond) or 2 (along a resultant polarity axis) of the four sp orbitals. These orientations allow easy movement, i.e. degrees of freedom, and thus lowers entropy minimally. But a non-hydrogen-bonding surface with a moderate curvature forces the water molecule to sit tight on the surface, spreading 3 hydrogen bonds tangential to the surface, which then become locked in a clathrate-like basket shape. Water molecules involved in this clathrate-like basket around the non-hydrogen-bonding surface are constrained in their orientation. Thus, any event that would minimize such a surface is entropically favored. For example, when two such hydrophobic particles come very close, the clathrate-like baskets surrounding them merge. This releases some of the water molecules into the bulk of the water, leading to an increase in entropy.
Another related and counter-intuitive example of entropic force is protein folding, which is a spontaneous process and where hydrophobic effect also plays a role. Structures of water-soluble proteins typically have a core in which hydrophobic side chains are buried from water, which stabilizes the folded state. Charged and polar side chains are situated on the solvent-exposed surface where they interact with surrounding water molecules. Minimizing the number of hydrophobic side chains exposed to water is the principal driving force behind the folding process, although formation of hydrogen bonds within the protein also stabilizes protein structure.
Colloids[edit]
Entropic forces are important and widespread in the physics of colloids, where they are responsible for the depletion force, and the ordering of hard particles, such as the crystallization of hard spheres, the isotropic-nematic transition in liquid crystal phases of hard rods, and the ordering of hard polyhedra. Because of this, entropic forces can be an important driver of self-assembly
Entropic forces arise in colloidal systems due to the osmotic pressure that comes from particle crowding. This was first discovered in, and is most intuitive for, colloid-polymer mixtures described by the Asakura–Oosawa model. In this model, polymers are approximated as finite-sized spheres that can penetrate one another, but cannot penetrate the colloidal particles. The inability of the polymers to penetrate the colloids leads to a region around the colloids in which the polymer density is reduced. If the regions of reduced polymer density around two colloids overlap with one another, by means of the colloids approaching one another, the polymers in the system gain an additional free volume that is equal to the volume of the intersection of the reduced density regions. The additional free volume causes an increase in the entropy of the polymers, and drives them to form locally dense-packed aggregates. A similar effect occurs in sufficiently dense colloidal systems without polymers, where osmotic pressure also drives the local dense packing of colloids into a diverse array of structures that can be rationally designed by modifying the shape of the particles. These effects are for anisotropic particles referred to as directional entropic forces.
Cytoskeleton[edit]
Contractile forces in biological cells are typically driven by molecular motors associated with the cytoskeleton. However, a growing body of evidence shows that contractile forces may also be of entropic origin. The foundational example is the action of microtubule crosslinker Ase1, which localizes to microtubule overlaps in the mitotic spindle. Molecules of Ase1 are confined to the microtubule overlap, where they are free to diffuse one-dimensionally. Analogically to an ideal gas in a container, molecules of Ase1 generate pressure on the overlap ends. This pressure drives the overlap expansion, which results in the contractile sliding of the microtubules. An analogous example was found in the actin cytoskeleton. Here, the actin-bundling protein anillin drives actin contractility in cytokinetic rings.
Controversial examples[edit]
Some forces that are generally regarded as conventional forces have been argued to be actually entropic in nature. These theories remain controversial and are the subject of ongoing work. Matt Visser, professor of mathematics at Victoria University of Wellington, NZ in "Conservative Entropic Forces" criticizes selected approaches but generally concludes:
There is no reasonable doubt concerning the physical reality of entropic forces, and no reasonable doubt that classical (and semi-classical) general relativity is closely related to thermodynamics. Based on the work of Jacobson, Thanu Padmanabhan, and others, there are also good reasons to suspect a thermodynamic interpretation of the fully relativistic Einstein equations might be possible.
Gravity[edit]
Main article: Entropic gravity
In 2009, Erik Verlinde argued that gravity can be explained as an entropic force. It claimed (similar to Jacobson's result) that gravity is a consequence of the "information associated with the positions of material bodies". This model combines the thermodynamic approach to gravity with Gerard 't Hooft's holographic principle. It implies that gravity is not a fundamental interaction, but an emergent phenomenon.
Other forces[edit]
In the wake of the discussion started by Verlinde, entropic explanations for other fundamental forces have been suggested, including Coulomb's law. The same approach was argued to explain dark matter, dark energy and Pioneer effect.
Links to adaptive behavior[edit]
It was argued that causal entropic forces lead to spontaneous emergence of tool use and social cooperation. Causal entropic forces by definition maximize entropy production between the present and future time horizon, rather than just greedily maximizing instantaneous entropy production like typical entropic forces.
A formal simultaneous connection between the mathematical structure of the discovered laws of nature, intelligence and the entropy-like measures of complexity was previously noted in 2000 by Andrei Soklakov in the context of Occam's razor principle.
See also[edit]
Colloids
Nanomechanics
Thermodynamics
Abraham–Lorentz force
Entropic gravity
Entropy
Introduction to entropy
Entropic elasticity of an ideal chain
Hawking radiation
Data clustering
Depletion force
Maximal entropy random walk | biology | 6331931 | https://sv.wikipedia.org/wiki/Trajektoria | Trajektoria | Trajektoria betecknar den bana i vilken en partikel rör sig i t. ex. en sjö eller i atmosfären. Genom beräkning av trajektorier kan man t. ex. följa föroreningars spridning i vatten och luft.
Ett rörligt föremål kan vara en projektil eller en satellit. Till exempel kan också vara en planetbana, en asteroid eller en komet som rör sig runt en central massa. En bana kan beskrivas matematiskt antingen genom geometrin hos banan, eller som positionen för det rörliga objektet över tiden.
I reglerteknik är en bana i tiden ordnad uppsättning av tillstånd i ett dynamiskt system. I diskret matematik, är en bana en sekvens av värden som räknats fram genom itererad tillämpning av en kartläggning för ett element från dess källa.
Trajektorians fysik
Ett välkänt exempel på en bana är banan för en projektil, såsom en kastad boll eller en gunga. I en mycket förenklad modell rör sig objektet enbart genom påverkan av ett likformigt gravitationskraftfält. Detta kan vara en god approximation för en sten som kastas en kortare sträcka, t.ex., vid ytan av månen. I denna enkla approximation, tar banan formen av en parabel. Generellt vid fastställandet av banor kan det vara nödvändigt att ta hänsyn till olikformiga gravitationskrafter och luftmotstånd (drift och aerodynamik). Detta är centralt för disciplinen ballistik.
Ett av de viktiga resultaten av Newtons mekanik var möjligheten att härleda Keplers lagar. I gravitationsfältet hos en masspunkt eller en sfäriskt symmetrisk utbredd massa (t.ex. solen), är banan för ett rörligt föremål en konisk sektion, vanligtvis en ellips eller en hyperbel. Detta överensstämmer med observerade banorna hos planeter, kometer och konstgjorda rymdfarkoster som en tämligen bra approximation, även för en komet som passerar nära solen, då den också påverkas av andra krafter, såsom solvinden och strålningstryck, som modifierar dess bana, och orsakar att kometen matar ut material i rymden.
Newtons teori utvecklades senare till den gren av teoretisk fysik som kallas klassisk mekanik. Den utnyttjar matematikerna differentialkalkyl (som de facto också initierats av Newton i hans ungdom). Under århundraden, har otaliga forskare bidragit till utvecklingen av dessa två discipliner. Klassisk mekanik blev den mest framträdande demonstrationen av kraften i rationellt tänkande i vetenskap och teknik. Den hjälper till att förstå och förutsäga ett stort antal olika av fenomen varav banor bara är ett exempel.
Betrakta en partikel av massa , som rör sig i ett potentialfält . Fysiskt sett representerar massan tröghet, och fältet representerar externa krafter, av en viss typ känd som kallas "konservativ". Det vill säga, givet på varje relevanta position, finns det ett sätt att bestämma den associerade kraft som skulle verka i denna position, säg från tyngdkraften. Alla krafter kan dock inte uttryckas på detta sätt.
Rörelsen hos partikeln beskrivs av en andra ordningens differentialekvation
with
På den högra sidan, är den kraft som ges i form av , gradienten av potentialen, tagen vid lägen längs banan. Detta är den matematiska formen av Newtons andra rörelselag: kraften är lika med massan gånger acceleration, för sådana situationer.
Källor
Bra Böckers lexikon, 1980.
Ballistik
Mekanik | swedish | 0.619625 |
cell_membrane_break_apart/cell-membranes-14052567.txt | This page has been archived and is no longer updated
Aa Aa Aa
# Cell Membranes
##
Cell membranes protect and organize cells. All cells have an outer plasma
membrane that regulates not only what enters the cell, but also how much of
any given substance comes in. Unlike prokaryotes, eukaryotic cells also
possess internal membranes that encase their organelles and control the
exchange of essential cell components. Both types of membranes have a
specialized structure that facilitates their gatekeeping function.
## What Are Cellular Membranes Made Of?
With few exceptions, cellular membranes — including plasma membranes and
internal membranes — are made of glycerophospholipids , molecules composed
of glycerol, a phosphate group, and two fatty acid chains. Glycerol is a
three-carbon molecule that functions as the backbone of these membrane lipids.
Within an individual glycerophospholipid, fatty acids are attached to the
first and second carbons, and the phosphate group is attached to the third
carbon of the glycerol backbone. Variable head groups are attached to the
phosphate. Space-filling models of these molecules reveal their cylindrical
shape, a geometry that allows glycerophospholipids to align side-by-side to
form broad sheets (Figure 1).
Figure 1: The lipid bilayer and the structure and composition of a
glycerophospholipid molecule
(A) The plasma membrane of a cell is a bilayer of glycerophospholipid
molecules. (B) A single glycerophospholipid molecule is composed of two major
regions: a hydrophilic head (green) and hydrophobic tails (purple). (C) The
subregions of a glycerophospholipid molecule; phosphatidylcholine is shown as
an example. The hydrophilic head is composed of a choline structure (blue) and
a phosphate (orange). This head is connected to a glycerol (green) with two
hydrophobic tails (purple) called fatty acids. (D) This view shows the
specific atoms within the various subregions of the phosphatidylcholine
molecule. Note that a double bond between two of the carbon atoms in one of
the hydrocarbon (fatty acid) tails causes a slight kink on this molecule, so
it appears bent.
© 2010 Nature Education All rights reserved.
Figure Detail
Glycerophospholipids are by far the most abundant lipids in cell membranes.
Like all lipids, they are insoluble in water, but their unique geometry causes
them to aggregate into bilayers without any energy input. This is because
they are two-faced molecules, with hydrophilic (water-loving) phosphate heads
and hydrophobic (water-fearing) hydrocarbon tails of fatty acids. In water,
these molecules spontaneously align — with their heads facing outward and
their tails lining up in the bilayer's interior. Thus, the hydrophilic heads
of the glycerophospholipids in a cell's plasma membrane face both the water-
based cytoplasm and the exterior of the cell.
Altogether, lipids account for about half the mass of cell membranes.
Cholesterol molecules, although less abundant than glycerophospholipids,
account for about 20 percent of the lipids in animal cell plasma membranes.
However, cholesterol is not present in bacterial membranes or mitochondrial
membranes. Also, cholesterol helps regulate the stiffness of membranes, while
other less prominent lipids play roles in cell signaling and cell recognition.
Figure 2: The glycerophospholipid bilayer with embedded transmembrane proteins
© 2010 Nature Education All rights reserved.
In addition to lipids, membranes are loaded with proteins. In fact, proteins
account for roughly half the mass of most cellular membranes. Many of these
proteins are embedded into the membrane and stick out on both sides; these are
called transmembrane proteins . The portions of these proteins that are
nested amid the hydrocarbon tails have hydrophobic surface characteristics,
and the parts that stick out are hydrophilic (Figure 2).
At physiological temperatures, cell membranes are fluid; at cooler
temperatures, they become gel-like. Scientists who model membrane structure
and dynamics describe the membrane as a fluid mosaic in which transmembrane
proteins can move laterally in the lipid bilayer. Therefore, the collection of
lipids and proteins that make up a cellular membrane relies on natural
biophysical properties to form and function. In living cells, however, many
proteins are not free to move. They are often anchored in place within the
membrane by tethers to proteins outside the cell, cytoskeletal elements inside
the cell, or both.
## What Do Membranes Do?
Cell membranes serve as barriers and gatekeepers. They are semi-permeable,
which means that some molecules can diffuse across the lipid bilayer but
others cannot. Small hydrophobic molecules and gases like oxygen and carbon
dioxide cross membranes rapidly. Small polar molecules, such as water and
ethanol, can also pass through membranes, but they do so more slowly. On the
other hand, cell membranes restrict diffusion of highly charged molecules,
such as ions, and large molecules, such as sugars and amino acids. The passage
of these molecules relies on specific transport proteins embedded in the
membrane.
Figure 3: Selective transport
Specialized proteins in the cell membrane regulate the concentration of
specific molecules inside the cell.
© 2010 Nature Education All rights reserved.
Membrane transport proteins are specific and selective for the molecules they
move, and they often use energy to catalyze passage. Also, these proteins
transport some nutrients against the concentration gradient, which requires
additional energy. The ability to maintain concentration gradients and
sometimes move materials against them is vital to cell health and maintenance.
Thanks to membrane barriers and transport proteins, the cell can accumulate
nutrients in higher concentrations than exist in the environment and,
conversely, dispose of waste products (Figure 3).
Other transmembrane proteins have communication-related jobs. These proteins
bind signals, such as hormones or immune mediators, to their extracellular
portions. Binding causes a conformational change in the protein that transmits
a signal to intracellular messenger molecules. Like transport proteins,
receptor proteins are specific and selective for the molecules they bind
(Figure 4).
Figure 4: Examples of the action of transmembrane proteins
Transporters carry a molecule (such as glucose) from one side of the plasma
membrane to the other. Receptors can bind an extracellular molecule
(triangle), and this activates an intracellular process. Enzymes in the
membrane can do the same thing they do in the cytoplasm of a cell: transform a
molecule into another form. Anchor proteins can physically link intracellular
structures with extracellular structures.
© 2010 Nature Education All rights reserved.
Figure Detail
Peripheral membrane proteins are associated with the membrane but are not
inserted into the bilayer. Rather, they are usually bound to other proteins in
the membrane. Some peripheral proteins form a filamentous network just under
the membrane that provides attachment sites for transmembrane proteins. Other
peripheral proteins are secreted by the cell and form an extracellular matrix
that functions in cell recognition.
## How Diverse Are Cell Membranes?
In contrast to prokaryotes, eukaryotic cells have not only a plasma membrane
that encases the entire cell, but also intracellular membranes that surround
various organelles. In such cells, the plasma membrane is part of an extensive
endomembrane system that includes the endoplasmic reticulum (ER), the nuclear
membrane, the Golgi apparatus , and lysosomes. Membrane components are
exchanged throughout the endomembrane system in an organized fashion. For
instance, the membranes of the ER and the Golgi apparatus have different
compositions, and the proteins that are found in these membranes contain
sorting signals, which are like molecular zip codes that specify their final
destination.
Mitochondria and chloroplasts are also surrounded by membranes, but they have
unusual membrane structures — specifically, each of these organelles has two
surrounding membranes instead of just one. The outer membrane of mitochondria
and chloroplasts has pores that allow small molecules to pass easily. The
inner membrane is loaded with the proteins that make up the electron transport
chain and help generate energy for the cell. The double membrane enclosures of
mitochondria and chloroplasts are similar to certain modern-day prokaryotes
and are thought to reflect these organelles' evolutionary origins .
## Conclusion
Membranes are made of lipids and proteins, and they serve a variety of barrier
functions for cells and intracellular organelles. Membranes keep the outside
"out" and the inside "in," allowing only certain molecules to cross and
relaying messages via a chain of molecular events
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| biology | 58159 | https://da.wikipedia.org/wiki/Cellemembran | Cellemembran | Cellemembran eller plasmamembran er en biologisk membran, der adskiller det indre af en celle fra omgivelserne. Historisk er cellemembranen desuden blevet kaldt plasmalemma. Den består af et dobbeltlag af lipider med indlejrede proteiner. Lipidernes upolære carbonkæder gør cellemembranen gennemtrængelig for upolære molekyler og visse små molekyler som kuldioxid (CO2) og ilt (O2), men uigennemtrængelig for ioner og de fleste polære molekyler. Passage af ioner og polære molekyler er imidlertid mulig i kontrolleret omfang via forskellige typer transmembrane proteiner, f.eks. kanaler og transportproteiner (herunder biologiske "pumper" som natrium-kalium-pumpen). Cellemembranen medvirker til en række vigtige cellulære processer, f.eks. celleadhæsion og cellesignalering, og tjener som fæste for det intracellulære cytoskelet og vigtige ekstracellulære strukturer, heriblandt cellevæggen og glykocalyxen (en ydre beklædning af glykoproteiner, der medvirker ved celle-celle-genkendelse). Cellesignaleringen foregår ved hjælp af receptorer (modtagermolekyler), der gør cellen i stand til at reagere på specifikke signalstoffer, f.eks. hormoner.
Struktur
Hovedstrukturen i en cellemembran er lipiddobbellaget. Studiet af cellemembranens fysiske egenskaber kaldes for biomembranfysik.
Lipiddobbeltlaget
Biologiske membraner er opbygget af amfifile lipidmolekyler. De består af et polært hoved og en lang, upolær hale. Hovedparten af lipiderne i cellemembranen indeholder én eller flere umættede kæder, hvis dobbeltbinding giver dem et "knæk"; dette knæk giver det samlede lipid en cylinderform. Cylinderformede lipider har en tendens til at danne et dobbeltlag med hinanden, således at de polære hoveder vender mod vandsiden og de upolære haler mod mellemrummet mellem de to lag. Er der tilstrækkeligt mange lipider, slutter dobbeltlaget sig spontant sammen til den termodynamisk mest stabile form, dvs. en kugle. Dette er tilfældet for levende celler. Såvel de hydrofile vekselvirkninger ved membranens overflade som hydrofobe vekselvirkninger mellem lipidmolekylernes alifatiske dele i membranens indre er med til at stabilisere og binde strukturen sammen. En brist i dobbeltlaget vil normalt lukke sig af sig selv.
Generelt er lipiddobbeltlaget uigennemtrængeligt for polære molekyler. Dobbeltlagets hydrofobe indre forhindrer polære molekyler (f.eks. aminosyrer, nukleinsyrer, kulhydrater, proteiner og ioner) i at diffundere gennem membranen, men tillader generelt passiv diffusion af hydrofobe molekyler. Cellen kan dermed kontrollere passagen af hydrofile stoffer via transmembrane proteiner som kanaler og transportproteiner.
Flippaser og scramblaser koncentrerer det negativt ladede fosfolipid fosfatidylserin på indersiden af membranen. Sammen med sialinsyre skaber dette endnu en barriere for ladede partikler og molekyler, der passerer gennem membranen.
Flydende mosaik-modellen
Ifølge den såkaldte flydende mosaik-model foreslået af de amerikanske forskere Seymour Jonathan Singer og Garth L. Nicolson i 1972 kan biologiske membraner opfattes som en todimensionel væske, hvori en stor mængde lipider og proteiner flyder rundt mere eller mindre frit. Vekselvirkninger mellem indlejrede membranproteiner og membranlipider giver anledning til protein-lipid-klynger, der bevæger sig rundt eller ”flyder” lateralt mellem hinanden – en flydende mosaik. Cellemembranens fluiditet afhænger af dens bestanddele og temperatur. Den store mængde proteiner i cellemembranen giver membranen en vis grad af struktur ved f.eks. at danne protein-protein-komplekser og "lipid rafts" (specialiserede mikrodomæner i cellemembranen indeholdende store mængder membranproteiner, kolesterol og en type lipider kaldt glykosphingolipider).
Bestanddele
Cellemembraner indeholder forskellige biomolekyler, først og fremmest lipider og proteiner. Stoffer optages i membranen eller fjernes fra den ved forskellige mekanismer:
Fusion af intracellulære vesikler med membranen (exocytose) udskiller ikke blot vesiklens indhold, men integrerer også vesikelmembranens bestanddele i cellemembranen. Omvendt kan cellemembranen skille sig af med materiale ved at afsnøre dele af sig selv som vesikler.
Hvis en membran er forbundet med en rørformet struktur lavet af membranmateriale, kan materialet fra røret trækkes ind i membranen.
Skønt koncentrationen af membranbestanddele i de omgivende væskefaser er ringe (idet stabile membranbestanddele er tungtopløselige i vand), foregår der en udveksling af molekyler mellem lipid- og vandfasen.
Lipider
Cellemembranen består af tre klasser af amfifile lipider: fosfolipider, glykolipider og steroler (herunder kolesterol). Mængdeforholdet afhænger af celletype, men hos de fleste celler er fosfolipiderne de talrigeste. Studier af røde blodlegemer har vist, at 30 % af deres cellemembraner udgøres af lipider.
Carbonkæderne i fosfolipiderne og glykolipiderne indeholder typisk et lige antal carbonatomer, som regel mellem 16 og 20. Fedtsyrekæder med 16 eller 18 carbonatomer er de almindeligste. Fedtsyrerne i et lipid kan enten være mættede eller umættede – de umættede er næsten altid på cis-formen. Længden og graden af umættethed af en fedtsyrekæde har vital betydning for lipidets rumlige opbygning og dermed membranens fluiditet, idet umættede kæder danner et "knæk", der forhindrer fedtsyrerne i at pakke sig tæt sammen. Dette sænker lipidets smeltepunkt og øger membranens fluiditet. Kolesterol mindsker derimod fluiditeten, da kolesterol giver cellemembranen højere smeltepunkt ved at reducere lipidernes bevægelsesfrihed.
Hele cellemembranen holdes sammen af londonbindinger mellem de hydrofobe fedtsyrekæder. Lipiderne flyder dog frit mellem hinanden. Under fysiologiske forhold opfører fosfolipidmolekylerne i membranen sig som flydende krystaller. Det betyder, at lipidmolekylerne frit kan diffundere rundt mellem hinanden i samme lag. Derimod er det en langsom proces at springe fra lag til lag. "Lipid rafts" og caveolae (latin for "små hulrum") er eksempler på kolesterolrige mikrodomæner i cellemembranen.
Kulhydrater
Cellemembraner indeholder kulhydrater, primært glykoproteiner og i mindre grad glykolipider (cerebrosider og gangliosider). På den intracellulære side sker der stort set aldrig glykosylering. Det gør der derimod på overfladen af cellen. Glykocalyxen er en tynd beklædning af kulhydratholdigt materiale omkring alle celler. Den spiller en vigtig rolle ved celleadhæsion, lymfocytrecirkulation samt andre celleinteraktioner. Glykocalyxen består af oligosakkarider indeholdende sialinsyre, hvis negative ladning danner en udvendig barriere mod ladede partikler.
Proteiner
Omkring 50 % af cellemembranens volumen udgøres af protein. Proteinerne udfører en række vigtige biologiske processer for cellen. Omtrent en tredjedel af gærsvampes gener koder specifikt for dem, og for multicellulære organismer er dette tal endda større.
Cellemembranen er en vigtig kontaktflade for celle-celle-kommunikation. Den indeholder derfor receptor- og genkendelsesproteiner, der sørger for den fysisk-kemiske kommunikation mellem cellen og dens omgivelser, f.eks. antigener, på sin ydre overflade. Membranproteinerne kan også tjene til celle-celle-kontakt, overfladegenkendelse, cytoskeletkontakt, cellesignalering, enzymaktivitet eller transport gennem cellemembranen.
Transmembrane membranproteiner må integreres i cellemembranen. Normalt føres færdigsyntetiserede proteiner ind i lumen af det ru endoplasmatiske reticulum (RER) gennem en proteinkanal, men membranproteiner indeholder et sted i deres sekvens en sekvens med ca. 20 hydrofobe aminosyrer. Denne skal udgøre den transmembrane del af proteinet og virker som en stop-transfer-sekvens, der stopper overføringen af proteinet gennem proteinkanalen. Proteinet vandrer derefter bort fra kanalen og lægger sig i RER-membranen, hvorfra det kan transporteres til Golgiapparatet og videre til cellemembranen ved hjælp af vesikler.
Variationer
Visse celletypers cellemembraner har specifikke navne, hvilket afspejler en varierende lipid- og proteinsammensætning:
Sarcolemma hos muskelceller
Oolemma hos ægceller
Axolemma hos neuronernes axoner
Funktion
Cellemembranen omgiver cellens cytoplasma og adskiller således de intracellulære komponenter fra det ekstracellulære miljø. Svampe, bakterier og planter har desuden en cellevæg, der yder cellen mekanisk støtte og forhindrer passage af større molekyler. Cellemembranen tjener også som fæste for cytoskelettet, der afstiver cellen indvendigt og opretholder dens form, og for den ekstracellulære matrix og andre celler, således at flere celler kan finde sammen og danne væv.
Stoftransport
Cellemembranen er selektivt permeabel (gennemtrængelig) og regulerer, hvad der passerer ind og ud af cellen. Passagen af stoffer gennem cellemembranen kan være passiv eller aktiv (energikrævende). Passagen af ladede partikler skaber sammen med tilstedeværelsen af negativt ladede fosfolipider på indersiden af membranen en spændingsforskel over membranen, cellens membranpotential, der varierer alt efter celletypen. Cellemembranen fungerer således som et selektivt filter, der kun tillader specifikke stoffer at komme ind eller ud. Transporten af stoffer gennem membranen foregår ved forskellige mekanismer:
1. Simpel diffusion og osmose: Nogle stoffer, f.eks. kuldioxid (CO2), ilt (O2) og vand (H2O), kan passere gennem membranens lipiddobbeltlag ved diffusion, som er en passiv proces. Fordi membranen fungerer som barriere for visse molekyler og ioner, kan disse forekomme i forskellige koncentrationer på hver side af membranen. En sådan koncentrationsforskel eller -gradient over en semipermeabel membran skaber et osmotisk tryk, der presser vandet i den retning, hvor koncentrationen er størst.
2. Faciliteret transport: Er ligesom diffusion drevet af en koncentrationsgradient, men foregår gennem kanaler eller ved hjælp af transportproteiner i membranen.
3. Pumper: Ioner, der skal transporteres ind eller ud af cellen imod en koncentrationsgradient, og store molekyler må transporteres gennem cellemembranen ved hjælp af såkaldte pumper, der forbruger energi fra cellen. Et eksempel på en sådan pumpe er natrium-kalium-pumpen (opdaget af Jens Christian Skou m.fl.), der pumper natriumioner (Na+) ud af cellen og kaliumioner (K+) ind i cellen. Transport via pumper er en form for aktiv transport.
4. Sekundært aktiv transport: Kemiske stoffer, der skal transporteres mod sin koncentrationsgradient, kan transporteres sammen med et andet stof, der bevæger sig med sin koncentrationsgradient, således at bevægelsen mod koncentrationsgradienten kan lykkes. Transporten af de to stoffer kan enten foregå i samme retning (symport) eller modsatrettet (antiport). Et eksempel på symport er transporten af glukose og natriumioner (Na+) ind i cellen ved hjælp af SGLT-2-cotransporteren (et transportprotein); hver natriumion, der passerer ind i cellen med en koncentrationsgradient ved hjælp af transporteren, "medbringer" et glukosemolekyle, der bevæger sig imod sin koncentrationsgradient. Den energi, der frigives ved passage af natriumionen, bruges af glukosemolekylet til at overvinde gradienten. Der sker derved intet energitab ved transporten, men natriumionernes koncentrationsgradient må opretholdes ved hjælp af natrium-kalium-pumpen, der forbruger energi. Et eksempel på antiport er den samtidige transport af Na+-ioner ind i cellen og hydrogenioner (H+) ud af cellen ved hjælp af den såkaldte Na+-H+-antiporter (et andet transportprotein), som medvirker til at holde cytosolens pH-værdi på ca. 7,2. Transporten af H+-ioner ud af cellen faciliteres af transporten af Na+-ioner ind i cellen pga. Na+-gradienten, som opretholdes af natrium-kalium-pumpen.
5. Endocytose: Ved endocytose omslutter en celle et molekyle og absorberer det. Cellemembranen danner en hulning indadtil (en invagination) hvori stoffet, der skal absorberes, fanges. Hulningen afsnøres derefter fra indersiden af membranen, hvilket skaber en vesikel, som indeholder stoffet. Absorption af faste partikler ved hjælp af endocytose kaldes også fagocytose, mens endocytose af væske (f.eks. vand), eventuelt med opløste ioner, kaldes pinocytose. Endocytose kræver energi og er således en form for aktiv transport.
6. Exocytose: Ligesom et stof kan transporteres ind i cellen ved invagination og dannelse af en vesikel, kan en vesikel fusionere med cellemembranen og afgive sit indhold til omgivelserne. Denne proces kaldes exocytose. Celler benytter exocytose bl.a. til at skille sig af med ufordøjede rester af stoffer, der er blevet ført ind ved endocytose, og til at udskille hormoner, neurotransmittere (for neuroners vedkommende) eller enzymer. Ved exocytose afsnøres en vesikel eller en vakuole fra Golgiapparatet, hvorefter den transporteres fra cellens indre til indersiden af cellemembranen via cytoskelettet. Her kommer vesikelmembranen i kontakt med cellemembranen. Lipidmolekylerne i de to dobbeltlag rearrangeres, hvorved de to membraner fusionerer. Dette fører til en åbning i den fusionerede membran, hvorigennem vesikelindholdet tømmer sig.
Celleadhæsion og cellesignalering
Cellemembraner kan danne forskellige “supramembranøse” strukturer som caveolae, fokale adhæsioner og forskellige typer celle-celle-forbindelser som desmosomer. Disse strukturer er typisk ansvarlige for celleadhæsion, kommunikation, endocytose og exocytose. De kan påvises ved elektronmikroskopi eller fluorescensmikroskopi. De består af celleadhæsionsmolekyler, f.eks. neuralcelleadhæsionsmolekyler (NCAM), integriner og cadhæriner.
Celleforankring
Forankringsproteiner kobler naboceller sammen, og kan have forskellige udseende og funktion. Desmosomer giver trækkraft, og evne til at modstå stor mekanisk stress, f.eks hudens væv.
Tight junctions kobler naboceller tæt sammen, for at forhindre at stoffer kan passere mellem cellerne, og danner altså en effektiv barriere. Fordøjelsessystemets væv har mange steder tight junctions der har den rolle at sørge for at passagen af næringsstoffer kan reguleres, ved at sørge for at stofferne transporteres direkte fra den apikale overflade, intracellulært gennem cellen, for bagefter at transporteres ud ved basalmembranen.
Gap junctions er intercellulære forbindelser der direkte forbinder cellers cytoplasma, og tillader transport af ioner, molekyler, og endda elektriske impulser. Et godt eksempel er i hjertemuskelcellerne, hvor gap junctions sørger for at myocardiet kontrakter synkront.
Cytoskelettet
Proteiner i cellemembranen tjener som fæste for cellens cytoskelet. Cytoskelettet findes under cellemembranen og udgør et indre stillads for cellen. Cytoskelettet danner desuden cilier og mikrovilli. Cilier (eller fimrehår) er bevægelige udløbere med et indre kompleks af mikrotubuli, der udvendigt er dækket af cellemembranen. I luftvejene medvirker cilier til at fjerne støvpartikler og mikroorganismer fanget i slimlaget. Mikrovilli er fingerlignende udløbere i cellemembranen på visse epitelcellers frie overflade (især i tarmen). Deres formål er at øge overfladearealet, hvilket øger absorptionen af næringsstoffer.
Prokaryoter
Gram-negative bakterier har både en cellemembran og en ydre membran adskilt af et periplasmatisk mellemrum. Andre prokaryoter har kun en cellemembran. Prokaryoter er også omgivet af en cellevæg bestående af peptidoglycaner (aminosyrer og kulhydrater). Visse eukaryoter (svampe- og planteceller) har også cellevægge, som dog ikke består af peptidoglycaner.
Se også
Membrankappe
Spike
Referencer
Eksterne henvisninger
Se "Cellemembranen – nogle væsentlige egenskaber" for en forenklet model af en cellemembran.
Cellebiologi | danish | 0.359622 |
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6. The Parathyroid Glands
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7. The Adrenal Glands
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8. The Pineal Gland
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9. Gonadal and Placental Hormones
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10. The Endocrine Pancreas
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11. Organs with Secondary Endocrine Functions
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12. Development and Aging of the Endocrine System
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19. The Cardiovascular System: Blood
1. Introduction
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2. An Overview of Blood
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3. Production of the Formed Elements
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4. Erythrocytes
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5. Leukocytes and Platelets
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6. Hemostasis
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7. Blood Typing
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20. The Cardiovascular System: The Heart
1. Introduction
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2. Heart Anatomy
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3. Cardiac Muscle and Electrical Activity
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21. Appendix
# Anatomy & Physiology
The Cellular Level of Organization
# The Cell Membrane
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### Learning Objectives
By the end of this section, you will be able to:
* Describe the molecular components that make up the cell membrane
* Explain the major features and properties of the cell membrane
* Differentiate between materials that can and cannot diffuse through the lipid bilayer
* Compare and contrast different types of passive transport with active transport, providing examples of each
Despite differences in structure and function, all living cells in
multicellular organisms have a surrounding cell membrane. As the outer layer
of your skin separates your body from its environment, the cell membrane (also
known as the plasma membrane) separates the inner contents of a cell from its
exterior environment. This cell membrane provides a protective barrier around
the cell and regulates which materials can pass in or out.
# Structure and Composition of the Cell Membrane
The cell membrane is an extremely pliable structure composed primarily of
back-to-back phospholipids (a “bilayer”). Cholesterol is also present, which
contributes to the fluidity of the membrane, and there are various proteins
embedded within the membrane that have a variety of functions.
A single phospholipid molecule has a phosphate group on one end, called the
“head,” and two side-by-side chains of fatty acids that make up the lipid
tails ( [link] ). The phosphate group is negatively charged, making the head
polar and hydrophilic—or “water loving.” A hydrophilic molecule (or region
of a molecule) is one that is attracted to water. The phosphate heads are thus
attracted to the water molecules of both the extracellular and intracellular
environments. The lipid tails, on the other hand, are uncharged, or nonpolar,
and are hydrophobic—or “water fearing.” A hydrophobic molecule (or region of
a molecule) repels and is repelled by water. Some lipid tails consist of
saturated fatty acids and some contain unsaturated fatty acids. This
combination adds to the fluidity of the tails that are constantly in motion.
Phospholipids are thus amphipathic molecules. An amphipathic molecule is one
that contains both a hydrophilic and a hydrophobic region. In fact, soap works
to remove oil and grease stains because it has amphipathic properties. The
hydrophilic portion can dissolve in water while the hydrophobic portion can
trap grease in micelles that then can be washed away.
Phospholipid Structure
A phospholipid molecule consists of a polar phosphate “head,” which is
hydrophilic and a non-polar lipid “tail,” which is hydrophobic. Unsaturated
fatty acids result in kinks in the hydrophobic tails.
The cell membrane consists of two adjacent layers of phospholipids. The lipid
tails of one layer face the lipid tails of the other layer, meeting at the
interface of the two layers. The phospholipid heads face outward, one layer
exposed to the interior of the cell and one layer exposed to the exterior (
[link] ). Because the phosphate groups are polar and hydrophilic, they are
attracted to water in the intracellular fluid. Intracellular fluid (ICF) is
the fluid interior of the cell. The phosphate groups are also attracted to the
extracellular fluid. Extracellular fluid (ECF) is the fluid environment
outside the enclosure of the cell membrane. Interstitial fluid (IF) is the
term given to extracellular fluid not contained within blood vessels. Because
the lipid tails are hydrophobic, they meet in the inner region of the
membrane, excluding watery intracellular and extracellular fluid from this
space. The cell membrane has many proteins, as well as other lipids (such as
cholesterol), that are associated with the phospholipid bilayer. An important
feature of the membrane is that it remains fluid; the lipids and proteins in
the cell membrane are not rigidly locked in place.
Phospolipid Bilayer
The phospholipid bilayer consists of two adjacent sheets of phospholipids,
arranged tail to tail. The hydrophobic tails associate with one another,
forming the interior of the membrane. The polar heads contact the fluid inside
and outside of the cell.
# Membrane Proteins
The lipid bilayer forms the basis of the cell membrane, but it is peppered
throughout with various proteins. Two different types of proteins that are
commonly associated with the cell membrane are the integral proteins and
peripheral protein ( [link] ). As its name suggests, an integral protein
is a protein that is embedded in the membrane. A channel protein is an
example of an integral protein that selectively allows particular materials,
such as certain ions, to pass into or out of the cell.
Cell Membrane
The cell membrane of the cell is a phospholipid bilayer containing many
different molecular components, including proteins and cholesterol, some with
carbohydrate groups attached.
Another important group of integral proteins are cell recognition proteins,
which serve to mark a cell’s identity so that it can be recognized by other
cells. A receptor is a type of recognition protein that can selectively bind
a specific molecule outside the cell, and this binding induces a chemical
reaction within the cell. A ligand is the specific molecule that binds to
and activates a receptor. Some integral proteins serve dual roles as both a
receptor and an ion channel. One example of a receptor-ligand interaction is
the receptors on nerve cells that bind neurotransmitters, such as dopamine.
When a dopamine molecule binds to a dopamine receptor protein, a channel
within the transmembrane protein opens to allow certain ions to flow into the
cell.
Some integral membrane proteins are glycoproteins. A glycoprotein is a
protein that has carbohydrate molecules attached, which extend into the
extracellular matrix. The attached carbohydrate tags on glycoproteins aid in
cell recognition. The carbohydrates that extend from membrane proteins and
even from some membrane lipids collectively form the glycocalyx. The
glycocalyx is a fuzzy-appearing coating around the cell formed from
glycoproteins and other carbohydrates attached to the cell membrane. The
glycocalyx can have various roles. For example, it may have molecules that
allow the cell to bind to another cell, it may contain receptors for hormones,
or it might have enzymes to break down nutrients. The glycocalyces found in a
person’s body are products of that person’s genetic makeup. They give each of
the individual’s trillions of cells the “identity” of belonging in the
person’s body. This identity is the primary way that a person’s immune defense
cells “know” not to attack the person’s own body cells, but it also is the
reason organs donated by another person might be rejected.
Peripheral proteins are typically found on the inner or outer surface of the
lipid bilayer but can also be attached to the internal or external surface of
an integral protein. These proteins typically perform a specific function for
the cell. Some peripheral proteins on the surface of intestinal cells, for
example, act as digestive enzymes to break down nutrients to sizes that can
pass through the cells and into the bloodstream.
# Transport across the Cell Membrane
One of the great wonders of the cell membrane is its ability to regulate the
concentration of substances inside the cell. These substances include ions
such as Ca ++ , Na \+ , K \+ , and Cl – ; nutrients including sugars,
fatty acids, and amino acids; and waste products, particularly carbon dioxide
(CO 2 ), which must leave the cell.
The membrane’s lipid bilayer structure provides the first level of control.
The phospholipids are tightly packed together, and the membrane has a
hydrophobic interior. This structure causes the membrane to be selectively
permeable. A membrane that has selective permeability allows only substances
meeting certain criteria to pass through it unaided. In the case of the cell
membrane, only relatively small, nonpolar materials can move through the lipid
bilayer (remember, the lipid tails of the membrane are nonpolar). Some
examples of these are other lipids, oxygen and carbon dioxide gases, and
alcohol. However, water-soluble materials—like glucose, amino acids, and
electrolytes—need some assistance to cross the membrane because they are
repelled by the hydrophobic tails of the phospholipid bilayer. All substances
that move through the membrane do so by one of two general methods, which are
categorized based on whether or not energy is required. Passive transport is
the movement of substances across the membrane without the expenditure of
cellular energy. In contrast, active transport is the movement of substances
across the membrane using energy from adenosine triphosphate (ATP).
## Passive Transport
In order to understand how substances move passively across a cell membrane,
it is necessary to understand concentration gradients and diffusion. A
concentration gradient is the difference in concentration of a substance
across a space. Molecules (or ions) will spread/diffuse from where they are
more concentrated to where they are less concentrated until they are equally
distributed in that space. (When molecules move in this way, they are said to
move down their concentration gradient.) Diffusion is the movement of
particles from an area of higher concentration to an area of lower
concentration. A couple of common examples will help to illustrate this
concept. Imagine being inside a closed bathroom. If a bottle of perfume were
sprayed, the scent molecules would naturally diffuse from the spot where they
left the bottle to all corners of the bathroom, and this diffusion would go on
until no more concentration gradient remains. Another example is a spoonful of
sugar placed in a cup of tea. Eventually the sugar will diffuse throughout the
tea until no concentration gradient remains. In both cases, if the room is
warmer or the tea hotter, diffusion occurs even faster as the molecules are
bumping into each other and spreading out faster than at cooler temperatures.
Having an internal body temperature around 98.6 ° F thus also aids in
diffusion of particles within the body.
Visit this link to see diffusion and how it is propelled by the kinetic
energy of molecules in solution. How does temperature affect diffusion rate,
and why?
Whenever a substance exists in greater concentration on one side of a
semipermeable membrane, such as the cell membranes, any substance that can
move down its concentration gradient across the membrane will do so. Consider
substances that can easily diffuse through the lipid bilayer of the cell
membrane, such as the gases oxygen (O 2 ) and CO 2 . O 2 generally
diffuses into cells because it is more concentrated outside of them, and CO 2
typically diffuses out of cells because it is more concentrated inside of
them. Neither of these examples requires any energy on the part of the cell,
and therefore they use passive transport to move across the membrane.
Before moving on, you need to review the gases that can diffuse across a cell
membrane. Because cells rapidly use up oxygen during metabolism, there is
typically a lower concentration of O 2 inside the cell than outside. As a
result, oxygen will diffuse from the interstitial fluid directly through the
lipid bilayer of the membrane and into the cytoplasm within the cell. On the
other hand, because cells produce CO 2 as a byproduct of metabolism, CO 2
concentrations rise within the cytoplasm; therefore, CO 2 will move from the
cell through the lipid bilayer and into the interstitial fluid, where its
concentration is lower. This mechanism of molecules moving across a cell
membrane from the side where they are more concentrated to the side where they
are less concentrated is a form of passive transport called simple diffusion (
[link] ).
Simple Diffusion across the Cell (Plasma) Membrane
The structure of the lipid bilayer allows small, uncharged substances such as
oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass
through the cell membrane, down their concentration gradient, by simple
diffusion.
Large polar or ionic molecules, which are hydrophilic, cannot easily cross the
phospholipid bilayer. Very small polar molecules, such as water, can cross via
simple diffusion due to their small size. Charged atoms or molecules of any
size cannot cross the cell membrane via simple diffusion as the charges are
repelled by the hydrophobic tails in the interior of the phospholipid bilayer.
Solutes dissolved in water on either side of the cell membrane will tend to
diffuse down their concentration gradients, but because most substances cannot
pass freely through the lipid bilayer of the cell membrane, their movement is
restricted to protein channels and specialized transport mechanisms in the
membrane. Facilitated diffusion is the diffusion process used for those
substances that cannot cross the lipid bilayer due to their size, charge,
and/or polarity ( [link] ). A common example of facilitated diffusion is the
movement of glucose into the cell, where it is used to make ATP. Although
glucose can be more concentrated outside of a cell, it cannot cross the lipid
bilayer via simple diffusion because it is both large and polar. To resolve
this, a specialized carrier protein called the glucose transporter will
transfer glucose molecules into the cell to facilitate its inward diffusion.
Facilitated Diffusion
(a) Facilitated diffusion of substances crossing the cell (plasma) membrane
takes place with the help of proteins such as channel proteins and carrier
proteins. Channel proteins are less selective than carrier proteins, and
usually mildly discriminate between their cargo based on size and charge. (b)
Carrier proteins are more selective, often only allowing one particular type
of molecule to cross.
As an example, even though sodium ions (Na \+ ) are highly concentrated
outside of cells, these electrolytes are charged and cannot pass through the
nonpolar lipid bilayer of the membrane. Their diffusion is facilitated by
membrane proteins that form sodium channels (or “pores”), so that Na \+ ions
can move down their concentration gradient from outside the cells to inside
the cells. There are many other solutes that must undergo facilitated
diffusion to move into a cell, such as amino acids, or to move out of a cell,
such as wastes. Because facilitated diffusion is a passive process, it does
not require energy expenditure by the cell.
Water also can move freely across the cell membrane of all cells, either
through protein channels or by slipping between the lipid tails of the
membrane itself. Osmosis is the diffusion of water through a semipermeable
membrane ( [link] ).
Osmosis
Osmosis is the diffusion of water through a semipermeable membrane down its
concentration gradient. If a membrane is permeable to water, though not to a
solute, water will equalize its own concentration by diffusing to the side of
lower water concentration (and thus the side of higher solute concentration).
In the beaker on the left, the solution on the right side of the membrane is
hypertonic.
The movement of water molecules is not itself regulated by cells, so it is
important that cells are exposed to an environment in which the concentration
of solutes outside of the cells (in the extracellular fluid) is equal to the
concentration of solutes inside the cells (in the cytoplasm). Two solutions
that have the same concentration of solutes are said to be isotonic (equal
tension). When cells and their extracellular environments are isotonic, the
concentration of water molecules is the same outside and inside the cells, and
the cells maintain their normal shape (and function).
Osmosis occurs when there is an imbalance of solutes outside of a cell versus
inside the cell. A solution that has a higher concentration of solutes than
another solution is said to be hypertonic , and water molecules tend to
diffuse into a hypertonic solution ( [link] ). Cells in a hypertonic
solution will shrivel as water leaves the cell via osmosis. In contrast, a
solution that has a lower concentration of solutes than another solution is
said to be hypotonic , and water molecules tend to diffuse out of a
hypotonic solution. Cells in a hypotonic solution will take on too much water
and swell, with the risk of eventually bursting. A critical aspect of
homeostasis in living things is to create an internal environment in which all
of the body’s cells are in an isotonic solution. Various organ systems,
particularly the kidneys, work to maintain this homeostasis.
Concentration of Solutions
A hypertonic solution has a solute concentration higher than another solution.
An isotonic solution has a solute concentration equal to another solution. A
hypotonic solution has a solute concentration lower than another solution.
Another mechanism besides diffusion to passively transport materials between
compartments is filtration. Unlike diffusion of a substance from where it is
more concentrated to less concentrated, filtration uses a hydrostatic pressure
gradient that pushes the fluid—and the solutes within it—from a higher
pressure area to a lower pressure area. Filtration is an extremely important
process in the body. For example, the circulatory system uses filtration to
move plasma and substances across the endothelial lining of capillaries and
into surrounding tissues, supplying cells with the nutrients. Filtration
pressure in the kidneys provides the mechanism to remove wastes from the
bloodstream.
## Active Transport
For all of the transport methods described above, the cell expends no energy.
Membrane proteins that aid in the passive transport of substances do so
without the use of ATP. During active transport, ATP is required to move a
substance across a membrane, often with the help of protein carriers, and
usually against its concentration gradient.
One of the most common types of active transport involves proteins that serve
as pumps. The word “pump” probably conjures up thoughts of using energy to
pump up the tire of a bicycle or a basketball. Similarly, energy from ATP is
required for these membrane proteins to transport substances—molecules or
ions—across the membrane, usually against their concentration gradients (from
an area of low concentration to an area of high concentration).
The sodium-potassium pump , which is also called Na \+ /K \+ ATPase,
transports sodium out of a cell while moving potassium into the cell. The Na
\+ /K \+ pump is an important ion pump found in the membranes of many types
of cells. These pumps are particularly abundant in nerve cells, which are
constantly pumping out sodium ions and pulling in potassium ions to maintain
an electrical gradient across their cell membranes. An electrical gradient
is a difference in electrical charge across a space. In the case of nerve
cells, for example, the electrical gradient exists between the inside and
outside of the cell, with the inside being negatively-charged (at around -70
mV) relative to the outside. The negative electrical gradient is maintained
because each Na \+ /K \+ pump moves three Na \+ ions out of the cell and
two K \+ ions into the cell for each ATP molecule that is used ( [link] ).
This process is so important for nerve cells that it accounts for the majority
of their ATP usage.
Sodium-Potassium Pump
The sodium-potassium pump is found in many cell (plasma) membranes. Powered by
ATP, the pump moves sodium and potassium ions in opposite directions, each
against its concentration gradient. In a single cycle of the pump, three
sodium ions are extruded from and two potassium ions are imported into the
cell.
Active transport pumps can also work together with other active or passive
transport systems to move substances across the membrane. For example, the
sodium-potassium pump maintains a high concentration of sodium ions outside of
the cell. Therefore, if the cell needs sodium ions, all it has to do is open a
passive sodium channel, as the concentration gradient of the sodium ions will
drive them to diffuse into the cell. In this way, the action of an active
transport pump (the sodium-potassium pump) powers the passive transport of
sodium ions by creating a concentration gradient. When active transport powers
the transport of another substance in this way, it is called secondary active
transport.
Symporters are secondary active transporters that move two substances in the
same direction. For example, the sodium-glucose symporter uses sodium ions to
“pull” glucose molecules into the cell. Because cells store glucose for
energy, glucose is typically at a higher concentration inside of the cell than
outside. However, due to the action of the sodium-potassium pump, sodium ions
will easily diffuse into the cell when the symporter is opened. The flood of
sodium ions through the symporter provides the energy that allows glucose to
move through the symporter and into the cell, against its concentration
gradient.
Conversely, antiporters are secondary active transport systems that transport
substances in opposite directions. For example, the sodium-hydrogen ion
antiporter uses the energy from the inward flood of sodium ions to move
hydrogen ions (H+) out of the cell. The sodium-hydrogen antiporter is used to
maintain the pH of the cell’s interior.
Other forms of active transport do not involve membrane carriers. Endocytosis
(bringing “into the cell”) is the process of a cell ingesting material by
enveloping it in a portion of its cell membrane, and then pinching off that
portion of membrane ( [link] ). Once pinched off, the portion of membrane
and its contents becomes an independent, intracellular vesicle. A vesicle is
a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer
membrane. Endocytosis often brings materials into the cell that must to be
broken down or digested. Phagocytosis (“cell eating”) is the endocytosis of
large particles. Many immune cells engage in phagocytosis of invading
pathogens. Like little Pac-men, their job is to patrol body tissues for
unwanted matter, such as invading bacterial cells, phagocytize them, and
digest them. In contrast to phagocytosis, pinocytosis (“cell drinking”)
brings fluid containing dissolved substances into a cell through membrane
vesicles.
Three Forms of Endocytosis
Endocytosis is a form of active transport in which a cell envelopes
extracellular materials using its cell membrane. (a) In phagocytosis, which is
relatively nonselective, the cell takes in a large particle. (b) In
pinocytosis, the cell takes in small particles in fluid. (c) In contrast,
receptor-mediated endocytosis is quite selective. When external receptors bind
a specific ligand, the cell responds by endocytosing the ligand.
Phagocytosis and pinocytosis take in large portions of extracellular material,
and they are typically not highly selective in the substances they bring in.
Cells regulate the endocytosis of specific substances via receptor-mediated
endocytosis. Receptor-mediated endocytosis is endocytosis by a portion of
the cell membrane that contains many receptors that are specific for a certain
substance. Once the surface receptors have bound sufficient amounts of the
specific substance (the receptor’s ligand), the cell will endocytose the part
of the cell membrane containing the receptor-ligand complexes. Iron, a
required component of hemoglobin, is endocytosed by red blood cells in this
way. Iron is bound to a protein called transferrin in the blood. Specific
transferrin receptors on red blood cell surfaces bind the iron-transferrin
molecules, and the cell endocytoses the receptor-ligand complexes.
In contrast with endocytosis, exocytosis (taking “out of the cell”) is the
process of a cell exporting material using vesicular transport ( [link] ).
Many cells manufacture substances that must be secreted, like a factory
manufacturing a product for export. These substances are typically packaged
into membrane-bound vesicles within the cell. When the vesicle membrane fuses
with the cell membrane, the vesicle releases it contents into the interstitial
fluid. The vesicle membrane then becomes part of the cell membrane. Cells of
the stomach and pancreas produce and secrete digestive enzymes through
exocytosis ( [link] ). Endocrine cells produce and secrete hormones that are
sent throughout the body, and certain immune cells produce and secrete large
amounts of histamine, a chemical important for immune responses.
Exocytosis
Exocytosis is much like endocytosis in reverse. Material destined for export
is packaged into a vesicle inside the cell. The membrane of the vesicle fuses
with the cell membrane, and the contents are released into the extracellular
space.
Pancreatic Cells’ Enzyme Products
The pancreatic acinar cells produce and secrete many enzymes that digest food.
The tiny black granules in this electron micrograph are secretory vesicles
filled with enzymes that will be exported from the cells via exocytosis. LM ×
2900. (Micrograph provided by the Regents of University of Michigan Medical
School © 2012)
View the University of Michigan WebScope to explore the tissue sample in
greater detail.
Diseases of the…
Cell: Cystic Fibrosis
Cystic fibrosis (CF) affects approximately 30,000 people in the United States,
with about 1,000 new cases reported each year. The genetic disease is most
well known for its damage to the lungs, causing breathing difficulties and
chronic lung infections, but it also affects the liver, pancreas, and
intestines. Only about 50 years ago, the prognosis for children born with CF
was very grim—a life expectancy rarely over 10 years. Today, with advances in
medical treatment, many CF patients live into their 30s.
The symptoms of CF result from a malfunctioning membrane ion channel called
the cystic fibrosis transmembrane conductance regulator, or CFTR. In healthy
people, the CFTR protein is an integral membrane protein that transports Cl –
ions out of the cell. In a person who has CF, the gene for the CFTR is
mutated, thus, the cell manufactures a defective channel protein that
typically is not incorporated into the membrane, but is instead degraded by
the cell.
The CFTR requires ATP in order to function, making its Cl – transport a form
of active transport. This characteristic puzzled researchers for a long time
because the Cl – ions are actually flowing down their concentration
gradient when transported out of cells. Active transport generally pumps ions
against their concentration gradient, but the CFTR presents an exception to
this rule.
In normal lung tissue, the movement of Cl – out of the cell maintains a Cl
– -rich, negatively charged environment immediately outside of the cell. This
is particularly important in the epithelial lining of the respiratory system.
Respiratory epithelial cells secrete mucus, which serves to trap dust,
bacteria, and other debris. A cilium (plural = cilia) is one of the hair-like
appendages found on certain cells. Cilia on the epithelial cells move the
mucus and its trapped particles up the airways away from the lungs and toward
the outside. In order to be effectively moved upward, the mucus cannot be too
viscous; rather it must have a thin, watery consistency. The transport of Cl
– and the maintenance of an electronegative environment outside of the cell
attract positive ions such as Na \+ to the extracellular space. The
accumulation of both Cl – and Na \+ ions in the extracellular space
creates solute-rich mucus, which has a low concentration of water molecules.
As a result, through osmosis, water moves from cells and extracellular matrix
into the mucus, “thinning” it out. This is how, in a normal respiratory
system, the mucus is kept sufficiently watered-down to be propelled out of the
respiratory system.
If the CFTR channel is absent, Cl – ions are not transported out of the cell
in adequate numbers, thus preventing them from drawing positive ions. The
absence of ions in the secreted mucus results in the lack of a normal water
concentration gradient. Thus, there is no osmotic pressure pulling water into
the mucus. The resulting mucus is thick and sticky, and the ciliated epithelia
cannot effectively remove it from the respiratory system. Passageways in the
lungs become blocked with mucus, along with the debris it carries. Bacterial
infections occur more easily because bacterial cells are not effectively
carried away from the lungs.
# Chapter Review
The cell membrane provides a barrier around the cell, separating its internal
components from the extracellular environment. It is composed of a
phospholipid bilayer, with hydrophobic internal lipid “tails” and hydrophilic
external phosphate “heads.” Various membrane proteins are scattered throughout
the bilayer, both inserted within it and attached to it peripherally. The cell
membrane is selectively permeable, allowing only a limited number of materials
to diffuse through its lipid bilayer. All materials that cross the membrane do
so using passive (non energy-requiring) or active (energy-requiring) transport
processes. During passive transport, materials move by simple diffusion or by
facilitated diffusion through the membrane, down their concentration gradient.
Water passes through the membrane in a diffusion process called osmosis.
During active transport, energy is expended to assist material movement across
the membrane in a direction against their concentration gradient. Active
transport may take place with the help of protein pumps or through the use of
vesicles.
# Interactive Link Questions
Visit this link to see diffusion and how it is propelled by the kinetic
energy of molecules in solution. How does temperature affect diffusion rate,
and why?
Higher temperatures speed up diffusion because molecules have more kinetic
energy at higher temperatures.
# Review Questions
Because they are embedded within the membrane, ion channels are examples of
________.
1. receptor proteins
2. integral proteins
3. peripheral proteins
4. glycoproteins
B
The diffusion of substances within a solution tends to move those substances
________ their ________ gradient.
1. up; electrical
2. up; electrochemical
3. down; pressure
4. down; concentration
D
Ion pumps and phagocytosis are both examples of ________.
1. endocytosis
2. passive transport
3. active transport
4. facilitated diffusion
C
Choose the answer that best completes the following analogy: Diffusion is to
________ as endocytosis is to ________.
1. filtration; phagocytosis
2. osmosis; pinocytosis
3. solutes; fluid
4. gradient; chemical energy
B
# Critical Thinking Questions
What materials can easily diffuse through the lipid bilayer, and why?
Only materials that are relatively small and nonpolar can easily diffuse
through the lipid bilayer. Large particles cannot fit in between the
individual phospholipids that are packed together, and polar molecules are
repelled by the hydrophobic/nonpolar lipids that line the inside of the
bilayer.
Why is receptor-mediated endocytosis said to be more selective than
phagocytosis or pinocytosis?
Receptor-mediated endocytosis is more selective because the substances that
are brought into the cell are the specific ligands that could bind to the
receptors being endocytosed. Phagocytosis or pinocytosis, on the other hand,
have no such receptor-ligand specificity, and bring in whatever materials
happen to be close to the membrane when it is enveloped.
What do osmosis, diffusion, filtration, and the movement of ions away from
like charge all have in common? In what way do they differ?
These four phenomena are similar in the sense that they describe the movement
of substances down a particular type of gradient. Osmosis and diffusion
involve the movement of water and other substances down their concentration
gradients, respectively. Filtration describes the movement of particles down a
pressure gradient, and the movement of ions away from like charge describes
their movement down their electrical gradient.
## Glossary
active transport
form of transport across the cell membrane that requires input of cellular energy
amphipathic
describes a molecule that exhibits a difference in polarity between its two ends, resulting in a difference in water solubility
cell membrane
membrane surrounding all animal cells, composed of a lipid bilayer interspersed with various molecules; also known as plasma membrane
channel protein
membrane-spanning protein that has an inner pore which allows the passage of one or more substances
concentration gradient
difference in the concentration of a substance between two regions
diffusion
movement of a substance from an area of higher concentration to one of lower concentration
electrical gradient
difference in the electrical charge (potential) between two regions
endocytosis
import of material into the cell by formation of a membrane-bound vesicle
exocytosis
export of a substance out of a cell by formation of a membrane-bound vesicle
extracellular fluid (ECF)
fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluid found in other reservoirs in the body
facilitated diffusion
diffusion of a substance with the aid of a membrane protein
glycocalyx
coating of sugar molecules that surrounds the cell membrane
glycoprotein
protein that has one or more carbohydrates attached
hydrophilic
describes a substance or structure attracted to water
hydrophobic
describes a substance or structure repelled by water
hypertonic
describes a solution concentration that is higher than a reference concentration
hypotonic
describes a solution concentration that is lower than a reference concentration
integral protein
membrane-associated protein that spans the entire width of the lipid bilayer
interstitial fluid (IF)
fluid in the small spaces between cells not contained within blood vessels
intracellular fluid (ICF)
fluid in the cytosol of cells
isotonic
describes a solution concentration that is the same as a reference concentration
ligand
molecule that binds with specificity to a specific receptor molecule
osmosis
diffusion of water molecules down their concentration gradient across a selectively permeable membrane
passive transport
form of transport across the cell membrane that does not require input of cellular energy
peripheral protein
membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane
phagocytosis
endocytosis of large particles
pinocytosis
endocytosis of fluid
receptor
protein molecule that contains a binding site for another specific molecule (called a ligand)
receptor-mediated endocytosis
endocytosis of ligands attached to membrane-bound receptors
selective permeability
feature of any barrier that allows certain substances to cross but excludes others
sodium-potassium pump
(also, Na \+ /K \+ ATP-ase) membrane-embedded protein pump that uses ATP to move Na \+ out of a cell and K \+ into the cell
vesicle
membrane-bound structure that contains materials within or outside of the cell
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| biology | 58159 | https://da.wikipedia.org/wiki/Cellemembran | Cellemembran | Cellemembran eller plasmamembran er en biologisk membran, der adskiller det indre af en celle fra omgivelserne. Historisk er cellemembranen desuden blevet kaldt plasmalemma. Den består af et dobbeltlag af lipider med indlejrede proteiner. Lipidernes upolære carbonkæder gør cellemembranen gennemtrængelig for upolære molekyler og visse små molekyler som kuldioxid (CO2) og ilt (O2), men uigennemtrængelig for ioner og de fleste polære molekyler. Passage af ioner og polære molekyler er imidlertid mulig i kontrolleret omfang via forskellige typer transmembrane proteiner, f.eks. kanaler og transportproteiner (herunder biologiske "pumper" som natrium-kalium-pumpen). Cellemembranen medvirker til en række vigtige cellulære processer, f.eks. celleadhæsion og cellesignalering, og tjener som fæste for det intracellulære cytoskelet og vigtige ekstracellulære strukturer, heriblandt cellevæggen og glykocalyxen (en ydre beklædning af glykoproteiner, der medvirker ved celle-celle-genkendelse). Cellesignaleringen foregår ved hjælp af receptorer (modtagermolekyler), der gør cellen i stand til at reagere på specifikke signalstoffer, f.eks. hormoner.
Struktur
Hovedstrukturen i en cellemembran er lipiddobbellaget. Studiet af cellemembranens fysiske egenskaber kaldes for biomembranfysik.
Lipiddobbeltlaget
Biologiske membraner er opbygget af amfifile lipidmolekyler. De består af et polært hoved og en lang, upolær hale. Hovedparten af lipiderne i cellemembranen indeholder én eller flere umættede kæder, hvis dobbeltbinding giver dem et "knæk"; dette knæk giver det samlede lipid en cylinderform. Cylinderformede lipider har en tendens til at danne et dobbeltlag med hinanden, således at de polære hoveder vender mod vandsiden og de upolære haler mod mellemrummet mellem de to lag. Er der tilstrækkeligt mange lipider, slutter dobbeltlaget sig spontant sammen til den termodynamisk mest stabile form, dvs. en kugle. Dette er tilfældet for levende celler. Såvel de hydrofile vekselvirkninger ved membranens overflade som hydrofobe vekselvirkninger mellem lipidmolekylernes alifatiske dele i membranens indre er med til at stabilisere og binde strukturen sammen. En brist i dobbeltlaget vil normalt lukke sig af sig selv.
Generelt er lipiddobbeltlaget uigennemtrængeligt for polære molekyler. Dobbeltlagets hydrofobe indre forhindrer polære molekyler (f.eks. aminosyrer, nukleinsyrer, kulhydrater, proteiner og ioner) i at diffundere gennem membranen, men tillader generelt passiv diffusion af hydrofobe molekyler. Cellen kan dermed kontrollere passagen af hydrofile stoffer via transmembrane proteiner som kanaler og transportproteiner.
Flippaser og scramblaser koncentrerer det negativt ladede fosfolipid fosfatidylserin på indersiden af membranen. Sammen med sialinsyre skaber dette endnu en barriere for ladede partikler og molekyler, der passerer gennem membranen.
Flydende mosaik-modellen
Ifølge den såkaldte flydende mosaik-model foreslået af de amerikanske forskere Seymour Jonathan Singer og Garth L. Nicolson i 1972 kan biologiske membraner opfattes som en todimensionel væske, hvori en stor mængde lipider og proteiner flyder rundt mere eller mindre frit. Vekselvirkninger mellem indlejrede membranproteiner og membranlipider giver anledning til protein-lipid-klynger, der bevæger sig rundt eller ”flyder” lateralt mellem hinanden – en flydende mosaik. Cellemembranens fluiditet afhænger af dens bestanddele og temperatur. Den store mængde proteiner i cellemembranen giver membranen en vis grad af struktur ved f.eks. at danne protein-protein-komplekser og "lipid rafts" (specialiserede mikrodomæner i cellemembranen indeholdende store mængder membranproteiner, kolesterol og en type lipider kaldt glykosphingolipider).
Bestanddele
Cellemembraner indeholder forskellige biomolekyler, først og fremmest lipider og proteiner. Stoffer optages i membranen eller fjernes fra den ved forskellige mekanismer:
Fusion af intracellulære vesikler med membranen (exocytose) udskiller ikke blot vesiklens indhold, men integrerer også vesikelmembranens bestanddele i cellemembranen. Omvendt kan cellemembranen skille sig af med materiale ved at afsnøre dele af sig selv som vesikler.
Hvis en membran er forbundet med en rørformet struktur lavet af membranmateriale, kan materialet fra røret trækkes ind i membranen.
Skønt koncentrationen af membranbestanddele i de omgivende væskefaser er ringe (idet stabile membranbestanddele er tungtopløselige i vand), foregår der en udveksling af molekyler mellem lipid- og vandfasen.
Lipider
Cellemembranen består af tre klasser af amfifile lipider: fosfolipider, glykolipider og steroler (herunder kolesterol). Mængdeforholdet afhænger af celletype, men hos de fleste celler er fosfolipiderne de talrigeste. Studier af røde blodlegemer har vist, at 30 % af deres cellemembraner udgøres af lipider.
Carbonkæderne i fosfolipiderne og glykolipiderne indeholder typisk et lige antal carbonatomer, som regel mellem 16 og 20. Fedtsyrekæder med 16 eller 18 carbonatomer er de almindeligste. Fedtsyrerne i et lipid kan enten være mættede eller umættede – de umættede er næsten altid på cis-formen. Længden og graden af umættethed af en fedtsyrekæde har vital betydning for lipidets rumlige opbygning og dermed membranens fluiditet, idet umættede kæder danner et "knæk", der forhindrer fedtsyrerne i at pakke sig tæt sammen. Dette sænker lipidets smeltepunkt og øger membranens fluiditet. Kolesterol mindsker derimod fluiditeten, da kolesterol giver cellemembranen højere smeltepunkt ved at reducere lipidernes bevægelsesfrihed.
Hele cellemembranen holdes sammen af londonbindinger mellem de hydrofobe fedtsyrekæder. Lipiderne flyder dog frit mellem hinanden. Under fysiologiske forhold opfører fosfolipidmolekylerne i membranen sig som flydende krystaller. Det betyder, at lipidmolekylerne frit kan diffundere rundt mellem hinanden i samme lag. Derimod er det en langsom proces at springe fra lag til lag. "Lipid rafts" og caveolae (latin for "små hulrum") er eksempler på kolesterolrige mikrodomæner i cellemembranen.
Kulhydrater
Cellemembraner indeholder kulhydrater, primært glykoproteiner og i mindre grad glykolipider (cerebrosider og gangliosider). På den intracellulære side sker der stort set aldrig glykosylering. Det gør der derimod på overfladen af cellen. Glykocalyxen er en tynd beklædning af kulhydratholdigt materiale omkring alle celler. Den spiller en vigtig rolle ved celleadhæsion, lymfocytrecirkulation samt andre celleinteraktioner. Glykocalyxen består af oligosakkarider indeholdende sialinsyre, hvis negative ladning danner en udvendig barriere mod ladede partikler.
Proteiner
Omkring 50 % af cellemembranens volumen udgøres af protein. Proteinerne udfører en række vigtige biologiske processer for cellen. Omtrent en tredjedel af gærsvampes gener koder specifikt for dem, og for multicellulære organismer er dette tal endda større.
Cellemembranen er en vigtig kontaktflade for celle-celle-kommunikation. Den indeholder derfor receptor- og genkendelsesproteiner, der sørger for den fysisk-kemiske kommunikation mellem cellen og dens omgivelser, f.eks. antigener, på sin ydre overflade. Membranproteinerne kan også tjene til celle-celle-kontakt, overfladegenkendelse, cytoskeletkontakt, cellesignalering, enzymaktivitet eller transport gennem cellemembranen.
Transmembrane membranproteiner må integreres i cellemembranen. Normalt føres færdigsyntetiserede proteiner ind i lumen af det ru endoplasmatiske reticulum (RER) gennem en proteinkanal, men membranproteiner indeholder et sted i deres sekvens en sekvens med ca. 20 hydrofobe aminosyrer. Denne skal udgøre den transmembrane del af proteinet og virker som en stop-transfer-sekvens, der stopper overføringen af proteinet gennem proteinkanalen. Proteinet vandrer derefter bort fra kanalen og lægger sig i RER-membranen, hvorfra det kan transporteres til Golgiapparatet og videre til cellemembranen ved hjælp af vesikler.
Variationer
Visse celletypers cellemembraner har specifikke navne, hvilket afspejler en varierende lipid- og proteinsammensætning:
Sarcolemma hos muskelceller
Oolemma hos ægceller
Axolemma hos neuronernes axoner
Funktion
Cellemembranen omgiver cellens cytoplasma og adskiller således de intracellulære komponenter fra det ekstracellulære miljø. Svampe, bakterier og planter har desuden en cellevæg, der yder cellen mekanisk støtte og forhindrer passage af større molekyler. Cellemembranen tjener også som fæste for cytoskelettet, der afstiver cellen indvendigt og opretholder dens form, og for den ekstracellulære matrix og andre celler, således at flere celler kan finde sammen og danne væv.
Stoftransport
Cellemembranen er selektivt permeabel (gennemtrængelig) og regulerer, hvad der passerer ind og ud af cellen. Passagen af stoffer gennem cellemembranen kan være passiv eller aktiv (energikrævende). Passagen af ladede partikler skaber sammen med tilstedeværelsen af negativt ladede fosfolipider på indersiden af membranen en spændingsforskel over membranen, cellens membranpotential, der varierer alt efter celletypen. Cellemembranen fungerer således som et selektivt filter, der kun tillader specifikke stoffer at komme ind eller ud. Transporten af stoffer gennem membranen foregår ved forskellige mekanismer:
1. Simpel diffusion og osmose: Nogle stoffer, f.eks. kuldioxid (CO2), ilt (O2) og vand (H2O), kan passere gennem membranens lipiddobbeltlag ved diffusion, som er en passiv proces. Fordi membranen fungerer som barriere for visse molekyler og ioner, kan disse forekomme i forskellige koncentrationer på hver side af membranen. En sådan koncentrationsforskel eller -gradient over en semipermeabel membran skaber et osmotisk tryk, der presser vandet i den retning, hvor koncentrationen er størst.
2. Faciliteret transport: Er ligesom diffusion drevet af en koncentrationsgradient, men foregår gennem kanaler eller ved hjælp af transportproteiner i membranen.
3. Pumper: Ioner, der skal transporteres ind eller ud af cellen imod en koncentrationsgradient, og store molekyler må transporteres gennem cellemembranen ved hjælp af såkaldte pumper, der forbruger energi fra cellen. Et eksempel på en sådan pumpe er natrium-kalium-pumpen (opdaget af Jens Christian Skou m.fl.), der pumper natriumioner (Na+) ud af cellen og kaliumioner (K+) ind i cellen. Transport via pumper er en form for aktiv transport.
4. Sekundært aktiv transport: Kemiske stoffer, der skal transporteres mod sin koncentrationsgradient, kan transporteres sammen med et andet stof, der bevæger sig med sin koncentrationsgradient, således at bevægelsen mod koncentrationsgradienten kan lykkes. Transporten af de to stoffer kan enten foregå i samme retning (symport) eller modsatrettet (antiport). Et eksempel på symport er transporten af glukose og natriumioner (Na+) ind i cellen ved hjælp af SGLT-2-cotransporteren (et transportprotein); hver natriumion, der passerer ind i cellen med en koncentrationsgradient ved hjælp af transporteren, "medbringer" et glukosemolekyle, der bevæger sig imod sin koncentrationsgradient. Den energi, der frigives ved passage af natriumionen, bruges af glukosemolekylet til at overvinde gradienten. Der sker derved intet energitab ved transporten, men natriumionernes koncentrationsgradient må opretholdes ved hjælp af natrium-kalium-pumpen, der forbruger energi. Et eksempel på antiport er den samtidige transport af Na+-ioner ind i cellen og hydrogenioner (H+) ud af cellen ved hjælp af den såkaldte Na+-H+-antiporter (et andet transportprotein), som medvirker til at holde cytosolens pH-værdi på ca. 7,2. Transporten af H+-ioner ud af cellen faciliteres af transporten af Na+-ioner ind i cellen pga. Na+-gradienten, som opretholdes af natrium-kalium-pumpen.
5. Endocytose: Ved endocytose omslutter en celle et molekyle og absorberer det. Cellemembranen danner en hulning indadtil (en invagination) hvori stoffet, der skal absorberes, fanges. Hulningen afsnøres derefter fra indersiden af membranen, hvilket skaber en vesikel, som indeholder stoffet. Absorption af faste partikler ved hjælp af endocytose kaldes også fagocytose, mens endocytose af væske (f.eks. vand), eventuelt med opløste ioner, kaldes pinocytose. Endocytose kræver energi og er således en form for aktiv transport.
6. Exocytose: Ligesom et stof kan transporteres ind i cellen ved invagination og dannelse af en vesikel, kan en vesikel fusionere med cellemembranen og afgive sit indhold til omgivelserne. Denne proces kaldes exocytose. Celler benytter exocytose bl.a. til at skille sig af med ufordøjede rester af stoffer, der er blevet ført ind ved endocytose, og til at udskille hormoner, neurotransmittere (for neuroners vedkommende) eller enzymer. Ved exocytose afsnøres en vesikel eller en vakuole fra Golgiapparatet, hvorefter den transporteres fra cellens indre til indersiden af cellemembranen via cytoskelettet. Her kommer vesikelmembranen i kontakt med cellemembranen. Lipidmolekylerne i de to dobbeltlag rearrangeres, hvorved de to membraner fusionerer. Dette fører til en åbning i den fusionerede membran, hvorigennem vesikelindholdet tømmer sig.
Celleadhæsion og cellesignalering
Cellemembraner kan danne forskellige “supramembranøse” strukturer som caveolae, fokale adhæsioner og forskellige typer celle-celle-forbindelser som desmosomer. Disse strukturer er typisk ansvarlige for celleadhæsion, kommunikation, endocytose og exocytose. De kan påvises ved elektronmikroskopi eller fluorescensmikroskopi. De består af celleadhæsionsmolekyler, f.eks. neuralcelleadhæsionsmolekyler (NCAM), integriner og cadhæriner.
Celleforankring
Forankringsproteiner kobler naboceller sammen, og kan have forskellige udseende og funktion. Desmosomer giver trækkraft, og evne til at modstå stor mekanisk stress, f.eks hudens væv.
Tight junctions kobler naboceller tæt sammen, for at forhindre at stoffer kan passere mellem cellerne, og danner altså en effektiv barriere. Fordøjelsessystemets væv har mange steder tight junctions der har den rolle at sørge for at passagen af næringsstoffer kan reguleres, ved at sørge for at stofferne transporteres direkte fra den apikale overflade, intracellulært gennem cellen, for bagefter at transporteres ud ved basalmembranen.
Gap junctions er intercellulære forbindelser der direkte forbinder cellers cytoplasma, og tillader transport af ioner, molekyler, og endda elektriske impulser. Et godt eksempel er i hjertemuskelcellerne, hvor gap junctions sørger for at myocardiet kontrakter synkront.
Cytoskelettet
Proteiner i cellemembranen tjener som fæste for cellens cytoskelet. Cytoskelettet findes under cellemembranen og udgør et indre stillads for cellen. Cytoskelettet danner desuden cilier og mikrovilli. Cilier (eller fimrehår) er bevægelige udløbere med et indre kompleks af mikrotubuli, der udvendigt er dækket af cellemembranen. I luftvejene medvirker cilier til at fjerne støvpartikler og mikroorganismer fanget i slimlaget. Mikrovilli er fingerlignende udløbere i cellemembranen på visse epitelcellers frie overflade (især i tarmen). Deres formål er at øge overfladearealet, hvilket øger absorptionen af næringsstoffer.
Prokaryoter
Gram-negative bakterier har både en cellemembran og en ydre membran adskilt af et periplasmatisk mellemrum. Andre prokaryoter har kun en cellemembran. Prokaryoter er også omgivet af en cellevæg bestående af peptidoglycaner (aminosyrer og kulhydrater). Visse eukaryoter (svampe- og planteceller) har også cellevægge, som dog ikke består af peptidoglycaner.
Se også
Membrankappe
Spike
Referencer
Eksterne henvisninger
Se "Cellemembranen – nogle væsentlige egenskaber" for en forenklet model af en cellemembran.
Cellebiologi | danish | 0.359622 |
cell_membrane_break_apart/cell_membrane.html.txt | # The Cell Membrane
The main component of the cell membrane is a phospholipid bi-layer or
sandwich. The heads (the phospho part) are polar while the tails (the
lipid part) are non-polar. The heads, which form the outer and inner linings,
are "hydrophilic" (water loving) while the tails that face the interior of the
cell membrane are "hydrophobic" (water fearing). Water is attracted to the
outsides (red) of the membrane but is prevented from going through the non-
polar interior (yellow) layer.
## Transport Across the Membrane
The membranes of the cell are semi-permeable. That means that while most
things are effectively kept in (or out), some can pass through directly. So
how do cells move things in and out? There are three methods.
1\. Diffusion : If a molecule is very small, such as oxygen or carbon
dioxide, diffusion does the trick. When the concentration of O 2 outside
the cell is higher than inside, O 2 molecules diffuse in, passing through
the membrane like it isn't even there. Similarly, when the concentration of
the waste gas CO 2 builds up inside the cell, it escapes naturally to the
outside where the concentration is lower. Diffusion requires no expenditure of
energy by the cell. It happens passively. While nature figured this out a long
time ago, we now make fabrics and medical devices that copy this process. Gore
Industries, one of the big employers in Flagstaff, makes a fabric called
"Gore-Tex" which repels large water droplets but allows smaller air molecules
to pass through, making the fabric "breathable."
The catch: While diffusion works well for the tiny single cell, it does not,
by itself, get the job done in a multi-cellular organism where the tissues are
buried deep inside the body. Imagine your bicep muscle while you are lifting
weights. The tissue, comprised of millions of cells, will quickly run out of
oxygen and build up carbon dioxide. Diffusion through the skin could not keep
up. This is where the circulatory system helps out. The smallest blood
vessels, the capillaries, run though these tissues. The blood from the lungs
releases oxygen to the cells (because O 2 is at lower concentration in the
tissues), and picks up carbon dioxide (because CO 2 is at higher
concentration in the tissues) and carries it back to the lungs to be exhaled.
This does require energy. It also explains why your breathing rate increases
when you exert yourself, and is one of the costs of being multi-cellular.
2\. Active Transport : Sometimes diffusion doesn't happen fast enough for
the cell's needs, and there are times when nutrients need to be stockpiled or
excreted at a higher concentration than would occur naturally by diffusion. In
this case, the cell uses energy to pump good things in, and bad things out,
through protein channels or gates. This process is called active transport.
3\. Endocytosis : Sometimes, a large object needs to be moved in or out of
the cell, but it's too big for the door. Think about moving a couch into your
apartment and you will get the idea. But you can't just cut a hole in the cell
membrane or all the good stuff inside would leak out, so how do you get
something in without letting your interior be exposed to the exterior? The
cell has a special trick that probably dates back to the days when all life
was single celled, and this was how cells ate. The single celled Amoeba
still consumes its food this way. It's called endocytosis, and it works like
this. Note in particular that the engulfed food item is gradually enclosed in
an "inside-out" section of the double-layered membrane, Pac-Man style! Once
the food particle is completely surrounded, the exterior membranes fuse and
the interior vacuole pinches off. By this method, the interior of the cell is
never directly exposed to the exterior environment. The one side effect of
this trick is that the membrane is now inside out, and that's interesting
because it gives us a clue about the origins of the cellular organelles.
Note that the vacuole has its membranes reversed! (Black outer and red inner)
| biology | 3297273 | https://sv.wikipedia.org/wiki/Mallophora%20testaceipes | Mallophora testaceipes | Mallophora testaceipes är en tvåvingeart som beskrevs av Macquart 1850. Mallophora testaceipes ingår i släktet Mallophora och familjen rovflugor. Inga underarter finns listade i Catalogue of Life.
Källor
Rovflugor
testaceipes | swedish | 1.438232 |
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# Plasma Membrane (Cell Membrane)
updated: April 29, 2024
## Definition
The plasma membrane, also called the cell membrane, is the membrane found in
all cells that separates the interior of the cell from the outside
environment. In bacterial and plant cells, a cell wall is attached to the
plasma membrane on its outside surface. The plasma membrane consists of a
lipid bilayer that is semipermeable. The plasma membrane regulates the
transport of materials entering and exiting the cell.
## Narration
The plasma membrane, or the cell membrane, provides protection for a cell. It
also provides a fixed environment inside the cell. And that membrane has
several different functions. One is to transport nutrients into the cell and
also to transport toxic substances out of the cell. Another is that the
membrane of the cell, which would be the plasma membrane, will have proteins
on it which interact with other cells. Those proteins can be glycoprotein,
meaning there's a sugar and a protein moiety, or they could be lipid proteins,
meaning there's a fat and a protein. And those proteins which stick outside of
the plasma membrane will allow for one cell to interact with another cell. The
cell membrane also provides some structural support for a cell. And there are
different types of plasma membranes in different types of cells, and the
plasma membrane has in it in general a lot of cholesterol as its lipid
component. That's different from certain other membranes within the cell. Now,
there are different plants and different microbes, such as bacteria and algae,
which have different protective mechanisms. In fact, they have a cell wall
outside of them, and that cell wall is much tougher and is structurally more
sound than a plasma membrane is.
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| biology | 1548641 | https://sv.wikipedia.org/wiki/Human%20Protein%20Atlas-projektet | Human Protein Atlas-projektet | Human Protein Atlas-projektet är ett svenskt initiativ som startades 2003 i syfte att systematiskt utforska människans samtliga proteiner (proteomet) på cell-, vävnads- och organnivå. För att lyckas med detta, används en strategi med integrerad omik, vilket inkluderar antikroppsbaserad vävnadsproteomik, transkriptomik, masspektrometri-baserad proteomik och systembiologi. All data finns fritt tillgänglig online på projektets databas och kunskapssida för att möjliggöra för forskare inom akademin och företag, samt för allmänheten, att utforska det humana proteomet. Databasen utgör en viktig startpunkt för identifiering av vävnads- och cellspecifika uttrycksmönster, samt för analys av kandidatproteiner som misstänks vara kopplade till hälsa och sjukdom.
Tolv sektioner
Human Protein Atlas består av tolv olika sektioner som är specialiserade på specifika aspekter av den omfattande analysen av det mänskliga proteomet.
Tissue - fördelning av människans proteiner i samtliga vävnader och organ i kroppen.
Brain - utforskning av proteinuttryck i däggdjurs-hjärnan genom integration av data från tre däggdjur (människa, gris och mus).
Single Cell Type - uttrycksnivåer av proteiner i människans olika celltyper.
Tissue Cell Type - utforskning av celltypsuttrycksspecificitet för alla humana proteinkodande gener.
Pathology - påverkan av proteinernas nivåer på överlevnad för cancerpatienter.
Disease - nivåer av protein i blodet hos patienter med olika sjukdomar, samt proteinpaneler för att förutsäga sjukdomar.
Immune Cell - uttrycksnivåer av proteiner hos människoblodets olika celltyper.
Blood Protein - nivåer av protein i blodet, samt distribution av de proteiner som utsöndras från olika celltyper i kroppen.
Subcellular - subcellulär lokalitet för proteiner i enskilda celler.
Cell Line - uttrycksnivåer av proteiner i olika människo-celllinjer.
Structure - prediktionsbaserade och experimentiellt framtagna 3D-modeller av proteinernas struktur med indikerade bindingsplatser för antikroppar och olika varianter i populationen och vid sjukdom.
Interaction - interaktionsnätverksdata baserat på protein-protein-interaktioner från IntAct-databasen samt metaboliska nätverk från metabolicatlas.org med mRNA-uttrycksdata för gener associerade med metabolism.
Övriga funktioner
I tillägg till HPA:s tolv sektioner för kartläggning av gen- och proteinuttryck, innehåller HPA:s webbsida även olika funktioner för att stödja utforskningen av HPA:s data och människans proteom, bl.a. utbildningsmaterial och fritt tillgänglig nedladdningsbar data.
Learn-sektionen på HPA:s webbsida innehåller utbildningsmaterial i form av information om antikroppsbaserade tekniker, en dictionary för histologi och utbildningsvideor. HPA:s dictionary är ett interaktivt verktyg för fri utforskning av högupplösta bilder av hela mikroskop-snitt från kroppens olika organ och vävnader, olika cancertyper och cellstrukturer. Utforskning av bilderna guidas med hjälp av detaljerade beskrivningar av de relevanta strukturella elementen i vävnaderna och cellerna. HPA har även producerat utbildningsvideor som utforskar människokroppen i 3D med hjälp av antikroppsbaserade data och ljusarkmikroskopi (eng: light sheet microscopy). Utbildningsvideorna finns fritt tillgängliga på HPA:s webbsida och på en YouTube-kanal.
Nedladdningsbar data - Den data som används till HPA har gjorts fritt tillgänglig på HPA:s webbsida för att uppmuntra och bidra till vidare studier inom forskningssamhället. Datat finns i 30 olika former och hittas på sidan för nedladdningsbara data.
Human Protein Atlas-projektet är ett samarbete mellan de svenska universiten Kungliga Tekniska högskolan, Uppsala universitet, Akademiska sjukhuset i Uppsala, Karolinska Institutet, Chalmers tekniska högskola, samt den nationella infrastrukturen SciLifeLab.
Referenser
Proteinkemi | swedish | 0.730375 |
count_bees/resources.txt | [ 
](https://www.thebeecause.org/ "The Bee Cause Project")
* [ 2023 Impact Report ](https://www.thebeecause.org/2023impactreport/)
* [ Our Story ](https://www.thebeecause.org/about/)
* [ About Us ](https://www.thebeecause.org/about/)
* [ Find our Hives ](https://www.thebeecause.org/ourhive/)
* [ The Hive ](https://www.thebeecause.org/hives/)
* [ The Bee Blog ](https://www.thebeecause.org/the-bee-blog/)
* [ Submit Your Story ](https://www.thebeecause.org/submit-your-story/)
* [ Get Involved ](https://www.thebeecause.org/get-involved/)
* [ Sponsorship Opportunities ](https://www.thebeecause.org/3-get-involved/bee-cause-sponsorship-opportunities/)
* Store
* [ Shop Bonfire ](https://www.thebeecause.org/shopbonfire/)
* [ Programs ](https://www.thebeecause.org/programs/)
* [ The Bee Grant ](https://www.thebeecause.org/the-bee-grant/)
* [ The Digital Hive ](https://www.thebeecause.org/the-digital-hive/)
* [ Resources ](https://www.thebeecause.org/resources/)
* [ 6 Week Bee Unit ](https://www.thebeecause.org/6-week-bee-unit/)
* [ Bee a Friend to Pollinators ](https://www.thebeecause.org/2-support-materials/bee-a-friend-to-pollinators-lesson-plan/)
* [ My Pollinator Journal ](https://www.thebeecause.org/2-support-materials/my-pollinator-journal/)
* [ OER Commons ](https://www.thebeecause.org/3-get-involved/volunteering/welcome-to-oer-commons-how-to-start-and-grow-your-bee-program/)
* [ Pollinator Insect Lesson (Grades 9-12) ](https://www.thebeecause.org/2-support-materials/bee-cause-pollinator-insect-unit-plan/)
* [ STEM Investigations ](https://www.thebeecause.org/2-support-materials/the-bee-cause-project-guide-for-stem-investigations/)
* [ Contact Us ](https://www.thebeecause.org/contact/)
* [ Donate ](https://www.thebeecause.org/donate/)
* [ Adopt a Pollinator ](https://www.thebeecause.org/adopt-a-pollinator/)
* [ ](https://www.instagram.com/thebeecause/)
* [ ](https://www.facebook.com/TheBeeCause/)
* [ 2023 Impact Report ](https://www.thebeecause.org/2023impactreport/)
* [ Our Story ](https://www.thebeecause.org/about/)
* [ About Us ](https://www.thebeecause.org/about/)
* [ Find our Hives ](https://www.thebeecause.org/ourhive/)
* [ The Hive ](https://www.thebeecause.org/hives/)
* [ The Bee Blog ](https://www.thebeecause.org/the-bee-blog/)
* [ Submit Your Story ](https://www.thebeecause.org/submit-your-story/)
* [ Get Involved ](https://www.thebeecause.org/get-involved/)
* [ Sponsorship Opportunities ](https://www.thebeecause.org/3-get-involved/bee-cause-sponsorship-opportunities/)
* Store
* [ Shop Bonfire ](https://www.thebeecause.org/shopbonfire/)
* [ Programs ](https://www.thebeecause.org/programs/)
* [ The Bee Grant ](https://www.thebeecause.org/the-bee-grant/)
* [ The Digital Hive ](https://www.thebeecause.org/the-digital-hive/)
* [ Resources ](https://www.thebeecause.org/resources/)
* [ 6 Week Bee Unit ](https://www.thebeecause.org/6-week-bee-unit/)
* [ Bee a Friend to Pollinators ](https://www.thebeecause.org/2-support-materials/bee-a-friend-to-pollinators-lesson-plan/)
* [ My Pollinator Journal ](https://www.thebeecause.org/2-support-materials/my-pollinator-journal/)
* [ OER Commons ](https://www.thebeecause.org/3-get-involved/volunteering/welcome-to-oer-commons-how-to-start-and-grow-your-bee-program/)
* [ Pollinator Insect Lesson (Grades 9-12) ](https://www.thebeecause.org/2-support-materials/bee-cause-pollinator-insect-unit-plan/)
* [ STEM Investigations ](https://www.thebeecause.org/2-support-materials/the-bee-cause-project-guide-for-stem-investigations/)
* [ Contact Us ](https://www.thebeecause.org/contact/)
* [ Donate ](https://www.thebeecause.org/donate/)
* [ Adopt a Pollinator ](https://www.thebeecause.org/adopt-a-pollinator/)
Explore lesson plans, teacher guides, grant resources, and more! All Bee Cause
Project resources and content are free to use and download with attribution
for your classroom and community. Please email [email protected] for
permission to re-use for commercial purposes.
* #### Resources
All Resources 1\. Bee Grant Required for Beekeepers Required for Educators
2\. Support Materials Agreements + Sample Templates Instructional Videos
Lesson Plans Outdoor Classrooms Pay It Forward 3\. Get Involved
Fundraising Sponsorship Volunteering
* #### Search
[  ](https://www.thebeecause.org/2-support-
materials/beewiseguide/)
[ Bee Wise Guide ](https://www.thebeecause.org/2-support-
materials/beewiseguide/)
[ ](https://www.thebeecause.org/2-support-materials/beewiseguide/)
[  ](https://www.thebeecause.org/2-support-
materials/i-speak-for-the-bees-project/)
[ I Speak for the Bees! Project ](https://www.thebeecause.org/2-support-
materials/i-speak-for-the-bees-project/)
Get ready to dive into the world of honey bees and speak out on behalf of
these precious pollinators.
[ ](https://www.thebeecause.org/2-support-materials/i-speak-for-the-bees-
project/)
[  ](https://www.thebeecause.org/2-support-materials/my-
pollinator-journal/)
[ My Pollinator Journal ](https://www.thebeecause.org/2-support-materials/my-
pollinator-journal/)
The My Pollinator Journal is designed to help your communities interact with
pollinators with hands-on activities and more.
[ ](https://www.thebeecause.org/2-support-materials/my-pollinator-journal/)
[  ](https://www.thebeecause.org/2-support-materials/bee-
campus-safety/)
[ Bee Campus Safety ](https://www.thebeecause.org/2-support-materials/bee-
campus-safety/)
The Bee Cause wants you to bee safe! Take these important steps to protect
your bees and your community.
[ ](https://www.thebeecause.org/2-support-materials/bee-campus-safety/)
[ 
](https://www.thebeecause.org/2-support-materials/lesson-plans/the-
pollinators-educators-guide/)
[ Bee Cause Film Circle: The Pollinators Film Educator’s Guide
](https://www.thebeecause.org/2-support-materials/lesson-plans/the-
pollinators-educators-guide/)
It's finally here, our first Film Circle movie for older students!!
[ ](https://www.thebeecause.org/2-support-materials/lesson-plans/the-
pollinators-educators-guide/)
[ 
](https://www.thebeecause.org/3-get-involved/volunteering/q-a-webinar-with-
author-shabazz-larkin/)
[ Q & A Webinar with Author Shabazz Larkin
](https://www.thebeecause.org/3-get-involved/volunteering/q-a-webinar-with-
author-shabazz-larkin/)
Engage your students with this unique video and Educator's Guide!
[ ](https://www.thebeecause.org/3-get-involved/volunteering/q-a-webinar-with-
author-shabazz-larkin/)
[  ](https://www.thebeecause.org/bee-
grant/how-to-install-a-bottom-entrance-beehive-with-the-bee-cause-project/)
[ Video: How to Install a Bottom Entrance Beehive with The Bee Cause Project
](https://www.thebeecause.org/bee-grant/how-to-install-a-bottom-entrance-
beehive-with-the-bee-cause-project/)
So you’ve received your observation hive. Now what? This video will guide you
through the installation process for your bottom
[ ](https://www.thebeecause.org/bee-grant/how-to-install-a-bottom-entrance-
beehive-with-the-bee-cause-project/)
[  ](https://www.thebeecause.org/bee-
grant/bee-advocate-hive-investigations-guide-for-a-bottom-entrance-hive/)
[ Video: Bee Advocate Hive Investigations Guide for a Bottom Entrance Hive
](https://www.thebeecause.org/bee-grant/bee-advocate-hive-investigations-
guide-for-a-bottom-entrance-hive/)
Are you a Bee Advocate? Learn how to investigate the bottom entrance beehive
to look out for everything you will
[ ](https://www.thebeecause.org/bee-grant/bee-advocate-hive-investigations-
guide-for-a-bottom-entrance-hive/)
[ 
](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-field-
trip-farm-to-table-educators-guide/)
[ Digital Field Trip: Farm to Table + Educator’s Guide
](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-field-
trip-farm-to-table-educators-guide/)
Join us for the Journey of Food, from the farm to the table! A farm-fresh
experience for you and your
[ ](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-
field-trip-farm-to-table-educators-guide/)
[ 
](https://www.thebeecause.org/3-get-involved/volunteering/welcome-to-oer-
commons-how-to-start-and-grow-your-bee-program/)
[ Welcome to OER Commons: How to Grow Your Pollinator Education Program
](https://www.thebeecause.org/3-get-involved/volunteering/welcome-to-oer-
commons-how-to-start-and-grow-your-bee-program/)
Explore our most up-to-date curriculum and other digital resources with this
free resource. “Bee” sure to check out even more
[ ](https://www.thebeecause.org/3-get-involved/volunteering/welcome-to-oer-
commons-how-to-start-and-grow-your-bee-program/)
[ 
](https://www.thebeecause.org/2-support-materials/lesson-plans/bee-cause-book-
club-educators-and-students-guides/)
[ Bee Cause Book Club: Educator’s and Student’s Guides
](https://www.thebeecause.org/2-support-materials/lesson-plans/bee-cause-book-
club-educators-and-students-guides/)
Need some literacy lesson plans to go with your pollinator curriculum? Try our
Book Club Resources! Fiction and nonfiction recommendations
[ ](https://www.thebeecause.org/2-support-materials/lesson-plans/bee-cause-
book-club-educators-and-students-guides/)
[ 
](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-field-
trip-a-hive-to-table-experience-educators-guide/)
[ Digital Field Trip: A Hive to Table Experience + Educator’s Guide
](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-field-
trip-a-hive-to-table-experience-educators-guide/)
Join our friends Ted Dennard and The National Honey Board on this 360-degree
field trip explaining how honey is made,
[ ](https://www.thebeecause.org/2-support-materials/lesson-plans/digital-
field-trip-a-hive-to-table-experience-educators-guide/)
[ 
](https://www.thebeecause.org/2-support-materials/lesson-plans/natures-
partners-pollinator-partnership-curriculum-guide/)
[ Nature’s Partners Pollinator Partnership Curriculum + Educator Guide
](https://www.thebeecause.org/2-support-materials/lesson-plans/natures-
partners-pollinator-partnership-curriculum-guide/)
Explore the Nature's Partners Curriculum for Grades 3-6. Created by the
Pollinator Partnership, this curriculum includes Bee Cause Project Teacher
[ ](https://www.thebeecause.org/2-support-materials/lesson-plans/natures-
partners-pollinator-partnership-curriculum-guide/)
[ 
](https://www.thebeecause.org/2-support-materials/digital-field-trip-honey-
harvest-video-educators-guide/)
[ Digital Field Trip: Honey Harvest Video + Educator’s Guide
](https://www.thebeecause.org/2-support-materials/digital-field-trip-honey-
harvest-video-educators-guide/)
Dive into the hive with the Honey Harvest Digital Field Trip! Your class takes
the journey from hive to honey
[ ](https://www.thebeecause.org/2-support-materials/digital-field-trip-honey-
harvest-video-educators-guide/)
[ 
](https://www.thebeecause.org/2-support-materials/digital-hive-video-
educators-guide/)
[ The Bee Cause Project Digital Hive Video + Educator’s Guide
](https://www.thebeecause.org/2-support-materials/digital-hive-video-
educators-guide/)
The Digital Hive Experience takes your students inside the hive! Educator's
Guide for lesson to accompany on this adventure.
[ ](https://www.thebeecause.org/2-support-materials/digital-hive-video-
educators-guide/)
[ 
](https://www.thebeecause.org/bee-grant/observation-hive-checklist-
maintenance-schedule/)
[ Bee Grant: Observation Hive Checklist + Maintenance Schedule
](https://www.thebeecause.org/bee-grant/observation-hive-checklist-
maintenance-schedule/)
Checklist and maintenance schedule for observation hive upkeep! Complete your
annual hive structure checks with this guide.
[ ](https://www.thebeecause.org/bee-grant/observation-hive-checklist-
maintenance-schedule/)
[ 
](https://www.thebeecause.org/bee-grant/bee-grant-observation-hive-management-
guide/)
[ Bee Grant: Observation Hive Management Guide
](https://www.thebeecause.org/bee-grant/bee-grant-observation-hive-management-
guide/)
Let's get started with your observation hive! The Bee Wise Guide takes you
from approval to implementation of the Bee
[ ](https://www.thebeecause.org/bee-grant/bee-grant-observation-hive-
management-guide/)
[ 
](https://www.thebeecause.org/bee-grant/bee-advocate-role-and-responsibility/)
[ Bee Grant: Bee Advocate Role + Responsibility
](https://www.thebeecause.org/bee-grant/bee-advocate-role-and-responsibility/)
Find out more about the Bee Advocate Role and how to lead your Bee Program!
[ ](https://www.thebeecause.org/bee-grant/bee-advocate-role-and-
responsibility/)
[  ](https://www.thebeecause.org/bee-grant/bee-grant-bee-
mentor-role-responsibility/)
[ Bee Grant: Bee Mentor Role + Responsibility
](https://www.thebeecause.org/bee-grant/bee-grant-bee-mentor-role-
responsibility/)
Find out more about the Bee Mentor Role and how this will bee your biggest
partner.
[ ](https://www.thebeecause.org/bee-grant/bee-grant-bee-mentor-role-
responsibility/)
[  ](https://www.thebeecause.org/bee-grant/classroom-calendar-
what-are-bees-up-to-year-round/)
[ Monthly Buzz Classroom Bee Calendar + Journal Prompts
](https://www.thebeecause.org/bee-grant/classroom-calendar-what-are-bees-up-
to-year-round/)
What's the buzz all about? Explore what the bees are up to by the month, and
then complete the companion
[ ](https://www.thebeecause.org/bee-grant/classroom-calendar-what-are-bees-up-
to-year-round/)
[ 
](https://www.thebeecause.org/2-support-materials/literature-circle-teachers-
guide-group-roles/)
[ Literature Circle Teacher’s Guide + Group Roles
](https://www.thebeecause.org/2-support-materials/literature-circle-teachers-
guide-group-roles/)
Calling all reading levels! Begin your literature circle with the pollinator
friendly reading list: books for all reading levels included!
[ ](https://www.thebeecause.org/2-support-materials/literature-circle-
teachers-guide-group-roles/)
[  ](https://www.thebeecause.org/bee-grant/how-to-build-your-
bee-club-campus-or-community/)
[ How to Build Your Bee Club ](https://www.thebeecause.org/bee-grant/how-to-
build-your-bee-club-campus-or-community/)
Start Your Own Bee Club! This guide helps you start your own on campus or in
your community.
[ ](https://www.thebeecause.org/bee-grant/how-to-build-your-bee-club-campus-
or-community/)
[  ](https://www.thebeecause.org/bee-grant/bee-
cause-curriculum-the-complete-6-week-bee-unit/)
[ Bee Cause Curriculum: The Complete 6 Week Bee Unit + Teacher Guides
](https://www.thebeecause.org/bee-grant/bee-cause-curriculum-the-
complete-6-week-bee-unit/)
The Complete 6 Week Bee Unit includes lesson plans and educator guides
specifically built to explore the lives of bees.
[ ](https://www.thebeecause.org/bee-grant/bee-cause-curriculum-the-
complete-6-week-bee-unit/)
[  ](https://www.thebeecause.org/bee-grant/how-to-
grow-your-bee-program/)
[ How to Grow Your Bee Program ](https://www.thebeecause.org/bee-grant/how-to-
grow-your-bee-program/)
Learn how to build a strong foundation for your Bee Program!
[ ](https://www.thebeecause.org/bee-grant/how-to-grow-your-bee-program/)
[  ](https://www.thebeecause.org/bee-grant/bee-
renewal-grant-overview/)
[ The Renewal Grant Overview ](https://www.thebeecause.org/bee-grant/bee-
renewal-grant-overview/)
This is your first stop if you are interested in applying for the Renewal
Grant! Find out exactly what this
[ ](https://www.thebeecause.org/bee-grant/bee-renewal-grant-overview/)
[  ](https://www.thebeecause.org/2-support-
materials/bee-a-friend-to-pollinators-lesson-plan/)
[ “Bee” a Friend to Pollinators Lesson Plan
](https://www.thebeecause.org/2-support-materials/bee-a-friend-to-pollinators-
lesson-plan/)
Explore your campus, home, or outdoor space for pollinator habitat readiness.
Assessment, core elements, and guided plan included!
[ ](https://www.thebeecause.org/2-support-materials/bee-a-friend-to-
pollinators-lesson-plan/)
[ 
](https://www.thebeecause.org/bee-grant/video-bee-advocate-hive-
investigations-guide/)
[ Video: Bee Advocate Hive Investigations Guide for a Top Entrance Hive
](https://www.thebeecause.org/bee-grant/video-bee-advocate-hive-
investigations-guide/)
Are you a Bee Advocate? Learn how to investigate the top entrance beehive to
look out for everything you will
[ ](https://www.thebeecause.org/bee-grant/video-bee-advocate-hive-
investigations-guide/)
[ 
](https://www.thebeecause.org/2-support-materials/bee-cause-pollinator-insect-
unit-plan/)
[ Bee Cause Pollinator Insect Unit Plan
](https://www.thebeecause.org/2-support-materials/bee-cause-pollinator-insect-
unit-plan/)
In this 9-12 Lesson Plan for High School Biology, students address insect and
honeybee anatomy, illustration, and identification.
[ ](https://www.thebeecause.org/2-support-materials/bee-cause-pollinator-
insect-unit-plan/)
[  ](https://www.thebeecause.org/2-support-
materials/the-bee-cause-project-guide-for-stem-investigations/)
[ The Bee Cause Project Guide for STEM Investigations
](https://www.thebeecause.org/2-support-materials/the-bee-cause-project-guide-
for-stem-investigations/)
In this K-12 STEAM lesson plan compilation, students explore different levels
of investigations within the observation hive.
[ ](https://www.thebeecause.org/2-support-materials/the-bee-cause-project-
guide-for-stem-investigations/)
[ 
](https://www.thebeecause.org/2-support-materials/outdoor-classroom-and-
observation-hive-habitat-building-plan-and-photos/)
[ Outdoor Classroom and Observation Hive Habitat Building Plan and Photos
](https://www.thebeecause.org/2-support-materials/outdoor-classroom-and-
observation-hive-habitat-building-plan-and-photos/)
Explore these construction plans for an outdoor classroom pavillion and space
to install an outdoor observation hive.
[ ](https://www.thebeecause.org/2-support-materials/outdoor-classroom-and-
observation-hive-habitat-building-plan-and-photos/)
[  ](https://www.thebeecause.org/bee-
grant/video-how-to-install-your-live-bees-in-the-observation-hive/)
[ Video: How to Install Your Live Bees in the Observation Hive
](https://www.thebeecause.org/bee-grant/video-how-to-install-your-live-bees-
in-the-observation-hive/)
Time for bees! This video is for Bee Mentors and Advocates who are ready to
install their live bees in
[ ](https://www.thebeecause.org/bee-grant/video-how-to-install-your-live-bees-
in-the-observation-hive/)
[  ](https://www.thebeecause.org/bee-
grant/video-how-to-install-your-observation-hive/)
[ Video: How to Install a Top Entrance Beehive with The Bee Cause Project
](https://www.thebeecause.org/bee-grant/video-how-to-install-your-observation-
hive/)
So you’ve received your observation hive. Now what? This video will guide you
through the installation process for your hive.
[ ](https://www.thebeecause.org/bee-grant/video-how-to-install-your-
observation-hive/)
[ 
](https://www.thebeecause.org/bee-grant/beekeeper-mentor-agreement-template/)
[ Beekeeper Mentor Agreement Template ](https://www.thebeecause.org/bee-
grant/beekeeper-mentor-agreement-template/)
Establish a great working relationship with your Beekeeper Mentor. This
template provides a starting agreement for hive support.
[ ](https://www.thebeecause.org/bee-grant/beekeeper-mentor-agreement-
template/)
[ 
](https://www.thebeecause.org/bee-grant/letter-of-understanding-for-schools/)
[ Letter of Understanding for Schools ](https://www.thebeecause.org/bee-
grant/letter-of-understanding-for-schools/)
Letter of Understanding for Bee Grant Applicants in Schools. This document is
if you are a school applying to the
[ ](https://www.thebeecause.org/bee-grant/letter-of-understanding-for-
schools/)
[ 
](https://www.thebeecause.org/bee-grant/letter-of-understanding-for-
nonprofits/)
[ Letter of Understanding for Nonprofits ](https://www.thebeecause.org/bee-
grant/letter-of-understanding-for-nonprofits/)
Letter of Understanding for Organizational Bee Grant Applicants. This document
is for you if you are a nonprofit!
[ ](https://www.thebeecause.org/bee-grant/letter-of-understanding-for-
nonprofits/)
[  ](https://www.thebeecause.org/bee-
grant/bee-grant-program-overview/)
[ Traditional Bee Grant Overview ](https://www.thebeecause.org/bee-grant/bee-
grant-program-overview/)
This is your Getting Started Guide! Start here to get a better picture of how
a Bee Grant will play
[ ](https://www.thebeecause.org/bee-grant/bee-grant-program-overview/)
[ 
](https://www.thebeecause.org/bee-grant/pay-it-forward-program/)
[ Pay-It-Forward Fundraiser Details ](https://www.thebeecause.org/bee-
grant/pay-it-forward-program/)
Do you need to raise funds for your Bee Grant program? Use the Pay-It-Forward
program with Savannah Bee Company! Open
[ ](https://www.thebeecause.org/bee-grant/pay-it-forward-program/)
[  ](https://www.thebeecause.org/3-get-involved/bee-cause-
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At the Hive Entrance: Look, Listen, Learn
By Susan Chernak McElroy on July 22, 2016
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Watching my bees enter their new hive. Oooh! There's the queen!
Watching my bees enter their new hive. Oooh! There’s the queen!
Most everything I need to know about my bees, I learn by sitting in front of my hives. Armed with an old stethoscope and a magnifying glass, I can be found on most summer afternoons sitting at the hive entry boards, spell-bound. In fact, I have chairs or stools stationed all around my bee yard. Sometimes, I bring a large jug of ice-tea and a book or magazine to read while the bees buzz in soft amber clouds around me.
I don’t consider this idle time, although it may look like it to the casual observer. I have read that if you are not getting into your hives at least every two weeks to do inspections, you are a poor beekeeper, or worse: a bee “haver.” However, my hours of observation time are my primary method of hive inspection, and I find the most of the information I need without the need for suiting up, lighting smokers, or disrupting the hard work of the hive.
My bee mentor, Jacqueline Freeman (www.spiritbee.com) calls this “Putting in your thousand hours—” not a thousand hours inside the hive, but observing the hive from the outside as you sit beside your bees patiently, over many months. In the beginning of my beekeeping seasons, I was a patient observer mostly because I was keeping three Warre’ hives. There were no viewing windows on the hives, and once a Warre’ begins building up, removing single combs is major surgical event for the bees, so I had to restrict my inspections to whatever I could see on the landing board. It was an education that has served me and my bees well. With viewing windows on my hives now, I feel like I am in bee observation heaven.
So, what can you learn from sitting at the hive?
Do I Have a Qeen?
This is something everyone who catches a swarm of bees will be wondering over their first month or two with the bees. I’ve seen queens entering a new hive often this year since I switched over to walking the bees into the hive rather than dumping them in. As my eyes adjust to the movement of thousands of humming, fanning bees marching up a covered plank into their new home, I’ve been blessed to see the tell-tale long abdomen of royalty, hurrying up the ramp with her escorts clustered around—and sometimes on top of—her.
Which bee is not like the others? A queen and her court dash into a barrel hive.
Which bee is not like the others? A queen and her court dash into a barrel hive.
If you are not lucky enough to see a queen on the ramp, looking for her inside the hive is a major disruption of the new colony, and can quickly convince them all to leave and find a home where foul-smelling giants with fat fingers do not go bumbling through the fragile new white combs. Bees do not welcome your inspections, which to them are invasions. Trust me on this. They will let you know with stings and head bumps when you have overextended your welcome. For some hives, just opening up the lid is overextending your welcome on some days.
So how can you know that you have a mated, working queen? With some practiced observation, you can see all you need to know at the hive entrance, or from your viewing window. This is what bees with healthy, mated queens do:
They bring in pollen as soon as they get a few wax combs built, usually within three to five days.
Wax building is strong and steady.
They move in a steady, purposeful way both from and to the hive.
There is busy activity on the landing board with bees guarding, cleaning, collecting nectar and pollen from returning bees, and carrying out hive detritus.
The sound of the hive is a smooth and steady hum. If you tap on the side, there will be a very short burst of louder humming that will immediately drop off to a normal hum state.
Hive numbers will drop, then slowly begin to rise.
Anywhere from a month to two months, you will begin seeing lovely clouds of bees spiraling slowly in front of the hive as new foragers set their inner GPS tracking chips in preparation for heading out into the field.
From the viewing window, you will learn to identify the look of new, sealed brood comb
In contrast, this is what you may see and hear if your hive is queenless:
Little pollen coming into the hive.
Bees milling about aimlessly on the entry board.
If you rap briefly on the hive, the bees will answer with a droning tone that slowly tapers off.
Not many bees come and go, and those that do don’t move with purpose. Purpose is something you identify only by watching hives over time.
This year, I started six new colonies from swarms. All but one were blessed with strong, successful queens. One was not. I merged that hive with another queen-right hive. All of these decisions I made were based only on what I could see from the entry boards and the viewing windows.
What’s Going On In There?
Are your bees building up well, or just hanging on? Are they attracting robbers? Are they weak in some way? Are they getting ready to swarm? Most of these answers are literally right in front of your nose. A strong hive shows increasing numbers of bees coming and going. Sometimes the landing boards in mid-summer look like a subway platform at rush hour.
These bearding girls swarmed later in the week.
These bearding girls swarmed later in the week.
Do you notice your hive bearding, that is, hanging in a dense clump from the front of the hive like a…well…beard? Your hive may be telling you that they are evaporating a lot of nectar in the hive and all superfluous bees need to hang outside for the time being. Or they might be preparing to swarm, depending on the time of the year. Sometimes in very hot weather, the bees will chill out on the landing board in a big beard.
If I see lots of fanning bees on the entry board, along with the bearders, I know honey is being processed. If I see rushing bees knocking hard into the bees in the beard, or jumping on their shoulders and shaking them, I know a swarm is about to take flight and soon!
Honey fanners: Their tails are pointed down.
Honey fanners: Their tails are pointed down.
Do you wonder if your bees have mites? If they are bearding, just look at them through a magnifying glass. It is simple to see mites that way. Actually, you don’t even need the magnifying glass. I can see mites on bees as they are coming or going from the hive. Sometimes, I’ll grab the mitey bee, pull the mite off, and let her go. It’s a small triumph, I agree, but it’s satisfying, nonetheless.
Do your bees “washboard,” moving forward and back in rows, using their feet to “wipe” the hive? No one knows what this really means, but I’ve also seen bees do this inside the hive from the viewing windows, and it is thought to be an indicator of a strong hive.
One of my hives attempting to eradicate mites by tossing out mite-weakened drones and drone pupae. I found hundreds of these on the floor by the hive over a period of a week last spring.
One of my hives attempting to eradicate mites by tossing out mite-weakened drones and drone pupae. I found hundreds of these on the floor by the hive over a period of a week last spring.
Do you have hygienic bees? This is all the rage right now: Bees who clean mites from themselves, each other, and remove mite-infested larvae. You may see your bees vigorously nibbling between the body creases of returning foragers, or see bees pulling out “purple eyed” pupae—immature bees that have white bodies and purple eyes—and tossing them off the landing board.
Do you see bees balling up and fighting on the landing board, or hear high-pitched, agitated buzzing with bees scurrying up the sides and face of your hive? This is a clear sign of robbing—stranger bees swooping in to steal honey from your bees.
Nasonov fanners: Tails pointed up/out, and tiny white gland evident at their tail end.
Nasonov fanners: Tails pointed up/out, and tiny white gland evident at their tail end.
Do you see many nasonov fanning bees on the landing board—bees with their tails hiked high in the air exposing the small, whitefish nasonov gland at the end of their abdomen? If you have a hive with a virgin queen, the bees will often send out a cadre of nasonov fanners to guide their young queen home from her mating flights.
If you are at the hive at the right moment, you may even get to see the ancient, yearly ritual of bees expelling their drones for the season—a melancholy time for me. It means my bee year is coming to a close. And it is hard to watch those fuzzy, clumsy drones get pushed out of the hive by the hundreds.
One of my favorite sights on the landing boards of my hives is the honey-kiss—two bees exchanging nectar, proboscises extending, antennae touching gently and excitedly.
Three Warre' hives...and a short green stool.
Three Warre’ hives…and a short green stool.
So, do I ever go into my hives? Certainly, but not as often as you might think necessary. To be honest, I only enter my hives a few times a year. And I find that to be plenty. Each time you enter a hive, you run the risk of injuring the queen. You upset the temperature balance in the hive, a balance critical to the development of the young bees. In cracking open the hive, you also break the propolis seal—that sticky red/brown stuff that is the external immune system of the bees—and allow the entry of pathogens. I have read that it takes bees two to four days to put their hive back in order after an inspection. I don’t want to make my bees spend their short, precious summer days having to repair the damage I’ve done by poking around in their sacred space.
On my knees "conversating" with my bees.
On my knees “conversating” with my bees.
Thankfully, I rarely need to. Am I a beekeeper or a bee haver? I like to identify as both. There is something to be said for meddling less in the complex daily life of the bees. Through patient observation, I am coming to trust the bees’ innate good sense and ancient wisdom more as the years go by. I learn a lot from good beekeepers, but I learn most sitting at the feet of my good bees.
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35 Comments
Leilani & Anthony Rosenbaum says:
July 30, 2016 at 12:46 pm
Hi, this is the second article we have read of your. Very interesting. We are new to Bee Keeping one full year in now. We 6 langstroth and 10 AZ hives from Slovenian now 3 that are established and we are trying to move our langstroth into the AZ. Look forward to more natural ways of Bee keeping.
Reply
Susan Chernak McElroy says:
August 1, 2016 at 3:43 pm
Congratulations on your first year of beekeeping! The Slovenian hives look really interesting. As you can tell, I’m a real fan of trying different kinds of hives. I love the more “natural” approach to beekeeping that is happening with so many backyard beekeepers these days. Less stressful on the bees and the keepers!
Reply
Larry Stines says:
August 20, 2016 at 2:56 am
Great article! I have been preaching less opening the hives for years! And you are absolutely correct, you can tell what is going on by careful observation! Thank you for the article!
Reply
Janice says:
March 25, 2017 at 1:12 pm
Just an FYI
Reply
Observing Honey Bee Behavior | Beekeeping365 says:
April 6, 2017 at 10:37 am
[…] Source: At the Hive Entrance: Look, Listen, Learn […]
Reply
Pamela says:
May 7, 2017 at 7:05 pm
Hello! This was one of the most detailed yet simplistic observations of bee keeping I have read so far. It reminds me of my way of gardening and the adage that less is more. Too much information out there can overwhelm the novice gardener and bee keeper….I let instinct, common sense, and the will to not “fix” or meddle in something that is not broken. I love that you only enter your hive a few times a year and they do just fine. I’ve often wondered about all the advice to do this and that with hives including the smoking and numerous inspections…how it impacted the bees’ natural rhythm…you have confirmed what I’ve always suspected (just a gut instinct and common sense). Thank you for sharing!
Reply
Pamela says:
May 7, 2017 at 7:11 pm
I also marveled at your observation of bees removing mites from themselves and others…and the “housekeeping” that goes on. It makes me wonder if this has always been the case and if the bee population is beginning to achieve strength again (demonstrating past natural mite defeating actions) after so much controversy, rebellion, and protesting about pesticides and herbicides being the cause of their decline.
Reply
Jelly mehrkam says:
May 8, 2017 at 5:04 pm
This is so helpful being a extremely new beekeeper of only a month now I’m trying to jam any and every bit of knowledge I can in to my brain about the bees and how to care for them.
Reply
Rob Schmidt - St Louis MO says:
June 15, 2017 at 11:19 pm
I love this article. I’ve read it multiple times and shared it with my bee friends.
Would you write more on what you can learn from observing your hive from the outside?
Reply
Angela says:
June 22, 2017 at 11:36 pm
I’m having issues with beetles. I’ve tried the beetle blaster and that did not work out so good. I lovey bees I enjoy just watching them come and go from the hive. Also my first year.
Reply
Leslie says:
June 23, 2017 at 5:02 pm
Since I’ve been keeping bees for a few months now I’ve gotten more advice from experienced beekeepers than you can believe. The most recent is I’ve got to treat for mites NOW. I just don’t want to do it. It seems barbaric. They’re doing so well and are calm and making lots of honey, and the activity at the landing boards seems really healthy to me. I don’t want to meddle. I might be dreaming but I feel like they will deal with the mites on their own. Do you think I’m in fantasy land? Given the way you “handle” your bees it seems like you don’t treat either. I’d really love to hear your thoughts on this.
Reply
Susan Chernak McElroy says:
July 9, 2017 at 3:44 am
As you guessed, I don’t treat my bees for mites. It is messy, dangerous, and if it worked we would no longer have mite problems, would we? I’m going down the path of Darwinian Beekeeping, where I let natural selection rather than human selection rule in my bee garden. It is hard to lose hives, and these days, most of us (conventional and alternative) lose a lot of hives. While I don’t treat, and don’t “manage” or intervene often in my hives, this does not mean I’m advocating not bothering to learn about bees. Whether I choose to intervene or not, I like to know what is going on with my bees, and most of that, I learn by reading and by observing my bees through the seasons. And the great thing about bees is that there is always something new to see and to learn.
Reply
mike kay says:
July 8, 2017 at 4:55 pm
I have a boat in my back yard that was totally decked with plywood.So you could walk around the whole boat. My neighbor did this ,kind of like a 15 foot barge so to speak. Well i ended up with it in my backyard . I flipped the boat upside down and kinda forgot about it until the other day. To my surprise it now house a swarm of honey bees.However you cannot see anything as it is full enclosed with only the plug hole as their entrance. I just found these bees and really am confused on what to do next.
Reply
Susan Chernak McElroy says:
July 9, 2017 at 3:47 am
Gee, I’d call that a fortuitous event! If you plan to leave the boat where it is at, you could just let the bees be and enjoy having them on your property. If you have reason to want them gone, go online and look for a beekeeping association/club near you who can help you rehome the hive.
Reply
Don says:
August 4, 2017 at 11:02 pm
Susan,
Very enjoyable reading. I agree that the less disruption to the hive, the better.
Thanks
Don
Reply
Judy Howell says:
October 14, 2017 at 7:34 pm
This is one of the best articles on beekeeping I have ever read, and reflected my own beliefs about beekeeping (although until you put it into words I did not know I felt that way). I have much to learn still, but enjoyed your article immensely.
Reply
Susan Chernak McElroy says:
October 15, 2017 at 1:48 am
Judy, I’m glad it resonated with you.This winter, I’ll be blogging here more about my “hands-off, eyes-on” beekeeping style.
Reply
Carole Haney says:
November 5, 2017 at 8:40 pm
Thank you for this article, this is what my dad is teaching me. All I read is put this on them and add that.. Nice to see someone who gets it.
Reply
Susan Chernak McElroy says:
November 5, 2017 at 10:18 pm
Thanks, Carole. I’m unorthodox in that I’m pretty much hands off with my bees. They do better that way.
Reply
Cathy says:
January 7, 2018 at 2:47 pm
Really enjoyed this post. I found myself a bee -haver when a large bee tree was taken down on my property. I never intended to become a “keeper.” I figured the wild bees knew more about what they needed than I did. They lived successfully in their tree for years without my help! I still think of myself as a hostess to the bees that live on my property. I try to provide accommodation for my (hive) guests, but hate intruding on their private lives. I also spend hours watching the hives, just as I spend hours watching my chickens, ducks and horses. You are so right about the conversation they will have with you if you let them.
Reply
Bonnie says:
June 16, 2019 at 9:13 pm
Great article! We recently got a nuc with a queen cell and no queen and it’s been stressful as we don’t want to open the hive during this precious time but also need to know what’s going on for the good of the whole colony. I have spent the last week staring at opening trying to understand what is going on without disturbing the hive and this article is exactly what I was looking for. I’ve read a lot as we are doing a top-bar hive but this has been one of the most helpful articles. Thank you so much!
Reply
Susan Chernak McElroy says:
June 17, 2019 at 2:50 am
Thanks, Bonnie. Our nonprofit (preservationbeekeeping.com) does bees very differently. You are on the right track not wanting to open the hive. We learned in Europe last year that when a hive is making a new queen, it is a very fragile time for the hive, and if interfered with, the colony may actually kill their new queen. So, we are told best not to poke a nose in for a good month. Also, we have experienced that the new queen may delay laying for weeks, perhaps as a self-treatment for varroa. Check out our website and FB page, as you will learn things there no one else is talking about.
Reply
Linda says:
August 11, 2019 at 3:22 am
Is there any non destructive, safe way to encourage a group of bees out of my chimney?
Reply
Susan Chernak McElroy says:
August 11, 2019 at 3:37 pm
Linda, yes, there is. The process is called a “trap out.” You can advertise on Craigslist that you are looking for a beekeeper to do a trap out from your chimney, and you should get some folks who know how to do this.
Reply
Bill Hill says:
August 29, 2019 at 1:55 am
I loved your article. Thank you for sharing.
I read the article in a recent Science issue, and it made me curious:
How many bees arrive or leave a minute?
How fast do they walk?
Do they fly inside the hive, or mostly walk?
What times do they start and stop their typical days?
Thank you very much for any help or redirection.
Best wishes. You really enjoy your life, I’m happy for you and all Nature lovers.
Aloha from Mililani Hawaii
Reply
Ben says:
January 20, 2020 at 12:51 pm
Another observation i like to do, is assess whether the bees are landing heavy or light especially on days with not much wind. If lots of bees with large pollen baskets are landing short and having to walk up to the platform then there is plenty of supplies available. If they are landing lightly with nothing in their baskets, right in front of the entrance, then there is a dearth of pollen.
Reply
Joe says:
February 7, 2020 at 7:11 pm
I have some terrible news for you. You do not in fact have a qeen. I am sorry for bee-ing the bearer of bad news, but honey, you are qeenless.
Reply
Christina says:
April 21, 2020 at 5:45 pm
Do you treat your hives for mites ?
Reply
Christina says:
April 21, 2020 at 5:48 pm
Do you harvest honey often?
Reply
Louise vergette says:
June 3, 2020 at 10:28 am
Hello Susan,
I was delighted to come across your backyard bees website. As a fellow Warre beekeeper it was so refreshing to find a beekeeper who believes in a “ hands off” approach to beekeeping. Like yourself I spend hours sitting outside my hives observing the bees, I never tire of watching them. All my hives, like yours are totally unagressive and because I don’t disturb the hives with frequent inspections and chemical dosings they are healthy, strong and content. Keep up the good work! Louise
Reply
Tony says:
July 15, 2020 at 3:56 am
I love sitting and watching my bees, I have only had them for 4 months now and they fascinate me. I have a 10 frame langstroth hive, I haven’t put the honey super on yet that may happen in the next couple of weeks depending on how full the brood super is.
Apparently I should smoke the bees every time I open the hive but I have read that smoke agitates the bees. Is it ok not to smoke the hive?
Reply
Thelostlander says:
July 22, 2020 at 5:37 am
I’m still a learner in beekeeping and started with my 1st box this spring. I’m very fond of sitting infront of the box and observing what the bees do and sometimes wonder what their each dance/move means.. your post has really been insightful. Thank you so much 🙂
Reply
Carole says:
August 1, 2020 at 4:49 pm
Last fall, because of various circumstances, I lost three hives….all of which, I believe, were due to my ignorance. I sealed up the hives for the winter. About three weeks ago I unsealed one hive. About a week ago honeybees started coming by the thousands. I’m afraid the are only robbing. Only an occasional bee with pollen enters.. guard bees stand in front of the entrance lined up facing entrance like soldiers. What do you think……robbing or looking for a new home?
Reply
Rob says:
August 17, 2020 at 7:44 pm
I like your article on observation (“At the Hive Entrance”)–a lot. I live in a small town in Alaska that is currently experiencing a boom in beginning beekeepers. I’ve been keeping bees for going on fifty years–seems hard to believe, but it’s true–which makes me by far the most experienced beekeeper in the area, and as such I answer a lot of questions, have a lot of mentoring sessions with beginners. My advice, over and over, is always some version of: Less is more; just about everything that you need to know about a hive is right there in plain view at the entrance; everything we know about bees, everything without exception, is rooted in someone sitting in front of a hive spending hours and hours just watching the bees go in and out; shed your preconceptions and learn to observe–the bees will teach you the only lessons you really need to learn.
I get an abundance of eye rolls, and I can imagine the eye rollers thinking, “God! I ask this guy a simple question, and instead of a simple answer, I get all this woo-woo crap! There’s gotta be someone in this town who can tell me what I want to know.” But I also get a lot of people who listen and follow my advice–not surprisingly those are my star students.
Thanks for publishing my thoughts almost exactly the way I would have expressed them–keep up the good work.
Rob Lund
Homer, Alaska
Reply
Cynthia says:
September 14, 2021 at 1:26 am
I just loved your very knowledgeable article. I am a very new bee keeper, but already I love my bees, and visit them every day and just watch them. Apparently, they can recognize me, and never threaten me in any way. They are magical creatures, and their society organization defies belief. The more I learn about them, the more amazed I am. Thank you so much
Reply
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Bees offer many benefits (honey and pollination, to name a few), but coming face to face with a bee hive, or worse, several bee hives, when you aren’t expecting it can be a frightening experience. Here are some beehive facts for keeping you and your family safe from stings.
What is a beehive?
There are many types, but commonly seen hives have a waxy appearance and a honeycomb shape with tiny openings where the bees live. Honey is stored in the upper portion of the comb while pollen is stored in the lower cavity.
Where are bee hives located?
Honey bees typically avoid nesting in occupied buildings, but when they do take up residence in one, they’re most often found in the eaves or soffits of a house, in east- or southeast-facing locations. Bees need just 1/8 of an inch to get into a cavity and will fill that cavity until it’s at capacity. Once all the cavities are filled, bees may move to the roofline.
It may seem that bees are not harming the building, but they can leave behind a sweet sticky mess that can attract other insects and even seep through ceilings or walls. If the nest is in the roof area, the repairs could be especially expensive.
Bees also tend to nest behind bricks, usually in places where no grout was applied to allow for ventilation, as well as between aluminum or wooden siding and drywall. Bee hives can also be found inside the 4-inch-by-4-inch spaces in cinder blocks and concrete, and if you have a shed for your lawnmower or pool supplies, hives may be settled underneath the floor.
The hollow of trees is a preferred location for honey bees. You may discover a droning sound (like that of an engine) coming from a dead or hollow tree on your property. Keep your distance so as not to disturb the swarm. Sometimes the tree is just a temporary resting place (about 72 hours) for the bees while more suitable locations are being scouted. Always practice caution.
What do I do if/when I find a beehive?
Bee hives set away from regular human activity should be left alone. However, should you find a hive in a high-traffic area where the bees will likely be disturbed, DO NOT attempt to remove it yourself. Handling bee hives is a duty best left to a trained beekeeper or pest specialist armed with the appropriate tools.
Make sure to notify anyone in the area of the location of the hive so no one accidentally upsets it. Maintain a safe distance from the beehive and call a beekeeper or professional pest specialist to come and safely remove the bees. Remember, even hives that look abandoned can potentially have a swarm still living inside.
Take a picture of the nest to show to the experts at Terminix®. We’re committed to defending your home and have more than 85 years of experience dealing with bees and other pests.
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count_bees/Poisson_distribution.txt |
In probability theory and statistics, the Poisson distribution is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time if these events occur with a known constant mean rate and independently of the time since the last event. It can also be used for the number of events in other types of intervals than time, and in dimension greater than 1 (e.g., number of events in a given area or volume).
The Poisson distribution is named after French mathematician Siméon Denis Poisson (/ˈpwɑːsɒn/; French pronunciation: [pwasɔ̃]). It plays an important role for discrete-stable distributions.
Under a Poisson distribution with the expectation of λ events in a given interval, the probability of k events in the same interval is:
For instance, consider a call center which receives, randomly, an average of λ = 3 calls per minute at all times of day. If the calls are independent, receiving one does not change the probability of when the next one will arrive. Under these assumptions, the number k of calls received during any minute has a Poisson probability distribution. Receiving k = 1 to 4 calls then has a probability of about 0.77, while receiving 0 or at least 5 calls has a probability of about 0.23.
Another example for which the Poisson distribution is a useful model is the number of radioactive decay events during a fixed observation period.
History[edit]
The distribution was first introduced by Siméon Denis Poisson (1781–1840) and published together with his probability theory in his work Recherches sur la probabilité des jugements en matière criminelle et en matière civile (1837). The work theorized about the number of wrongful convictions in a given country by focusing on certain random variables N that count, among other things, the number of discrete occurrences (sometimes called "events" or "arrivals") that take place during a time-interval of given length. The result had already been given in 1711 by Abraham de Moivre in De Mensura Sortis seu; de Probabilitate Eventuum in Ludis a Casu Fortuito Pendentibus . This makes it an example of Stigler's law and it has prompted some authors to argue that the Poisson distribution should bear the name of de Moivre.
In 1860, Simon Newcomb fitted the Poisson distribution to the number of stars found in a unit of space.
A further practical application was made by Ladislaus Bortkiewicz in 1898. Bortkiewicz showed that the frequency with which soldiers in the Prussian army were accidentally killed by horse kicks could be well modeled by a Poisson distribution..
Definitions[edit]
Probability mass function[edit]
A discrete random variable X is said to have a Poisson distribution, with parameter
λ
>
0
,
{\displaystyle \lambda >0,}
if it has a probability mass function given by:
f
(
k
;
λ
)
=
Pr
(
X
=
k
)
=
λ
k
e
−
λ
k
!
,
{\displaystyle f(k;\lambda )=\Pr(X{=}k)={\frac {\lambda ^{k}e^{-\lambda }}{k!}},}
where
k is the number of occurrences (
k
=
0
,
1
,
2
,
…
{\displaystyle k=0,1,2,\ldots }
)
e is Euler's number (
e
=
2.71828
…
{\displaystyle e=2.71828\ldots }
)
k! = k(k–1) ··· (3)(2)(1) is the factorial.
The positive real number λ is equal to the expected value of X and also to its variance.
λ
=
E
(
X
)
=
Var
(
X
)
.
{\displaystyle \lambda =\operatorname {E} (X)=\operatorname {Var} (X).}
The Poisson distribution can be applied to systems with a large number of possible events, each of which is rare. The number of such events that occur during a fixed time interval is, under the right circumstances, a random number with a Poisson distribution.
The equation can be adapted if, instead of the average number of events
λ
,
{\displaystyle \lambda ,}
we are given the average rate
r
{\displaystyle r}
at which events occur. Then
λ
=
r
t
,
{\displaystyle \lambda =rt,}
and:
P
(
k
events in interval
t
)
=
(
r
t
)
k
e
−
r
t
k
!
.
{\displaystyle P(k{\text{ events in interval }}t)={\frac {(rt)^{k}e^{-rt}}{k!}}.}
Examples[edit]
Chewing gum on a sidewalk. The number of pieces on a single tile is approximately Poisson distributed.
The Poisson distribution may be useful to model events such as:
the number of meteorites greater than 1-meter diameter that strike Earth in a year;
the number of laser photons hitting a detector in a particular time interval;
the number of students achieving a low and high mark in an exam; and
locations of defects and dislocations in materials.
Examples of the occurrence of random points in space are: the locations of asteroid impacts with earth (2-dimensional), the locations of imperfections in a material (3-dimensional), and the locations of trees in a forest (2-dimensional).
Assumptions and validity[edit]
The Poisson distribution is an appropriate model if the following assumptions are true:
k is the number of times an event occurs in an interval and k can take values 0, 1, 2, ... .
The occurrence of one event does not affect the probability that a second event will occur. That is, events occur independently.
The average rate at which events occur is independent of any occurrences. For simplicity, this is usually assumed to be constant, but may in practice vary with time.
Two events cannot occur at exactly the same instant; instead, at each very small sub-interval, either exactly one event occurs, or no event occurs.
If these conditions are true, then k is a Poisson random variable, and the distribution of k is a Poisson distribution.
The Poisson distribution is also the limit of a binomial distribution, for which the probability of success for each trial equals λ divided by the number of trials, as the number of trials approaches infinity (see Related distributions).
Examples of probability for Poisson distributions[edit]
On a particular river, overflow floods occur once every 100 years on average. Calculate the probability of k = 0, 1, 2, 3, 4, 5, or 6 overflow floods in a 100-year interval, assuming the Poisson model is appropriate.
Because the average event rate is one overflow flood per 100 years, λ = 1
P
(
k
overflow floods in 100 years
)
=
λ
k
e
−
λ
k
!
=
1
k
e
−
1
k
!
{\displaystyle P(k{\text{ overflow floods in 100 years}})={\frac {\lambda ^{k}e^{-\lambda }}{k!}}={\frac {1^{k}e^{-1}}{k!}}}
P
(
k
=
0
overflow floods in 100 years
)
=
1
0
e
−
1
0
!
=
e
−
1
1
≈
0.368
{\displaystyle P(k=0{\text{ overflow floods in 100 years}})={\frac {1^{0}e^{-1}}{0!}}={\frac {e^{-1}}{1}}\approx 0.368}
P
(
k
=
1
overflow flood in 100 years
)
=
1
1
e
−
1
1
!
=
e
−
1
1
≈
0.368
{\displaystyle P(k=1{\text{ overflow flood in 100 years}})={\frac {1^{1}e^{-1}}{1!}}={\frac {e^{-1}}{1}}\approx 0.368}
P
(
k
=
2
overflow floods in 100 years
)
=
1
2
e
−
1
2
!
=
e
−
1
2
≈
0.184
{\displaystyle P(k=2{\text{ overflow floods in 100 years}})={\frac {1^{2}e^{-1}}{2!}}={\frac {e^{-1}}{2}}\approx 0.184}
k
P(k overflow floods in 100 years)
0
0.368
1
0.368
2
0.184
3
0.061
4
0.015
5
0.003
6
0.0005
The probability for 0 to 6 overflow floods in a 100-year period.
It has been reported that the average number of goals in a World Cup soccer match is approximately 2.5 and the Poisson model is appropriate.
Because the average event rate is 2.5 goals per match, λ = 2.5 .
P
(
k
goals in a match
)
=
2.5
k
e
−
2.5
k
!
{\displaystyle P(k{\text{ goals in a match}})={\frac {2.5^{k}e^{-2.5}}{k!}}}
P
(
k
=
0
goals in a match
)
=
2.5
0
e
−
2.5
0
!
=
e
−
2.5
1
≈
0.082
{\displaystyle P(k=0{\text{ goals in a match}})={\frac {2.5^{0}e^{-2.5}}{0!}}={\frac {e^{-2.5}}{1}}\approx 0.082}
P
(
k
=
1
goal in a match
)
=
2.5
1
e
−
2.5
1
!
=
2.5
e
−
2.5
1
≈
0.205
{\displaystyle P(k=1{\text{ goal in a match}})={\frac {2.5^{1}e^{-2.5}}{1!}}={\frac {2.5e^{-2.5}}{1}}\approx 0.205}
P
(
k
=
2
goals in a match
)
=
2.5
2
e
−
2.5
2
!
=
6.25
e
−
2.5
2
≈
0.257
{\displaystyle P(k=2{\text{ goals in a match}})={\frac {2.5^{2}e^{-2.5}}{2!}}={\frac {6.25e^{-2.5}}{2}}\approx 0.257}
k
P(k goals in a World Cup soccer match)
0
0.082
1
0.205
2
0.257
3
0.213
4
0.133
5
0.067
6
0.028
7
0.010
The probability for 0 to 7 goals in a match.
Once in an interval events: The special case of λ = 1 and k = 0[edit]
Suppose that astronomers estimate that large meteorites (above a certain size) hit the earth on average once every 100 years ( λ = 1 event per 100 years), and that the number of meteorite hits follows a Poisson distribution. What is the probability of k = 0 meteorite hits in the next 100 years?
P
(
k
=
0 meteorites hit in next 100 years
)
=
1
0
e
−
1
0
!
=
1
e
≈
0.37.
{\displaystyle P(k={\text{0 meteorites hit in next 100 years}})={\frac {1^{0}e^{-1}}{0!}}={\frac {1}{e}}\approx 0.37.}
Under these assumptions, the probability that no large meteorites hit the earth in the next 100 years is roughly 0.37. The remaining 1 − 0.37 = 0.63 is the probability of 1, 2, 3, or more large meteorite hits in the next 100 years.
In an example above, an overflow flood occurred once every 100 years (λ = 1). The probability of no overflow floods in 100 years was roughly 0.37, by the same calculation.
In general, if an event occurs on average once per interval (λ = 1), and the events follow a Poisson distribution, then P(0 events in next interval) = 0.37. In addition, P(exactly one event in next interval) = 0.37, as shown in the table for overflow floods.
Examples that violate the Poisson assumptions[edit]
The number of students who arrive at the student union per minute will likely not follow a Poisson distribution, because the rate is not constant (low rate during class time, high rate between class times) and the arrivals of individual students are not independent (students tend to come in groups). The non-constant arrival rate may be modeled as a mixed Poisson distribution, and the arrival of groups rather than individual students as a compound Poisson process.
The number of magnitude 5 earthquakes per year in a country may not follow a Poisson distribution, if one large earthquake increases the probability of aftershocks of similar magnitude.
Examples in which at least one event is guaranteed are not Poisson distributed; but may be modeled using a zero-truncated Poisson distribution.
Count distributions in which the number of intervals with zero events is higher than predicted by a Poisson model may be modeled using a zero-inflated model.
Properties[edit]
Descriptive statistics[edit]
The expected value and variance of a Poisson-distributed random variable are both equal to λ.
The coefficient of variation is
λ
−
1
/
2
,
{\textstyle \lambda ^{-1/2},}
while the index of dispersion is 1.
The mean absolute deviation about the mean is
E
[
|
X
−
λ
|
]
=
2
λ
⌊
λ
⌋
+
1
e
−
λ
⌊
λ
⌋
!
.
{\displaystyle \operatorname {E} [\ |X-\lambda |\ ]={\frac {2\lambda ^{\lfloor \lambda \rfloor +1}e^{-\lambda }}{\lfloor \lambda \rfloor !}}.}
The mode of a Poisson-distributed random variable with non-integer λ is equal to
⌊
λ
⌋
,
{\displaystyle \lfloor \lambda \rfloor ,}
which is the largest integer less than or equal to λ. This is also written as floor(λ). When λ is a positive integer, the modes are λ and λ − 1.
All of the cumulants of the Poisson distribution are equal to the expected value λ. The n th factorial moment of the Poisson distribution is λ .
The expected value of a Poisson process is sometimes decomposed into the product of intensity and exposure (or more generally expressed as the integral of an "intensity function" over time or space, sometimes described as "exposure").
Median[edit]
Bounds for the median (
ν
{\displaystyle \nu }
) of the distribution are known and are sharp:
λ
−
ln
2
≤
ν
<
λ
+
1
3
.
{\displaystyle \lambda -\ln 2\leq \nu <\lambda +{\frac {1}{3}}.}
Higher moments[edit]
The higher non-centered moments, mk of the Poisson distribution, are Touchard polynomials in λ:
m
k
=
∑
i
=
0
k
λ
i
{
k
i
}
,
{\displaystyle m_{k}=\sum _{i=0}^{k}\lambda ^{i}{\begin{Bmatrix}k\\i\end{Bmatrix}},}
where the braces { } denote Stirling numbers of the second kind. In other words,
E
[
X
]
=
λ
,
E
[
X
(
X
−
1
)
]
=
λ
2
,
E
[
X
(
X
−
1
)
(
X
−
2
)
]
=
λ
3
,
⋯
{\displaystyle E[X]=\lambda ,\quad E[X(X-1)]=\lambda ^{2},\quad E[X(X-1)(X-2)]=\lambda ^{3},\cdots }
When the expected value is set to λ = 1, Dobinski's formula implies that the n‑th moment is equal to the number of partitions of a set of size n.
A simple upper bound is:
m
k
=
E
[
X
k
]
≤
(
k
log
(
k
/
λ
+
1
)
)
k
≤
λ
k
exp
(
k
2
2
λ
)
.
{\displaystyle m_{k}=E[X^{k}]\leq \left({\frac {k}{\log(k/\lambda +1)}}\right)^{k}\leq \lambda ^{k}\exp \left({\frac {k^{2}}{2\lambda }}\right).}
Sums of Poisson-distributed random variables[edit]
If
X
i
∼
Pois
(
λ
i
)
{\displaystyle X_{i}\sim \operatorname {Pois} (\lambda _{i})}
for
i
=
1
,
…
,
n
{\displaystyle i=1,\dotsc ,n}
are independent, then
∑
i
=
1
n
X
i
∼
Pois
(
∑
i
=
1
n
λ
i
)
.
{\textstyle \sum _{i=1}^{n}X_{i}\sim \operatorname {Pois} \left(\sum _{i=1}^{n}\lambda _{i}\right).}
A converse is Raikov's theorem, which says that if the sum of two independent random variables is Poisson-distributed, then so are each of those two independent random variables.
Maximum entropy[edit]
It is a maximum-entropy distribution among the set of generalized binomial distributions
B
n
(
λ
)
{\displaystyle B_{n}(\lambda )}
with mean
λ
{\displaystyle \lambda }
and
n
→
∞
{\displaystyle n\rightarrow \infty }
, where a generalized binomial distribution is defined as a distribution of the sum of N independent but not identically distributed Bernoulli variables.
Other properties[edit]
The Poisson distributions are infinitely divisible probability distributions.
The directed Kullback–Leibler divergence of
P
=
Pois
(
λ
)
{\displaystyle P=\operatorname {Pois} (\lambda )}
from
P
0
=
Pois
(
λ
0
)
{\displaystyle P_{0}=\operatorname {Pois} (\lambda _{0})}
is given by
D
KL
(
P
∥
P
0
)
=
λ
0
−
λ
+
λ
log
λ
λ
0
.
{\displaystyle \operatorname {D} _{\text{KL}}(P\parallel P_{0})=\lambda _{0}-\lambda +\lambda \log {\frac {\lambda }{\lambda _{0}}}.}
If
λ
≥
1
{\displaystyle \lambda \geq 1}
is an integer, then
Y
∼
Pois
(
λ
)
{\displaystyle Y\sim \operatorname {Pois} (\lambda )}
satisfies
Pr
(
Y
≥
E
[
Y
]
)
≥
1
2
{\displaystyle \Pr(Y\geq E[Y])\geq {\frac {1}{2}}}
and
Pr
(
Y
≤
E
[
Y
]
)
≥
1
2
.
{\displaystyle \Pr(Y\leq E[Y])\geq {\frac {1}{2}}.}
Bounds for the tail probabilities of a Poisson random variable
X
∼
Pois
(
λ
)
{\displaystyle X\sim \operatorname {Pois} (\lambda )}
can be derived using a Chernoff bound argument.
P
(
X
≥
x
)
≤
(
e
λ
)
x
e
−
λ
x
x
,
for
x
>
λ
,
{\displaystyle P(X\geq x)\leq {\frac {(e\lambda )^{x}e^{-\lambda }}{x^{x}}},{\text{ for }}x>\lambda ,}
P
(
X
≤
x
)
≤
(
e
λ
)
x
e
−
λ
x
x
,
for
x
<
λ
.
{\displaystyle P(X\leq x)\leq {\frac {(e\lambda )^{x}e^{-\lambda }}{x^{x}}},{\text{ for }}x<\lambda .}
The upper tail probability can be tightened (by a factor of at least two) as follows:
P
(
X
≥
x
)
≤
e
−
D
KL
(
Q
∥
P
)
max
(
2
,
4
π
D
KL
(
Q
∥
P
)
)
,
for
x
>
λ
,
{\displaystyle P(X\geq x)\leq {\frac {e^{-\operatorname {D} _{\text{KL}}(Q\parallel P)}}{\max {(2,{\sqrt {4\pi \operatorname {D} _{\text{KL}}(Q\parallel P)}}})}},{\text{ for }}x>\lambda ,}
where
D
KL
(
Q
∥
P
)
{\displaystyle \operatorname {D} _{\text{KL}}(Q\parallel P)}
is the Kullback–Leibler divergence of
Q
=
Pois
(
x
)
{\displaystyle Q=\operatorname {Pois} (x)}
from
P
=
Pois
(
λ
)
{\displaystyle P=\operatorname {Pois} (\lambda )}
.
Inequalities that relate the distribution function of a Poisson random variable
X
∼
Pois
(
λ
)
{\displaystyle X\sim \operatorname {Pois} (\lambda )}
to the Standard normal distribution function
Φ
(
x
)
{\displaystyle \Phi (x)}
are as follows:
Φ
(
sign
(
k
−
λ
)
2
D
KL
(
Q
−
∥
P
)
)
<
P
(
X
≤
k
)
<
Φ
(
sign
(
k
+
1
−
λ
)
2
D
KL
(
Q
+
∥
P
)
)
,
for
k
>
0
,
{\displaystyle \Phi \left(\operatorname {sign} (k-\lambda ){\sqrt {2\operatorname {D} _{\text{KL}}(Q_{-}\parallel P)}}\right)<P(X\leq k)<\Phi \left(\operatorname {sign} (k+1-\lambda ){\sqrt {2\operatorname {D} _{\text{KL}}(Q_{+}\parallel P)}}\right),{\text{ for }}k>0,}
where
D
KL
(
Q
−
∥
P
)
{\displaystyle \operatorname {D} _{\text{KL}}(Q_{-}\parallel P)}
is the Kullback–Leibler divergence of
Q
−
=
Pois
(
k
)
{\displaystyle Q_{-}=\operatorname {Pois} (k)}
from
P
=
Pois
(
λ
)
{\displaystyle P=\operatorname {Pois} (\lambda )}
and
D
KL
(
Q
+
∥
P
)
{\displaystyle \operatorname {D} _{\text{KL}}(Q_{+}\parallel P)}
is the Kullback–Leibler divergence of
Q
+
=
Pois
(
k
+
1
)
{\displaystyle Q_{+}=\operatorname {Pois} (k+1)}
from
P
{\displaystyle P}
.
Poisson races[edit]
Let
X
∼
Pois
(
λ
)
{\displaystyle X\sim \operatorname {Pois} (\lambda )}
and
Y
∼
Pois
(
μ
)
{\displaystyle Y\sim \operatorname {Pois} (\mu )}
be independent random variables, with
λ
<
μ
,
{\displaystyle \lambda <\mu ,}
then we have that
e
−
(
μ
−
λ
)
2
(
λ
+
μ
)
2
−
e
−
(
λ
+
μ
)
2
λ
μ
−
e
−
(
λ
+
μ
)
4
λ
μ
≤
P
(
X
−
Y
≥
0
)
≤
e
−
(
μ
−
λ
)
2
{\displaystyle {\frac {e^{-({\sqrt {\mu }}-{\sqrt {\lambda }})^{2}}}{(\lambda +\mu )^{2}}}-{\frac {e^{-(\lambda +\mu )}}{2{\sqrt {\lambda \mu }}}}-{\frac {e^{-(\lambda +\mu )}}{4\lambda \mu }}\leq P(X-Y\geq 0)\leq e^{-({\sqrt {\mu }}-{\sqrt {\lambda }})^{2}}}
The upper bound is proved using a standard Chernoff bound.
The lower bound can be proved by noting that
P
(
X
−
Y
≥
0
∣
X
+
Y
=
i
)
{\displaystyle P(X-Y\geq 0\mid X+Y=i)}
is the probability that
Z
≥
i
2
,
{\textstyle Z\geq {\frac {i}{2}},}
where
Z
∼
Bin
(
i
,
λ
λ
+
μ
)
,
{\textstyle Z\sim \operatorname {Bin} \left(i,{\frac {\lambda }{\lambda +\mu }}\right),}
which is bounded below by
1
(
i
+
1
)
2
e
−
i
D
(
0.5
‖
λ
λ
+
μ
)
,
{\textstyle {\frac {1}{(i+1)^{2}}}e^{-iD\left(0.5\|{\frac {\lambda }{\lambda +\mu }}\right)},}
where
D
{\displaystyle D}
is relative entropy (See the entry on bounds on tails of binomial distributions for details). Further noting that
X
+
Y
∼
Pois
(
λ
+
μ
)
,
{\displaystyle X+Y\sim \operatorname {Pois} (\lambda +\mu ),}
and computing a lower bound on the unconditional probability gives the result. More details can be found in the appendix of Kamath et al..
Related distributions[edit]
As a Binomial distribution with infinitesimal time-steps[edit]
The Poisson distribution can be derived as a limiting case to the binomial distribution as the number of trials goes to infinity and the expected number of successes remains fixed — see law of rare events below. Therefore, it can be used as an approximation of the binomial distribution if n is sufficiently large and p is sufficiently small. The Poisson distribution is a good approximation of the binomial distribution if n is at least 20 and p is smaller than or equal to 0.05, and an excellent approximation if n ≥ 100 and n p ≤ 10. Letting
F
B
{\displaystyle F_{\mathrm {B} }}
and
F
P
{\displaystyle F_{\mathrm {P} }}
be the respective cumulative density functions of the binomial and Poisson distributions, one has:
F
B
(
k
;
n
,
p
)
≈
F
P
(
k
;
λ
=
n
p
)
.
{\displaystyle F_{\mathrm {B} }(k;n,p)\ \approx \ F_{\mathrm {P} }(k;\lambda =np).}
One derivation of this uses probability-generating functions. Consider a Bernoulli trial (coin-flip) whose probability of one success (or expected number of successes) is
λ
≤
1
{\displaystyle \lambda \leq 1}
within a given interval. Split the interval into n parts, and perform a trial in each subinterval with probability
λ
n
{\displaystyle {\tfrac {\lambda }{n}}}
. The probability of k successes out of n trials over the entire interval is then given by the binomial distribution
p
k
(
n
)
=
(
n
k
)
(
λ
n
)
k
(
1
−
λ
n
)
n
−
k
{\displaystyle p_{k}^{(n)}={\binom {n}{k}}\left({\frac {\lambda }{n}}\right)^{\!k}\left(1{-}{\frac {\lambda }{n}}\right)^{\!n-k}}
,
whose generating function is:
P
(
n
)
(
x
)
=
∑
k
=
0
n
p
k
(
n
)
x
k
=
(
1
−
λ
n
+
λ
n
x
)
n
.
{\displaystyle P^{(n)}(x)=\sum _{k=0}^{n}p_{k}^{(n)}x^{k}=\left(1-{\frac {\lambda }{n}}+{\frac {\lambda }{n}}x\right)^{n}.}
Taking the limit as n increases to infinity (with x fixed) and applying the product limit definition of the exponential function, this reduces to the generating function of the Poisson distribution:
lim
n
→
∞
P
(
n
)
(
x
)
=
lim
n
→
∞
(
1
+
λ
(
x
−
1
)
n
)
n
=
e
λ
(
x
−
1
)
=
∑
k
=
0
∞
e
−
λ
λ
k
k
!
x
k
.
{\displaystyle \lim _{n\to \infty }P^{(n)}(x)=\lim _{n\to \infty }\left(1{+}{\tfrac {\lambda (x-1)}{n}}\right)^{n}=e^{\lambda (x-1)}=\sum _{k=0}^{\infty }e^{-\lambda }{\frac {\lambda ^{k}}{k!}}x^{k}.}
General[edit]
If
X
1
∼
P
o
i
s
(
λ
1
)
{\displaystyle X_{1}\sim \mathrm {Pois} (\lambda _{1})\,}
and
X
2
∼
P
o
i
s
(
λ
2
)
{\displaystyle X_{2}\sim \mathrm {Pois} (\lambda _{2})\,}
are independent, then the difference
Y
=
X
1
−
X
2
{\displaystyle Y=X_{1}-X_{2}}
follows a Skellam distribution.
If
X
1
∼
P
o
i
s
(
λ
1
)
{\displaystyle X_{1}\sim \mathrm {Pois} (\lambda _{1})\,}
and
X
2
∼
P
o
i
s
(
λ
2
)
{\displaystyle X_{2}\sim \mathrm {Pois} (\lambda _{2})\,}
are independent, then the distribution of
X
1
{\displaystyle X_{1}}
conditional on
X
1
+
X
2
{\displaystyle X_{1}+X_{2}}
is a binomial distribution. Specifically, if
X
1
+
X
2
=
k
,
{\displaystyle X_{1}+X_{2}=k,}
then
X
1
|
X
1
+
X
2
=
k
∼
B
i
n
o
m
(
k
,
λ
1
/
(
λ
1
+
λ
2
)
)
.
{\displaystyle X_{1}|X_{1}+X_{2}=k\sim \mathrm {Binom} (k,\lambda _{1}/(\lambda _{1}+\lambda _{2})).}
More generally, if X1, X2, ..., Xn are independent Poisson random variables with parameters λ1, λ2, ..., λn then
given
∑
j
=
1
n
X
j
=
k
,
{\displaystyle \sum _{j=1}^{n}X_{j}=k,}
it follows that
X
i
|
∑
j
=
1
n
X
j
=
k
∼
B
i
n
o
m
(
k
,
λ
i
∑
j
=
1
n
λ
j
)
.
{\displaystyle X_{i}{\Big |}\sum _{j=1}^{n}X_{j}=k\sim \mathrm {Binom} \left(k,{\frac {\lambda _{i}}{\sum _{j=1}^{n}\lambda _{j}}}\right).}
In fact,
{
X
i
}
∼
M
u
l
t
i
n
o
m
(
k
,
{
λ
i
∑
j
=
1
n
λ
j
}
)
.
{\displaystyle \{X_{i}\}\sim \mathrm {Multinom} \left(k,\left\{{\frac {\lambda _{i}}{\sum _{j=1}^{n}\lambda _{j}}}\right\}\right).}
If
X
∼
P
o
i
s
(
λ
)
{\displaystyle X\sim \mathrm {Pois} (\lambda )\,}
and the distribution of
Y
{\displaystyle Y}
conditional on X = k is a binomial distribution,
Y
∣
(
X
=
k
)
∼
B
i
n
o
m
(
k
,
p
)
,
{\displaystyle Y\mid (X=k)\sim \mathrm {Binom} (k,p),}
then the distribution of Y follows a Poisson distribution
Y
∼
P
o
i
s
(
λ
⋅
p
)
.
{\displaystyle Y\sim \mathrm {Pois} (\lambda \cdot p).}
In fact, if, conditional on
{
X
=
k
}
,
{\displaystyle \{X=k\},}
{
Y
i
}
{\displaystyle \{Y_{i}\}}
follows a multinomial distribution,
{
Y
i
}
∣
(
X
=
k
)
∼
M
u
l
t
i
n
o
m
(
k
,
p
i
)
,
{\displaystyle \{Y_{i}\}\mid (X=k)\sim \mathrm {Multinom} \left(k,p_{i}\right),}
then each
Y
i
{\displaystyle Y_{i}}
follows an independent Poisson distribution
Y
i
∼
P
o
i
s
(
λ
⋅
p
i
)
,
ρ
(
Y
i
,
Y
j
)
=
0.
{\displaystyle Y_{i}\sim \mathrm {Pois} (\lambda \cdot p_{i}),\rho (Y_{i},Y_{j})=0.}
The Poisson distribution is a special case of the discrete compound Poisson distribution (or stuttering Poisson distribution) with only a parameter. The discrete compound Poisson distribution can be deduced from the limiting distribution of univariate multinomial distribution. It is also a special case of a compound Poisson distribution.
For sufficiently large values of λ, (say λ>1000), the normal distribution with mean λ and variance λ (standard deviation
λ
{\displaystyle {\sqrt {\lambda }}}
) is an excellent approximation to the Poisson distribution. If λ is greater than about 10, then the normal distribution is a good approximation if an appropriate continuity correction is performed, i.e., if P(X ≤ x), where x is a non-negative integer, is replaced by P(X ≤ x + 0.5).
F
P
o
i
s
s
o
n
(
x
;
λ
)
≈
F
n
o
r
m
a
l
(
x
;
μ
=
λ
,
σ
2
=
λ
)
{\displaystyle F_{\mathrm {Poisson} }(x;\lambda )\approx F_{\mathrm {normal} }(x;\mu =\lambda ,\sigma ^{2}=\lambda )}
Variance-stabilizing transformation: If
X
∼
P
o
i
s
(
λ
)
,
{\displaystyle X\sim \mathrm {Pois} (\lambda ),}
then
Y
=
2
X
≈
N
(
2
λ
;
1
)
,
{\displaystyle Y=2{\sqrt {X}}\approx {\mathcal {N}}(2{\sqrt {\lambda }};1),}
and
Y
=
X
≈
N
(
λ
;
1
/
4
)
.
{\displaystyle Y={\sqrt {X}}\approx {\mathcal {N}}({\sqrt {\lambda }};1/4).}
Under this transformation, the convergence to normality (as
λ
{\displaystyle \lambda }
increases) is far faster than the untransformed variable. Other, slightly more complicated, variance stabilizing transformations are available, one of which is Anscombe transform. See Data transformation (statistics) for more general uses of transformations.
If for every t > 0 the number of arrivals in the time interval [0, t] follows the Poisson distribution with mean λt, then the sequence of inter-arrival times are independent and identically distributed exponential random variables having mean 1/λ.
The cumulative distribution functions of the Poisson and chi-squared distributions are related in the following ways:
F
Poisson
(
k
;
λ
)
=
1
−
F
χ
2
(
2
λ
;
2
(
k
+
1
)
)
integer
k
,
{\displaystyle F_{\text{Poisson}}(k;\lambda )=1-F_{\chi ^{2}}(2\lambda ;2(k+1))\quad \quad {\text{ integer }}k,}
and
P
(
X
=
k
)
=
F
χ
2
(
2
λ
;
2
(
k
+
1
)
)
−
F
χ
2
(
2
λ
;
2
k
)
.
{\displaystyle P(X=k)=F_{\chi ^{2}}(2\lambda ;2(k+1))-F_{\chi ^{2}}(2\lambda ;2k).}
Poisson approximation[edit]
Assume
X
1
∼
Pois
(
λ
1
)
,
X
2
∼
Pois
(
λ
2
)
,
…
,
X
n
∼
Pois
(
λ
n
)
{\displaystyle X_{1}\sim \operatorname {Pois} (\lambda _{1}),X_{2}\sim \operatorname {Pois} (\lambda _{2}),\dots ,X_{n}\sim \operatorname {Pois} (\lambda _{n})}
where
λ
1
+
λ
2
+
⋯
+
λ
n
=
1
,
{\displaystyle \lambda _{1}+\lambda _{2}+\dots +\lambda _{n}=1,}
then
(
X
1
,
X
2
,
…
,
X
n
)
{\displaystyle (X_{1},X_{2},\dots ,X_{n})}
is multinomially distributed
(
X
1
,
X
2
,
…
,
X
n
)
∼
Mult
(
N
,
λ
1
,
λ
2
,
…
,
λ
n
)
{\displaystyle (X_{1},X_{2},\dots ,X_{n})\sim \operatorname {Mult} (N,\lambda _{1},\lambda _{2},\dots ,\lambda _{n})}
conditioned on
N
=
X
1
+
X
2
+
…
X
n
.
{\displaystyle N=X_{1}+X_{2}+\dots X_{n}.}
This means, among other things, that for any nonnegative function
f
(
x
1
,
x
2
,
…
,
x
n
)
,
{\displaystyle f(x_{1},x_{2},\dots ,x_{n}),}
if
(
Y
1
,
Y
2
,
…
,
Y
n
)
∼
Mult
(
m
,
p
)
{\displaystyle (Y_{1},Y_{2},\dots ,Y_{n})\sim \operatorname {Mult} (m,\mathbf {p} )}
is multinomially distributed, then
E
[
f
(
Y
1
,
Y
2
,
…
,
Y
n
)
]
≤
e
m
E
[
f
(
X
1
,
X
2
,
…
,
X
n
)
]
{\displaystyle \operatorname {E} [f(Y_{1},Y_{2},\dots ,Y_{n})]\leq e{\sqrt {m}}\operatorname {E} [f(X_{1},X_{2},\dots ,X_{n})]}
where
(
X
1
,
X
2
,
…
,
X
n
)
∼
Pois
(
p
)
.
{\displaystyle (X_{1},X_{2},\dots ,X_{n})\sim \operatorname {Pois} (\mathbf {p} ).}
The factor of
e
m
{\displaystyle e{\sqrt {m}}}
can be replaced by 2 if
f
{\displaystyle f}
is further assumed to be monotonically increasing or decreasing.
Bivariate Poisson distribution[edit]
This distribution has been extended to the bivariate case. The generating function for this distribution is
g
(
u
,
v
)
=
exp
[
(
θ
1
−
θ
12
)
(
u
−
1
)
+
(
θ
2
−
θ
12
)
(
v
−
1
)
+
θ
12
(
u
v
−
1
)
]
{\displaystyle g(u,v)=\exp[(\theta _{1}-\theta _{12})(u-1)+(\theta _{2}-\theta _{12})(v-1)+\theta _{12}(uv-1)]}
with
θ
1
,
θ
2
>
θ
12
>
0
{\displaystyle \theta _{1},\theta _{2}>\theta _{12}>0}
The marginal distributions are Poisson(θ1) and Poisson(θ2) and the correlation coefficient is limited to the range
0
≤
ρ
≤
min
{
θ
1
θ
2
,
θ
2
θ
1
}
{\displaystyle 0\leq \rho \leq \min \left\{{\sqrt {\frac {\theta _{1}}{\theta _{2}}}},{\sqrt {\frac {\theta _{2}}{\theta _{1}}}}\right\}}
A simple way to generate a bivariate Poisson distribution
X
1
,
X
2
{\displaystyle X_{1},X_{2}}
is to take three independent Poisson distributions
Y
1
,
Y
2
,
Y
3
{\displaystyle Y_{1},Y_{2},Y_{3}}
with means
λ
1
,
λ
2
,
λ
3
{\displaystyle \lambda _{1},\lambda _{2},\lambda _{3}}
and then set
X
1
=
Y
1
+
Y
3
,
X
2
=
Y
2
+
Y
3
.
{\displaystyle X_{1}=Y_{1}+Y_{3},X_{2}=Y_{2}+Y_{3}.}
The probability function of the bivariate Poisson distribution is
Pr
(
X
1
=
k
1
,
X
2
=
k
2
)
=
exp
(
−
λ
1
−
λ
2
−
λ
3
)
λ
1
k
1
k
1
!
λ
2
k
2
k
2
!
∑
k
=
0
min
(
k
1
,
k
2
)
(
k
1
k
)
(
k
2
k
)
k
!
(
λ
3
λ
1
λ
2
)
k
{\displaystyle \Pr(X_{1}=k_{1},X_{2}=k_{2})=\exp \left(-\lambda _{1}-\lambda _{2}-\lambda _{3}\right){\frac {\lambda _{1}^{k_{1}}}{k_{1}!}}{\frac {\lambda _{2}^{k_{2}}}{k_{2}!}}\sum _{k=0}^{\min(k_{1},k_{2})}{\binom {k_{1}}{k}}{\binom {k_{2}}{k}}k!\left({\frac {\lambda _{3}}{\lambda _{1}\lambda _{2}}}\right)^{k}}
Free Poisson distribution[edit]
The free Poisson distribution with jump size
α
{\displaystyle \alpha }
and rate
λ
{\displaystyle \lambda }
arises in free probability theory as the limit of repeated free convolution
(
(
1
−
λ
N
)
δ
0
+
λ
N
δ
α
)
⊞
N
{\displaystyle \left(\left(1-{\frac {\lambda }{N}}\right)\delta _{0}+{\frac {\lambda }{N}}\delta _{\alpha }\right)^{\boxplus N}}
as N → ∞.
In other words, let
X
N
{\displaystyle X_{N}}
be random variables so that
X
N
{\displaystyle X_{N}}
has value
α
{\displaystyle \alpha }
with probability
λ
N
{\textstyle {\frac {\lambda }{N}}}
and value 0 with the remaining probability. Assume also that the family
X
1
,
X
2
,
…
{\displaystyle X_{1},X_{2},\ldots }
are freely independent. Then the limit as
N
→
∞
{\displaystyle N\to \infty }
of the law of
X
1
+
⋯
+
X
N
{\displaystyle X_{1}+\cdots +X_{N}}
is given by the Free Poisson law with parameters
λ
,
α
.
{\displaystyle \lambda ,\alpha .}
This definition is analogous to one of the ways in which the classical Poisson distribution is obtained from a (classical) Poisson process.
The measure associated to the free Poisson law is given by
μ
=
{
(
1
−
λ
)
δ
0
+
ν
,
if
0
≤
λ
≤
1
ν
,
if
λ
>
1
,
{\displaystyle \mu ={\begin{cases}(1-\lambda )\delta _{0}+\nu ,&{\text{if }}0\leq \lambda \leq 1\\\nu ,&{\text{if }}\lambda >1,\end{cases}}}
where
ν
=
1
2
π
α
t
4
λ
α
2
−
(
t
−
α
(
1
+
λ
)
)
2
d
t
{\displaystyle \nu ={\frac {1}{2\pi \alpha t}}{\sqrt {4\lambda \alpha ^{2}-(t-\alpha (1+\lambda ))^{2}}}\,dt}
and has support
[
α
(
1
−
λ
)
2
,
α
(
1
+
λ
)
2
]
.
{\displaystyle [\alpha (1-{\sqrt {\lambda }})^{2},\alpha (1+{\sqrt {\lambda }})^{2}].}
This law also arises in random matrix theory as the Marchenko–Pastur law. Its free cumulants are equal to
κ
n
=
λ
α
n
.
{\displaystyle \kappa _{n}=\lambda \alpha ^{n}.}
Some transforms of this law[edit]
We give values of some important transforms of the free Poisson law; the computation can be found in e.g. in the book Lectures on the Combinatorics of Free Probability by A. Nica and R. Speicher
The R-transform of the free Poisson law is given by
R
(
z
)
=
λ
α
1
−
α
z
.
{\displaystyle R(z)={\frac {\lambda \alpha }{1-\alpha z}}.}
The Cauchy transform (which is the negative of the Stieltjes transformation) is given by
G
(
z
)
=
z
+
α
−
λ
α
−
(
z
−
α
(
1
+
λ
)
)
2
−
4
λ
α
2
2
α
z
{\displaystyle G(z)={\frac {z+\alpha -\lambda \alpha -{\sqrt {(z-\alpha (1+\lambda ))^{2}-4\lambda \alpha ^{2}}}}{2\alpha z}}}
The S-transform is given by
S
(
z
)
=
1
z
+
λ
{\displaystyle S(z)={\frac {1}{z+\lambda }}}
in the case that
α
=
1.
{\displaystyle \alpha =1.}
Weibull and Stable count[edit]
Poisson's probability mass function
f
(
k
;
λ
)
{\displaystyle f(k;\lambda )}
can be expressed in a form similar to the product distribution of a Weibull distribution and a variant form of the stable count distribution.
The variable
(
k
+
1
)
{\displaystyle (k+1)}
can be regarded as inverse of Lévy's stability parameter in the stable count distribution:
f
(
k
;
λ
)
=
∫
0
∞
1
u
W
k
+
1
(
λ
u
)
[
(
k
+
1
)
u
k
N
1
k
+
1
(
u
k
+
1
)
]
d
u
,
{\displaystyle f(k;\lambda )=\displaystyle \int _{0}^{\infty }{\frac {1}{u}}\,W_{k+1}({\frac {\lambda }{u}})\left[\left(k+1\right)u^{k}\,{\mathfrak {N}}_{\frac {1}{k+1}}\left(u^{k+1}\right)\right]\,du,}
where
N
α
(
ν
)
{\displaystyle {\mathfrak {N}}_{\alpha }(\nu )}
is a standard stable count distribution of shape
α
=
1
/
(
k
+
1
)
,
{\displaystyle \alpha =1/\left(k+1\right),}
and
W
k
+
1
(
x
)
{\displaystyle W_{k+1}(x)}
is a standard Weibull distribution of shape
k
+
1.
{\displaystyle k+1.}
Statistical inference[edit]
See also: Poisson regression
Parameter estimation[edit]
Given a sample of n measured values
k
i
∈
{
0
,
1
,
…
}
,
{\displaystyle k_{i}\in \{0,1,\dots \},}
for i = 1, ..., n, we wish to estimate the value of the parameter λ of the Poisson population from which the sample was drawn. The maximum likelihood estimate is
λ
^
M
L
E
=
1
n
∑
i
=
1
n
k
i
.
{\displaystyle {\widehat {\lambda }}_{\mathrm {MLE} }={\frac {1}{n}}\sum _{i=1}^{n}k_{i}\ .}
Since each observation has expectation λ so does the sample mean. Therefore, the maximum likelihood estimate is an unbiased estimator of λ. It is also an efficient estimator since its variance achieves the Cramér–Rao lower bound (CRLB). Hence it is minimum-variance unbiased. Also it can be proven that the sum (and hence the sample mean as it is a one-to-one function of the sum) is a complete and sufficient statistic for λ.
To prove sufficiency we may use the factorization theorem. Consider partitioning the probability mass function of the joint Poisson distribution for the sample into two parts: one that depends solely on the sample
x
{\displaystyle \mathbf {x} }
, called
h
(
x
)
{\displaystyle h(\mathbf {x} )}
, and one that depends on the parameter
λ
{\displaystyle \lambda }
and the sample
x
{\displaystyle \mathbf {x} }
only through the function
T
(
x
)
.
{\displaystyle T(\mathbf {x} ).}
Then
T
(
x
)
{\displaystyle T(\mathbf {x} )}
is a sufficient statistic for
λ
.
{\displaystyle \lambda .}
P
(
x
)
=
∏
i
=
1
n
λ
x
i
e
−
λ
x
i
!
=
1
∏
i
=
1
n
x
i
!
×
λ
∑
i
=
1
n
x
i
e
−
n
λ
{\displaystyle P(\mathbf {x} )=\prod _{i=1}^{n}{\frac {\lambda ^{x_{i}}e^{-\lambda }}{x_{i}!}}={\frac {1}{\prod _{i=1}^{n}x_{i}!}}\times \lambda ^{\sum _{i=1}^{n}x_{i}}e^{-n\lambda }}
The first term
h
(
x
)
{\displaystyle h(\mathbf {x} )}
depends only on
x
{\displaystyle \mathbf {x} }
. The second term
g
(
T
(
x
)
|
λ
)
{\displaystyle g(T(\mathbf {x} )|\lambda )}
depends on the sample only through
T
(
x
)
=
∑
i
=
1
n
x
i
.
{\textstyle T(\mathbf {x} )=\sum _{i=1}^{n}x_{i}.}
Thus,
T
(
x
)
{\displaystyle T(\mathbf {x} )}
is sufficient.
To find the parameter λ that maximizes the probability function for the Poisson population, we can use the logarithm of the likelihood function:
ℓ
(
λ
)
=
ln
∏
i
=
1
n
f
(
k
i
∣
λ
)
=
∑
i
=
1
n
ln
(
e
−
λ
λ
k
i
k
i
!
)
=
−
n
λ
+
(
∑
i
=
1
n
k
i
)
ln
(
λ
)
−
∑
i
=
1
n
ln
(
k
i
!
)
.
{\displaystyle {\begin{aligned}\ell (\lambda )&=\ln \prod _{i=1}^{n}f(k_{i}\mid \lambda )\\&=\sum _{i=1}^{n}\ln \!\left({\frac {e^{-\lambda }\lambda ^{k_{i}}}{k_{i}!}}\right)\\&=-n\lambda +\left(\sum _{i=1}^{n}k_{i}\right)\ln(\lambda )-\sum _{i=1}^{n}\ln(k_{i}!).\end{aligned}}}
We take the derivative of
ℓ
{\displaystyle \ell }
with respect to λ and compare it to zero:
d
d
λ
ℓ
(
λ
)
=
0
⟺
−
n
+
(
∑
i
=
1
n
k
i
)
1
λ
=
0.
{\displaystyle {\frac {\mathrm {d} }{\mathrm {d} \lambda }}\ell (\lambda )=0\iff -n+\left(\sum _{i=1}^{n}k_{i}\right){\frac {1}{\lambda }}=0.\!}
Solving for λ gives a stationary point.
λ
=
∑
i
=
1
n
k
i
n
{\displaystyle \lambda ={\frac {\sum _{i=1}^{n}k_{i}}{n}}}
So λ is the average of the ki values. Obtaining the sign of the second derivative of L at the stationary point will determine what kind of extreme value λ is.
∂
2
ℓ
∂
λ
2
=
−
λ
−
2
∑
i
=
1
n
k
i
{\displaystyle {\frac {\partial ^{2}\ell }{\partial \lambda ^{2}}}=-\lambda ^{-2}\sum _{i=1}^{n}k_{i}}
Evaluating the second derivative at the stationary point gives:
∂
2
ℓ
∂
λ
2
=
−
n
2
∑
i
=
1
n
k
i
{\displaystyle {\frac {\partial ^{2}\ell }{\partial \lambda ^{2}}}=-{\frac {n^{2}}{\sum _{i=1}^{n}k_{i}}}}
which is the negative of n times the reciprocal of the average of the ki. This expression is negative when the average is positive. If this is satisfied, then the stationary point maximizes the probability function.
For completeness, a family of distributions is said to be complete if and only if
E
(
g
(
T
)
)
=
0
{\displaystyle E(g(T))=0}
implies that
P
λ
(
g
(
T
)
=
0
)
=
1
{\displaystyle P_{\lambda }(g(T)=0)=1}
for all
λ
.
{\displaystyle \lambda .}
If the individual
X
i
{\displaystyle X_{i}}
are iid
P
o
(
λ
)
,
{\displaystyle \mathrm {Po} (\lambda ),}
then
T
(
x
)
=
∑
i
=
1
n
X
i
∼
P
o
(
n
λ
)
.
{\textstyle T(\mathbf {x} )=\sum _{i=1}^{n}X_{i}\sim \mathrm {Po} (n\lambda ).}
Knowing the distribution we want to investigate, it is easy to see that the statistic is complete.
E
(
g
(
T
)
)
=
∑
t
=
0
∞
g
(
t
)
(
n
λ
)
t
e
−
n
λ
t
!
=
0
{\displaystyle E(g(T))=\sum _{t=0}^{\infty }g(t){\frac {(n\lambda )^{t}e^{-n\lambda }}{t!}}=0}
For this equality to hold,
g
(
t
)
{\displaystyle g(t)}
must be 0. This follows from the fact that none of the other terms will be 0 for all
t
{\displaystyle t}
in the sum and for all possible values of
λ
.
{\displaystyle \lambda .}
Hence,
E
(
g
(
T
)
)
=
0
{\displaystyle E(g(T))=0}
for all
λ
{\displaystyle \lambda }
implies that
P
λ
(
g
(
T
)
=
0
)
=
1
,
{\displaystyle P_{\lambda }(g(T)=0)=1,}
and the statistic has been shown to be complete.
Confidence interval[edit]
The confidence interval for the mean of a Poisson distribution can be expressed using the relationship between the cumulative distribution functions of the Poisson and chi-squared distributions. The chi-squared distribution is itself closely related to the gamma distribution, and this leads to an alternative expression. Given an observation k from a Poisson distribution with mean μ, a confidence interval for μ with confidence level 1 – α is
1
2
χ
2
(
α
/
2
;
2
k
)
≤
μ
≤
1
2
χ
2
(
1
−
α
/
2
;
2
k
+
2
)
,
{\displaystyle {\tfrac {1}{2}}\chi ^{2}(\alpha /2;2k)\leq \mu \leq {\tfrac {1}{2}}\chi ^{2}(1-\alpha /2;2k+2),}
or equivalently,
F
−
1
(
α
/
2
;
k
,
1
)
≤
μ
≤
F
−
1
(
1
−
α
/
2
;
k
+
1
,
1
)
,
{\displaystyle F^{-1}(\alpha /2;k,1)\leq \mu \leq F^{-1}(1-\alpha /2;k+1,1),}
where
χ
2
(
p
;
n
)
{\displaystyle \chi ^{2}(p;n)}
is the quantile function (corresponding to a lower tail area p) of the chi-squared distribution with n degrees of freedom and
F
−
1
(
p
;
n
,
1
)
{\displaystyle F^{-1}(p;n,1)}
is the quantile function of a gamma distribution with shape parameter n and scale parameter 1. This interval is 'exact' in the sense that its coverage probability is never less than the nominal 1 – α.
When quantiles of the gamma distribution are not available, an accurate approximation to this exact interval has been proposed (based on the Wilson–Hilferty transformation):
k
(
1
−
1
9
k
−
z
α
/
2
3
k
)
3
≤
μ
≤
(
k
+
1
)
(
1
−
1
9
(
k
+
1
)
+
z
α
/
2
3
k
+
1
)
3
,
{\displaystyle k\left(1-{\frac {1}{9k}}-{\frac {z_{\alpha /2}}{3{\sqrt {k}}}}\right)^{3}\leq \mu \leq (k+1)\left(1-{\frac {1}{9(k+1)}}+{\frac {z_{\alpha /2}}{3{\sqrt {k+1}}}}\right)^{3},}
where
z
α
/
2
{\displaystyle z_{\alpha /2}}
denotes the standard normal deviate with upper tail area α / 2.
For application of these formulae in the same context as above (given a sample of n measured values ki each drawn from a Poisson distribution with mean λ), one would set
k
=
∑
i
=
1
n
k
i
,
{\displaystyle k=\sum _{i=1}^{n}k_{i},}
calculate an interval for μ = n λ , and then derive the interval for λ.
Bayesian inference[edit]
In Bayesian inference, the conjugate prior for the rate parameter λ of the Poisson distribution is the gamma distribution. Let
λ
∼
G
a
m
m
a
(
α
,
β
)
{\displaystyle \lambda \sim \mathrm {Gamma} (\alpha ,\beta )}
denote that λ is distributed according to the gamma density g parameterized in terms of a shape parameter α and an inverse scale parameter β:
g
(
λ
∣
α
,
β
)
=
β
α
Γ
(
α
)
λ
α
−
1
e
−
β
λ
for
λ
>
0
.
{\displaystyle g(\lambda \mid \alpha ,\beta )={\frac {\beta ^{\alpha }}{\Gamma (\alpha )}}\;\lambda ^{\alpha -1}\;e^{-\beta \,\lambda }\qquad {\text{ for }}\lambda >0\,\!.}
Then, given the same sample of n measured values ki as before, and a prior of Gamma(α, β), the posterior distribution is
λ
∼
G
a
m
m
a
(
α
+
∑
i
=
1
n
k
i
,
β
+
n
)
.
{\displaystyle \lambda \sim \mathrm {Gamma} \left(\alpha +\sum _{i=1}^{n}k_{i},\beta +n\right).}
Note that the posterior mean is linear and is given by
E
[
λ
|
k
1
,
…
,
k
n
]
=
α
+
∑
i
=
1
n
k
i
β
+
n
.
{\displaystyle E[\lambda |k_{1},\ldots ,k_{n}]={\frac {\alpha +\sum _{i=1}^{n}k_{i}}{\beta +n}}.}
It can be shown that gamma distribution is the only prior that induces linearity of the conditional mean. Moreover, a converse result exists which states that if the conditional mean is close to a linear function in the
L
2
{\displaystyle L_{2}}
distance than the prior distribution of λ must be close to gamma distribution in Levy distance.
The posterior mean E[λ] approaches the maximum likelihood estimate
λ
^
M
L
E
{\displaystyle {\widehat {\lambda }}_{\mathrm {MLE} }}
in the limit as
α
→
0
,
β
→
0
,
{\displaystyle \alpha \to 0,\beta \to 0,}
which follows immediately from the general expression of the mean of the gamma distribution.
The posterior predictive distribution for a single additional observation is a negative binomial distribution, sometimes called a gamma–Poisson distribution.
Simultaneous estimation of multiple Poisson means[edit]
Suppose
X
1
,
X
2
,
…
,
X
p
{\displaystyle X_{1},X_{2},\dots ,X_{p}}
is a set of independent random variables from a set of
p
{\displaystyle p}
Poisson distributions, each with a parameter
λ
i
,
{\displaystyle \lambda _{i},}
i
=
1
,
…
,
p
,
{\displaystyle i=1,\dots ,p,}
and we would like to estimate these parameters. Then, Clevenson and Zidek show that under the normalized squared error loss
L
(
λ
,
λ
^
)
=
∑
i
=
1
p
λ
i
−
1
(
λ
^
i
−
λ
i
)
2
,
{\textstyle L(\lambda ,{\hat {\lambda }})=\sum _{i=1}^{p}\lambda _{i}^{-1}({\hat {\lambda }}_{i}-\lambda _{i})^{2},}
when
p
>
1
,
{\displaystyle p>1,}
then, similar as in Stein's example for the Normal means, the MLE estimator
λ
^
i
=
X
i
{\displaystyle {\hat {\lambda }}_{i}=X_{i}}
is inadmissible.
In this case, a family of minimax estimators is given for any
0
<
c
≤
2
(
p
−
1
)
{\displaystyle 0<c\leq 2(p-1)}
and
b
≥
(
p
−
2
+
p
−
1
)
{\displaystyle b\geq (p-2+p^{-1})}
as
λ
^
i
=
(
1
−
c
b
+
∑
i
=
1
p
X
i
)
X
i
,
i
=
1
,
…
,
p
.
{\displaystyle {\hat {\lambda }}_{i}=\left(1-{\frac {c}{b+\sum _{i=1}^{p}X_{i}}}\right)X_{i},\qquad i=1,\dots ,p.}
Occurrence and applications[edit]
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Some applications of the Poisson distribution to count data (number of events):
telecommunication: telephone calls arriving in a system,
astronomy: photons arriving at a telescope,
chemistry: the molar mass distribution of a living polymerization,
biology: the number of mutations on a strand of DNA per unit length,
management: customers arriving at a counter or call centre,
finance and insurance: number of losses or claims occurring in a given period of time,
seismology: asymptotic Poisson model of risk for large earthquakes,
radioactivity: decays in a given time interval in a radioactive sample,
optics: number of photons emitted in a single laser pulse (a major vulnerability of quantum key distribution protocols, known as Photon Number Splitting).
More examples of counting events that may be modelled as Poisson processes include:
soldiers killed by horse-kicks each year in each corps in the Prussian cavalry. This example was used in a book by Ladislaus Bortkiewicz (1868–1931),
yeast cells used when brewing Guinness beer. This example was used by William Sealy Gosset (1876–1937),
phone calls arriving at a call centre within a minute. This example was described by A.K. Erlang (1878–1929),
goals in sports involving two competing teams,
deaths per year in a given age group,
jumps in a stock price in a given time interval,
times a web server is accessed per minute (under an assumption of homogeneity),
mutations in a given stretch of DNA after a certain amount of radiation,
cells infected at a given multiplicity of infection,
bacteria in a certain amount of liquid,
photons arriving on a pixel circuit at a given illumination over a given time period,
landing of V-1 flying bombs on London during World War II, investigated by R. D. Clarke in 1946.
In probabilistic number theory, Gallagher showed in 1976 that, if a certain version of the unproved prime r-tuple conjecture holds, then the counts of prime numbers in short intervals would obey a Poisson distribution.
Law of rare events[edit]
Main article: Poisson limit theorem
Comparison of the Poisson distribution (black lines) and the binomial distribution with n = 10 (red circles), n = 20 (blue circles), n = 1000 (green circles). All distributions have a mean of 5. The horizontal axis shows the number of events k. As n gets larger, the Poisson distribution becomes an increasingly better approximation for the binomial distribution with the same mean.
The rate of an event is related to the probability of an event occurring in some small subinterval (of time, space or otherwise). In the case of the Poisson distribution, one assumes that there exists a small enough subinterval for which the probability of an event occurring twice is "negligible". With this assumption one can derive the Poisson distribution from the Binomial one, given only the information of expected number of total events in the whole interval.
Let the total number of events in the whole interval be denoted by
λ
.
{\displaystyle \lambda .}
Divide the whole interval into
n
{\displaystyle n}
subintervals
I
1
,
…
,
I
n
{\displaystyle I_{1},\dots ,I_{n}}
of equal size, such that
n
>
λ
{\displaystyle n>\lambda }
(since we are interested in only very small portions of the interval this assumption is meaningful). This means that the expected number of events in each of the n subintervals is equal to
λ
/
n
.
{\displaystyle \lambda /n.}
Now we assume that the occurrence of an event in the whole interval can be seen as a sequence of n Bernoulli trials, where the
i
{\displaystyle i}
-th Bernoulli trial corresponds to looking whether an event happens at the subinterval
I
i
{\displaystyle I_{i}}
with probability
λ
/
n
.
{\displaystyle \lambda /n.}
The expected number of total events in
n
{\displaystyle n}
such trials would be
λ
,
{\displaystyle \lambda ,}
the expected number of total events in the whole interval. Hence for each subdivision of the interval we have approximated the occurrence of the event as a Bernoulli process of the form
B
(
n
,
λ
/
n
)
.
{\displaystyle {\textrm {B}}(n,\lambda /n).}
As we have noted before we want to consider only very small subintervals. Therefore, we take the limit as
n
{\displaystyle n}
goes to infinity.
In this case the binomial distribution converges to what is known as the Poisson distribution by the Poisson limit theorem.
In several of the above examples — such as, the number of mutations in a given sequence of DNA—the events being counted are actually the outcomes of discrete trials, and would more precisely be modelled using the binomial distribution, that is
X
∼
B
(
n
,
p
)
.
{\displaystyle X\sim {\textrm {B}}(n,p).}
In such cases n is very large and p is very small (and so the expectation n p is of intermediate magnitude). Then the distribution may be approximated by the less cumbersome Poisson distribution
X
∼
Pois
(
n
p
)
.
{\displaystyle X\sim {\textrm {Pois}}(np).}
This approximation is sometimes known as the law of rare events, since each of the n individual Bernoulli events rarely occurs.
The name "law of rare events" may be misleading because the total count of success events in a Poisson process need not be rare if the parameter n p is not small. For example, the number of telephone calls to a busy switchboard in one hour follows a Poisson distribution with the events appearing frequent to the operator, but they are rare from the point of view of the average member of the population who is very unlikely to make a call to that switchboard in that hour.
The variance of the binomial distribution is 1 − p times that of the Poisson distribution, so almost equal when p is very small.
The word law is sometimes used as a synonym of probability distribution, and convergence in law means convergence in distribution. Accordingly, the Poisson distribution is sometimes called the "law of small numbers" because it is the probability distribution of the number of occurrences of an event that happens rarely but has very many opportunities to happen. The Law of Small Numbers is a book by Ladislaus Bortkiewicz about the Poisson distribution, published in 1898.
Poisson point process[edit]
Main article: Poisson point process
The Poisson distribution arises as the number of points of a Poisson point process located in some finite region. More specifically, if D is some region space, for example Euclidean space R, for which |D|, the area, volume or, more generally, the Lebesgue measure of the region is finite, and if N(D) denotes the number of points in D, then
P
(
N
(
D
)
=
k
)
=
(
λ
|
D
|
)
k
e
−
λ
|
D
|
k
!
.
{\displaystyle P(N(D)=k)={\frac {(\lambda |D|)^{k}e^{-\lambda |D|}}{k!}}.}
Poisson regression and negative binomial regression[edit]
Poisson regression and negative binomial regression are useful for analyses where the dependent (response) variable is the count (0, 1, 2, ... ) of the number of events or occurrences in an interval.
Other applications in science[edit]
In a Poisson process, the number of observed occurrences fluctuates about its mean λ with a standard deviation
σ
k
=
λ
.
{\displaystyle \sigma _{k}={\sqrt {\lambda }}.}
These fluctuations are denoted as Poisson noise or (particularly in electronics) as shot noise.
The correlation of the mean and standard deviation in counting independent discrete occurrences is useful scientifically. By monitoring how the fluctuations vary with the mean signal, one can estimate the contribution of a single occurrence, even if that contribution is too small to be detected directly. For example, the charge e on an electron can be estimated by correlating the magnitude of an electric current with its shot noise. If N electrons pass a point in a given time t on the average, the mean current is
I
=
e
N
/
t
{\displaystyle I=eN/t}
; since the current fluctuations should be of the order
σ
I
=
e
N
/
t
{\displaystyle \sigma _{I}=e{\sqrt {N}}/t}
(i.e., the standard deviation of the Poisson process), the charge
e
{\displaystyle e}
can be estimated from the ratio
t
σ
I
2
/
I
.
{\displaystyle t\sigma _{I}^{2}/I.}
An everyday example is the graininess that appears as photographs are enlarged; the graininess is due to Poisson fluctuations in the number of reduced silver grains, not to the individual grains themselves. By correlating the graininess with the degree of enlargement, one can estimate the contribution of an individual grain (which is otherwise too small to be seen unaided). Many other molecular applications of Poisson noise have been developed, e.g., estimating the number density of receptor molecules in a cell membrane.
Pr
(
N
t
=
k
)
=
f
(
k
;
λ
t
)
=
(
λ
t
)
k
e
−
λ
t
k
!
.
{\displaystyle \Pr(N_{t}=k)=f(k;\lambda t)={\frac {(\lambda t)^{k}e^{-\lambda t}}{k!}}.}
In causal set theory the discrete elements of spacetime follow a Poisson distribution in the volume.
The Poisson distribution also appears in quantum mechanics, especially quantum optics. Namely, for a quantum harmonic oscillator system in a coherent state, the probability of measuring a particular energy level has a Poisson distribution.
Computational methods[edit]
The Poisson distribution poses two different tasks for dedicated software libraries: evaluating the distribution
P
(
k
;
λ
)
{\displaystyle P(k;\lambda )}
, and drawing random numbers according to that distribution.
Evaluating the Poisson distribution[edit]
Computing
P
(
k
;
λ
)
{\displaystyle P(k;\lambda )}
for given
k
{\displaystyle k}
and
λ
{\displaystyle \lambda }
is a trivial task that can be accomplished by using the standard definition of
P
(
k
;
λ
)
{\displaystyle P(k;\lambda )}
in terms of exponential, power, and factorial functions. However, the conventional definition of the Poisson distribution contains two terms that can easily overflow on computers: λ and k!. The fraction of λ to k! can also produce a rounding error that is very large compared to e, and therefore give an erroneous result. For numerical stability the Poisson probability mass function should therefore be evaluated as
f
(
k
;
λ
)
=
exp
[
k
ln
λ
−
λ
−
ln
Γ
(
k
+
1
)
]
,
{\displaystyle \!f(k;\lambda )=\exp \left[k\ln \lambda -\lambda -\ln \Gamma (k+1)\right],}
which is mathematically equivalent but numerically stable. The natural logarithm of the Gamma function can be obtained using the lgamma function in the C standard library (C99 version) or R, the gammaln function in MATLAB or SciPy, or the log_gamma function in Fortran 2008 and later.
Some computing languages provide built-in functions to evaluate the Poisson distribution, namely
R: function dpois(x, lambda);
Excel: function POISSON( x, mean, cumulative), with a flag to specify the cumulative distribution;
Mathematica: univariate Poisson distribution as PoissonDistribution[
λ
{\displaystyle \lambda }
], bivariate Poisson distribution as MultivariatePoissonDistribution[
θ
12
,
{\displaystyle \theta _{12},}
{
θ
1
−
θ
12
,
{\displaystyle \theta _{1}-\theta _{12},}
θ
2
−
θ
12
{\displaystyle \theta _{2}-\theta _{12}}
}],.
Random variate generation[edit]
Further information: Non-uniform random variate generation
The less trivial task is to draw integer random variate from the Poisson distribution with given
λ
.
{\displaystyle \lambda .}
Solutions are provided by:
R: function rpois(n, lambda);
GNU Scientific Library (GSL): function gsl_ran_poisson
A simple algorithm to generate random Poisson-distributed numbers (pseudo-random number sampling) has been given by Knuth:
algorithm poisson random number (Knuth):
init:
Let L ← e, k ← 0 and p ← 1.
do:
k ← k + 1.
Generate uniform random number u in [0,1] and let p ← p × u.
while p > L.
return k − 1.
The complexity is linear in the returned value k, which is λ on average. There are many other algorithms to improve this. Some are given in Ahrens & Dieter, see § References below.
For large values of λ, the value of L = e may be so small that it is hard to represent. This can be solved by a change to the algorithm which uses an additional parameter STEP such that e does not underflow:
algorithm poisson random number (Junhao, based on Knuth):
init:
Let λLeft ← λ, k ← 0 and p ← 1.
do:
k ← k + 1.
Generate uniform random number u in (0,1) and let p ← p × u.
while p < 1 and λLeft > 0:
if λLeft > STEP:
p ← p × e
λLeft ← λLeft − STEP
else:
p ← p × e
λLeft ← 0
while p > 1.
return k − 1.
The choice of STEP depends on the threshold of overflow. For double precision floating point format the threshold is near e, so 500 should be a safe STEP.
Other solutions for large values of λ include rejection sampling and using Gaussian approximation.
Inverse transform sampling is simple and efficient for small values of λ, and requires only one uniform random number u per sample. Cumulative probabilities are examined in turn until one exceeds u.
algorithm Poisson generator based upon the inversion by sequential search:
init:
Let x ← 0, p ← e, s ← p.
Generate uniform random number u in [0,1].
while u > s do:
x ← x + 1.
p ← p × λ / x.
s ← s + p.
return x.
See also[edit]
Binomial distribution
Compound Poisson distribution
Conway–Maxwell–Poisson distribution
Erlang distribution
Exponential distribution
Gamma distribution
Hermite distribution
Index of dispersion
Negative binomial distribution
Poisson clumping
Poisson point process
Poisson regression
Poisson sampling
Poisson wavelet
Queueing theory
Renewal theory
Robbins lemma
Skellam distribution
Tweedie distribution
Zero-inflated model
Zero-truncated Poisson distribution | biology | 207244 | https://da.wikipedia.org/wiki/Surreelle%20tal | Surreelle tal | Indenfor matematik er surreelle tal elementerne i et legeme, som både indeholder de reelle tal og uendeligt store og små tal.
Definitionen og konstruktionen af surreelle tal stammer fra John Horton Conway. De blev første gang beskrevet i Donald Knuth's bog: "How Two Ex-Students Turned on to Pure Mathematics and Found Total Happiness" fra 1974. I bogen bruger Knuth ordet surreelle tal, for det Conway tidligere havde bare havde kaldt tal. Conway beskrev de surreelle tal og brugte dem til at analysere spil i bogen "On numbers and Games" fra 1976.
Konstruktionen af de surreelle tal
De surreelle tal kan defineres ud fra kun to regler:
Konstruktionsreglen: Hvis L og R (L og R står for det engelsk left og right, som betyder hhv. venstre og højre) er to mængder, sådan at intet element i L er mindre end eller lig noget element i R, er {L|R} et surreelt tal.
Sammenligningsreglen: Hvis x={XL|XR} og y={YL|YR} så gælder x ≤ y hvis og kun hvis y ikke er mindre end eller lig noget element i XL, og intet element i YR er mindre end eller lig x.
Med disse definitioner findes der surreelle tal x og y så x≤y og y≤x. Man definerer derfor:
x==y hvis og kun hvis x≤y og y≤x. De to lighedstegn betyder at x og y er ækvivalente, og man siger at x og y tilhører samme ækvivalentklasse.
Det ses at definitionen er rekursiv: Når man har defineret nogle tal, kan man bruge dem til at definere flere tal, osv. Da man til at starte med ikke kender nogle surreelle tal, bliver men nødt til at starte med at definere et tal ved hjælp at den tomme mængde. Det ses at { { } | { } } opfylder kravene for at være et surreelt tal, for der er jo ikke noget element i nogle af mængderne, som ikke opfylder kravene. Man vælger ofte at undlade de indre parenteser, så { { } | { } } skrives ofte som { | }. Dette tal kalder man 0.
Nu hvor man har et surreelt tal, kan man prøve at definere flere. Der er tre muligheder:
{ 0 | }, { | 0 } og { 0 | 0 }.
{ 0 | 0 } er dog ikke et surreelt tal, da 0≤0, men de to andre tal opfylder kravene. Ved hjælp af sammenligningsreglen ses at:
{ | 0 }<{ | }<{ 0 | }
Hvor < betyder "≤ men ikke ==". Man kalder nu {|0} for -1 og {0|} for 1. Med disse tre tal, kan vi definere endnu flere tal:
{ | −1 } == { | −1, 0 } == { | −1, 1 } == { | −1, 0, 1 } <
{ | 0, 1 } == −1 <
{ −1 | 0 } == { −1 | 0, 1 } <
{ −1 | } == { | 1 } == { −1 | 1 } == 0 <
{ 0 | 1 } == { −1, 0 | 1 } <
{ −1, 0 | } == 1 <
{ 1 | } == { 0, 1 | } == { −1, 1 | } == { −1, 0, 1 | }
Dermed er der 4 nye ækvivalentklasser, dvs. klasser af tal, som er ækvivalente: [{ | −1 }], [{ −1 | 0 }], [{ 0 | 1 }] og [{ 1 | }]. { | −1 } er tallet før -1 og kaldes derfor -2. Tilsvarende er { 1 | } tallet efter 1 og der kaldes derfor 2. { −1 | 0 } er tallet mellem -1 og 0, og det kaldes derfor -½, og tilsvarende kaldes { 0 | 1 } for ½. Klassen af tal, der er ækvivalente med x kaldes x. Dermed har vi nu ækvivalentklasserne: -2, -1, -½, 0, ½, 1 og 2. Hvis man bruger et tal x1 til at definere y1, og man erstatter x1 med et andet tal x2, fra samme ækvivalensklasse, får man et tal y2, som er i samme ækvivalensklasse som y1. F.eks: { | 0, 1 } == { | { | 1 }, 1 }. Det afgørende er derfor hvilken ækvivalensklasse et tal tilhører. Man kan derfor skrive:
{ | −1 } == { | −1, 0 } == { | −1, 1 } == { | −1, 0, 1 } <
{ |0, 1 } == −1 <
{ −1 | 0 } == { −1| 0, 1 } <
{ −1 | } == { | 1 } == { −1 | 1 } == 0 <
{ 0 | 1 } == { −1, 0 | 1 } <
{ −1, 0 | } == 1 <
{ 1 | } == { 0, 1 | } == { −1, 1 | } == { −1, 0, 1 | }
som også kan skrives som:
−2 < −1 < −1/2 < 0 < 1/2 < 1 < 2.
Konstruktion af surreelle tal med endelig induktion
Ovenstående konstruktion af de simpleste surreelle tal skete i trin. Man definerer Sn som mængden af surreelle tal, der er dannet efter n'te trin, hvor konstruktionen af 0 regnes som 0'te trin. Mere formelt defineres Sn således:
S0={0}
Si+1 er foreningsmængden af Si og alle de tal, der kan dannes ved hjælp af en delmængde af tallene i Si.
Der gælder nu:
S0 = { 0 }
S1 = { −1 < 0 < 1 }
S2 = { −2 < −1 < −1/2 < 0 < 1/2 < 1 < 2}
S3 = { −3 < −2 < −1 1/2 < −1 < −3/4 < −1/2 < −1/4 < 0 < 1/4 < 1/2 < 3/4 < 1 < 1 1/2 < 2 < 3 }
S4 = ...
Man kan se at:
For hvert trin stiger maksimum med 1, og minimum falder med 1.
For hvert trin kommer der et nyt tal mellem to på hinanden følgende tal.
Mængden af alle surreelle tal, som bliver dannet i et trin Si, kaldes Sω. Denne mængde består netop af tal af formen:
a/2b
hvor b>0. Dermed kan tal som 1/3, 1/5, 2/5,... ikke dannes i et endeligt antal trin. Disse og mange andre tal kan dog dannes, hvis man tillader uendeligt mange trin.
Konstruktion af alle surreelle tal
Når man først har defineret Sω, kan man ligesom før finde Sω+1. Til forskel fra før har vi nu uendeligt mange surreelle tal, og mængderne L og R kan derfor have uendeligt mange elementer. Man kan derfor definerer de surreelle tal for alle brøker. F.eks.:
1/3 = { { a / 2b in Sω | 3a < 2b } | { a / 2b in Sω | 3a > 2b } }
På tilsvarende vis kan man definerer alle reelle tal kun ved at bruge tal fra Sω. F.eks.:
π = {3, 25/8, 201/64, ... | ..., 101/32, 51/16, 13/4, 7/2, 4}
Derfor er alle reelle tal i Sω+1. Man kan også definerer mange andre surreelle tal. F.eks.:
ε = { 0 | ..., 1/16, 1/8, 1/4, 1/2, 1 }
Dette er altså et positivt tal, der er mindre end ethvert andet positivt tal. I Sω+1 er også uendeligt:
ω = { Sω | }
Dette er dog ikke de eneste uendeligt store og små surreelle tal der findes. I Sω+2 findes tallene:
2ε = { ε | ..., ε + 1/16, ε + 1/8, ε + 1/4, ε + 1/2, ε + 1 }
ε / 2 = { 0 | ε }
ω + 1 = { ω | }
ω − 1 = { Sω | ω }
Dette kan fortsættes på samme måde som med de hele tal. Man kan altså definerer: ...,ω − 2 ,ω − 1, ω, ω + 1, ω + 2,...
På samme måde som man definerer Sω, kan man også definerer S2ω: S2ω er mængden af alle surreelle tal, som findes i en mængde Sω+i. I mængden S2ω+1 finde nu tal som:
ω + ω = { ω + Sω | }
ω/2 = { Sω | ω − Sω }
Her betyder et tal plus en mængde, at man lægger tallet til alle elementer i mængden, og minus defineres tilsvarende.
Potenser af uendelig
Man kan også definere potenser af uendelig. F.eks. kvadratroden af ω, og ωω. Man kan endda definere ωx for ethvert surreelt tal x.
Noter
Ekstern henvisning
Forklaring af de surreelle tal af Claus Tøndering (på engelsk)
Tal
Matematisk logik | danish | 0.761696 |
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* How to Start a Bee Hive in 7 Steps
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# How to Start a Bee Hive in 7 Steps
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Starting a bee colony for the first time may be stressful and confusing, but
Mann Lake is here to help new beekeepers. Our guide outlines all the necessary
steps and information to lay the foundation of a successful beekeeping
experience. From setting up to understanding honey bees, let’s equip you with
everything you need to start your colony with confidence.
## 1\. Determine the Location of Your Apiary
Choosing the [ location of your new hive ](https://www.mannlakeltd.com/mann-
lake-blog/how-to-place-your-beehive-in-the-perfect-location/) is an important
step in setting your hive up for success. This entails more considerations
than you might think. Even factors such as close proximity to pollution
sources or pesticide use could affect your colony’s health.
Conduct a careful study of your proposed site beforehand to ensure it’s safe
for the bees. To start, try to pick a location that has the following:
* Easy access
* Protection from the elements
* Plenty of sunlight
* Level ground
* Access to resources
**Hive Hint:** Bees are creatures of habit. Frequent changes in their
environment can hamper their work, so aim to keep things like hive location
consistent.
---
## 2\. Determine How Many Colonies You Need
The most important part of beekeeping is the bees. It’s recommended to start
with a minimum of two colonies. Having two hives provides a helpful comparison
and gives you access to resources should one colony be stronger than the
other.
Make sure that you [ pre-order your honey bees
](https://www.mannlakeltd.com/shop-all-categories/hive-components/bees) early!
If you’re not sure what breed is the best fit for your apiary, read more about
the [ common varieties of honey bees ](https://www.mannlakeltd.com/mann-lake-
blog/education-the-common-varieties-of-honey-bees/) .
Consider the size of your property, too. Managing honey bees requires space
for the hives, bee flight paths, and your own movement area. Try to account
for the possibility of expansion in the future. Successful beekeeping often
motivates keepers to increase their colonies, so evaluate your space with this
growth potential in mind.
## 3\. Order Equipment Ahead of Time
Order the [ equipment ](https://www.mannlakeltd.com/) you need at least a
month prior to the bees’ arrival. This ensures that you’re ready when your
bees arrive.
Learning the proper operations of each [ hive tool
](https://www.mannlakeltd.com/beekeeping-tools-more/) is also essential. This
helps avoid any misuse that could potentially harm your bees. For instance,
understanding the proper way to use a smoker can make the difference between
calming your bees and causing them unnecessary stress.
### Supplies Needed to Start a Colony
The following items will help you be fully prepared and ready to initiate your
beekeeping journey in a seamless way. Ensure that you have everything on this
list before you start.
* Feeder
* Hive tool
* Protective clothing
* Smoker and [ smoker fuel ](https://www.mannlakeltd.com/beekeeping/supplies/smoker-fuel/1-2-lb-227-g-smoker-fuel/)
* Liquid feed, like Pro-Sweet
* [ Pollen substitutes ](https://www.mannlakeltd.com/feeding-medications/pollen-substitutes-protein/) , like Ultra Bee or Bee Pro
* Hive components, like hive stand, bottom board, hive bodies (use only one until the colony is established), honey supers, frames, inner cover, outer cover, and queen bees excluder
**Recommended Tip:** If you plan on preparing your own sugar water mix, we
recommend adding a stimulant such as Pro-Health that will help prevent the
fermentation process.
---
## 4\. Setup the Hive Before Bees Arrive
After your bees and equipment are ordered, get ready to set up your hives in
your apiary. Make sure that the hives are set up prior to the bees’ arrival.
Be more prepared by surrounding your honey bee hive with a windbreak like a
fence or hedging. This could provide added protection during strong winds or
harsh winters. Evaluate potential threats such as mite infestation beforehand
so you’re better equipped to maintain a healthy colony.
## 5\. Introducing Bees to the Hive
Once the hive setup is complete, it’s time to introduce your bees. Depending
on your order, the bees may arrive packaged or in a nucleus colony. Careful
and gentle introduction is crucial to acclimate the bees to their new
environment.
Immediately after arrival, install the bees into the hive. [ Package bees
](https://www.mannlakeltd.com/honey-bees/live-package-bees/) may require a
slightly different method versus a nuc, so do your research. Remember,
successful hive introduction is the first significant milestone in your
beekeeping journey.
Establish the queen bee within the hive, which essentially means ensuring the
worker bees accept her. This process may take several days, but you’ll know
it’s successful when you start observing worker bees feeding her through the
cage.
## 6\. Feeding Your Bees
Early-stage bee colonies often require supplemental feeding to thrive. It’s
crucial, especially if natural food sources around the hive are scarce. You
can initiate feeding with options like sugar syrup or a dedicated feed like
Pro-Sweet, depending on the recommended dietary needs of the bees.
The feed can be administered using a [ hive-top feeder
](https://www.mannlakeltd.com/feeding-medications/bee-feeders/) , entrance
feeder, or frame feeder. Each of these methods has unique advantages and
considerations depending on your particular beekeeping situation.
The following table provides a comparison of these three common feeding
methods.
**Feature** | **Hive Top Feeder** | **Entrance Feeder** | **Frame Feeder**
---|---|---|---
Description | Sits on top of the hive frames | Placed at the hive's
entrance | Replaces one of the frames inside the hive
Capacity | Large, can hold several gallons of syrup | Smaller capacity,
usually up to 1 quart | Varies, but typically holds 1–2 gallons
Ease of Refilling | Can be refilled without opening the hive entirely |
Needs to be refilled more frequently due to smaller size | Requires opening
the hive and removing frames for refilling
Accessibility | Easy for bees to access without leaving the hive | Bees
need to leave the hive to access | Integrated into the hive, easy access for
bees
Protection from Robbers | Better protected from robbing by other bees and
insects | More exposed, higher risk of attracting robbers | Inside the
hive, so less risk of robbery
Monitoring Consumption | Easy to monitor without disturbing bees | Easy to
monitor, but can disturb bees at the entrance | Harder to monitor without
disturbing the hive
Suitability for Winter | Suitable for winter feeding due to large capacity
and less heat loss | Less suitable for winter as it requires bees to go
outside | Suitable, especially when placed in the middle of the hive
Cost | Generally more expensive due to larger size | Less expensive |
Moderate cost, depending on size and material
##
## 7\. First Week Observations
In your first week, observe the bees’ activities without disrupting them. Look
for bees getting in and out of the hive, a sign of an active, healthy hive.
Watch for [ bees carrying pollen ](https://www.mannlakeltd.com/blog/how-do-
bees-collect-pollen/) back, indicating the presence of a brood and a
functioning queen bee.
Pay attention to possible threats like mites or any signs of diseases like
unusual behavior or dead bees. It’s important to catch such issues early when
management is easier and more effective.
Monitor the hive environment, too. Ensure the hive maintains a dry interior
and a fluctuating temperature conducive to the bees. This first week sets the
stage for the health and prosperity of your hive.
## Common Mistakes to Avoid When Starting Your Bee Hive
Certain mistakes can significantly impair your hive’s health and productivity.
Understanding these common errors on the front end can ensure your beekeeping
journey is successful and sweet right from the start! Let’s tread ahead
carefully to avoid the common pitfalls.
### Not Doing Enough Research
It’s tempting to jump straight into the world of beekeeping, but without a
firm understanding of the variety of bees, their habits, and their needs, this
could prove harmful to your bee colonies.
Successful beekeeping also involves adhering to your community’s specific
guidelines. Familiarize yourself with local beekeeping laws. Every location
has its unique set of regulations about keeping bees, and overlooking such
regulations could lead to compliance issues.
### Improper Hive Setup
An incorrectly set up hive can stress out your bees, disturb their natural
routines, and potentially decrease honey collection and production.
The components of the hive should be properly arranged to mimic the bees’
natural environment. An upright orientation, enough space for comb building,
and ease of access are non-negotiables for a stress-free hive.
### Neglecting Regular Hive Inspections
Caring for a colony isn’t a set-and-forget task; it requires constant
observation and timely interventions. Regular [ hive inspections
](https://www.mannlakeltd.com/blog/tips-for-conducting-a-hive-inspection/) can
ensure your bees’ well-being and enhance productivity.
During regular inspections, you get to understand the behavior and health of
your bees, identify potential issues, and take necessary actions. Not paying
attention to this step could risk colony collapse.
### Over-Harvesting Honey
One of the key goals of beekeeping is honey production. However, remember that
honey is also the primary food source for your bees. Over-harvesting can leave
them malnourished, especially during colder seasons.
Knowing the right time to harvest is essential. The rule of thumb suggests
waiting until at least [ 80% of the frames
](https://www.dummies.com/article/home-auto-hobbies/hobby-
farming/beekeeping/how-to-know-when-to-harvest-honey-from-your-
beehive-188377/#:~:text=When%20a%20shallow%20frame%20contains%2080%20percent%20or%20more%20of%20sealed%2C%20capped%20honey%2C%20you%E2%80%99re%20welcome%20to%20remove%20and%20harvest%20this%20frame.)
are fully capped. So, practicing patience is key to a successful bee-
harvesting experience.
### Ignoring Signs of Illness or Parasites
Bee colonies can be susceptible to various diseases and pests. Ignoring signs
of such hazards can rapidly escalate to severe hive health deterioration.
Early detection allows for quick responses to protect the colony and prevent
the spread of diseases.
Common red flags include a sudden drop in colony population, irregular brood
pattern, or unusual bee behavior. Pests such as hive beetles, wax moths, or
the dreaded Varroa mites also pose significant threats to colonies.
**Quick Fact:** Varroa mites, among the smallest of bee pests, are actually
visible to the naked eye. Timely detection can save your hive!
---
###
### Inadequate Preparation for Winter
Bees have specific needs to survive winter, and preparing the hives for colder
months is a key task. A common mistake local beekeepers make is neglecting or
inadequately winterizing their hives, risking the survival of their colonies.
Insufficient honey reserves can lead to starvation during months when forage
is sparse. Ensure that your bees have a sufficient food supply for winter.
Provide extra insulation to fight cold drafts but also ensure moisture control
to avoid mold growth inside the hive.
## Ready to Buzz: Sealing Success in Beekeeping
Starting a bee hive demands care and a keen eye for detail. The bee colony’s
health and honey yield rest on the beekeepers’ willingness to learn and adapt.
So, begin this journey with readiness, follow the right steps, and understand
the common pitfalls. Soon enough, the sweet reward of honey and the pride of a
healthy, bustling colony will be yours.
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stars_disappear_when_look/Lens.txt |
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.
Lenses are used in various imaging devices such as telescopes, binoculars, and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia.
History[edit]
See also: History of optics and Camera lens
This section needs expansion with: history after 1758. You can help by adding to it. (January 2012)
Light being refracted by a spherical glass container full of water. Roger Bacon, 13th century
Lens for LSST, a planned sky surveying telescope
The word lens comes from lēns, the Latin name of the lentil (a seed of a lentil plant), because a double-convex lens is lentil-shaped. The lentil also gives its name to a geometric figure.
Some scholars argue that the archeological evidence indicates that there was widespread use of lenses in antiquity, spanning several millennia. The so-called Nimrud lens is a rock crystal artifact dated to the 7th century BCE which may or may not have been used as a magnifying glass, or a burning glass. Others have suggested that certain Egyptian hieroglyphs depict "simple glass meniscal lenses".
The oldest certain reference to the use of lenses is from Aristophanes' play The Clouds (424 BCE) mentioning a burning-glass.
Pliny the Elder (1st century) confirms that burning-glasses were known in the Roman period.
Pliny also has the earliest known reference to the use of a corrective lens when he mentions that Nero was said to watch the gladiatorial games using an emerald (presumably concave to correct for nearsightedness, though the reference is vague). Both Pliny and Seneca the Younger (3 BC–65 AD) described the magnifying effect of a glass globe filled with water.
Ptolemy (2nd century) wrote a book on Optics, which however survives only in the Latin translation of an incomplete and very poor Arabic translation.
The book was, however, received by medieval scholars in the Islamic world, and commented upon by Ibn Sahl (10th century), who was in turn improved upon by Alhazen (Book of Optics, 11th century). The Arabic translation of Ptolemy's Optics became available in Latin translation in the 12th century (Eugenius of Palermo 1154). Between the 11th and 13th century "reading stones" were invented. These were primitive plano-convex lenses initially made by cutting a glass sphere in half. The medieval (11th or 12th century) rock crystal Visby lenses may or may not have been intended for use as burning glasses.
Spectacles were invented as an improvement of the "reading stones" of the high medieval period in Northern Italy in the second half of the 13th century. This was the start of the optical industry of grinding and polishing lenses for spectacles, first in Venice and Florence in the late 13th century, and later in the spectacle-making centres in both the Netherlands and Germany.
Spectacle makers created improved types of lenses for the correction of vision based more on empirical knowledge gained from observing the effects of the lenses (probably without the knowledge of the rudimentary optical theory of the day). The practical development and experimentation with lenses led to the invention of the compound optical microscope around 1595, and the refracting telescope in 1608, both of which appeared in the spectacle-making centres in the Netherlands.
Further information: History of the telescope
With the invention of the telescope and microscope there was a great deal of experimentation with lens shapes in the 17th and early 18th centuries by those trying to correct chromatic errors seen in lenses. Opticians tried to construct lenses of varying forms of curvature, wrongly assuming errors arose from defects in the spherical figure of their surfaces. Optical theory on refraction and experimentation was showing no single-element lens could bring all colours to a focus. This led to the invention of the compound achromatic lens by Chester Moore Hall in England in 1733, an invention also claimed by fellow Englishman John Dollond in a 1758 patent.
Construction of simple lenses[edit]
Most lenses are spherical lenses: their two surfaces are parts of the surfaces of spheres. Each surface can be convex (bulging outwards from the lens), concave (depressed into the lens), or planar (flat). The line joining the centres of the spheres making up the lens surfaces is called the axis of the lens. Typically the lens axis passes through the physical centre of the lens, because of the way they are manufactured. Lenses may be cut or ground after manufacturing to give them a different shape or size. The lens axis may then not pass through the physical centre of the lens.
Toric or sphero-cylindrical lenses have surfaces with two different radii of curvature in two orthogonal planes. They have a different focal power in different meridians. This forms an astigmatic lens. An example is eyeglass lenses that are used to correct astigmatism in someone's eye.
Types of simple lenses[edit]
Types of lenses
Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses, since its shape minimizes some aberrations.
If the lens is biconvex or plano-convex, a collimated beam of light passing through the lens converges to a spot (a focus) behind the lens. In this case, the lens is called a positive or converging lens. For a thin lens in air, the distance from the lens to the spot is the focal length of the lens, which is commonly represented by f in diagrams and equations. An extended hemispherical lens is a special type of plano-convex lens, in which the lens's curved surface is a full hemisphere and the lens is much thicker than the radius of curvature.
Another extreme case of a thick convex lens is a ball lens, whose shape is completely round. When used in novelty photography it is often called a "lensball". A ball-shaped lens has the advantage of being omnidirectional, but for most optical glass types, its focal point lies close to the ball's surface . Because of the ball's curvature extremes compared to the lens size, optical aberration is much worse than thin lenses, with the notable exception of chromatic aberration.
Biconvex lens
If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam, after passing through the lens, appears to emanate from a particular point on the axis in front of the lens. For a thin lens in air, the distance from this point to the lens is the focal length, though it is negative with respect to the focal length of a converging lens.
Biconcave lens
Meniscus lenses: negative (top) and positive (bottom)
Convex-concave (meniscus) lenses can be either positive or negative, depending on the relative curvatures of the two surfaces. A negative meniscus lens has a steeper concave surface (with a shorter radius than the convex surface) and is thinner at the centre than at the periphery. Conversely, a positive meniscus lens has a steeper convex surface (with a shorter radius than the concave surface) and is thicker at the centre than at the periphery.
An ideal thin lens with two surfaces of equal curvature would have zero optical power, meaning that it would neither converge nor diverge light. All real lenses have a nonzero thickness, however, which makes a real lens with identical curved surfaces slightly positive. To obtain exactly zero optical power, a meniscus lens must have slightly unequal curvatures to account for the effect of the lens' thickness.
For a spherical surface[edit]
Simulation of refraction at spherical surface at Desmos
For a single refraction for a circular boundary, the relation between object and image is given by
n
2
v
+
n
1
u
=
n
2
−
n
1
R
{\displaystyle {\frac {n_{2}}{v}}+{\frac {n_{1}}{u}}={\frac {n_{2}-n_{1}}{R}}}
where R is the radius of the spherical surface, n2 is the refractive index of the surface, and n1 is the refractive index of medium.
Applying this on the two spherical surfaces of a thin lens leads to the lens maker's formula.
Derivation[edit]
The four cases of spherical refraction
Applying Snell's law on the spherical surface,
n
1
sin
i
=
n
2
sin
r
.
{\displaystyle n_{1}\sin i=n_{2}\sin r\,.}
Also in the diagram,
tan
(
i
−
θ
)
=
h
u
tan
(
θ
−
r
)
=
h
v
sin
θ
=
h
R
{\displaystyle {\begin{aligned}\tan(i-\theta )&={\frac {h}{u}}\\\tan(\theta -r)&={\frac {h}{v}}\\\sin \theta &={\frac {h}{R}}\end{aligned}}}
Using small angle approximation and eliminating i, r, and θ,
n
2
v
+
n
1
u
=
n
2
−
n
1
R
.
{\displaystyle {\frac {n_{2}}{v}}+{\frac {n_{1}}{u}}={\frac {n_{2}-n_{1}}{R}}\,.}
Lensmaker's equation[edit]
The position of the focus of a spherical lens depends on the radii of curvature of the two facets.
The focal length of a lens in air can be calculated from the lensmaker's equation:
1
f
=
(
n
−
1
)
[
1
R
1
−
1
R
2
+
(
n
−
1
)
d
n
R
1
R
2
]
,
{\displaystyle {\frac {1}{\ f\ }}=(n-1)\left[{\frac {1}{\ R_{1}\ }}-{\frac {1}{\ R_{2}\ }}+{\frac {\ (n-1)\ d\ }{n\ R_{1}R_{2}}}\right]\ ,}
where
f is the (effective) focal length of the lens;
n is the refractive index of the lens material;
R1 is the (signed, see below) radius of curvature of the lens surface closer to the light source;
R2 is the radius of curvature of the lens surface farther from the light source; and
d is the thickness of the lens (the distance along the lens axis between the two surface vertices).
The focal length f is with respect to the principal planes of the lens, and the locations of the planes
h
1
{\textstyle h_{1}}
and
h
2
{\textstyle h_{2}}
with respect to the respective lens vertices are given by the following formulas, where it is a positive value if it is right to the respective vertex.
h
1
=
−
f
(
n
−
1
)
d
R
2
n
{\displaystyle h_{1}=-{\frac {f(n-1)d}{R_{2}n}}}
h
2
=
−
f
(
n
−
1
)
d
R
1
n
{\displaystyle h_{2}=-{\frac {f(n-1)d}{R_{1}n}}}
f is positive for converging lenses, and negative for diverging lenses. The reciprocal of the focal length, f, is the optical power of the lens. If the focal length is in metres, this gives the optical power in dioptres (inverse metres).
Lenses have the same focal length when light travels from the back to the front as when light goes from the front to the back. Other properties of the lens, such as the aberrations are not the same in both directions.
Sign convention for radii of curvature R1 and R2[edit]
Main article: Radius of curvature (optics)
The signs of the lens' radii of curvature indicate whether the corresponding surfaces are convex or concave. The sign convention used to represent this varies, but in this article a positive R indicates a surface's center of curvature is further along in the direction of the ray travel (right, in the accompanying diagrams), while negative R means that rays reaching the surface have already passed the center of curvature. Consequently, for external lens surfaces as diagrammed above, R1 > 0 and R2 < 0 indicate convex surfaces (used to converge light in a positive lens), while R1 < 0 and R2 > 0 indicate concave surfaces. The reciprocal of the radius of curvature is called the curvature. A flat surface has zero curvature, and its radius of curvature is infinite.
Thin lens approximation[edit]
If d is small compared to R1 and R2 then the thin lens approximation can be made. For a lens in air, f is then given by
1
f
≈
(
n
−
1
)
[
1
R
1
−
1
R
2
]
.
{\displaystyle {\frac {1}{\ f\ }}\approx \left(n-1\right)\left[{\frac {1}{\ R_{1}\ }}-{\frac {1}{\ R_{2}\ }}\right]\,.}
Imaging properties[edit]
As mentioned above, a positive or converging lens in air focuses a collimated beam travelling along the lens axis to a spot (known as the focal point) at a distance f from the lens. Conversely, a point source of light placed at the focal point is converted into a collimated beam by the lens. These two cases are examples of image formation in lenses. In the former case, an object at an infinite distance (as represented by a collimated beam of waves) is focused to an image at the focal point of the lens. In the latter, an object at the focal length distance from the lens is imaged at infinity. The plane perpendicular to the lens axis situated at a distance f from the lens is called the focal plane.
If the distances from the object to the lens and from the lens to the image are S1 and S2 respectively, for a lens of negligible thickness (thin lens), in air, the distances are related by the thin lens formula:
1
f
=
1
S
1
+
1
S
2
.
{\displaystyle {1 \over f}={1 \over S_{1}}+{1 \over S_{2}}\,.}
This can also be put into the "Newtonian" form:
f
2
=
x
1
x
2
,
{\displaystyle f^{2}=x_{1}x_{2}\,,}
where
x
1
=
S
1
−
f
{\displaystyle x_{1}=S_{1}-f}
and
x
2
=
S
2
−
f
.
{\displaystyle x_{2}=S_{2}-f\,.}
A camera lens forms a real image of a distant object.
The above equations also hold for a thick lens if
S
1
{\textstyle S_{1}}
,
S
2
{\textstyle S_{2}}
, and
f
{\textstyle f}
are with respect to the principal plans of the lens (
f
{\textstyle f}
as the effective focal length in this case). If an object is placed at a distance S1 > f from a positive lens of focal length f, we will find an image at a distance S2 according to this formula. If a screen is placed at a distance S2 on the opposite side of the lens, an image is formed on it. This sort of image, which can be projected onto a screen or image sensor, is known as a real image. This is the principle of the camera, and also of the human eye, in which the retina serves as the image sensor.
The focusing adjustment of a camera adjusts S2, as using an image distance different from that required by this formula produces a defocused (fuzzy) image for an object at a distance of S1 from the camera. Put another way, modifying S2 causes objects at a different S1 to come into perfect focus.
Virtual image formation using a positive lens as a magnifying glass.
In some cases, S2 is negative, indicating that the image is formed on the opposite side of the lens from where those rays are being considered. Since the diverging light rays emanating from the lens never come into focus, and those rays are not physically present at the point where they appear to form an image, this is called a virtual image. Unlike real images, a virtual image cannot be projected on a screen, but appears to an observer looking through the lens as if it were a real object at the location of that virtual image. Likewise, it appears to a subsequent lens as if it were an object at that location, so that second lens could again focus that light into a real image, S1 then being measured from the virtual image location behind the first lens to the second lens. This is exactly what the eye does when looking through a magnifying glass. The magnifying glass creates a (magnified) virtual image behind the magnifying glass, but those rays are then re-imaged by the lens of the eye to create a real image on the retina.
A negative lens produces a demagnified virtual image.A Barlow lens (B) reimages a virtual object (focus of red ray path) into a magnified real image (green rays at focus)
Using a positive lens of focal length f, a virtual image results when S1 < f, the lens thus being used as a magnifying glass (rather than if S1 ≫ f as for a camera). Using a negative lens (f < 0) with a real object (S1 > 0) can only produce a virtual image (S2 < 0), according to the above formula. It is also possible for the object distance S1 to be negative, in which case the lens sees a so-called virtual object. This happens when the lens is inserted into a converging beam (being focused by a previous lens) before the location of its real image. In that case even a negative lens can project a real image, as is done by a Barlow lens.
Real image of a lamp is projected onto a screen (inverted). Reflections of the lamp from both surfaces of the biconvex lens are visible.A convex lens (f ≪ S1) forming a real, inverted image (as the image formed by the objective lens of a telescope or binoculars) rather than the upright, virtual image as seen in a magnifying glass(f > S1). This real image may also be viewed when put on a screen.
For a thin lens, the distances S1 and S2 are measured from the object and image to the position of the lens, as described above. When the thickness of the lens is not much smaller than S1 and S2 or there are multiple lens elements (a compound lens), one must instead measure from the object and image to the principal planes of the lens. If distances S1 or S2 pass through a medium other than air or vacuum a more complicated analysis is required.
Magnification[edit]
The linear magnification of an imaging system using a single lens is given by
M
=
−
S
2
S
1
=
f
f
−
S
1
,
{\displaystyle M=-{\frac {S_{2}}{S_{1}}}={\frac {f}{f-S_{1}}}\,,}
where M is the magnification factor defined as the ratio of the size of an image compared to the size of the object. The sign convention here dictates that if M is negative, as it is for real images, the image is upside-down with respect to the object. For virtual images M is positive, so the image is upright.
This magnification formula provides two easy ways to distinguish converging (f > 0) and diverging (f < 0) lenses: For an object very close to the lens (0 < S1 < |f|), a converging lens would form a magnified (bigger) virtual image, whereas a diverging lens would form a demagnified (smaller) image; For an object very far from the lens (S1 > |f| > 0), a converging lens would form an inverted image, whereas a diverging lens would form an upright image.
Linear magnification M is not always the most useful measure of magnifying power. For instance, when characterizing a visual telescope or binoculars that produce only a virtual image, one would be more concerned with the angular magnification—which expresses how much larger a distant object appears through the telescope compared to the naked eye. In the case of a camera one would quote the plate scale, which compares the apparent (angular) size of a distant object to the size of the real image produced at the focus. The plate scale is the reciprocal of the focal length of the camera lens; lenses are categorized as long-focus lenses or wide-angle lenses according to their focal lengths.
Using an inappropriate measurement of magnification can be formally correct but yield a meaningless number. For instance, using a magnifying glass of 5 cm focal length, held 20 cm from the eye and 5 cm from the object, produces a virtual image at infinity of infinite linear size: M = ∞. But the angular magnification is 5, meaning that the object appears 5 times larger to the eye than without the lens. When taking a picture of the moon using a camera with a 50 mm lens, one is not concerned with the linear magnification M ≈ −50 mm / 380000 km = −1.3×10. Rather, the plate scale of the camera is about 1°/mm, from which one can conclude that the 0.5 mm image on the film corresponds to an angular size of the moon seen from earth of about 0.5°.
In the extreme case where an object is an infinite distance away, S1 = ∞, S2 = f and M = −f/∞ = 0, indicating that the object would be imaged to a single point in the focal plane. In fact, the diameter of the projected spot is not actually zero, since diffraction places a lower limit on the size of the point spread function. This is called the diffraction limit.
Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.
Aberrations[edit]
Optical aberration
Defocus
Tilt
Spherical aberration
Astigmatism
Coma
Distortion
Petzval field curvature
Chromatic aberration
vte
Main article: Optical aberration
Lenses do not form perfect images, and a lens always introduces some degree of distortion or aberration that makes the image an imperfect replica of the object. Careful design of the lens system for a particular application minimizes the aberration. Several types of aberration affect image quality, including spherical aberration, coma, and chromatic aberration.
Spherical aberration[edit]
Main article: Spherical aberration
Spherical aberration occurs because spherical surfaces are not the ideal shape for a lens, but are by far the simplest shape to which glass can be ground and polished, and so are often used. Spherical aberration causes beams parallel to, but distant from, the lens axis to be focused in a slightly different place than beams close to the axis. This manifests itself as a blurring of the image. Spherical aberration can be minimised with normal lens shapes by carefully choosing the surface curvatures for a particular application. For instance, a plano-convex lens, which is used to focus a collimated beam, produces a sharper focal spot when used with the convex side towards the beam source.
Coma[edit]
Main article: Coma (optics)
Coma, or comatic aberration, derives its name from the comet-like appearance of the aberrated image. Coma occurs when an object off the optical axis of the lens is imaged, where rays pass through the lens at an angle to the axis θ. Rays that pass through the centre of a lens of focal length f are focused at a point with distance f tan θ from the axis. Rays passing through the outer margins of the lens are focused at different points, either further from the axis (positive coma) or closer to the axis (negative coma). In general, a bundle of parallel rays passing through the lens at a fixed distance from the centre of the lens are focused to a ring-shaped image in the focal plane, known as a comatic circle. The sum of all these circles results in a V-shaped or comet-like flare. As with spherical aberration, coma can be minimised (and in some cases eliminated) by choosing the curvature of the two lens surfaces to match the application. Lenses in which both spherical aberration and coma are minimised are called bestform lenses.
Chromatic aberration[edit]
Main article: Chromatic aberration
Chromatic aberration is caused by the dispersion of the lens material—the variation of its refractive index, n, with the wavelength of light. Since, from the formulae above, f is dependent upon n, it follows that light of different wavelengths is focused to different positions. Chromatic aberration of a lens is seen as fringes of colour around the image. It can be minimised by using an achromatic doublet (or achromat) in which two materials with differing dispersion are bonded together to form a single lens. This reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not produce perfect correction. The use of achromats was an important step in the development of the optical microscope. An apochromat is a lens or lens system with even better chromatic aberration correction, combined with improved spherical aberration correction. Apochromats are much more expensive than achromats.
Different lens materials may also be used to minimise chromatic aberration, such as specialised coatings or lenses made from the crystal fluorite. This naturally occurring substance has the highest known Abbe number, indicating that the material has low dispersion.
Other types of aberration[edit]
Other kinds of aberration include field curvature, barrel and pincushion distortion, and astigmatism.
Aperture diffraction[edit]
Even if a lens is designed to minimize or eliminate the aberrations described above, the image quality is still limited by the diffraction of light passing through the lens' finite aperture. A diffraction-limited lens is one in which aberrations have been reduced to the point where the image quality is primarily limited by diffraction under the design conditions.
Compound lenses [edit]
See also: Photographic lens, Doublet (lens), Triplet lens, and Achromatic lens
Simple lenses are subject to the optical aberrations discussed above. In many cases these aberrations can be compensated for to a great extent by using a combination of simple lenses with complementary aberrations. A compound lens is a collection of simple lenses of different shapes and made of materials of different refractive indices, arranged one after the other with a common axis.
The simplest case is where lenses are placed in contact: if the lenses of focal lengths f1 and f2 are "thin", the combined focal length f of the lenses is given by
1
f
=
1
f
1
+
1
f
2
.
{\displaystyle {\frac {1}{f}}={\frac {1}{f_{1}}}+{\frac {1}{f_{2}}}\,.}
Since 1/f is the power of a lens, it can be seen that the powers of thin lenses in contact are additive.
If two thin lenses are separated in air by some distance d, the focal length for the combined system is given by
1
f
=
1
f
1
+
1
f
2
−
d
f
1
f
2
.
{\displaystyle {\frac {1}{f}}={\frac {1}{f_{1}}}+{\frac {1}{f_{2}}}-{\frac {d}{f_{1}f_{2}}}\,.}
The distance from the front focal point of the combined lenses to the first lens is called the front focal length (FFL):
FFL
=
f
1
(
f
2
−
d
)
(
f
1
+
f
2
)
−
d
,
.
{\displaystyle {\text{FFL}}={\frac {f_{1}(f_{2}-d)}{(f_{1}+f_{2})-d}},.}
Similarly, the distance from the second lens to the rear focal point of the combined system is the back focal length (BFL):
BFL
=
f
2
(
d
−
f
1
)
d
−
(
f
1
+
f
2
)
.
{\displaystyle {\text{BFL}}={\frac {f_{2}(d-f_{1})}{d-(f_{1}+f_{2})}}\,.}
As d tends to zero, the focal lengths tend to the value of f given for thin lenses in contact.
If the separation distance is equal to the sum of the focal lengths (d = f1 + f2), the FFL and BFL are infinite. This corresponds to a pair of lenses that transform a parallel (collimated) beam into another collimated beam. This type of system is called an afocal system, since it produces no net convergence or divergence of the beam. Two lenses at this separation form the simplest type of optical telescope. Although the system does not alter the divergence of a collimated beam, it does alter the width of the beam. The magnification of such a telescope is given by
M
=
−
f
2
f
1
,
{\displaystyle M=-{\frac {f_{2}}{f_{1}}}\,,}
which is the ratio of the output beam width to the input beam width. Note the sign convention: a telescope with two convex lenses (f1 > 0, f2 > 0) produces a negative magnification, indicating an inverted image. A convex plus a concave lens (f1 > 0 > f2) produces a positive magnification and the image is upright. For further information on simple optical telescopes, see Refracting telescope § Refracting telescope designs.
Non spherical types[edit]
An aspheric biconvex lens.
Cylindrical lenses have curvature along only one axis. They are used to focus light into a line, or to convert the elliptical light from a laser diode into a round beam. They are also used in motion picture anamorphic lenses.
Aspheric lenses have at least one surface that is neither spherical nor cylindrical. The more complicated shapes allow such lenses to form images with less aberration than standard simple lenses, but they are more difficult and expensive to produce. These were formerly complex to make and often extremely expensive, but advances in technology have greatly reduced the manufacturing cost for such lenses.
Close-up view of a flat Fresnel lens.
A Fresnel lens has its optical surface broken up into narrow rings, allowing the lens to be much thinner and lighter than conventional lenses. Durable Fresnel lenses can be molded from plastic and are inexpensive.
Lenticular lenses are arrays of microlenses that are used in lenticular printing to make images that have an illusion of depth or that change when viewed from different angles.
Bifocal lens has two or more, or a graduated, focal lengths ground into the lens.
A gradient index lens has flat optical surfaces, but has a radial or axial variation in index of refraction that causes light passing through the lens to be focused.
An axicon has a conical optical surface. It images a point source into a line along the optic axis, or transforms a laser beam into a ring.
Diffractive optical elements can function as lenses.
Superlenses are made from negative index metamaterials and claim to produce images at spatial resolutions exceeding the diffraction limit. The first superlenses were made in 2004 using such a metamaterial for microwaves. Improved versions have been made by other researchers. As of 2014 the superlens has not yet been demonstrated at visible or near-infrared wavelengths.
A prototype flat ultrathin lens, with no curvature has been developed.
Uses[edit]
A watch with a plano-convex lens over the date indicator
A single convex lens mounted in a frame with a handle or stand is a magnifying glass.
Lenses are used as prosthetics for the correction of refractive errors such as myopia, hypermetropia, presbyopia, and astigmatism. (See corrective lens, contact lens, eyeglasses, intraocular lens.) Most lenses used for other purposes have strict axial symmetry; eyeglass lenses are only approximately symmetric. They are usually shaped to fit in a roughly oval, not circular, frame; the optical centres are placed over the eyeballs; their curvature may not be axially symmetric to correct for astigmatism. Sunglasses' lenses are designed to attenuate light; sunglass lenses that also correct visual impairments can be custom made.
Other uses are in imaging systems such as monoculars, binoculars, telescopes, microscopes, cameras and projectors. Some of these instruments produce a virtual image when applied to the human eye; others produce a real image that can be captured on photographic film or an optical sensor, or can be viewed on a screen. In these devices lenses are sometimes paired up with curved mirrors to make a catadioptric system where the lens's spherical aberration corrects the opposite aberration in the mirror (such as Schmidt and meniscus correctors).
Convex lenses produce an image of an object at infinity at their focus; if the sun is imaged, much of the visible and infrared light incident on the lens is concentrated into the small image. A large lens creates enough intensity to burn a flammable object at the focal point. Since ignition can be achieved even with a poorly made lens, lenses have been used as burning-glasses for at least 2400 years. A modern application is the use of relatively large lenses to concentrate solar energy on relatively small photovoltaic cells, harvesting more energy without the need to use larger and more expensive cells.
Radio astronomy and radar systems often use dielectric lenses, commonly called a lens antenna to refract electromagnetic radiation into a collector antenna.
Lenses can become scratched and abraded. Abrasion-resistant coatings are available to help control this.
See also[edit]
Anti-fogging treatment of optical surfaces
Back focal plane
Bokeh
Cardinal point (optics)
Caustic (optics)
Eyepiece
F-number
Gravitational lens
Lens (anatomy)
List of lens designs
Numerical aperture
Optical coatings
Optical lens design
Photochromic lens
Prism (optics)
Ray tracing
Ray transfer matrix analysis
Notes[edit]
^ The variant spelling lense is sometimes seen. While it is listed as an alternative spelling in some dictionaries, most mainstream dictionaries do not list it as acceptable.
Brians, Paul (2003). Common Errors in English. Franklin, Beedle & Associates. p. 125. ISBN 978-1-887902-89-2. Retrieved 28 June 2009. Reports "lense" as listed in some dictionaries, but not generally considered acceptable.
Merriam-Webster's Medical Dictionary. Merriam-Webster. 1995. p. 368. ISBN 978-0-87779-914-6. Lists "lense" as an acceptable alternate spelling.
"Lens or Lense – Which is Correct?". writingexplained.org. 30 April 2017. Analyses the almost negligible frequency of use and concludes that the misspelling is a result of a wrong singularisation of the plural (lenses). | biology | 96851 | https://sv.wikipedia.org/wiki/Objektiv | Objektiv | Ett objektiv är en optisk lins eller sammansättning av linser som används i en kamera för att skapa bilder av objekt, antingen på fotografisk film eller på andra medier som kan lagra en bild kemiskt eller elektroniskt. Ljusmängden som når det ljuskänsliga mediet bestäms genom en kombination av exponeringstid och bländaröppning. Hur mycket ljus som erfordras för att avbilda objektet bestäms av mediets känslighet och ljusförhållandet vid objektet.
Det är ingen avgörande skillnad i principen för ett objektiv som används i en stillbildskamera, en videokamera, ett teleskop, mikroskop, eller annan utrustning, men detaljutformningen och konstruktionen är olika. Ett objektiv kan vara fast monterat på en kamera, eller det kan vara utbytbart med andra objektiv av olika brännvidder, ljusstyrkor och andra egenskaper. Några av de vanliga typerna av kameralinser inkluderar ultravidvinkelobjektiv, vidvinkelobjektiv, objektiv med en fast brännvidd ("prime lens"), objektiv med manuell eller automatisk fokusering etc.
Allmänt
Ett objektiv kan vara fast vid kamerahuset eller utbytbart (som i en systemkamera). Vanligtvis finns en fokuseringsmekanism samt en mekanism för att välja bländarvärde som reglerar hur mycket ljus som ska släppas in genom objektivet. Beroende på kameratyp kan det också finnas en integrerad slutare.
De allra flesta objektiv idag är försedda med antireflexbehandling till exempel av typ multicoating. Det är i princip ett mycket tunt metalloxidskikt som ångas på objektivets yta. Tjockleken skall vara en kvarts ljusvåglängd och ljusreflexen släcks ut genom interferens. Första lagret gör bäst verkan, men fabrikanterna har tävlat med varandra och lagt på upp till sju lager. Ett äldre objektiv med endast ett lager antireflexbehandling bör inte automatiskt dömas ut, andra egenskaper är viktigare.
Ett annat problem som den som har en systemkamera råkar ut för är att objektiven har en viss filterverkan. De stora tillverkarna försöker hålla samma färggång i sina objektivserier men den som använder piratobjektiv brukar märka en viss skillnad. Objektivets färgningstendens justeras med olika glaskombinationer och antireflexskikt på linsytorna. Ett objektivs upplösning är optimerat för negativ/sensorformatet – det betyder att tillverkaren försöker att få så bra data som möjligt inom respektive format. En tumregel är emellertid att bildens kvalitet ökar med negativ/sensorstorleken. Objektivets slipning och polering är en viktig faktor, men glasämnets kvalitet är utslagsgivande för ett objektivs kvalité.
Glasämnet som skall användas för optiska ändamål bör svalna långsamt vid tillverkningsprocessen. Då kan mikroskopiska luftbubblor ta sig ut ur glasmassan medan den ännu är het och mjuk. Speciellt tysk kvalitetsoptik var fordom känd för en bra glassammansättning.
Skärpa / kontrast
Det som normalt uppfattas som skärpa i ett objektiv består i själva verket av en kombination av upplösning och kontrast, det vill säga gradienten och skillnaden i ljusstyrka mellan det mörkaste och det ljusaste i motivet.
Ett objektivs upplösning mäts i linjepar per millimeter och brukar ligga kring 80 som bäst men ligger närmare 60 för de bästa kommersiella DSLR-objektiven. Moderna bildsensorer med en upplösning över 36 MP (megapixel) har pixelstorlekar under 5 microns. Detta kan jämföras med en upplösning av 100 linjepar per millimeter. Den snabba utvecklingen av bildsensorer driver därför fram en ny generation av kameraobjektiv med högre upplösning och med image stabilizer eller bildstabilisering, också kallat vibration reduction eller vibrationsreduktion, inbyggd i objektivet. Ett objektiv med inbyggd bildstabilisering är av speciell vikt för handhållen fotografering och för fotografering med objektiv av långa fokallängder och kort skärpedjup (= stora bländare) där även den minsta rörelse eller vibration av kameran resulterar i synlig oskärpa i den slutliga bilden.
Den vetenskapliga metoden att mäta ett objektivs kontrast är i kontrastöverföringen, varför fotohandeln tillhandahåller särskilda testkartor som fotografen kan använda sig av för att få en uppfattning om kvaliteten på ett objektiv.
Objektiv med fasta fokallängder mellan 50 och 100 mm uppnår normalt högre upplösning och kontrast än mer extrema objektiv som teleobjektiv eller vidvinkelobjektiv. Objektiv med fasta fokallängder producerar också som regel märkbart högre upplösning och kontrast än mer komplicerade zoom-objektiv.
Vissa linser i ett objektiv kan vara arrangerade som en grupp och agerar då som ett integrerat optiskt element genom att de individuella linserna i gruppen är limmade till varandra utan mellanrum och utan luft mellan linserna. En grupp linser sätts på detta sätt samman med ett kitt eller lim. Man brukade använda kanadabalsam, som har samma brytningsindex som objektivglas, men på grund av dess bristande motståndskraft mot temperaturförändringar och nedbrytning används numera framför allt UV-bestrålade epoxilim för att sammanfoga linser till grupper.
För att lättare kunna relatera upplösningsförmågan av ett objektiv till den av en kameras bildsensor så har testföretaget DxO Labs infört begreppet P-MP vilket står för Perceptual Mega Pixel. P-MP representerar en översättning från det endimensionella begreppet linjepar per millimeter till en tvådimensionell betraktelse liknande MP eller megapixel för en bildsensor.
Ett objektivs upplösningsförmåga uttryckt i P-MP är då direkt jämförbart med en bildsensors upplösning uttryckt i MP. Genom att veta objektivets P-MP och bildsensorns MP kan man då lätt avgöra vad som kommer att begränsa en kameras bildkvalitet och till vilken grad. Inom optik gäller att den "svagaste länken" avgör den slutliga bildkvaliteten. Med dagens högupplösta bildsensorer är det som regel objektivet som utgör denna begränsning. Har man ett objektiv vars P-MP påtagligt underskrider bildsensorns MP så blir den slutliga bildens upplösning i stort sett samma som objektivets, och når alltså aldrig bildsensorn potentiella upplösning. Har man å andra sidan ett objektiv vars upplösning uttryckt i P-MP matchar bildsensorns upplösning uttryckt i MP så kan man i korthet säga att objektivets upplösning och skärpa matchar och ger full utdelning av bildsensorns förmåga till upplösning och detaljrikedom.
Objektivets ljusstyrka
Den största bländaröppningen för ett objektiv kallas dess bländartal (F-tal). Ju lägre tal desto mer ljus släpps in genom objektivet – desto mer ljusstarkt är det. På objektiv för SLR-kameror finns det vanligtvis en automatiskt mekanism som håller bländaren vidöppen under fokusering, men sluter till det inställda värdet då bilden tas. Denna mekanism är mycket användbar på ljusstarka objektiv, medan långa teleobjektiv som har låg ljusstyrka, är nästan lika praktiska när de är helt manuella.
Ursprunget till måttet är helt enkelt förhållandet mellan objektivets brännvidd och bländarens fysiska diameter. Detta innebär att ett 50 mm objektiv med en maximal bländaröppning av 6,25 mm har ett bländartal som är 50/6.25 = 8.
Eftersom bländartalet är ett rent geometriskt tal så påverkas det inte av ett objektivs ljustransmission vilket uttrycks som ett T-tal. Skall man noggrant jämföra två olika objektivs ljusstyrka så ger F-talet eller bländartalet endast en approximativ jämförelse medan transmissionstalet, eller T-talet är kompenserat för verklig ljustransmission och ger en noggrannare jämförelse. Den huvudsakliga orsaken till skillnader i T-tal mellan objektiv med samma F-tal är antalet linser i objektivet, glaskvaliteten i linserna och kvaliteten av antireflexbeläggningar på objektivets individuella linser.
Brännvidd
Den viktigaste egenskapen förutom bländartalet är brännvidden, som vanligtvis anges i millimeter (centimeter fram till omkring 1960), och som placerar objektivet i någon av följande kategorier:
Normalobjektiv
Vidvinkelobjektiv
Teleobjektiv
Zoomobjektiv
Beroende på om objektivet har en variabel eller fast brännvidd, kategoriseras det som antingen ett zoomobjektiv eller ett objektiv med fast brännvidd. Zoomobjektiv kan delas upp i:
vidvinkelzoom
normalzoom
telezoom
Superzoom kallas ibland ett objektiv som spänner över flera zoner av ovanstående.
Zoomfaktor 1x
I specifikationerna för systemkameror (det vill säga kameror med utbytbart objektiv) anges ofta den optiska zoomfaktorn till 1 gång (1×). Detta beror på att kameran (kamerahuset) i sig inte avgör zoomomfånget utan denna beror i stället på vilket objektiv som används. För objektiv med fast brännvidd är zoomfaktorn 1×.
Specialoptik och specialfotografering
Makro
Ett makroobjektiv är ett objektiv som är avsett för extrema närbilder. Makroområdet brukar räknas från en avbildningsskala på sensorn/negativet från 1:1 (naturlig storlek) till förstoring 10:1. Större avbildningsskala brukar räknas som mikrofotografering.
Som alternativ till ett makroobjektiv kan man använda en förlängningslins (extender) som fästs mellan objektivet och kamerahuset eller närbildslins (försättslins) som skruvas i objektivets filtergänga. Båda förlänger objektivets brännvidd. Ett annat alternativ är mellanringar – enkla rör utan linser, med eller utan elektrisk koppling för objektivets automatik – som monteras på samma sätt som en förlängningslins. Mellanringarna säljs oftast i set om tre, med olika bredd, som kan användas i olika kombinationer. Mellanringarna minskar objektivets närgräns med större avbildningsskala som följd. Objektivet går då inte längre att fokusera på oändligt avstånd.
Brännvidden på ett makroobjektiv brukar motsvara ett normalobjektiv, ibland längre. Fördelen med längre brännvidd är att man kan fotografera på längre avstånd från objektet, till exempel skygga insekter. Med längre brännvidd blir också skärpezonen kortare och motivet framhävs.
Med mellanringar blir det ett - beroende på mellanringens bredd - kraftigt ljusbortfall. Detta motverkas med blixt. Vid större avbildningsskala är en ringblixt att föredra, eftersom kombinationen objektiv och mellanringar kan komma att skugga blixtljuset. Med försättslins blir det inget ljusbortfall, å andra sidan ökar oskärpan i kanterna.
Perspektivkorrektion
Dessa objektiv måste teckna en bild som är avsevärt större än sensor- eller filmformatet, dels för att undvika kraftig vinjettering och andra avbildningsfel, dels för att bilden inte ska helt försvinna mot kanten. Vanligt är att man måste blända ner objektivet ett par steg, samt om möjligt undvika de yttersta lägena för förskjutning/vinkling – då ligger man nämligen nära gränsen för det område där objektivet tecknar skarpt.
Tilt- och shiftdelen av objektivet går att rotera kring den optiska axeln, så man kan få den önskade effekten oavsett hur kameran är positionerad i förhållande till motivet.
Shift
Shift är att förskjuta objektivet i höjd- och/eller sidled utan att vinkla det i förhållande till kamerahuset.
Vanligt användningsområde är fotografering av arkitektur. Om man tar bild på en hög byggnad rakt framifrån, kan man ofta inte backa tillräckligt långt tillbaka, utan måste luta kameran uppåt för att få med hela motivet. Då faller perspektivet drastiskt och byggnaden synes smalna av kraftigt uppåt. Detta motverkas genom att man ställer kameran horisontellt och höjer objektivet parallellt uppåt. Det gör vertikala linjer raka även på bilden.
Motsvarande gäller naturligtvis om man vill ha med hela framsidan och inte står mitt framför huset.
Tilt
Tilt kallas det när objektivet vinklas i förhållande till kamerahuset (fokalplanet). Detta förändrar hur skärpeplanet ligger över motivet (enligt Scheimpflugs princip).
Den omedelbara effekten är att man kan till exempel fotografera nära marken mitt på en fotbollsplan och få skärpa i gräset hela vägen till målet. Observera att skärpeplanet då ligger i stort sett längs marken, och eventuella spelare i förgrunden tappar i skärpa upp mot huvudet.
Tilt-and-Shift
Det finns även objektiv med möjlighet till både förskjutning och vinkling, samt vissa där det går att göra helt oberoende av varandra.
En storformats studiokamera av typ balkkamera behöver inga speciella objektiv för tilt-and-shift. På grund av konstruktionen av typ optisk bänk, kan man med alla objektiv vinkla och/eller förskjuta helt fritt, eftersom både bakstycket (filmkassetten) och objektivet åker på en släde med en bälg mellan varandra.
Fisheye
Fisheyeobjektiv är vidvinklar med extremt kort brännvidd. Bildvinkeln är upp till 180° – och ännu mer – mot 90° för ett 21 mm-objektiv för 35 mm film.
Avbildningsfelet koma är i stort sett eliminerat (jämför andra vidvinklar). Motljusskydd är sällan relevant och filter svåra att anbringa – objektivets frontlins buktar ofta ut långt framför metallhöljet. Eventuella filter anbringas i stället i en särskild hållare bakom objektivet.
Med vissa fisheyeobjektiv tecknas inte sensor-/filmformatet fullt ut, utan bilden blir en cirkel mitt på en i övrigt helt svart ruta, medan andra tecknar formatet fullt ut, och den diagonala bildvinkeln är 180°.
Vinjettering (se nedan), närmast bildens yttre kanter, är tydlig och något att räkna med.
Spegeltele
För att förkorta den fysiska längden på ett extremt teleobjektiv konstruerade flera stora japanska tillverkare sådana objektiv på samma sätt som ett spegelteleskop. I dessa reflekteras det inkommande ljuset två gånger inne i objektivet via två speglar. Därmed kunde den fysiska längden bringas ner till hälften av brännvidden och till och med något mer. Detta sker dock på bekostnad av objektivets yttre diameter. Spegelobjektiv blir mycket lättare än motsvarande brännvidd i ett konventionellt objektiv. Dessutom är sfärisk aberration nästan eliminerad i dessa s.k. katadioptriska system.
I ett spegeltele är sekundärspegeln (den främre) fastsatt vid ljusets ingångsöppning och syns utifrån som en rund platta mitt i frontlinsen. Primärspegeln (den bakre) är fastsatt längre in i strålgången och är ringformad. Primärspegeln, där ljuset infaller först, är oftast konkav, medan sekundärspegeln oftast är konvex.
Ett spegeltele har vissa egenheter – till exempel är det krångligt att blända ner, i stället har man gråfilter i strålgången bakom objektivet. Likaså syns vid bokeh ringartade oskärpemönster (typ "stekta lökringar") i stället för ifyllda cirklar, m m. Konstruktionen är numera inte så vanlig.
Soft-fokus
Optiken i äldre billiga kameror tecknade inte helt skarpt och var därför lite "förlåtande" vid porträttfotografering. För att åstadkomma motsvarande effekt med dagens moderna objektiv finns särskilda softfokusobjektiv. På objektivets fullt skarpa bild kan man med dessa softfokusobjektiv överlagra en bild som inte är helt i fokus. Ibland kan man välja grad av oskärpa i bilden. Andra sätt är att låta fotografen välja graden av kromatiskt aberration (se dito) i bilden, eller att i stället för bländare ha inläggsskivor med centralt större hål som bländare omgivet av mindre hål cirkulärt runt det – detta ger flera bilder överlagrade på varandra.
Dessutom finns speciella filterliknande försättslinser som ger en viss ljusspridning.
En enkel och billig lösning, som ger en liknande effekt, är att helt enkelt smeta lite vaselin på ett UV/Haze/Skylight-filter.
Softfokusoptik används särskilt för porträttfotografering och är typiskt korta teleobjektiv, cirka 85–135 mm. Normalobjektiv (50 mm) förekommer också.
Objektivets avbildningsfel
De flesta optiska aberrationer ökar ju längre man kommer bort från den optiska axeln. Därmed får man sämre skärpa i bildens kanter och framför allt hörn.
Avbildningsfel i objektiv är naturligtvis allt som avviker från en teoretisk perfekt avbildning. Avbildningsfelen kan delas in i brytningsfel och övriga avbildningsfel. Brytningsfelen är sfärisk och kromatisk aberration, astigmatism, koma och distorsion. Avbildningsfelen är i huvudsak av följande typer:
Sfärisk aberration
Kromatisk aberration
Astigmatism
Koma
Distorsion
Vinjettering
Överstrålning
Diffraktion
Avbildningsfel vid bokeh (fokal oskärpa)
Reflexer i linselement
Sfärisk aberration
Sfärisk aberration innebär att ljus utanför objektivets (eller spegelns för spegeloptik) optiska axel bryts i en fokalpunkt framför filmplanet – ju längre bort från axeln, desto större fel. För att korrigera för detta kan en spegel göras parabolisk. Ett objektivs glas släpper igenom ljus och här kan den sfäriska aberrationen korrigeras på flera sätt, dels genom motverkande linselement i strålgången, dels genom asfäriska linselement, vilket är den exklusivaste och dyraste metoden.
Kromatisk aberration
Kromatisk aberration har inte enbart med färgfotografering att göra utan påverkar negativt kvaliteten likaväl på svartvit fotografering. Skälet är att tillverkningsmaterialet (glas/plaster) i linser har olika brytningsindex för olika färger.
Objektiv kallas akromatiska om de är färgkorrigerade i två grundfärger, exempelvis blått och grönt. Ställs det mycket höga krav på objektiv, finns apokromatiska som är korrigerade i tre grundfärger. I båda fallen har tillverkare försett objektivet med linsgrupper av olika glassorter. Man talar om kronglas- och flintglastyper.
Reprofotograferingsobjektiv är i regel apokromater som skall visa särskilt god planhållning, det är objektivets förmåga att hålla brännpunkten över hela film- respektive sensorplanet, även kallat skärpeplanet eller fokalplanet.
De flesta objektiv är sedan länge färgkorrigerade akromater.
Astigmatism
När optiken har olika fokusplan i olika plan eller riktningar, t.ex. vertikal och horisontell riktning, kallas detta för astigmatism. Astigmatisk återgivning är med nya tillverkningsmetoder och nya glasmaterial och kombinationer inget problem i dagens objektiv, men tidigare angavs ibland för objektiven att de var "anastigmatiska", det vill säga inte hade detta optiska fel.
Koma
Koma är ett avbildningsfel där ljusstrålar som ligger utanför den optiska axeln sprids och avbildas som en kometsvans (latin: ’’koma’’ = svans). Effekten kan minskas genom att blända ner.
Distorsion
När raka linjer tecknas av optiken som böjda kallas det för distorsion (alternativt distortion). Man skiljer på följande typer:
Kuddformig distorsion är när en rak linje är i mitten böjd mot in mot den optiska axeln. En rät rektangel tecknas som en lätt inbuktad kudde; därav namnet.
Tunnformig distorsion är när en rät linje är i mitten böjd bort från den optiska axeln. En rektangel tecknas som en tunna med lock och botten buktande utåt.
Vågformig distorsion är ett kompromissförsök att minska synintrycket av distorsion genom en optikkonstruktion, där raka linjer omväxlande böjer än åt det ena och än åt det andra hållet som en ganska platt sinuskurva (se figur). Vid stor våglängd och låg amplitud blir effekten en nästan rak linje.
För ett extremt vidvinkelzoomobjektiv kan distorsionen växla vid zoomning; t.ex. tunnformig distorsion vid kortaste brännvidden stegvis övergående via distorsionsfri avbildning till kuddformig distorsion vid längsta brännvidden.
Även andra motivdetaljer än raka linjer påverkas av distorsion, men den syns mindre tydligt där.
Vinjettering
Mot kanterna av bildplanet (filmen eller sensorn) sprids ett ljusknippe av given storlek ut över en större area än om samma knippe faller nära den optiska axeln. På ett icke-korrigerat objektiv resulterar detta i att kanterna av bilden blir mörkare än mitten. Detta fenomen kallas för vinjettering.
Överstrålning
Även för ett utmärkt objektiv, faller normalt dess kontrastöverföring (skärpa) i hörnen. Detta märks främst på att gränsen mellan en mörk och en ljus area blir alltmer diffus – lite ljus liksom sprids över på det mörkare. Man säger att objektivet förlorar randskärpa utåt från den optiska axeln.
Denna randskärpa ska inte förväxlas med den typ av randkontrast, som åstadkoms vid framkallning av svartvita bilder på fotopapper. Då kan man låta pappret ligga still i framkallaren efter att initialt rört som vanligt. Framkallare förbrukas snabbare och i större omfattning av mörka partier. Vid randen mellan tydligt mörka och ljusa partier vandrar oförbrukad framkallare över från ljusa partier en liten bit in i mörka, medan förbrukad vandrar från mörkt till ljust. Detta skapar en mikroskopisk spalt av extra mörkt i randen av det mörka partiet och extra ljust i det ljusa partiet. De mycket smala spalterna uppfattas inte av ögat annat än att bilden verkar skarpare.
Överstrålning beror inte enbart av objektivet, utan även av det medium man avbildar på – film eller sensor.
Analog fotografi
Det här fenomenet är tydligt vid traditionell fotografi med film. Ljuset passerar först genom det ljuskänsliga gelatinskiktet och reflekteras försvagat från filmbasen (acetat, eller förr celluloid), med utfallsvinkel samma som infallsvinkeln, och belyser gelatinet en gång till fast förskjutet ut mot kanterna. Därefter kommer en svagare sekundär reflex från filmbasens baksida… Detta problem växer med avståndet till den optiska axeln bl a på grund av den flackare vinkeln – reflexerna kommer längre bort från idealpunkten.
Digital fotografi
Även digitalkamerans sensorer har liknande problem, men av annat skäl. Sensorn är uppbyggd av små linselement (ungefär: pixlar), vilka inte har nollstorlek. Ju längre ut från optiska axeln, desto snedare faller ljuset mot den mikroskopiska linsen som inte förmår att bryta den rakt inåt mot den ideala punkten, utan lite snett utåt från den optiska axeln. Med Leica M9 har man försökt motverka detta med att inte ha linserna likformigt och ekvidistant utspridda över sensorn, utan alltmer skjuvade mot optiska axeln, ju längre från axeln de ligger. Detta ger en lokal shift-effekt.
Diffraktion
Ett objektivs skärpa når nästan alltid sin högsta punkt mellan bländare 8–11, sedan faller skärpan igen beroende på s.k. kniveggsdiffraktion i bländaren. Diffraktion bildas naturligtvis alltid vid bländaröppningens kant, men med allt mindre bländaröppning ökar andelen diffrakterat ljus i den totala ljusmängden som passerar igenom.
Diffraktion, samt viss vinjettering och koma, är i princip de enda avbildningsfel som förekommer i en hålkamera.
Diffraktionen beror på ljusets fysiska natur som vågrörelse, och enda sättet att minska diffraktionen är att öka bländaröppningen. Ett objektiv som är avsett att ge högsta möjliga skärpa, som t.ex. objektivet i ett teleskop, brukar konstrueras så att diffraktionen är den dominerande orsaken till oskärpan. Ett sådant objektiv kallas för diffraktionsbegränsat, och ju större ett diffraktionsbegränsat objektiv är, desto skarpare bilder ger det. Diffraktionsbegränsade objektiv brukar ha mycket små synfält (ett par grader eller t.o.m. mindre) där skärpan är optimal.
Bokeh
Bokeh definieras som "det sätt som optiken återger objekt som inte ligger i fokus".
Bokeh uppträder främst med tele- eller makrooptik samt vid stor bländare i övrig optik – i alla dessa fall har objektivet kort skärpedjup. Ljuspunkter bortom fokus i bakgrunden framträder inte som runda, utan har formen av objektivets bländaröppning. Detta kan motverkas vid tillverkningen genom att bländarkonstruktionen görs så, att bländaröppningen blir så rund som möjligt. Oskarpa punkter i bakgrunden kan också verka rotera kring den optiska axeln. Runda punkter blir då ovala och krökta radiellt kring optiska axeln.
Reflexer i linselement
Starka ljuskällor, till exempel direkt solljus som infaller rakt in i objektivet, skapar reflexer inne bland objektivets linselement. Dessa störningar uppträder vanligen som spökbilder (över själva motivet) av objektivets bländaröppning i varierande storlek. Denna typ kallas linsöverstrålning eller flare på engelska.
Likaså kan ljus som infaller snett mot en del av frontlinsen ge slöjbildning. Det visar sig som om en ytterst tunn gråvit slöja låg över en del av motivet.
Dessa båda fenomen motverkas med antireflexbehandling och motljusskydd.
Objektivets anpassning till enögda spegelreflexkameror
Spegelreflexkameran har en spegel som fälls undan (senast) när fotografen tar bilden. Denna spegelrörelse kräver ett visst utrymme. Objektivkonstruktörerna måste förse bakre delen på objektivet med en korrigerande linsgrupp som förkortar konstruktionen bakåt, så att spegeln inte slår i bakersta linsen. Normal- och vidvinkelobjektiv för spegelreflex konstrueras därför som omvända teleobjektiv, även kallade retrofokusobjektiv.
Liknande problematik finns även för mätsökarkameror med ljusmätning i strålgången, samt att vid extrem vidvinkel kan till och med en eventuell ridåslutare komma åt ett icke-retrofokusobjektiv.
Antal linser
Ju större ljusstyrka respektive ju kortare brännvidd ett objektiv har, desto fler linser innehåller objektivet. Orsaken är att ljuset i strålgången nästan faller parallellt med den optiska axeln vid långa brännvidder, och objektivet kan då klara sig med endast två linser (refraktor). I andra extremfallet, när man har ett supervidvinkelobjektiv som vinklar till och med bakåt i 220° bildvinkel, utsätts ljusstrålarna som ligger långt utanför den optiska axeln för kraftiga aberrationer. Det kan krävas många linser för att korrigera dessa fel; vidvinkelobjektiv kan ha upp till ett tjugotal linser. Således är linsbehovet i stort omvänt proportionellt mot brännvidden.
Klassiska objektiv
Några nämnvärda objektivkonstruktioner:
Cooke Triplet
Elmar
Tessar
Sonnar
Planar
Angénieux retrofokus
Källor
LIFE Library of Photography:
The Camera
Light and Film
Color
Noter och referenser
Se även
Bländare
Slutare
Makroobjektiv
Fotografiska filter
Optik
Utbytbar optik
Fotografi | swedish | 0.453623 |
stars_disappear_when_look/Cone_cell.txt |
Cone cells or cones are photoreceptor cells in the retinas of vertebrates' eyes. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cones function best in relatively bright light, called the photopic region, as opposed to rod cells, which work better in dim light, or the scotopic region. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. Conversely, they are absent from the optic disc, contributing to the blind spot. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration being towards the macula.
Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer detail and more rapid changes in images because their response times to stimuli are faster than those of rods. Cones are normally one of three types: S-cones, M-cones and L-cones. Each type expresses a different opsin: OPN1SW, OPN1MW, and OPN1LW, respectively. These cones are sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and longer-wavelength light respectively. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, humans have trichromatic vision. Being color blind can change this, and there have been some verified reports of people with four types of cones, giving them tetrachromatic vision.
The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation; different individuals will have cones with different color sensitivity.
Structure[edit]
Types[edit]
Humans normally have three types of cones, usually designated L, M and S for long, medium and short wavelengths respectively. The first responds the most to light of the longer red wavelengths, peaking at about 560 nm. The majority of the human cones are of the long type. The second most common type responds the most to light of yellow to green medium-wavelength, peaking at 530 nm. M cones make up about a third of cones in the human eye. The third type responds the most to blue short-wavelength light, peaking at 420 nm, and make up only around 2% of the cones in the human retina. The three types have peak wavelengths in the range of 564–580 nm, 534–545 nm, and 420–440 nm, respectively, depending on the individual. Such a difference is caused by the different opsins they carry, OPN1LW, OPN1MW, and OPN1SW, respectively, the forms of which affect the absorption of retinaldehyde. The CIE 1931 color space is an often-used model of spectral sensitivities of the three cells of an average human.
While it has been discovered that there exists a mixed type of bipolar cells that bind to both rod and cone cells, bipolar cells still predominantly receive their input from cone cells.
Other animals might have a different number of cone types (see Color vision).
Shape and arrangement[edit]
Cone cell structure
Cone cells are somewhat shorter than rods, but wider and tapered, and are much less numerous than rods in most parts of the retina, but greatly outnumber rods in the fovea. Structurally, cone cells have a cone-like shape at one end where a pigment filters incoming light, giving them their different response curves. They are typically 40–50 µm long, and their diameter varies from 0.5 to 4.0 µm, being smallest and most tightly packed at the center of the eye at the fovea. The S cone spacing is slightly larger than the others.
Photobleaching can be used to determine cone arrangement. This is done by exposing dark-adapted retina to a certain wavelength of light that paralyzes the particular type of cone sensitive to that wavelength for up to thirty minutes from being able to dark-adapt, making it appear white in contrast to the grey dark-adapted cones when a picture of the retina is taken. The results illustrate that S cones are randomly placed and appear much less frequently than the M and L cones. The ratio of M and L cones varies greatly among different people with regular vision (e.g. values of 75.8% L with 20.0% M versus 50.6% L with 44.2% M in two male subjects).
Like rods, each cone cell has a synaptic terminal, inner and outer segments, as well as an interior nucleus and various mitochondria. The synaptic terminal forms a synapse with a neuron bipolar cell. The inner and outer segments are connected by a cilium. The inner segment contains organelles and the cell's nucleus, while the outer segment contains the light-absorbing materials.
The outer segments of cones have invaginations of their cell membranes that create stacks of membranous disks. Photopigments exist as transmembrane proteins within these disks, which provide more surface area for light to affect the pigments. In cones, these disks are attached to the outer membrane, whereas they are pinched off and exist separately in rods. Neither rods nor cones divide, but their membranous disks wear out and are worn off at the end of the outer segment, to be consumed and recycled by phagocytic cells.
Function[edit]
Bird, reptilian, and monotreme cone cells
The difference in the signals received from the three cone types allows the brain to perceive a continuous range of colors, through the opponent process of color vision. (Rod cells have a peak sensitivity at 498 nm, roughly halfway between the peak sensitivities of the S and M cones.)
All of the receptors contain the protein photopsin, with variations in its conformation causing differences in the optimum wavelengths absorbed.
The color yellow, for example, is perceived when the L cones are stimulated slightly more than the M cones, and the color red is perceived when the L cones are stimulated significantly more than the M cones. Similarly, blue and violet hues are perceived when the S receptor is stimulated more. S Cones are most sensitive to light at wavelengths around 420 nm. However, the lens and cornea of the human eye are increasingly absorptive to shorter wavelengths, and this sets the short wavelength limit of human-visible light to approximately 380 nm, which is therefore called 'ultraviolet' light. People with aphakia, a condition where the eye lacks a lens, sometimes report the ability to see into the ultraviolet range. At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.
Cones also tend to possess a significantly elevated visual acuity because each cone cell has a lone connection to the optic nerve, therefore, the cones have an easier time telling that two stimuli are isolated. Separate connectivity is established in the
inner plexiform layer so that each connection is parallel.
The response of cone cells to light is also directionally nonuniform, peaking at a direction that receives light from the center of the pupil; this effect is known as the Stiles–Crawford effect.
It is possible that S cones may play a role in the regulation of the circadian system and the secretion of melatonin but this role is not clear yet. The exact contribution of S cone activation to circadian regulation is unclear but any potential role would be secondary to the better established role of melanopsin (see also Intrinsically photosensitive retinal ganglion cell).
Color afterimage[edit]
Sensitivity to a prolonged stimulation tends to decline over time, leading to neural adaptation. An interesting effect occurs when staring at a particular color for a minute or so. Such action leads to an exhaustion of the cone cells that respond to that color – resulting in the afterimage. This vivid color aftereffect can last for a minute or more.
Associated diseases[edit]
Achromatopsia (Rod monochromacy) - a form of monochromacy with no functional cones
Blue cone monochromacy - a rare form of monochromacy with only functional S-cones
Congenital red–green color blindness - partial color blindness include protanopia, deuteranopia, etc.
Oligocone trichromacy - poor visual acuity and impairment of cone function according to ERG, but without significant color vision loss.
Bradyopsia - photopic vision cannot respond quickly to stimuli.
Bornholm eye disease - X-linked recessive myopia, astigmatism, impaired visual acuity and red-green dichromacy.
Cone dystrophy - a degenerative loss of cone cells
Retinoblastoma - a type of cancer originating from cone precursor cells
See also[edit]
Disc shedding
Double cones
RG color space
Tetrachromacy
Melanopsin
Color vision
List of distinct cell types in the adult human body | biology | 51868 | https://sv.wikipedia.org/wiki/%C3%96ga | Öga | Ett öga () är ett anatomiskt organ för att förnimma ljus. Olika typer av ljuskänsliga organ finns i nästan hela djurriket. De enklaste varianterna särskiljer bara om omgivningen är mörk eller ljus. Mer komplexa ögon används för att ge ett synsinne. Många komplexa organismer, såsom däggdjur, fåglar, reptiler och fiskar har två ögon som är placerade i samma plan och vars intryck tolkas som en enda, tredimensionell "bild", liksom hos människan. Andra djurarter, till exempel kaniner och kameleonter har ögonen i olika plan och får två separata bilder.
Ögontyper
Hos de flesta ryggradsdjur och vissa blötdjur fungerar ögat genom att projicera bilder på en ljuskänslig näthinna (retina). Signaler skickas därifrån till hjärnan via synnerven. Sådana ögon är ofta ungefär sfäriska och fyllda med en genomskinlig geleartad substans som kallas glaskropp, har en lins som fokuserar ljuset, och en iris som reglerar hur mycket ljus som kommer in i ögat.
Ögon hos bläckfiskar, fiskar, amfibiska djur och ormar har ofta en fast linsform och fokuserar blicken genom att teleskopera ögat (på samma sätt som en kamera fokuserar).
Arter som skiljer sig mycket åt kan ha väldigt olika typer av ögon, men de tenderar att likna varandra i funktion och utseende när de är fullt utvecklade. Blötdjurens ögon verkar till exempel ha utvecklats från andra organ än ryggradsdjurens ögon, och kan vara ett exempel på hur evolutionen lett till samma slutresultat. Ryggradsdjurens ögon utvecklades från hjärnceller under den embryoniska tiden, medan blötdjurens ögon växte in från hudceller. Ryggradsdjurens näthinnor har lager med neuroner framför de ljuskänsliga cellerna, medan blötdjurens näthinnor har de ljuskänsliga cellerna framför neuronerna, och har därför ingen blind fläck och möjligen skarpare syn, men också långsammare bildåterhämtning från näthinnan och därför sämre sinne för rörelser. Vissa huvudfotningar har ingen fysisk lins, utan en väldigt liten ljusöppning (ungefär som en camera obscura). Vissa blötdjur har en konkav spegel för att fokusera ljuset tillsammans med en lins.
Fasettögon finns hos leddjur, och ger en pixel-baserad bild (inte flera bilder som många tror). Varje sensor har sin egen lins och ljuskänsliga celler. Vissa ögon har upp emot 28 000 sådana sensorer, arrangerade i ett hexagonalt nät, vilket kan ge ett 360-gradigt synfält. Fasettögon är väldigt känsliga för rörelser. Vissa leddjurs fasettögon har ett fåtal fasetter var med en näthinna som kan skapa en bild, vilket ger en syn baserad på flera bilder, alla ur olika vinklar, sammansmälta till en bild med mycket hög upplösning.
Djurrikets troligen mest komplicerade ögon är fasettögonen hos stomatopoder, mantisräkor, en grupp bland kräftdjuren. Färgseendet är mycket avancerat med det största kända antalet färgreceptorer, och de kan se i 12 färgkanaler (jfr 3 hos människan), s.k. hyperspektralt seende. Varje enskilt öga har även djupseende. Vidare kan de se polariserat ljus och bedöma polarisationsplanet, och de kan också se ultraviolett och kanske infrarött ljus.
Trilobiterna, som nu är utdöda, hade unika fasettögon med genomskinliga kalk-kristaller som linser. (De flesta andra leddjur har mjuka ögon.) Antalet linser i sådana ögon varierar - vissa hade bara en, andra hade flera tusen linser per öga.
Några av de enklaste ögonen återfinns hos djur såsom sniglar, och kan inte se i den vardagliga betydelsen. De har ljuskänsliga celler, men ingen lins och inget annat sätt att projicera en bild på de cellerna. De kan särskilja mellan ljust och mörkt (dag och natt) men inte mer. Det gör att sniglar kan undvika direkt solljus.
Ögats evolutionära utveckling
Hur en så komplex struktur som ögats projicering skulle ha kunnat utvecklats av sig självt sägs ofta vara en svår fråga för evolutionsteorin. Darwin behandlade ämnet i sin Om arternas uppkomst genom att hävda att det inte var så konstigt om de mest primitiva varianterna också hade en funktion, och därefter muterade lite i taget.
Forskarna Dan-Eric Nilsson och Susanne Pelger i Lund har visat genom teoretiska beräkningar att ett primitivt optiskt sinnesorgan skulle kunna ha utvecklats till ett komplext människolikt öga på en rimlig tid (mindre än en miljon år), enbart genom små mutationer och naturliga urvalsprocesser.
Ögon i olika djurarter visar att de har anpassats till sina omgivningar. Till exempel har rovfåglar skarpare blick än människor, och vissa rovfåglar som jagar på dagen kan se ultraviolett ljus. Dessutom visar de parallella utvecklingarna av ryggradsdjursögon och blötdjursögon att det inte är konstigt att ögat har utvecklats genom evolution.
Anatomi
Hos en nyfödd människa är ögats diameter omkring 17 mm och hos en vuxen människa är ögongloben omkring 25 mm i diameter. Ögat slutar växa ungefär i 6–7-årsåldern.
Däggdjursögon är konstruerade för att fokusera ljus på näthinnan. Alla delar som ljuset färdas genom innan det når näthinnan är glasklart genomskinliga för att förhindra en förlust i ljusstyrka innan det når näthinnan. Hornhinnan i kombination med linsen ser till att ljusstrålarna fokuseras på näthinnan. Ljuset orsakar kemiska förändringar i de ljuskänsliga cellerna i näthinnan, som aktiveras och skickar nervimpulser till hjärnan.
Ljuset, som kommer in i ögat via ett yttre medium såsom luft eller vatten, passerar först hornhinnan och vidare in i den främre ögonkammaren. Hornhinnan, som är rundad, står för den huvudsakliga (2/3) brytningen av ljuset. Den främre ögonkammaren är fylld med kammarvätska, en helt klar vätska som till sin sammansättning liknar blodserum. Trycket från kammarvätskan spänner ut hornhinnan så att den blir helt konvex, vilket är nödvändigt för att ljuset ska samlas på linsen. Den främre ögonkammaren avgränsas bakåt av iris, en ring av i huvudsak lucker bindväv och stråk av glatt muskulatur. I iris finns gott om melanocyter, som producerar färgämnet melanin. Mängden melanin avgör ögonfärgen. Mitt i iris finns ett hål, pupillen. Pupillens storlek regleras av en ringmuskel (m. sphincter pupillae) och ett radialt muskelstråk (m. dilator pupillae). Pupillen fungerar som bländaren på en kamera, och ser till att ljusnivån i ögat hålls konstant. Om för mycket ljus släpps in skulle näthinnan skadas, och om för lite ljus släpps in ser ögat inget. Innanför irisen finns den bakre ögonkammaren. Denna begränsas bakåt av linsen, en konvex, fjädrande skiva som fokuserar ljuset på näthinnan. Innan ljuset når näthinnan måste det ta sig genom glaskroppen, en geléartad struktur som fyller ut ögats insida. Glaskroppens uppgift är framförallt att stadga upp ögat, men även att bryta ljuset.
Linsen är via tunna trådar fäst vid utskott i corpus ciliare, som omsluter den ringformiga ciliarmuskeln. För att se ett föremål som befinner sig långt borta, slappnar ciliarmuskeln av och får större diameter, vilket leder till att linsen dras ut och blir plattare. När ciliarmuskeln drar ihop sig fjädrar linsen tillbaka till en tjockare, mer konvex form. När vi åldras, förlorar linsen gradvis sin förmåga att fjädra tillbaka, och det leder till att det blir svårt att fokusera på näraliggande föremål. Det finns flera brytningsfel som kommer av hornhinnan och linsens form, och från ögats längd, till exempel översynthet, närsynthet, och astigmatism.
Omkring glaskroppen finns tre lager av vävnader:
Ytterst finns tunica externa bulbi, som delas in i tre delar, senhinnan (sclera), gränsregionen (limbus) och hornhinnan (cornea). Senhinnan hjälper till att hålla ögats form och förhindrar oönskad ljusgenomträngning. Utseendemässigt är senhinnan normalt vit, tjockast kring synnerven och tunnast vid ögonmusklernas fästen och i området där synnerven passerar (lamina cribrosa). Senhinnan består av bindväv innehållande framför allt kollagen.
I mitten finns tunica vasculosa bulbi eller uvea, som även den delas in i tre delar, regnbågshinnan (iris), strålkroppen (corpus ciliare, ciliarkroppen) och åderhinnan (choroidea, koroidea). Melanocyter i åderhinnan ger ögats inre dess mörka färg, som förhindrar att det bildas störande reflexer i ögat. Åderhinnan innehåller också kapillärer, som levererar syre och näring till näthinnans fem yttersta lager och fraktar bort restprodukter. Näthinnans fem innersta lager får näring från retinas centrala artär som kommer in i ögat tillsammans med synnerven och vars kärlförgreningar ligger i näthinnans nervfiberlager. Näthinnan innehåller även pigmentepitel (med melanin) och de ljuskänsliga tapparna och stavarna samt nerver.
Innerst finns tunica interna bulbi, som delas in i näthinnans seende och inte seende del. Gränsen mellan dessa två heter ora serrata.
För att maximera ljusabsorptionen är näthinnan slät. Den har dock två punkter som är annorlunda: blinda fläcken, den punkt där synnerven går in, och i centrum gula fläcken (macula lutea) med bäst synskärpa. I denna finns centralgropen (fovea centralis), som är en liten grop klädd enbart med tappar.
Tappar och stavar
Näthinnan innehåller två typer av ljuskänsliga celler: tappar och stavar. Trots att de har samma uppbyggnad och metabolism, har de väldigt olika funktioner.
Stavarna är mycket ljuskänsliga, vilket gör att de fungerar även i mycket svagt ljus. Det är de här cellerna som gör att människor och djur kan se i exempelvis månljus. Dock kan de inte skilja mellan olika färger, och de har dålig synskärpa (det vill säga de har svårt att skilja på detaljer). Det är därför som saker verkar få mindre färg, ju mörkare omgivningen blir.
Tapparna å andra sidan ger hög synskärpa under goda ljusförhållanden. Ju tätare tapparna sitter, desto högre blir synskärpan. Olika sorters tappceller reagerar också på olika färger (våglängder av ljus), vilket gör dessa ansvariga för en organisms färgseende. Tapparna har även en möjlighet att bli trötta efter ett intensivt synintryck. Om man till exempel tittar intensivt på ett rött streck på marken så ser man ett grönt streck om man tittar på en vit yta. Det beror på att tapparna blir trötta och de sänder inte lika mycket röda signaler längre, då verkar den delen av synfältet mer grön (alltså motsatsfärgen) än resten av synfältet och därför ser man då ett grönt streck.
Hos däggdjur och fåglar med god syn finns det ofta ett eller flera områden i ögats näthinna med extra mycket tappar. Hos människan (och en del andra djur) finns denna i en rund, lite tunnare fördjupning av näthinnan. Denna grop kallas för gula fläcken eller fovea (fullständigt latinskt namn: fovea centralis, centrala gropen) och sitter rakt bakom linsen. En del djur har en horisontellt formad fovea vilket gör att deras detaljseende fungerar bra längs med hela horisonten. Många fåglar har två foveor som även innehåller mycket fler tappar än hos exempelvis människan och som därmed ger dem ytterligare skarpare syn.
Eftersom tapparna behöver mycket ljus för att fungera optimalt blir det problem för exempelvis astronomer, då de inte kan se på ljussvaga stjärnor med ögats vanliga fokus, där ljuset inte är tillräckligt för att stimulera tapparna. Därför betraktar ofta astronomer stjärnorna genom "ögonvrån" (genom att titta lite bredvid), där andelen ljuskänsligare stavar är högre.
Både tappar och stavar är alltså känsliga för ljus, men för ljus av olika frekvenser. De innehåller båda ett pigmenterat ljusreceptor-protein, som i stavarna heter rhodopsin, i tapparna iodopsin. Både tappar och stavars ljusreceptorprotein består av en proteindel (stavar: opsin, tappar: fotodopsin), som är associerad med retinal, som inte är ett protein utan syntetiseras från vitamin A i näthinnans pigmentepitel. Processen som ljusreceptorproteinerna genomgår är likartade - när proteinet utsätts för elektromagnetisk strålning av en särskild våglängd och intensitet (det vill säga ljus inom det synliga spektret) bryts retinalet ned från sin normala konfiguration (11-cis-retinal) till en isoform (transretinal). Retinalen släpper också från opsinet/fotodopsinet. Denna process startar en signalväg som stänger jonkanaler i cellmembranet vilket förorsakar en impuls som så småningom når hjärnans syncentrum.
I närmare detalj fungerar rhodopsinet/iodopsinet i princip som en så kallad G-protein-kopplad receptor, vars aktivering leder till att ett enzym, cGMP-fosfodiesteras, börjar omvandla signalmolekylen cGMP till 5'-GMP. Då cGMP behövs för öppning av natriumkanalerna leder spjälkning till stängning vilket ger en hyperpolarisering av cellen. Denna hyperpolarisering leder till att utsöndringen av neurotransmittorer till synapsen avbryts. Detta kan verka bakvänt, men i näthinnans fotoreceptorer har neurotransmittorerna en inhiberande effekt på synapsen, och utsöndras normalt konstant. Att de slutar utsöndras leder på så sätt till aktivering av synapsen.
Flera sensoriska celler är kopplade till samma bipolära nervcell, som sedan är kopplad till en enda ganglie (nervknut) som skickar informationen vidare till syncentrat. Men tapparna i fovea är ofta kopplade individuellt till de bipolära cellerna och behöver sällan dela ganglie. Ju flera sensoriska celler som delar ganglie desto mindre skarp blir bilden från den delen av näthinnan.
Enligt den trikromatiska färgteorin uttyds färger genom att iodopsinet i tapparna finns i olika varianter. En typ bryts ner av den specifika ljusvåglängd som kommer från rött ljus, en från grönt ljus och en från blått ljus, medan den fjärde typen av tappar är känslig för ultraviolett ljus. Människan och andra högre utvecklade apor har tre typer av tappar som främst reagerar på blått, grönt och rött. De flesta andra däggdjur har två typer av tappar som främst regarera på blått och grönt medan fåglar har fyra typer av tappar så att de förutom blått, grönt och rött också kan se ultraviolett ljus. Sköldpaddor har sex olika typer av tappar. Om alla tre typer stimuleras lika mycket, ser man vitt, och om ingen stimuleras ser man svart. Oftast stimuleras de olika typerna olika mycket, vilket leder till att man ser olika färger. De tre färgerna kallas primärfärger. Om man blandar två av dem får man sekundärfärger, och blandar man två sekundärfärger får man tertiärfärger, och så vidare. Felfunktion hos någon av tapptyperna ledar till olika grad av färgblindhet. För rovfåglarna blir det mer komplicerat.
Ögats rörelser
Det finns sex yttre ögonmuskler med ursprung från ögonhålan som fäster på ögonbulbens sidor. Dessa styr rörelserna av ögat och håller det kvar i ögonhålan. Fyra av de sex musklerna är raka muskler (rectus), som något förenklat vrider ögat i varsin riktning. Musculus rectus lateralis vrider ögat lateralt, m. rectus medialis vrider ögat medialt, m. rectus superior och inferior vrider ögat uppåt respektive nedåt. De två kvarvarande musklerna är de sneda ögonmusklerna, m. obliquus superior och m. obliquus inferior. M. obliquus superior löper genom en ligamentring, trochlea, i anteromediala ögonhåletaket. Från denna går sedan muskeln bakåt och fäster på laterala och posteriora sidan av ögat. Vid kontraktion av muskeln kommer ögat då att vridas inåt och nedåt. M. obliquus inferior utgår från främre delen av ögonhålan och går bakåt för att fästa posterolateralt. Rörelsen blir då vridning utåt och uppåt. Tre av de raka ögonmusklerna, m. rectus superior, inferior och medialis) samt den undre sneda ögonmuskeln (m. obliquus inferior) innerveras av den tredje (III) kranialnerven, nervus oculomotorius, medan m. obliquus superior innerveras av fjärde kranialnerven (IV), nervus trochlearis, och m. rectus lateralis av sjätte kranialnerven (VI), nervus abducens. Bilden till höger visar även m. levator palpebrae superioris, som lyfter det övre ögonlocket, samt ganglion ciliare, som styr pupillkontraktion och ackommodation.
Ögats skyddsmekanismer
Ögat är omgivet av korta hårstrån som kallas ögonfransar. De är till för att skydda ögat mot vattendroppar, damm och andra partiklar som skulle kunna komma in i ögat. Varje öga har tårkörtlar. De sänder kontinuerligt ut vätska som sprids ut över ögat när man blinkar. Detta förhindrar att ögat torkar ut. Om ögonfransarna misslyckats med sin uppgift och släppt in smuts i ögat, producerar tårkörtlarna extra mycket vätska för att skölja rent och då blinkar man samtidigt för att pressa ut smutsen.
Ögonproblem och -sjukdomar
Se separat artikel om ögonsjukdomar samt sammanställningen i :Kategori:Ögonsjukdomar.
Se även
Kikare
Oftalmologi
Optiker
Tårar
Ögonfärg
Ögonkontakt
Ögonrörelser
Källor
Kandel, Schwartz, Jessell "Principles of Neural Science", 4/e, McGraw-Hill: Health Professions Division, 2000,
Malm, Liedholm "Akut neurologi" (1986), 7:e upplagan 2004,
Wikipedia:Basartiklar | swedish | 0.502005 |
stars_disappear_when_look/Rod_cell.txt | Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light.
Structure[edit]
Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the eye. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 120 million rod cells compared to 6 to 7 million cone cells.
Like cones, rod cells have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, usually a bipolar cell or a horizontal cell. The inner and outer segments are connected by a cilium, which lines the distal segment. The inner segment contains organelles and the cell's nucleus, while the rod outer segment (abbreviated to ROS), which is pointed toward the back of the eye, contains the light-absorbing materials.
A human rod cell is about 2 microns in diameter and 100 microns long. Rods are not all morphologically the same; in mice, rods close to the outer plexiform synaptic layer display a reduced length due to a shortened synaptic terminal.
Function[edit]
Photoreception[edit]
Anatomy of a Rod Cell
In vertebrates, activation of a photoreceptor cell is a hyperpolarization (inhibition) of the cell. When they are not being stimulated, such as in the dark, rod cells and cone cells depolarize and release a neurotransmitter spontaneously. This neurotransmitter hyperpolarizes the bipolar cell. Bipolar cells exist between photoreceptors and ganglion cells and act to transmit signals from the photoreceptors to the ganglion cells. As a result of the bipolar cell being hyperpolarized, it does not release its transmitter at the bipolar-ganglion synapse and the synapse is not excited.
Activation of photopigments by light sends a signal by hyperpolarizing the rod cell, leading to the rod cell not sending its neurotransmitter, which leads to the bipolar cell then releasing its transmitter at the bipolar-ganglion synapse and exciting the synapse.
Depolarization of rod cells (causing release of their neurotransmitter) occurs because in the dark, cells have a relatively high concentration of cyclic guanosine 3'-5' monophosphate (cGMP), which opens ion channels (largely sodium channels, though calcium can enter through these channels as well). The positive charges of the ions that enter the cell down its electrochemical gradient change the cell's membrane potential, cause depolarization, and lead to the release of the neurotransmitter glutamate. Glutamate can depolarize some neurons and hyperpolarize others, allowing photoreceptors to interact in an antagonistic manner.
When light hits photoreceptive pigments within the photoreceptor cell, the pigment changes shape. The pigment, called rhodopsin (conopsin is found in cone cells) comprises a large protein called opsin (situated in the plasma membrane), attached to which is a covalently bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A). The retinal exists in the 11-cis-retinal form when in the dark, and stimulation by light causes its structure to change to all-trans-retinal. This structural change causes an increased affinity for the regulatory protein called transducin (a type of G protein). Upon binding to rhodopsin, the alpha subunit of the G protein replaces a molecule of GDP with a molecule of GTP and becomes activated. This replacement causes the alpha subunit of the G protein to dissociate from the beta and gamma subunits of the G protein. As a result, the alpha subunit is now free to bind to the cGMP phosphodiesterase (an effector protein). The alpha subunit interacts with the inhibitory PDE gamma subunits and prevents them from blocking catalytic sites on the alpha and beta subunits of PDE, leading to the activation of cGMP phosphodiesterase, which hydrolyzes cGMP (the second messenger), breaking it down into 5'-GMP. Reduction in cGMP allows the ion channels to close, preventing the influx of positive ions, hyperpolarizing the cell, and stopping the release of the neurotransmitter glutamate. Though cone cells primarily use the neurotransmitter substance acetylcholine, rod cells use a variety. The entire process by which light initiates a sensory response is called visual phototransduction.
Activation of a single unit of rhodopsin, the photosensitive pigment in rods, can lead to a large reaction in the cell because the signal is amplified. Once activated, rhodopsin can activate hundreds of transducin molecules, each of which in turn activates a phosphodiesterase molecule, which can break down over a thousand cGMP molecules per second. Thus, rods can have a large response to a small amount of light.
As the retinal component of rhodopsin is derived from vitamin A, a deficiency of vitamin A causes a deficit in the pigment needed by rod cells. Consequently, fewer rod cells are able to sufficiently respond in darker conditions, and as the cone cells are poorly adapted for sight in the dark, blindness can result. This is night-blindness.
Reversion to the resting state[edit]
Rods make use of three inhibitory mechanisms (negative feedback mechanisms) to allow a rapid revert to the resting state after a flash of light.
Firstly, there exists a rhodopsin kinase (RK) which would phosphorylate the cytosolic tail of the activated rhodopsin on the multiple serines, partially inhibiting the activation of transducin. Also, an inhibitory protein - arrestin then binds to the phosphorylated rhodopsins to further inhibit the rhodopsin activity.
While arrestin shuts off rhodopsin, an RGS protein (functioning as a GTPase-activating proteins(GAPs)) drives the transducin (G-protein) into an "off" state by increasing the rate of hydrolysis of the bounded GTP to GDP.
When the cGMP concentration falls, the previously open cGMP sensitive channels close, leading to a reduction in the influx of calcium ions. The associated decrease in the concentration of calcium ions stimulates the calcium ion-sensitive proteins, which then activate the guanylyl cyclase to replenish the cGMP, rapidly restoring it to its original concentration. This opens the cGMP sensitive channels and causes a depolarization of the plasma membrane.
Desensitization[edit]
When the rods are exposed to a high concentration of photons for a prolonged period, they become desensitized (adapted) to the environment.
As rhodopsin is phosphorylated by rhodopsin kinase (a member of the GPCR kinases(GRKs)), it binds with high affinity to the arrestin. The bound arrestin can contribute to the desensitization process in at least two ways. First, it prevents the interaction between the G protein and the activated receptor. Second, it serves as an adaptor protein to aid the receptor to the clathrin-dependent endocytosis machinery (to induce receptor-mediated endocytosis).
Sensitivity[edit]
A rod cell is sensitive enough to respond to a single photon of light and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity (or image resolution) because the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually.
Wavelength absorbance of short (S), medium (M) and long (L) wavelength cones compared to that of rods (R).
Rod cells also respond more slowly to light than cones and the stimuli they receive are added over roughly 100 milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes, such as quickly changing images, is less accurate than that of cones.
Experiments by George Wald and others showed that rods are most sensitive to wavelengths of light around 498 nm (green-blue), and insensitive to wavelengths longer than about 640 nm (red). This is responsible for the Purkinje effect: as intensity dims at twilight, the rods take over, and before color disappears completely, peak sensitivity of vision shifts towards the rods' peak sensitivity (blue-green).
See also[edit]
List of distinct cell types in the adult human body | biology | 3876621 | https://sv.wikipedia.org/wiki/Rodopsin | Rodopsin | Rodopsin eller synpurpur är ljuskänsliga G-proteinkopplade receptorer i ögat, som gör det möjligt att se även vid svaga ljusförhållanden. De är purpurröda molekyler som utgörs av så kallade stavopsiner och retinaldehyd. Rodopsiner finns i de ljuskänsliga cellerna i ögats näthinna, stavarna. Havslevande bakterier har visat sig använda rodopsiner för att hämta solenergi.
I omgivningar med svag belysning sker det en adaption i ögat, så att ögat anpassar sig till mörkret genom att det gradvis i stavarna byggs upp mer och mer synpurpur. Detta är orsaken till att synen stadigt (under ca 30 min) förbättras i mörka omgivningar.
I starkt ljus spaltas rodopsin, och detta är förenklat uttryckt den utlösande faktorn till en aktionspotential.
Rodopsin kräver bland annat A-vitamin för att kunna byggas upp; brist på vitaminen kan därför medföra nattblindhet.
Bakteriella rodopsiner
Vissa prokaryoter ger ifrån sig protonpumpar som kallas bakterierodopsiner, proteorodopsiner och xanthorodopsiner för att utföra fototrofi. Likt djurs visuella pigment, innehåller dessa en retinal kromofor (fastän den är all-trans, snarare än 11-cis form) och har sju transmembranproteina alfahelixar; De är dock inte kopplade till ett G protein. Prokaryota halorodopsiner är ljusaktiverade kloridpumpar. Encelliga flagellat alger innehåller kanalrodopsiner, vilka uppträder som ljus-styrda katjonskanaler, när de avges i heterologa system. Många andra pro- och eukaryota organismer (särskilt svamp såsom Neurospora) avger rodopsin jonpumpar eller sensoriska rodopsiner av hittills okänd funktion. Medan alla mikrobiella rodopsiner har signifikant sekvenshomologi till varandra, har de ingen detekterbar sekvens homologi till den G-protein-coupled receptor (GPCR) familjen, till vilken djurs visuella rodopsiner hör. Mikrobiologiska rodopsiner och GPCRer är möjligen evolutionärt relaterade, baserat på deras tre-dimensionella strukturers likhet. De har därför hänförts till samma superfamilj i Structural Classification of Proteins (SCOP).
Noter och referenser
Alberts, Bray, Johnson, Lewis, Raff, Roberts & Walker; Essential Cell Biology, Garland Publishing, New York (1998).
Fysiologi
he:אופסין#רודופסין | swedish | 0.468557 |
stars_disappear_when_look/Eye.txt |
An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system.
In higher organisms, the eye is a complex optical system that collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain.
Eyes with resolving power have come in ten fundamentally different forms, classified into compound eyes and non-compound eyes. Compound eyes are made up of multiple small visual units, and are common on insects and crustaceans. Non-compound eyes have a single lens and focus light onto the retina to form a single image. This type of eye is common in mammals. The human eye is a non-compound eye.
The simplest eyes are pit eyes. They are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light.
Eyes enable several photo response functions that are independent of vision. In an organism that has more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.
Overview
Eye of a European bison
Human eye, a refractive cornea type eye.
Complex eyes distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception. In other organisms, particularly prey animals, eyes are located to maximise the field of view, such as in rabbits and horses, which have monocular vision.
The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla. In most vertebrates and some molluscs, the eye allows light to enter and project onto a light-sensitive layer of cells known as the retina. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals which are transmitted to the brain via the optic nerve to produce vision. Such eyes are typically spheroid, filled with the transparent gel-like vitreous humour, possess a focusing lens, and often an iris. Muscles around the iris change the size of the pupil, regulating the amount of light that enters the eye and reducing aberrations when there is enough light. The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a camera.
The compound eyes of the arthropods are composed of many simple facets which, depending on anatomical detail, may give either a single pixelated image or multiple images per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors arranged hexagonally, which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image. With each eye producing a different image, a fused, high-resolution image is produced in the brain.
The eyes of a mantis shrimp (here Odontodactylus scyllarus) are considered the most complex in the whole animal kingdom.
The mantis shrimp has the world's most complex colour vision system. It has detailed hyperspectral colour vision.
Trilobites, now extinct, had unique compound eyes. Clear calcite crystals formed the lenses of their eyes. They differ in this from most other arthropods, which have soft eyes. The number of lenses in such an eye varied widely; some trilobites had only one while others had thousands of lenses per eye.
In contrast to compound eyes, simple eyes have a single lens. Jumping spiders have one pair of large simple eyes with a narrow field of view, augmented by an array of smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a type of simple eye (stemmata) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive, and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more. Ocelli, some of the simplest eyes, are found in animals such as some of the snails. They have photosensitive cells but no lens or other means of projecting an image onto those cells. They can distinguish between light and dark but no more, enabling them to avoid direct sunlight.
In organisms dwelling near deep-sea vents, compound eyes are adapted to see the infra-red light produced by the hot vents, allowing the creatures to avoid being boiled alive.
Types
There are ten different eye layouts. Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. "Simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being ciliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the Cnidaria also possess ciliated cells,
and some gastropods and annelids possess both.
Some organisms have photosensitive cells that do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. These are not considered eyes because they lack enough structure to be considered an organ, and do not produce an image.
Every technological method of capturing an optical image that humans commonly use occurs in nature, with the exception of zoom and Fresnel lenses.
Non-compound eyes
Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and Cubozoa.
Pit eyes
Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100 µm. The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.
Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see infrared sensing in snakes). However, pit organs are fitted with receptors rather different from photoreceptors, namely a specific transient receptor potential channel (TRP channels) called TRPV1. The main difference is that photoreceptors are G-protein coupled receptors but TRP are ion channels.
Spherical lens eye
The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable. The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina. This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration. Such a non-homogeneous lens is necessary for the focal length to drop from about 4 times the lens radius, to 2.5 radii.
Heterogeneous eyes have evolved at least nine times: four or more times in gastropods, once in the copepods, once in the annelids, once in the cephalopods, and once in the chitons, which have aragonite lenses. No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown".
This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles.
The ocelli of insects bear a simple lens, but their focal point usually lies behind the retina; consequently, those can not form a sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain. Focusing the image would also cause the sun's image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.
This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).
Multiple lenses
Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia, has two lenses in each eye, arranged like those in a telescope. Such arrangements are rare and poorly understood, but represent an alternative construction.
Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have a refractive cornea: these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.
Refractive cornea
A refractive cornea type eye of a human. The cornea is the clear domed part covering the anterior chamber of the eye.
In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air. In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous lens material (see Luneburg lens), or with an aspheric shape. Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens.
As mentioned above, a refractive cornea is only useful out of water. In water, there is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water—penguins and seals, for example—lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea.
Reflector eyes
An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at a central point. The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.
Many small organisms such as rotifers, copepods and flatworms use such organs, but these are too small to produce usable images. Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.
There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.
Compound eyes
Main article: Compound eye
Further information: Arthropod eye
An image of a house fly compound eye surface by using scanning electron microscope
Anatomy of the compound eye of an insect
Arthropods such as this blue bottle fly have compound eyes.
A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light. Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius.
Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image. Compound eyes are common in arthropods, annelids and some bivalved molluscs. Compound eyes in arthropods grow at their margins by the addition of new ommatidia.
Apposition eyes
Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum. Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point. (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.)
Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.
Superposition eyes
The second type is named the superposition eye. The superposition eye is divided into three types:
refracting,
reflecting and
parabolic superposition
The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur, is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution. In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses.
Parabolic superposition
This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.
Other
Another kind of compound eye, found in males of Order Strepsiptera, employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites. Because each eyelet is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels.
Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies, have specialised zones of ommatidia organised into a fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.
There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye.
Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera. This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.
The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the shadow cast by its opaque body.
Nutrients
The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle.
The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.
Evolution
Main article: Evolution of the eye
Evolution of the mollusc eye
Photoreception is phylogenetically very old, with various theories of phylogenesis. The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 650-600 million years ago, and the PAX6 gene is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race" among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as the vertebrates, that were only forced into the photopic environment at a late stage).
Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite their distant common ancestry. Phenotypic convergence of the geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye, but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes and different lens crystallins show.
The very earliest "eyes", called eye-spots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source.
Through gradual change, the eye-spots of species living in well-lit environments depressed into a shallow "cup" shape. The ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes. However, the ancestors of modern hagfish, thought to be the protovertebrate, were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes.
The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.
The gap between tissue layers naturally formed a biconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.
Relationship to life requirements
Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre.
Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition. Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia. Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example, if the animal is on a slope.
An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey. In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger "upper-eyes", and may lose the lower portion of their eyes altogether. In the giant Antarctic isopod Glyptonotus a small ventral compound eye is physically completely separated from the much larger dorsal compound eye. Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.
Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop. On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.
It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.
Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this also allows them to track predators or prey without moving the head.
Physiology
Visual acuity
The eye of a red-tailed hawk
Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells. It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye.
For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD. A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.
Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair. A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.
However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals. Compound eyes have a much lower acuity than vertebrate eyes.
Colour perception
Main article: Colour vision
"Colour vision is the faculty of the organism to distinguish lights of different spectral qualities." All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm.
This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.
The most sensitive pigment, rhodopsin, has a peak response at 500 nm. Small changes to the genes coding for this protein can tweak the peak response by a few nm; pigments in the lens can also filter incoming light, changing the peak response. Many organisms are unable to discriminate between colours, seeing instead in shades of grey; colour vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells evolved. Even if organisms are physically capable of discriminating different colours, this does not necessarily mean that they can perceive the different colours; only with behavioural tests can this be deduced.
Most organisms with colour vision can detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light—this precludes the possibility of any UV light being detected, as it does not even reach the retina.
Rods and cones
The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. The optic nerves send off impulses through these fibres to the brain.
Pigmentation
The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related—although problems of convergence do exist.
Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides.
The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.
There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells. The eyes of vertebrates usually contain ciliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes. Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form. C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins. Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins—but r-opsins are yet to be found in this group. Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.
Additional images
The structures of the eye labelled
Another view of the eye and the structures of the eye labelled
See also
Accommodation (vertebrate eye) (focusing)
Adaptation (eye) (night vision)
Capsule of lens
Cornea
Emission theory (vision)
Eye color
Eye development
Eye disease
Eye injury
Eye movement
Eyelid
Lens (vertebrate anatomy)
Nictitating membrane
Ophthalmology
Orbit (anatomy)
Simple eye in invertebrates
Tapetum lucidum
Tears
Notes
^ There is no universal consensus on the precise total number of phyla Animalia; the stated figure varies slightly from author to author. | biology | 51868 | https://sv.wikipedia.org/wiki/%C3%96ga | Öga | Ett öga () är ett anatomiskt organ för att förnimma ljus. Olika typer av ljuskänsliga organ finns i nästan hela djurriket. De enklaste varianterna särskiljer bara om omgivningen är mörk eller ljus. Mer komplexa ögon används för att ge ett synsinne. Många komplexa organismer, såsom däggdjur, fåglar, reptiler och fiskar har två ögon som är placerade i samma plan och vars intryck tolkas som en enda, tredimensionell "bild", liksom hos människan. Andra djurarter, till exempel kaniner och kameleonter har ögonen i olika plan och får två separata bilder.
Ögontyper
Hos de flesta ryggradsdjur och vissa blötdjur fungerar ögat genom att projicera bilder på en ljuskänslig näthinna (retina). Signaler skickas därifrån till hjärnan via synnerven. Sådana ögon är ofta ungefär sfäriska och fyllda med en genomskinlig geleartad substans som kallas glaskropp, har en lins som fokuserar ljuset, och en iris som reglerar hur mycket ljus som kommer in i ögat.
Ögon hos bläckfiskar, fiskar, amfibiska djur och ormar har ofta en fast linsform och fokuserar blicken genom att teleskopera ögat (på samma sätt som en kamera fokuserar).
Arter som skiljer sig mycket åt kan ha väldigt olika typer av ögon, men de tenderar att likna varandra i funktion och utseende när de är fullt utvecklade. Blötdjurens ögon verkar till exempel ha utvecklats från andra organ än ryggradsdjurens ögon, och kan vara ett exempel på hur evolutionen lett till samma slutresultat. Ryggradsdjurens ögon utvecklades från hjärnceller under den embryoniska tiden, medan blötdjurens ögon växte in från hudceller. Ryggradsdjurens näthinnor har lager med neuroner framför de ljuskänsliga cellerna, medan blötdjurens näthinnor har de ljuskänsliga cellerna framför neuronerna, och har därför ingen blind fläck och möjligen skarpare syn, men också långsammare bildåterhämtning från näthinnan och därför sämre sinne för rörelser. Vissa huvudfotningar har ingen fysisk lins, utan en väldigt liten ljusöppning (ungefär som en camera obscura). Vissa blötdjur har en konkav spegel för att fokusera ljuset tillsammans med en lins.
Fasettögon finns hos leddjur, och ger en pixel-baserad bild (inte flera bilder som många tror). Varje sensor har sin egen lins och ljuskänsliga celler. Vissa ögon har upp emot 28 000 sådana sensorer, arrangerade i ett hexagonalt nät, vilket kan ge ett 360-gradigt synfält. Fasettögon är väldigt känsliga för rörelser. Vissa leddjurs fasettögon har ett fåtal fasetter var med en näthinna som kan skapa en bild, vilket ger en syn baserad på flera bilder, alla ur olika vinklar, sammansmälta till en bild med mycket hög upplösning.
Djurrikets troligen mest komplicerade ögon är fasettögonen hos stomatopoder, mantisräkor, en grupp bland kräftdjuren. Färgseendet är mycket avancerat med det största kända antalet färgreceptorer, och de kan se i 12 färgkanaler (jfr 3 hos människan), s.k. hyperspektralt seende. Varje enskilt öga har även djupseende. Vidare kan de se polariserat ljus och bedöma polarisationsplanet, och de kan också se ultraviolett och kanske infrarött ljus.
Trilobiterna, som nu är utdöda, hade unika fasettögon med genomskinliga kalk-kristaller som linser. (De flesta andra leddjur har mjuka ögon.) Antalet linser i sådana ögon varierar - vissa hade bara en, andra hade flera tusen linser per öga.
Några av de enklaste ögonen återfinns hos djur såsom sniglar, och kan inte se i den vardagliga betydelsen. De har ljuskänsliga celler, men ingen lins och inget annat sätt att projicera en bild på de cellerna. De kan särskilja mellan ljust och mörkt (dag och natt) men inte mer. Det gör att sniglar kan undvika direkt solljus.
Ögats evolutionära utveckling
Hur en så komplex struktur som ögats projicering skulle ha kunnat utvecklats av sig självt sägs ofta vara en svår fråga för evolutionsteorin. Darwin behandlade ämnet i sin Om arternas uppkomst genom att hävda att det inte var så konstigt om de mest primitiva varianterna också hade en funktion, och därefter muterade lite i taget.
Forskarna Dan-Eric Nilsson och Susanne Pelger i Lund har visat genom teoretiska beräkningar att ett primitivt optiskt sinnesorgan skulle kunna ha utvecklats till ett komplext människolikt öga på en rimlig tid (mindre än en miljon år), enbart genom små mutationer och naturliga urvalsprocesser.
Ögon i olika djurarter visar att de har anpassats till sina omgivningar. Till exempel har rovfåglar skarpare blick än människor, och vissa rovfåglar som jagar på dagen kan se ultraviolett ljus. Dessutom visar de parallella utvecklingarna av ryggradsdjursögon och blötdjursögon att det inte är konstigt att ögat har utvecklats genom evolution.
Anatomi
Hos en nyfödd människa är ögats diameter omkring 17 mm och hos en vuxen människa är ögongloben omkring 25 mm i diameter. Ögat slutar växa ungefär i 6–7-årsåldern.
Däggdjursögon är konstruerade för att fokusera ljus på näthinnan. Alla delar som ljuset färdas genom innan det når näthinnan är glasklart genomskinliga för att förhindra en förlust i ljusstyrka innan det når näthinnan. Hornhinnan i kombination med linsen ser till att ljusstrålarna fokuseras på näthinnan. Ljuset orsakar kemiska förändringar i de ljuskänsliga cellerna i näthinnan, som aktiveras och skickar nervimpulser till hjärnan.
Ljuset, som kommer in i ögat via ett yttre medium såsom luft eller vatten, passerar först hornhinnan och vidare in i den främre ögonkammaren. Hornhinnan, som är rundad, står för den huvudsakliga (2/3) brytningen av ljuset. Den främre ögonkammaren är fylld med kammarvätska, en helt klar vätska som till sin sammansättning liknar blodserum. Trycket från kammarvätskan spänner ut hornhinnan så att den blir helt konvex, vilket är nödvändigt för att ljuset ska samlas på linsen. Den främre ögonkammaren avgränsas bakåt av iris, en ring av i huvudsak lucker bindväv och stråk av glatt muskulatur. I iris finns gott om melanocyter, som producerar färgämnet melanin. Mängden melanin avgör ögonfärgen. Mitt i iris finns ett hål, pupillen. Pupillens storlek regleras av en ringmuskel (m. sphincter pupillae) och ett radialt muskelstråk (m. dilator pupillae). Pupillen fungerar som bländaren på en kamera, och ser till att ljusnivån i ögat hålls konstant. Om för mycket ljus släpps in skulle näthinnan skadas, och om för lite ljus släpps in ser ögat inget. Innanför irisen finns den bakre ögonkammaren. Denna begränsas bakåt av linsen, en konvex, fjädrande skiva som fokuserar ljuset på näthinnan. Innan ljuset når näthinnan måste det ta sig genom glaskroppen, en geléartad struktur som fyller ut ögats insida. Glaskroppens uppgift är framförallt att stadga upp ögat, men även att bryta ljuset.
Linsen är via tunna trådar fäst vid utskott i corpus ciliare, som omsluter den ringformiga ciliarmuskeln. För att se ett föremål som befinner sig långt borta, slappnar ciliarmuskeln av och får större diameter, vilket leder till att linsen dras ut och blir plattare. När ciliarmuskeln drar ihop sig fjädrar linsen tillbaka till en tjockare, mer konvex form. När vi åldras, förlorar linsen gradvis sin förmåga att fjädra tillbaka, och det leder till att det blir svårt att fokusera på näraliggande föremål. Det finns flera brytningsfel som kommer av hornhinnan och linsens form, och från ögats längd, till exempel översynthet, närsynthet, och astigmatism.
Omkring glaskroppen finns tre lager av vävnader:
Ytterst finns tunica externa bulbi, som delas in i tre delar, senhinnan (sclera), gränsregionen (limbus) och hornhinnan (cornea). Senhinnan hjälper till att hålla ögats form och förhindrar oönskad ljusgenomträngning. Utseendemässigt är senhinnan normalt vit, tjockast kring synnerven och tunnast vid ögonmusklernas fästen och i området där synnerven passerar (lamina cribrosa). Senhinnan består av bindväv innehållande framför allt kollagen.
I mitten finns tunica vasculosa bulbi eller uvea, som även den delas in i tre delar, regnbågshinnan (iris), strålkroppen (corpus ciliare, ciliarkroppen) och åderhinnan (choroidea, koroidea). Melanocyter i åderhinnan ger ögats inre dess mörka färg, som förhindrar att det bildas störande reflexer i ögat. Åderhinnan innehåller också kapillärer, som levererar syre och näring till näthinnans fem yttersta lager och fraktar bort restprodukter. Näthinnans fem innersta lager får näring från retinas centrala artär som kommer in i ögat tillsammans med synnerven och vars kärlförgreningar ligger i näthinnans nervfiberlager. Näthinnan innehåller även pigmentepitel (med melanin) och de ljuskänsliga tapparna och stavarna samt nerver.
Innerst finns tunica interna bulbi, som delas in i näthinnans seende och inte seende del. Gränsen mellan dessa två heter ora serrata.
För att maximera ljusabsorptionen är näthinnan slät. Den har dock två punkter som är annorlunda: blinda fläcken, den punkt där synnerven går in, och i centrum gula fläcken (macula lutea) med bäst synskärpa. I denna finns centralgropen (fovea centralis), som är en liten grop klädd enbart med tappar.
Tappar och stavar
Näthinnan innehåller två typer av ljuskänsliga celler: tappar och stavar. Trots att de har samma uppbyggnad och metabolism, har de väldigt olika funktioner.
Stavarna är mycket ljuskänsliga, vilket gör att de fungerar även i mycket svagt ljus. Det är de här cellerna som gör att människor och djur kan se i exempelvis månljus. Dock kan de inte skilja mellan olika färger, och de har dålig synskärpa (det vill säga de har svårt att skilja på detaljer). Det är därför som saker verkar få mindre färg, ju mörkare omgivningen blir.
Tapparna å andra sidan ger hög synskärpa under goda ljusförhållanden. Ju tätare tapparna sitter, desto högre blir synskärpan. Olika sorters tappceller reagerar också på olika färger (våglängder av ljus), vilket gör dessa ansvariga för en organisms färgseende. Tapparna har även en möjlighet att bli trötta efter ett intensivt synintryck. Om man till exempel tittar intensivt på ett rött streck på marken så ser man ett grönt streck om man tittar på en vit yta. Det beror på att tapparna blir trötta och de sänder inte lika mycket röda signaler längre, då verkar den delen av synfältet mer grön (alltså motsatsfärgen) än resten av synfältet och därför ser man då ett grönt streck.
Hos däggdjur och fåglar med god syn finns det ofta ett eller flera områden i ögats näthinna med extra mycket tappar. Hos människan (och en del andra djur) finns denna i en rund, lite tunnare fördjupning av näthinnan. Denna grop kallas för gula fläcken eller fovea (fullständigt latinskt namn: fovea centralis, centrala gropen) och sitter rakt bakom linsen. En del djur har en horisontellt formad fovea vilket gör att deras detaljseende fungerar bra längs med hela horisonten. Många fåglar har två foveor som även innehåller mycket fler tappar än hos exempelvis människan och som därmed ger dem ytterligare skarpare syn.
Eftersom tapparna behöver mycket ljus för att fungera optimalt blir det problem för exempelvis astronomer, då de inte kan se på ljussvaga stjärnor med ögats vanliga fokus, där ljuset inte är tillräckligt för att stimulera tapparna. Därför betraktar ofta astronomer stjärnorna genom "ögonvrån" (genom att titta lite bredvid), där andelen ljuskänsligare stavar är högre.
Både tappar och stavar är alltså känsliga för ljus, men för ljus av olika frekvenser. De innehåller båda ett pigmenterat ljusreceptor-protein, som i stavarna heter rhodopsin, i tapparna iodopsin. Både tappar och stavars ljusreceptorprotein består av en proteindel (stavar: opsin, tappar: fotodopsin), som är associerad med retinal, som inte är ett protein utan syntetiseras från vitamin A i näthinnans pigmentepitel. Processen som ljusreceptorproteinerna genomgår är likartade - när proteinet utsätts för elektromagnetisk strålning av en särskild våglängd och intensitet (det vill säga ljus inom det synliga spektret) bryts retinalet ned från sin normala konfiguration (11-cis-retinal) till en isoform (transretinal). Retinalen släpper också från opsinet/fotodopsinet. Denna process startar en signalväg som stänger jonkanaler i cellmembranet vilket förorsakar en impuls som så småningom når hjärnans syncentrum.
I närmare detalj fungerar rhodopsinet/iodopsinet i princip som en så kallad G-protein-kopplad receptor, vars aktivering leder till att ett enzym, cGMP-fosfodiesteras, börjar omvandla signalmolekylen cGMP till 5'-GMP. Då cGMP behövs för öppning av natriumkanalerna leder spjälkning till stängning vilket ger en hyperpolarisering av cellen. Denna hyperpolarisering leder till att utsöndringen av neurotransmittorer till synapsen avbryts. Detta kan verka bakvänt, men i näthinnans fotoreceptorer har neurotransmittorerna en inhiberande effekt på synapsen, och utsöndras normalt konstant. Att de slutar utsöndras leder på så sätt till aktivering av synapsen.
Flera sensoriska celler är kopplade till samma bipolära nervcell, som sedan är kopplad till en enda ganglie (nervknut) som skickar informationen vidare till syncentrat. Men tapparna i fovea är ofta kopplade individuellt till de bipolära cellerna och behöver sällan dela ganglie. Ju flera sensoriska celler som delar ganglie desto mindre skarp blir bilden från den delen av näthinnan.
Enligt den trikromatiska färgteorin uttyds färger genom att iodopsinet i tapparna finns i olika varianter. En typ bryts ner av den specifika ljusvåglängd som kommer från rött ljus, en från grönt ljus och en från blått ljus, medan den fjärde typen av tappar är känslig för ultraviolett ljus. Människan och andra högre utvecklade apor har tre typer av tappar som främst reagerar på blått, grönt och rött. De flesta andra däggdjur har två typer av tappar som främst regarera på blått och grönt medan fåglar har fyra typer av tappar så att de förutom blått, grönt och rött också kan se ultraviolett ljus. Sköldpaddor har sex olika typer av tappar. Om alla tre typer stimuleras lika mycket, ser man vitt, och om ingen stimuleras ser man svart. Oftast stimuleras de olika typerna olika mycket, vilket leder till att man ser olika färger. De tre färgerna kallas primärfärger. Om man blandar två av dem får man sekundärfärger, och blandar man två sekundärfärger får man tertiärfärger, och så vidare. Felfunktion hos någon av tapptyperna ledar till olika grad av färgblindhet. För rovfåglarna blir det mer komplicerat.
Ögats rörelser
Det finns sex yttre ögonmuskler med ursprung från ögonhålan som fäster på ögonbulbens sidor. Dessa styr rörelserna av ögat och håller det kvar i ögonhålan. Fyra av de sex musklerna är raka muskler (rectus), som något förenklat vrider ögat i varsin riktning. Musculus rectus lateralis vrider ögat lateralt, m. rectus medialis vrider ögat medialt, m. rectus superior och inferior vrider ögat uppåt respektive nedåt. De två kvarvarande musklerna är de sneda ögonmusklerna, m. obliquus superior och m. obliquus inferior. M. obliquus superior löper genom en ligamentring, trochlea, i anteromediala ögonhåletaket. Från denna går sedan muskeln bakåt och fäster på laterala och posteriora sidan av ögat. Vid kontraktion av muskeln kommer ögat då att vridas inåt och nedåt. M. obliquus inferior utgår från främre delen av ögonhålan och går bakåt för att fästa posterolateralt. Rörelsen blir då vridning utåt och uppåt. Tre av de raka ögonmusklerna, m. rectus superior, inferior och medialis) samt den undre sneda ögonmuskeln (m. obliquus inferior) innerveras av den tredje (III) kranialnerven, nervus oculomotorius, medan m. obliquus superior innerveras av fjärde kranialnerven (IV), nervus trochlearis, och m. rectus lateralis av sjätte kranialnerven (VI), nervus abducens. Bilden till höger visar även m. levator palpebrae superioris, som lyfter det övre ögonlocket, samt ganglion ciliare, som styr pupillkontraktion och ackommodation.
Ögats skyddsmekanismer
Ögat är omgivet av korta hårstrån som kallas ögonfransar. De är till för att skydda ögat mot vattendroppar, damm och andra partiklar som skulle kunna komma in i ögat. Varje öga har tårkörtlar. De sänder kontinuerligt ut vätska som sprids ut över ögat när man blinkar. Detta förhindrar att ögat torkar ut. Om ögonfransarna misslyckats med sin uppgift och släppt in smuts i ögat, producerar tårkörtlarna extra mycket vätska för att skölja rent och då blinkar man samtidigt för att pressa ut smutsen.
Ögonproblem och -sjukdomar
Se separat artikel om ögonsjukdomar samt sammanställningen i :Kategori:Ögonsjukdomar.
Se även
Kikare
Oftalmologi
Optiker
Tårar
Ögonfärg
Ögonkontakt
Ögonrörelser
Källor
Kandel, Schwartz, Jessell "Principles of Neural Science", 4/e, McGraw-Hill: Health Professions Division, 2000,
Malm, Liedholm "Akut neurologi" (1986), 7:e upplagan 2004,
Wikipedia:Basartiklar | swedish | 0.502005 |
stars_disappear_when_look/Star.txt |
A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 10 to 10 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.
A star's life begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen, helium, and trace heavier elements. Its total mass mainly determines its evolution and eventual fate. A star shines for most of its active life due to the thermonuclear fusion of hydrogen into helium in its core. This process releases energy that traverses the star's interior and radiates into outer space. At the end of a star's lifetime as a fusor, its core becomes a stellar remnant: a white dwarf, a neutron star, or—if it is sufficiently massive—a black hole.
Stellar nucleosynthesis in stars or their remnants creates almost all naturally occurring chemical elements heavier than lithium. Stellar mass loss or supernova explosions return chemically enriched material to the interstellar medium. These elements are then recycled into new stars. Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability, distance, and motion through space—by carrying out observations of a star's apparent brightness, spectrum, and changes in its position in the sky over time.
Stars can form orbital systems with other astronomical objects, as in planetary systems and star systems with two or more stars. When two such stars orbit closely, their gravitational interaction can significantly impact their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.
Etymology
The word "star" ultimately derives from the Proto-Indo-European root "h₂stḗr" also meaning star, but further analyzable as h₂eh₁s- ("to burn", also the source of the word "ash") + -tēr (agentive suffix). Compare Latin stella, Greek aster, German Stern. Some scholars believe the word is a borrowing from Akkadian "istar" (venus), however some doubt that suggestion. Star is cognate (shares the same root) with the following words: asterisk, asteroid, astral, constellation, Esther.
Observation history
See also: Stars in astrology
People have interpreted patterns and images in the stars since ancient times. This 1690 depiction of the constellation of Leo, the lion, is by Johannes Hevelius.
Historically, stars have been important to civilizations throughout the world. They have been part of religious practices, used for celestial navigation and orientation, to mark the passage of seasons, and to define calendars.
Early astronomers recognized a difference between "fixed stars", whose position on the celestial sphere does not change, and "wandering stars" (planets), which move noticeably relative to the fixed stars over days or weeks. Many ancient astronomers believed that the stars were permanently affixed to a heavenly sphere and that they were immutable. By convention, astronomers grouped prominent stars into asterisms and constellations and used them to track the motions of the planets and the inferred position of the Sun. The motion of the Sun against the background stars (and the horizon) was used to create calendars, which could be used to regulate agricultural practices. The Gregorian calendar, currently used nearly everywhere in the world, is a solar calendar based on the angle of the Earth's rotational axis relative to its local star, the Sun.
The oldest accurately dated star chart was the result of ancient Egyptian astronomy in 1534 BC. The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period (c. 1531 BC – c. 1155 BC).
Stars in the night sky
The first star catalogue in Greek astronomy was created by Aristillus in approximately 300 BC, with the help of Timocharis. The star catalog of Hipparchus (2nd century BC) included 1,020 stars, and was used to assemble Ptolemy's star catalogue. Hipparchus is known for the discovery of the first recorded nova (new star). Many of the constellations and star names in use today derive from Greek astronomy.
Despite the apparent immutability of the heavens, Chinese astronomers were aware that new stars could appear. In 185 AD, they were the first to observe and write about a supernova, now known as SN 185. The brightest stellar event in recorded history was the SN 1006 supernova, which was observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers. The SN 1054 supernova, which gave birth to the Crab Nebula, was also observed by Chinese and Islamic astronomers.
Medieval Islamic astronomers gave Arabic names to many stars that are still used today and they invented numerous astronomical instruments that could compute the positions of the stars. They built the first large observatory research institutes, mainly to produce Zij star catalogues. Among these, the Book of Fixed Stars (964) was written by the Persian astronomer Abd al-Rahman al-Sufi, who observed a number of stars, star clusters (including the Omicron Velorum and Brocchi's Clusters) and galaxies (including the Andromeda Galaxy). According to A. Zahoor, in the 11th century, the Persian polymath scholar Abu Rayhan Biruni described the Milky Way galaxy as a multitude of fragments having the properties of nebulous stars, and gave the latitudes of various stars during a lunar eclipse in 1019.
According to Josep Puig, the Andalusian astronomer Ibn Bajjah proposed that the Milky Way was made up of many stars that almost touched one another and appeared to be a continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars on 500 AH (1106/1107 AD) as evidence.
Early European astronomers such as Tycho Brahe identified new stars in the night sky (later termed novae), suggesting that the heavens were not immutable. In 1584, Giordano Bruno suggested that the stars were like the Sun, and may have other planets, possibly even Earth-like, in orbit around them, an idea that had been suggested earlier by the ancient Greek philosophers, Democritus and Epicurus, and by medieval Islamic cosmologists such as Fakhr al-Din al-Razi. By the following century, the idea of the stars being the same as the Sun was reaching a consensus among astronomers. To explain why these stars exerted no net gravitational pull on the Solar System, Isaac Newton suggested that the stars were equally distributed in every direction, an idea prompted by the theologian Richard Bentley.
The Italian astronomer Geminiano Montanari recorded observing variations in luminosity of the star Algol in 1667. Edmond Halley published the first measurements of the proper motion of a pair of nearby "fixed" stars, demonstrating that they had changed positions since the time of the ancient Greek astronomers Ptolemy and Hipparchus.
William Herschel was the first astronomer to attempt to determine the distribution of stars in the sky. During the 1780s, he established a series of gauges in 600 directions and counted the stars observed along each line of sight. From this, he deduced that the number of stars steadily increased toward one side of the sky, in the direction of the Milky Way core. His son John Herschel repeated this study in the southern hemisphere and found a corresponding increase in the same direction. In addition to his other accomplishments, William Herschel is noted for his discovery that some stars do not merely lie along the same line of sight, but are physical companions that form binary star systems.
The science of stellar spectroscopy was pioneered by Joseph von Fraunhofer and Angelo Secchi. By comparing the spectra of stars such as Sirius to the Sun, they found differences in the strength and number of their absorption lines—the dark lines in stellar spectra caused by the atmosphere's absorption of specific frequencies. In 1865, Secchi began classifying stars into spectral types. The modern version of the stellar classification scheme was developed by Annie J. Cannon during the early 1900s.
The first direct measurement of the distance to a star (61 Cygni at 11.4 light-years) was made in 1838 by Friedrich Bessel using the parallax technique. Parallax measurements demonstrated the vast separation of the stars in the heavens. Observation of double stars gained increasing importance during the 19th century. In 1834, Friedrich Bessel observed changes in the proper motion of the star Sirius and inferred a hidden companion. Edward Pickering discovered the first spectroscopic binary in 1899 when he observed the periodic splitting of the spectral lines of the star Mizar in a 104-day period. Detailed observations of many binary star systems were collected by astronomers such as Friedrich Georg Wilhelm von Struve and S. W. Burnham, allowing the masses of stars to be determined from computation of orbital elements. The first solution to the problem of deriving an orbit of binary stars from telescope observations was made by Felix Savary in 1827.
The twentieth century saw increasingly rapid advances in the scientific study of stars. The photograph became a valuable astronomical tool. Karl Schwarzschild discovered that the color of a star and, hence, its temperature, could be determined by comparing the visual magnitude against the photographic magnitude. The development of the photoelectric photometer allowed precise measurements of magnitude at multiple wavelength intervals. In 1921 Albert A. Michelson made the first measurements of a stellar diameter using an interferometer on the Hooker telescope at Mount Wilson Observatory.
Important theoretical work on the physical structure of stars occurred during the first decades of the twentieth century. In 1913, the Hertzsprung-Russell diagram was developed, propelling the astrophysical study of stars. Successful models were developed to explain the interiors of stars and stellar evolution. Cecilia Payne-Gaposchkin first proposed that stars were made primarily of hydrogen and helium in her 1925 PhD thesis. The spectra of stars were further understood through advances in quantum physics. This allowed the chemical composition of the stellar atmosphere to be determined.
Infrared image from NASA's Spitzer Space Telescope showing hundreds of thousands of stars in the Milky Way galaxy
With the exception of rare events such as supernovae and supernova imposters, individual stars have primarily been observed in the Local Group, and especially in the visible part of the Milky Way (as demonstrated by the detailed star catalogues available for the Milky Way galaxy) and its satellites. Individual stars such as Cepheid variables have been observed in the M87 and M100 galaxies of the Virgo Cluster, as well as luminous stars in some other relatively nearby galaxies. With the aid of gravitational lensing, a single star (named Icarus) has been observed at 9 billion light-years away.
Designations
Main articles: Stellar designation, Astronomical naming conventions, and Star catalogue
The concept of a constellation was known to exist during the Babylonian period. Ancient sky watchers imagined that prominent arrangements of stars formed patterns, and they associated these with particular aspects of nature or their myths. Twelve of these formations lay along the band of the ecliptic and these became the basis of astrology. Many of the more prominent individual stars were given names, particularly with Arabic or Latin designations.
As well as certain constellations and the Sun itself, individual stars have their own myths. To the Ancient Greeks, some "stars", known as planets (Greek πλανήτης (planētēs), meaning "wanderer"), represented various important deities, from which the names of the planets Mercury, Venus, Mars, Jupiter and Saturn were taken. (Uranus and Neptune were Greek and Roman gods, but neither planet was known in Antiquity because of their low brightness. Their names were assigned by later astronomers.)
Circa 1600, the names of the constellations were used to name the stars in the corresponding regions of the sky. The German astronomer Johann Bayer created a series of star maps and applied Greek letters as designations to the stars in each constellation. Later a numbering system based on the star's right ascension was invented and added to John Flamsteed's star catalogue in his book "Historia coelestis Britannica" (the 1712 edition), whereby this numbering system came to be called Flamsteed designation or Flamsteed numbering.
The internationally recognized authority for naming celestial bodies is the International Astronomical Union (IAU). The International Astronomical Union maintains the Working Group on Star Names (WGSN) which catalogs and standardizes proper names for stars. A number of private companies sell names of stars which are not recognized by the IAU, professional astronomers, or the amateur astronomy community. The British Library calls this an unregulated commercial enterprise, and the New York City Department of Consumer and Worker Protection issued a violation against one such star-naming company for engaging in a deceptive trade practice.
Units of measurement
Although stellar parameters can be expressed in SI units or Gaussian units, it is often most convenient to express mass, luminosity, and radii in solar units, based on the characteristics of the Sun. In 2015, the IAU defined a set of nominal solar values (defined as SI constants, without uncertainties) which can be used for quoting stellar parameters:
nominal solar luminosity
L☉ = 3.828×10 W
nominal solar radius
R☉ = 6.957×10 m
The solar mass M☉ was not explicitly defined by the IAU due to the large relative uncertainty (10) of the Newtonian constant of gravitation G. Since the product of the Newtonian constant of gravitation and solar mass
together (GM☉) has been determined to much greater precision, the IAU defined the nominal solar mass parameter to be:
nominal solar mass parameter:
GM☉ = 1.3271244×10 m/s
The nominal solar mass parameter can be combined with the most recent (2014) CODATA estimate of the Newtonian constant of gravitation G to derive the solar mass to be approximately 1.9885×10 kg. Although the exact values for the luminosity, radius, mass parameter, and mass may vary slightly in the future due to observational uncertainties, the 2015 IAU nominal constants will remain the same SI values as they remain useful measures for quoting stellar parameters.
Large lengths, such as the radius of a giant star or the semi-major axis of a binary star system, are often expressed in terms of the astronomical unit—approximately equal to the mean distance between the Earth and the Sun (150 million km or approximately 93 million miles). In 2012, the IAU defined the astronomical constant to be an exact length in meters: 149,597,870,700 m.
Formation and evolution
Main article: Stellar evolution
Stellar evolution of low-mass (left cycle) and high-mass (right cycle) stars, with examples in italics
Stars condense from regions of space of higher matter density, yet those regions are less dense than within a vacuum chamber. These regions—known as molecular clouds—consist mostly of hydrogen, with about 23 to 28 percent helium and a few percent heavier elements. One example of such a star-forming region is the Orion Nebula. Most stars form in groups of dozens to hundreds of thousands of stars. Massive stars in these groups may powerfully illuminate those clouds, ionizing the hydrogen, and creating H II regions. Such feedback effects, from star formation, may ultimately disrupt the cloud and prevent further star formation.
All stars spend the majority of their existence as main sequence stars, fueled primarily by the nuclear fusion of hydrogen into helium within their cores. However, stars of different masses have markedly different properties at various stages of their development. The ultimate fate of more massive stars differs from that of less massive stars, as do their luminosities and the impact they have on their environment. Accordingly, astronomers often group stars by their mass:
Very low mass stars, with masses below 0.5 M☉, are fully convective and distribute helium evenly throughout the whole star while on the main sequence. Therefore, they never undergo shell burning and never become red giants. After exhausting their hydrogen they become helium white dwarfs and slowly cool. As the lifetime of 0.5 M☉ stars is longer than the age of the universe, no such star has yet reached the white dwarf stage.
Low mass stars (including the Sun), with a mass between 0.5 M☉ and ~2.25 M☉ depending on composition, do become red giants as their core hydrogen is depleted and they begin to burn helium in core in a helium flash; they develop a degenerate carbon-oxygen core later on the asymptotic giant branch; they finally blow off their outer shell as a planetary nebula and leave behind their core in the form of a white dwarf.
Intermediate-mass stars, between ~2.25 M☉ and ~8 M☉, pass through evolutionary stages similar to low mass stars, but after a relatively short period on the red-giant branch they ignite helium without a flash and spend an extended period in the red clump before forming a degenerate carbon-oxygen core.
Massive stars generally have a minimum mass of ~8 M☉. After exhausting the hydrogen at the core these stars become supergiants and go on to fuse elements heavier than helium. Many end their lives when their cores collapse and they explode as supernovae.
Star formation
Main article: Star formation
Artist's conception of the birth of a star within a dense molecular cloudA cluster of approximately 500 young stars lies within the nearby W40 stellar nursery.
The formation of a star begins with gravitational instability within a molecular cloud, caused by regions of higher density—often triggered by compression of clouds by radiation from massive stars, expanding bubbles in the interstellar medium, the collision of different molecular clouds, or the collision of galaxies (as in a starburst galaxy). When a region reaches a sufficient density of matter to satisfy the criteria for Jeans instability, it begins to collapse under its own gravitational force.
As the cloud collapses, individual conglomerations of dense dust and gas form "Bok globules". As a globule collapses and the density increases, the gravitational energy converts into heat and the temperature rises. When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibrium, a protostar forms at the core. These pre-main-sequence stars are often surrounded by a protoplanetary disk and powered mainly by the conversion of gravitational energy. The period of gravitational contraction lasts about 10 million years for a star like the sun, up to 100 million years for a red dwarf.
Early stars of less than 2 M☉ are called T Tauri stars, while those with greater mass are Herbig Ae/Be stars. These newly formed stars emit jets of gas along their axis of rotation, which may reduce the angular momentum of the collapsing star and result in small patches of nebulosity known as Herbig–Haro objects.
These jets, in combination with radiation from nearby massive stars, may help to drive away the surrounding cloud from which the star was formed.
Early in their development, T Tauri stars follow the Hayashi track—they contract and decrease in luminosity while remaining at roughly the same temperature. Less massive T Tauri stars follow this track to the main sequence, while more massive stars turn onto the Henyey track.
Most stars are observed to be members of binary star systems, and the properties of those binaries are the result of the conditions in which they formed. A gas cloud must lose its angular momentum in order to collapse and form a star. The fragmentation of the cloud into multiple stars distributes some of that angular momentum. The primordial binaries transfer some angular momentum by gravitational interactions during close encounters with other stars in young stellar clusters. These interactions tend to split apart more widely separated (soft) binaries while causing hard binaries to become more tightly bound. This produces the separation of binaries into their two observed populations distributions.
Main sequence
Main article: Main sequence
Stars spend about 90% of their lifetimes fusing hydrogen into helium in high-temperature-and-pressure reactions in their cores. Such stars are said to be on the main sequence and are called dwarf stars. Starting at zero-age main sequence, the proportion of helium in a star's core will steadily increase, the rate of nuclear fusion at the core will slowly increase, as will the star's temperature and luminosity.
The Sun, for example, is estimated to have increased in luminosity by about 40% since it reached the main sequence 4.6 billion (4.6×10) years ago.
Every star generates a stellar wind of particles that causes a continual outflow of gas into space. For most stars, the mass lost is negligible. The Sun loses 10 M☉ every year, or about 0.01% of its total mass over its entire lifespan. However, very massive stars can lose 10 to 10 M☉ each year, significantly affecting their evolution. Stars that begin with more than 50 M☉ can lose over half their total mass while on the main sequence.
An example of a Hertzsprung–Russell diagram for a set of stars that includes the Sun (center) (see Classification)
The time a star spends on the main sequence depends primarily on the amount of fuel it has and the rate at which it fuses it. The Sun is expected to live 10 billion (10) years. Massive stars consume their fuel very rapidly and are short-lived. Low mass stars consume their fuel very slowly. Stars less massive than 0.25 M☉, called red dwarfs, are able to fuse nearly all of their mass while stars of about 1 M☉ can only fuse about 10% of their mass. The combination of their slow fuel-consumption and relatively large usable fuel supply allows low mass stars to last about one trillion (10×10) years; the most extreme of 0.08 M☉ will last for about 12 trillion years. Red dwarfs become hotter and more luminous as they accumulate helium. When they eventually run out of hydrogen, they contract into a white dwarf and decline in temperature. Since the lifespan of such stars is greater than the current age of the universe (13.8 billion years), no stars under about 0.85 M☉ are expected to have moved off the main sequence.
Besides mass, the elements heavier than helium can play a significant role in the evolution of stars. Astronomers label all elements heavier than helium "metals", and call the chemical concentration of these elements in a star, its metallicity. A star's metallicity can influence the time the star takes to burn its fuel, and controls the formation of its magnetic fields, which affects the strength of its stellar wind. Older, population II stars have substantially less metallicity than the younger, population I stars due to the composition of the molecular clouds from which they formed. Over time, such clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres.
Post–main sequence
Main articles: Subgiant, Red giant, Horizontal branch, Red clump, and Asymptotic giant branch
Betelgeuse as seen by ALMA. This is the first time that ALMA has observed the surface of a star and resulted in the highest-resolution image of Betelgeuse available.
As stars of at least 0.4 M☉ exhaust the supply of hydrogen at their core, they start to fuse hydrogen in a shell surrounding the helium core. The outer layers of the star expand and cool greatly as they transition into a red giant. In some cases, they will fuse heavier elements at the core or in shells around the core. As the stars expand, they throw part of their mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. In about 5 billion years, when the Sun enters the helium burning phase, it will expand to a maximum radius of roughly 1 astronomical unit (150 million kilometres), 250 times its present size, and lose 30% of its current mass.
As the hydrogen-burning shell produces more helium, the core increases in mass and temperature. In a red giant of up to 2.25 M☉, the mass of the helium core becomes degenerate prior to helium fusion. Finally, when the temperature increases sufficiently, core helium fusion begins explosively in what is called a helium flash, and the star rapidly shrinks in radius, increases its surface temperature, and moves to the horizontal branch of the HR diagram. For more massive stars, helium core fusion starts before the core becomes degenerate, and the star spends some time in the red clump, slowly burning helium, before the outer convective envelope collapses and the star then moves to the horizontal branch.
After a star has fused the helium of its core, it begins fusing helium along a shell surrounding the hot carbon core. The star then follows an evolutionary path called the asymptotic giant branch (AGB) that parallels the other described red-giant phase, but with a higher luminosity. The more massive AGB stars may undergo a brief period of carbon fusion before the core becomes degenerate. During the AGB phase, stars undergo thermal pulses due to instabilities in the core of the star. In these thermal pulses, the luminosity of the star varies and matter is ejected from the star's atmosphere, ultimately forming a planetary nebula. As much as 50 to 70% of a star's mass can be ejected in this mass loss process. Because energy transport in an AGB star is primarily by convection, this ejected material is enriched with the fusion products dredged up from the core. Therefore, the planetary nebula is enriched with elements like carbon and oxygen. Ultimately, the planetary nebula disperses, enriching the general interstellar medium. Therefore, future generations of stars are made of the "star stuff" from past stars.
Massive stars
Main articles: Supergiant star, Hypergiant, and Wolf–Rayet star
Onion-like layers at the core of a massive, evolved star just before core collapses
During their helium-burning phase, a star of more than 9 solar masses expands to form first a blue supergiant and then a red supergiant. Particularly massive stars may evolve to a Wolf–Rayet star, characterised by spectra dominated by emission lines of elements heavier than hydrogen, which have reached the surface due to strong convection and intense mass loss, or from stripping of the outer layers.
When helium is exhausted at the core of a massive star, the core contracts and the temperature and pressure rises enough to fuse carbon (see Carbon-burning process). This process continues, with the successive stages being fueled by neon (see neon-burning process), oxygen (see oxygen-burning process), and silicon (see silicon-burning process). Near the end of the star's life, fusion continues along a series of onion-layer shells within a massive star. Each shell fuses a different element, with the outermost shell fusing hydrogen; the next shell fusing helium, and so forth.
The final stage occurs when a massive star begins producing iron. Since iron nuclei are more tightly bound than any heavier nuclei, any fusion beyond iron does not produce a net release of energy.
Collapse
As a star's core shrinks, the intensity of radiation from that surface increases, creating such radiation pressure on the outer shell of gas that it will push those layers away, forming a planetary nebula. If what remains after the outer atmosphere has been shed is less than roughly 1.4 M☉, it shrinks to a relatively tiny object about the size of Earth, known as a white dwarf. White dwarfs lack the mass for further gravitational compression to take place. The electron-degenerate matter inside a white dwarf is no longer a plasma. Eventually, white dwarfs fade into black dwarfs over a very long period of time.
The Crab Nebula, remnants of a supernova that was first observed around 1050 AD
In massive stars, fusion continues until the iron core has grown so large (more than 1.4 M☉) that it can no longer support its own mass. This core will suddenly collapse as its electrons are driven into its protons, forming neutrons, neutrinos, and gamma rays in a burst of electron capture and inverse beta decay. The shockwave formed by this sudden collapse causes the rest of the star to explode in a supernova. Supernovae become so bright that they may briefly outshine the star's entire home galaxy. When they occur within the Milky Way, supernovae have historically been observed by naked-eye observers as "new stars" where none seemingly existed before.
A supernova explosion blows away the star's outer layers, leaving a remnant such as the Crab Nebula. The core is compressed into a neutron star, which sometimes manifests itself as a pulsar or X-ray burster. In the case of the largest stars, the remnant is a black hole greater than 4 M☉. In a neutron star the matter is in a state known as neutron-degenerate matter, with a more exotic form of degenerate matter, QCD matter, possibly present in the core.
The blown-off outer layers of dying stars include heavy elements, which may be recycled during the formation of new stars. These heavy elements allow the formation of rocky planets. The outflow from supernovae and the stellar wind of large stars play an important part in shaping the interstellar medium.
Binary stars
Binary stars' evolution may significantly differ from that of single stars of the same mass. For example, when any star expands to become a red giant, it may overflow its Roche lobe, the surrounding region where material is gravitationally bound to it; if stars in a binary system are close enough, some of that material may overflow to the other star, yielding phenomena including contact binaries, common-envelope binaries, cataclysmic variables, blue stragglers, and type Ia supernovae. Mass transfer leads to cases such as the Algol paradox, where the most-evolved star in a system is the least massive.
The evolution of binary star and higher-order star systems is intensely researched since so many stars have been found to be members of binary systems. Around half of Sun-like stars, and an even higher proportion of more massive stars, form in multiple systems, and this may greatly influence such phenomena as novae and supernovae, the formation of certain types of star, and the enrichment of space with nucleosynthesis products.
The influence of binary star evolution on the formation of evolved massive stars such as luminous blue variables, Wolf–Rayet stars, and the progenitors of certain classes of core collapse supernova is still disputed. Single massive stars may be unable to expel their outer layers fast enough to form the types and numbers of evolved stars that are observed, or to produce progenitors that would explode as the supernovae that are observed. Mass transfer through gravitational stripping in binary systems is seen by some astronomers as the solution to that problem.
Distribution
Artist's impression of the Sirius system, a white dwarf star in orbit around an A-type main-sequence star
Stars are not spread uniformly across the universe but are normally grouped into galaxies along with interstellar gas and dust. A typical large galaxy like the Milky Way contains hundreds of billions of stars. There are more than 2 trillion (10) galaxies, though most are less than 10% the mass of the Milky Way. Overall, there are likely to be between 10 and 10 stars (more stars than all the grains of sand on planet Earth). Most stars are within galaxies, but between 10 and 50% of the starlight in large galaxy clusters may come from stars outside of any galaxy.
A multi-star system consists of two or more gravitationally bound stars that orbit each other. The simplest and most common multi-star system is a binary star, but systems of three or more stars exist. For reasons of orbital stability, such multi-star systems are often organized into hierarchical sets of binary stars. Larger groups are called star clusters. These range from loose stellar associations with only a few stars to open clusters with dozens to thousands of stars, up to enormous globular clusters with hundreds of thousands of stars. Such systems orbit their host galaxy. The stars in an open or globular cluster all formed from the same giant molecular cloud, so all members normally have similar ages and compositions.
Many stars are observed, and most or all may have originally formed in gravitationally bound, multiple-star systems. This is particularly true for very massive O and B class stars, 80% of which are believed to be part of multiple-star systems. The proportion of single star systems increases with decreasing star mass, so that only 25% of red dwarfs are known to have stellar companions. As 85% of all stars are red dwarfs, more than two thirds of stars in the Milky Way are likely single red dwarfs.
In a 2017 study of the Perseus molecular cloud, astronomers found that most of the newly formed stars are in binary systems. In the model that best explained the data, all stars initially formed as binaries, though some binaries later split up and leave single stars behind.
This view of NGC 6397 includes stars known as blue stragglers for their location on the Hertzsprung–Russell diagram.
The nearest star to the Earth, apart from the Sun, is Proxima Centauri, 4.2465 light-years (40.175 trillion kilometres) away. Travelling at the orbital speed of the Space Shuttle, 8 kilometres per second (29,000 kilometres per hour), it would take about 150,000 years to arrive. This is typical of stellar separations in galactic discs. Stars can be much closer to each other in the centres of galaxies and in globular clusters, or much farther apart in galactic halos.
Due to the relatively vast distances between stars outside the galactic nucleus, collisions between stars are thought to be rare. In denser regions such as the core of globular clusters or the galactic center, collisions can be more common. Such collisions can produce what are known as blue stragglers. These abnormal stars have a higher surface temperature and thus are bluer than stars at the main sequence turnoff in the cluster to which they belong; in standard stellar evolution, blue stragglers would already have evolved off the main sequence and thus would not be seen in the cluster.
Characteristics
Almost everything about a star is determined by its initial mass, including such characteristics as luminosity, size, evolution, lifespan, and its eventual fate.
Age
Main article: Stellar age estimation
Most stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.8 billion years old—the observed age of the universe. The oldest star yet discovered, HD 140283, nicknamed Methuselah star, is an estimated 14.46 ± 0.8 billion years old. (Due to the uncertainty in the value, this age for the star does not conflict with the age of the universe, determined by the Planck satellite as 13.799 ± 0.021).
The more massive the star, the shorter its lifespan, primarily because massive stars have greater pressure on their cores, causing them to burn hydrogen more rapidly. The most massive stars last an average of a few million years, while stars of minimum mass (red dwarfs) burn their fuel very slowly and can last tens to hundreds of billions of years.
Lifetimes of stages of stellar evolution in billions of years
Initial Mass (M☉)
Main Sequence
Subgiant
First Red Giant
Core He Burning
1.0
9.33
2.57
0.76
0.13
1.6
2.28
0.03
0.12
0.13
2.0
1.20
0.01
0.02
0.28
5.0
0.10
0.0004
0.0003
0.02
Chemical composition
See also: Metallicity and Molecules in stars
When stars form in the present Milky Way galaxy, they are composed of about 71% hydrogen and 27% helium, as measured by mass, with a small fraction of heavier elements. Typically the portion of heavy elements is measured in terms of the iron content of the stellar atmosphere, as iron is a common element and its absorption lines are relatively easy to measure. The portion of heavier elements may be an indicator of the likelihood that the star has a planetary system.
As of 2005 the star with the lowest iron content ever measured is the dwarf HE1327-2326, with only 1/200,000th the iron content of the Sun. By contrast, the super-metal-rich star μ Leonis has nearly double the abundance of iron as the Sun, while the planet-bearing star 14 Herculis has nearly triple the iron. Chemically peculiar stars show unusual abundances of certain elements in their spectrum; especially chromium and rare earth elements. Stars with cooler outer atmospheres, including the Sun, can form various diatomic and polyatomic molecules.
Diameter
Main articles: List of largest known stars, List of smallest stars, and Solar radius
Some of the well-known stars with their apparent colors and relative sizes
Due to their great distance from the Earth, all stars except the Sun appear to the unaided eye as shining points in the night sky that twinkle because of the effect of the Earth's atmosphere. The Sun is close enough to the Earth to appear as a disk instead, and to provide daylight. Other than the Sun, the star with the largest apparent size is R Doradus, with an angular diameter of only 0.057 arcseconds.
The disks of most stars are much too small in angular size to be observed with current ground-based optical telescopes, and so interferometer telescopes are required to produce images of these objects. Another technique for measuring the angular size of stars is through occultation. By precisely measuring the drop in brightness of a star as it is occulted by the Moon (or the rise in brightness when it reappears), the star's angular diameter can be computed.
Stars range in size from neutron stars, which vary anywhere from 20 to 40 km (25 mi) in diameter, to supergiants like Betelgeuse in the Orion constellation, which has a diameter about 1,000 times that of the Sun with a much lower density.
Kinematics
Main article: Stellar kinematics
The Pleiades, an open cluster of stars in the constellation of Taurus. These stars share a common motion through space.
The motion of a star relative to the Sun can provide useful information about the origin and age of a star, as well as the structure and evolution of the surrounding galaxy. The components of motion of a star consist of the radial velocity toward or away from the Sun, and the traverse angular movement, which is called its proper motion.
Radial velocity is measured by the doppler shift of the star's spectral lines and is given in units of km/s. The proper motion of a star, its parallax, is determined by precise astrometric measurements in units of milli-arc seconds (mas) per year. With knowledge of the star's parallax and its distance, the proper motion velocity can be calculated. Together with the radial velocity, the total velocity can be calculated. Stars with high rates of proper motion are likely to be relatively close to the Sun, making them good candidates for parallax measurements.
When both rates of movement are known, the space velocity of the star relative to the Sun or the galaxy can be computed. Among nearby stars, it has been found that younger population I stars have generally lower velocities than older, population II stars. The latter have elliptical orbits that are inclined to the plane of the galaxy. A comparison of the kinematics of nearby stars has allowed astronomers to trace their origin to common points in giant molecular clouds, and are referred to as stellar associations.
Magnetic field
Main article: Stellar magnetic field
Surface magnetic field of SU Aur (a young star of T Tauri type), reconstructed by means of Zeeman–Doppler imaging
The magnetic field of a star is generated within regions of the interior where convective circulation occurs. This movement of conductive plasma functions like a dynamo, wherein the movement of electrical charges induce magnetic fields, as does a mechanical dynamo. Those magnetic fields have a great range that extend throughout and beyond the star. The strength of the magnetic field varies with the mass and composition of the star, and the amount of magnetic surface activity depends upon the star's rate of rotation. This surface activity produces starspots, which are regions of strong magnetic fields and lower than normal surface temperatures. Coronal loops are arching magnetic field flux lines that rise from a star's surface into the star's outer atmosphere, its corona. The coronal loops can be seen due to the plasma they conduct along their length. Stellar flares are bursts of high-energy particles that are emitted due to the same magnetic activity.
Young, rapidly rotating stars tend to have high levels of surface activity because of their magnetic field. The magnetic field can act upon a star's stellar wind, functioning as a brake to gradually slow the rate of rotation with time. Thus, older stars such as the Sun have a much slower rate of rotation and a lower level of surface activity. The activity levels of slowly rotating stars tend to vary in a cyclical manner and can shut down altogether for periods of time. During
the Maunder Minimum, for example, the Sun underwent a
70-year period with almost no sunspot activity.
Mass
Main article: Stellar mass
One of the most massive stars known is Eta Carinae, which, with 100–150 times as much mass as the Sun, will have a lifespan of only several million years. Studies of the most massive open clusters suggests 150 M☉ as a rough upper limit for stars in the current era of the universe. This
represents an empirical value for the theoretical limit on the mass of forming stars due to increasing radiation pressure on the accreting gas cloud. Several stars in the R136 cluster in the Large Magellanic Cloud have been measured with larger masses, but
it has been determined that they could have been created through the collision and merger of massive stars in close binary systems, sidestepping the 150 M☉ limit on massive star formation.
The reflection nebula NGC 1999 is brilliantly illuminated by V380 Orionis. The black patch of sky is a vast hole of empty space and not a dark nebula as previously thought.
The first stars to form after the Big Bang may have been larger, up to 300 M☉, due
to the complete absence of elements heavier than lithium in their composition. This generation of supermassive population III stars is likely to have existed in the very early universe (i.e., they are observed to have a high redshift), and may have started the production of chemical elements heavier than hydrogen that are needed for the later formation of planets and life. In June 2015, astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z = 6.60.
With a mass only 80 times that of Jupiter (MJ), 2MASS J0523-1403 is the smallest known star undergoing nuclear fusion in its core. For
stars with metallicity similar to the Sun, the theoretical minimum mass the star can have and still undergo fusion at the core, is estimated to be about 75 MJ. When the metallicity is very low, the minimum star size seems to be about 8.3% of the solar mass, or about 87 MJ. Smaller bodies called brown dwarfs, occupy a poorly defined grey area between stars and gas giants.
The combination of the radius and the mass of a star determines its surface gravity. Giant stars have a much lower surface gravity than do main sequence stars, while the opposite is the case for degenerate, compact stars such as white dwarfs. The surface gravity can influence the appearance of a star's spectrum, with higher gravity causing a broadening of the absorption lines.
Rotation
Main article: Stellar rotation
The rotation rate of stars can be determined through spectroscopic measurement, or more exactly determined by tracking their starspots. Young stars can have a rotation greater than 100 km/s at the equator. The B-class star Achernar, for example, has an equatorial velocity of about 225 km/s or greater, causing its equator to bulge outward and giving it an equatorial diameter that is more than 50% greater than between the poles. This rate of rotation is just below the critical velocity of 300 km/s at which speed the star would break apart. By contrast, the Sun rotates once every 25–35 days depending on latitude, with an equatorial velocity of 1.93 km/s. A main sequence star's magnetic field and the stellar wind serve to slow its rotation by a significant amount as it evolves on the main sequence.
Degenerate stars have contracted into a compact mass, resulting in a rapid rate of rotation. However they have relatively low rates of rotation compared to what would be expected by conservation of angular momentum—the tendency of a rotating body to compensate for a contraction in size by increasing its rate of spin. A large portion of the star's angular momentum is dissipated as a result of mass loss through the stellar wind. In spite of this, the rate of rotation for a pulsar can be very rapid. The pulsar at the heart of the Crab nebula, for example, rotates 30 times per second. The rotation rate of the pulsar will gradually slow due to the emission of radiation.
Temperature
The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius, and is often estimated from the star's color index. The temperature is normally given in terms of an effective temperature, which is the temperature of an idealized black body that radiates its energy at the same luminosity per surface area as the star. The effective temperature is only representative of the surface, as the temperature increases toward the core. The temperature in the core region of a star is several million kelvins.
The stellar temperature will determine the rate of ionization of various elements, resulting in characteristic absorption lines in the spectrum. The surface temperature of a star, along with its visual absolute magnitude and absorption features, is used to classify a star (see classification below).
Massive main sequence stars can have surface temperatures of 50,000 K. Smaller stars such as the Sun have surface temperatures of a few thousand K. Red giants have relatively low surface temperatures of about 3,600 K; but they have a high luminosity due to their large exterior surface area.
Radiation
The energy produced by stars, a product of nuclear fusion, radiates to space as both electromagnetic radiation and particle radiation. The particle radiation emitted by a star is manifested as the stellar wind, which
streams from the outer layers as electrically charged protons and alpha and beta particles. A steady stream of almost massless neutrinos emanate directly from the star's core.
The production of energy at the core is the reason stars shine so brightly: every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element, gamma ray photons are released from the nuclear fusion product. This energy is converted to other forms of electromagnetic energy of lower frequency, such as visible light, by the time it reaches the star's outer layers.
The color of a star, as determined by the most intense frequency of the visible light, depends on the temperature of the star's outer layers, including its photosphere. Besides visible light, stars emit forms of electromagnetic radiation that are invisible to the human eye. In fact, stellar electromagnetic radiation spans the entire electromagnetic spectrum, from the longest wavelengths of radio waves through infrared, visible light, ultraviolet, to the shortest of X-rays, and gamma rays. From the standpoint of total energy emitted by a star, not all components of stellar electromagnetic radiation are significant, but all frequencies provide insight into the star's physics.
Using the stellar spectrum, astronomers can determine the surface temperature, surface gravity, metallicity and rotational velocity of a star. If the distance of the star is found, such as by measuring the parallax, then the luminosity of the star can be derived. The mass, radius, surface gravity, and rotation period can then be estimated based on stellar models. (Mass can be calculated for stars in binary systems by measuring their orbital velocities and distances. Gravitational microlensing has been used to measure the mass of a single star.) With these parameters, astronomers can estimate the age of the star.
Luminosity
The luminosity of a star is the amount of light and other forms of radiant energy it radiates per unit of time. It has units of power. The luminosity of a star is determined by its radius and surface temperature. Many stars do not radiate uniformly across their entire surface. The rapidly rotating star Vega, for example, has a higher energy flux (power per unit area) at its poles than along its equator.
Patches of the star's surface with a lower temperature and luminosity than average are known as starspots. Small, dwarf stars such as the Sun generally have essentially featureless disks with only small starspots. Giant stars have much larger, more obvious starspots, and
they exhibit strong stellar limb darkening. That is, the brightness decreases towards the edge of the stellar disk. Red dwarf flare stars such as UV Ceti may possess prominent starspot features.
Magnitude
Main articles: Apparent magnitude and Absolute magnitude
The apparent brightness of a star is expressed in terms of its apparent magnitude. It is a function of the star's luminosity, its distance from Earth, the extinction effect of interstellar dust and gas, and the altering of the star's light as it passes through Earth's atmosphere. Intrinsic or absolute magnitude is directly related to a star's luminosity, and is the apparent magnitude a star would be if the distance between the Earth and the star were 10 parsecs (32.6 light-years).
Number of stars brighter than magnitude
Apparentmagnitude
Number of stars
0
4
1
15
2
48
3
171
4
513
5
1,602
6
4,800
7
14,000
Both the apparent and absolute magnitude scales are logarithmic units: one whole number difference in magnitude is equal to a brightness variation of about 2.5 times (the 5th root of 100 or approximately 2.512). This means that a first magnitude star (+1.00) is about 2.5 times brighter than a second magnitude (+2.00) star, and about 100 times brighter than a sixth magnitude star (+6.00). The faintest stars visible to the naked eye under good seeing conditions are about magnitude +6.
On both apparent and absolute magnitude scales, the smaller the magnitude number, the brighter the star; the larger the magnitude number, the fainter the star. The brightest stars, on either scale, have negative magnitude numbers. The variation in brightness (ΔL) between two stars is calculated by subtracting the magnitude number of the brighter star (mb) from the magnitude number of the fainter star (mf), then using the difference as an exponent for the base number 2.512; that is to say:
Δ
m
=
m
f
−
m
b
{\displaystyle \Delta {m}=m_{\mathrm {f} }-m_{\mathrm {b} }}
2.512
Δ
m
=
Δ
L
{\displaystyle 2.512^{\Delta {m}}=\Delta {L}}
Relative to both luminosity and distance from Earth, a star's absolute magnitude (M) and apparent magnitude (m) are not equivalent; for example, the bright star Sirius has an apparent magnitude of −1.44, but it has an absolute magnitude of +1.41.
The Sun has an apparent magnitude of −26.7, but its absolute magnitude is only +4.83. Sirius, the brightest star in the night sky as seen from Earth, is approximately 23 times more luminous than the Sun, while Canopus, the second brightest star in the night sky with an absolute magnitude of −5.53, is approximately 14,000 times more luminous than the Sun. Despite Canopus being vastly more luminous than Sirius, the latter star appears the brighter of the two. This is because Sirius is merely 8.6 light-years from the Earth, while Canopus is much farther away at a distance of 310 light-years.
The most luminous known stars have absolute magnitudes of roughly −12, corresponding to 6 million times the luminosity of the Sun. Theoretically, the least luminous stars are at the lower limit of mass at which stars are capable of supporting nuclear fusion of hydrogen in the core; stars just above this limit have been located in the NGC 6397 cluster. The faintest red dwarfs in the cluster are absolute magnitude 15, while a 17th absolute magnitude white dwarf has been discovered.
Classification
Main article: Stellar classification
Surface temperature ranges fordifferent stellar classes
Class
Temperature
Sample star
O
33,000 K or more
Zeta Ophiuchi
B
10,500–30,000 K
Rigel
A
7,500–10,000 K
Altair
F
6,000–7,200 K
Procyon A
G
5,500–6,000 K
Sun
K
4,000–5,250 K
Epsilon Indi
M
2,600–3,850 K
Proxima Centauri
The current stellar classification system originated in the early 20th century, when stars were classified from A to Q based on the strength of the hydrogen line. It was thought that the hydrogen line strength was a simple linear function of temperature. Instead, it was more complicated: it strengthened with increasing temperature, peaked near 9000 K, and then declined at greater temperatures. The classifications were since reordered by temperature, on which the modern scheme is based.
Stars are given a single-letter classification according to their spectra, ranging from type O, which are very hot, to M, which are so cool that molecules may form in their atmospheres. The main classifications in order of decreasing surface temperature are: O, B, A, F, G, K, and M. A variety of rare spectral types are given special classifications. The most common of these are types L and T, which classify the coldest low-mass stars and brown dwarfs. Each letter has 10 sub-divisions, numbered from 0 to 9, in order of decreasing temperature. However, this system breaks down at extreme high temperatures as classes O0 and O1 may not exist.
In addition, stars may be classified by the luminosity effects found in their spectral lines, which correspond to their spatial size and is determined by their surface gravity. These range from 0 (hypergiants) through III (giants) to V (main sequence dwarfs); some authors add VII (white dwarfs). Main sequence stars fall along a narrow, diagonal band when graphed according to their absolute magnitude and spectral type. The Sun is a main sequence G2V yellow dwarf of intermediate temperature and ordinary size.
There is additional nomenclature in the form of lower-case letters added to the end of the spectral type to indicate peculiar features of the spectrum. For example, an "e" can indicate the presence of emission lines; "m" represents unusually strong levels of metals, and "var" can mean variations in the spectral type.
White dwarf stars have their own class that begins with the letter D. This is further sub-divided into the classes DA, DB, DC, DO, DZ, and DQ, depending on the types of prominent lines found in the spectrum. This is followed by a numerical value that indicates the temperature.
Variable stars
Main article: Variable star
The asymmetrical appearance of Mira, an oscillating variable star
Variable stars have periodic or random changes in luminosity because of intrinsic or extrinsic properties. Of the intrinsically variable stars, the primary types can be subdivided into three principal groups.
During their stellar evolution, some stars pass through phases where they can become pulsating variables. Pulsating variable stars vary in radius and luminosity over time, expanding and contracting with periods ranging from minutes to years, depending on the size of the star. This category includes Cepheid and Cepheid-like stars, and long-period variables such as Mira.
Eruptive variables are stars that experience sudden increases in luminosity because of flares or mass ejection events. This group includes protostars, Wolf-Rayet stars, and flare stars, as well as giant and supergiant stars.
Cataclysmic or explosive variable stars are those that undergo a dramatic change in their properties. This group includes novae and supernovae. A binary star system that includes a nearby white dwarf can produce certain types of these spectacular stellar explosions, including the nova and a Type 1a supernova. The explosion is created when the white dwarf accretes hydrogen from the companion star, building up mass until the hydrogen undergoes fusion. Some novae are recurrent, having periodic outbursts of moderate amplitude.
Stars can vary in luminosity because of extrinsic factors, such as eclipsing binaries, as well as rotating stars that produce extreme starspots. A notable example of an eclipsing binary is Algol, which regularly varies in magnitude from 2.1 to 3.4 over a period of 2.87 days.
Structure
Main article: Stellar structure
Internal structures of main sequence stars with masses indicated in solar masses, convection zones with arrowed cycles, and radiative zones with red flashes. Left to right, a red dwarf, a yellow dwarf, and a blue-white main sequence star
The interior of a stable star is in a state of hydrostatic equilibrium: the forces on any small volume almost exactly counterbalance each other. The balanced forces are inward gravitational force and an outward force due to the pressure gradient within the star. The pressure gradient is established by the temperature gradient of the plasma; the outer part of the star is cooler than the core. The temperature at the core of a main sequence or giant star is at least on the order of 10 K. The resulting temperature and pressure at the hydrogen-burning core of a main sequence star are sufficient for nuclear fusion to occur and for sufficient energy to be produced to prevent further collapse of the star.
As atomic nuclei are fused in the core, they emit energy in the form of gamma rays. These photons interact with the surrounding plasma, adding to the thermal energy at the core. Stars on the main sequence convert hydrogen into helium, creating a slowly but steadily increasing proportion of helium in the core. Eventually the helium content becomes predominant, and energy production ceases at the core. Instead, for stars of more than 0.4 M☉, fusion occurs in a slowly expanding shell around the degenerate helium core.
In addition to hydrostatic equilibrium, the interior of a stable star will maintain an energy balance of thermal equilibrium. There is a radial temperature gradient throughout the interior that results in a flux of energy flowing toward the exterior. The outgoing flux of energy leaving any layer within the star will exactly match the incoming flux from below.
The radiation zone is the region of the stellar interior where the flux of energy outward is dependent on radiative heat transfer, since convective heat transfer is inefficient in that zone. In this region the plasma will not be perturbed, and any mass motions will die out. Where this is not the case, then the plasma becomes unstable and convection will occur, forming a convection zone. This can occur, for example, in regions where very high energy fluxes occur, such as near the core or in areas with high opacity (making radiatative heat transfer inefficient) as in the outer envelope.
The occurrence of convection in the outer envelope of a main sequence star depends on the star's mass. Stars with several times the mass of the Sun have a convection zone deep within the interior and a radiative zone in the outer layers. Smaller stars such as the Sun are just the opposite, with the convective zone located in the outer layers. Red dwarf stars with less than 0.4 M☉ are convective throughout, which prevents the accumulation of a helium core. For most stars the convective zones will vary over time as the star ages and the constitution of the interior is modified.
A cross-section of the Sun
The photosphere is that portion of a star that is visible to an observer. This is the layer at which the plasma of the star becomes transparent to photons of light. From here, the energy generated at the core becomes free to propagate into space. It is within the photosphere that sun spots, regions of lower than average temperature, appear.
Above the level of the photosphere is the stellar atmosphere. In a main sequence star such as the Sun, the lowest level of the atmosphere, just above the photosphere, is the thin chromosphere region, where spicules appear and stellar flares begin. Above this is the transition region, where the temperature rapidly increases within a distance of only 100 km (62 mi). Beyond this is the corona, a volume of super-heated plasma that can extend outward to several million kilometres. The existence of a corona appears to be dependent on a convective zone in the outer layers of the star. Despite its high temperature, the corona emits very little light, due to its low gas density. The corona region of the Sun is normally only visible during a solar eclipse.
From the corona, a stellar wind of plasma particles expands outward from the star, until it interacts with the interstellar medium. For the Sun, the influence of its solar wind extends throughout a bubble-shaped region called the heliosphere.
Nuclear fusion reaction pathways
Main article: Stellar nucleosynthesis
Overview of the proton–proton chainThe carbon-nitrogen-oxygen cycle
When nuclei fuse, the mass of the fused product is less than the mass of the original parts. This lost mass is converted to electromagnetic energy, according to the mass–energy equivalence relationship
E
=
m
c
2
{\displaystyle E=mc^{2}}
. A variety of nuclear fusion reactions take place in the cores of stars, that depend upon their mass and composition.
The hydrogen fusion process is temperature-sensitive, so a moderate increase in the core temperature will result in a significant increase in the fusion rate. As a result, the core temperature of main sequence stars only varies from 4 million kelvin for a small M-class star to 40 million kelvin for a massive O-class star.
In the Sun, with a 16-million-kelvin core, hydrogen fuses to form helium in the proton–proton chain reaction:
4H → 2H + 2e + 2νe(2 x 0.4 MeV)
2e + 2e → 2γ (2 x 1.0 MeV)
2H + 2H → 2He + 2γ (2 x 5.5 MeV)
2He → He + 2H (12.9 MeV)
There are a couple other paths, in which He and He combine to form Be, which eventually (with the addition of another proton) yields two He, a gain of one.
All these reactions result in the overall reaction:
4H → He + 2γ + 2νe (26.7 MeV)
where γ is a gamma ray photon, νe is a neutrino, and H and He are isotopes of hydrogen and helium, respectively. The energy released by this reaction is in millions of electron volts. Each individual reaction produces only a tiny amount of energy, but because enormous numbers of these reactions occur constantly, they produce all the energy necessary to sustain the star's radiation output. In comparison, the combustion of two hydrogen gas molecules with one oxygen gas molecule releases only 5.7 eV.
In more massive stars, helium is produced in a cycle of reactions catalyzed by carbon called the carbon-nitrogen-oxygen cycle.
In evolved stars with cores at 100 million kelvin and masses between 0.5 and 10 M☉, helium can be transformed into carbon in the triple-alpha process that uses the intermediate element beryllium:
He + He + 92 keV → Be
He + Be + 67 keV → C
C → C + γ + 7.4 MeV
For an overall reaction of:
Overview of consecutive fusion processes in massive stars
3He → C + γ + 7.2 MeV
In massive stars, heavier elements can be burned in a contracting core through the neon-burning process and oxygen-burning process. The final stage in the stellar nucleosynthesis process is the silicon-burning process that results in the production of the stable isotope iron-56. Any further fusion would be an endothermic process that consumes energy, and so further energy can only be produced through gravitational collapse.
Duration of the main phases of fusion for a 20 M☉ star
Fuelmaterial
Temperature(million kelvins)
Density(kg/cm)
Burn duration(τ in years)
H
37
0.0045
8.1 million
He
188
0.97
1.2 million
C
870
170
976
Ne
1,570
3,100
0.6
O
1,980
5,550
1.25
S/Si
3,340
33,400
0.0315
See also
Fusor (astronomy)
Outline of astronomy
Sidereal time
Star clocks
Star count
Stars and planetary systems in fiction | biology | 12273 | https://da.wikipedia.org/wiki/Stjerne | Stjerne | En stjerne er en glødende kugle af plasma, der er i dynamisk balance, idet den holdes sammen af tyngdekraften og udspilet af strålingstrykket fra dens indre fusionsprocesser. Den nærmeste stjerne i forhold til Jorden er Solen, der er kilden til det meste af den energi der er til rådighed på Jorden. Andre stjerner er synlige på himlen, når de ikke overstråles af Solens lys. En stjerne skinner, fordi fusion i dens kerne frigør energi der transporteres gennem stjernens indre og derefter stråler ud i rummet fra stjernens overflade i form af elektromagnetiske bølger. Desuden vil der være en såkaldt solvind, der er en strøm af ladede partikler som føres væk fra stjernen af strålingstrykket. En del af den udsendte elektromagnetiske stråling ligger i det synlige område. Næsten alle grundstoffer tungere end hydrogen og helium er skabt i det indre af stjerner. Det meste af det lys, som vi kan se kommer fra stjerner.
Astronomer kan bestemme massen, alderen, den kemiske sammensætning og mange andre egenskaber ved en stjerne gennem observation af dens spektrum, luminositet, og i visse tilfælde den egenbevægelse gennem rummet. En stjernes masse er altafgørende for dens udvikling som stjerne og dermed dens skæbne. Andre karakteristiske egenskaber ved en stjerne er bestemt ved dens udviklingshistorie, herunder dens diameter, rotation, bevægelse og temperatur. Et plot af stjerners temperaturer mod deres luminositet, kendt som et Hertzsprung-Russell diagram (H–R diagram), muliggør at finde alder og udviklingstrin for en stjerne.
Udgangspunktet for dannelsen af stjerner er skyer af interstellar gas, der primært består af brint, helium samt en meget lille andel af tungere grundstoffer. Hvis en sådan sky begynder at trække sig sammen på grund af de interne tyngdekræfter, så stiger tryk, tæthed og temperaturer. Er der brint nok, nåes det punkt, hvor de centrale dele er varme og tætte nok til at sætte gang i fusionsprocesser og en stjerne er født. Den del af stjernen der ligger uden for kernen transporterer den frembragte energi væk ved en kombination af varmelednings og varmestrålings-processer. Disse processer skaber et udadrettet tryk, der er i balance med gravitationskraften. Stjerner i denne tilstand af ligevægt ligger i den såkaldte hovedserie i Hertzsprung-Russell-diagrammet.
Hvis den stofmængde der er til rådighed, er mindre end ca. 0,08 gange vor Sols masse (ca. 11 Jupitermasser), kommer kerneområdet aldrig op på tryk- og temperaturforhold der tillader fusionsprocesserne. I stedet skabes en såkaldt brun dværg – et lyssvagt legeme som frigør energi ved gravitationel sammentrækning i stedet for kernereaktioner.
Når brintbeholdningen i stjernens indre er ved at slippe op, »vinder« presset af tyngden af det omkringliggende materiale og presser kernen sammen indtil en ny fusionsproces, triple-alfa-processen (hvor 3 heliumatomer samles til en kerne af et kulstofatom), kan finde sted: Varmen fra denne proces blæser de ydre lag af stjernen udad, så disse udvider sig og køles ned: Stjernen er nu det astronomerne kalder for en rød kæmpe (eller evt. rød superkæmpe).
Tunge stjerner kan fortsætte med at fusionere stadig støre atomkerner, indtil de ender i en reaktion der danner jern: Dette grundstof er »endestationen«, fordi kerneomdannelse af jernatomer kræver en nettotilførsel af energi, dvs. de bruger mere energi på fusionen end de producerer ved den.
Når der ikke længere produceres energi i en stjernes indre, vil tyngden fra de ydre dele af stjernen presse den nu »døde« kerne sammen. Stjerner som vor egen sol vil blot falde sammen til en varm og lille stjerne af den slags der kaldes for en hvid dværg: Denne producerer ikke »ny« energi, men køler blot ganske langsomt af.
For stjerner der er mere end ca. halvanden gange så tung som Solen, kan atomerne i kernens materiale ikke »bære vægten« af det sammensynkende materiale: Elektronerne omkring atomkernerne bliver ganske enkelt mast ind i kernen, hvor de reagerer med protonerne og danner neutroner. Denne kollaps er temmelig voldsom, og blæser de ydre dele af stjernen væk. Tilbage er blot et massivt legeme af tætpakkede neutroner – en såkaldt neutronstjerne.
Når endnu større stjerner kollapser, kan end ikke sammenpressede neutroner »bære vægten«, og slutproduktet er et såkaldt sort hul – et legeme så tæt, at den lokale tyngdekraft omkring det er for stærk til at selv lys kan forlade det.
Binære og flerstjernesystemer består af to eller flere stjerner der er gravitationelt forbundne og som hovedregel bevæger sig i stabile baner om hinanden. Hvis to sådanne stjerner er tæt nok på hinanden, kan de have en væsentlig indflydelse på hinandens livsforløb.
Ikke alle stjerner er ens, dette er de ikke fordi de kan være dannet under forskellige forhold. Der er nogen stjerner der har mere gas og har samt mere materiale til rådighed end andre stjerner har.
Observationel historie
Stjerner har været vigtige i alle kulturer. De har været forbundet med religiøse forestillinger og ceremonier og været anvendt til navigation.
Mange af oldtidens astronomer mente at stjernerne var fast forbundet med en himmelsk sfære, og derfor urokkelige. Stjerner blev inddelt i stjernebilleder af astronomer og de brugte dem til følge planetbevægelserne og den tilsyneladende bevægelse af Solen. Bevægelsen af Solen imod baggrundsstjernerne blev brugt til at lave kalendere, der kunne bruges til at planlægge landbrugets rytme. Den Gregorianske kalender, der bruges i stort set hele verden, er en solkalender baseret på vinklen mellem Jordens rotationsakse relativt til Solen.
Det ældste nøjagtigt daterede stjernekort er fra det gamle Egypten og stammer fra 1534 f.Kr. Islamiske astronomer gav arabiske navne til mange stjerner der stadigt bruges i dag, og de opfandt talrige astronomiske instrumenter der kunne bruges til at udregne stjernepositioner.
I det 11. århundrede beskrev Abū Rayhān al-Bīrūnī Mælkevejen som en samling af fragmenter der havde egenskaber som tågede stjerner, og angav også breddegraderne for forskellige stjerner under en måneformørkelse i 1019.
På trods af den udbredte forestilling om himmelkuglens uforanderlighed, var kinesiske astronomer klar over at der kunne dukke nye stjerner op på himmelen. Tidlige europæiske astronomer som Tycho Brahe
identificerede nye stjerner på nattehimmelen (senere kaldet novae), hvilket antydede at himmelkuglen ikke var uforanderlig. I 1584 foreslog Giordano Bruno at stjernerne faktisk var sole, og kunne have planeter, måske endda jordlignende, i kredsløb omkring sig. Denne ide var tidligere blevet rejst af de græske filosoffer Demokrit og Epikur. I det efterfølgende århundrede blev der efterhånden konsensus imellem astronomer om at stjernerne var fjerne sole. For at forklare hvorfor disse stjerner ikke udøvede nogen nettotiltrækning på solsystemet foreslog Isaac Newton at stjernerne var jævnt fordelt i enhver retning, en ide der oprindeligt stammede fra teologen Richard Bentley.
Den italienske astronom Geminiano Montanari optegnede observerede variationer i lysstyrken fra Algol i 1667. Edmund Halley udgav de første målinger af egenbevægelsen for nære "fiks"stjerner idet han viste at de havde ændret position siden optegnelserne fra Ptolemæus og Hipparchos.
Den første direkte måling af afstanden til en stjerne (61 Cygni i afstanden 11.4 lysår) blev lavet i 1838 af Friedrich Bessel der brugte en parallaksemetode. Parallaksemålingerne påviste de store afstande der er imellem stjernerne.
William Herschel var den første astronom der forsøgte af bestemme fordelingen af stjernerne på himmelen. Gennem 1780'erne lavede han en serie af målinger i 600 retninger, og talte antallet af stjerner langs hver sigtelinje. Ud fra dette sluttede han at antallet af stjerner stiger jævnt imod den ene side at stjernehimmelen imod Mælkevejen's center. Hans søn John Herschel gentog studiet i den sydlige himmelkugle og fandt noget tilsvarende der.
Ud over hans andre bedrifter, er William Herschel også kendt for hans opdagelse af at nogle stjerner ikke bare ligger på den samme sigtelinje, men er fysiske dobbeltstjerner i form at binære stjernesystemer.
Stjernespektroskopi blev grundlagt af Fraunhofer og Angelo Secchi. Ved at sammenligne stjernespektre af stjerner såsom Sirius med Solen, fandt de forskelle i styrken og antallet af absorptionslinier, der er de mørke linjer i et stjernespekter som skyldes absorption i stjerneatmosfæren. I 1865 begyndte Secchi at inddele stjerner i spektralklasser.
Observation af dobbeltstjerner tiltog i vigtighed gennem det 19'ende århundrede. I 1834 observerede Friedrich Bessel en ændring i egenbevægelsen for Sirius og sluttede sig til eksistensen af en skjult ledsagestjerne. Edward Pickering opdagede den første spektroskopiske dobbeltstjerne i 1899 da han observerede en periodisk opsplitning af spektrallinjerne i stjernen Mizar med en periode på 104 dage. Detaljerede observationer af mange dobbeltstjernesystemer blev samlet af astronomer såsom William Struve og S. W. Burnham, hvilket muliggjorde bestemmelse af stjernernes masse ud fra baneelementerne. Den første løsning på problemet med at finde banen for en dobbeltstjerne fra kikkertobservationer blev givet af Felic Savary i 1827.
I det 20'ende århundrede skete der en hurtig udvikling i det videnskabelige studie af stjerner. Fotografiet blev et værdifuldt astronomisk værktøj. Karl Schwarzschild opdagede at en stjernes farve, og dermed dens temperatur, kunne bestemmes ved at sammenligne den visuelle størrelsesklasse med den fotografiske.
Udviklingen af den fotoelektriske lysmåler muliggjorde meget præcise målinger af størrelsesklassen i forskellige bølgelængdeintervaller. I 1921 lavede Albert A. Michelson de første målinger af en stjernediameter ved at bruge et interferometer på Hooker telescope.
I de første tiår af det tyvende århundrede skete der store fremskridt i forståelsen af stjerners fysik. I 1913 blev det såkaldte Hertzsprung-Russell diagram udviklet og der blev opstillet succesfulde modeller til at forklare de indre forhold i en stjerne og stjerneudvikling. Stjernespektre blev forklaret med succes gennem anvendelse af kvantemekanik. Dette muliggjorde bestemmelse af den kemiske sammensætning af stjerneatmosfærerne. Cecilia Payne-Gaposchkin var først til at foreslå, at stjerner var lavet primært af hydrogen og helium i hendes 1925 ph.d.-afhandling.
Navngivning af stjerner
Ideen om stjernetegn eksisterede i den Babyloniske tid. Astronomiske iagttagere i oldtiden forestillede sig at fremtrædende stjerner dannede mønstre, og de forbandt disse med særlige sider af naturen og deres myter. Tolv af disse billeder lå langs ekliptika og disse dannede baggrund for astrologi.
Mange af de mere fremtrædende enkeltstjerner blev også navngivet specielt med arabiske og latinske betegnelser.
Såvel som særlige stjernebilleder og Solen selv, har stjerner deres egen mytologi. De blev betragtet som sjæle af afdøde eller guder. Et eksempel er stjernen Algol, der tænktes at repræsentere Medusas øje.
I 1603 udgav den tyske astronom Johann Bayer 'Uranometria', der var det første atlas over hele stjernehimlen, som kunne ses med det blotte øje. Han gav hver stjerne en betegnelse med et græsk bogstav og genitivformen af konstellationens navn, efter lysstyrken. Den klareste stjerne i et stjernebillede hed Alfa, den næstklareste hed Beta osv. Nogle gange tog han fejl, fx er Beta Geminorum (Pollux) den klareste i Tvillingerne mens Alfa Geminorum (Castor) kun er den næstklareste. Der er kun 24 græske bogstaver, så Bayer brugte de latinske minuskler (a-z) til de 25.- til 50.-klareste stjerner og latinske majuskler (A-Z) for de 51.- til 75.-klareste.
Senere opfandt den engelske astronom John Flamsteed et system med tal, der senere skulle blive kendt som Flamsteed betegnelser. Stjernerne fik numre efter stigende rektascension. Talrige andre systemer er siden blevet skabt i forbindelse med udgivelse af stjernekort. Det betyder fx at stjernen Deneb også betegnes; Alfa Cygni, 50 Cygni, HIP 102098 mm.
Den eneste organisation, der anerkendes af det videnskabelige samfund som havende autoritet til at navngive stjerner og andre himmellegemer, er den Internationale Astronomiske Union (IAU).
Måleenheder
De fleste stjerneparametre udtrykkes i SI-enheder per konvention,men CGS enheder bruges også. Masse, luminositet, og radius opgives som regel i solenheder. Disse er oplistet herunder:
Større mål, såsom radius af kæmpestjerner eller storaksen i et binært stjernesystem, opgives ofte i astronomiske enheder (AU), der er defineret som middelafstanden mellem Jorden og Solen, omkring 149,6 millioner km eller 93 millioner miles.
Dannelse af protostjerner
Dannelsen af en stjerne begynder med en gravitationel ustabilitet inde i en molekylsky, ofte udløst af chokbølger fra supernovaer eller sammenstød af to galakser.
Når et område opnår en tilstrækkelig høj densitet til at opfylde kritereiet for Jeans instabilitet begynder den at kollapse under sin egen gravitationskraft.
Når skyen kollapser, dannes individuelle ansamlinger af tæt støv og gas, det der kaldes Bok globuler. Disse kan indeholde op til 50 solmasser stof. Når en sådan ansamling sammentrækkes og tætheden øges, så bliver gravitationsenergien omsat til varme og temperaturen stiger. Når protostjerneskyen har nået hydrostatisk ligevægt, dannes der en protostjerne i det indre. Disse stjerner, der ligger på tærsklen til hovedserien, er ofte omgivet af en protoplanetarisk skive. Perioden med gravitationel sammentrækning varer omkring 10-15 millioner år.
Tidlige stjerner med en masse mindre end 2 solmasser kaldes T-Tauri-stjerner, mens dem med en større masse er Herbig Ae/Be stjerner.
Disse nyfødte stjerner udsender jets af gas langs deres rotationsakse, hvorved der fremkommer tågeagtige områder kaldet Herbig-Haro objekter.
Hovedserien
Stjerner tilbringer omkring 90% af deres levetid med at fusionere hydrogen til helium ved høj temperatur og tryk i stjernens kerne. Stjerner i denne fase siges at ligge på hovedserien og kaldes dværgstjerner. Andelen af helium i stjernens kerne vil stige støt i den tid stjernen er på hovedserien. For at opretholde den nødvendige styrke af kernereaktionerne er det derfor nødvendigt at temperaturen og lysstyrken af stjernen langsomt øges.
Det anslås at Solen har øget sin luminositet med omkring 40% siden den nåede hovedserien for 4.6 milliarder år siden.
Enhver stjerne frembringer en solvind af partikler der er årsag til en kontinuerlig strøm af gas ud i rummet. For de fleste stjerners vedkommende er den tabte masse ubetydelig. Solen taber 10−14 solmasser hvert år, hvilket svarer til 0.01% af dens samlede masse i hele dens levetid. Imidlertid kan meget store stjerner tabe 10−7 til 10−4 solmasser hvert år, hvilket påvirker deres udvikling i betydelig grad. Stjerner der begynder med mere end 50 solmasser kan tabe over halvdelen af deres masse mens de er på hovedserien.
Tiden som en stjerne tilbringer på hovedserien afhænger primært af den mængde brændstof den har til rådighed og farten hvormed det omsættes. Med andre ord, dens begyndelsesmasse og dens lysstyrke. For Solen, anslås denne tid til at være 10 milliarder år. Store stjerner brænder deres brændsel meget hurtigt og har kort levetid. Små stjerner (kaldet røde dværge) brænder deres brændsel meget langsomt og lever i 10-100 milliarder år. Ved enden af deres levetid bliver de ganske enkelt svagere og svagere indtil de til sidst bliver sorte dværge. Da levetiden for en sådan stjerne er større end universets nuværende anslåede alder på 13.7 milliarder år, regner man ikke med at der eksisterer nogle endnu.
Udover massen, kan andelen af grundstoffer tungere end helium spille en betydelig rolle i udviklingen af stjerner. I astronomi kaldes alle grundstoffer tungere end helium for "metaller" og koncentrationen af disse grundstoffer kaldes metallicitet. Metalliciteten kan påvirke den tid en stjerne er om at omsætte sit brændstof, kan styre dannelsen af magnetiske felter og ændre styrken af solvinden. Gamle stjerner tilhørende population II har betydeligt mindre metallicitet end yngre stjerner hørende til population I. Forskellen skyldes sammensætningen af de skyer de blev dannet af. Over tid vil disse skyer blive beriget med tungere grundstoffer når gamle stjerner dør og udkaster en del af deres atmosfære.
Tiden efter hovedserien
Når stjerner med mindst 0.4 solmasser har opbrugt deres forsyning af hydrogen i kernen, vil de ydre lag udvides og afkøles, så der dannes en rød kæmpestjerne. Om 5 milliarder år, når Solen bliver til en rød kæmpestjerne vil den sluge både Merkur og måske Venus. Modeller forudsiger at Solen vil udvides til 99% af den nuværende jordbaneradius. Samtidigt vil jordbanen dog være vokset til omkring 1.7 AU på grund af Solens massetab, og vil således undgå at blive opslugt. Imidlertid vil havene og atmosfæren være fordampet da Solens luminositet øges flere tusind gange. I en rød kæmpestjerne op til 2.25 solmasser vil brintfusion fortsætte i en skal rundt om kernen. Til sidst er kernen tilstrækkeligt komprimeret til at heliumfusion kan begynde og stjernen vil nu gradvist trække sig sammen og øge sin overfladetemperatur. For større stjerner går kernen direkte fra at fusionere hydrogen til at fusionere helium.
Efter at stjernen har opbrugt helium i kernen fortsætter fusionen i en skal rundt om en varm kerne af kulstof og ilt. Stjernen følger så en udvikling der løber parallelt med den første røde kæmpestjerne fase, men med en højere overfladetemperatur.
Massive stjerner
I helium-fusioneringsfasen vil stjerne med mere end 9 solmasser udvides og blive til røde superkæmper. Når helium er opbrugt, kan de fortsætte med at fusionere grundstoffer tungere end helium. Kernen sammentrækkes indtil temperatur og tryk er store nok til at fusionere kulstof. Denne proces fortsætter, hvor de forskellige stadier er fusion af oxygen, neon , silicium og svovl.
Nær slutningen af stjernens levetid, kan fusion foregå i en række af løgformede skaller inde i stjernen. I hver skal fusioneres forskellige grundstoffer, idet den yderste fusionerer hydrogen. Den næste fusionerer helium og så videre.
Slutstadiet nås når stjernen begynder at producere jern. Da jernkerner er hårdere bundet end alle de efterfølgende tungere kerner, ville det ikke frigøre nettoenergi hvis de blev fusioneret, tværtimod ville processen kræve tilførsel af energi. Da jernkernerne samtidigt er svagere bundet end alle lettere kerner, kan energi heller ikke frigøres ved fission.
I forholdsvist gamle, tunge stjerner vil en stor kerne af inaktivt jern derfor opsamles i kernen. De tungere grundstoffer i disse stjerner kan arbejde sig op til overfladen og der dannes en såkaldt Wolf-Rayet stjerne med en tæt solvind som spreder den ydre atmosfære.
Kollaps
En udviklet stjerne af middelstørrelse vil nu sprede sine yderste lag som en planetarisk tåge. Hvis det der er tilbage efter at den ydre atmosfære er afkastet er mindre end 1.4 solmasser, vil den synke sammen til et forholdsvist lille objekt (cirka på størrelse md jorden) der ikke er massiv nok til at yderligere sammentrækning kan finde sted. Dette kaldes en hvid dværg. Hvide dværge vil efterhånden blive til sorte dværge over et meget langt tidsrum.
I tungere stjerner vil fusionsprocesserne fortsætte indtil jernkernen har vokset sig så stor (mere end 1.4 solmasser) at den ikke længere kan bære sin egen vægt. Den vil da pludseligt synke sammen når elektroner bliver drevet ind i kernen og der dannes neutroner og neutrinoer. Chokbølgen der forårsages af sammensynkningen får resten af stjernen til at eksplodere i en supernova. Supernovaer er så lysstærke at de for en tid kan overstråle hele stjernens egen galakse. Når de er forekommet i Mælkevejen er de historisk blevet forklaret som nye stjerner der dukkede op på et sted hvor der ikke var nogen før.
Det meste af stoffet i stjernen bliver blæst væk ved supernovaeksplosionen (idet der dannes tåger som Krabbetågen) og hvad der bliver tilbage er en neutronstjerne (der af og til giver sig til kende i form af en pulsar eller en røntgenkilde) eller for de tungeste stjerners vedkommende (store nok til at efterlade en rest på mere end 4 solmasser), et sort hul. I en neutronstjerne er stoffet i en tilstand der kaldes neutron-degenereret. For nuværende vides det ikke hvilken tilstand stoffet i et sort hul er i.
De afblæste ydre lag af en døende stjerne indeholder tungere grundstoffer, der kan genbruges i en ny stjernedannelse. Disse tungere grundstoffer muliggør dannelse af planeter. Udstrømningen fra supernovaer og solvinden fra store stjerner spiller en vigtig rolle i dannelsen af de interstellare gasskyer.
Fordeling
Ud over isolerede stjerner, findes der flerstjerne-systemer der består af flere gravitationelt bundne stjerner i kredsløb om hinanden. Det mest almindelige er dobbeltstjerner, men systemer med tre eller flere stjerner findes også. Af stabilitetsmæssige grunde er den slags flerstjernesystemer ofte opdelt i et antal dobbeltstjernesystemer.
Større grupper af stjerner kaldes stjernehobe. Disse varierer fra løse konstellationer med nogle få stjerner, op til store hobe med hundredtusindvis af stjerner.
Det har længe været antaget at flertallet af stjerner var en del af flerstjernesystemer. Dette er specielt tydeligt for meget massive stjerner tilhørende klasse O og B, hvor 80% tilhører et flerstjernesystem. Imidlertid tiltager andelen af enkeltstjerner for mindre stjernestørrelse, så kun 25% af de røde dværge har en ledsagestjerne.
Da 85% af alle stjerner er røde dværge, er det sandsynligt at de fleste stjerner i Mælkevejen har været alene fra starten.
Stjerner er ikke spredt ensartet i universet, men er normalt samlet i grupper i galakser sammen med interstellart gas og støv. En typisk galakse indeholder hundredvis af milliarder af stjerner, og der er mere end 100 milliarder galakser i det observerbare univers. Selv om det ofte antages at stjerner kun eksisterer i galakser er intergalaktiske stjerner blevet observeret.
Astronomer anslår at der er mindst (7×1022) stjerner i det observerbare univers. Det er 230 milliarder gange så mange som de 300 milliarder i Mælkevejen.
Den stjerne der er nærmest Jorden, bortset fra Solen, er Proxima Centauri, der er 1012 kilometer, eller 4,2 lysår væk. Hvis man rejste med kredsløbshastigheden for Space Shuttlen, omkring 30.000 kilometer/time ville det tage 150.000 år at nå derud. Afstande som disse er typiske inde i en galakseskive. I kuglehobe og galaksecentre kan stjerner være meget tættere på hinanden og i galaktiske haloer kan de være meget længere væk fra hinanden.
Grundet de temmelig store afstande mellem stjerner uden for galaksekernerne, antages det at kollisioner mellem stjerner er sjældne. I tættere områder som kernerne i kuglehobe eller i galaksecentrer, kan sammenstød være mere hyppige.
Sådanne kollisioner kan frembringe såkaldte blå outsidere. Disse abnorme stjerner har en højere overfladetemperatur end andre hovedseriestjerner med samme luminositet i hoben.
Karakteristika
Stort set alt hvad der vedrører en stjerne bestemmes af dens startmasse, herunder træk som luminositet og størrelse, såvel som udvikling, levetid og endelig skæbne.
Alder
De fleste stjerner er mellem 1 milliard og 10 milliarder år gamle. Nogle stjerner er tæt på 13.7 milliarder år gamle. Den ældste observerede stjerne der er observeret til dato er HE 1523-0901 med en anslået alder på 13.2 milliarder år.
Jo tungere en stjerne er, des kortere er dens levetid. Det skyldes primært at tunge stjerner har et højere tryk i kernen, hvilket betyder at hydrogen fusionerer hurtigere. De tungeste stjerner har en gennemsnitslevetid på omkring 1 million år, mens de letteste stjerner kan leve i hundredvis af millioner af år.
Kemisk sammensætning
Når stjerner dannes består de af omkring 70% hydrogen og 28% helium efter masse og en mindre andel af tungere grundstoffer. Typisk måles andelen at tungere grundstoffer ud fra jernindholdet i stjernens atmosfære, da jern er et almindeligt grundstof og jernets absorptionslinjer er forholdsvist nemme at måle. Fordi molekylskyerne som stjerner dannes fra bliver beriget med tungere grundstoffer ved supernovaeksplosioner, kan måling af en stjernes kemiske sammensætning bruges til at bestemme dens alder. Mængden af tungere grundstoffer kan også være en indikator for sandsynligheden for at finde et planetsystem om stjernen.
Stjernen med det hidtil mindst målte jernindhold er dværgen HE1327-2326, der kun har 1/200000 af Solens jernindhold. Som modsætning har den supermetalholdige stjerne mu Leonis næsten det dobbelte jernindhold af Solen, mens den planetbærende stjerne 14 Hercules har næsten det tredobbelte jernindhold.
Der findes også kemisk specielle stjerner der har en usædvanlig overvægt af specielle grundstoffer i deres spektrum, specielt chrom og sjældne jordarter.
Diameter
På grund af deres store afstand fra Jorden, forekommer alle stjerner bortset fra Solen at være prikker på nattehimlen set med det blotte øje. Bevægelser i jordens atmosfære gør at stjernerne blinker. Solen er også en stjerne, men den er tæt nok på Jorden til at ligne en skive, og til at give dagslys. Bortset fra solen, er stjernen med den største tilsyneladende størrelse R Doradus, med en vinkeldiameter på 0.057 buesekuender
Skiverne for de fleste stjerner er alt for små i vinkeldiameter til at kunne observeres med et jordbaseret teleskop, og derfor må der anvendes interferometriske metoder til at få et billede af disse objekter. En anden teknik til at måle vinkeldiameter af stjerner er gennem okkultation. Ved præcise målinger af faldet i en stjernes lysstyrke når den bliver dækket af månen (eller tilvæksten når den kommer frem igen), kan stjernens vinkeldiameter beregnes.
Stjerner varierer i størrelse fra neutronstjerner, der varierer mellem 20 og 40 km i diameter, til røde superkæmper som Betelgeuse i Orion, der har en diameter på omkring 650 gange Solen, omkring 0.9 milliarder kilometer.
Kinematik
Bevægelsen af en stjerne i forhold til Solen kan give nyttig information omkring oprindelsen og alderen for stjernen, såvel som opbygningen og udviklingen af den omgivende galakse. Komponenenterne af en stjernes bevægelse er radial hastighed imod eller væk fra Solen, og tværbevægelse der kaldes den sande bevægelse.
Radialhastighed måles ved dopplerskiftet af stjernens spektrallinjer, og er givet i enheder af km/s. Den sande bevægelse for ens stjerne bestemmes ved præcise astrometriske målinger i enheder af mille-buesekunder per år. Ved at finde stjernens parallakse, kan den sande bevægelse omsættes til hastighedsenheder. Stjerner med høje sande bevægelser er formentligt tæt på Solen, hvilket gør dem velegnede emner til parallaksemåling.
Når begge bevægelser er kendt, kan hastigheden igennem rummet i forhold til Solen bestemmes. Iblandt nære stjerner, har man fundet at population I stjerner generelt har en lavere hastighed en ældre, population II stjerner. De sidstnævnte har elliptiske baner der hælder i forhold til galakseplanet. Sammenligning af nære stjerner har også ført til bestemmelse af stjerneforbindelser. Disse er formentlig grupper at stjerner der har et fælles udgangspunkt i meget store gasskyer.
Magnetfelt
En stjernes magnetfelt frembringes når områder i det indre af stjernen hvor der er konveksions bevægelser. Disse bevægelser af elektrisk ledende plasma fungerer som en dynamo, og frembringer magnetiske felter med udstrækning igennem hele stjernen. Styrken af det magnetiske felt afhænger af stjernens masse og sammensætning, og størrelsen af den magnetiske overfladeaktivitet afhænger af stjernens roatition. Denne overflade aktivitet producerer solpletter, der er områder med en lavere temperatur end den omgivende overflade. koronabuer er magnetisek felter der i en bue rækker ud i koronaen fra aktive områder. flares er udbrud af højenergetiske partikler der udsendes af samme magnetiske aktivitet.
Unge, hurtigroterende stjerner har en tendens til at have høj overfladeaktivitet på grund af deres magnetfelt. Magnetfeltet kan påvirke solvinden, og dermed langsomt bremse rotationen som stjernen bliver ældre. Derfor har stjerner der er ældre end Solen en meget lavere rotationshastighed og en lavere overfladeaktivitet. Overfladeaktiviteten i langsomt roterende stjerner har en tendens til at variere cyklisk og kan helt ophøre i perioder.
Masse
En af de tungeste stjerner der kendes er Eta Carinae med en masse på 100-150 gange Solen. Dens levetid er højst et par millioner år. Et nyligt studie af Arches cluster antyder af 150 solmasser er grænsen for stjerner i det nuværende stadie af universets udvikling. Forklaringen på denne grænse er ikke kendt præcis, men skyldes delvist Eddington luminositen der definerer en grænseværdi for den luminositet der kan passerer gennem en stjerneatmosfære uden at blæse gasser ud i rummet.
De første stjerner efter Big Bang kan have været meget større, op til 300 solmasser eller mere pga. det totale fravær af tungere grundstoffer end lithium i deres sammensætning. Denne generation af supermassive population III stjerner er længe uddøde og er kun teoretisk beskrevet.
Med en masse på omkring 93 Jupitermasser, er AB Doradus C, en ledsager til AB Doradus A, den letteste kendte stjerne der har fusion i kernen.
For stjerner med en metallicitet som Solen, er den teoretiske minimumsmasse som en stjerne kan have og stadigt have fusion i kernen vurderet til at være omkring 75 Jupitermasser.
Når metalliciteten er meget lav, viser et nyligt studie af de svageste stjerner, at minimumsstørrelsen for en stjerne er omkring 8.3% af en solmasse, eller omkring 87 Jupitermasser. Mindre legemer kaldes brune dværge, og udfylder en gråzone mellem stjerner og gasgiganter
Kombinationen af radius og masse for en stjerne definerer overfladegravitationen. Kæmpestjerner har en meget lavere overfladegravitation end hovedseriestjerner, mens det omvendte er tilfældet for hvide dværge. Overfladegravitationen kan have indflydelse på en stjernes spektrum, idet højere gravitation udbreder absorptionslinierne.
Rotation
En stjernes rotation kan bedømmes gennem spektroskopiske målinger, eller mere nøjagtigt ved at følge bevægelsen af solpletter.
Unge stjerner kan have en rotation hurtigere en 100 km/s ved ækvator. Klasse B-stjernen Achernar, har f.eks. en ækvatorialhastighed på omkring 225 km/s eller mere, hvilket giver den en ækvatorialdiameter der er 50% støre end afstanden mellem polerne. Denne hastighed er lige under den kritiske på 300 km/s hvor stjernen ville gå i stykker. I modsætning hertil roterer Solen kun en gang på 25-35 dage med en rotationshastighed på 1,994 km/s. Stjernens magnetfelt og solvinden bremser en hovedseriestjernes rotationshastighed med en betydelig andel, alt imens den udvikler sig på hovedserien.
Degenererede stjerner er trukket sammen til en kompakt masse, hvilket bevirker en hurtig rotation. De har dog en forholdsvis lav rotationshastighed i forhold til hvad der skulle ventes fra bevarelse af bevægelsesmængdemomentet. Det forklares ved at en del af stjernens bevægelsesmængdemoment overføres via massetab i solvinden. På trods af det, kan en pulsar have en meget hurtig rotation. Pulsaren i midten af krabbetågen roterer f.eks. 30 gange i sekundet. Rotationen vil langsomt aftage grundet udsendelse af stråling.
Temperatur
Overfladetemperaturen for en hovedseriestjerne er bestemt af dens energiproduktion i kernen og dens radius. Den estimeres ofte ud fra dens farveindeks.
Stjernens temperatur angives som dens effektive temperatur, dvs. at den er temperaturen af et ideelt sortlegeme, der udsender energi med den samme intensitet som stjernen. Bemærk at den effektive temperatur kun er en omtrentlig værdi og at stjerner har en temperaturgradient der aftager meget stærkt med tiltagende afstand fra kernen.
Stjernens temperatur bestemmer hvor hurtigt forskellige grundstoffer ioniseres, hvilket bevirker et karakteristisk absorptionsspektrum. Overfladetemperaturen sammen med den abolutte størrelsesklasse og absorptionslinjer bruges til at klassificere stjerner.
Hovedseriestjerner med stor masse kan have en overfladetemperatur på op til 60.000 Kelvin (K). Mindre stjerner som Solen har en overfladetemperatur på 5-10.000 K. Røde kæmper har en relativt lav overfladetemperatur på omkring 3.600 K, men de har en høj luminositet grundet deres meget store overflade. Røde dværgstjerner har samme lave effektive temperatur, men pga. deres ringe størrelse er de de svagest lysende af alle stjerner.
Stråling
En stjernes energiproduktion er et af resultaterne af den kernefusion, som foregår i stjernens kerne. Energien stråles ud i rummet som både elektromagnetisk stråling og partikelstråling. Denne sidste kaldes solvinden, der består af en strøm af elektrisk ladede partikler såsom frie protoner, alfa partikler, og beta partikler, der strømmer fra stjernens ydre lag; dertil en strøm af neutrinoer direkte fra stjernens kerne.
Produktionen af energi i kernen er årsagen til, at stjerner lyser. Hver gang to eller tre kerner smelter sammen til en ny kerne af et tungere grundstof, bliver der frigjort elektromagnetisk stråling i form af gammastråler. Denne energi bliver omsat til stråling med større bølgelængder, bl.a. synligt lys, pga. kombination og rekombination (indfangning og frigivelse) af fotoner undervejs fra kernen til stjernens overflade.
Udover synligt lys udsender en stjerne også elektromagnetisk stråling med mange andre bølgelængder. Faktisk spænder en stjernes spektrum over hele det elektromagnetiske spektrum.
Ved at bruge spektroskopi kan astronomer bestemme overfladetemperaturen, overfladegravitationen, metalliciteten, magnetisme og stjernens rotationshastighed. Hvis afstanden til stjernen er kendt, kan stjernens absolutte størrelsesklasse og dens luminositet bestemmes.
Stjerners masse, radius, overfladegravitation og egenrotationsperiode kan direkte observeres for dobbeltstjerner og disse observationer danner derefter grundlag for stjernemodeller, som kan benyttes til med god præcision at bestemme samme data for enkeltstjerner.
En stjernes farve er bestemt af hvor, det synlige lys har sin største intensitet. Dette afhænger af temperaturen af stjernens ydre lag, som kaldes fotosfæren.
Strålingens styrke
De mest massive stjerner, superkæmpestjerner af spektralklasse O3Ia-0, som dannes i dag (de yngste stjerner er 3. og 4. generationsstjerner), har en masse, der er omkring 3.300 gange så stor som de mindste stjerner, som dannes og nogensinde er dannet, nemlig røde dværge af spektralklasse M9V.
Man kunne forledes til at tro, at stjerner med de største masser også lever længst, men for stjerner gælder i høj grad "lev stærkt og dø ung", idet en stjerne med stor masse også forbruger denne med meget stor hastighed. De mindste stjerner, med ca. 0,08 solmasser udsender ca. 0.00015 gange Solens energi og lever omkring 45.000.000.000 år, hvorimod de mest massive stjerner udsender ca. 5.900.000.000 gange så megen energi pr. tidsenhed som de mindste stjerner, og lever i mindre end 1.000.000 år. De mindste stjerner lever følgelig omkring 50.000 gange så lang tid som de mest massive.
Den udsendte stråling afhænger af stjernens temperatur og dens radius.
Det er indlysende, at sammenligner man to kugleformede legemer med samme temperatur, men med forskellig overfladestørrelse, vil det med den største overflade udstråle mere energi en det med den mindste overflade. Overfladens størrelse afhænger af kvadratet på radius; er radius fx tre gange så stor, er overfladen tilsvarende 3² = 9 gange så stor.
Det er også velkendt, at sammenligner man to legemer med forskellig temperatur, fx en finger og et rødglødende søm, udstråler sømmet betydelig mere energi end fingeren.
Det er derimod ikke umiddelbart indlysende, at energiudstrålingen afhænger af temperaturen i fjerde potens.
Formlen for en stjernes udstråling af lys er
hvor
er stjernens radius
er stjernens temperatur i Kelvin
Sammenligner vi fire velkendte stjerner, nemlig Solen, Sirius, Betelgeuze, Deneb og dertil den mest massive af alle kendte stjerner R136a1 , har vi følgende data (indexeret med Solens masse og radius = 1, og sorteret efter lysstyrke):
hvor L☉ er Solens visuelle lysstyrke.
Strålingens maksimumbølgelængde
Udstrålingen har sit maksimum ved en bølgelængde (λmax), som afhænger af stjernens temperatur.
Jo højere temperatur, desto kortere bølgelængde. Bølgelængden ved maksimum udregnes ved hjælp af den nemme formel for Wiens forskydningslov, en empirisk bestemt konstant divideret med stjernens effektive temperatur.
nm
Sammenligner vi de samme fem stjerner som i tabellen ovenfor, får vi (sorteret efter bølgelængde):
Umiddelbart kan det virke overraskende, at Solens maksimumudstråling er i det blågrønne område, men Solen udsender jo ligesom andre stjerner lys i mange bølgelængder. Det er velkendt fra fysikforsøg med et tresidet prisme, at vi ser blandingen af de mange farver som en enkelt farve, nemlig gullig-hvid.
Som det ses på billedet, har kurverne over strålingens maksimumbølgelængde på en måde en vis lighed med en fisk: Et lille hoved (til venstre), en stor krop og en lang, smal hale. Hovedet består af strålingen med den højeste energi, for meget varme stjerner fra røntgenstråling til ultraviolet, kroppen hovedsagelig af synligt lys og halen af stråling med den lav energi, nemlig infrarød.
Størrelsesklasse
Den tilsyneladende lysstyrke for en stjerne angives ved dens tilsyneladende størrelsesklasse, der er lysstyrken af stjernen med hensyn til stjernens luminositet, afstand fra Jorden, og variationer i stjernelyset når det passerer gennem Jordens atmosfære.
Absolut størrelsesklasse er den tilsyneladende størrelsesklasse som stjernen ville have hvis den var i afstanden 10 parsec fra Jorden (32.6 lysår), og den er direkte afhængig af stjernens luminositet.
Både den tilsyneladende og den abolutte størrelsesskala har logaritmiske enheder. En enhed i forskel på størrelsesklasse svarer til en forskel i intensitet på omkring en faktor 2.5, da 5'te roden af 100 er omkring 2.512. Dette betyder at en stjerne af første størrelsesklasse (+1.00) er omkring 2.5 gange klarere end en (+2.00) stjerne, og omkring 100 gange klarere end en (+6.00) stjerne. De svageste stjerner der er synlige med det blotte øje har en størrelsesklasse på omkring +6.
På både den tilsyneladende og den absolutte skala svarer et mindre tal til en klarere stjerne. De klareste stjerner på hver skala har negativ størrelsesklasse. Variationen i intensitet mellem to stjerner udregnes ved at trække størrelsesklassen af den klare stjerne fra størrelsesklassen for den svage, og derefter opløfte 2.512 til denne forskel.
variation i klarhed
Den absolutte størrelsesklasse og den tilsyneladende størrelsesklasse er ikke ens for en bestemt stjerne. Solen har f.eks. en tilsyneladende størrelsesklasse på -26.7 og en absolut størrelsesklasse på 4.83.
Sirius, den klareste stjerne på nattehimmelen har tilsyneladende størrelsesklasse på -1.44 og en absolut på 1.41. (dette skyldes at den ligger tættere på Jorden end 10 parsec og derfor ville synes svagere i standardafstanden).
En stjerne med en højere luminositet end en anden, vil synes svagere hvis den er længere væk fra Jorden end den anden og vice versa.
Stjernen med den højest kendte absolutte størrelsesklasse er LBV 1806-20, med en abslut størrelsesklasse på -14.2. Denne stjerne har en luminositet der er 5000000 gange større end Solen.
Klassifikation
Hovedartikel: Spektralklasse
Der er forskellige klassifikationer af stjerner svarende til deres spektra,varierende fra type O, som er meget varme, til M, som er så kølige at der kan dannes molekyler i deres atmosfære. Hovedklassifikationen der følger faldende temperatur er: O, B, A, F, G, K, og M. Et udvalg af specielle spektraltyper har specielle klassifikationer. De mest almindelige er L og T, der klassificerer de koldeste stjerner med lav masse og brune dværge.
Hvert bogstav har en underinddeling fra 0 til 9. Dette system følger nøje temperaturen, men bryder ned i den varmeste ende af spektret.
Der eksisterer formentlig ikke O0 og O1 stjerner.
Derudover kan stjerner klassificeres ved "luminositets-effekter" observeret i deres spektrallinjer, der har forbindelse med den rumlige udstrækning og afhænger af overfladegravitationen. Disse går fra 0 (for at undgå forveksling mellem O og 0 kaldes denne klasse ofte Ia-0) (superkæmper) gennem V (hovedseriestjerner) til D (hvide dværge). De fleste stjerner hører til på hovedserien, der består af stjerner som fusionerer hydrogen. De samles i et smalt bånd, når den absolutte størrelsesklasse og spektraltype afbildes mod hinanden. Vores Sol er en hovedseriestjerne G2V (gul "dværg"), der er af middel temperatur og ordinær størrelse.
Yderligere nomenklatur i form af bogstaver kan følge spektraltypen for at vise specielle træk. F.eks indikerer et "e" tilstedeværelsen af emissionslinjer; "m" repræsenterer store niveauer af metal og "var" kan betyde variationer i spektraltypen.
Hvide dværge har deres egen klasse, der begynder med bogstaverne D. Den er underinddelt i klasserne DA, DB, DC, DO, DZ, og DQ, afhængigt af typen af fremtrædende linjer i spektret.
Dette følges af numeriske værdier der indikerer temperatur indekset.
Variable stjerner
Variable stjerner har periodiske tilfældige variationer i deres luminositet på grund af indre eller ydre egenskaber. I de indre variable stjerner kan de primære typer inddeles i tre hovedgrupper.
Gennem deres udvikling passerer nogle stjerner igennem faser hvor de kan blive pulserende variable. Pulserende variable stjerner variere i radius og luminositet ovet tid, idet de udvider sig og trækker sig sammen med perioder fra minutter til år, afhængig af stjernens størrelse.
Denne kategori omfatter Cepheider og cepheidelignende stjerner, og langperiodiske variable stjerner som Mira
Udbruds-variable stjerner , er stjerner der oplever en pludselig stigning i luminositet på grund af flares eller tilfældige udkastninger af masse.
Denne gruppe omfatter protostjerner, Wolf-Rayet stjerner, og Flare stjerner, såvel som kæmper og superkæmper.
Kataklysmiske eller eksplosive variable gennemgår en dramatisk ændring i deres egenskaber. Denne gruppe inkluderer novaer og supernovaer. Et binært stjernesystem der inkluderer en hvid dværg kan producere særlige typer af stjerneeksplosioner, inkluderende novaen og en type 1a supernova. Eksplosionen skabes når den hvide dværg samler hydrogen fra en ledsagestjerne, og opbygger masse indtil hydrogenet undergår fusion. Nogle novaer er gengangere, idet de har periodiske udbrud af moderat amplitude.
Stjerner kan også variere i lysstyrke på grund af ydre faktorer, som skyggende ledsagestjerner.
Opbygning
Det indre af en stjerne er i hydrostatisk ligevægt: kræfterne på ethvert lille volumen udbalancerer næsten hinanden. De balancerende kræfter er gravitationen indad og et udadrettet tryk skabt af temperaturforskellen i stjernen. Denne trykgradient opretholdes af temperaturforskellene idet kernen er varmere end de ydre dele af stjernen. Temperaturen i kernen af en hovedseriestjerne er mindst af størrelsesorden 107 K. Den resulterende temperatur og det tilhørende tryk er tilstrækkeligt til at opretholde kernefusion og til at skabe den nødvendige trykgradient der indgår i den hydrostatiske ligevægt.
Når atomkerner smeltes sammen i kernen, udsendes der energi i form af gammastråler. Disse fotoner vekselvirker med den omgivende plasma, hvilket tilfører yderligere energi til kernen. Stjerner på hovedserien omsætter hydrogen til helium, og opbygger på denne måde langsomt en stigende mængde af helium i kernen. Til sidst er heliumindholdet dominerende og energiproduktionen i kernen standser. For stjerner med mere end 0.4 solmasser vil fusionen i stedet fortsætte i en langsomt voksende skal rundt om den degenererede heliumkerne.
Udover den hydrostatiske ligevægt vil det indre af en stabil stjerne også opretholde en termisk ligevægt. Der er en radial temperaturgradient gennem det indre, der resulterer i en energistrøm der flyder udad. Den mængde af energi der forlader ethvert cirkulært snit i stjernen vil svare til det der modtages indefra.
Strålingszonen er området i stjernens indre, hvor stråling er tilstrækkeligt effektiv til at opretholde energistrømmen. I dette område er plasmaet ikke forstyrret og enhver bevægelse vil dø ud. Hvis dette ikke er tilfældet vil plasmaet blive ustabilt og der vil forekomme konvektion, idet der dannes en konvektionszone. Dette kan ske i områder med meget store energistrømme, som nær kernen eller i områder der er uigennemsigtige som i den ydre skal.
Forekomsten af konvektion i kappen af en hovedseriestjerne afhænger af massen. Stjerner med mange gange Solens masse har en en konvektionszone dybt i det indre og en strålingszone i de ydre lag. Mindre stjerner som Solen er modsat, med konvektionszonen i de ydre lag.
Røde dværgstjerner med mindre end 0.4 Solmasser er konvektive hele vejen igennem, hvilket forhindrer at der opsamles helium i kernen. For de fleste stjerners vedkommende vil konvektionszonerne også variere over tid som stjernen ældes og det indre af stjernen ændres.
Den del af stjernen, der er synlig for en iagttager, kaldes fotosfæren. Det er det lag hvor stjernens plasma bliver gennemsigtigt for fotoner. Herfra udstråles den energi der er frembragt i stjernens indre. Det er i fotosfæren at solpletter forekommer.
Over fotosfæren er stjerneatmosfæren. I en hovedseriestjerne som Solen, er den nederste del af atmosfæren den tynde kromosfære hvorfra der udgår spikuler og flares.
Denne er omgivet af et overgangsområde, hvor temperaturen stiger hurtigt på en afstand af kun 100 km. Over dette er koronaen, et område af superophedet plasma, der kan have en udstrækning på flere millioner km.
På trods af sin høje temperatur udsender koronaen kun lidt lys. Koronaen er normalt kun synlig ved solformørkelse.
Fra koronaen udgår en solvind af plasma, der strækker sig ud fra stjernen indtil det når ud i det interstellare rum, hvor det vekselvirker med det stof der er tilstede der.
Kernereaktioner
En mængde forskellige kernereaktioner finder sted i kernen af stjerner, afhængig af deres masse og sammensætning,som en del af stjernens kernesyntese. Nettomassen af den fusionerede atomkerne er mindre end summen af dens enkeltdele. Denne tabte masse er omsat til energi, i overensstemmelse med masse-energi ækvivalensen E = mc²
Brintfusionen er temperaturfølsom, så en moderat stigning i kernetemperaturen vil resultere i en betydelig stigning i fusionshastigheden. Som et resultat varierer kernetemperaturen for en hovedseriestjerne fra 4 millioner Kelvin for en lille M-klasse stjerne til 40 millioner Kelvin for en tung O-klasse stjerne.
I Solen, der har en kernetemperatur på omkring 15 millioner Kelvin, smelter brint sammen til helium i proton-proton kernereaktionen
41H → 2²H + 2e+ + 2νe (4.0 MeV + 1.0 MeV)
21H + 2²H → 23He + 2γ (5.5 MeV)
23He → 4He + 21H (12.9 MeV)
Nettoreaktionen kan skrives således:
41H → 4He + 2e+ + 2γ + 2νe (26.7 MeV)
hvor e+ er en positron, γ er en gamma foton,
νe er en neutrino, og H og He er isotoper af hydrogen og helium. Energien frigjort ved denne reaktion er af størrelsesordenen millioner af elektronvolt, der kun er en lille energimængde, men til gengæld sker der et enormt antal reaktioner sideløbende.
I mere massive stjerner produceres helium i en cyklus af reaktioner der er katalyseret af kulstof, den såkaldte carbon-nitrogen-oxygen cyklus
I udviklede stjerner med kerner der har temperatur på 100 millioner Kelvin og masser mellem 0.5 og 10 solmasser, kan helium forvandles til kulstof i triple-alfa-processen der bruger beryllium som mellemled:
4He + 4He + 92 keV → 8*Be
4He + 8*Be + 67 keV → 12*C
12*C → 12C + γ + 7.4 MeV
Nettoreaktionen er:
34He → 12C + γ + 7.2 MeV
I tunge stjerner kan grundstoffer fusionere i en såkaldt neon proces og i en oxygen-proces. Det sidste trin i kernesyntesen er siliciumfusion der resulteter i dannelse af isotopen Fe-56. Fusion kan da ikke forekomme andet end gennem en endoterm proces og derfor kan kun gravitationel sammensynkning producere yderligere energi.
Eksemplet herunder viser tiden der er nødvendig, for at en stjerne på 20 solmasser bruger alt sit kernebrændsel. For en O-klasse hovedseriestjerne, ville det svare til en stjerne med 8 gange solradius og 62000 gange Solens luminositet.
Farver og spektralklasser
Lyset fra en stjerne har et spektrum (farvesammensætning) der fortæller noget om stjernens temperatur og stofsammensætning, i det mindste for så vidt angår de lysudsendende dele af stjernens overflade. Af den grund inddeler man stjerner i forskellige spektralklasser – sorteret efter faldende, tilsvarende temperatur hedder stjernernes spektralklasser:
O, B, A, F, G, K, M, R, N, S
Den lidt »tilfældige« bogstavfølge skyldes at klassifikationssystemet blev opfundet inden man lærte den nærmere betydning af de forskellige klasser. Man kan huske rækkefølgen ved hjælp af denne memotekniske remse: »Oh, be a fine girl/guy, kiss me right now, sweetie!«.
Hvis man varmer f.eks. et stykke jern op, vil det først blive rødglødende, siden skifter lyset fra gløden over orange og gult til »hvidglødende«: På samme måde er lyset de koldeste stjerner (med overfladetemperaturer på et par tusinde celsiusgrader) rødligt, mens varmere stjerner udsender gult, orange og hvidt lys – Solen med sin overfladetemperatur på knap 6000 °C, klassificeres således som en »gul« stjerne af astronomerne.
Og der findes langt varmere stjerner: De der er »varmere end hvidglødende« har et blåt skær i deres lys, fordi de udsender mest af det kortbølgede, blå lys. De varmeste blandt disse blå stjerner har overfladetemperaturer på henved 45.000 °C.
Symbolik
Stjernen henviser til stjernen over Betlehem, der bebudede Jesu fødsel og førte vise mænd fra Østerland til stalden, hvor de fandt "jødernes nyfødte konge".
Se også
Dobbeltstjerne
Tycho-2 kataloget
Stjernenavne
Fodnoter
Eksterne henvisninger
Konstellationer
Monsterstjerne med 300 gange Solens masse
Det astrofysiske grundlag for liv I
Astronomisk Selskab, Astronomisk guide: Stjernerne på Himlen
Curious About Astronomy? Stars, Curious About Astronomy? Stars, Questions
NASA: Chandra X-ray Observatory News , Harvard: Chandra X-ray Observatory News
Hubblesite: Star
13 June, 2003, BBCNews: Strange star puzzles astronomers Citat: "...Achernar, otherwise known as Alpha Eridani...fairly close to us, being about 145 light-years distant...."
2003-11-28, Science Daily: Biggest Star In Our Galaxy Sits Within A Rugby-ball Shaped Cocoon Citat: "...Eta Carinae...100 times more massive than our Sun and 5 million times as luminous. This star has now entered the final stage of its life and is highly unstable..."
13 January 2005, Physicsweb: All change for stellar evolution | danish | 0.430352 |
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Machine Learning , Neuro and Cognitive Science
# Neural Networks Help Us Understand How the Brain Recognizes Numbers
New research using artificial intelligence suggests that number sense in
humans may be learned, rather than innate. This tool may help us understand
mathematical disabilities.
Jul 13, 2023
|
Grace Huckins
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Image
Over the past half-century, neuroscientists have made extraordinary strides in
understanding the human brain by inserting wires into the brains of animals
like cats, rats, and monkeys and characterizing how their neurons fire. Though
such experiments can’t be done as easily in people, looking at neurons in
animals has nevertheless helped scientists understand the underpinnings of
phenomena such as optical illusions , memory, and drug addiction .
But animal brains have their limitations. Some sophisticated human behaviors,
like mathematical reasoning, are beyond the reach of animals – and even if
animals can be trained to use numbers, it’s unclear whether they learn about
them in the same way humans do, given that they don’t have the same capacity
for language. So when Vinod Menon , Stanford professor of psychiatry and
behavioral sciences and member of Stanford HAI and the Wu Tsai
Neurosciences Institute , and Percy Mistry , a research scholar in Menon’s
lab, wanted to try to understand how children learn about numbers, they didn’t
look to biology. Instead, they decided to try to approximate the process of
human number learning using a deep neural network.
Deep neural networks were originally modeled after the brain, and they have
been widely used to probe the inner workings of the visual system. So by
training a brain-like network to recognize numbers, Menon and Mistry were able
to gather evidence about number learning in humans that would have been
impossible to obtain otherwise. Their results, published in Nature
Communications , suggest that an innate number sense may not be as important
as other researchers have proposed.
Because there are limitations to neurophysiological experiments that can be
conducted ethically in humans, this type of research could prove essential to
understanding the human brain’s complex capabilities, Menon says. “It’s hard
to make inroads into understanding the neural mechanisms of complex human
cognitive processes without building models like this.”
## Testing ‘Spontaneous Number Neurons’
In a previous study , researchers trained a deep neural network to recognize
images and discovered, to their surprise, that some neurons in the network
were sensitive to numbers – they responded especially strongly to pictures of
a particular number of objects, despite never having been trained to identify
the number of objects in an image. These results seemed to lend credence to
the idea that numerosity is, in some sense, innate: that children may have a
sense for numbers without being explicitly taught about them, and that future
learning could depend on that sense.
But no one had actually tested whether those “spontaneous number neurons” help
with number learning. To do so, one would have to first take a neural network
trained to recognize objects, identify its number-sensitive neurons, retrain
that network to report the number of objects in an image, and then see whether
those neurons help the network learn that task – which is precisely what
Mistry, Menon, and their colleagues did.
They found that the spontaneous number neurons didn’t help with learning at
all. Most neurons that started out number-sensitive either lost that number
sensitivity over the course of training or became sensitive to a different
number. And the neurons that did stay responsive to the same numbers didn’t
seem to be doing anything particularly essential: Removing them from the
network during the learning process didn’t have any effect on the network’s
final performance.
## Bridging AI and Human Intelligence
While this study was entirely performed on computers, there’s reason to think
it could have something to say about how human brains work. The team
intentionally started with an object-recognition network that had previously
been demonstrated to resemble parts of the monkey visual system – and after
training, number-sensitive neurons in the neural network behaved like number-
sensitive neurons in the monkey brain.
Without invasive human experiments, it’s impossible to make the same
comparisons between the network and the human brain. But the team found other
ways to attack the problem. Looking at the pool of number-sensitive neurons as
a whole, they found that the network used two different strategies for telling
different numbers apart. One strategy used a linear number line, where the
endpoints – 1 and 9 – were easy to distinguish, but numbers in the middle – 4,
5, and 6 – were harder to tell apart. The second strategy, however, was based
around the midpoint of the number line – so 4, 5, and 6 were perceived as very
different from each other. This same pattern is seen in humans as they
learn: As they develop their number sense, children start out sensitive to low
and high numbers, but over time they start using the midpoint of the number
line as a reference point as well. “It was exciting to observe the emergence
of number line representations similar to those seen in children, even though
we did not explicitly train the neural network to do so,” Menon said.
It would be premature to conclude, however, that human children learn in
exactly the same way that this neural network does. The model is ultimately “a
very, very simple approximation of what the brain is doing, even with all its
complexity,” Mistry says. That simplicity makes the network easier to study
and train, but it also limits how much it can tell us about human biology.
Nevertheless, the model does an impressive enough job of approximating the
number learning process in children that Mistry and Menon have high hopes for
its future. Menon has spent years studying dyscalculia, a disability that
affects numerical and mathematical skills. The team’s goal now is to use the
network to study potential neural mechanisms for dyscalculia, by implementing
those mechanisms in the network and seeing how they interfere with number
learning.
“We can make hypotheses about different mechanisms that might be possible
causes and evaluate which might be relevant. We can even look at possible
interventions,” Mistry says. “We can use this model as a sandbox.”
The study, “ Learning-induced reorganization of number neurons and emergence
of numerical representations in a biologically inspired neural network ,”
published in Nature Communications this June. Other Stanford contributors
include postdoctoral fellows Anthony Strock and Ruizhe Liu, and coterm student
Griffin Young.
Stanford HAI’s mission is to advance AI research, education, policy and
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| biology | 792495 | https://da.wikipedia.org/wiki/Kognitionsvidenskab | Kognitionsvidenskab | Kognitionsvidenskab er betegnelsen for den tværfaglige undersøgelse af tænkning (kognition) og tænkningens underliggende processer. Kognitionsvidenskaben undersøger både hvad tænkning er, hvad den kan, og hvordan den opstår. Fokus er på, hvordan information optages gennem sanserne (perception), opbevares i hukommelsen, bearbejdes, og videreformidles gennem sproget og den sociale interaktion. Kognitionsvidenskab samler en række forskningsretninger, såsom psykologi, lingvistik, filosofi, neurovidenskab, datalogi og antropologi. Udforskningen af kognitionen er primært kvantitativt eksperimentel, suppleret med computermodeller af f.eks. kunstig intelligens.
Historisk baggrund
Kognitionsvidenskaben har rødder tilbage til antikkens filosoffer, bl.a. Platon og Aristoteles, men som forskningsretning er den et barn af 1950’erne, hvor psykologi, antropologi og lingvistik gennemgik en forvandling, og hvor datalogien og neurovidenskaben opstod som selvstændige forskningsområder..
En stor del af det teoretiske grundlag for studiet af kognitive processer blev lagt inden for de fremstormende videnskaber om computere og databehandling i 1940’erne og 1950’erne med bl.a. Alan Turing og John von Neumann som bannerførere. Computeren blev - og er - vigtig for kognitionsvidenskaben, både som metafor for hvordan den menneskelige informationsbehandling tænkes at foregå, og som instrument til at udvikle og teste modeller for kognitive processer. I midten af 50’erne begyndte Allan Newell og Hebert A. Simon at arbejde med udviklingen af kunstig intelligens i form af computerprogrammer, der simulerede menneskelig problemløsning. Andre forsøg på udvikling af kunstig intelligens med brug af neurale netværk, hvor den menneskelige hjerne bruges som inspiration til computersystemer, snarere end omvendt, er en anden vigtig historisk forudsætning for kognitionsvidenskab. Dette arbejde havde sit udspring i den tidlige kybernetik med bl.a. Walter Pitts og Warren McCulloch som vigtige tidlige skikkelser.
Kognitionsvidenskaben opstod desuden til en vis grad som en reaktion imod behaviorismen. Behaviorismen var den dominerende forskningsretning inden for psykologien i 1950'erne. Under indflydelse af blandt andre Ivan Pavlov argumenterede den for, at adfærd og adfærdens kobling til eksterne stimuli under læring var de eneste processer, der var mulige og relevante at studere. Mentale processer blev ikke anset for tilgængelige for undersøgelser. Et afgørende vendepunkt kom, da en af behaviorismens fremmeste fortalere, adfærdsforskeren B.F. Skinner i sin bog Verbal Behavior fra 1957 forsøgte at beskrive sproget som stimulus-respons læring efter behavioristiske forskrifter. Skinner hævdede at forståelsen af ord bygger på indlæring under kobling af ordet selv med oplevelse af ordets betydning. I en sønderlemmende kritik argumenterede lingvisten Noam Chomsky for at man med behaviorismens tilgang til sprog kun ville kunne forstå sætningen ‘Pengene eller livet’, hvis man havde ‘tidligere erfaring med hvad at være død’. Chomsky argumenterede for nødvendigheden af at inddrage mentale og eventuelt medfødte processer i forklaringen af den menneskelige sprogevne.
Begrebet kognitionsvidenskab (eng.: Cognitive Science) blev første gang brugt i 1973 af Christopher Longuet-Higgins i en rapport om kunstig intelligens. I 1977 udkom det første nummer af det videnskabelige tidsskrift Cognitive Science og i 1979 blev Cognitive Science Society, det første kognitionsvidenskabelige selskab dannet og samme år blev den første egentlige kognitionsvidenskabelige konference afholdt i La Jolla i Californien.
Undersøgelsesniveauer
En central iagttagelse inden for kognitionsvidenskaben har været, at de samme fænomener kan undersøges på kvalitativt forskellige måder. David Marr redegjorde for tre forskellige niveauer: Det computationelle niveau, det algoritmiske niveau og implementeringsniveauet.
Det computationelle niveau
På det computationelle niveau undersøges indholdet af - og formålet med en given proces. En person kan f.eks. have som opgave at huske et tidspunkt og et sted, fordi vedkommende har en aftale. Eller i et mere simpelt forsøg, kan en person høre og læse en række ord og så forsøge at afgøre om det hun lige har hørt er det samme som det der kom før, selv om det var et læst ord. Forsøgspersonens opgave er altså at sammenligne en lyd med et billede og afgøre om disse to kvalitativt forskellige sanseindtryk er forbundet med det samme betydningsindhold.
Det algoritmiske niveau
Hvis man spørger personen, hvordan vedkommende bærer sig ad med at huske sin aftale, så vil de fleste være ude af stand til at give et fornuftigt svar. Vi kan bare huske - eller også glemmer vi. På samme måde forholder det sig, hvis vi skal sammenligne et læst ord med et hørt. Selvom de er væsensforskellige sanseindtryk, så har vi alligevel fornemmelsen af at ordet kan være 'det samme'. Vi må formode, at det ikke er tilfældigt og at der gives processer, som muliggør at vi husker. Hvis vi skal afgøre om et ord vi har hørt er det samme, som et ord vi har læst, må vi formode, at der foregår en art 'oversættelse' af ordene, enten til et symbolsk format, hvor sansedelen af ordet er fjernet, eller fra den ene sansemodalitet til den anden, sådan at de to ord kommer til at optræde i samme 'format'.
Når en computer udfører en opgave, så gør den det som regel ved at gennemløbe et program, der fortæller den, hvad den skal gøre. På samme måde kan vi forestille os, at mennesker har “programmer’” der gør dem i stand til at udføre opgaver. Disse programmer må køre ved hjælp af en form for programmeringssprog. Konkret kan vi forestille os, at nervecellerne i hjernen er koblet til hinanden og udveksler informationer. Disse informationer og de lovmæssigheder, som de udviser, udgør det algoritmiske niveau.
Men der kan også være beskrivelser på det algoritmiske niveau som er uafhængige af ideen om at processerne foregår i hjerner. Man kan beskrive processerne ved hjælp af teoretiske modeller og simuleringer og dermed danne sig en idé om hvordan det overhovedet kan lade sig gøre at huske noget. Derefter kan man teste, om måden en model arbejder på, ligner den måde som den naturlige kognition løser opgaven på. En teoretisk model vil f.eks. kunne bruges til at forudsige i hvilke situationer en proces går godt og hvornår den slår fejl. Hvis modellen glemmer sine aftaler efter samme mønster som mennesker typisk gør, så kan det være en indikation af at de to systemer ligner hinanden.
Implementeringsniveauet
Mens det algoritmiske niveau beskriver processerne, så beskriver implementeringsniveauet den “hardware”, som processerne foregår i. For den menneskelige kognitions vedkommende udgøres dette niveau af nervecellerne selv og af den struktur, som de er organiseret i. En korrekt model for den menneskelige kognition på det algoritmiske niveau må naturligvis tage implementeringsniveauet med i betragtning. Når vi skal huske en aftale kan det være, at vi snarere end at huske en specifik adresse, går lidt rundt i nabolaget, og så genkender huset, når vi finder det. En sådan løsning er afhængig af, at vi konkret kan bevæge os, og at de strukturer i vores hjerne (bl.a. hippocampus) som er involveret i at huske steder, har konkrete forbindelser til synsbarken i hjernens nakkelap. Synsbarken er det primære område for visuel perception og på implementeringsniveauet er dette igen affødt af, at der er stærke nerveforbindelser til øjne og nethinde. På samme måde er hørebarken direkte forbundet med det indre øre. Hvis vi skal sammenligne et ord, som er kommet ind gennem hørelsen med et, som kom ind gennem synssansen, må de to signaler nødvendigvis møde hinanden et sted, og det er måske ikke så overraskende, hvis vi ser mere hjerneaktivitet i de områder der ligger midtimellem synsbarken og hørebarken. På implementeringsniveauet giver det i hvert fald mening.
Undersøgelsesmetoder
Kognitionsvidenskaben opstod ganske vist som et brud med behaviorismen, men overtog behaviorismens målsætning om videnskabelighed i undersøgelsen af de menneskelige tankeprocesser. Dette betyder, at kognitionsforskere i vidt omfang er skeptiske over for subjektive fortolkninger og introspektion, hvilket ellers er udbredte metoder inden for de humanistiske forskningsmiljøer som kognitionsvidenskaben trækker på. I stedet søger kognitionsvidenskaben efter naturvidenskabeligt forbillede at etablere falsificerbare teorier og teste hypoteser ved hjælp af eksperimenter.
Adfærdseksperimenter
Ved at studere adfærd kan man indimellem lære noget om de kognitive processer, der ligger bag adfærden. De mest anvendte er adfærdseksperimenter er:
Responstidsforsøg. Allerede i 1868 publicerede F.C. Donders en artikel der foreslog, at forskellen i den tid, som det tog at udføre nært beslægtede opgaver kunne bruges til at sige noget om de underlæggende processer. Hvis en forsøgsperson skal afgøre om et ord er det samme som det forrige ord, så vil forsøgspersonen i gennemsnit være omkring 100 ms hurtigere, hvis ordet er en gentagelse, sammenlignet med hvis det er et nyt ord. Deraf kan man konkludere, at det er en simplere proces at genkende et ord end at forstå et nyt ord, selvom ordet måske er ganske velkendt (f.eks. ‘fisk’). Vores ordgenkendelse er altså afhængig af den forudgående kontekst. Kognitive modeller for ordgenkendelse må derfor indarbejde denne observation.
Psykofysiske eksperimenter. Her bruges ofte meget simple stimuli til at afsøge grænserne for den menneskelige kognitions formåen, f.eks. om en forsøgsperson kan skelne mellem to stimuli såsom forskelle i lydstyrke eller farvetone. Her kan man både lære noget om styrkerne og begrænsningerne i det perceptuelle system. Mennesker kan f.eks. ikke høre de samme lyde som en flagermus eller skelne de samme dufte som en hund, men vi har et veludviklet farvesyn.
Eye tracking. Her filmes forsøgspersonens øjne hvorved øjnenes bevægelser kan følges. hermed kan man lære noget om, hvad det kognitive system opfatter som interessant. Øjnene har en tendens til at se derhen, hvor overraskende eller vigtige fænomener optræder, eller hvor vi har en forventning om, at noget vil ske. Øjenbevægelser siger også noget om vores fordomme. Hvis vi f.eks. præsenteres for en skorstensfejer i en fortælling og der samtidig præsenteres et billede af en mand og en kvinde på en skærm, så vil vi have en tendens til kigge mest på manden, fordi vi har en forventning om at en skorstensfejer typisk er en mand.
Hjerneskanning og neurofysiologi
Hjerneskanningseksperimenter bruges til enten at undersøge hjernens struktur, hvorved viden om implementeringsniveauet kan opnås eller til at undersøge hjernens funktion, hvorved teorier omkring samspillet mellem implementeringsniveauet og de algoritmiske og computationelle niveauer kan testes.
MR-skanning eller Magnetisk resonans skanning er den oftest benyttede metode til undersøgelse af hjernens struktur. Fordelen ved metoden er, at den er uden bivirkninger for deltageren, som således kan deltage i undersøgelser så ofte og så længe som nødvendigt. I skanneren udnyttes, at atomers spin indretter sig efter et stærkt magnetfelt, men at denne tilpasning kan påvirkes med radiobølger. Efterhånden som atomernes spin igen retter sig ind efter magnetfeltet, udsendes radiobølger, som kan måles. Men da atomerne retter sig ind i forskelligt tempo alt efter hvilket miljø, de befinder sig i, kan man måle en forskel, alt efter om signalet f.eks. kommer fra fedt eller vand. Disse forskelle kan bruge til at skabe billeder af hjernens forskellige vævstyper.
fMRI-skanning eller funktionel magnetisk resonsans-skanning bruger de samme principper som den strukturelle MR-skanning, men i stedet udnyttes det at signalet fra skanneren er forskelligt alt efter hvor meget ilt hjernens blod indeholder. Hermed har man et mål, som indirekte afspejler iltforbruget i hjernen og dermed hjernens aktivitetsniveau. Ved at optage billeder hurtigt efter hinanden kan ændringer i iltningen over tid måles. Derved kan det undersøges om der er steder i hjernen, som ændrer deres iltforbrug efter typen af opgave, som forsøgspersonen udfører.
PET-skanning eller positron-emissions-tomografi bruger radioaktive sporstoffer, som lokaliseres, når de når hjernen. Metoden benyttes blandt andet til at undersøge neurotransmitteres funktion, f.eks. dopamin og serotonin. På grund af bivirkningerne fra strålingen, benyttes metoden kun i mindre omfang på raske forsøgspersoner.
EEG eller elektroencefalografi er en metode hvor udsving i de elektriske potentialer, som skabes af hjerneaktivitet, måles med elektroder oven på hovedet. I forhold til fMRI har metoden den fordel, at potentialerne mere direkte afspejler nervecellernes aktivitet med en meget høj tidslig opløsning. Til gengæld kan man kun dårligt lokalisere selve signalet. Metoden bruges derfor først og fremmest til at måle ‘hvornår’ en given kognitiv proces foregår. EEGs styrke er, at udstyret er relativt billigt og kan transporteres ud i felten.
MEG eller magnetoencefalografi udnytter, at der ved en elektrisk strøm dannes et magnetfelt. MEG måler i princippet på det samme elektriske signal fra hjernen som EEG, men kilden til magnetfeltet er lettere at lokalisere i hjernen, da magnetfeltet ikke forstyrres af at passere kranie og hud. Man får derfor en noget bedre rumlig opløsning, samtidig med at den høje tidslige opløsning bevares.
Patient- og dyreforsøg
En anden måde at undersøge forholdet mellem implementeringsniveauet og de algoritmiske og computationelle niveauer er ved at udføre adfærdseksperimenter på patienter eller dyr hvor hjernen har taget skade. Et eksempel på denne type undersøgelser finder vi ved den kognitive neurovidenskabs fødsel i 1861, hvor Paul Broca undersøgte en patient, som havde mistet evnen til at tale, uden at intellektet tilsyneladende havde taget alvorligt skade. Da patienten døde, undersøgte Broca hans hjerne og fandt, at patienten havde en udtalt skade på venstre frontallap. Broca fremsatte derfor den hypotese, at dette område var hjernens talecenter. Senere undersøgelser bekræftede dette fund. Området kaldes i dag Brocas område.
Ved dyreforsøg kan man gå mere drastisk til værks og påføre en skade, hvorved ændringer i adfærd kan studeres. Desuden kan der indføres elektroder i selve hjernen hvorved hjernens aktivitet kan måles direkte ved kilden. Herved har man f.eks. opdaget at et område ved navn hippocampus rummer celler, der holder styr på hvorhenne vi befinder os.. Indopererede elektroder bruges i sjældne tilfælde til at studere menneskelig kognition, typisk i situationer hvor elektroder indføres for at lokalisere områder med epileptisk aktivitet.
Computersimulering
Computermodeller kræver en matematisk og formel beskrivelse af et problem, der kan omformes til en algoritme og implementeres i et computersystem. Herefter kan modellen testes med data af forskellig art. Der er to primære tilgange til computermodeller:
Symbolske modeller, der løser problemer ved at referere til en database og finde den rette løsning på et givet input.
Neurale netværksmodeller, derimod bygger på et system er enheder (‘noder’) der er forbundne på en måde, der er inspireret af nervecellers netværk. Styrken af forbindelsen mellem de enkelte noder kan forandre sig, og ved at ændre styrken alt efter hvor godt systemet løser en opgave, kan modellen “lære” at løse en opgave. I modsætning til det symbolske netværk, ligger løsningen af opgaven ikke et bestemt sted i systemet, men opstår som summen af de mange forbindelser i netværket.
Forskningsområder
beslutningsteori
bevidsthed
ekspertise
emotioner
hjernefunktion
hukommelse
intelligens
kognitiv udvikling
kunstig intelligens
læring
motivation
neurale netværk
opmærksomhed
perception
problemløsning
social kognition
sprog
sproglig udvikling
tænkning
Kognitionsvidenskab versus kognitionspsykologi
Kognitionsvidenskab er nært beslægtet med kognitionspsykologi, og grænsen mellem de to felter er ikke altid helt klar. Men oftest regnes kognitionspsykologi som en del af kognitionsvidenskab, der har et bredere sigte i kraft af sin integration af flere fagområder. Kognitionspsykologi har også traditionelt en højere grad af anvendelsessigte i behandling af patienter, mens kognitionsvidenskab er mere optaget af det teoretiske grundlag. Historisk set var psykologien en mindre del af kognitionsvidenskaben, men den er blevet mere og mere dominerende over årene.
Uddannelse i kognitionsvidenskab
Den første bachelorgrad i kognitionsvidenskab blev uddelt i 1982 fra Vassar College i staten New York. Siden da har mere end 100 universiteter i mere end 30 lande udbudt universitetsstudier i kognitionsvidenskab. De fleste førende amerikanske universiteter udbyder en bachelor i kognitionsvidenskab (f.eks. Stanford University, UC Berkeley, UC San Diego, Harvard University, Yale University, MIT, Columbia University, Johns Hopkins University). Uddannelsen findes også i de nordiske lande, f.eks. Linköpings Universitet, Universitetet i Bergen og Helsinki Universitet. I Tyskland findes der bl.a. en uddannelse i kognitionsvidenskab ved universitetet i Osnabrück.
I Danmark
I Danmark har flere universiteter udbudt uddannelser, som henter inspiration fra kognitionsvidenskaben. Københavns Universitet udbyder f.eks. en kandidatuddannelse i IT og Kognition samt i Kognition og Kommunikation og på Aarhus Universitet kan man læse Kognitiv semiotik.
Fra 2015 udbyder Aarhus Universitet desuden en bachelorgrad (B.Sc.) i kognitionsvidenskab.
Referencer
Psykologi
Kognitionspsykologi
Mentale processer
Neurovidenskab
Datalogi
Kunstig intelligens
Antropologi
Filosofi
Lingvistik | danish | 0.550683 |
brain_train_neural_network/Hebbian_theory.txt | Hebbian theory is a neuropsychological theory claiming that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell. It is an attempt to explain synaptic plasticity, the adaptation of brain neurons during the learning process. It was introduced by Donald Hebb in his 1949 book The Organization of Behavior. The theory is also called Hebb's rule, Hebb's postulate, and cell assembly theory. Hebb states it as follows:
The theory is often summarized as "Cells that fire together wire together." However, Hebb emphasized that cell A needs to "take part in firing" cell B, and such causality can occur only if cell A fires just before, not at the same time as, cell B. This aspect of causation in Hebb's work foreshadowed what is now known about spike-timing-dependent plasticity, which requires temporal precedence.
The theory attempts to explain associative or Hebbian learning, in which simultaneous activation of cells leads to pronounced increases in synaptic strength between those cells. It also provides a biological basis for errorless learning methods for education and memory rehabilitation. In the study of neural networks in cognitive function, it is often regarded as the neuronal basis of unsupervised learning.
Hebbian engrams and cell assembly theory[edit]
Hebbian theory concerns how neurons might connect themselves to become engrams. Hebb's theories on the form and function of cell assemblies can be understood from the following:
The general idea is an old one, that any two cells or systems of cells that are repeatedly active at the same time will tend to become 'associated' so that activity in one facilitates activity in the other.
Hebb also wrote:
When one cell repeatedly assists in firing another, the axon of the first cell develops synaptic knobs (or enlarges them if they already exist) in contact with the soma of the second cell.
[D. Alan Allport] posits additional ideas regarding cell assembly theory and its role in forming engrams, along the lines of the concept of auto-association, described as follows:
If the inputs to a system cause the same pattern of activity to occur repeatedly, the set of active elements constituting that pattern will become increasingly strongly inter-associated. That is, each element will tend to turn on every other element and (with negative weights) to turn off the elements that do not form part of the pattern. To put it another way, the pattern as a whole will become 'auto-associated'. We may call a learned (auto-associated) pattern an engram.
Work in the laboratory of Eric Kandel has provided evidence for the involvement of Hebbian learning mechanisms at synapses in the marine gastropod Aplysia californica. Experiments on Hebbian synapse modification mechanisms at the central nervous system synapses of vertebrates are much more difficult to control than are experiments with the relatively simple peripheral nervous system synapses studied in marine invertebrates. Much of the work on long-lasting synaptic changes between vertebrate neurons (such as long-term potentiation) involves the use of non-physiological experimental stimulation of brain cells. However, some of the physiologically relevant synapse modification mechanisms that have been studied in vertebrate brains do seem to be examples of Hebbian processes. One such study reviews results from experiments that indicate that long-lasting changes in synaptic strengths can be induced by physiologically relevant synaptic activity working through both Hebbian and non-Hebbian mechanisms.
Principles[edit]
From the point of view of artificial neurons and artificial neural networks, Hebb's principle can be described as a method of determining how to alter the weights between model neurons. The weight between two neurons increases if the two neurons activate simultaneously, and reduces if they activate separately. Nodes that tend to be either both positive or both negative at the same time have strong positive weights, while those that tend to be opposite have strong negative weights.
The following is a formulaic description of Hebbian learning: (many other descriptions are possible)
w
i
j
=
x
i
x
j
{\displaystyle \,w_{ij}=x_{i}x_{j}}
where
w
i
j
{\displaystyle w_{ij}}
is the weight of the connection from neuron
j
{\displaystyle j}
to neuron
i
{\displaystyle i}
and
x
i
{\displaystyle x_{i}}
the input for neuron
i
{\displaystyle i}
. Note that this is pattern learning (weights updated after every training example). In a Hopfield network, connections
w
i
j
{\displaystyle w_{ij}}
are set to zero if
i
=
j
{\displaystyle i=j}
(no reflexive connections allowed). With binary neurons (activations either 0 or 1), connections would be set to 1 if the connected neurons have the same activation for a pattern.
When several training patterns are used the expression becomes an average of individual ones:
w
i
j
=
1
p
∑
k
=
1
p
x
i
k
x
j
k
{\displaystyle w_{ij}={\frac {1}{p}}\sum _{k=1}^{p}x_{i}^{k}x_{j}^{k}}
where
w
i
j
{\displaystyle w_{ij}}
is the weight of the connection from neuron
j
{\displaystyle j}
to neuron
i
{\displaystyle i}
,
p
{\displaystyle p}
is the number of training patterns and
x
i
k
{\displaystyle x_{i}^{k}}
the
k
{\displaystyle k}
-th input for neuron
i
{\displaystyle i}
. This is learning by epoch (weights updated after all the training examples are presented), being last term applicable to both discrete and continuous training sets. Again, in a Hopfield network, connections
w
i
j
{\displaystyle w_{ij}}
are set to zero if
i
=
j
{\displaystyle i=j}
(no reflexive connections).
A variation of Hebbian learning that takes into account phenomena such as blocking and many other neural learning phenomena is the mathematical model of Harry Klopf. Klopf's model reproduces a great many biological phenomena, and is also simple to implement.
Relationship to unsupervised learning, stability, and generalization[edit]
Because of the simple nature of Hebbian learning, based only on the coincidence of pre- and post-synaptic activity, it may not be intuitively clear why this form of plasticity leads to meaningful learning. However, it can be shown that Hebbian plasticity does pick up the statistical properties of the input in a way that can be categorized as unsupervised learning.
This can be mathematically shown in a simplified example. Let us work under the simplifying assumption of a single rate-based neuron of rate
y
(
t
)
{\displaystyle y(t)}
, whose inputs have rates
x
1
(
t
)
.
.
.
x
N
(
t
)
{\displaystyle x_{1}(t)...x_{N}(t)}
. The response of the neuron
y
(
t
)
{\displaystyle y(t)}
is usually described as a linear combination of its input,
∑
i
w
i
x
i
{\displaystyle \sum _{i}w_{i}x_{i}}
, followed by a response function
f
{\displaystyle f}
:
y
=
f
(
∑
i
=
1
N
w
i
x
i
)
.
{\displaystyle y=f\left(\sum _{i=1}^{N}w_{i}x_{i}\right).}
As defined in the previous sections, Hebbian plasticity describes the evolution in time of the synaptic weight
w
{\displaystyle w}
:
d
w
i
d
t
=
η
x
i
y
.
{\displaystyle {\frac {dw_{i}}{dt}}=\eta x_{i}y.}
Assuming, for simplicity, an identity response function
f
(
a
)
=
a
{\displaystyle f(a)=a}
, we can write
d
w
i
d
t
=
η
x
i
∑
j
=
1
N
w
j
x
j
{\displaystyle {\frac {dw_{i}}{dt}}=\eta x_{i}\sum _{j=1}^{N}w_{j}x_{j}}
or in matrix form:
d
w
d
t
=
η
x
x
T
w
.
{\displaystyle {\frac {d\mathbf {w} }{dt}}=\eta \mathbf {x} \mathbf {x} ^{T}\mathbf {w} .}
As in the previous chapter, if training by epoch is done an average
⟨
…
⟩
{\displaystyle \langle \dots \rangle }
over discrete or continuous (time) training set of
x
{\displaystyle \mathbf {x} }
can be done:
d
w
d
t
=
⟨
η
x
x
T
w
⟩
=
η
⟨
x
x
T
⟩
w
=
η
C
w
.
{\displaystyle {\frac {d\mathbf {w} }{dt}}=\langle \eta \mathbf {x} \mathbf {x} ^{T}\mathbf {w} \rangle =\eta \langle \mathbf {x} \mathbf {x} ^{T}\rangle \mathbf {w} =\eta C\mathbf {w} .}
where
C
=
⟨
x
x
T
⟩
{\displaystyle C=\langle \,\mathbf {x} \mathbf {x} ^{T}\rangle }
is the correlation matrix of the input under the additional assumption that
⟨
x
⟩
=
0
{\displaystyle \langle \mathbf {x} \rangle =0}
(i.e. the average of the inputs is zero). This is a system of
N
{\displaystyle N}
coupled linear differential equations. Since
C
{\displaystyle C}
is symmetric, it is also diagonalizable, and the solution can be found, by working in its eigenvectors basis, to be of the form
w
(
t
)
=
k
1
e
η
α
1
t
c
1
+
k
2
e
η
α
2
t
c
2
+
.
.
.
+
k
N
e
η
α
N
t
c
N
{\displaystyle \mathbf {w} (t)=k_{1}e^{\eta \alpha _{1}t}\mathbf {c} _{1}+k_{2}e^{\eta \alpha _{2}t}\mathbf {c} _{2}+...+k_{N}e^{\eta \alpha _{N}t}\mathbf {c} _{N}}
where
k
i
{\displaystyle k_{i}}
are arbitrary constants,
c
i
{\displaystyle \mathbf {c} _{i}}
are the eigenvectors of
C
{\displaystyle C}
and
α
i
{\displaystyle \alpha _{i}}
their corresponding eigen values.
Since a correlation matrix is always a positive-definite matrix, the eigenvalues are all positive, and one can easily see how the above solution is always exponentially divergent in time.
This is an intrinsic problem due to this version of Hebb's rule being unstable, as in any network with a dominant signal the synaptic weights will increase or decrease exponentially. Intuitively, this is because whenever the presynaptic neuron excites the postsynaptic neuron, the weight between them is reinforced, causing an even stronger excitation in the future, and so forth, in a self-reinforcing way. One may think a solution is to limit the firing rate of the postsynaptic neuron by adding a non-linear, saturating response function
f
{\displaystyle f}
, but in fact, it can be shown that for any neuron model, Hebb's rule is unstable. Therefore, network models of neurons usually employ other learning theories such as BCM theory, Oja's rule, or the generalized Hebbian algorithm.
Regardless, even for the unstable solution above, one can see that, when sufficient time has passed, one of the terms dominates over the others, and
w
(
t
)
≈
e
η
α
∗
t
c
∗
{\displaystyle \mathbf {w} (t)\approx e^{\eta \alpha ^{*}t}\mathbf {c} ^{*}}
where
α
∗
{\displaystyle \alpha ^{*}}
is the largest eigenvalue of
C
{\displaystyle C}
. At this time, the postsynaptic neuron performs the following operation:
y
≈
e
η
α
∗
t
c
∗
x
{\displaystyle y\approx e^{\eta \alpha ^{*}t}\mathbf {c} ^{*}\mathbf {x} }
Because, again,
c
∗
{\displaystyle \mathbf {c} ^{*}}
is the eigenvector corresponding to the largest eigenvalue of the correlation matrix between the
x
i
{\displaystyle x_{i}}
s, this corresponds exactly to computing the first principal component of the input.
This mechanism can be extended to performing a full PCA (principal component analysis) of the input by adding further postsynaptic neurons, provided the postsynaptic neurons are prevented from all picking up the same principal component, for example by adding lateral inhibition in the postsynaptic layer. We have thus connected Hebbian learning to PCA, which is an elementary form of unsupervised learning, in the sense that the network can pick up useful statistical aspects of the input, and "describe" them in a distilled way in its output.
Limitations[edit]
Despite the common use of Hebbian models for long-term potentiation, Hebb's principle does not cover all forms of synaptic long-term plasticity. Hebb did not postulate any rules for inhibitory synapses, nor did he make predictions for anti-causal spike sequences (presynaptic neuron fires after the postsynaptic neuron). Synaptic modification may not simply occur only between activated neurons A and B, but at neighboring synapses as well. All forms of hetero synaptic and homeostatic plasticity are therefore considered non-Hebbian. An example is retrograde signaling to presynaptic terminals. The compound most commonly identified as fulfilling this retrograde transmitter role is nitric oxide, which, due to its high solubility and diffusivity, often exerts effects on nearby neurons. This type of diffuse synaptic modification, known as volume learning, is not included in the traditional Hebbian model.
Hebbian learning account of mirror neurons[edit]
Hebbian learning and spike-timing-dependent plasticity have been used in an influential theory of how mirror neurons emerge. Mirror neurons are neurons that fire both when an individual performs an action and when the individual sees or hears another perform a similar action. The discovery of these neurons has been very influential in explaining how individuals make sense of the actions of others, by showing that, when a person perceives the actions of others, the person activates the motor programs which they would use to perform similar actions. The activation of these motor programs then adds information to the perception and helps predict what the person will do next based on the perceiver's own motor program. A challenge has been to explain how individuals come to have neurons that respond both while performing an action and while hearing or seeing another perform similar actions.
Christian Keysers and David Perrett suggested that as an individual performs a particular action, the individual will see, hear, and feel the performing of the action. These re-afferent sensory signals will trigger activity in neurons responding to the sight, sound, and feel of the action. Because the activity of these sensory neurons will consistently overlap in time with those of the motor neurons that caused the action, Hebbian learning predicts that the synapses connecting neurons responding to the sight, sound, and feel of an action and those of the neurons triggering the action should be potentiated. The same is true while people look at themselves in the mirror, hear themselves babble, or are imitated by others. After repeated experience of this re-afference, the synapses connecting the sensory and motor representations of an action are so strong that the motor neurons start firing to the sound or the vision of the action, and a mirror neuron is created.
Evidence for that perspective comes from many experiments that show that motor programs can be triggered by novel auditory or visual stimuli after repeated pairing of the stimulus with the execution of the motor program (for a review of the evidence, see Giudice et al., 2009). For instance, people who have never played the piano do not activate brain regions involved in playing the piano when listening to piano music. Five hours of piano lessons, in which the participant is exposed to the sound of the piano each time they press a key is proven sufficient to trigger activity in motor regions of the brain upon listening to piano music when heard at a later time. Consistent with the fact that spike-timing-dependent plasticity occurs only if the presynaptic neuron's firing predicts the post-synaptic neuron's firing, the link between sensory stimuli and motor programs also only seem to be potentiated if the stimulus is contingent on the motor program.
See also[edit]
Dale's principle
Coincidence detection in neurobiology
Leabra
Metaplasticity
Tetanic stimulation
Synaptotropic hypothesis
Neuroplasticity
Behaviorism | biology | 1177729 | https://sv.wikipedia.org/wiki/Hebbs%20teori | Hebbs teori | Hebbs teori (även kallad Hebbs postulat eller Hebbs regel) är en teori inom neurovetenskapen som föreslår en mekanism för vad som händer med nervcellerna i hjärnan när inlärning sker, och hur dessa nervceller anpassar sig. Teorin lades fram av Donald Olding Hebb 1949. Teorin beskriver en mekanism för hur synapserna blir mer effektiva.
Teorin säger att en upprepande eller kvarvarande stimulering kommer att leda till en tillväxtprocess eller metabolisk förändring i den ena eller båda cellerna som leder till en ökad effektivitet i synapsen.
Teorin sammanfattas vanligtvis med "celler som avfyras tillsammans, sammankopplas" (eng. "cells that fire together, wire together"). Även om detta är en överförenkling som inte ska tas bokstavligen har teorin använts för att förklara vissa typer av associationsinlärning. Vid denna typ av inlärning kommer simultan aktivering av celler leda till en uttalad ökning i synaptisk styrka – denna inlärning är känd som hebbiansk inlärning.
Hebbs engram och cellsammanslutningsteori
Hebbs teori behandlar hur neuron skulle kunna sammankopplas för att bilda ett engram.
Gordon Allport placerar ytterligare idéer angående cellsammankopplingsteorin och dess roll i formering av engram, i linje med auto-association.
Hebbs teori har blivit den primära basen för den vanliga tanken att engram är neurala nät eller neurala nätverk, vid analyserande från ett holistiskt synsätt.
Eric R. Kandel har visat vissa bevis för denna teori genom att studera den vattenlevande snigeln Aplysia californica.
Experiment på mekanismer som modifierar Hebbs synaps i det centrala nervsystemets synapser hos ryggradsdjur är mycket svårare att kontrollera än hos de relativt enkla perifera nervsystem med sypapser som finns hos marina ryggradslösa djur. Mycket av arbetet hos långvariga synaptiska experiment mellan neuron (såsom long-term potentiation) involverar användandet av icke-fysiologisk experimentell stimulering av neuron.
Dock verkar några fysiologiskt relevanta synapsmodifieringar hos mekanismerna som studerats hos ryggradsdjur vara exempel på hebbianska processer. Sammanställningar av experiment pekar på att långvariga förändringar i synaptisk styrka kan induceras av fysiologiskt relevant synaptisk aktivitet genom både hebbianska och icke-hebbianska mekanismer.
Principer
Utifrån perspektivet av artificiella neuron och artificiella neurala nätverk, kan Hebbs teori användas för att beskriva hur man ska förändra viktningen mellan modell och neuron. Viktningen mellan två neuron ökar ifall bägge neuron aktiveras simultant och minskar ifall de aktiveras separat. Nod-par som tenderar ha en inbördes enhetlighet (antingen positiva eller negativa) vid samma tidpunkt, har stark positiv viktning och de som tenderar att ha motsatt förhållande har stark negativ viktning.
Denna ursprungliga princip är kanske den enklaste formen av viktningsurval. Den kan relativt enkelt omkodas till ett datorprogram och sedan användas för att vikta ett nätverk. Detta medför flera användningsområden för hebbiansk inlärning. Idag används termen hebbiansk inlärning som ett generellt samlingsnamn för olika former av matematiska abstraktioner av den ursprungliga principen som Hebb lade fram.
Se även
BCM teori
Long-term potentiation
Minne
Metaplasticitet
Neurala nätverk
Källor
Litteratur
Externa länkar
Översikt
Hebbian Learning tutorial (Part 1: Novelty Filtering, Part 2: PCA)
Neurofysiologi | swedish | 0.473422 |
brain_train_neural_network/neural-networks.txt | What is a neural network?
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What is a neural network?
A neural network is a machine learning program, or model, that makes
decisions in a manner similar to the human brain, by using processes that
mimic the way biological neurons work together to identify phenomena, weigh
options and arrive at conclusions.
Every neural network consists of layers of nodes, or artificial neurons—an
input layer, one or more hidden layers, and an output layer. Each node
connects to others, and has its own associated weight and threshold. If the
output of any individual node is above the specified threshold value, that
node is activated, sending data to the next layer of the network. Otherwise,
no data is passed along to the next layer of the network.
Neural networks rely on training data to learn and improve their accuracy over
time. Once they are fine-tuned for accuracy, they are powerful tools in
computer science and artificial intelligence , allowing us to classify and
cluster data at a high velocity. Tasks in speech recognition or image
recognition can take minutes versus hours when compared to the manual
identification by human experts. One of the best-known examples of a neural
network is Google’s search algorithm.
Neural networks are sometimes called artificial neural networks (ANNs) or
simulated neural networks (SNNs). They are a subset of machine learning, and
at the heart of deep learning models.
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How do neural networks work?
Think of each individual node as its own linear regression model, composed
of input data, weights, a bias (or threshold), and an output. The formula
would look something like this:
∑wixi + bias = w1x1 + w2x2 + w3x3 + bias
output = f(x) = 1 if ∑w1x1 + b>= 0; 0 if ∑w1x1 + b < 0
Once an input layer is determined, weights are assigned. These weights help
determine the importance of any given variable, with larger ones contributing
more significantly to the output compared to other inputs. All inputs are then
multiplied by their respective weights and then summed. Afterward, the output
is passed through an activation function, which determines the output. If that
output exceeds a given threshold, it “fires” (or activates) the node, passing
data to the next layer in the network. This results in the output of one node
becoming in the input of the next node. This process of passing data from one
layer to the next layer defines this neural network as a feedforward network.
Let’s break down what one single node might look like using binary values. We
can apply this concept to a more tangible example, like whether you should go
surfing (Yes: 1, No: 0). The decision to go or not to go is our predicted
outcome, or y-hat. Let’s assume that there are three factors influencing your
decision-making:
1. Are the waves good? (Yes: 1, No: 0)
2. Is the line-up empty? (Yes: 1, No: 0)
3. Has there been a recent shark attack? (Yes: 0, No: 1)
Then, let’s assume the following, giving us the following inputs:
* X1 = 1, since the waves are pumping
* X2 = 0, since the crowds are out
* X3 = 1, since there hasn’t been a recent shark attack
Now, we need to assign some weights to determine importance. Larger weights
signify that particular variables are of greater importance to the decision or
outcome.
* W1 = 5, since large swells don’t come around often
* W2 = 2, since you’re used to the crowds
* W3 = 4, since you have a fear of sharks
Finally, we’ll also assume a threshold value of 3, which would translate to a
bias value of –3. With all the various inputs, we can start to plug in values
into the formula to get the desired output.
Y-hat = (1*5) + (0*2) + (1*4) – 3 = 6
If we use the activation function from the beginning of this section, we can
determine that the output of this node would be 1, since 6 is greater than 0.
In this instance, you would go surfing; but if we adjust the weights or the
threshold, we can achieve different outcomes from the model. When we observe
one decision, like in the above example, we can see how a neural network could
make increasingly complex decisions depending on the output of previous
decisions or layers.
In the example above, we used perceptrons to illustrate some of the
mathematics at play here, but neural networks leverage sigmoid neurons, which
are distinguished by having values between 0 and 1. Since neural networks
behave similarly to decision trees, cascading data from one node to another,
having x values between 0 and 1 will reduce the impact of any given change of
a single variable on the output of any given node, and subsequently, the
output of the neural network.
As we start to think about more practical use cases for neural networks, like
image recognition or classification, we’ll leverage supervised learning, or
labeled datasets, to train the algorithm. As we train the model, we’ll want to
evaluate its accuracy using a cost (or loss) function. This is also commonly
referred to as the mean squared error (MSE). In the equation below,
* i represents the index of the sample,
* y-hat is the predicted outcome,
* y is the actual value, and
* m is the number of samples.
𝐶𝑜𝑠𝑡 𝐹𝑢𝑛𝑐𝑡𝑖𝑜𝑛= 𝑀𝑆𝐸=1/2𝑚 ∑129_(𝑖=1)^𝑚▒(𝑦 ̂^((𝑖) )−𝑦^((𝑖) ) )^2
Ultimately, the goal is to minimize our cost function to ensure correctness of
fit for any given observation. As the model adjusts its weights and bias, it
uses the cost function and reinforcement learning to reach the point of
convergence, or the local minimum. The process in which the algorithm adjusts
its weights is through gradient descent, allowing the model to determine the
direction to take to reduce errors (or minimize the cost function). With each
training example, the parameters of the model adjust to gradually converge at
the minimum.
See this IBM Developer article for a deeper explanation of the quantitative
concepts involved in neural networks .
Most deep neural networks are feedforward, meaning they flow in one direction
only, from input to output. However, you can also train your model through
backpropagation; that is, move in the opposite direction from output to input.
Backpropagation allows us to calculate and attribute the error associated with
each neuron, allowing us to adjust and fit the parameters of the model(s)
appropriately.
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Types of neural networks
Neural networks can be classified into different types, which are used for
different purposes. While this isn’t a comprehensive list of types, the below
would be representative of the most common types of neural networks that
you’ll come across for its common use cases:
The perceptron is the oldest neural network, created by Frank Rosenblatt in
1958.
Feedforward neural networks, or multi-layer perceptrons (MLPs), are what we’ve
primarily been focusing on within this article. They are comprised of an input
layer, a hidden layer or layers, and an output layer. While these neural
networks are also commonly referred to as MLPs, it’s important to note that
they are actually comprised of sigmoid neurons, not perceptrons, as most real-
world problems are nonlinear. Data usually is fed into these models to train
them, and they are the foundation for computer vision, natural language
processing , and other neural networks.
Convolutional neural networks (CNNs) are similar to feedforward networks, but
they’re usually utilized for image recognition, pattern recognition, and/or
computer vision. These networks harness principles from linear algebra,
particularly matrix multiplication, to identify patterns within an image.
Recurrent neural networks (RNNs) are identified by their feedback loops.
These learning algorithms are primarily leveraged when using time-series data
to make predictions about future outcomes, such as stock market predictions or
sales forecasting.
##
Neural networks vs. deep learning
Deep Learning and neural networks tend to be used interchangeably in
conversation, which can be confusing. As a result, it’s worth noting that the
“deep” in deep learning is just referring to the depth of layers in a neural
network. A neural network that consists of more than three layers—which would
be inclusive of the inputs and the output—can be considered a deep learning
algorithm. A neural network that only has two or three layers is just a basic
neural network.
To learn more about the differences between neural networks and other forms of
artificial intelligence, like machine learning, please read the blog post “
AI vs. Machine Learning vs. Deep Learning vs. Neural Networks: What’s the
Difference? ”
History of neural networks
The history of neural networks is longer than most people think. While the
idea of “a machine that thinks” can be traced to the Ancient Greeks, we’ll
focus on the key events that led to the evolution of thinking around neural
networks, which has ebbed and flowed in popularity over the years:
1943: Warren S. McCulloch and Walter Pitts published “ A logical calculus of
the ideas immanent in nervous activity (link resides outside ibm.com)” This
research sought to understand how the human brain could produce complex
patterns through connected brain cells, or neurons. One of the main ideas that
came out of this work was the comparison of neurons with a binary threshold to
Boolean logic (i.e., 0/1 or true/false statements).
1958: Frank Rosenblatt is credited with the development of the perceptron,
documented in his research, “ The Perceptron: A Probabilistic Model for
Information Storage and Organization in the Brain ” (link resides outside
ibm.com). He takes McCulloch and Pitt’s work a step further by introducing
weights to the equation. Leveraging an IBM 704, Rosenblatt was able to get a
computer to learn how to distinguish cards marked on the left vs. cards marked
on the right.
1974: While numerous researchers contributed to the idea of backpropagation,
Paul Werbos was the first person in the US to note its application within
neural networks within his PhD thesis (link resides outside ibm.com).
1989: Yann LeCun published a paper (link resides outside ibm.com)
illustrating how the use of constraints in backpropagation and its integration
into the neural network architecture can be used to train algorithms. This
research successfully leveraged a neural network to recognize hand-written zip
code digits provided by the U.S. Postal Service.
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| biology | 764724 | https://da.wikipedia.org/wiki/Kunstigt%20neuralt%20netv%C3%A6rk | Kunstigt neuralt netværk | Kunstige neurale netværk (KNN, engelsk ANN) er modeller, der er mere eller mindre inspireret af biologiske neurale netværk. Typisk forsøges der benyttet matematiske stærke værktøjer til at implementere modellerne. Der findes mange modeller både mht. netværks- og neuronopbygning.
Vi ved ikke (2007) hvordan biologiske neurale netværk lærer, trænes og virker. Det vides ikke hvordan en enkelt biologisk neuron virker - og neuroner kommer i flere hundreder varianter, og det vides heller ikke, hvad neuroner semantisk kommunikerer. Så modellerne har ikke så meget med virkelighedens neuroner at gøre, men på trods af det har man lavet kunstige neurale netværk, der er noget af det bedste til fx robust at klassificere input-mønstre.
Modeller
McCulloch-Pitts-neuronen
I en af de mest simple modeller for neuronopbygning, McCulloch-Pitts-neuronen, kan signalerne, en neuron kan udsende, kun antage to former: enten 1 eller 0. Det vil sige, enten udsender en neuron et signal, eller så gør den ikke. Dette udgående signal afhænger af summeringen af de indgående signaler, en neuron modtager fra andre neuroner, samt størrelsen på en tærskelværdi (en Heaviside trinfunktion af summeringen). I denne neuronmodel er det altså tærskelværdien, der ud fra inputtet bestemmer, om outputtet skal være 0 eller 1.
I andre og mere generelt anvendelige modeller for neuronopbygning end McCulloch-Pitts-neuronen, er inputtet fra hver neuron til en anden neuron vægtet og trinfunktionen er erstattet med en anden funktion, fx sigmoid-funktionen. I disse modeller er oplæring af netværket til en given opgave et vigtigt element. Oplæringen består i justering af vægtene f.eks. ved at vise netværket et inputmønster igen og igen, og ud fra en sammenholdning med netværkets output hertil og det ønskede output, udfører man en vægtjustering. Ved McCulloch-Pitts-neuronen antages det, at et netværk baseret på denne neuronmodel allerede er oplært, dvs. hér tærskelværdien allerede er indstillet til den givne opgave.
I 1959 blev neurocomputeren Mark I perceptronen konstrueret. Den byggede på McCulloch-Pitts neuronmodel, men i udvidet form, og kunne anvendes til tegngenkendelse. Generelt er kunstige neurale netværk gode til mønstergenkendelse samt klassifikation af disse og finder derfor anvendelse inden for datalogien. Neurale netværk har bl.a. været anvendt til matching af fingeraftryk, genkendelse af proteinstrukturer og endda til at styre en bil.
Enkeltlags-perceptron
En enkeltlags-perceptron er et feedforward-netværk, hvilket indebærer, at intet output fra en neuron bruges som input til en neuron tidligere i netværket (Modsat et Hopfield-netværk eksempelvis).
En enkeltlags-perceptron er simpel at opbygge, da den kun har et input-lag (holdeplads for input-værdier) og et output-lag.
Enkeltlags-perceptronen kan kun modellere lineært adskillelige funktioner som de boolske and, or og not, hvorimod den ikke kan modellere en XOR-funktion, da den ikke er lineært adskillelig.
Flerlags-perceptron
Som enkeltlags-perceptronen er flerlags-perceptronen et feedforward-netværk. I modsætning til enkeltlags-perceptronen har den tilføjet (minimum) et lag mellem inputlaget og outputlaget, der gør den i stand til at modellere enhver delmængde af Rn (Universelle approksimationsteorem).
Aktiveringsfunktioner
Neuronerne i et neuralt netværk bruger forskellige aktiveringsfunktioner. Neuronens output er aktiveringsfunktionen af inputet.
I neuronlaget l er outputtet sigmoid, som er aktiveringsfunktionen, af summen af de vægtede inputneuroner plus en bias. Sigmoidfunktion er en ikke-lineær aktiveringsfunktion som har en funktionsværdi mellem 0 og 1, og defineres som følgende:
Ikke-lineære aktiveringsfunktionerne er vigtige for et neuralt netværk, da man ikke ville kunne træne et neuralt netværk til at efterligne ikke-linære-funktioner uden dem. Andre eksempler på aktiveringsfunktioner er:
Referencer
Eksterne henvisninger
Søren Brunak og Benny Lautrup, Neurale netværk: Computere med intuition, Nysyn Munksgaard, 1988.
Forecasting Financial Markests using Artificial Neural Networks
Kunstig intelligens & deep learning på innolabcapital.com henet 7. april 2018
Kunstig intelligens | danish | 0.46394 |
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Machine Learning , Neuro and Cognitive Science
# How Artificial Neural Networks Help Us Understand Neural Networks in the
Human Brain
Experts from psychology, neuroscience, and AI settle a seemingly intractable
historical debate in neuroscience — opening a world of possibilities for using
AI to study the brain.
Jul 27, 2021
|
Andrew Myers
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Image
Neuroscience is a relatively young discipline. This is especially true in
relation to the physical sciences. While we understand a great deal about how,
for example, physical properties emerge from atomic/subatomic forces,
comparatively little is known about how intelligent behavior emerges from
neural function.
In order to make traction on this problem, neuroscientists often rely on
intuitive concepts like "perception" and "memory," enabling them to understand
the relationship between the brain and behavior. In this way, the field has
begun to characterize neural function in broad strokes.
For example, in primates we know that the ventral visual stream (VVS) supports
visual perception, while the medial temporal lobe (MTL) enables memory-related
behaviors.
> Read the study: When the Ventral Visual Stream is Not Enough: A Deep
> Learning Account of Medical Temporal Lobe Involvement in Perception
But using these concepts to describe and categorize neural processing does not
mean we understand the neural functions that support these behaviors. At least
not as physicists understand electrons. Illustrating this point, the field’s
reliance on these concepts has led to enduring neuroscientific debates: Where
does perception end and memory begin? Does the brain draw distinctions, as we
do in the language we use to describe it?
This question is not mere semantics. By understanding how the brain functions
in neurotypical cases (i.e., an idealized, but fictional “normal” brain), it
might be possible to better support individuals experiencing pathological
memory-related brain states, such as post-traumatic stress disorder.
Unfortunately, even after decades of research, characterizing the relationship
between these “perceptual” and “mnemonic” systems has resulted in a seemingly
intractable debate, frustrating attempts to apply our knowledge of the brain
to more applied settings.
Neuroscientists on either side of this debate would look at identical
experimental data and interpret them in radically different ways: One group of
scientists claims that the MTL is involved in both memory and perception,
while the other claims that the MTL is responsible only for memory-related
behaviors.
To better understand how the MTL supports these behaviors, tyler bonnen, a
Stanford doctoral candidate in psychology and trainee in the Wu Tsai
Neurosciences Institute 's Mind, Brain, Computation and Technology Program,
has been working with Daniel Yamins , an assistant professor of psychology
and of computer science and member of the Stanford Institute for Human-
Centered Artificial Intelligence (HAI), as well as Anthony Wagner , a
professor of psychology and director of The Memory Lab at Stanford.
Their recent work , published in the journal Neuron, proposes a novel
computational framework for addressing this problem: using state-of-the-art
computational tools from artificial intelligence to disentangle the
relationship between perception and memory within the human brain.
“The concepts of perception and memory have been valuable in psychology in
that they have allowed us to learn a great deal about neural function — but
only to a point,” bonnen says. “These terms eventually fall short of fully
explaining how the brain supports these behaviors. We can see this quite
clearly in the historical debate over the perceptual functions of the MTL;
because experimentalists were forced to rely on their intuitions for what
counted as perception and memory, they had different interpretations of the
data. Data that, according to our results, are in fact consistent with a
single, unified model.”
### A Fresh Solution
The research team’s solution was to leverage recent advances in a field of
artificial intelligence known as computer vision. This field is among the most
highly developed areas of AI. More specifically, the research team used
computational models that are able to predict neural responses in the primate
visual system: task-optimized convolutional neural networks (CNNs).
“These models are not just ‘good’ at predicting visual behavior,” bonnen says.
“These models do a better job of predicting neural responses in the primate
visual system than any of the models neuroscientists had developed explicitly
for this purpose. For our project this is useful because it enables us to use
these models as a proxy for the human visual system.”
Leveraging these tools enabled bonnen to rerun historical experiments, which
have been used as evidence to support both sides of the debate over MTL
involvement in perception.
First, they collected stimuli and behavioral data from 30 previously published
experiments. Then, using the exact same stimuli as in the original experiments
(the same images, the same compositions, and the same order of presentation,
etc.) they determined how well the model performed these tasks. Finally,
bonnen compared the model performance directly with the behavior of
experimental participants.
“Our results were striking. Across experiments in this literature, our
modeling framework was able to predict the behavior of MTL-lesioned subjects
(i.e., subjects lacking an MTL because of neural injury). However, MTL-intact
subjects were able to outperform our computational model,” bonnen says. “These
results clearly implicate MTL in what have long been described as perceptual
behaviors, resolving decades of apparent inconsistencies.”
But bonnen hesitates when asked whether the MTL is involved in perception.
“While that interpretation is entirely consistent with our findings, we’re not
concerned with which words people should use to describe these MTL-dependent
abilities . We’re more interested in using this modeling approach to
understand how the MTL supports such enchanting — indeed, at times,
indescribable — behaviors.”
“The critical difference between our work and what has come before us,” bonnen
stresses, “is not any new theoretical advance, it’s our method: We challenge
the AI system to solve the same problems that confront humans, generating
intelligent behaviors directly from experimental inputs — e.g., pixels.”
### Settling Old Scores, Opening New Ones
The research team’s work provides a case study on the limitations of
contemporary neuroscientific approaches, as well as a promising path forward:
using novel tools from AI to formalize our understanding of neural function
“Demonstrating the utility of this approach in the context of a seemingly
intractable neuroscientific debate,” bonnen offers, “we have provided a
powerful proof-of-principle: These biologically plausible computational
methods can help us understand neural systems beyond canonical visual
cortices.” For the MTL, this holds potential not only for understanding
memory-related behaviors but also developing novel ways of helping people who
suffer from memory-related pathologies, such as post-traumatic stress
disorder.
bonnen cautions that the algorithms needed to understand these affective and
memory-related behaviors are not as developed as the computer vision models he
deployed in the current study. They don’t yet exist and would need to be
developed, ideally in ways that reflect the same biological systems that
support these behaviors. Nonetheless, artificial intelligence has already
offered powerful tools to formalize our intuitions of animal behavior, greatly
improving our understanding of the brain.
Stanford HAI's mission is to advance AI research, education, policy and
practice to improve the human condition. Learn more .
## More News Topics
Machine Learning , Neuro and Cognitive Science
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| biology | 792495 | https://da.wikipedia.org/wiki/Kognitionsvidenskab | Kognitionsvidenskab | Kognitionsvidenskab er betegnelsen for den tværfaglige undersøgelse af tænkning (kognition) og tænkningens underliggende processer. Kognitionsvidenskaben undersøger både hvad tænkning er, hvad den kan, og hvordan den opstår. Fokus er på, hvordan information optages gennem sanserne (perception), opbevares i hukommelsen, bearbejdes, og videreformidles gennem sproget og den sociale interaktion. Kognitionsvidenskab samler en række forskningsretninger, såsom psykologi, lingvistik, filosofi, neurovidenskab, datalogi og antropologi. Udforskningen af kognitionen er primært kvantitativt eksperimentel, suppleret med computermodeller af f.eks. kunstig intelligens.
Historisk baggrund
Kognitionsvidenskaben har rødder tilbage til antikkens filosoffer, bl.a. Platon og Aristoteles, men som forskningsretning er den et barn af 1950’erne, hvor psykologi, antropologi og lingvistik gennemgik en forvandling, og hvor datalogien og neurovidenskaben opstod som selvstændige forskningsområder..
En stor del af det teoretiske grundlag for studiet af kognitive processer blev lagt inden for de fremstormende videnskaber om computere og databehandling i 1940’erne og 1950’erne med bl.a. Alan Turing og John von Neumann som bannerførere. Computeren blev - og er - vigtig for kognitionsvidenskaben, både som metafor for hvordan den menneskelige informationsbehandling tænkes at foregå, og som instrument til at udvikle og teste modeller for kognitive processer. I midten af 50’erne begyndte Allan Newell og Hebert A. Simon at arbejde med udviklingen af kunstig intelligens i form af computerprogrammer, der simulerede menneskelig problemløsning. Andre forsøg på udvikling af kunstig intelligens med brug af neurale netværk, hvor den menneskelige hjerne bruges som inspiration til computersystemer, snarere end omvendt, er en anden vigtig historisk forudsætning for kognitionsvidenskab. Dette arbejde havde sit udspring i den tidlige kybernetik med bl.a. Walter Pitts og Warren McCulloch som vigtige tidlige skikkelser.
Kognitionsvidenskaben opstod desuden til en vis grad som en reaktion imod behaviorismen. Behaviorismen var den dominerende forskningsretning inden for psykologien i 1950'erne. Under indflydelse af blandt andre Ivan Pavlov argumenterede den for, at adfærd og adfærdens kobling til eksterne stimuli under læring var de eneste processer, der var mulige og relevante at studere. Mentale processer blev ikke anset for tilgængelige for undersøgelser. Et afgørende vendepunkt kom, da en af behaviorismens fremmeste fortalere, adfærdsforskeren B.F. Skinner i sin bog Verbal Behavior fra 1957 forsøgte at beskrive sproget som stimulus-respons læring efter behavioristiske forskrifter. Skinner hævdede at forståelsen af ord bygger på indlæring under kobling af ordet selv med oplevelse af ordets betydning. I en sønderlemmende kritik argumenterede lingvisten Noam Chomsky for at man med behaviorismens tilgang til sprog kun ville kunne forstå sætningen ‘Pengene eller livet’, hvis man havde ‘tidligere erfaring med hvad at være død’. Chomsky argumenterede for nødvendigheden af at inddrage mentale og eventuelt medfødte processer i forklaringen af den menneskelige sprogevne.
Begrebet kognitionsvidenskab (eng.: Cognitive Science) blev første gang brugt i 1973 af Christopher Longuet-Higgins i en rapport om kunstig intelligens. I 1977 udkom det første nummer af det videnskabelige tidsskrift Cognitive Science og i 1979 blev Cognitive Science Society, det første kognitionsvidenskabelige selskab dannet og samme år blev den første egentlige kognitionsvidenskabelige konference afholdt i La Jolla i Californien.
Undersøgelsesniveauer
En central iagttagelse inden for kognitionsvidenskaben har været, at de samme fænomener kan undersøges på kvalitativt forskellige måder. David Marr redegjorde for tre forskellige niveauer: Det computationelle niveau, det algoritmiske niveau og implementeringsniveauet.
Det computationelle niveau
På det computationelle niveau undersøges indholdet af - og formålet med en given proces. En person kan f.eks. have som opgave at huske et tidspunkt og et sted, fordi vedkommende har en aftale. Eller i et mere simpelt forsøg, kan en person høre og læse en række ord og så forsøge at afgøre om det hun lige har hørt er det samme som det der kom før, selv om det var et læst ord. Forsøgspersonens opgave er altså at sammenligne en lyd med et billede og afgøre om disse to kvalitativt forskellige sanseindtryk er forbundet med det samme betydningsindhold.
Det algoritmiske niveau
Hvis man spørger personen, hvordan vedkommende bærer sig ad med at huske sin aftale, så vil de fleste være ude af stand til at give et fornuftigt svar. Vi kan bare huske - eller også glemmer vi. På samme måde forholder det sig, hvis vi skal sammenligne et læst ord med et hørt. Selvom de er væsensforskellige sanseindtryk, så har vi alligevel fornemmelsen af at ordet kan være 'det samme'. Vi må formode, at det ikke er tilfældigt og at der gives processer, som muliggør at vi husker. Hvis vi skal afgøre om et ord vi har hørt er det samme, som et ord vi har læst, må vi formode, at der foregår en art 'oversættelse' af ordene, enten til et symbolsk format, hvor sansedelen af ordet er fjernet, eller fra den ene sansemodalitet til den anden, sådan at de to ord kommer til at optræde i samme 'format'.
Når en computer udfører en opgave, så gør den det som regel ved at gennemløbe et program, der fortæller den, hvad den skal gøre. På samme måde kan vi forestille os, at mennesker har “programmer’” der gør dem i stand til at udføre opgaver. Disse programmer må køre ved hjælp af en form for programmeringssprog. Konkret kan vi forestille os, at nervecellerne i hjernen er koblet til hinanden og udveksler informationer. Disse informationer og de lovmæssigheder, som de udviser, udgør det algoritmiske niveau.
Men der kan også være beskrivelser på det algoritmiske niveau som er uafhængige af ideen om at processerne foregår i hjerner. Man kan beskrive processerne ved hjælp af teoretiske modeller og simuleringer og dermed danne sig en idé om hvordan det overhovedet kan lade sig gøre at huske noget. Derefter kan man teste, om måden en model arbejder på, ligner den måde som den naturlige kognition løser opgaven på. En teoretisk model vil f.eks. kunne bruges til at forudsige i hvilke situationer en proces går godt og hvornår den slår fejl. Hvis modellen glemmer sine aftaler efter samme mønster som mennesker typisk gør, så kan det være en indikation af at de to systemer ligner hinanden.
Implementeringsniveauet
Mens det algoritmiske niveau beskriver processerne, så beskriver implementeringsniveauet den “hardware”, som processerne foregår i. For den menneskelige kognitions vedkommende udgøres dette niveau af nervecellerne selv og af den struktur, som de er organiseret i. En korrekt model for den menneskelige kognition på det algoritmiske niveau må naturligvis tage implementeringsniveauet med i betragtning. Når vi skal huske en aftale kan det være, at vi snarere end at huske en specifik adresse, går lidt rundt i nabolaget, og så genkender huset, når vi finder det. En sådan løsning er afhængig af, at vi konkret kan bevæge os, og at de strukturer i vores hjerne (bl.a. hippocampus) som er involveret i at huske steder, har konkrete forbindelser til synsbarken i hjernens nakkelap. Synsbarken er det primære område for visuel perception og på implementeringsniveauet er dette igen affødt af, at der er stærke nerveforbindelser til øjne og nethinde. På samme måde er hørebarken direkte forbundet med det indre øre. Hvis vi skal sammenligne et ord, som er kommet ind gennem hørelsen med et, som kom ind gennem synssansen, må de to signaler nødvendigvis møde hinanden et sted, og det er måske ikke så overraskende, hvis vi ser mere hjerneaktivitet i de områder der ligger midtimellem synsbarken og hørebarken. På implementeringsniveauet giver det i hvert fald mening.
Undersøgelsesmetoder
Kognitionsvidenskaben opstod ganske vist som et brud med behaviorismen, men overtog behaviorismens målsætning om videnskabelighed i undersøgelsen af de menneskelige tankeprocesser. Dette betyder, at kognitionsforskere i vidt omfang er skeptiske over for subjektive fortolkninger og introspektion, hvilket ellers er udbredte metoder inden for de humanistiske forskningsmiljøer som kognitionsvidenskaben trækker på. I stedet søger kognitionsvidenskaben efter naturvidenskabeligt forbillede at etablere falsificerbare teorier og teste hypoteser ved hjælp af eksperimenter.
Adfærdseksperimenter
Ved at studere adfærd kan man indimellem lære noget om de kognitive processer, der ligger bag adfærden. De mest anvendte er adfærdseksperimenter er:
Responstidsforsøg. Allerede i 1868 publicerede F.C. Donders en artikel der foreslog, at forskellen i den tid, som det tog at udføre nært beslægtede opgaver kunne bruges til at sige noget om de underlæggende processer. Hvis en forsøgsperson skal afgøre om et ord er det samme som det forrige ord, så vil forsøgspersonen i gennemsnit være omkring 100 ms hurtigere, hvis ordet er en gentagelse, sammenlignet med hvis det er et nyt ord. Deraf kan man konkludere, at det er en simplere proces at genkende et ord end at forstå et nyt ord, selvom ordet måske er ganske velkendt (f.eks. ‘fisk’). Vores ordgenkendelse er altså afhængig af den forudgående kontekst. Kognitive modeller for ordgenkendelse må derfor indarbejde denne observation.
Psykofysiske eksperimenter. Her bruges ofte meget simple stimuli til at afsøge grænserne for den menneskelige kognitions formåen, f.eks. om en forsøgsperson kan skelne mellem to stimuli såsom forskelle i lydstyrke eller farvetone. Her kan man både lære noget om styrkerne og begrænsningerne i det perceptuelle system. Mennesker kan f.eks. ikke høre de samme lyde som en flagermus eller skelne de samme dufte som en hund, men vi har et veludviklet farvesyn.
Eye tracking. Her filmes forsøgspersonens øjne hvorved øjnenes bevægelser kan følges. hermed kan man lære noget om, hvad det kognitive system opfatter som interessant. Øjnene har en tendens til at se derhen, hvor overraskende eller vigtige fænomener optræder, eller hvor vi har en forventning om, at noget vil ske. Øjenbevægelser siger også noget om vores fordomme. Hvis vi f.eks. præsenteres for en skorstensfejer i en fortælling og der samtidig præsenteres et billede af en mand og en kvinde på en skærm, så vil vi have en tendens til kigge mest på manden, fordi vi har en forventning om at en skorstensfejer typisk er en mand.
Hjerneskanning og neurofysiologi
Hjerneskanningseksperimenter bruges til enten at undersøge hjernens struktur, hvorved viden om implementeringsniveauet kan opnås eller til at undersøge hjernens funktion, hvorved teorier omkring samspillet mellem implementeringsniveauet og de algoritmiske og computationelle niveauer kan testes.
MR-skanning eller Magnetisk resonans skanning er den oftest benyttede metode til undersøgelse af hjernens struktur. Fordelen ved metoden er, at den er uden bivirkninger for deltageren, som således kan deltage i undersøgelser så ofte og så længe som nødvendigt. I skanneren udnyttes, at atomers spin indretter sig efter et stærkt magnetfelt, men at denne tilpasning kan påvirkes med radiobølger. Efterhånden som atomernes spin igen retter sig ind efter magnetfeltet, udsendes radiobølger, som kan måles. Men da atomerne retter sig ind i forskelligt tempo alt efter hvilket miljø, de befinder sig i, kan man måle en forskel, alt efter om signalet f.eks. kommer fra fedt eller vand. Disse forskelle kan bruge til at skabe billeder af hjernens forskellige vævstyper.
fMRI-skanning eller funktionel magnetisk resonsans-skanning bruger de samme principper som den strukturelle MR-skanning, men i stedet udnyttes det at signalet fra skanneren er forskelligt alt efter hvor meget ilt hjernens blod indeholder. Hermed har man et mål, som indirekte afspejler iltforbruget i hjernen og dermed hjernens aktivitetsniveau. Ved at optage billeder hurtigt efter hinanden kan ændringer i iltningen over tid måles. Derved kan det undersøges om der er steder i hjernen, som ændrer deres iltforbrug efter typen af opgave, som forsøgspersonen udfører.
PET-skanning eller positron-emissions-tomografi bruger radioaktive sporstoffer, som lokaliseres, når de når hjernen. Metoden benyttes blandt andet til at undersøge neurotransmitteres funktion, f.eks. dopamin og serotonin. På grund af bivirkningerne fra strålingen, benyttes metoden kun i mindre omfang på raske forsøgspersoner.
EEG eller elektroencefalografi er en metode hvor udsving i de elektriske potentialer, som skabes af hjerneaktivitet, måles med elektroder oven på hovedet. I forhold til fMRI har metoden den fordel, at potentialerne mere direkte afspejler nervecellernes aktivitet med en meget høj tidslig opløsning. Til gengæld kan man kun dårligt lokalisere selve signalet. Metoden bruges derfor først og fremmest til at måle ‘hvornår’ en given kognitiv proces foregår. EEGs styrke er, at udstyret er relativt billigt og kan transporteres ud i felten.
MEG eller magnetoencefalografi udnytter, at der ved en elektrisk strøm dannes et magnetfelt. MEG måler i princippet på det samme elektriske signal fra hjernen som EEG, men kilden til magnetfeltet er lettere at lokalisere i hjernen, da magnetfeltet ikke forstyrres af at passere kranie og hud. Man får derfor en noget bedre rumlig opløsning, samtidig med at den høje tidslige opløsning bevares.
Patient- og dyreforsøg
En anden måde at undersøge forholdet mellem implementeringsniveauet og de algoritmiske og computationelle niveauer er ved at udføre adfærdseksperimenter på patienter eller dyr hvor hjernen har taget skade. Et eksempel på denne type undersøgelser finder vi ved den kognitive neurovidenskabs fødsel i 1861, hvor Paul Broca undersøgte en patient, som havde mistet evnen til at tale, uden at intellektet tilsyneladende havde taget alvorligt skade. Da patienten døde, undersøgte Broca hans hjerne og fandt, at patienten havde en udtalt skade på venstre frontallap. Broca fremsatte derfor den hypotese, at dette område var hjernens talecenter. Senere undersøgelser bekræftede dette fund. Området kaldes i dag Brocas område.
Ved dyreforsøg kan man gå mere drastisk til værks og påføre en skade, hvorved ændringer i adfærd kan studeres. Desuden kan der indføres elektroder i selve hjernen hvorved hjernens aktivitet kan måles direkte ved kilden. Herved har man f.eks. opdaget at et område ved navn hippocampus rummer celler, der holder styr på hvorhenne vi befinder os.. Indopererede elektroder bruges i sjældne tilfælde til at studere menneskelig kognition, typisk i situationer hvor elektroder indføres for at lokalisere områder med epileptisk aktivitet.
Computersimulering
Computermodeller kræver en matematisk og formel beskrivelse af et problem, der kan omformes til en algoritme og implementeres i et computersystem. Herefter kan modellen testes med data af forskellig art. Der er to primære tilgange til computermodeller:
Symbolske modeller, der løser problemer ved at referere til en database og finde den rette løsning på et givet input.
Neurale netværksmodeller, derimod bygger på et system er enheder (‘noder’) der er forbundne på en måde, der er inspireret af nervecellers netværk. Styrken af forbindelsen mellem de enkelte noder kan forandre sig, og ved at ændre styrken alt efter hvor godt systemet løser en opgave, kan modellen “lære” at løse en opgave. I modsætning til det symbolske netværk, ligger løsningen af opgaven ikke et bestemt sted i systemet, men opstår som summen af de mange forbindelser i netværket.
Forskningsområder
beslutningsteori
bevidsthed
ekspertise
emotioner
hjernefunktion
hukommelse
intelligens
kognitiv udvikling
kunstig intelligens
læring
motivation
neurale netværk
opmærksomhed
perception
problemløsning
social kognition
sprog
sproglig udvikling
tænkning
Kognitionsvidenskab versus kognitionspsykologi
Kognitionsvidenskab er nært beslægtet med kognitionspsykologi, og grænsen mellem de to felter er ikke altid helt klar. Men oftest regnes kognitionspsykologi som en del af kognitionsvidenskab, der har et bredere sigte i kraft af sin integration af flere fagområder. Kognitionspsykologi har også traditionelt en højere grad af anvendelsessigte i behandling af patienter, mens kognitionsvidenskab er mere optaget af det teoretiske grundlag. Historisk set var psykologien en mindre del af kognitionsvidenskaben, men den er blevet mere og mere dominerende over årene.
Uddannelse i kognitionsvidenskab
Den første bachelorgrad i kognitionsvidenskab blev uddelt i 1982 fra Vassar College i staten New York. Siden da har mere end 100 universiteter i mere end 30 lande udbudt universitetsstudier i kognitionsvidenskab. De fleste førende amerikanske universiteter udbyder en bachelor i kognitionsvidenskab (f.eks. Stanford University, UC Berkeley, UC San Diego, Harvard University, Yale University, MIT, Columbia University, Johns Hopkins University). Uddannelsen findes også i de nordiske lande, f.eks. Linköpings Universitet, Universitetet i Bergen og Helsinki Universitet. I Tyskland findes der bl.a. en uddannelse i kognitionsvidenskab ved universitetet i Osnabrück.
I Danmark
I Danmark har flere universiteter udbudt uddannelser, som henter inspiration fra kognitionsvidenskaben. Københavns Universitet udbyder f.eks. en kandidatuddannelse i IT og Kognition samt i Kognition og Kommunikation og på Aarhus Universitet kan man læse Kognitiv semiotik.
Fra 2015 udbyder Aarhus Universitet desuden en bachelorgrad (B.Sc.) i kognitionsvidenskab.
Referencer
Psykologi
Kognitionspsykologi
Mentale processer
Neurovidenskab
Datalogi
Kunstig intelligens
Antropologi
Filosofi
Lingvistik | danish | 0.550683 |
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##### Chm Blog Curatorial Insights
# How Do Neural Network Systems Work?
#### By Hansen Hsu | August 05, 2020
## Share
Editor's Note: This blog is a companion to AI and Play, Part 2: Go and Deep
Learning .
"But What Is a Neural Nework?" Video: Courtesy Grant Sanderson, 3Blue1Brown.
As the name suggests, artificial neural networks are modeled on biological
neural networks in the brain. The brain is made up of cells called neurons,
which send signals to each other through connections known as synapses.
Neurons transmit electrical signals to other neurons based on the signals they
themselves receive from other neurons. An artificial neuron simulates how a
biological neuron behaves by adding together the values of the inputs it
receives. If this is above some threshold, it sends its own signal to its
output, which is then received by other neurons. However, a neuron doesn’t
have to treat each of its inputs with equal weight. Each of its inputs can be
adjusted by multiplying it by some weighting factor. Say, if input A were
twice as important as input B, then input A would have a weight of 2. Weights
can also be negative, if the value of that input is unimportant.
Diagram of a simple feed-forward artificial neural network, with one “hidden
layer,” also known as a “perceptron.” Image: Wikipedia.
Each neuron is thus connected to other neurons in the network through these
synaptic connections, whose values are weighted, and the signals propagating
through the network are strengthened or dampened by these weight values. The
process of training involves adjusting these weight values so that the final
output of the network gives you the right answer.
Diagram of a perceptron, from Frank Rosenblatt’s “The Design of an Intelligent
Automaton,” published by the Cornell Aeronautical Laboratory, 1958. The
“Association System” corresponds to a single “hidden layer” in modern neural
networks. Image: Cornell University Library, Division of Rare and Manuscript
Collections.
The simplest version of an artificial neural network, based on Rosenblatt’s
perceptron, has three layers of neurons. The first is the input layer. This
takes input values–say, the pixels of a photograph. The outputs of this first
layer of neurons are connected to a middle layer, called the “hidden” layer.
The outputs of these “hidden” neurons are then connected to the final output
layer. This final layer is what gives you the answer to what the network has
been trained to do. For example, a network can be trained to recognize photos
of cats. The output layer of the network would then have two outputs, “cat” or
“not cat.” Given a dataset of photos which a human has labeled with either
“cat” or “not cat,” the network is trained by adjusting its weights so that
when it sees a new unlabeled cat photo, it outputs a greater than 90 percent
probability that it is a cat, or less than 10 percent if it is not. Neural
networks can classify things into more than two categories as well, for
example handwritten characters 0-9 or the 26 letters of the alphabet.
Perceptrons were limited by having only a single middle “hidden” layer of
neurons. Although Rosenblatt knew having more inner hidden layers would be
helpful, he did not find a way to train such a network. It wasn’t until
connectionists in the 1980s, like Geoffrey Hinton, applied the algorithm known
as “backpropagation” to training networks with multiple hidden layers, that
this problem was solved. Networks with many hidden layers are also known as
“multilayer perceptrons” or as “deep” neural networks, hence the term “deep”
learning. How many layers and how many neurons an artificial neural network
should have is known as its “architecture,” and figuring out the best one for
a particular problem is currently a process of trial and error and closer to
an art than a science. Ironically at the very heart of today’s neural network
design lies a big space for human ingenuity.
The example above used a labeled dataset to determine whether a picture was a
cat or not. Training with such human-labeled data constitutes what is called
“supervised” learning, because it is supervised by human labels. Much of
today’s deep learning systems are powered by such supervised systems, and it
is here that human biases in the pre-labeled data can bias the network too.
There are two other kinds of machine learning. Unsupervised learning simply
gives the network unlabeled data, and asks it to try to find patterns and
clusters of similarity in items on its own, and humans come in after the fact
to give some names to the clusters the network has found. Unsupervised
learning can be combined with supervised learning to pre-train a network that
is then trained with labeled data, greatly reducing training time with
supervised learning alone. A third type of machine learning is called
reinforcement learning. Reinforcement learning is generally used in games.
Instead of being given external data of winning and losing games, the system
generates this data by playing itself over and over again, getting better each
time. Reinforcement learning was inspired by ideas of how children learn to do
good things through rewards and avoid doing bad things via punishments.
DeepMind used a combination of supervised and reinforcement learning to create
AlphaGo.
## Related
* AI and Play, Part 1: How Games Have Driven Two Schools of AI Research
* AI and Play, Part 2: Go and Deep Learning
## About The Author
Hansen Hsu is a historian and sociologist of technology, and curator of the
CHM Software History Center. He works at the intersection of the histories of
personal computing, graphical user interfaces, object-oriented programming,
and software engineering.
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| biology | 764724 | https://da.wikipedia.org/wiki/Kunstigt%20neuralt%20netv%C3%A6rk | Kunstigt neuralt netværk | Kunstige neurale netværk (KNN, engelsk ANN) er modeller, der er mere eller mindre inspireret af biologiske neurale netværk. Typisk forsøges der benyttet matematiske stærke værktøjer til at implementere modellerne. Der findes mange modeller både mht. netværks- og neuronopbygning.
Vi ved ikke (2007) hvordan biologiske neurale netværk lærer, trænes og virker. Det vides ikke hvordan en enkelt biologisk neuron virker - og neuroner kommer i flere hundreder varianter, og det vides heller ikke, hvad neuroner semantisk kommunikerer. Så modellerne har ikke så meget med virkelighedens neuroner at gøre, men på trods af det har man lavet kunstige neurale netværk, der er noget af det bedste til fx robust at klassificere input-mønstre.
Modeller
McCulloch-Pitts-neuronen
I en af de mest simple modeller for neuronopbygning, McCulloch-Pitts-neuronen, kan signalerne, en neuron kan udsende, kun antage to former: enten 1 eller 0. Det vil sige, enten udsender en neuron et signal, eller så gør den ikke. Dette udgående signal afhænger af summeringen af de indgående signaler, en neuron modtager fra andre neuroner, samt størrelsen på en tærskelværdi (en Heaviside trinfunktion af summeringen). I denne neuronmodel er det altså tærskelværdien, der ud fra inputtet bestemmer, om outputtet skal være 0 eller 1.
I andre og mere generelt anvendelige modeller for neuronopbygning end McCulloch-Pitts-neuronen, er inputtet fra hver neuron til en anden neuron vægtet og trinfunktionen er erstattet med en anden funktion, fx sigmoid-funktionen. I disse modeller er oplæring af netværket til en given opgave et vigtigt element. Oplæringen består i justering af vægtene f.eks. ved at vise netværket et inputmønster igen og igen, og ud fra en sammenholdning med netværkets output hertil og det ønskede output, udfører man en vægtjustering. Ved McCulloch-Pitts-neuronen antages det, at et netværk baseret på denne neuronmodel allerede er oplært, dvs. hér tærskelværdien allerede er indstillet til den givne opgave.
I 1959 blev neurocomputeren Mark I perceptronen konstrueret. Den byggede på McCulloch-Pitts neuronmodel, men i udvidet form, og kunne anvendes til tegngenkendelse. Generelt er kunstige neurale netværk gode til mønstergenkendelse samt klassifikation af disse og finder derfor anvendelse inden for datalogien. Neurale netværk har bl.a. været anvendt til matching af fingeraftryk, genkendelse af proteinstrukturer og endda til at styre en bil.
Enkeltlags-perceptron
En enkeltlags-perceptron er et feedforward-netværk, hvilket indebærer, at intet output fra en neuron bruges som input til en neuron tidligere i netværket (Modsat et Hopfield-netværk eksempelvis).
En enkeltlags-perceptron er simpel at opbygge, da den kun har et input-lag (holdeplads for input-værdier) og et output-lag.
Enkeltlags-perceptronen kan kun modellere lineært adskillelige funktioner som de boolske and, or og not, hvorimod den ikke kan modellere en XOR-funktion, da den ikke er lineært adskillelig.
Flerlags-perceptron
Som enkeltlags-perceptronen er flerlags-perceptronen et feedforward-netværk. I modsætning til enkeltlags-perceptronen har den tilføjet (minimum) et lag mellem inputlaget og outputlaget, der gør den i stand til at modellere enhver delmængde af Rn (Universelle approksimationsteorem).
Aktiveringsfunktioner
Neuronerne i et neuralt netværk bruger forskellige aktiveringsfunktioner. Neuronens output er aktiveringsfunktionen af inputet.
I neuronlaget l er outputtet sigmoid, som er aktiveringsfunktionen, af summen af de vægtede inputneuroner plus en bias. Sigmoidfunktion er en ikke-lineær aktiveringsfunktion som har en funktionsværdi mellem 0 og 1, og defineres som følgende:
Ikke-lineære aktiveringsfunktionerne er vigtige for et neuralt netværk, da man ikke ville kunne træne et neuralt netværk til at efterligne ikke-linære-funktioner uden dem. Andre eksempler på aktiveringsfunktioner er:
Referencer
Eksterne henvisninger
Søren Brunak og Benny Lautrup, Neurale netværk: Computere med intuition, Nysyn Munksgaard, 1988.
Forecasting Financial Markests using Artificial Neural Networks
Kunstig intelligens & deep learning på innolabcapital.com henet 7. april 2018
Kunstig intelligens | danish | 0.46394 |
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What is a neural network? A computer scientist explains
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# What is a neural network? A computer scientist explains
Tam Nguyen, assistant professor • January 15, 2021
Editor’s note: One of the central technologies of artificial intelligence is
neural networks. In this interview , Tam Nguyen, a professor of computer
science at the University of Dayton, explains how neural networks, programs in
which a series of algorithms try to simulate the human brain work.
## What are some examples of neural networks that are familiar to most
people?
There are many applications of neural networks. One common example is your
smartphone camera’s ability to recognize faces.
Driverless cars are equipped with multiple cameras which try to recognize
other vehicles, traffic signs and pedestrians by using neural networks, and
turn or adjust their speed accordingly.
Neural networks try to simulate the brain by processing data through layers of
artificial neurons. MF3d / E+ via Getty Images
Neural networks are also behind the text suggestions you see while writing
texts or emails, and even in the translations tools available online.
## Does the network need to have prior knowledge of something to be able to
classify or recognize it?
Yes, that’s why there is a need to use big data in training neural networks.
They work because they are trained on vast amounts of data to then recognize,
classify and predict things.
In the driverless cars example, it would need to look at millions of images
and video of all the things on the street and be told what each of those
things is. When you click on the images of crosswalks to prove that you’re not
a robot while browsing the internet, it can also be used to help train a
neural network . Only after seeing millions of crosswalks, from all different
angles and lighting conditions, would a self-driving car be able to recognize
them when it’s driving around in real life.
More complicated neural networks are actually able to teach themselves. In the
video linked below, the network is given the task of going from point A to
point B, and you can see it trying all sorts of things to try to get the model
to the end of the course, until it finds one that does the best job.
Some neural networks can work together to create something new. In this
example , the networks create virtual faces that don’t belong to real people
when you refresh the screen. One network makes an attempt at creating a face,
and the other tries to judge whether it is real or fake. They go back and
forth until the second one cannot tell that the face created by the first is
fake.
Humans take advantage of big data too. A person perceives around 30 frames or
images per second, which means 1,800 images per minute, and over 600 million
images per year. That is why we should give neural networks a similar
opportunity to have the big data for training.
## How does a basic neural network work?
A neural network is a network of artificial neurons programmed in software. It
tries to simulate the human brain, so it has many layers of “neurons” just
like the neurons in our brain. The first layer of neurons will receive inputs
like images, video, sound, text, etc. This input data goes through all the
layers, as the output of one layer is fed into the next layer.
Let’s take an example of a neural network that is trained to recognize dogs
and cats. The first layer of neurons will break up this image into areas of
light and dark. This data will be fed into the next layer to recognize edges.
The next layer would then try to recognize the shapes formed by the
combination of edges. The data would go through several layers in a similar
fashion to finally recognize whether the image you showed it is a dog or a cat
according to the data it’s been trained on.
These networks can be incredibly complex and consist of millions of parameters
to classify and recognize the input it receives.
## Why are we seeing so many applications of neural networks now?
Actually neural networks were invented a long time ago, in 1943, when Warren
McCulloch and Walter Pitts created a computational model for neural networks
based on algorithms. Then the idea went through a long hibernation because the
immense computational resources needed to build neural networks did not exist
yet.
Recently, the idea has come back in a big way, thanks to advanced
computational resources like graphical processing units (GPUs). They are chips
that have been used for processing graphics in video games, but it turns out
that they are excellent for crunching the data required to run neural networks
too. That is why we now see the proliferation of neural networks.
Tam Nguyen is an assistant professor in the Department of Computer Science at
the University of Dayton.
This article is republished from The Conversation under a Creative Commons
license. Read the original article . [Understand new developments in
science, health and technology, each week. Subscribe to The Conversation’s
science newsletter .]
### When exercise makes you sick to your stomach
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| biology | 6231093 | https://sv.wikipedia.org/wiki/Psi2%20Draconis | Psi2 Draconis | {{DISPLAYTITLE:Psi2 Draconis}}
Psi2 Draconis (ψ² Draconis) är en vit jättestjärna i stjärnbilden Draken.
Den befinner sig på 723,2 ljusårs (221 parsec) avstånd från Jorden och kan ses med blotta ögat på norra stjärnhimlen, med en skenbar magnitud på 5,43.
Egenskaper
Spektralklass F2III
F2
Psi2 Draconis är av spektraltyp/-klass F2III, där "F2" innebär att den är vit och har en fotosfär-temperatur på omkring . Den är så något svalare än den tidigare A-klassen men varmare än vår sol som är av spektralklass G2V.
Hos stjärnor av spektralklass F syns inte lika starka väte-linjer som hos A-klassen och det har istället börjat synas mer absorptionslinjer från de mindre metallerna.
III
Psi2 Draconis avger ca 530 gånger mer energi än solen från dess fotosfär. Beteckningen "III" anger att luminositeten, ljusstyrkan, är betydligt större än hos en huvudseriestjärna med samma temperatur. Ju högre siffra desto lägre luminositet, och "V" motsvarar ljusstyrkan hos huvudseriestjärnor, den vanligaste gruppen stjärnor i sin spektralklass.
Detta innebär att Psi2 Draconis också är betydligt större än de flesta och den är klassificerad som en jättestjärna. Den beräknas ha en massa som är omkring dubbelt så stor som solens massa och en radie som är ca 17 gånger solens.
Referenser
Externa länkar
https://www.universeguide.com/star/psi2draconis
http://stars.astro.illinois.edu/sow/psidra.html
Stjärnbilden Draken
Vita jättar
Bayerobjekt
HR-objekt
HD-objekt
Flamsteedobjekt | swedish | 1.312943 |
strange_things_in_light/Floater.txt | Floaters or eye floaters are sometimes visible deposits (e.g., the shadows of tiny structures of protein or other cell debris projected onto the retina) within the eye's vitreous humour ("the vitreous"), which is normally transparent, or between the vitreous and retina.
They can become particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky.
Each floater can be measured by its size, shape, consistency, refractive index, and motility. They are also called muscae volitantes (Latin for 'flying flies'), or mouches volantes (from the same phrase in French). The vitreous usually starts out transparent, but imperfections may gradually develop as one ages. The common type of floater, present in most people's eyes, is due to these degenerative changes of the vitreous. The perception of floaters, which may be annoying or problematic to some people, is known as myodesopsia, or, less commonly, as myodaeopsia, myiodeopsia, or myiodesopsia. It is not often treated, except in severe cases, where vitrectomy (surgery), laser vitreolysis, and medication may be effective.
Floaters are visible either because of the shadows imperfections cast on the retina, or because of the refraction of light that passes through them, and can appear alone or together with several others as a clump in one's visual field. They may appear as spots, threads, or fragments of "cobwebs", which float slowly before the observer's eyes, and move especially in the direction the eyes move. As these objects exist within the eye itself, they are not optical illusions but are entoptic phenomena (caused by the eye itself). They are not to be confused with visual snow, which is similar to the static on a television screen, although these two conditions may co-exist as part of a number of visual disturbances which include starbursts, trails, and afterimages.
Signs and symptoms[edit]
External videos What are those floaty things in your eye? - Michael Mauser, 4:04, TED-Ed
Floaters are from objects in pockets of liquid within the vitreous humour, the thick fluid or gel that fills the eye, or between the vitreous and the retina. The vitreous humour, or vitreous body, is a jelly-like, transparent substance that fills the majority of the eye. It lies within the vitreous chamber behind the lens, and is one of the four optical components of the eye. Thus, floaters follow the rapid motions of the eye, while drifting slowly within the pocket of liquid. When they are first noticed, the natural reaction is to attempt to look directly at them. However, attempting to shift one's gaze toward them can be difficult because floaters follow the motion of the eye, remaining to the side of the direction of gaze. Floaters are, in fact, visible only because they do not remain perfectly fixed within the eye. Although the blood vessels of the eye also obstruct light, they are invisible under normal circumstances because they are fixed in location relative to the retina, and the brain "tunes out" stabilized images through neural adaptation.
Floaters are particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Despite the name "floaters", many of these specks have a tendency to sink toward the bottom of the eyeball, in whichever way the eyeball is oriented; the supine position (looking up or lying back) tends to concentrate them near the fovea, which is the center of gaze, while the textureless and evenly lit sky forms an ideal background against which to view them. The brightness of the daytime sky also causes the eyes' pupils to contract, reducing the aperture, which makes floaters less blurry and easier to see.
Floaters present at birth usually remain lifelong, while those that appear later may disappear within weeks or months. They are not uncommon, and do not cause serious problems for most people. A survey of optometrists in 2002 suggested that an average of 14 patients per month per optometrist presented with symptoms of floaters in the UK. However, floaters are more than a nuisance and a distraction to those with severe cases, especially if the spots seem constantly to drift through the field of vision. The shapes are shadows projected onto the retina by tiny structures of protein or other cell debris discarded over the years and trapped in the vitreous humour or between the vitreous and retina. Floaters can even be seen when the eyes are closed on especially bright days, when sufficient light penetrates the eyelids to cast the shadows. It is not, however, only elderly persons who are troubled by floaters; they can also become a problem to younger people, especially if they are myopic. They are also common after cataract or clear lens extraction operations or after trauma.
Floaters are able to catch and refract light in ways that somewhat blur vision temporarily until the floater moves to a different area. Often they trick persons who are troubled by floaters into thinking they see something out of the corner of their eye that really is not there. Most persons come to terms with the problem, after a time, and learn to ignore their floaters. For persons with severe floaters it is nearly impossible to ignore completely the large masses that constantly stay within almost direct view.
In the case of young people, particularly those under 35, symptomatic floaters are likely suspended within a posterior region of the eye known as the pre-macular bursa. Such floaters appear well-defined and usually bear the appearance of a 'crystal worm' or cobweb. Due to their proximity to the retina, the floaters have a significant effect on the visual field for patients. In addition, such floaters are often in the central visual axis as it moves with the intravitreal currents of the eye. Research on floaters of the pre-macular bursa are very minimal and safe treatment for patients with this disturbance that does not warrant major vitrectomy has yet to be discovered. Moreover, the cause and prognosis for such floaters also remains to be found. Some doctors suggest such floaters may resolve over time, should the floaters move away from the retina.
Causes[edit]
There are various causes for the appearance of floaters, of which the most common are described here.
Floaters can occur when eyes age; in rare cases, floaters may be a sign of retinal detachment or a retinal tear.
Vitreous syneresis[edit]
Vitreous syneresis (liquefaction) and contraction with age can cause vitreous floaters. Additionally, trauma or injury to the globe can cause them.
Vitreous detachments and retinal detachments[edit]
Weiss ring: a large, ring shaped floater that is sometimes seen if the vitreous body releases from the back of the eye
In time, the liquefied vitreous body loses support and its framework contracts. This leads to posterior vitreous detachment, in which the vitreous membrane is released from the sensory retina. During this detachment, the shrinking vitreous can stimulate the retina mechanically, causing the patient to see random flashes across the visual field, sometimes referred to as "flashers", a symptom more formally referred to as photopsia. The ultimate release of the vitreous around the optic nerve head sometimes makes a large floater appear, usually in the shape of a ring ("Weiss ring"). As a complication, part of the retina might be torn off by the departing vitreous membrane, in a process known as retinal detachment. This will often leak blood into the vitreous, which is seen by the patient as a sudden appearance of numerous small dots, moving across the whole field of vision. Retinal detachment requires immediate medical attention, as it can easily cause blindness. Consequently, both the appearance of flashes and the sudden onset of numerous small floaters should be rapidly investigated by an eye care provider.
Posterior vitreous detachment is more common in people who:
are nearsighted;
have undergone cataract surgery or clear lens extraction;
have had Nd:YAG laser surgery of the eye;
have had inflammation inside the eye.
Regression of the hyaloid artery[edit]
The hyaloid artery, an artery running through the vitreous humour during the fetal stage of development, regresses in the third trimester of pregnancy. Its disintegration can sometimes leave cell matter.
Other common causes[edit]
Patients with retinal tears may experience floaters if red blood cells are released from leaky blood vessels, and those with uveitis or vitritis, as in toxoplasmosis, may experience multiple floaters and decreased vision due to the accumulation of white blood cells in the vitreous humour.
Other causes for floaters include cystoid macular edema and asteroid hyalosis. The latter is an anomaly of the vitreous humour, whereby calcium clumps attach themselves to the collagen network. The bodies that are formed in this way move slightly with eye movement, but then return to their fixed position.
Diagnosis[edit]
Floaters are often readily observed by an ophthalmologist or an optometrist with the use of an ophthalmoscope or slit lamp. However, if the floater is near the retina, it may not be visible to the observer even if it appears large to the patient.
Increasing background illumination or using a pinhole to effectively decrease pupil diameter may allow a person to obtain a better view of his or her own floaters. The head may be tilted in such a way that one of the floaters drifts towards the central axis of the eye. In the sharpened image the fibrous elements are more conspicuous.
The presence of retinal tears with new onset of floaters was surprisingly high (14%; 95% confidence interval, 12–16%) as reported in a meta-analysis published as part of the Rational Clinical Examination Series in the Journal of the American Medical Association. Patients with new onset flashes and/or floaters, especially when associated with visual loss or restriction in the visual field, should seek more urgent ophthalmologic evaluation.
Treatment[edit]
While surgeries do exist to correct for severe cases of floaters, there are no medications (including eye drops) that can correct for this vitreous deterioration. Floaters are often caused by the normal aging process and will usually become less bothersome as a person learns to ignore them. Looking up/down and left/right will cause the floaters to leave the direct field of vision as the vitreous humour swirls around due to the sudden movement. If floaters significantly increase in numbers and/or severely affect vision, then one of the below treatments may be necessary.
As of 2017, insufficient evidence is available to compare the safety and efficacy of surgical vitrectomy with laser vitreolysis for the treatment of floaters. A 2017 Cochrane Review did not find any relevant studies that compared the two treatments.
Aggressive marketing campaigns have promoted the use of laser vitreolysis for the treatment of floaters. No strong evidence currently exists for the treatment of floaters with laser vitreolysis. The strongest available evidence comparing these two treatment modalities are retrospective case series.
Surgery[edit]
Vitrectomy may be successful in treating more severe cases. The technique usually involves making three openings through the part of the sclera known as the pars plana. Of these small gauge instruments, one is an infusion port to resupply a saline solution and maintain the pressure of the eye, the second is a fiber optic light source, and the third is a vitrector. The vitrector has a reciprocating cutting tip attached to a suction device. This design reduces traction on the retina via the vitreous material. A variant sutureless, self-sealing technique is sometimes used.
Like most invasive surgical procedures, however, vitrectomy carries a risk of complications, including: retinal detachment, anterior vitreous detachment and macular edema – which can threaten vision or worsen existing floaters (in the case of retinal detachment).
Laser vitreolysis[edit]
Laser vitreolysis is a possible treatment option for the removal of vitreous strands and opacities (floaters). In this procedure an ophthalmic laser (usually a yttrium aluminium garnet (YAG) laser) applies a series of nanosecond pulses of low-energy laser light to evaporate the vitreous opacities and to sever the vitreous strands. When performed with a YAG laser designed specifically for vitreolysis, reported side effects and complications associated with vitreolysis are rare. However, YAG lasers have traditionally been designed for use in the anterior portion of the eye, i.e. posterior capsulotomy and iridotomy treatments. As a result, they often provide a limited view of the vitreous, which can make it difficult to identify the targeted floaters and membranes. They also carry a high risk of damage to surrounding ocular tissue. Accordingly, vitreolysis is not widely practised, being performed by very few specialists. One of them, John Karickhoff, has performed the procedure more than 1,400 times and claims a 90 percent success rate. However, the MedicineNet web site states that "there is no evidence that this [laser treatment] is effective. The use of a laser also poses significant risks to the vision in what is otherwise a healthy eye."
Medication[edit]
Enzymatic vitreolysis has been trialed to treat vitreomacular adhesion (VMA) and anomalous posterior vitreous detachment. Although the mechanism of action may have an effect on clinically significant floaters, as of March 2015 there are no clinical trials being undertaken to determine whether this may be a therapeutic alternative to either conservative management, or vitrectomy.
Atropine[edit]
Dropping low doses of atropine onto the eye dilates the pupil, thus reducing shadow formation on the retina by floaters.
Research[edit]
The VDM project aims to find an effective, low-risk treatment for floaters. So far, there have been studies using colloidal gold or indocyanine green (ICG) injected into the eye followed by a low-energy laser to target problematic floaters, and this has shown to be successful on vitreous opacities obtained during vitrectomy and in rabbits.
Epidemiology[edit]
A vitreous detachment typically affects patients older than the age of 50 and increases in prevalence by age 80. Individuals who are myopic or nearsighted have an increased risk of vitreous floaters. Additionally, eyes with an inflammatory disease after direct trauma to the globe or have recently undergone eye surgery have an increased chance of developing a vitreous floater. Men and women appear to be affected equally.
In other animals[edit]
It has been theorized that non-human animals are capable of seeing floaters, as most mammals have anatomically similar eye structures to humans. However, floaters in animals are capable of damaging their vision. Animals with synchysis have an increased risk for retinal detachment and may also require surgery.
See also[edit]
Blue field entoptic phenomenon, alias Scheerer's phenomenon – tiny bright dots moving quickly in the visual field.
Ocular straylight
Phosphene
Scotoma
Synchysis scintillans | biology | 616271 | https://no.wikipedia.org/wiki/Strabisme | Strabisme | Strabisme, til vanlig kalt skjeling, er en tilstand der øynene ikke er rettet mot samme punkt. Vanligvis rettes det ene øyet mot objektet som pasienten ser på. På grunn av feil lengde eller feil bruk av musklene som bestemmer øyeeplets stilling vil det andre øyet se en annen retning. Bildet som dannes på netthinnen på det andre øyet er så langt unna at hjernen ikke greier å samkjøre de to bildene. Hjernen vil da la være å benytte bildet fra det andre øyet. Ved ubehandlet skjeling vil det andre øyet bli utrent og bildet benyttes ikke. Småbarn med strabisme trenes til å bruke det dårligste øyet ved på dekke det beste øyet med lapp deler av tiden.
Samsyn
Samsyn er en funksjon der øynene stilles mot samme objekt og begge øynenes bilder blir tolket av hjernen. Siden bildene er litt forskjellige på grunn av avstanden mellom øynene oppfatter hjernen et dybdesyn, stereoskopisk syn, som gir en betydelig bedret avstandsbedømmelse.
Det finnes teknikker for stereoskopiske bilder. View-Master er en gammel betraktningsenhet man kunne kjøpe hjul med små bilder der hvert øye har et eget okular og bildene betraktes stereoskopisk.
Skjelingen kan være tilstede på ett eller begge øynene, og kan ha ulik retning (opp, ned, innover, utover). Det vanligste er innoverskjeling. Betydelig sjeldnere er oppad- og nedadskjeling. Dersom skjelingen opptrer konstant, kalles det "manifest strabisme", og vil kunne påvises ved for eksempel Hirschbergtesten. Det eksisterer også en type kalt "intermitterende strabisme" som bare opptrer når personen er trøtt og uopplagt. Dersom skjeling kun kan påvises når en dekker til ett og ett øye ved en såkalt Covertest, foreligger skjult skjeling eller såkalt "latent strabisme".
Hos ungdommer og voksne som har autisme, adhd, utviklingshemmning eller andre utviklingsforstyrrelser i tillegg til skjeling, kan briller med prisme og lapp på det friske øyet prøves før operasjon.
Ca 3-4% av befolkningen i Norge plages av strabisme i en eller annen form.
Behandling
Lappbehandling som beskrevet ovenfor tar sikte på å bevare samsyn og avstandssyn.
Ortoptist er en yrkesgruppe som er utdannet i øyeundersøkelser, optikk og i treningsmetoder for blant annet å kunne gi øvelser for øyeeplets muskler slik at de ved trening skal greie å stille øynene i riktig posisjon. Pasienter som skjeler vil ofte ha nytte av slik trening.
Det er aktuelt å bruke briller med innlagt prisme som tillater øyet å stå i litt feil retning, men som flytter bildet slik at pasienten likevel oppnår samsyn.
Siden musklene som styrer øyeeplet kan være for korte eller for lange, kan en del pasienter med skjeling hjelpes ved å flytte festet av muskelen på øyeeplet. Slik operasjon kan også i noen tilfelle gjøres av hensyn til det kosmetiske, dersom pasienten har store problemer med andres reaksjon på at pasienten skjeler.
Se også
Samsyn
Ortoptist
Sykdommer i øyet og øyets omgivelser | norwegian_bokmål | 0.55826 |
strange_things_in_light/weird-shapes-and-lines-on-solid-shapes-and-low-light-on-cycles.txt | Skip to main content
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# Weird shapes and lines on solid shapes and low light on cycles
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Asked 6 years, 8 months ago
Modified 6 years, 8 months ago
Viewed 532 times
0
$\begingroup$
I'm new to blender and I have been using blender cycles the lighting is weird
and low in my render and another issue is that my shaped are glitching out and
showing random lines and shapes on solid objects. I thought It was connecting
all vertices but I tested it by remaking the object but no luck.
* cycles-render-engine
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edited Aug 8, 2017 at 16:27
user1853
asked Aug 8, 2017 at 6:40
Maxspeed7 Maxspeed7
1
$\endgroup$
1
* 2
$\begingroup$ Please clarify what you mean, it is not clear what the issue
is, and please keep only one question per post, if you have multiple problems
post them separately. $\endgroup$
– Duarte Farrajota Ramos ♦
Aug 8, 2017 at 6:46
Add a comment |
## 2 Answers 2
Sorted by: Reset to default
Highest score (default) Date modified (newest first) Date created (oldest
first)
2
$\begingroup$
From your picture, the shape glitching looks like Z-fighting . This happens
when you have two objects (or faces of the same object) that occupy the same
space. If it is Z-fighting, it will probably flicker when you move around in
the viewport.
To fix it, try moving the object around. You can also try going into Edit
mode, selecting all the vertices, and pressing ` W ` > Remove Doubles . (This
is also good to do just on general principle—even just canceling a Shift+D
will create duplicate vertices in the same spot.)
I don't know about the lighting issue; can you post a picture of the rendered
view so I can see what it looks like?
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edited Aug 8, 2017 at 14:03
answered Aug 8, 2017 at 13:51
SilverWolf SilverWolf
1,914 1 1 gold badge 9 9 silver badges 23 23 bronze badges
$\endgroup$
Add a comment |
0
$\begingroup$
The lines are coming because of the scene clipping value maybe.You can change
it here: Generally it should be 10cm and 100km then it should work fine and
for the low lighting maybe you can change it in world settings.
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answered Aug 8, 2017 at 6:56
j.akshat j.akshat
167 1 1 bronze badge
$\endgroup$
3
* 1
$\begingroup$ Each scene may need its own values for clipping, but 10 cm for
low clipping and 100 km for high are crazy values for probably any scene out
there. It's also not clear how is the world lighting related to clipping in
the scene. $\endgroup$
– Mr Zak
Aug 8, 2017 at 8:52
* $\begingroup$ but those clipping values might solve the problem and the world lighting is not for clipping,its for the low light in the scene which is asked to be corrected in the question. $\endgroup$
– j.akshat
Aug 8, 2017 at 10:04
* 1
$\begingroup$ As a general rule, clipping distance should be set to a range
that fits the scene, no more, no less. Having an extremely large range means
less precision and might yield to Z-fighting errors.. $\endgroup$
– user1853
Aug 8, 2017 at 17:25
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| biology | 1795331 | https://sv.wikipedia.org/wiki/Apple%20Ipad%20Mini | Apple Ipad Mini | Ipad mini (skrivs "iPad mini" i marknadsföring), annonserad den 23 oktober 2012 , är en mindre variant (7,85 tum) från Apple Inc av bolagets tidigare lanserade surfplatta Ipad (9,7 tum).
Annonsering
Ipad mini annonserades som en av flera olika produktnyheter (Macbook Pro 13 tum med Retina-skärm, ny Imac, ny Mac mini, ny Ipad och första generationen av Ipad mini) vid en direktsänd presentation av företaget Apples högst uppsatta chefer (Phil Schiller och VD Tim Cook) den 23 oktober 2012 .
Kompatibilitet med Ipad
Ipad mini har samma skärmupplösning som första två generationerna av Ipad, vilket är 1024 × 768. Det medför att alla existerande Ipad-appar är kompatibla och ej behöver anpassas.
Specifikationer (generation 1)
WiFi-modellen:
Operativsystem: iOS (version 9)
Skärm: 7,9 tum pekskärm med 1024 × 768 pixlar och pixeltätheten 163 ppi
Lagring: 16, 32 eller 64 gigabyte
Processor: Apple A5
WiFi: 802.11n (och a/b/g)
Bluetooth: 4.0
Positionering: WiFi
Kabelkontakt: Apples egen Lightning-kontakt (för laddning, HDMI-adapter, synkronisering med dator, med mera)
Kamera, fram: 720p (video), 1,2 megapixel (foto)
Kamera, bak: 1080p (video), 5 megapixel (foto)
Batteri: 16,3 watt-timmar (inbyggt)
Mobilversionen adderar:
Mobilnät: 3G och LTE (fåtal frekvensband)
Typ av SIM-kort: Nano-SIM
Positionering: A-GPS och GLONASS
Pris i Sverige vid lansering, inklusive moms:
16 GB: 2995 kr (4195 kr för 3G/LTE-modell)
32 GB: 3795 kr (4995 kr för 3G/LTE-modell)
64 GB: 4595 kr (5795 kr för 3G/LTE-modell)
Pris i USA vid lansering, exklusive moms:
16 GB: 329 dollar (459 dollar för 3G/LTE-modell)
32 GB: 429 dollar (559 dollar för 3G/LTE-modell)
64 GB: 529 dollar (659 dollar för 3G/LTE-modell)
Specifikationer (generation 2)
WiFi-modellen:
Operativsystem: iOS (version 9)
Skärm: 7,9 tum pekskärm med 2048 x 1536 pixlar (retina) och pixeltätheten 326 ppi
Lagring: 16 eller 32 gigabyte
Processor: Apple A7
WiFi: 802.11n (och a/b/g)
Bluetooth: 4.0
Positionering: WiFi, Digital kompass
Kabelkontakt: Apples egen Lightning-kontakt (för laddning, HDMI-adapter, synkronisering med dator, med mera)
Kamera, fram: 720p (video), 1,2 megapixel (foto)
Kamera, bak: 1080p (video), 5 megapixel (foto)
Batteri: 23,8 watt-timmar (inbyggt)
Mobilversionen adderar:
Mobilnät: 3G och LTE (band 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26)
Typ av SIM-kort: Nano-SIM
Positionering: A-GPS, GLONASS och mobilnät
Pris i Sverige i april 2016, inklusive moms:
16 GB: 2795 kr (4095 kr för 3G/LTE-modell)
32 GB: 3295 kr (4595 kr för 3G/LTE-modell)
Pris i USA i april 2016, exklusive moms
16 GB: 269 dollar (399 dollar för 3G/LTE-modell)
32 GB: 319 dollar (449 dollar för 3G/LTE-modell)
Externa länkar
Ipad:s officiella webbplats
Ipad mini:s specifikationer
Referenser
Apple-hårdvara
Datateknik
de:Apple iPad#iPad mini | swedish | 0.958748 |
strange_things_in_light/5587-strange-asteroid-shapes-explained.html.txt | Skip to main content
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1. The Universe
2. Solar System
3. Asteroids
# Strange Asteroid Shapes Explained
News
By Lee Pullen
published 3 July 2008
* * * * * * *
The main belt is between the orbits of Mars and Jupiter, and contains
countless asteroids. (Image credit: diagram — Minor Planet Center; image —
NASA/Johns Hopkins University Applied Physics Laboratory)
Theasteroids that pepper our solar system come in all shapes, sizes and ages.
Whatcauses such a variety among space rocks has been something of a mystery,
untilnow.
Researchershave been using a vast database to study a staggering 11,735
asteroids. Theyhave discovered that asteroids change shape over time, and they
think they knowthe reason why.
Gyula Szab? from the University of Szeged [Hungary] is the lead author of the
study, which was published in the July edition of Icarus .He explains,
"There are several hundred thousand asteroidsin our solar system. They orbit
the sun, but because they are small theirsurface gravity is low. This means
that many have strange, irregular shapes."
Scientistslike Gyula think that about one third of known asteroids belong to
groupscalled "families." These clusters probably formed from piles ofdebris
after largerobjects collided .
Resolved to save time
Determining the shapes of these asteroids presented difficulties for Gyula and
his colleague Laszlo Kiss from the University of Sydney. The most accurate
data about asteroids comes from spacecraft fly-bys , but only a few
asteroids have been examined that way. Radar observations can only be made of
objects that get close to the Earth . Telescopes produce detailed images,
but only for the largest asteroids.
Anotheroption for obtaining information about asteroids is called "time-
resolvedphotometry." The technique is surprisingly simple: By observing
asteroidsas they spin in space and then studying the amount of light
reflected,scientists can get an idea of their shape. Getting accurate results
from thismethod can take a long time, but the researchers realised that
digital skysurveys could speed up the process. Such projects study thousands
of objectsevery night. The Sloan Digital Sky Survey, for instance, mainly
looks at starsand galaxies, but it also has gathered data on asteroids.
## Get the Space.com Newsletter
Breaking space news, the latest updates on rocket launches, skywatching events
and more!
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aged 16 or over.
"Thisprocedure was very economical," says Gyula. "Using photometry,astronomers
have determined shapes for about 1,200 asteroids in the past 30 to40 years. We
derived the shapes for ten times more asteroids, but in half anhour!"
Surprising results
"Theresults were really surprising," says Gyula. "We saw there werefamilies
that included many elongated asteroids, and there were other oneswhich
consisted of mostly spheroidal bodies."
Inyoung groups of asteroids there are a great variety of shapes, hinting
thatthey formed relatively recently from fragments of rock that later
boundtogether. Asteroids in older families tend to be rounder. It seems to
take onebillion to two billion years for irregular asteroids to be transformed
intosmooth balls.
Butwhat changes the asteroids' shape? Gyula and his team have shown that
asteroidschange shape from elongated to roughly spherical due to being
impacted duringtheir lifetimes. They are like pebbles on the beach that become
worn smoothover many years -- only in space, erosion is caused by small
impacts as rocksknock into each other and chip pieces off.
Impactspecialist Jonti Horner from the UK's Open University agrees with Gyula.
"Theresults make sense," he says. "Catastrophic impacts create a hugeslew of
fragment shapes, like the shards of a broken bottle. The debris thenare
weathered over time and smoothed towards sphericality by small impacts."
Impactsare part of the fundamental processes in our solar system. They were
part ofthe planet formation process 4.5 billion years ago, and stilloccur
today . "Sometimes astronomers have to be archeologists, too,"says Gyula.
"This work is a fine example of how we can deduce abillion-year process from
the world we observe today."
Hopefully,this research will not only teach us more about how the solar system
operates,but will help us prepare for future impact events. Learning all we
can aboutasteroids could help us avoid disaster if we ever detect a large,
fast-movingone on a collision coursewith the Earth .
* Holesin the Earth: 170 and Counting
* KnockingBack Rocks
* Asteroid Top Spin
Join our Space Forums to keep talking space on the latest missions, night sky
and more! And if you have a news tip, correction or comment, let us know at:
[email protected].
Lee Pullen
Social Links Navigation
Contributing Writer
Lee Pullen is a science writer and communicator from the city of Bristol, UK.
He has a degree in Astronomy and a master’s in Science Communication. He has
written for numerous organizations, including the European Space Agency and
the European Southern Observatory. In his spare time Lee enjoys taking photos
of the night sky, and runs the website Urban Astrophotography .
More about science astronomy
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Happy Earth Day 2024! NASA picks 6 new airborne missions to study our changing
planet
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| biology | 8246429 | https://sv.wikipedia.org/wiki/3615%20Safronov | 3615 Safronov | 3615 Safronov eller 1983 WZ är en asteroid i huvudbältet som upptäcktes den 29 november 1983 av den amerikanske astronomen Edward L.G. Bowell vid Anderson Mesa Station. Den är uppkallad efter den sovjetiske astronomen
Asteroiden har en diameter på ungefär 25 kilometer och den tillhör asteroidgruppen Themis.
Referenser
Huvudbältesasteroider
Themis-asteroider
Småplaneter namngivna efter personer
Astronomiska upptäckter av E Bowell
Astronomiska upptäckter 1983 | swedish | 0.552088 |
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# Why Do I See Halos Around Lights?
Medically reviewed by Ann Marie Griff, O.D. — By Jacquelyn Cafasso on
May 23, 2019
* Causes
* Treatments
* Prevention
* When to see a doctor
* Takeaway
Seeing halos around light sources can be a typical response to bright lights
but can also occur with eye disorders, especially if you experience additional
symptoms, like pain or blurriness.
Seeing bright circles or rings around a light source, like a headlight, can be
a cause of concern. These bright circles of light around a light source are
often referred to as “halos.” Halos around lights are most often noticed at
nighttime or when you’re in a dimly lit room.
Halos can sometimes be a normal response to bright lights. Halos can also be
caused by wearing eyeglasses or corrective lenses (contact lenses), or they
can be a side effect of cataract or LASIK surgery.
However, if the halos appear suddenly, are very bothersome, or they’re
accompanied by pain, blurred vision, or other symptoms, they could be a sign
of a serious eye disorder.
People who are developing an eye condition known as cataracts, for example,
may start seeing halos due to changes in the lens of the eye. The halos are a
result in diffraction of light entering your eye.
If you’re seeing halos around lights, it’s a good idea to schedule an
appointment with an ophthalmologist or optometrist (eye doctor) so they can
properly examine your eyes and find out if there is an underlying cause.
##
Causes
Halos around lights are caused by diffraction, or bending of the light
entering your eye. There are many eye conditions that can cause this to
happen. These include:
### Cataracts
A cataract is a cloudy area that forms in the lens of the eye. Cataracts
develop slowly and are common in older people. Clouding of the lens can cause
diffraction of light entering the eye, which means you’ll see halos around
light sources.
Other symptoms of cataracts include:
* blurry vision
* trouble seeing at night
* increased sensitivity to glare
* double vision
### Cataract surgery
Cataract surgery involves replacing your cloudy lens with a custom intraocular
lens (IOL). Seeing halos around lights can sometimes be a side effect of the
new lens.
### Fuchs’ dystrophy
Fuchs’ dystrophy is an eye disorder that causes the clear layer on the front
of your eye (cornea) to swell. The abnormalities in the cornea can cause
someone with Fuchs’ dystrophy to see halos around lights.
Other symptoms include:
* sensitivity to light
* cloudy vision
* swelling
* difficulty driving at night
* eye discomfort
Fuchs’ dystrophy is usually inherited, and symptoms don’t usually appear until
people reach their 50s or 60s.
### Glaucoma
Glaucoma is a condition caused by optic nerve damage related to high pressure
in the fluid circulating in the front of the eye. Glaucoma is a leading cause
of blindness in the United States.
One type of glaucoma known as acute-angle closure glaucoma is considered a
medical emergency. Symptoms of acute glaucoma usually appear suddenly. If you
suddenly start seeing halos or colored rings around lights, it could be a sign
of acute glaucoma.
Other symptoms include
* blurred vision
* eye pain and redness
* nausea
* vomiting
* headache
* weakness
See a doctor immediately if you have any of these symptoms.
### Kerataconus
Kerataconus occurs when the cornea progressively thins and causes a cone-like
bulge to develop on the eye. This results in visual impairment and may cause
you to see halos around lights. The cause of kerataconus isn’t known.
Other signs and symptoms of keratoconus include:
* blurred vision
* frequent changes in eye glass prescription
* light sensitivity
* difficulty driving at night
* eye irritation or pain
### Photokeratitis
It’s possible for your eyes to become sunburned if they’re exposed to too much
of the sun’s ultraviolet (UV) light. In addition to seeing halos around
lights, the most common symptoms of sunburned eyes, or photokeratitis,
include:
* pain, burning, and a gritty feeling in the eyes
* sensitivity to light
* headache
* blurred vision
These symptoms usually go away on their own within a day or two. See a doctor
if they don’t subside or if the pain is severe.
### LASIK surgery
Some corrective eye procedures, such as LASIK (laser in-situ keratomileusis)
surgery, can also result in halos as a side effect. The halos usually only
last for a few weeks after the surgery. More modern types of LASIK are less
likely to cause this side effect.
### Ocular migraine
An ocular migraine is a rare type of migraine that causes visual
disturbances . Along with a severe headache, people who experience ocular
migraines may see flashing or shimmering lights, zigzagging lines, and halos
around lights.
### Wearing glasses or contact lenses
Wearing corrective lenses, like eyeglasses and contact lenses, can also cause
a halo effect when looking at a bright source of light. Researchers are
working on developing contact and intraocular lenses that minimize the halo
effect.
### Dry eyes
When the eye’s surface is too dry, it can become irregular, and light entering
the eye can scatter. This can cause you to see halos around lights, especially
at night.
Symptoms of dry eye include:
* stinging
* burning
* pain
* redness of the eye
Symptoms are often made worse by reading, using a computer, or being in a dry
environment for a long period of time.
##
Treatments
Treatment will depend on the underlying cause of seeing halos around lights.
* Migraine: Seeing halos as a result of a migraine will usually resolve when the migraine recedes. If you have frequent migraines, a doctor may prescribe medicine to prevent future migraines such as fremanezumab ( Ajovy ) or galcanezumab ( Emgality ).
* Cataracts: They usually get worse over time, but they’re not considered a medical emergency. Cataract surgery should be done at some point to prevent vision loss. This surgery involves replacing your cloudy lens with a custom intraocular lens (IOL). Surgery to remove cataracts is a very common procedure and is highly effective.
* Glaucoma: Treatment for acute glaucoma involves a laser surgery to make a new opening in the iris to allow for increased movement of fluid.
* Fuchs’ dystrophy: This can also be treated with surgery to replace the inner layer of the cornea or to transplant the cornea with a healthy one from a donor.
* Keratoconus: This can be managed with prescription rigid gas permeable (RGP) contact lenses. In severe cases, a corneal transplant may be needed.
* LASIK: If you recently had LASIK surgery, wear sunglasses when outside to reduce the severity of halos.
* Sunburned eyes: If your eyes are sunburned, try placing a washcloth soaked in cold water over your closed eyes and taking an over-the-counter (OTC) pain reliever. Wear sunglasses and a hat when you go outside. Preservative-free artificial tears can help provide relief from the pain and burning.
##
Prevention
Eye disorders, such as cataracts, can’t always be prevented, but you can take
steps to delay their progression. A few ways to keep your eyes healthy and
prevent eye disorders that could make you see halos around lights include the
following tips:
* Protect your eyes from ultraviolet (UV) radiation by staying out of the sun, wearing a hat, or wearing sunglasses with UV protection.
* If you have diabetes, make sure to control your blood sugar levels.
* Eat a diet is rich in vitamin C, vitamin A, and carotenoids; these can be found in leafy green vegetables, like spinach and kale.
* Maintain a healthy weight.
* Avoid excess alcohol.
* Stop smoking.
To prevent several of the eye disorders associated with seeing halos around
lights, it’s important to have regular eye examinations , especially after
you turn 40.
##
When to see a doctor
If you start noticing halos around lights, it’s a good idea to schedule an
appointment with an eye doctor for a regular checkup to make sure you’re not
developing any eye disorders.
If you’re having any of the following symptoms, see an eye doctor as soon as
possible:
* any sudden changes in vision
* suddenly seeing spots and floaters in your field of vision
* blurred vision
* eye pain
* double vision
* sudden blind spot in one eye
* darkening vision
* sudden narrowed field of vision
* poor night vision
* dry, red, and itchy eyes
Prompt intervention is essential to avoid permanent vision loss for acute
glaucoma, so don’t delay your appointment.
##
The bottom line
Seeing halos around lights could mean that you’re developing a serious eye
disorder such as cataracts or glaucoma. Occasionally, seeing halos around
lights is a side effect of LASIK surgery, cataract surgery, or from wearing
eyeglasses or contact lenses.
Having a regular eye exam is the best way to prevent or manage vision
problems, especially as you get older.
If you haven’t had an eye exam in more than a year, or if you suddenly notice
any vision changes such as halos around lights or strong glare during the day,
schedule a visit with an eye doctor for a checkup.
Last medically reviewed on May 23, 2019
### How we reviewed this article:
Sources
History
Healthline has strict sourcing guidelines and relies on peer-reviewed studies,
academic research institutions, and medical associations. We avoid using
tertiary references. You can learn more about how we ensure our content is
accurate and current by reading our editorial policy .
* Boyd K. (2019). What is Fuchs' dystrophy?
https://www.aao.org/eye-health/diseases/what-is-fuchs-dystrophy
* Glaucoma (n.d.)
https://www.hopkinsmedicine.org/wilmer/conditions/glaucoma_faq1.html
* Mayo Clinic Staff. (2018). Cataracts.
https://www.mayoclinic.org/diseases-conditions/cataracts/symptoms-
causes/syc-20353790
* Mayo Clinic Staff. (2018). LASIK eye surgery.
https://www.mayoclinic.org/tests-procedures/lasik-eye-
surgery/about/pac-20384774
* Sugrue D. (2015). Keeping vision’s “halo effect” at arm’s length.
https://www.elsevier.com/connect/keeping-visions-halo-effect-at-arms-length
* Understanding KC. (n.d.).
https://www.nkcf.org/understanding-kc/
Our experts continually monitor the health and wellness space, and we update
our articles when new information becomes available.
Current Version
May 23, 2019
Written By
Jacquelyn Cafasso
Edited By
Heather Hobbs
Medically Reviewed By
Ann Marie Griff, OD
Share this article
Medically reviewed by Ann Marie Griff, O.D. — By Jacquelyn Cafasso on
May 23, 2019
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| biology | 3961804 | https://sv.wikipedia.org/wiki/Duanes%20syndrom | Duanes syndrom | Duanes syndrom är ett ärftligt ögonsymtomkomplex med rubbningar i ögonmuskelaktiviteten. Det kännetecknas av oförmåga att röra ögat utåt.
Syndromet beskrevs först av oftalmologerna Jakob Stilling (1887) och Siegmund Türk (1896). Syndromet uppkallades senare efter den amerikansk ögonläkaren Alexander Duane, som beskrev rubbningen mera i detalj.
Det finns tre olika typer av detta syndrom:
Duanes syndrom typ 1: Förmågan att röra det/de påverkade ögat/ögonen utåt mot örat är begränsad, men förmågan att röra det/dem inåt mot näsan är mer eller mindre normal. Det drabbade ögats ögonspringa (rima) minskar och bulben dras in i orbita (retraheras) när det blickar in mot näsan (adduktion). När det riktas utåt (abduktion) sker det omvända.
Duanes syndrom typ 2: Förmågan att röra det/de påverkade ögat/ögonen inåt mot näsan är begränsad, medan förmågan att röra ögat/ögonen utåt är normal eller endast något begränsad. Det drabbade ögats ögonspringa (rima) minskar och bulben dras in i orbita (retraheras) när det blickar in mot näsan (adduktion). När det riktas utåt (abduktion) sker det omvända.
Duanes syndrom typ 3: Förmågan att röra det/de påverkade ögat/ögonen såväl inåt mot näsan som utåt mot örat är begränsad. Det drabbade ögats ögonspringa (rima) minskar och bulben dras in i orbita (retraheras) när det blickar in mot näsan (adduktion). När det riktas utåt (abduktion) sker det omvända.
Referenser
Noter
Ögonsjukdomar | swedish | 0.942619 |
strange_things_in_light/bizarre-phenomena-that-lit-up-the-sky-and-their-scientific-explanations.txt | Skip to main content
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1. Space
# 10 bizarre phenomena that lit up the sky (and their scientific
explanations)
Countdowns
By Harry Baker
published 19 August 2023
From UFO-like rings and whirlpools of light to rainbow clouds and laser lines,
here are 10 strange visual phenomena that can be easily explained by science.
* * * * * * *
Comments (0)
Weird lights appear in the sky way more often than most people realize. Often,
photos of these bizarre light shows come with wild speculation about what
caused them, from aliens to secret military weapons.
But unfortunately for conspiracy theorists, there is always a more Earthly
scientific explanation for these luminous displays. From UFO -like rings to
blood-red arcs, here are 10 bizarre atmospheric light shows with a
surprisingly simple explanation.
## Eerie UFO-like ring
A halo of red light briefly appeared in the night sky above a town in Italy.
(Image credit: Valter Binotto)
This bizarre disk of red light appeared to briefly flash above the town of
Possagno in northern Italy , hanging in the sky for just a few milliseconds
before abruptly vanishing.
The fluorescent frisbee is known as an "emission of light and very low-
frequency perturbations due to electromagnetic pulse sources," or elve It's an
atmospheric disturbance created when lightning produces an electromagnetic
pulse that hits Earth's ionosphere — the ionized part of the upper atmosphere
that stretches between 50 and 400 miles (80 and 650 kilometers) above the
ground. The red color is given off by excited nitrogen atoms in the
ionosphere.
This luminous halo appeared during an intense thunderstorm around 175 miles
(280 km) southeast of Possagno. But forced perspective made the massive ring,
which had a diameter of around 225 miles (360 km), seemingly hang above the
town.
## Light arcs and halos
The sun surrounded by shining halos and arcs of light. (Image credit: Alan
Fitzsimmons)
This photo, which was captured by an astronomer at Queen's University Belfast
in Northern Ireland, shows a spectacular set of luminous arcs and halos
shining around the sun .
Ethereal lights like these are created by sunlight shining through millions of
tiny, perfectly positioned ice crystals in the upper atmosphere. The miniature
hexagonal crystals refract light similarly to a prism, and when strong winds
orient them in the same direction, the light they warp combines to produce
lines of light.
The image shows at least three different optical phenomena: a 22-degree halo,
which is the large circle surrounding the sun ; a pair of "sundogs" — the
bright points on each side of the 22-degree halo; and a complete parhelic
circle — the line that bisects the circle — which is the rarest of this type
of phenomenon. The image may also include features of a circumscribed halo and
a supralateral arc, which form the "eyelids" above and below the 22-degree
halo.
Individually, all these phenomena can be relatively common, but seeing them
all together at once is extremely rare.
## Bizarre blue blobs
This photo taken from the ISS above the South China Sea shows a pair of
unrelated bright blue blobs in Earth's atmosphere. (Image credit: NASA Earth
Observatory)
An astronaut on board the International Space Station (ISS) snapped this image
of two bizarre blue blobs of light glimmering in our planet's atmosphere .
Intriguingly, the two blobs are completely unrelated to one another and just
happened to occur at the same time.
The light blob at the bottom of the image,is a massive lightning strike that
occurred next to a large, circular gap in the top of the clouds. This caused
the lightning to illuminate the surrounding walls of the cloudy caldera-like
structure, creating a striking luminous ring.
The blue blob in the top right of the image is the result of warped light from
the moon . The moon's orientation in relation to the ISS meant the light it
reflected back from the sun passed through the planet's atmosphere,
transforming it into a bright blue blob with a fuzzy halo.
## Ethereal whirlpool of light
A blue spiral of light outshines auroras in Alaska. (Image credit: Todd
Salat/AuroraHunter.com)
This ethereal whirlpool of blue light appeared in the night sky above Alaska
, briefly stealing the limelight from a strong auroral display. But the
bizarre, spiral-shaped object had nothing to do with the dancing polar lights.
The luminous spiral was made from frozen rocket fuel that was ejected by the
fast-spinning, detached second stage of one of SpaceX's Falcon 9 rockets. Due
to its high altitude, the frozen fuel reflected sunlight back to Earth, making
it stand out in the night sky. Lights like these can last for several minutes
before the frozen fuel crystals disperse.
A similar spiral was also filmed forming and then disappearing in the night
sky above Hawaii . Astronomers have nicknamed the swirling light "SpaceX
spirals" and believe they will become more common as the number of SpaceX
launches increases.
## Blood-red arc
A hazy river of red light hangs in the sky above Denmark. (Image credit:
Ruslan Merzlyakov)
A bright red streak of light appeared in the sky above parts of Scandinavia
after a powerful solar storm slammed into Earth. But the bright red band was
not an aurora — it was something much rarer.
The unusual phenomenon is known as a stable auroral red arc (SAR) — but
despite the name, it is neither an aurora nor particularly stable. Unlike
auroras, which appear when solar radiation excites gas molecules in the upper
atmosphere, SARs form when atmospheric gas is superheated by Earth's ring
current system — a massive loop of electric current that surrounds our planet.
Both phenomena become more likely after solar storms weaken Earth's
magnetosphere.
For unknown reasons, only oxygen is heated up during a SAR, which means these
phenomena always emit the same shade of red.
## Rainbow clouds
These bizarre rainbow-colored clouds appeared during the night in the Arctic.
(Image credit: Jónína Guðrún Óskarsdóttir)
These multicolored clouds were spotted shining in the night sky above the
Arctic .
The clouds, known as polar stratospheric clouds (PSCs), only form in the
stratosphere — the second layer of Earth's atmosphere — at temperatures below
minus 114 degrees Fahrenheit (minus 81 degrees Celsius). Normally, the
stratosphere is too dry for clouds to form, but at extremely low temperatures,
widely spaced water molecules begin to coalesce into tiny ice crystals that
become clouds.
As sunlight shines through these crystal clouds, it gets scattered, creating
multiple different wavelengths of light, which gives the clouds their rainbow
colors. Due to the extreme altitude of the clouds, sunlight can hit the
crystals and scatter above an observer even if the sun is beyond the horizon,
which is when these clouds appear brightest.
## Bright green laser lines
A time-lapse image of the green laser pulses flashing across the night sky in
Hawaii. (Image credit: National Observatory of Japan)
This image, which was captured by a telescope on Hawaii's tallest peak, Mauna
Kea, shows bright green laser lines flashing across the night sky .
The lines, which appeared one after the other, only lasted for around a
second. But they inspired online comparisons with "digital rain," or the lines
of green computer code that fall vertically down the screen during the
"Matrix" movies.
But these lines aren't evidence we are living in the matrix. Instead, they
came from lasers fired from NASA's ICESat-2 satellite, which measures the
amount of ice in Earth's cryosphere — the part of Earth covered by solid
precipitation, including snow, sea ice, lake and river ice, icebergs,
glaciers, ice sheets and ice shelves.
## Stunning STEVE
A vibrant, purple STEVE cuts across the night sky above above Badlands
National Park in South Dakota. (Image credit: Evan Ludes/Framed By Nature)
This bizarre, aurora-like streak of light, known as STEVE, was spotted across
several U.S. states in the wake of a major solar storm in early 2023.
STEVE, or a "strong thermal emission velocity enhancement," is a rare
phenomenon that creates a solid ribbon of light that hangs in the air for up
to an hour. The ribbon is created by a river of hot plasma, or ionized gas,
that breaks through Earth's weakened magnetosphere during solar storms. The
flow of plasma is uniform and constant, which means the same gas remains
excited and continuously gives off the same light.
STEVE can occur much further away from Earth's poles than auroras tend to
appear, although scientists are still unsure why.
## Shining rainbow rings
These rainbow rings spotted surrounding the sun in Finland had a surprising
origin. (Image credit: Mikko Peussa)
Something was in the air when this image of concentric rainbow-colored rings
was snapped in Finland. And it turns out that something was pollen.
Multicolored rings such as these, known as "pollen coronas," form when
sunlight scatters off thousands of pollen grains in the air. This creates a
diffraction pattern, in which individual wavelengths of light cancel each
other out and only allow certain colors to be seen by the observer. Individual
grains are also illuminated and appear as bright spots in the image.
The pollen in the image comes from pine trees ( Pinus sylvestris ), which
have air sacs that help them float (as well as making them look like Mickey
Mouse ears).
Pollen coronas only appear when pollen concentrations are very high and can
only be clearly seen when the sun or full moon is partially obscured.
## Bleeding sky
A red streak of light appeared in the sky above Arizona shortly after a SpaceX
rocket launch. (Image credit: Jeremy Perez)
A blood-red streak of light was left behind in the sky above Arizona after
one of SpaceX's Falcon 9 rockets punched a hole in Earth's ionosphere.
"Ionospheric holes" are created when a rocket's second stage burns fuel
between 125 and 185 miles (200 and 300 km) above Earth's surface. At this
height, the carbon dioxide and water vapor from the rocket's exhaust cause
ionized oxygen atoms to recombine or form back into diatomic oxygen molecules,
creating a gap in the plasma. This also excites the molecules and causes them
to emit energy in the form of light.
Scientists have known about ionospheric holes for a while, but they are
becoming more common as the number of rocket launches increases. The holes
pose no threat to people on the surface, and they naturally close up within a
few hours as the recombined gases get re-ionized.
## Sign up for the Live Science daily newsletter now
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Senior Staff Writer
Harry is a U.K.-based senior staff writer at Live Science. He studied marine
biology at the University of Exeter before training to become a journalist. He
covers a wide range of topics including space exploration, planetary science,
space weather, climate change, animal behavior, evolution and paleontology.
His feature on the upcoming solar maximum was shortlisted in the "top scoop"
category at the National Council for the Training of Journalists (NCTJ) Awards
for Excellence in 2023.
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| biology | 16485 | https://da.wikipedia.org/wiki/Solvind | Solvind | Solvind er den modulerede, vedvarende udstråling af store mængder partikler fra Solen. Solvinden er solens kosmiske stråling.
Solvind kan muligvis bruges som drivkraft til rumfartøjer ved hjælp af store sejl eller skærme. Accelerationen vil være lille, men den opnåede hastighed kunne blive betydelig selv i astronomiske afstande. Teorien er dog anfægtet og mangler stadig at blive testet i praksis, hvilket dog blev forsøgt i 2005 med opsendelsen af Cosmos 1. Det blev dog rapporteret d. 26. juni 2005 at man ikke kunne få kontakt med sonden efter opsendelsen.
Se også
solplet, Solstorm, Soludbrud
polarlys (nordlys, sydlys)
Jordens atmosfære
Van Allen-bælterne
Kildehenvisninger
http://www.sciencenet.dk (Nyheder)
Eksterne henvisninger
Comon.dk, 24. oktober 2003: Geomagnetisk storm kan forstyrre elektronisk kommunikation
01. juli 1999, Ing.dk: Beskyttelsen forsvinder når polerne bytter plads
Anfægtelsen
31 October, 2003, BBCNews: Solar storm surge 'not over yet' Citat: "...aircraft traversing the north Atlantic were confined to a narrow corridor to minimise radiation exposure..."
NASA, ESA: Hot Shots from SOHO: X-whatever Flare! , spaceweather.com: Record-setting Solar Flares
2003-11-07, ScienceDaily: It's Official: The Biggest Solar X-ray Flare Ever Is Classified As X28 Citat: "...this flare saturated the X-ray detectors on several monitoring satellites..."
2003-12-05, Science Daily: Stormy Space Weather Slips Through Cracks Citat: "...The fact that IMAGE was able to view the proton aurora for more than nine hours, until IMAGE progressed in its orbit to where it could not observe the aurora, implies the crack remained continuously open..."
Solen
Rumplasma
Astronomi
Ioniserende stråling | danish | 0.760903 |
hot_water_bacteria/Hand.txt |
A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "hand" and fingerprints extremely similar to human fingerprints) are often described as having "hands" instead of paws on their front limbs. The raccoon is usually described as having "hands" though opposable thumbs are lacking.
Some evolutionary anatomists use the term hand to refer to the appendage of digits on the forelimb more generally—for example, in the context of whether the three digits of the bird hand involved the same homologous loss of two digits as in the dinosaur hand.
The human hand usually has five digits: four fingers plus one thumb; these are often referred to collectively as five fingers, however, whereby the thumb is included as one of the fingers. It has 27 bones, not including the sesamoid bone, the number of which varies among people, 14 of which are the phalanges (proximal, intermediate and distal) of the fingers and thumb. The metacarpal bones connect the fingers and the carpal bones of the wrist. Each human hand has five metacarpals and eight carpal bones.
Fingers contain some of the densest areas of nerve endings in the body, and are the richest source of tactile feedback. They also have the greatest positioning capability of the body; thus, the sense of touch is intimately associated with hands. Like other paired organs (eyes, feet, legs) each hand is dominantly controlled by the opposing brain hemisphere, so that handedness—the preferred hand choice for single-handed activities such as writing with a pencil—reflects individual brain functioning.
Among humans, the hands play an important function in body language and sign language. Likewise, the ten digits of two hands and the twelve phalanges of four fingers (touchable by the thumb) have given rise to number systems and calculation techniques.
Structure
Many mammals and other animals have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The scientific use of the term hand in this sense to distinguish the terminations of the front paws from the hind ones is an example of anthropomorphism. The only true grasping hands appear in the mammalian order of primates. Hands must also have opposable thumbs, as described later in the text.
The hand is located at the distal end of each arm. Apes and monkeys are sometimes described as having four hands, because the toes are long and the hallux is opposable and looks more like a thumb, thus enabling the feet to be used as hands.
The word "hand" is sometimes used by evolutionary anatomists to refer to the appendage of digits on the forelimb such as when researching the homology between the three digits of the bird hand and the dinosaur hand.
An adult human male's hand weighs about a pound.
Areas
Human hand parts
Areas of the human hand include:
The palm (volar), which is the central region of the anterior part of the hand, located superficially to the metacarpus. The skin in this area contains dermal papillae to increase friction, such as are also present on the fingers and used for fingerprints.
The opisthenar area (dorsal) is the corresponding area on the posterior part of the hand.
The heel of the hand is the area anteriorly to the bases of the metacarpal bones, located in the proximal part of the palm. It is the area that sustains most pressure when using the palm of the hand for support, such as in handstand.
There are five digits attached to the hand, notably with a nail fixed to the end in place of the normal claw. The four fingers can be folded over the palm which allows the grasping of objects. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:
index finger, pointer finger, forefinger, or 2nd digit
middle finger or long finger or 3rd digit
ring finger or 4th digit
little finger, pinky finger, small finger, baby finger, or 5th digit
The thumb (connected to the first metacarpal bone and trapezium) is located on one of the sides, parallel to the arm. A reliable way of identifying human hands is from the presence of opposable thumbs. Opposable thumbs are identified by the ability to be brought opposite to the fingers, a muscle action known as opposition.
Bones
Bones of the human hand
Hand-bone animation (metacarpal movement is exaggerated, other than on the thumb)
Image showing the carpal bones
The skeleton of the human hand consists of 27 bones: the eight short carpal bones of the wrist are organized into a proximal row (scaphoid, lunate, triquetral and pisiform) which articulates with the bones of the forearm, and a distal row (trapezium, trapezoid, capitate and hamate), which articulates with the bases of the five metacarpal bones of the hand. The heads of the metacarpals will each in turn articulate with the bases of the proximal phalanx of the fingers and thumb. These articulations with the fingers are the metacarpophalangeal joints known as the knuckles. At the palmar aspect of the first metacarpophalangeal joints are small, almost spherical bones called the sesamoid bones. The fourteen phalanges make up the fingers and thumb, and are numbered I-V (thumb to little finger) when the hand is viewed from an anatomical position (palm up). The four fingers each consist of three phalanx bones: proximal, middle, and distal. The thumb only consists of a proximal and distal phalanx. Together with the phalanges of the fingers and thumb these metacarpal bones form five rays or poly-articulated chains.
Because supination and pronation (rotation about the axis of the forearm) are added to the two axes of movements of the wrist, the ulna and radius are sometimes considered part of the skeleton of the hand.
There are numerous sesamoid bones in the hand, small ossified nodes embedded in tendons; the exact number varies between people: whereas a pair of sesamoid bones are found at virtually all thumb metacarpophalangeal joints, sesamoid bones are also common at the interphalangeal joint of the thumb (72.9%) and at the metacarpophalangeal joints of the little finger (82.5%) and the index finger (48%). In rare cases, sesamoid bones have been found in all the metacarpophalangeal joints and all distal interphalangeal joints except that of the long finger.
The articulations are:
interphalangeal articulations of hand (the hinge joints between the bones of the digits)
metacarpophalangeal joints (where the digits meet the palm)
intercarpal articulations (where the palm meets the wrist)
wrist (may also be viewed as belonging to the forearm).
Arches
Arches of the handRed: one of the oblique archesBrown: one of the longitudinal arches of the digitsDark green: transverse carpal archLight green: transverse metacarpal arch
The fixed and mobile parts of the hand adapt to various everyday tasks by forming bony arches: longitudinal arches (the rays formed by the finger bones and their associated metacarpal bones), transverse arches (formed by the carpal bones and distal ends of the metacarpal bones), and oblique arches (between the thumb and four fingers):
Of the longitudinal arches or rays of the hand, that of the thumb is the most mobile (and the least longitudinal). While the ray formed by the little finger and its associated metacarpal bone still offers some mobility, the remaining rays are firmly rigid. The phalangeal joints of the index finger, however, offer some independence to its finger, due to the arrangement of its flexor and extension tendons.
The carpal bones form two transversal rows, each forming an arch concave on the palmar side. Because the proximal arch simultaneously has to adapt to the articular surface of the radius and to the distal carpal row, it is by necessity flexible. In contrast, the capitate, the "keystone" of the distal arch, moves together with the metacarpal bones and the distal arch is therefore rigid. The stability of these arches is more dependent of the ligaments and capsules of the wrist than of the interlocking shapes of the carpal bones, and the wrist is therefore more stable in flexion than in extension. The distal carpal arch affects the function of the CMC joints and the hands, but not the function of the wrist or the proximal carpal arch. The ligaments that maintain the distal carpal arches are the transverse carpal ligament and the intercarpal ligaments (also oriented transversally). These ligaments also form the carpal tunnel and contribute to the deep and superficial palmar arches. Several muscle tendons attaching to the TCL and the distal carpals also contribute to maintaining the carpal arch.
Compared to the carpal arches, the arch formed by the distal ends of the metacarpal bones is flexible due to the mobility of the peripheral metacarpals (thumb and little finger). As these two metacarpals approach each other, the palmar gutter deepens. The central-most metacarpal (middle finger) is the most rigid. It and its two neighbors are tied to the carpus by the interlocking shapes of the metacarpal bones. The thumb metacarpal only articulates with the trapezium and is therefore completely independent, while the fifth metacarpal (little finger) is semi-independent with the fourth metacarpal (ring finger) which forms a transitional element to the fifth metacarpal.
Together with the thumb, the four fingers form four oblique arches, of which the arch of the index finger functionally is the most important, especially for precision grip, while the arch of the little finger contribute an important locking mechanism for power grip. The thumb is undoubtedly the "master digit" of the hand, giving value to all the other fingers. Together with the index and middle finger, it forms the dynamic tridactyl configuration responsible for most grips not requiring force. The ring and little fingers are more static, a reserve ready to interact with the palm when great force is needed.
See also: arches of the foot
Muscles
Main article: Muscles of the hand
Muscles and other structures of wrist and palm
The muscles acting on the hand can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.
Intrinsic
The intrinsic muscle groups are the thenar (thumb) and hypothenar (little finger) muscles; the interosseous muscles (four dorsally and three volarly) originating between the metacarpal bones; and the lumbrical muscles arising from the deep flexor (and are special because they have no bony origin) to insert on the dorsal extensor hood mechanism.
Extrinsic
Extensor compartments of wrist (back of hand)
The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.
The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor used, for instance, for pointing. The extensors are situated within 6 separate compartments.
Compartment 1 (Most radial)
Compartment 2
Compartment 3
Compartment 4
Compartment 5
Compartment 6 (Most ulnar)
Abductor pollicis longus
Extensor carpi radialis longus
Extensor pollicis longus
Extensor indicis
Extensor digiti minimi
Extensor carpi ulnaris
Extensor pollicis brevis
Extensor carpi radialis brevis
Extensor digitorum communis
The first four compartments are located in the grooves present on the dorsum of inferior side of radius while the 5th compartment is in between radius and ulna. The 6th compartment is in the groove on the dorsum of inferior side of ulna.
Nerve supply
Cutaneous innervation of the upper limb
The hand is innervated by the radial, median, and ulnar nerves.
Motor
The radial nerve supplies the finger extensors and the thumb abductor, thus the muscles that extends at the wrist and metacarpophalangeal joints (knuckles); and that abducts and extends the thumb.
The median nerve supplies the flexors of the wrist and digits, the abductors and opponens of the thumb, the first and second lumbrical.
The ulnar nerve supplies the remaining intrinsic muscles of the hand.
All muscles of the hand are innervated by the brachial plexus (C5–T1) and can be classified by innervation:
Nerve
Muscles
Radial
Extensors: carpi radialis longus and brevis, digitorum, digiti minimi, carpi ulnaris, pollicis longus and brevis, and indicis.Other: abductor pollicis longus.
Median
Flexors: carpi radialis, pollicis longus, digitorum profundus (half), superficialis, and pollicis brevis (superficial head).Other: palmaris longus. abductor pollicis brevis, opponens pollicis, and first and second lumbricals.
Ulnar
Flexor carpi ulnaris, flexor digitorum profundus (half), palmaris brevis, flexor digiti minimi, abductor digiti minimi, opponens digiti minimi, adductor pollicis, flexor pollicis brevis (deep head), palmar and dorsal interossei, and third and fourth lumbricals.
Sensory
The radial nerve supplies the skin on the back of the hand from the thumb to the ring finger and the dorsal aspects of the index, middle, and half ring fingers as far as the proximal interphalangeal joints.
The median nerve supplies the palmar side of the thumb, index, middle, and half ring fingers. Dorsal branches innervates the distal phalanges of the index, middle, and half ring fingers.
The ulnar nerve supplies the ulnar third of the hand, both at the palm and the back of the hand, and the little and half ring fingers.
There is a considerable variation to this general pattern, except for the little finger and volar surface of the index finger. For example, in some individuals, the ulnar nerve supplies the entire ring finger and the ulnar side of the middle finger, whilst, in others, the median nerve supplies the entire ring finger.
Blood supply
Hand arteries
The hand is supplied with blood from two arteries, the ulnar artery and the radial artery. These arteries form three arches over the dorsal and palmar aspects of the hand, the dorsal carpal arch (across the back of the hand), the deep palmar arch, and the superficial palmar arch. Together these three arches and their anastomoses provide oxygenated blood to the palm, the fingers, and the thumb.
The hand is drained by the dorsal venous network of the hand with deoxygenated blood leaving the hand via the cephalic vein and the basilic vein.
Skin
Left: Papillary ridges of palmRight: Sexual dimorphism
The glabrous (hairless) skin on the front of the hand, the palm, is relatively thick and can be bent along the hand's flexure lines where the skin is tightly bound to the underlying tissue and bones. Compared to the rest of the body's skin, the hands' palms (as well as the soles of the feet) are usually lighter—and even much lighter in dark-skinned individuals, compared to the other side of the hand. Indeed, genes specifically expressed in the dermis of palmoplantar skin inhibit melanin production and thus the ability to tan, and promote the thickening of the stratum lucidum and stratum corneum layers of the epidermis. All parts of the skin involved in grasping are covered by papillary ridges (fingerprints) acting as friction pads. In contrast, the hairy skin on the dorsal side is thin, soft, and pliable, so that the skin can recoil when the fingers are stretched. On the dorsal side, the skin can be moved across the hand up to 3 cm (1.2 in); an important input the cutaneous mechanoreceptors.
The web of the hand is a "fold of skin which connects the digits". These webs, located between each set of digits, are known as skin folds (interdigital folds or plica interdigitalis). They are defined as "one of the folds of skin, or rudimentary web, between the fingers and toes".
Variation
Further information: Digit ratio
The ratio of the length of the index finger to the length of the ring finger in adults is affected by the level of exposure to male sex hormones of the embryo in utero. This digit ratio is below 1 for both sexes but it is lower in males than in females on average.
Clinical significance
X-ray of the left hand of a ten-year-old boy with polydactyly
A number of genetic disorders affect the hand. Polydactyly is the presence of more than the usual number of fingers. One of the disorders that can cause this is Catel-Manzke syndrome. The fingers may be fused in a disorder known as syndactyly. Or there may be an absence of one or more central fingers—a condition known as ectrodactyly. Additionally, some people are born without one or both hands (amelia). Hereditary multiple exostoses of the forearm—also known as hereditary multiple osteochondromas—is another cause of hand and forearm deformity in children and adults.
There are several cutaneous conditions that can affect the hand including the nails.
The autoimmune disease rheumatoid arthritis can affect the hand, particularly the joints of the fingers.
Some conditions can be treated by hand surgery. These include carpal tunnel syndrome, a painful condition of the hand and fingers caused by compression of the median nerve, and Dupuytren's contracture, a condition in which fingers bend towards the palm and cannot be straightened. Similarly, injury to the ulnar nerve may result in a condition in which some of the fingers cannot be flexed.
A common fracture of the hand is a scaphoid fracture—a fracture of the scaphoid bone, one of the carpal bones. This is the commonest carpal bone fracture and can be slow to heal due to a limited blood flow to the bone. There are various types of fracture to the base of the thumb; these are known as Rolando fractures, Bennet's fracture, and Gamekeeper's thumb. Another common fracture, known as Boxer's fracture, is to the neck of a metacarpal. One can also have a broken finger.
Evolution
Hands of a Javanese tree shrew and a human
The prehensile hands and feet of primates evolved from the mobile hands of semi-arboreal tree shrews that lived about 60 million years ago. This development has been accompanied by important changes in the brain and the relocation of the eyes to the front of the face, together allowing the muscle control and stereoscopic vision necessary for controlled grasping. This grasping, also known as power grip, is supplemented by the precision grip between the thumb and the distal finger pads made possible by the opposable thumbs. Hominidae (great apes including humans) acquired an erect bipedal posture about 3.6 million years ago, which freed the hands from the task of locomotion and paved the way for the precision and range of motion in human hands. Functional analyses of the features unique to the hand of modern humans have shown that they are consistent with the stresses and requirements associated with the effective use of paleolithic stone tools. It is possible that the refinement of the bipedal posture in the earliest hominids evolved to facilitate the use of the trunk as leverage in accelerating the hand.
While the human hand has unique anatomical features, including a longer thumb and fingers that can be controlled individually to a higher degree, the hands of other primates are anatomically similar and the dexterity of the human hand can not be explained solely on anatomical factors. The neural machinery underlying hand movements is a major contributing factor; primates have evolved direct connections between neurons in cortical motor areas and spinal motoneurons, giving the cerebral cortex monosynaptic control over the motoneurons of the hand muscles; placing the hands "closer" to the brain. The recent evolution of the human hand is thus a direct result of the development of the central nervous system, and the hand, therefore, is a direct tool of our consciousness—the main source of differentiated tactile sensations—and a precise working organ enabling gestures—the expressions of our personalities.
A gorilla, a large extant primate with small thumbs, and the hand skeleton of Ardipithecus ramidus, a large Pliocene primate with relatively human-like thumbs
There are nevertheless several primitive features left in the human hand, including pentadactyly (having five fingers), the hairless skin of the palm and fingers, and the os centrale found in human embryos, prosimians, and apes. Furthermore, the precursors of the intrinsic muscles of the hand are present in the earliest fishes, reflecting that the hand evolved from the pectoral fin and thus is much older than the arm in evolutionary terms.
The proportions of the human hand are plesiomorphic (shared by both ancestors and extant primate species); the elongated thumbs and short hands more closely resemble the hand proportions of Miocene apes than those of extant primates. Humans did not evolve from knuckle-walking apes, and chimpanzees and gorillas independently acquired elongated metacarpals as part of their adaptation to their modes of locomotion. Several primitive hand features most likely present in the chimpanzee–human last common ancestor (CHLCA) and absent in modern humans are still present in the hands of Australopithecus, Paranthropus, and Homo floresiensis. This suggests that the derived changes in modern humans and Neanderthals did not evolve until 2.5 to 1.5 million years ago or after the appearance of the earliest Acheulian stone tools, and that these changes are associated with tool-related tasks beyond those observed in other hominins. The thumbs of Ardipithecus ramidus, an early hominin, are almost as robust as in humans, so this may be a primitive trait, while the palms of other extant higher primates are elongated to the extent that some of the thumb's original function has been lost (most notably in highly arboreal primates such as the spider monkey). In humans, the big toe is thus more derived than the thumb.
There is a hypothesis suggesting the form of the modern human hand is especially conducive to the formation of a compact fist, presumably for fighting purposes. The fist is compact and thus effective as a weapon. It also provides protection for the fingers. However, this is not widely accepted to be one of the primary selective pressures acting on hand morphology throughout human evolution, with tool use and production being thought to be far more influential.
Additional images
Illustration of hand and wrist bones
Bones of the left hand. Volar surface.
Bones of the left hand. Dorsal surface.
Static adult human physical characteristics of the hand
X-ray showing joints
Hand bone anatomy
See also
This article uses anatomical terminology.
Dactylonomy
Dermatoglyphics
Finger-counting
Finger tracking
Handstand
Hand strength
Hand walking
Human skeletal changes due to bipedalism
Knuckle-walking
Palmistry—fortune-telling based on lines in hand palms
Manus (anatomy)
Mudra—Hindu term for hand gestures | biology | 174942 | https://da.wikipedia.org/wiki/Finger | Finger | En finger er et af de fem bevægelige lemmer, som sidder yderst på hånden hos mennesker og visse andre arter, som aber. Fingrene bruges blandt andet til at føle og gribe med. Yderst på fingrene sidder neglene. De skal beskytte fingrene, som er meget følsomme. Der er to led i en finger, ligeså vel som i en tå.
Etymologi
Ordet finger kan som mange andre ord for ydre anatomi føres langt tilbage.
Det urgermanske rekonstruerede ord er *fingraz.
Om det kan føres videre til et urindoeuropæisk rekonstrueret ord er mere usikkert.
En hypotese er at det udviklet fra *fanhaną som betyder noget i retning af gribe eller fange, mens en mere sandsynlig hypotese er at det har forbindelse til ordet for 5 *penkʷe.
Navne på fingrene og deres funktion
Mennesket er udstyret med tommelfingre, også kaldt tommeltot, som almindeligvis er den tykkeste og nederst placerede finger. Den er placeret således, at de kan bøjes i en anden retning end resten af fingrene. Dette giver bedre gribemuligheder, og dermed bedre evne til at manipulere objekter fysisk.
Navnene på de enkelte fingre er:
Pegefinger er den, der sidder nærmest tommelfingeren. Den er en af de mest brugte, da den ofte bruges til at angive retninger, placeringer osv. for andre.
Langefinger er den midterste og længste finger på en hånd. Den bliver også kaldet langemand.
Ringfinger er den tredje fra tommelfingeren. Dens navn kommer af, at ringe (vielsesringe osv.) som regel bliver sat på denne finger.
Lillefinger er den fjerde fra tommelfingeren. Den er som regel mindre end de andre, bortset fra tommelfingeren, hvorfor den har fået dette navn.
Fingeraftryk
Et fingeraftryk er et billede af de riller der findes på en fingers blomme. Det består fordybninger i overhuden og indeholder strukturer som buer, cirkler og spiraler. Når en person sætter sin finger på en overflade overføres der en gengivelse af fingeraftrykket. Dette sker fordi der på overfladen af af huden sidder vand og fedtstoffer, som trykkes af. På stoffer som papir kan aminosyrer i fingeraftrykket fremkaldes med bestemte kemikalier. Fingeraftrykket er unikt for personen, idet det aldrig er observeret at to personer har identiske fingeraftryk.
Se også
Fingerlængdeforholdet
Håndtegn
Fingeren (gestus)
V-tegn
Dupuytrens kontraktur, populært kaldt "kuskefingre" eller "vikingesygdommen".
Polydactyli
Referencer
Eksterne henvisninger
Bevægeapparatets anatomi | danish | 0.564904 |
hot_water_bacteria/Bacteria.txt |
Bacteria (/bækˈtɪəriə/ ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Like all animals, humans carry vast numbers (approximately 10 to 10) of bacteria. Most are in the gut, though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague. The most common fatal bacterial diseases are respiratory infections. Antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. Bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium, copper and other metals in the mining sector, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.
Etymology
Rod-shaped Bacillus subtilis
The word bacteria is the plural of the Neo-Latin bacterium, which is the Latinisation of the Ancient Greek βακτήριον (baktḗrion), the diminutive of βακτηρία (baktēría), meaning "staff, cane", because the first ones to be discovered were rod-shaped.
Origin and early evolution
Main article: Evolution of bacteria
Further information: Earliest known life forms, Evolutionary history of life, and Timeline of evolution
Phylogenetic tree of Bacteria, Archaea and Eucarya, with the last universal common ancestor (LUCA) at the root.
The ancestors of bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. The most recent common ancestor (MRCA) of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. The earliest life on land may have been bacteria some 3.22 billion years ago.
Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya (sometimes in highly reduced form, e.g. in ancient "amitochondrial" protozoa). Later, some eukaryotes that already contained mitochondria also engulfed cyanobacteria-like organisms, leading to the formation of chloroplasts in algae and plants. This is known as primary endosymbiosis.
Habitat
Bacteria are ubiquitous, living in every possible habitat on the planet including soil, underwater, deep in Earth's crust and even such extreme environments as acidic hot springs and radioactive waste. There are thought to be approximately 2×10 bacteria on Earth, forming a biomass that is only exceeded by plants. They are abundant in lakes and oceans, in arctic ice, and geothermal springs where they provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. They live on and in plants and animals. Most do not cause diseases, are beneficial to their environments, and are essential for life. The soil is a rich source of bacteria and a few grams contain around a thousand million of them. They are all essential to soil ecology, breaking down toxic waste and recycling nutrients. They are even found in the atmosphere and one cubic metre of air holds around one hundred million bacterial cells. The oceans and seas harbour around 3 x 10 bacteria which provide up to 50% of the oxygen humans breathe. Only around 2% of bacterial species have been fully studied.
Extremophile bacteria
Habitat
Species
Reference
Cold (minus 15 °C Antarctica)
Cryptoendoliths
Hot (70–100 °C geysers)
Thermus aquaticus
Radiation, 5MRad
Deinococcus radiodurans
Saline, 47% salt (Dead Sea, Great Salt Lake)
several species
Acid pH 3
several species
Alkaline pH 12.8
betaproteobacteria
Space (6 years on a NASA satellite)
Bacillus subtilis
3.2 km underground
several species
High pressure (Mariana Trench – 1200 atm)
Moritella, Shewanella and others
Morphology
Further information: Bacterial cell structure § Cell morphology
Bacteria display many cell morphologies and arrangements
Size. Bacteria display a wide diversity of shapes and sizes. Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0.5–5.0 micrometres in length. However, a few species are visible to the unaided eye—for example, Thiomargarita namibiensis is up to half a millimetre long, Epulopiscium fishelsoni reaches 0.7 mm, and Thiomargarita magnifica can reach even 2 cm in length, which is 50 times larger than other known bacteria. Among the smallest bacteria are members of the genus Mycoplasma, which measure only 0.3 micrometres, as small as the largest viruses. Some bacteria may be even smaller, but these ultramicrobacteria are not well-studied.
Shape. Most bacterial species are either spherical, called cocci (singular coccus, from Greek kókkos, grain, seed), or rod-shaped, called bacilli (sing. bacillus, from Latin baculus, stick). Some bacteria, called vibrio, are shaped like slightly curved rods or comma-shaped; others can be spiral-shaped, called spirilla, or tightly coiled, called spirochaetes. A small number of other unusual shapes have been described, such as star-shaped bacteria. This wide variety of shapes is determined by the bacterial cell wall and cytoskeleton and is important because it can influence the ability of bacteria to acquire nutrients, attach to surfaces, swim through liquids and escape predators.
The range of sizes shown by prokaryotes (Bacteria), relative to those of other organisms and biomolecules.
Multicellularity. Most bacterial species exist as single cells; others associate in characteristic patterns: Neisseria forms diploids (pairs), streptococci form chains, and staphylococci group together in "bunch of grapes" clusters. Bacteria can also group to form larger multicellular structures, such as the elongated filaments of Actinomycetota species, the aggregates of Myxobacteria species, and the complex hyphae of Streptomyces species. These multicellular structures are often only seen in certain conditions. For example, when starved of amino acids, myxobacteria detect surrounding cells in a process known as quorum sensing, migrate towards each other, and aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100,000 bacterial cells. In these fruiting bodies, the bacteria perform separate tasks; for example, about one in ten cells migrate to the top of a fruiting body and differentiate into a specialised dormant state called a myxospore, which is more resistant to drying and other adverse environmental conditions.
Biofilms. Bacteria often attach to surfaces and form dense aggregations called biofilms, and larger formations known as microbial mats. These biofilms and mats can range from a few micrometres in thickness to up to half a metre in depth, and may contain multiple species of bacteria, protists and archaea. Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures, such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients. In natural environments, such as soil or the surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated bacteria.
Cellular structure
Further information: Bacterial cell structure
Structure and contents of a typical Gram-positive bacterial cell (seen by the fact that only one cell membrane is present).
Intracellular structures
The bacterial cell is surrounded by a cell membrane, which is made primarily of phospholipids. This membrane encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential components of the cytoplasm within the cell. Unlike eukaryotic cells, bacteria usually lack large membrane-bound structures in their cytoplasm such as a nucleus, mitochondria, chloroplasts and the other organelles present in eukaryotic cells. However, some bacteria have protein-bound organelles in the cytoplasm which compartmentalize aspects of bacterial metabolism, such as the carboxysome. Additionally, bacteria have a multi-component cytoskeleton to control the localisation of proteins and nucleic acids within the cell, and to manage the process of cell division.
Many important biochemical reactions, such as energy generation, occur due to concentration gradients across membranes, creating a potential difference analogous to a battery. The general lack of internal membranes in bacteria means these reactions, such as electron transport, occur across the cell membrane between the cytoplasm and the outside of the cell or periplasm. However, in many photosynthetic bacteria, the plasma membrane is highly folded and fills most of the cell with layers of light-gathering membrane. These light-gathering complexes may even form lipid-enclosed structures called chlorosomes in green sulfur bacteria.
An electron micrograph of Halothiobacillus neapolitanus cells with carboxysomes inside, with arrows highlighting visible carboxysomes. Scale bars indicate 100 nm.
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome with its associated proteins and RNA. Like all other organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and archaea.
Some bacteria produce intracellular nutrient storage granules, such as glycogen, polyphosphate, sulfur or polyhydroxyalkanoates. Bacteria such as the photosynthetic cyanobacteria, produce internal gas vacuoles, which they use to regulate their buoyancy, allowing them to move up or down into water layers with different light intensities and nutrient levels.
Extracellular structures
Further information: Cell envelope
Around the outside of the cell membrane is the cell wall. Bacterial cell walls are made of peptidoglycan (also called murein), which is made from polysaccharide chains cross-linked by peptides containing D-amino acids. Bacterial cell walls are different from the cell walls of plants and fungi, which are made of cellulose and chitin, respectively. The cell wall of bacteria is also distinct from that of achaea, which do not contain peptidoglycan. The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin (produced by a fungus called Penicillium) is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.
There are broadly speaking two different types of cell wall in bacteria, that classify bacteria into Gram-positive bacteria and Gram-negative bacteria. The names originate from the reaction of cells to the Gram stain, a long-standing test for the classification of bacterial species.
Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids. In contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. Most bacteria have the Gram-negative cell wall, and only members of the Bacillota group and actinomycetota (previously known as the low G+C and high G+C Gram-positive bacteria, respectively) have the alternative Gram-positive arrangement. These differences in structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only Gram-positive bacteria and is ineffective against Gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas aeruginosa. Some bacteria have cell wall structures that are neither classically Gram-positive or Gram-negative. This includes clinically important bacteria such as mycobacteria which have a thick peptidoglycan cell wall like a Gram-positive bacterium, but also a second outer layer of lipids.
In many bacteria, an S-layer of rigidly arrayed protein molecules covers the outside of the cell. This layer provides chemical and physical protection for the cell surface and can act as a macromolecular diffusion barrier. S-layers have diverse functions and are known to act as virulence factors in Campylobacter species and contain surface enzymes in Bacillus stearothermophilus.
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
Flagella are rigid protein structures, about 20 nanometres in diameter and up to 20 micrometres in length, that are used for motility. Flagella are driven by the energy released by the transfer of ions down an electrochemical gradient across the cell membrane.
Fimbriae (sometimes called "attachment pili") are fine filaments of protein, usually 2–10 nanometres in diameter and up to several micrometres in length. They are distributed over the surface of the cell, and resemble fine hairs when seen under the electron microscope. Fimbriae are believed to be involved in attachment to solid surfaces or to other cells, and are essential for the virulence of some bacterial pathogens. Pili (sing. pilus) are cellular appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or sex pili (see bacterial genetics, below). They can also generate movement where they are called type IV pili.
Glycocalyx is produced by many bacteria to surround their cells, and varies in structural complexity: ranging from a disorganised slime layer of extracellular polymeric substances to a highly structured capsule. These structures can protect cells from engulfment by eukaryotic cells such as macrophages (part of the human immune system). They can also act as antigens and be involved in cell recognition, as well as aiding attachment to surfaces and the formation of biofilms.
The assembly of these extracellular structures is dependent on bacterial secretion systems. These transfer proteins from the cytoplasm into the periplasm or into the environment around the cell. Many types of secretion systems are known and these structures are often essential for the virulence of pathogens, so are intensively studied.
Endospores
Further information: Endospore
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
Some genera of Gram-positive bacteria, such as Bacillus, Clostridium, Sporohalobacter, Anaerobacter, and Heliobacterium, can form highly resistant, dormant structures called endospores. Endospores develop within the cytoplasm of the cell; generally, a single endospore develops in each cell. Each endospore contains a core of DNA and ribosomes surrounded by a cortex layer and protected by a multilayer rigid coat composed of peptidoglycan and a variety of proteins.
Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, such as high levels of UV light, gamma radiation, detergents, disinfectants, heat, freezing, pressure, and desiccation. In this dormant state, these organisms may remain viable for millions of years. Endospores even allow bacteria to survive exposure to the vacuum and radiation of outer space, leading to the possibility that bacteria could be distributed throughout the Universe by space dust, meteoroids, asteroids, comets, planetoids, or directed panspermia.
Endospore-forming bacteria can cause disease; for example, anthrax can be contracted by the inhalation of Bacillus anthracis endospores, and contamination of deep puncture wounds with Clostridium tetani endospores causes tetanus, which, like botulism, is caused by a toxin released by the bacteria that grow from the spores. Clostridioides difficile infection, a common problem in healthcare settings, is caused by spore-forming bacteria.
Metabolism
Further information: Microbial metabolism
Bacteria exhibit an extremely wide variety of metabolic types. The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy, but these traits often do not correspond with modern genetic classifications. Bacterial metabolism is classified into nutritional groups on the basis of three major criteria: the source of energy, the electron donors used, and the source of carbon used for growth.
Phototrophic bacteria derive energy from light using photosynthesis, while chemotrophic bacteria breaking down chemical compounds through oxidation, driving metabolism by transferring electrons from a given electron donor to a terminal electron acceptor in a redox reaction. Chemotrophs are further divided by the types of compounds they use to transfer electrons. Bacteria that derive electrons from inorganic compounds such as hydrogen, carbon monoxide, or ammonia are called lithotrophs, while those that use organic compounds are called organotrophs. Still, more specifically, aerobic organisms use oxygen as the terminal electron acceptor, while anaerobic organisms use other compounds such as nitrate, sulfate, or carbon dioxide.
Many bacteria, called heterotrophs, derive their carbon from other organic carbon. Others, such as cyanobacteria and some purple bacteria, are autotrophic, meaning they obtain cellular carbon by fixing carbon dioxide. In unusual circumstances, the gas methane can be used by methanotrophic bacteria as both a source of electrons and a substrate for carbon anabolism.
Nutritional types in bacterial metabolism
Nutritional type
Source of energy
Source of carbon
Examples
Phototrophs
Sunlight
Organic compounds (photoheterotrophs) or carbon fixation (photoautotrophs)
Cyanobacteria, Green sulfur bacteria, Chloroflexota, or Purple bacteria
Lithotrophs
Inorganic compounds
Organic compounds (lithoheterotrophs) or carbon fixation (lithoautotrophs)
Thermodesulfobacteriota, Hydrogenophilaceae, or Nitrospirota
Organotrophs
Organic compounds
Organic compounds (chemoheterotrophs) or carbon fixation (chemoautotrophs)
Bacillus, Clostridium, or Enterobacteriaceae
In many ways, bacterial metabolism provides traits that are useful for ecological stability and for human society. For example, diazotrophs have the ability to fix nitrogen gas using the enzyme nitrogenase. This trait, which can be found in bacteria of most metabolic types listed above, leads to the ecologically important processes of denitrification, sulfate reduction, and acetogenesis, respectively. Bacterial metabolic processes are important drivers in biological responses to pollution; for example, sulfate-reducing bacteria are largely responsible for the production of the highly toxic forms of mercury (methyl- and dimethylmercury) in the environment. Nonrespiratory anaerobes use fermentation to generate energy and reducing power, secreting metabolic by-products (such as ethanol in brewing) as waste. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves.
Growth and reproduction
Further information: Bacterial growth
Many bacteria reproduce through binary fission, which is compared to mitosis and meiosis in this image.
A culture of Salmonella
A colony of Escherichia coli
Unlike in multicellular organisms, increases in cell size (cell growth) and reproduction by cell division are tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction. Under optimal conditions, bacteria can grow and divide extremely rapidly, and some bacterial populations can double as quickly as every 17 minutes. In cell division, two identical clone daughter cells are produced. Some bacteria, while still reproducing asexually, form more complex reproductive structures that help disperse the newly formed daughter cells. Examples include fruiting body formation by myxobacteria and aerial hyphae formation by Streptomyces species, or budding. Budding involves a cell forming a protrusion that breaks away and produces a daughter cell.
In the laboratory, bacteria are usually grown using solid or liquid media. Solid growth media, such as agar plates, are used to isolate pure cultures of a bacterial strain. However, liquid growth media are used when the measurement of growth or large volumes of cells are required. Growth in stirred liquid media occurs as an even cell suspension, making the cultures easy to divide and transfer, although isolating single bacteria from liquid media is difficult. The use of selective media (media with specific nutrients added or deficient, or with antibiotics added) can help identify specific organisms.
Most laboratory techniques for growing bacteria use high levels of nutrients to produce large amounts of cells cheaply and quickly. However, in natural environments, nutrients are limited, meaning that bacteria cannot continue to reproduce indefinitely. This nutrient limitation has led the evolution of different growth strategies (see r/K selection theory). Some organisms can grow extremely rapidly when nutrients become available, such as the formation of algal and cyanobacterial blooms that often occur in lakes during the summer. Other organisms have adaptations to harsh environments, such as the production of multiple antibiotics by Streptomyces that inhibit the growth of competing microorganisms. In nature, many organisms live in communities (e.g., biofilms) that may allow for increased supply of nutrients and protection from environmental stresses. These relationships can be essential for growth of a particular organism or group of organisms (syntrophy).
Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase, a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The second phase of growth is the logarithmic phase, also known as the exponential phase. The log phase is marked by rapid exponential growth. The rate at which cells grow during this phase is known as the growth rate (k), and the time it takes the cells to double is known as the generation time (g). During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth is the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport. The final phase is the death phase where the bacteria run out of nutrients and die.
Genetics
Main article: Bacterial genetics
Helium ion microscopy image showing T4 phage infecting E. coli. Some of the attached phage have contracted tails indicating that they have injected their DNA into the host. The bacterial cells are ~ 0.5 µm wide.
Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacteria Carsonella ruddii, to 12,200,000 base pairs (12.2 Mbp) in the soil-dwelling bacteria Sorangium cellulosum. There are many exceptions to this; for example, some Streptomyces and Borrelia species contain a single linear chromosome, while some Vibrio species contain more than one chromosome. Some bacteria contain plasmids, small extra-chromosomal molecules of DNA that may contain genes for various useful functions such as antibiotic resistance, metabolic capabilities, or various virulence factors.
Bacteria genomes usually encode a few hundred to a few thousand genes. The genes in bacterial genomes are usually a single continuous stretch of DNA. Although several different types of introns do exist in bacteria, these are much rarer than in eukaryotes.
Bacteria, as asexual organisms, inherit an identical copy of the parent's genome and are clonal. However, all bacteria can evolve by selection on changes to their genetic material DNA caused by genetic recombination or mutations. Mutations arise from errors made during the replication of DNA or from exposure to mutagens. Mutation rates vary widely among different species of bacteria and even among different clones of a single species of bacteria. Genetic changes in bacterial genomes emerge from either random mutation during replication or "stress-directed mutation", where genes involved in a particular growth-limiting process have an increased mutation rate.
Some bacteria transfer genetic material between cells. This can occur in three main ways. First, bacteria can take up exogenous DNA from their environment in a process called transformation. Many bacteria can naturally take up DNA from the environment, while others must be chemically altered in order to induce them to take up DNA. The development of competence in nature is usually associated with stressful environmental conditions and seems to be an adaptation for facilitating repair of DNA damage in recipient cells. Second, bacteriophages can integrate into the bacterial chromosome, introducing foreign DNA in a process known as transduction. Many types of bacteriophage exist; some infect and lyse their host bacteria, while others insert into the bacterial chromosome. Bacteria resist phage infection through restriction modification systems that degrade foreign DNA, and a system that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact with in the past, which allows them to block virus replication through a form of RNA interference. Third, bacteria can transfer genetic material through direct cell contact via conjugation.
In ordinary circumstances, transduction, conjugation, and transformation involve transfer of DNA between individual bacteria of the same species, but occasionally transfer may occur between individuals of different bacterial species, and this may have significant consequences, such as the transfer of antibiotic resistance. In such cases, gene acquisition from other bacteria or the environment is called horizontal gene transfer and may be common under natural conditions.
Behaviour
Movement
Main article: Bacterial motility
Transmission electron micrograph of Desulfovibrio vulgaris showing a single flagellum at one end of the cell. Scale bar is 0.5 micrometers long.
Many bacteria are motile (able to move themselves) and do so using a variety of mechanisms. The best studied of these are flagella, long filaments that are turned by a motor at the base to generate propeller-like movement. The bacterial flagellum is made of about 20 proteins, with approximately another 30 proteins required for its regulation and assembly. The flagellum is a rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane for power.
The different arrangements of bacterial flagella: A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous
Bacteria can use flagella in different ways to generate different kinds of movement. Many bacteria (such as E. coli) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and makes their movement a three-dimensional random walk. Bacterial species differ in the number and arrangement of flagella on their surface; some have a single flagellum (monotrichous), a flagellum at each end (amphitrichous), clusters of flagella at the poles of the cell (lophotrichous), while others have flagella distributed over the entire surface of the cell (peritrichous). The flagella of a unique group of bacteria, the spirochaetes, are found between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves.
Two other types of bacterial motion are called twitching motility that relies on a structure called the type IV pilus, and gliding motility, that uses other mechanisms. In twitching motility, the rod-like pilus extends out from the cell, binds some substrate, and then retracts, pulling the cell forward.
Motile bacteria are attracted or repelled by certain stimuli in behaviours called taxes: these include chemotaxis, phototaxis, energy taxis, and magnetotaxis. In one peculiar group, the myxobacteria, individual bacteria move together to form waves of cells that then differentiate to form fruiting bodies containing spores. The myxobacteria move only when on solid surfaces, unlike E. coli, which is motile in liquid or solid media.
Several Listeria and Shigella species move inside host cells by usurping the cytoskeleton, which is normally used to move organelles inside the cell. By promoting actin polymerisation at one pole of their cells, they can form a kind of tail that pushes them through the host cell's cytoplasm.
Communication
See also: Prokaryote § Sociality
A few bacteria have chemical systems that generate light. This bioluminescence often occurs in bacteria that live in association with fish, and the light probably serves to attract fish or other large animals.
Bacteria often function as multicellular aggregates known as biofilms, exchanging a variety of molecular signals for intercell communication and engaging in coordinated multicellular behaviour.
The communal benefits of multicellular cooperation include a cellular division of labour, accessing resources that cannot effectively be used by single cells, collectively defending against antagonists, and optimising population survival by differentiating into distinct cell types. For example, bacteria in biofilms can have more than five hundred times increased resistance to antibacterial agents than individual "planktonic" bacteria of the same species.
One type of intercellular communication by a molecular signal is called quorum sensing, which serves the purpose of determining whether the local population density is sufficient to support investment in processes that are only successful if large numbers of similar organisms behave similarly, such as excreting digestive enzymes or emitting light. Quorum sensing enables bacteria to coordinate gene expression and to produce, release, and detect autoinducers or pheromones that accumulate with the growth in cell population.
Classification and identification
Main article: Bacterial taxonomy
Further information: Scientific classification, Systematics, Bacterial phyla, and Clinical pathology
Streptococcus mutans visualised with a Gram stain.
Phylogenetic tree showing the diversity of bacteria, compared to other organisms. Here bacteria are represented by three main supergroups: the CPR ultramicrobacterias, Terrabacteria and Gracilicutes according to recent genomic analyzes (2019).
Classification seeks to describe the diversity of bacterial species by naming and grouping organisms based on similarities. Bacteria can be classified on the basis of cell structure, cellular metabolism or on differences in cell components, such as DNA, fatty acids, pigments, antigens and quinones. While these schemes allowed the identification and classification of bacterial strains, it was unclear whether these differences represented variation between distinct species or between strains of the same species. This uncertainty was due to the lack of distinctive structures in most bacteria, as well as lateral gene transfer between unrelated species. Due to lateral gene transfer, some closely related bacteria can have very different morphologies and metabolisms. To overcome this uncertainty, modern bacterial classification emphasises molecular systematics, using genetic techniques such as guanine cytosine ratio determination, genome-genome hybridisation, as well as sequencing genes that have not undergone extensive lateral gene transfer, such as the rRNA gene. Classification of bacteria is determined by publication in the International Journal of Systematic Bacteriology, and Bergey's Manual of Systematic Bacteriology. The International Committee on Systematic Bacteriology (ICSB) maintains international rules for the naming of bacteria and taxonomic categories and for the ranking of them in the International Code of Nomenclature of Bacteria.
Historically, bacteria were considered a part of the Plantae, the Plant kingdom, and were called "Schizomycetes" (fission-fungi). For this reason, collective bacteria and other microorganisms in a host are often called "flora".
The term "bacteria" was traditionally applied to all microscopic, single-cell prokaryotes. However, molecular systematics showed prokaryotic life to consist of two separate domains, originally called Eubacteria and Archaebacteria, but now called Bacteria and Archaea that evolved independently from an ancient common ancestor. The archaea and eukaryotes are more closely related to each other than either is to the bacteria. These two domains, along with Eukarya, are the basis of the three-domain system, which is currently the most widely used classification system in microbiology. However, due to the relatively recent introduction of molecular systematics and a rapid increase in the number of genome sequences that are available, bacterial classification remains a changing and expanding field. For example, Cavalier-Smith argued that the Archaea and Eukaryotes evolved from Gram-positive bacteria.
The identification of bacteria in the laboratory is particularly relevant in medicine, where the correct treatment is determined by the bacterial species causing an infection. Consequently, the need to identify human pathogens was a major impetus for the development of techniques to identify bacteria.
The Gram stain, developed in 1884 by Hans Christian Gram, characterises bacteria based on the structural characteristics of their cell walls. The thick layers of peptidoglycan in the "Gram-positive" cell wall stain purple, while the thin "Gram-negative" cell wall appears pink. By combining morphology and Gram-staining, most bacteria can be classified as belonging to one of four groups (Gram-positive cocci, Gram-positive bacilli, Gram-negative cocci and Gram-negative bacilli). Some organisms are best identified by stains other than the Gram stain, particularly mycobacteria or Nocardia, which show acid fastness on Ziehl–Neelsen or similar stains. Other organisms may need to be identified by their growth in special media, or by other techniques, such as serology.
Culture techniques are designed to promote the growth and identify particular bacteria while restricting the growth of the other bacteria in the sample. Often these techniques are designed for specific specimens; for example, a sputum sample will be treated to identify organisms that cause pneumonia, while stool specimens are cultured on selective media to identify organisms that cause diarrhea while preventing growth of non-pathogenic bacteria. Specimens that are normally sterile, such as blood, urine or spinal fluid, are cultured under conditions designed to grow all possible organisms. Once a pathogenic organism has been isolated, it can be further characterised by its morphology, growth patterns (such as aerobic or anaerobic growth), patterns of hemolysis, and staining.
As with bacterial classification, identification of bacteria is increasingly using molecular methods, and mass spectroscopy. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. Diagnostics using DNA-based tools, such as polymerase chain reaction, are increasingly popular due to their specificity and speed, compared to culture-based methods. These methods also allow the detection and identification of "viable but nonculturable" cells that are metabolically active but non-dividing. However, even using these improved methods, the total number of bacterial species is not known and cannot even be estimated with any certainty. Following present classification, there are a little less than 9,300 known species of prokaryotes, which includes bacteria and archaea; but attempts to estimate the true number of bacterial diversity have ranged from 10 to 10 total species—and even these diverse estimates may be off by many orders of magnitude.
Phyla
Main article: Bacterial phyla
The following phyla have been validly published according to the Bacteriological Code:
Acidobacteriota
Actinomycetota
Aquificota
Armatimonadota
Atribacterota
Bacillota
Bacteroidota
Balneolota
Bdellovibrionota
Caldisericota
Calditrichota
Campylobacterota
Chlamydiota
Chlorobiota
Chloroflexota
Chrysiogenota
Coprothermobacterota
Deferribacterota
Deinococcota
Dictyoglomota
Elusimicrobiota
Fibrobacterota
Fusobacteriota
Gemmatimonadota
Ignavibacteriota
Lentisphaerota
Mycoplasmatota
Myxococcota
Nitrospinota
Nitrospirota
Planctomycetota
Pseudomonadota
Rhodothermota
Spirochaetota
Synergistota
Thermodesulfobacteriota
Thermomicrobiota
Thermotogota
Verrucomicrobiota
Interactions with other organisms
Further information: Microbes in human culture
Overview of bacterial infections and main species involved.
Despite their apparent simplicity, bacteria can form complex associations with other organisms. These symbiotic associations can be divided into parasitism, mutualism and commensalism.
Commensals
The word "commensalism" is derived from the word "commensal", meaning "eating at the same table" and all plants and animals are colonised by commensal bacteria. In humans and other animals, millions of them live on the skin, the airways, the gut and other orifices.
Referred to as "normal flora", or "commensals", these bacteria usually cause no harm but may occasionally invade other sites of the body and cause infection. Escherichia coli is a commensal in the human gut but can cause urinary tract infections. Similarly, streptococci, which are part of the normal flora of the human mouth, can cause heart disease.
Predators
Some species of bacteria kill and then consume other microorganisms; these species are called predatory bacteria. These include organisms such as Myxococcus xanthus, which forms swarms of cells that kill and digest any bacteria they encounter. Other bacterial predators either attach to their prey in order to digest them and absorb nutrients or invade another cell and multiply inside the cytosol. These predatory bacteria are thought to have evolved from saprophages that consumed dead microorganisms, through adaptations that allowed them to entrap and kill other organisms.
Mutualists
Certain bacteria form close spatial associations that are essential for their survival. One such mutualistic association, called interspecies hydrogen transfer, occurs between clusters of anaerobic bacteria that consume organic acids, such as butyric acid or propionic acid, and produce hydrogen, and methanogenic archaea that consume hydrogen. The bacteria in this association are unable to consume the organic acids as this reaction produces hydrogen that accumulates in their surroundings. Only the intimate association with the hydrogen-consuming archaea keeps the hydrogen concentration low enough to allow the bacteria to grow.
In soil, microorganisms that reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking) carry out nitrogen fixation, converting nitrogen gas to nitrogenous compounds. This serves to provide an easily absorbable form of nitrogen for many plants, which cannot fix nitrogen themselves. Many other bacteria are found as symbionts in humans and other organisms. For example, the presence of over 1,000 bacterial species in the normal human gut flora of the intestines can contribute to gut immunity, synthesise vitamins, such as folic acid, vitamin K and biotin, convert sugars to lactic acid (see Lactobacillus), as well as fermenting complex undigestible carbohydrates. The presence of this gut flora also inhibits the growth of potentially pathogenic bacteria (usually through competitive exclusion) and these beneficial bacteria are consequently sold as probiotic dietary supplements.
Nearly all animal life is dependent on bacteria for survival as only bacteria and some archaea possess the genes and enzymes necessary to synthesize vitamin B12, also known as cobalamin, and provide it through the food chain. Vitamin B12 is a water-soluble vitamin that is involved in the metabolism of every cell of the human body. It is a cofactor in DNA synthesis and in both fatty acid and amino acid metabolism. It is particularly important in the normal functioning of the nervous system via its role in the synthesis of myelin.
Pathogens
Main article: Pathogenic bacteria
Neisseria gonorrhoeae and pus cells from a penile discharge (Gram stain)
Colour-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells
The body is continually exposed to many species of bacteria, including beneficial commensals, which grow on the skin and mucous membranes, and saprophytes, which grow mainly in the soil and in decaying matter. The blood and tissue fluids contain nutrients sufficient to sustain the growth of many bacteria. The body has defence mechanisms that enable it to resist microbial invasion of its tissues and give it a natural immunity or innate resistance against many microorganisms. Unlike some viruses, bacteria evolve relatively slowly so many bacterial diseases also occur in other animals.
If bacteria form a parasitic association with other organisms, they are classed as pathogens. Pathogenic bacteria are a major cause of human death and disease and cause infections such as tetanus (caused by Clostridium tetani), typhoid fever, diphtheria, syphilis, cholera, foodborne illness, leprosy (caused by Mycobacterium leprae) and tuberculosis (caused by Mycobacterium tuberculosis). A pathogenic cause for a known medical disease may only be discovered many years later, as was the case with Helicobacter pylori and peptic ulcer disease. Bacterial diseases are also important in agriculture, and bacteria cause leaf spot, fire blight and wilts in plants, as well as Johne's disease, mastitis, salmonella and anthrax in farm animals.
In bacterial vaginosis, beneficial bacteria in the vagina (top) are displaced by pathogens (bottom). Gram stain.
Each species of pathogen has a characteristic spectrum of interactions with its human hosts. Some organisms, such as Staphylococcus or Streptococcus, can cause skin infections, pneumonia, meningitis and sepsis, a systemic inflammatory response producing shock, massive vasodilation and death. Yet these organisms are also part of the normal human flora and usually exist on the skin or in the nose without causing any disease at all. Other organisms invariably cause disease in humans, such as Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms. One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever. Chlamydia, another phylum of obligate intracellular parasites, contains species that can cause pneumonia or urinary tract infection and may be involved in coronary heart disease. Some species, such as Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium, are opportunistic pathogens and cause disease mainly in people who are immunosuppressed or have cystic fibrosis. Some bacteria produce toxins, which cause diseases. These are endotoxins, which come from broken bacterial cells, and exotoxins, which are produced by bacteria and released into the environment. The bacterium Clostridium botulinum for example, produces a powerful exotoxin that cause respiratory paralysis, and Salmonellae produce an endotoxin that causes gastroenteritis. Some exotoxins can be converted to toxoids, which are used as vaccines to prevent the disease.
Bacterial infections may be treated with antibiotics, which are classified as bacteriocidal if they kill bacteria or bacteriostatic if they just prevent bacterial growth. There are many types of antibiotics, and each class inhibits a process that is different in the pathogen from that found in the host. An example of how antibiotics produce selective toxicity are chloramphenicol and puromycin, which inhibit the bacterial ribosome, but not the structurally different eukaryotic ribosome. Antibiotics are used both in treating human disease and in intensive farming to promote animal growth, where they may be contributing to the rapid development of antibiotic resistance in bacterial populations. Infections can be prevented by antiseptic measures such as sterilising the skin prior to piercing it with the needle of a syringe, and by proper care of indwelling catheters. Surgical and dental instruments are also sterilised to prevent contamination by bacteria. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection.
Significance in technology and industry
Bacteria, often lactic acid bacteria, such as Lactobacillus species and Lactococcus species, in combination with yeasts and moulds, have been used for thousands of years in the preparation of fermented foods, such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt.
The ability of bacteria to degrade a variety of organic compounds is remarkable and has been used in waste processing and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. Fertiliser was added to some of the beaches in Prince William Sound in an attempt to promote the growth of these naturally occurring bacteria after the 1989 Exxon Valdez oil spill. These efforts were effective on beaches that were not too thickly covered in oil. Bacteria are also used for the bioremediation of industrial toxic wastes. In the chemical industry, bacteria are most important in the production of enantiomerically pure chemicals for use as pharmaceuticals or agrichemicals.
Bacteria can also be used in place of pesticides in biological pest control. This commonly involves Bacillus thuringiensis (also called BT), a Gram-positive, soil-dwelling bacterium. Subspecies of this bacteria are used as Lepidopteran-specific insecticides under trade names such as Dipel and Thuricide. Because of their specificity, these pesticides are regarded as environmentally friendly, with little or no effect on humans, wildlife, pollinators, and most other beneficial insects.
Because of their ability to quickly grow and the relative ease with which they can be manipulated, bacteria are the workhorses for the fields of molecular biology, genetics, and biochemistry. By making mutations in bacterial DNA and examining the resulting phenotypes, scientists can determine the function of genes, enzymes, and metabolic pathways in bacteria, then apply this knowledge to more complex organisms. This aim of understanding the biochemistry of a cell reaches its most complex expression in the synthesis of huge amounts of enzyme kinetic and gene expression data into mathematical models of entire organisms. This is achievable in some well-studied bacteria, with models of Escherichia coli metabolism now being produced and tested. This understanding of bacterial metabolism and genetics allows the use of biotechnology to bioengineer bacteria for the production of therapeutic proteins, such as insulin, growth factors, or antibodies.
Because of their importance for research in general, samples of bacterial strains are isolated and preserved in Biological Resource Centers. This ensures the availability of the strain to scientists worldwide.
History of bacteriology
For the history of microbiology, see Microbiology. For the history of bacterial classification, see Bacterial taxonomy. For the natural history of Bacteria, see Last universal common ancestor.
Antonie van Leeuwenhoek, the first microbiologist and the first person to observe bacteria using a microscope.
Bacteria were first observed by the Dutch microscopist Antonie van Leeuwenhoek in 1676, using a single-lens microscope of his own design. He then published his observations in a series of letters to the Royal Society of London. Bacteria were Leeuwenhoek's most remarkable microscopic discovery. Their size was just at the limit of what his simple lenses could resolve, and, in one of the most striking hiatuses in the history of science, no one else would see them again for over a century. His observations also included protozoans which he called animalcules, and his findings were looked at again in the light of the more recent findings of cell theory.
Christian Gottfried Ehrenberg introduced the word "bacterium" in 1828. In fact, his Bacterium was a genus that contained non-spore-forming rod-shaped bacteria, as opposed to Bacillus, a genus of spore-forming rod-shaped bacteria defined by Ehrenberg in 1835.
Louis Pasteur demonstrated in 1859 that the growth of microorganisms causes the fermentation process and that this growth is not due to spontaneous generation (yeasts and molds, commonly associated with fermentation, are not bacteria, but rather fungi). Along with his contemporary Robert Koch, Pasteur was an early advocate of the germ theory of disease. Before them, Ignaz Semmelweis and Joseph Lister had realised the importance of sanitized hands in medical work. Semmelweis, who in the 1840s formulated his rules for handwashing in the hospital, prior to the advent of germ theory, attributed disease to "decomposing animal organic matter." His ideas were rejected and his book on the topic condemned by the medical community. After Lister, however, doctors started sanitizing their hands in the 1870s.
Robert Koch, a pioneer in medical microbiology, worked on cholera, anthrax and tuberculosis. In his research into tuberculosis, Koch finally proved the germ theory, for which he received a Nobel Prize in 1905. In Koch's postulates, he set out criteria to test if an organism is the cause of a disease, and these postulates are still used today.
Ferdinand Cohn is said to be a founder of bacteriology, studying bacteria from 1870. Cohn was the first to classify bacteria based on their morphology.
Though it was known in the nineteenth century that bacteria are the cause of many diseases, no effective antibacterial treatments were available. In 1910, Paul Ehrlich developed the first antibiotic, by changing dyes that selectively stained Treponema pallidum—the spirochaete that causes syphilis—into compounds that selectively killed the pathogen. Ehrlich, who had been awarded a 1908 Nobel Prize for his work on immunology, pioneered the use of stains to detect and identify bacteria, with his work being the basis of the Gram stain and the Ziehl–Neelsen stain.
A major step forward in the study of bacteria came in 1977 when Carl Woese recognised that archaea have a separate line of evolutionary descent from bacteria. This new phylogenetic taxonomy depended on the sequencing of 16S ribosomal RNA and divided prokaryotes into two evolutionary domains, as part of the three-domain system.
See also
Bacteriohopanepolyol
Genetically modified bacteria
Marine prokaryotes | biology | 164678 | https://no.wikipedia.org/wiki/Mutualisme%20%28biologi%29 | Mutualisme (biologi) | Mutualisme i biologi er en interaksjon mellom to arter der begge arter drar fordel av interaksjonen. Mutualisme en form for symbiose.
Velkjente eksempler på mutualisme er: lav, der en sopp og en alge eller blågrønnbakterie lever sammen og soppen sørger for bl.a. vann, næringssalter og beskyttelse og algen/blågrønnbakterien sørger for karbohydrater via fotosyntese. Pussefisk som leppefisker som spiser parasitter fra større fisk. Dyrepollinering der pollinatoren skaffer seg en ressurs, ofte mat, og planta oppnår befruktning. Nitrogenfikserende bakterier som finnes i røttene til flere plantegrupper og som tilfører planta nitrogenoksider samtidig som bakteriene er beskytta mot luftas oksygen.
Hvor tett koblingen er mellom de to organismene er varierer, i noen tilfelle er en eller begge totalt avhengig av mutualismen for å overleve eller reprodusere. Dette kalles obligat mutualisme. I andre tilfeller er avhengigheten ikke livsnødvendig, den er fakultativ. Eksempler på begge typer finnes inne pollinering. I de fleste tilfeller vil både planta og dyret kunne nyttiggjøre seg flere ulike arter og mutualismen mellom to bestemte arter er fakultativ. Imidlertid er det noen tilfeller der en planteart er helt avhengig av en insektart. Slik obligat mutalisme finnes mellom fiken og fikenveps og trolig mellom Madaskars stjerneorkide (Anaegraceum sesquipedale) og dens pollinator, Xanthopan morgani praedicta.
Økologi | norwegian_bokmål | 0.687766 |
hot_water_bacteria/Water_heating.txt | Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
Domestically, water is traditionally heated in vessels known as water heaters, kettles, cauldrons, pots, or coppers. These metal vessels that heat a batch of water do not produce a continual supply of heated water at a preset temperature. Rarely, hot water occurs naturally, usually from natural hot springs. The temperature varies with the consumption rate, becoming cooler as flow increases.
Appliances that provide a continual supply of hot water are called water heaters, hot water heaters, hot water tanks, boilers, heat exchangers, geysers (Southern Africa and the Arab world), or calorifiers. These names depend on region, and whether they heat potable or non-potable water, are in domestic or industrial use, and their energy source. In domestic installations, potable water heated for uses other than space heating is also called domestic hot water (DHW).
Fossil fuels (natural gas, liquefied petroleum gas, oil), or solid fuels are commonly used for heating water. These may be consumed directly or may produce electricity that, in turn, heats water. Electricity to heat water may also come from any other electrical source, such as nuclear power or renewable energy. Alternative energy such as solar energy, heat pumps, hot water heat recycling, and geothermal heating can also heat water, often in combination with backup systems powered by fossil fuels or electricity.
Densely populated urban areas of some countries provide district heating of hot water. This is especially the case in Scandinavia, Finland and Poland. District heating systems supply energy for water heating and space heating from combined heat and power (CHP) plants such as incinerators, central heat pumps, waste heat from industries, geothermal heating, and central solar heating. Actual heating of tap water is performed in heat exchangers at the consumers' premises. Generally the consumer has no in-building backup system as redundancy is usually significant on the district heating supply side.
Today, in the United States, domestic hot water used in homes is most commonly heated with natural gas, electric resistance, or a heat pump. Electric heat pump water heaters are significantly more efficient than electric resistance water heaters, but also more expensive to purchase. Some energy utilities offer their customers funding to help offset the higher first cost of energy efficient water heaters.
Types of water heating appliances[edit]
Electric-tank–type storage water heater (US)
Hot water used for space heating may be heated by fossil fuels in a boiler, while potable water may be heated in a separate appliance. This is common practice in the US, especially when warm-air space heating is usually employed.
Storage water heaters (tank-type)[edit]
Main article: Storage water heater
Gas furnace (top) and storage water heater (bottom) (Germany)
In household and commercial usage, most North American and Southern Asian water heaters are the tank type, also called storage water heaters. These consist of a cylindrical vessel or container that keeps water continuously hot and ready to use. Typical sizes for household use range from 75–400 L (20–100 US gallons). These may use electricity, natural gas, propane, heating oil, solar, or other energy sources. Natural gas heaters are most popular in the US and most European countries, since the gas is often conveniently piped throughout cities and towns and currently is the cheapest to use. In the United States, typical natural gas water heaters for households without unusual needs are 150–190 L (40–50 US gal) with a burner rated at 10.0–11.7 kilowatts (34,000–40,000 BTU/h).
This is a popular arrangement where higher flow rates are required for limited periods. Water is heated in a pressure vessel that can withstand a hydrostatic pressure close to that of the incoming mains supply. A pressure reducing valve is sometimes employed to limit the pressure to a safe level for the vessel. In North America, these vessels are called hot water tanks, and may incorporate an electrical resistance heater, a heat pump, or a gas or oil burner that heats water directly.
Where hot-water space heating boilers are installed, domestic hot water cylinders are usually heated indirectly by primary water from the boiler, or by an electric immersion heater (often as backup to the boiler). In the UK these vessels are called indirect cylinders and direct cylinders, respectively. Additionally, if these cylinders form part of a sealed system, providing mains-pressure hot water, they are known as unvented cylinders. In the US, when connected to a boiler, they are called indirect-fired water heaters.
Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, storing the heat for later use. The disadvantage is that over time, heat escapes through the tank wall and the water cools down, activating the heating system to heat the water back up, so investing in a tank with better insulation improves this standby efficiency. Additionally, when heavy use exhausts the hot water, there is a significant delay before hot water is available again. Larger tanks tend to provide hot water with less temperature fluctuation at moderate flow rates.
Volume storage water heaters in the United States and New Zealand are typically vertical cylindrical tanks, usually standing on the floor, a 'cylinder tray' or on a platform raised a short distance above the floor. Volume storage water heaters in Spain are typically horizontal. In India, they are mainly vertical. In apartments they can be mounted in the ceiling space over laundry-utility rooms. In Australia, gas and electric outdoor tank heaters have mainly been used (with high temperatures to increase effective capacity), but solar roof tanks are becoming fashionable.
Tiny point-of-use (POU) electric storage water heaters with capacities ranging from 8–32 L (2–6 gallons) are made for installation in kitchen and bath cabinets or on the wall above a sink. They typically use low power heating elements, about 1 kW to 1.5 kW, and can provide hot water long enough for hand washing, or, if plumbed into an existing hot water line, until hot water arrives from a remote high capacity water heater. They may be used when retrofitting a building with hot water plumbing is too costly or impractical. Since they maintain water temperature thermostatically, they can only supply a continuous flow of hot water at extremely low flow rates, unlike high-capacity tankless heaters.
In tropical countries like Singapore and India, a storage water heater may vary from 10 L to 35 L. Smaller water heaters are sufficient, as ambient weather temperatures and incoming water temperature are moderate. The Coldest regions in India like Kashmir, people are mostly dependent on the storage type electric water heaters. Mostly 50L or 75L Storage type electric water heaters are connected to overhead water source.
Point-of-use (POU) vs centralized hot water[edit]
A locational design decision may be made between point-of-use and centralized water heaters. Centralized water heaters are more traditional, and are still a good choice for small buildings. For larger buildings with intermittent or occasional hot water use, multiple POU water heaters may be a better choice, since they can reduce long waits for hot water to arrive from a remote heater. The decision where to locate the water heater(s) is only partially independent of the decision of a tanked vs. tankless water heater, or the choice of energy source for the heat.
Instantaneous water heaters (tankless-type)[edit]
Main article: Tankless water heating
See also: Instant hot water dispenser and Electric water boiler
The inside of a hydraulically operated two-stage tankless heater, heated by single phase electric power. The copper tank contains heating elements with 7.2 kW maximum power.
Tankless water heaters—also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters—are gaining in popularity. These high-power water heaters instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil. Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication.
Tankless heaters may be installed throughout a household at more than one point-of-use (POU), far from a central water heater, or larger centralized models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a plentiful continuous flow of hot water (as compared to a limited flow of continuously heated hot water from conventional tank water heaters), and potential energy savings under some conditions. The main disadvantage is their much higher initial costs; a US study in Minnesota reported a 20- to 40-year payback for the tankless water heaters. In a comparison to a less efficient natural gas fired hot water tank, on-demand natural gas will cost 30% more over its useful life.
Stand-alone appliances for quickly heating water for domestic usage are known in North America as tankless or on demand water heaters. In some places, they are called multipoint heaters, geysers or ascots. In Australia and New Zealand they are called instantaneous hot water units. In Argentina they are called calefones. In that country calefones use gas instead of electricity, although gas powered tankless water heaters can also be found in other countries. A similar wood-fired appliance was known as the chip heater.
A common arrangement where hot-water space heating is employed is for a boiler also to heat potable water, providing a continuous supply of hot water without extra equipment. Appliances that can supply both space-heating and domestic hot water are called combination (or combi) boilers. Though on-demand heaters provide a continuous supply of domestic hot water, the rate at which they can produce it is limited by the thermodynamics of heating water from the available fuel supplies.
Electric shower heads[edit]
An example of a poorly installed electric shower head in Guatemala.
An electric shower head has an electric heating element which heats water as it passes through. These self-heating shower heads are specialized point-of-use (POU) tankless water heaters, and are widely used in some countries.
Invented in Brazil in the 1930s due to a lack of central gas distribution and used frequently since the 1940s, the electric shower is a home appliance often seen in South and Central American countries due to the higher costs of gas distribution, combined with households that in most cases do not support conventional water heaters. Earlier models were made of chromed copper or brass, which were expensive, but since 1970, units made of injected plastics are popular due to low prices similar to that of a hair dryer.
Electric showers have a simple electric system, working like a coffee maker, but with a larger water flow. A flow switch turns on the device when water flows through it. Once the water is stopped, the device turns off automatically. An ordinary electric shower often but not always has three heat settings: high (5.5 kW), low (2.5 kW), or cold (0 W) to use when a central heater system is available or in hot seasons. Higher power (up to 7.5 KW) and lower power (up to 3.2 KW) versions are also made, as well as versions with 4 heat settings or a variable heat setting.
Energy usage[edit]
The power consumption of electric showers in the max. heating setting is about 5.5 kW for 120 V and 7.5 kW for 220 V. The lower costs with electric showers compared to the higher costs with tank boilers is due to the time of use: an electric shower uses energy only while the water flows, while a tank boiler works many times a day to keep a quantity of standing water hot for use throughout the day and night. Moreover, the transfer of electric energy to the water in an electric shower head is very efficient, approaching 100%. Electric showers may save energy compared to electric tank heaters, which lose some standby heat.
1500W Immersion heater with sheathed element, designed to be immersed in a small vessel such as a carafe or bucket. Since it does not detect the presence of a liquid, it can become very hot if run dry, posing a hazard.
Safety[edit]
There is a wide range of electric shower heads, with various designs and types of heating controls. The heating element of an electric shower is immersed in the water stream, using an often replaceable nichrome resistive heating element which is often not sheathed and electrically isolated, in which case isolation is provided by earthing electrodes that directly touch the water before it exits the head. Electric shower heads with sheathed and electrically isolated heating elements are often marketed as such (chuveiros blindados in Portuguese) and are more expensive. Due to electrical safety standards as well as cost, modern electric showers are made of plastic instead of using metallic casings like in the past.
As an electrical appliance that uses more electric current than a clothes washer or a hair dryer, an electric shower installation requires careful planning, and generally is intended to be wired directly from the electrical distribution box with a dedicated circuit breaker and ground system. A poorly installed system with old aluminum wires, bad connections or an unconnected ground wire (which is often the case) may be dangerous, as the wires can overheat or electric current may leak via the water stream through the body of the user to earth.
Solar water heaters[edit]
Direct-gain solar heater panels with integrated storage tank
Flat-plate solar thermal collector, viewed from roof-level
Main article: Solar water heating
Increasingly, solar powered water heaters are being used. Their solar collectors are installed outside dwellings, typically on the roof or walls or nearby, and the potable hot water storage tank is typically a pre-existing or new conventional water heater, or a water heater specifically designed for solar thermal. In Cyprus and Israel 90 percent of homes have solar water heating systems.
The most basic solar thermal models are the direct-gain type, in which the potable water is directly sent into the collector. Many such systems are said to use integrated collector storage (ICS), as direct-gain systems typically have storage integrated within the collector. Heating water directly is inherently more efficient than heating it indirectly via heat exchangers, but such systems offer very limited freeze protection (if any), can easily heat water to temperatures unsafe for domestic use, and ICS systems suffer from severe heat loss on cold nights and cold, cloudy days.
By contrast, indirect or closed-loop systems do not allow potable water through the panels, but rather pump a heat transfer fluid (either water or a water/antifreeze mix) through the panels. After collecting heat in the panels, the heat transfer fluid flows through a heat exchanger, transferring its heat to the potable hot water. When the panels are cooler than the storage tank or when the storage tank has already reached its maximum temperature, the controller in closed-loop systems stops the circulation pumps. In a drainback system, the water drains into a storage tank contained in conditioned or semi-conditioned space, protected from freezing temperatures. With antifreeze systems, however, the pump must be run if the panel temperature gets too hot (to prevent degradation of the antifreeze) or too cold (to prevent the water/antifreeze mixture from freezing.)
Flat panel collectors are typically used in closed-loop systems. Flat panels, which often resemble skylights, are the most durable type of collector, and they also have the best performance for systems designed for temperatures within 56 °C (100 °F) of ambient temperature. Flat panels are regularly used in both pure water and antifreeze systems.
Another type of solar collector is the evacuated tube collector, which are intended for cold climates that do not experience severe hail and/or applications where high temperatures are needed (i.e., over 94 °C [201 °F]). Placed in a rack, evacuated tube collectors form a row of glass tubes, each containing absorption fins attached to a central heat-conducting rod (copper or condensation-driven). The evacuated description refers to the vacuum created in the glass tubes during the manufacturing process, which results in very low heat loss and lets evacuated tube systems achieve extreme temperatures, far in excess of water's boiling point.
Geothermal heating[edit]
In countries like Iceland and New Zealand, and other volcanic regions, water heating may be done using geothermal heating, rather than combustion.
Gravity-fed system[edit]
Where a space-heating water boiler is employed, the traditional arrangement in the UK and Ireland is to use boiler-heated (primary) water to heat potable (secondary) water contained in a cylindrical vessel (usually made of copper)—which is supplied from a cold water storage vessel or container, usually in the roof space of the building. This produces a fairly steady supply of DHW (domestic hot water) at low static pressure head but usually with a good flow. In most other parts of the world, water heating appliances do not use a cold water storage vessel or container, but heat water at pressures close to that of the incoming mains water supply.
Other improvements[edit]
Other improvements to water heaters include check valve devices at their inlet and outlet, cycle timers, electronic ignition in the case of fuel-using models, sealed air intake systems in the case of fuel-using models, and pipe insulation. The sealed air-intake system types are sometimes called "band-joist" intake units. "High-efficiency" condensing units can convert up to 98% of the energy in the fuel to heating the water. The exhaust gases of combustion are cooled and are mechanically ventilated either through the roof or through an exterior wall. At high combustion efficiencies a drain must be supplied to handle the water condensed out of the combustion products, which are primarily carbon dioxide and water vapor.
In traditional plumbing in the UK, the space-heating boiler is set up to heat a separate hot water cylinder or water heater for potable hot water. Such water heaters are often fitted with an auxiliary electrical immersion heater for use if the boiler is out of action for a time. Heat from the space-heating boiler is transferred to the water heater vessel/container by means of a heat exchanger, and the boiler operates at a higher temperature than the potable hot water supply. Most potable water heaters in North America are completely separate from the space heating units, due to the popularity of HVAC/forced air systems in North America.
Residential combustion water heaters manufactured since 2003 in the United States have been redesigned to resist ignition of flammable vapors and incorporate a thermal cutoff switch, per ANSI Z21.10.1. The first feature attempts to prevent vapors from flammable liquids and gases in the vicinity of the heater from being ignited and thus causing a house fire or explosion. The second feature prevents tank overheating due to unusual combustion conditions. These safety requirements were made in response to homeowners storing, or spilling, gasoline or other flammable liquids near their water heaters and causing fires. Since most of the new designs incorporate some type of flame arrestor screen, they require monitoring to make sure they do not become clogged with lint or dust, reducing the availability of air for combustion. If the flame arrestor becomes clogged, the thermal cutoff may act to shut down the heater.
A wetback stove (NZ), wetback heater (NZ), or back boiler (UK), is a simple household secondary water heater using incidental heat. It typically consists of a hot water pipe running behind a fireplace or stove (rather than hot water storage), and has no facility to limit the heating. Modern wetbacks may run the pipe in a more sophisticated design to assist heat-exchange. These designs are being forced out by government efficiency regulations that do not count the energy used to heat water as 'efficiently' used.
History[edit]
Display of water heaters used in the past
Kerosene water heater, 1917
Another type of water heater developed in Europe predated the storage model. In London, England, in 1868, a painter named Benjamin Waddy Maughan invented the first instantaneous domestic water heater that did not use solid fuel. Named the geyser after an Icelandic gushing hot spring, Maughan's invention made cold water at the top flow through pipes that were heated by hot gases from a burner at the bottom. Hot water then flowed into a sink or tub. The invention was somewhat dangerous because there was no flue to remove heated gases from the bathroom. A water heater is still sometimes called a geyser in the UK.
Maughn's invention influenced the work of a Norwegian mechanical engineer named Edwin Ruud. The first automatic, storage tank-type gas water heater was invented around 1889 by Ruud after he immigrated to Pittsburgh, Pennsylvania (US). The Ruud Manufacturing Company, still in existence today, made many advancements in tank-type and tankless water heater design and operation.
Thermodynamics and economics[edit]
Gas-fired tankless condensing boiler with hot water storage tank (US)
Water typically enters residences in the US at about 10 °C (50 °F), depending on latitude and season. Hot water temperatures of 50 °C (122 °F) are usual for dish-washing, laundry and showering, which requires that the heater raise the water temperature about 40 °C (72 °F) if the hot water is mixed with cold water at the point of use. The Uniform Plumbing Code reference shower flow rate is 9.5 L (2.5 US gal) per minute. Sink and dishwasher usages range from 4–11 L (1–3 US gal) per minute.
Natural gas is often measured by volume or heat content. Common units of measurement by volume are cubic metre or cubic feet at standard conditions or by heat content in kilowatt hours, British thermal units (BTU) or therm, which is equal to 100,000 BTU. A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A US gallon of water weighs 8.3 pounds (3.8 kg). To raise 230 L (60 US gal) of water from 10 °C (50 °F) to 50 °C (122 °F) at 90% efficiency requires 60 × 8.3 × (122 − 50) × 1.11 = 39,840 BTU. A 46 kW (157,000 BTU/h) heater, as might exist in a tankless heater, would take about 15 minutes to do this. At $1 per therm, the cost of the gas would be about 40 cents. In comparison, a typical 230 L (60 US gal) tank electric water heater has a 4.5 kW (15,000 BTU/h) heating element, which at 100% efficient results in a heating time of about 2.34 hours. At $0.16/kWh the electricity would cost $1.68.
Energy efficiencies of water heaters in residential use can vary greatly, particularly depending on manufacturer and model. However, electric heaters tend to be slightly more efficient (not counting power station losses) with recovery efficiency (how efficiently energy transfers to the water) reaching about 98%. Gas-fired heaters have maximum recovery efficiencies of only about 82–94% (the remaining heat is lost with the flue gasses). Overall energy factors can be as low as 80% for electric and 50% for gas systems. Natural gas and propane tank water heaters with energy factors of 62% or greater, as well as electric tank water heaters with energy factors of 93% or greater, are considered high-efficiency units. Energy Star-qualified natural gas and propane tank water heaters (as of September 2010) have energy factors of 67% or higher, which is usually achieved using an intermittent pilot together with an automatic flue damper, baffle blowers, or power venting.
Direct electric resistance tank water heaters are not included in the Energy Star program; however, the Energy Star program does include electric heat pump units with energy factors of 200% or higher. Tankless gas water heaters (as of 2015) must have an energy factor of 90% or higher for Energy Star qualification. Since electricity production in thermal plants has efficiency levels ranging from only 15% to slightly over 55% (combined cycle gas turbine), with around 40% typical for thermal power stations, direct resistance electric water heating may be the least energy efficient option.
However, use of a heat pump can make electric water heaters much more energy efficient and lead to a decrease in carbon dioxide emissions, even more so if a low carbon source of electricity is used. Using district heating utilizing waste heat from electricity generation and other industries to heat residences and hot water gives an increased overall efficiency, removing the need for burning fossil fuel or using high energy value electricity to produce heat in the individual home.
Fundamentally, it takes a great deal of energy to heat water, as one may experience when waiting to boil a gallon of water on a stove. For this reason, tankless on-demand water heaters require a powerful energy source. A standard 120V, 15-ampere rated wall electric outlet, by comparison, only sources enough power to warm a disappointingly small amount of water: about 0.17 US gal (0.64 L) per minute at 40 °C (72 °F) temperature elevation.
The energy used by an electric water heater can be reduced by as much as 18% through optimal schedule and temperature control that is based on knowledge of the usage pattern.
US minimum requirements[edit]
On April 16, 2015, as part of the National Appliance Energy Conservation Act (NAECA), new minimum standards for efficiency of residential water heaters set by the United States Department of Energy went into effect. All new gas storage tank water heaters with capacities smaller than 55 US gal (210 L; 46 imp gal) sold in the United States in 2015 or later shall have an energy factor of at least 60% (for 50-US-gallon units, higher for smaller units), increased from the pre-2015 minimum standard of 58% energy factor for 50-US-gallon gas units. Electric storage tank water heaters with capacities less than 55 US gallons sold in the United States shall have an energy factor of at least 95%, increased from the pre-2015 minimum standard of 90% for 50-US-gallon electric units.
Under the 2015 standard, for the first time, storage water heaters with capacities of 55 US gallons or larger now face stricter efficiency requirements than those of 50 US gallons or less. Under the pre-2015 standard, a 75 US gal (280 L; 62 imp gal) gas storage water heater with a nominal input of 22 kW (75,000 BTU/h) or less was able to have an energy factor as low as 53%, while under the 2015 standard, the minimum energy factor for a 75-US-gallon gas storage tank water heater is now 74%, which can only be achieved by using condensing technology. Storage water heaters with a nominal input of 22 kW (75,000 BTU/h) or greater are not currently affected by these requirements, since energy factor is not defined for such units. An 80 US gal (300 L; 67 imp gal) electric storage tank water heater was able to have a minimum energy factor of 86% under the pre-2015 standard, while under the 2015 standard, the minimum energy factor for an 80-gallon electric storage tank water heater is now 197%, which is only possible with heat pump technology. This rating measures efficiency at the point of use.
Depending on how electricity is generated, overall efficiency may be much lower. For example, in a traditional coal plant, only about 30–35% of the energy in the coal ends up as electricity on the other end of the generator. Losses on the electrical grid (including line losses and voltage transformation losses) reduce electrical efficiency further. According to data from the Energy Information Administration, transmission and distribution losses in 2005 consumed 6.1% of net generation. In contrast, 90% of natural gas's energy value is
delivered to the consumer. (In neither case is the energy expended exploring, developing and extracting coal or natural gas resources included in the quoted efficiency numbers.) Gas tankless water heaters shall have an energy factor of 82% or greater under the 2015 standards, which corresponds to the pre-2015 Energy Star standard.
In 2022 the Department of Energy proposed rules that would take effect in 2026 and would effectively eliminate inefficient non-condensing gas water heaters in commercial buildings. Non-condensing models waste heat, while condensing models capture and used otherwise lost energy. The change will reduce emissions by 38 million tons of carbon dioxide over 30 years and reduce buildings' energy costs.
Water heater safety[edit]
Explosion hazard[edit]
Temperature/pressure safety valve installed atop a tank-type water heater (US)
Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed. A safety device called a temperature and pressure relief (T&P or TPR) valve, is normally fitted on the top of the water heater to dump water if the temperature or pressure becomes too high. Most plumbing codes require that a discharge pipe be connected to the valve to direct the flow of discharged hot water to a drain, typically a nearby floor drain, or outside the living space. Some building codes allow the discharge pipe to terminate in the garage.
If a gas or propane fired water heater is installed in a garage or basement, many plumbing codes require that it be elevated at least 18 in (46 cm) above the floor to reduce the potential for fire or explosion due to spillage or leakage of combustible liquids in the garage. Furthermore, certain local codes mandate that tank-type heaters in new and retrofit installations must be secured to an adjacent wall by a strap or anchor to prevent tipping over and breaking the water and gas pipes in the event of an earthquake.
For older houses where the water heater is part of the space heating boiler, and plumbing codes allow, some plumbers install an automatic gas shutoff (such as the "Watts 210") in addition to a TPR valve. When the device senses that the temperature reaches 99 °C (210 °F), it shuts off the gas supply and prevents further heating. In addition, an expansion tank or exterior pressure relief valve must be installed to prevent pressure buildup in the plumbing from rupturing pipes, valves, or the water heater.
Thermal burns (scalding)[edit]
Main article: Scalding
Scalding injury to right hand
Scalding is a serious concern with any water heater. Human skin burns quickly at high temperature, in less than 5 seconds at 60 °C (140 °F), but much slower at 53 °C (127 °F) — it takes a full minute for a second degree burn. Older people and children often receive serious scalds due to disabilities or slow reaction times. In the United States and elsewhere it is common practice to put a tempering valve or thermostatic mixing valve on the outlet of the water heater. The result of automatically mixing hot and cold water via a tempering valve is referred to as "tempered water".
A tempering valve mixes enough cold water with the hot water from the heater to keep the outgoing water temperature fixed at a more moderate temperature, often set to 50 °C (122 °F). Without a tempering valve, reduction of the water heater's setpoint temperature is the most direct way to reduce scalding. However, for sanitation, hot water is needed at a temperature that can cause scalding. This may be accomplished by using a supplemental heater in an appliance that requires hotter water.
Most residential dishwashing machines, for example, include an internal electric heating element for increasing the water temperature above that provided by a domestic water heater.
Bacterial contamination[edit]
Bacterial colonies of Legionella pneumophila (indicated by arrows)
Two conflicting safety issues affect water heater temperature—the risk of scalding from excessively hot water greater than 55 °C (131 °F), and the risk of incubating bacteria colonies, particularly Legionella, in water that is not hot enough to kill them. Both risks are potentially life-threatening and are balanced by setting the water heater's thermostat to 55 °C (131 °F). The European Guidelines for Control and Prevention of Travel Associated Legionnaires' Disease recommend that hot water should be stored at 60 °C (140 °F) and distributed so that a temperature of at least 50 °C (122 °F) and preferably 55 °C (131 °F) is achieved within one minute at points of use.
If there is a dishwasher without a booster heater, it may require a water temperature within a range of 57–60 °C (135–140 °F) for optimum cleaning, but tempering valves set to no more than 55 °C (131 °F) can be applied to faucets to avoid scalding. Tank temperatures above 60 °C (140 °F) may produce limescale deposits, which could later harbor bacteria, in the water tank. Higher temperatures may also increase etching of glassware in the dishwasher.
Tank thermostats are not a reliable guide to the internal temperature of the tank. Gas-fired water tanks may have no temperature calibration shown. An electric thermostat shows the temperature at the elevation of the thermostat, but water lower in the tank can be considerably cooler. An outlet thermometer is a better indication of water temperature.
In the renewable energy industry (solar and heat pumps, in particular) the conflict between daily thermal Legionella control and high temperatures, which may drop system performance, is subject to heated debate. In a paper seeking a green exemption from normal Legionellosis safety standards, Europe's top CEN solar thermal technical committee TC 312 asserts that a 50% fall in performance would occur if solar water heating systems were heated to the base daily. However some solar simulator analysis work using Polysun 5 suggests that an 11% energy penalty is a more likely figure. Whatever the context, both energy efficiency and scalding safety requirements push in the direction of considerably lower water temperatures than the legionella pasteurization temperature of around 60 °C (140 °F).
Legionella pneumophila has been detected at the point of use downstream from horizontally-mounted electric water heaters with volumes of 150 Liters.
However, legionella can be safely and easily controlled with good design and engineering protocols. For instance raising the temperature of water heaters once a day or even once every few days to 55 °C (131 °F) at the coldest part of the water heater for 30 minutes effectively controls legionella. In all cases and in particular energy efficient applications, Legionnaires' disease is more often than not the result of engineering design issues that do not take into consideration the impact of stratification or low flow.
It is also possible to control Legionella risks by chemical treatment of the water. This technique allows lower water temperatures to be maintained in the pipework without the associated Legionella risk. The benefit of lower pipe temperatures is that the heat loss rate is reduced and thus the energy consumption is reduced.
See also[edit]
Aquastat
Architectural engineering
Condensing boiler
Electric water boiler
Energy conservation
Heat trap
Joule heating
List of home appliances
Outdoor wood-fired boiler
Solar water heating
Thermal immersion circulator
Water heat recycling | biology | 682941 | https://sv.wikipedia.org/wiki/Vattenkylning | Vattenkylning | Vattenkylning är kylning av ett värmealstrande objekt genom att låta vatten – som för ändamålet är lämpligt genom att ha en förhållandevis mycket hög specifik värmekapacitet och därigenom kan ta upp stora mängder energi under jämförelsevis liten temperaturhöjning – uppta överskottsvärme och sprida denna till lämplig plats.
Värme som (oönskad) biprodukt
Mindre motorer, både elektriska motorer och förbränningsmotorer, och andra objekt som utvecklar värme under bruk, kan kylas tillräckligt med hjälp av den omgivande luften, sk. luftkylning. När motorn blir större (och hålls någorlunda kompakt), eller då energiförbrukningen ökar, så räcker detta så småningom inte längre till. Man kan till viss del avhjälpa detta genom att öka den yta som motorn uppvisar mot luften genom att låta värmen ledas ut till kylflänsar, eller låta en fläkt öka flödet av luft som passerar motorn och dess kylflänsar. Men effektivare för större objekt är att införa ett system där vatten tar upp värmeenergin vid värmekällan och på något vis får rinna till en kylare som är speciellt designad för att så effektivt som möjligt överföra vattnets värmeenergi till den omgivande luften.
På detta vis uppnår man att det värmealstrande objektet kan designas med målet att göra dess funktion så effektiv som möjligt, och inte tvingas till kompromisser angående funktionen gentemot luftkylningens krav på stor yta mot den omgivande luften.
Beroende på om vattnets cirkulation mellan värmealstrande objekt och kylare sker genom en pump, eller genom konvektion - kallt vatten som passerat kylaren sjunker, medan det vattnet som passerar värmekällan stiger - så delas kylsystemen in i aktiva system och passiva system. De aktiva kan hantera större mängder värme genom att vattenflödets hastighet kan ökas, medan de passiva saknar rörliga delar, och därmed är praktiskt taget fullständigt ljudlösa.
Kraftproduktion
I de allra flesta av dagens kärnkraftreaktorer kyls reaktorhärden kontinuerligt av vatten, men här är målet att använda det övertryck som bildas av det varma vattnet (i en tryckvattenreaktor; i en kokvattenreaktor låter man vattnet koka och använder då istället ångan) för att driva en eller flera turbiner. Som alternativ till vatten som kylmedium kan nämnas gas (till exempel helium, kväve eller koldioxid) och flytande metaller, till exempel kvicksilver, smält natrium eller en natrium-kalium-legering som är flytande vid rumstemperatur.
Kylning | swedish | 0.556282 |
hot_water_bacteria/Effectofhandwashingw.txt | Figure - available via license: Creative Commons Attribution 3.0 Unported
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Effect of handwashing with water alone or soap and water compared to no handwashing. P-values derived from logistic regression adjusted for within-person correlation, except * where p-value was derived from Fishers exact test ignoring within-person correlation. The design effect due to within-person clustering was low (around 1.2–1.3). Note different y-axis scales in top vs. bottom panels.
Effect of handwashing with water alone or soap and water compared to no handwashing. P-values derived from logistic regression adjusted for within-person correlation, except * where p-value was derived from Fishers exact test ignoring within-person correlation. The design effect due to within-person clustering was low (around 1.2–1.3). Note different y-axis scales in top vs. bottom panels.
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Effect of handwashing with water alone or soap and water compared to no...
The Effect of Handwashing with Water or Soap on Bacterial Contamination of Hands
Article
Full-text available
Dec 2011
Maxine Burton
Emma Cobb
Peter Donachie[...]
Wolf-Peter Schmidt
Handwashing is thought to be effective for the prevention of transmission of diarrhoea pathogens. However it is not conclusive that handwashing with soap is more effective at reducing contamination with bacteria associated with diarrhoea than using water only. In this study 20 volunteers contaminated their hands deliberately by touching door handle...
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... Of all the human organs, the hands are often more exposed to environmental contamination which makes them a means for transmitting microorganisms from one person to another as they are able to harbour transient microbes [4]. Sometimes, the organisms are from the human skin as normal flora while other times, they may have been deposited through air. ...
Investigation of the Multidrug Resistance Pattern of Bacteria Isolated from Car and Office Door Handles in a Tertiary Institution
Article
Mar 2024
C. Testimonies Adebayo-OlajideA. Dakoru GoodheadEkeneokot E. UcheUsman-Wali Maryam
Multidrug-resistant bacteria have posed a public health concern over the years, especially with the difficulty and cost of treatment of infections they cause. Fomites such as door handles are thus potent means through which pathogens are transmitted from one person to another as contact with them is made. This study thus involves isolating antibiotic-resistant bacteria from car and office door handles in a university environment. Using the simple random sampling method, twenty samples (20) from car door handles and twenty samples (20) from office door handles were collected, the isolation of bacteria was done using standard microbiological procedures and identification of the isolates was done using cultural, microscopic and biochemical characterization. Determination of the antibiotic sensitivity pattern of the isolates was done using the Kirby-Bauer disc diffusion method on Muller Hinton agar. Antibiotics used included Ofloxacin (5 µg), Gentamicin (10 µg), Ceftriaxone (30 µg), Augmentin (30 µg), Ciprofloxacin (5 µg), Erythromycin (5 µg), Streptomycin (30 µg) and Cloxacillin (30 µg). The results showed a significant frequency of occurrence of Staphylococcus aureus at 35% and Klebsiella pneumoniae having least at 5%. From car door handles, S. epidermidis recorded 37% while K. pneumoniae recorded the least with 17.4%. The isolates exhibited resistance to antibiotics including Augmentin and Ceftriaxone (≤22 mm) while they were more susceptible to Ofloxacin (≥16 mm). All the K. pneumoniae isolated from car door handles exhibited resistance to Augmentin and Ceftriaxone. These results show that these surfaces could be a possible reservoir of infections caused by resistant bacteria, leading to difficulty in the treatment of infections caused by them.
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... Diseases transmitted by direct physical contact are best prevented by effective hand washing (33). However, using contaminated hand soap from refillable dispensers can result in Gram-negative bacteria colonizing the hands in public settings, thus increasing daily risk of infection threshold (not shown) is 1 x 10 −6 (or 1 infection per 1,000,000 individuals). ...
Eye infection risks from Pseudomonas aeruginosa via hand soap and eye drops
Article
Full-text available
Mar 2024APPL ENVIRON MICROB
Anna GitterKristina D. MenaKarla S. Mendez
Fuqing WuCharles P. Gerba
Eye infections from bacterial contamination of bulk-refillable liquid soap dispensers and artificial tear eye drops continue to occur, resulting in adverse health outcomes that include impaired vision or eye enucleation. Pseudomonas aeruginosa (P. aeruginosa), a common cause of eye infections, can grow in eye drop containers and refillable soap dispensers to high numbers. To assess the risk of eye infection, a quantitative microbial risk assessment for P. aeruginosa was conducted to predict the probability of an eye infection for two potential exposure scenarios: (i) individuals using bacteria-contaminated eye drops and (ii) contact lens wearers washing their hands with bacteria-contaminated liquid soap prior to placing the lens. The median risk of an eye infection using contaminated eye drops and hand soap for both single and multiple exposure events (per day) ranged from 10–1 to 10⁻⁴, with contaminated eye drops having the greater risk. The concentration of P. aeruginosa was identified as the parameter contributing the greatest variance on eye infection risk; therefore, the prevalence and level of bacterial contamination of the product would have the greatest influence on health risk. Using eye drops in a single-use container or with preservatives can mitigate bacterial growth, and using non-refillable soap dispensers is recommended to reduce contamination of hand soap. Given the opportunistic nature of P. aeruginosa and its ability to thrive in unique environments, additional safeguards to mitigate bacterial growth and exposure are warranted. IMPORTANCE Pseudomonas aeruginosa (P. aeruginosa) is a pathogen that can persist in a variety of unusual environments and continues to pose a significant risk for public health. This quantitative microbial risk assessment (QMRA) estimates the potential human health risks, specifically for eye infections, associated with exposure to P. aeruginosa in bacteria-contaminated artificial tear eye drops and hand soap. This study applies the risk assessment framework of QMRA to evaluate eye infection risks through both consumer products. The study examines the prevalence of this pathogen in eye drops and soap, as well as the critical need to implement measures that will mitigate bacterial exposure (e.g., single-use soap dispensers and eye drops with preservatives). Additionally, limitations and challenges are discussed, including the need to incorporate data regarding consumer practices, which may improve exposure assessments and health risk estimates.
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... In healthcare, it is crucial to uphold proper hand hygiene as it represents a highly effective preventive measure in reducing infections [1] and managing the spread of illnesses [2,3]. Improper hand hygiene among healthcare workers is responsible for approximately 40% of healthcare-associated infections. ...
ResMFuse-Net: Residual-based multilevel fused network with spatial–temporal features for hand hygiene monitoring
Article
Full-text available
Mar 2024APPL INTELL
Sohaib AsifXinyi Xu
Ming ZhaoXuehan ChenYusen Zhu
The automation of hand hygiene monitoring is critical in healthcare for ensuring clean hands and preventing infectious disease spread. While advancements have been made, existing methods have limitations in accurately detecting and classifying handwashing actions. This paper addresses these limitations and introduces the Residual-Based Multilevel Fused Network (ResMFuse-Net) as a novel approach to automate the quality assurance of hand hygiene procedures. Our model integrates advanced techniques, including feature fusion, model compression, a feature fusion block (FFB), and a modified separable residual block (SE-ResB). The proposed model fused two networks into one trainable feature extraction pipeline, and applies model compression to retain the core blocks that are crucial for propagating strong and robust features while conserving a significant fraction of the computing resources. Additionally, we introduce a FFB that includes ConvLSTM and alpha dropout to learn spatial dependencies, establish correlations between frames in a video, and mitigate overfitting. This paper introduces a SE-ResB, which is a customized residual component composed of separable convolutions and LeakyReLU activation. The SE-ResB is incorporated to handle the fused features and generate a more diverse set of features, leading to considerable performance enhancements. This study also includes an ablation analysis that highlights the importance of each component. The proposed ResMFuse-Net is evaluated on two datasets: a newly created handwashing dataset (451 videos) and a publicly available dataset (656 videos). Achieving a recognition accuracy of 97.61% on the handwashing dataset and 98.69% on the other dataset, the ResMFuse-Net outperforms previous methods with fewer parameters and FLOPs, demonstrating its efficiency and cost-effectiveness.
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... Seventy to eighty percent of the chemicals used have been found tainted with bacteria [17]. Poor hand hygiene can cause used objects to become contaminated with bacteria like S. aureus and B. cereus [24]. All product categories had fungus contamination; however, the foundation, lipstick, and mascara had the greatest rates. ...
Isolation and Identification of Harmful Microorganisms from the Shared Cosmetic Products in Delhi NCR Region
Article
Full-text available
Feb 2024
Gyan Vandana Yadav
Sandhya Khunger
Sunil KumarMukul MudgalMukesh Sharma
The usage of shared cosmetics increases the chances of microbiological contamination, which can lead to negative health repercussions for users. Cosmetics are commonly used for personal grooming and aesthetic requirements, however it is usual for several users to share these products. The purpose of this research was conducted to identify the different types of microbial contamination, bacterial or fungal in lipsticks, blush, foundation, and mascara. The study included 48 swab samples of foundation, lipstick, blush, and mascara from Delhi and Gurugram parlors (shared products). Swab samples were collected under sterile conditions and cultured on enriched Blood agar, whereas fungi identification samples were cultured on Sabouraud dextrose agar. The identification of isolated bacteria was confirmed using culture media, Gram staining, biochemical tests, and a Vitek 2GP card for species-level identification. Staphylococcus hominis was perhaps the most common bacterial isolate, followed by Staphylococcus epidermidis and Bacillus cereus, Streptococcus pyogenes, and Bacillus cereus were found. Lipsticks, foundations, and blushes were more infected with Gram +ve and Gram-ve bacteria. However, mascara had less contamination than lipstick, the foundation, and blush; these contaminated beauty products led to the spread of pathogenic bacteria, which can cause a variety of diseases in humans.
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... The other reason might be the quality of the handwashing water. Pieces of evidence revealed that bacterial contamination of hands is significantly affected by handwashing water (54,55). ...
Prevalence and antimicrobial susceptibility profile of bacteria isolated from the hands of housemaids in Jimma City, Ethiopia
Article
Full-text available
Jan 2024
Tadele Shiwito AngoNegalgn Byadgie GelawGirma Mamo ZegeneTizita TeshomeTesfalem Getahun
Introduction Bacterial pathogens continue to be a major cause of foodborne gastroenteritis in humans and remain a public health problem. Housemaids operating inside a kitchen could be the source of infection and may transmit disease-inflicting pathogens through contaminated hands. Objective This study aimed to assess the prevalence and antimicrobial susceptibility profile of bacteria isolated from the hands of housemaids in Jimma City, Ethiopia. Methods A laboratory-based cross-sectional study was employed among 234 housemaids. Hand swab samples from the dominant hand of the study participants were collected under sterile conditions following standard operating procedures. Then, in the laboratory, the swabs were inoculated aseptically using streak-plating methods on the growth media, such as mannitol salt agar [Staphylococcus aureus and coagulase-negative staphylococci], MacConkey agar [Klebsiella species and Proteus species], salmonella-shigella agar [Salmonella species and Shigella species], and eosin methylene blue agar [Escherichia coli (E. coli)]. In addition, a set of biochemical tests was applied to examine bacterial species. Data were double-entered into EpiData version 3.1 and then exported to the Statistical Package for Social Science (SPSS) version 26 for further analysis. Descriptive analyses were summarized using frequency and percentage. Results The proportion of housemaids’ hands containing one or more positive bacterial isolates was 72% (95% CI: 66.2, 77.8). The dominant bacterial isolates were Staphylococcus aureus (31.6%), Escherichia coli (21.3%), Salmonella species (1.3%), Shigella species (6.7%), Klebsiella species (23.1%) and Proteus species (14.7%). Fingernail status (AOR =15.31, 95% CI: 10.372, 22.595) and the removal of a watch, ring, and bracelet during hand washing (AOR = 20.844, 95% CI: 2.190, 9.842) were significantly associated with the prevalence of bacterial isolation. Most Staphylococcus aureus isolates were susceptible to chloramphenicol (98.6%). Escherichia coli isolates were susceptible to tetracycline (75%), ceftriaxone (79.2%), chloramphenicol (87.5%), and ceftazidime (77.1%). Eighty percent of isolated Shigella species were susceptible to chloramphenicol and gentamicin respectively. In addition, Klebsiella and Proteus species exhibited high susceptibility to chloramphenicol. However, their isolates showed resistance against a number of the tested antimicrobials. Staphylococcus aureus isolates (28.2%) were resistance to tetracycline. Moreover, One-quarter of Escherichia coli isolates were resistance to tetracycline, ceftriaxone, chloramphenicol, and ceftazidime. Whereas 46.7% and 48.5% of isolated Shigella species and Proteus species were resistance to tetracycline and ceftriaxone. Conclusion The hands of housemaids are important potential sources of pathogenic bacteria that would result in the potential risk of foodborne diseases. Most bacteria isolates were resistant to tetracycline, ceftriaxone, and ceftazidime. Therefore, practicing good hand hygiene helps to prevent and control the spread of antimicrobial-resistant microbes.
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... Apart from causing diseases when transmitted from one person to another, they run the risk of contaminating blood products if proper cleaning of the antecubital fossa is not carried out [25]. Cleaning the skin with soap and water is more effective than washing the skin with just water or no hand washing at all [26]. Cleaning the skin with just water is ineffective because bacteria are mixed with the oil on the skin. ...
Blood Donor Arm Cleaning – Another Step towards Preventing the Contamination of Blood Products for Transfusion Purposes
Article
Full-text available
Jan 2024
Nathalie Gatt
Jean Pierre Gialanze
Nancy Spiteri
Vanessa Zammit
Blood Establishments strive to provide blood and blood derivatives that are safe for transfusion. A recurrent concern is providing blood components that are free from bacterial contamination. Bacterial and fungal contamination of blood products is nowadays a major apprehension when it comes to transfusion adverse events. Over the years, several disinfection products and protocols have been devised to mitigate the risks of such contaminants, nonetheless, sepsis is still the leading cause of transfusion reaction fatalities. This fact raises the question of whether disinfection on its own is sufficient for preventing such outcomes.
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... In fact, washing hands with running water and drying were accepted as not sufficient to remove bacteria from hands (who et al., 2016). Further, handwashing with non-antibacterial soap was considered more effective in removing bacteria from hands than handwashing with water only (Burton et al., 2011). However, hand sanitiser was explained as not much critical in food handling, while handwashing with lukewarm water and liquid soap could lead to an acceptable level of hand hygiene (Valero et al., 2016). ...
Evaluation of knowledge, attitudes, and practices of estate managers on food safety of black tea manufacturing in the Uva region of Sri Lanka
Article
Full-text available
Dec 2023
K. P. M. Kahandage
I. Wickramasinghe
S. B. Navaratne
W. A. J. P. Wijesinghe
Sri Lankan black tea is renowned for its high quality and regarded as a brand that is chemically safe, ozone-friendly, and ethically acceptable with accountable stakeholders in the supply chain. Meantime, food safety has become one of the mandated food attributes that is heavily concern by stakeholders even at the estate level. Hence, this study aimed to determine the level of knowledge, attitudes, and practice (KAP) of managers at black tea manufacturing in the Uva region of Sri Lanka regarding basic food safety concerns. Data were collected from 30 respondents at 30 black tea manufacturing factories in the Uva region using a stratified random sampling technique. A pre-tested interviewer-administered questionnaire based on KAP of basic food safety was utilized and collected data were analyzed using descriptive analysis and correlation analysis. The study indicated that the mean percentage of knowledge was satisfactory (93.1%), and the mean score for attitudes and practices of food safety was 4.7±0.4 (X±SD) and 4.6±0.5 (X±SD), respectively. However, this study depicted that the knowledge of food safety influenced managers’ attitudes (0.421, P<0.05) but not their food safety behaviour. Further, they believed that food safety management systems would be a means of directing their black tea to the international market (76.7%), while pledging the concerns of food safety (70%). However, it was depicted that constraints with food handlers (100%) and financial difficulties (73.3%) hugely affected the implementation of food safety management systems at the black tea manufacturing factories in the Uva region of Sri Lanka. Hence, this study suggests continuous, periodical but short training to sustain the practice of handling teas safely in the Uva region of Sri Lanka.
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... A large body of empirical studies in household and community settings have demonstrated the effectiveness of hand washing in reducing other respiratory illnesses around the world, be that through campaigns or through the presence of the facility itself. Washing hands with soap (both plain and antibacterial soap) is a proven mechanism to eliminate bacteria and respiratory viruses [31][32][33]. A systematic review of eight studies from a pool of 410 articles found that hand washing lowered the risk of respiratory infection, with risk reductions ranging from 6% to 44%, but noted that a greater number of rigorous studies are urgently needed [34]. ...
Estimating spatially disaggregated probability of severe COVID-19 and the impact of handwashing interventions: The case of Zimbabwe
Article
Full-text available
Nov 2023PLOS ONE
George JosephSveta MilushevaHugh Sturrock
Tonderai MapakoYi Rong Hoo
Introduction The severity of COVID-19 disease varies substantially between individuals, with some infections being asymptomatic while others are fatal. Several risk factors have been identified that affect the progression of SARS-CoV-2 to severe COVID-19. They include age, smoking and presence of underlying comorbidities such as respiratory illness, HIV, anemia and obesity. Given that respiratory illness is one such comorbidity and is affected by hand hygiene, it is plausible that improving access to handwashing could lower the risk of severe COVID-19 among a population. In this paper, we estimate the potential impact of improved access to handwashing on the risk of respiratory illness and its knock-on impact on the risk of developing severe COVID-19 disease across Zimbabwe. Methods Spatial generalized additive models were applied to cluster level data from the 2015 Demographic and Health Survey. These models were used to generate continuous (1km resolution) estimates of risk factors for severe COVID-19, including prevalence of major comorbidities (respiratory illness, HIV without viral load suppression, anemia and obesity) and prevalence of smoking, which were aggregated to district level alongside estimates of the proportion of the population under 50 from Worldpop data. The risk of severe COVID-19 was then calculated for each district using published estimates of the relationship between comorbidities, smoking and age (under 50) and severe COVID-19. Two scenarios were then simulated to see how changing access to handwashing facilities could have knock on implications for the prevalence of severe COVID-19 in the population. Results This modeling conducted in this study shows that (1) current risk of severe disease is heterogeneous across the country, due to differences in individual characteristics and household conditions and (2) that if the quantifiable estimates on the importance of handwashing for transmission are sound, then improvements in handwashing access could lead to reductions in the risk of severe COVID-19 of up to 16% from the estimated current levels across all districts. Conclusions Taken alongside the likely impact on transmission of SARS-CoV-2 itself, as well as countless other pathogens, this result adds further support for the expansion of access to handwashing across the country. It also highlights the spatial differences in risk of severe COVID-19, and thus the opportunity for better planning to focus limited resources in high-risk areas in order to potentially reduce the number of severe cases.
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... Thus, hands serve as the vehicle of infectious disease transmission, especially amongst people living and working in close proximity to one another, such as dormitories, classrooms, camps etc. Close environments, doorknobs and other inanimate objects serving as resting vehicles of transmission all contribute to increased infection rates among these groups [14]. Human hands usually constitute microorganisms both as part of the body's normal flora and transient microorganisms contracted from the environment [15]. Although it is nearly impossible for the hands to be free of microorganisms and usually harbour microorganisms both as residents and transients, the presence and transfer of pathogenic microorganisms could occur between people who access the same areas or surfaces may lead to chronic or acute illnesses [15,16]. ...
... Human hands usually constitute microorganisms both as part of the body's normal flora and transient microorganisms contracted from the environment [15]. Although it is nearly impossible for the hands to be free of microorganisms and usually harbour microorganisms both as residents and transients, the presence and transfer of pathogenic microorganisms could occur between people who access the same areas or surfaces may lead to chronic or acute illnesses [15,16]. Therefore, the study aimed to investigate the microorganisms isolated from the hands of students of the Federal University of Lafia, Nasarawa State, Nigeria. ...
... Additionally, these microorganisms, being opportunistic human pathogens, pose implications for food safety, particularly in the case of enterotoxin-producing strains of staphylococci linked to food poisoning [27]. Bacillus spp, known for bearing resistant spores, was also prevalent and has implications for human pathogenesis and food spoilage [15]. The presence of Klebsiella spp, Escherichia coli, Salmonella spp, and Enterococcus faecalis might suggest compromised personal and domestic hygiene, especially concerning hand contamination after restroom visits, thereby potentially predisposing individuals to diseases [15]. ...
Hand Carriage of Microorganisms by Students of Federal University of Lafia, Nasarawa State, Nigeria
Article
Full-text available
Oct 2023
Peter Uteh Upla
Bashiru Eya SaniOsuyi Gerard UyiIgoche Naomi Ibe
Gladys Abel Angbalaga
Microbes from the body's regular flora and transient microorganisms from the environment are found on human hands. Hands can also be used to spread disease from one person to another, especially among close persons. This study aimed to isolate and identify microorganisms from students' hands and assess the occurrence of these bacteria based on gender, level of study, faculty, and hand area (palm and nails swab). Using the pour plate method, a total of sixty (60) hand swab samples (thirty (30) from both palm and nails) were collected and tested for bacterial and fungal presence. Bacteria isolated were Staphylococcus epidermidis (80.00 %), Staphylococcus aureus (75.00 %), Enterococcus spp (50.00 %), Micrococcus spp (46.67 %), Escherichia coli (45.00 %), Klebsiella spp (45.00 %), Bacillus spp (30.00 %), Salmonella spp (13.33 %) and Streptococcus spp (10.00 %). The fungi isolated were Aspergillus niger (45.00 %), Penicillium spp (23.33 %), Mucor spp (21.67 %), Candida spp (20.00 %) and Saccharomyces spp (15.00 %). Gender, level of study, faculty, and area of hand swab revealed no statistically significant variation in the presence of numerous bacterial and fungal species at p<0.05. These findings revealed that the microbial burden on students' hands was significant and was unaffected by gender, level of study, or faculty. To improve students' overall health, appropriate hygiene, including regular handwashing practice, and public education about the importance of hands in disease transmission should be supported.
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... Moreover, some respondents describe using soap as challenging because it is a new practice, and they believe washing with water is enough to make hands physically clean. Experimental trials have shown that HWWS is more effective in removing bacteria than using water alone (Burton et al. 2011;Amin et al. 2014). Similarly, our findings showed that the use of soap was twice as effective as using water alone in eliminating bacteria. ...
... HWWS for 20 s has been highlighted as an effective method for removing bacteria from the hands (WHO 2009). Wetting the hands with water and scrubbing with soap creates a lather that traps and eliminates these bacteria (Burton et al. 2011). Although some students performed handwashing for more than 20 s, only 6% of them scrubbed their hands with soap for that entire duration, while others did so briefly. ...
Effect of handwashing on the reduction of Escherichia coli on children's hands in urban slum Indonesia
Article
Full-text available
Oct 2023J WATER HEALTH
Mahmud Aditya Rifqi
Umi Hamidah
Neni Sintawardani
Hidenori Harada
Taro Yamauchi
Poor hand hygiene practice has been linked to an increase in the number of infections among children in urban slums. Hands are considered an intersection for bacterial transmission, but it is unclear whether the handwashing technique affects bacteria elimination. This study investigated the effect of handwashing on the concentration of Escherichia coli (E. coli) and factors related to its reduction among children in an urban slum in Bandung, Indonesia. We observed handwashing and conducted repeated hand swabs before and after handwashing among 137 participants. The mean E. coli concentration on the hands decreased after handwashing, with a higher reduction in E. coli count among students who used soap and had soap contact for more than 10 s during handwashing. Cleaning in-between fingers, using soap, soap contact for more than 10 s, and drying hands with a single-use towel were effective factors for reducing E. coli concentration after handwashing (p < 0.05). More than half of the swab samples (59%) tested positive for E. coli after handwashing, indicating that the children's handwashing technique was not effective in completely removing E. coli from the hands. Moreover, sustained and consistent handwashing practice as a daily behavior in children would maximize the effect.
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TermsPrivacyCopyrightImprint | biology | 154233 | https://no.wikipedia.org/wiki/Parasittvepser | Parasittvepser | Evanioidea
Megalyroidea
Proctotrupomorpha
Ichneumonoidea
Stephanidae
Trigonalyidae
Parasittvepser omfatter mesteparten av de parasittoide (snyltende) artene blant stilkvepsene. De legger eggene sine i andre dyr, ofte insekter, som så brukes som vert for parasittvepsenes larver. Vanligvis legges eggene i larver eller nymfer, men også i selve eggene, slik artene i familiegruppen Trichogrammatidae gjør.
Vertene spises opp innifra og dør når parasittvepsens larver har blitt voksne (imago) og forlater verten.
Selv om de fleste parasittvepser er parasittoider, fins det unntak. Dessuten fins det også parasittoide vepser blant broddvepsene.
De mest kjente gruppene av parasittvepser er snyltevepser, gallvepser og chalcidider. Mange av artene blir brukt som biologisk kontroll av skadedyr.
Parasittvepser har i tradisjonell systematikk blitt brukt som systematisk betegnelse under de vitenskapelige navnene «Terebrantia» eller «Parasitica». De utgjør imidlertid ikke noen fullstendig slektskapsgruppe, men representerer en grad av utvikling og er en parafyletisk gruppe som har gitt opphav til broddvepsene.
Eksterne lenker
Vepser | norwegian_bokmål | 1.082402 |
hot_water_bacteria/Hand_washing.txt |
Hand washing (or handwashing), also known as hand hygiene, is the act of cleaning one's hands with soap or handwash and water to remove viruses/bacteria/microorganisms, dirt, grease, or other harmful and unwanted substances stuck to the hands. Drying of the washed hands is part of the process as wet and moist hands are more easily recontaminated. If soap and water are unavailable, hand sanitizer that is at least 60% (v/v) alcohol in water can be used as long as hands are not visibly excessively dirty or greasy. Hand hygiene is central to preventing the spread of infectious diseases in home and everyday life settings.
The World Health Organization (WHO) recommends washing hands for at least 20 seconds before and after certain activities. These include the five critical times during the day where washing hands with soap is important to reduce fecal-oral transmission of disease: after using the toilet (for urination, defecation, menstrual hygiene), after cleaning a child's bottom (changing diapers), before feeding a child, before eating and before/after preparing food or handling raw meat, fish, or poultry.
When neither hand washing nor using hand sanitizer is possible, hands can be cleaned with uncontaminated ash and clean water, although the benefits and harms are uncertain for reducing the spread of viral or bacterial infections. However, frequent hand washing can lead to skin damage due to drying of the skin. Moisturizing lotion is often recommended to keep the hands from drying out; dry skin can lead to skin damage which can increase the risk for the transmission of infection.
The United States Centers for Disease Control and Prevention (CDC) recommends the following steps when washing one's hands for the prevention of transmission of disease:
The most commonly missed areas are the thumb, the wrist, the areas between the fingers, and under fingernails. Artificial nails and chipped nail polish may harbor microorganisms.
There are five critical times during the day where washing hands with soap is important to reduce fecal-oral transmission of disease: after using the toilet (for urination, defecation, menstrual hygiene), after cleaning a child's bottom (changing diapers), before feeding a child, before eating and before/after preparing food or handling raw meat, fish, or poultry. Other occasions when correct handwashing technique should be practiced in order to prevent the transmission of disease include before and after treating a cut or wound; after sneezing, coughing, or blowing your nose; after touching animal waste or handling animals; and after touching garbage.
Hand washing has many significant health benefits, including minimizing the spread of influenza, COVID-19, and other infectious diseases; preventing infectious causes of diarrhea; decreasing respiratory infections;
and reducing infant mortality rate at home birth deliveries. A 2013 study showed that improved hand washing practices may lead to small improvements in the length growth in children under five years of age. In developing countries, childhood mortality rates related to respiratory and diarrheal diseases can be reduced by introducing simple behavioral changes, such as hand washing with soap. This simple action can reduce the rate of mortality from these diseases by almost 50%. Interventions that promote hand washing can reduce diarrhoea episodes by about a third, and this is comparable to providing clean water in low income areas. 48% of reductions in diarrhoea episodes can be associated with hand washing with soap.
Handwashing with soap is the single most effective and inexpensive way to prevent diarrhea and acute respiratory infections (ARI), as automatic behavior performed in homes, schools, and communities worldwide. Pneumonia, a major ARI, is the number one cause of mortality among children under five years old, taking the lives of an estimated 1.8 million children per year. Diarrhea and pneumonia together account for almost 3.5 million child deaths annually. According to UNICEF, turning handwashing with soap before eating and after using the toilet into an ingrained habit can save more lives than any single vaccine or medical intervention, cutting deaths from diarrhea by almost half and deaths from acute respiratory infections by one-quarter. Hand washing is usually integrated with other sanitation interventions as part of water, sanitation, and hygiene (WASH) programmes. Hand washing also protects against impetigo which is transmitted through direct physical contact.
A small detrimental effect of handwashing is that frequent hand washing can lead to skin damage due to the drying of the skin. A 2012 Danish study found that excessive hand washing can lead to an itchy, flaky skin condition known as contact dermatitis, which is especially common among health-care workers.
In many countries, there is a low rate of hand washing with soap. A study of hand washing in 54 countries in 2015 found that on average, 38.7% of households practiced hand washing with soap.
A 2014 study showed that Saudi Arabia had the highest rate of 97%; the United States near the middle with 77%; and China with the lowest rate of 23%.
Several behavior change methodologies now exist to increase uptake of the behavior of hand washing with soap at the critical times.
Group hand washing for school children at set times of the day is one option in developing countries to engrain hand washing in children's behaviors. The "Essential Health Care Program" implemented by the Department of Education in the Philippines is an example of at scale action to promote children's health and education. Deworming twice a year, supplemented with washing hands daily with soap, brushing teeth daily with fluoride, is at the core of this national program. It has also been successfully implemented in Indonesia.
Removal of microorganisms from skin is enhanced by the addition of soaps or detergents to water. Soap and detergents are surfactants that kill microorganisms by disorganizing their membrane lipid bilayer and denaturing their proteins. It also emulsifies oils, enabling them to be carried away by running water.
Solid soap, because of its reusable nature, may hold bacteria acquired from previous uses. A small number of studies which have looked at the bacterial transfer from contaminated solid soap have concluded transfer is unlikely as the bacteria are rinsed off with the foam. The CDC still states "liquid soap with hands-free controls for dispensing is preferable".
Antibacterial soaps have been heavily promoted to a health-conscious public. To date, there is no evidence that using recommended antiseptics or disinfectants selects for antibiotic-resistant organisms in nature. However, antibacterial soaps contain common antibacterial agents such as triclosan, which has an extensive list of resistant strains of organisms. So, even if antibiotic resistant strains are not selected for by antibacterial soaps, they might not be as effective as they are marketed to be. Besides the surfactant and skin-protecting agent, the sophisticated formulations may contain acids (acetic acid, ascorbic acid, lactic acid) as pH regulator, antimicrobially active benzoic acid and further skin conditioners (aloe vera, vitamins, menthol, plant extracts).
A 2007 meta-analysis from the University of Oregon School of Public Health indicated that plain soaps are as effective as consumer-grade anti-bacterial soaps containing triclosan in preventing illness and removing bacteria from the hands. Dissenting, a 2011 meta-analysis in the Journal of Food Protection argued that when properly formulated, triclosan can grant a small but detectable improvement, as can chlorhexidine gluconate, iodophor, or povidone.
Hot water that is still comfortable for washing hands is not hot enough to kill bacteria. Bacteria grow much faster at body temperature (37 °C). WHO considers warm soapy water to be more effective than cold, soapy water at removing natural oils which hold soils and bacteria. But CDC mentions that warm water causes skin irritations more often and its ecological footprint is more significant. Water temperatures from 4 to 40 °C do not differ significantly regarding removal of microbes. The most important factor is proper scrubbing.
Contrary to popular belief, scientific studies have shown that using warm water has no effect on reducing the microbial load on hands. Using hot water for handwashing can even be regarded as a waste of energy.
In situations where hand washing with soap is not an option (e.g., when in a public place with no access to wash facilities), a waterless hand sanitizer such as an alcohol hand gel can be used. They can be used in addition to hand washing to minimize risks when caring for "at-risk" groups. To be effective, alcohol hand gels should contain not less than 60%v/v alcohol. Enough hand antiseptic or alcohol rub must be used to thoroughly wet or cover both hands. The front and back of both hands and between and the ends of all fingers must be rubbed for approximately 30 seconds until the liquid, foam or gel is dry. Finger tips must be washed well too, rubbing them in both palms.
A hand sanitizer or hand antiseptic is a non-water-based hand hygiene agent. In the late 1990s and early part of the 21st century, alcohol rub non-water-based hand hygiene agents (also known as alcohol-based hand rubs, antiseptic hand rubs, or hand sanitizers) began to gain popularity. Most are based on isopropyl alcohol or ethanol formulated together with a thickening agent such as Carbomer (polymer of acrylic acid) into a gel, or a humectant such as glycerin into a liquid, or foam for ease of use and to decrease the drying effect of the alcohol. Adding diluted hydrogen peroxide increases further the antimicrobial activity.
Hand sanitizers are most effective against bacteria and less effective against some viruses. Alcohol-based hand sanitizers are almost entirely ineffective against norovirus (or Norwalk) type viruses, the most common cause of contagious gastroenteritis.
US Centers for Disease Control and Prevention recommend hand washing with soap over hand sanitizer rubs, particularly when hands are visibly dirty. The increasing use of these agents is based on their ease of use and rapid killing activity against micro-organisms; however, they should not serve as a replacement for proper hand washing unless soap and water are unavailable. Despite their effectiveness, non-water agents do not cleanse the hands of organic material, but simply disinfect them. It is for this reason that hand sanitizers are not as effective as soap and water at preventing the spread of many pathogens, since the pathogens remain on the hands.
Hand washing using hand sanitizing wipes is an alternative during traveling in the absence of soap and water. Alcohol-based hand sanitizer should contain at least 60% alcohol.
Many people in low-income communities cannot afford soap and use ash or soil instead. The World Health Organization recommended ash or sand as an alternative to soap when soap is not available. Use of ash is common in rural areas of developing countries and has in experiments been shown at least as effective as soap for removing pathogens. However, evidence to support the use of ash to wash hands is of poor quality. It is not clear if washing hands with ash is effective at reducing viral or bacterial spreading compared to washing with mud, not washing, or with washing with water alone. One concern is that if the soil or ash is contaminated with microorganisms it may increase the spread of disease rather than decrease it, however, there is also no clear evidence to determine the level of risk. Like soap, ash is also a disinfecting agent because in contact with water, it forms an alkaline solution.
Various low-cost options can be made to facilitate hand washing where tap-water and/or soap is not available e.g. pouring water from a hanging jerrycan or gourd with suitable holes and/or using ash if needed in developing countries.
In situations with limited water supply (such as schools or rural areas in developing countries), there are water-conserving solutions, such as "tippy-taps" and other low-cost options. A tippy-tap is a simple technology using a jug suspended by a rope, and a foot-operated lever to pour a small amount of water over the hands and a bar of soap.
Low-cost hand washing technologies for households may differ from facilities for multiple users. For households, options include tippy taps, bucket/container with tap (such as a Veronica Bucket), conventional tap with/without basin, valve/tap fitted to bottles, bucket and cup, camp sink. Options for multiple users include: adapting household technologies for multiple users, water container fitted to a pipe with multiple taps, water container fitted to a pipe with holes.
Several companies around the globe have developed technologies that aim to improve the hand washing process. Among the different inventions, there are eco-friendly devices that use 90% less
water and 60% less soap compared to hand washing under a faucet. Another device uses
light-based rays to detect contaminants on the hands after they have been washed.
Certain environments are especially sensitive to the transmission of pathogenic microorganisms, like health care and food production. Organizations attempting to prevent infection transmission in these environments have started using programmed washing cycles that provide sufficient time for scrubbing the hands with soap and rinsing them with water. Combined with AI-powered software, these technological advancements turn the hand-washing process into digital data, allowing individuals to receive insights and improve their hand hygiene practices.
Effective drying of the hands is an essential part of the hand hygiene process. Therefore, the proper drying of hands after washing should be an integral part of the hand hygiene process in health care.
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) are clear and straightforward concerning hand hygiene, and recommend paper towels and hand dryers equally. Both have stressed the importance of frequent and thorough hand washing followed by their complete drying as a means to stop the spread of pathogens, like COVID-19. Specifically, the World Health Organization recommends that everyone "frequently clean [their] hands..." and "dry [them] thoroughly by using paper towels or a warm air dryer." The CDC report that, "Both [clean towels or air hand dryers] are effective ways to dry hands."
A study in 2020 found that hand dryers and paper towels were both found to be equally hygienic hand-drying solutions.
However, there is some debate over the most effective form of drying in public toilets. A growing volume of research suggests paper towels are much more hygienic than the electric hand dryers found in many public toilets. A review in 2012 concluded that "From a hygiene standpoint, paper towels are superior to air dryers; therefore, paper towels should be recommended for use in locations in which hygiene is paramount, such as hospitals and clinics."
Jet-air dryers were found to be capable of blowing micro-organisms from the hands and the unit and potentially contaminating other users and the environment up to 2 metres (6.6 feet) away. In the same study in 2008 (sponsored by the paper-towel industry the European Tissue Symposium), use of a warm-air hand dryer spread micro-organisms only up to 0.25 metres (0.82 feet) from the dryer, and paper towels showed no significant spread of micro-organisms. No studies have found a correlation to hand dryers and human health, however, making these findings inconsequential.
Making hand washing facilities accessible (inclusive) to everyone is crucial to maintain hand washing behavior. Considerations for accessibility include age, disability, seasonality (with rains and muddiness), location and more. Important aspects for good accessibility include: Placement of the technology, paths, ramps, steps, type of tap, soap placement.
Medical hand-washing became mandatory long after Hungarian physician Ignaz Semmelweis discovered its effectiveness (in 1846) in preventing disease in a hospital environment. There are electronic devices that provide feedback to remind hospital staff to wash their hands when they forget. One study has found decreased infection rates with their use.
Medical hand-washing is for a minimum of 15 seconds, using generous amounts of soap and water or gel to lather and rub each part of the hands. Hands should be rubbed together with digits interlocking. If there is debris under fingernails, a bristle brush may be used to remove it. Since pathogens may remain in the water on the hands, it is important to rinse well and wipe dry with a clean towel. After drying, the paper towel should be used to turn off the water (and open any exit door if necessary). This avoids re-contaminating the hands from those surfaces.
The purpose of hand-washing in the health-care setting is to remove pathogenic microorganisms ("germs") and avoid transmitting them. The New England Journal of Medicine reports that a lack of hand-washing remains at unacceptable levels in most medical environments, with large numbers of doctors and nurses routinely forgetting to wash their hands before touching patients, thus transmitting microorganisms. One study showed that proper hand-washing and other simple procedures can decrease the rate of catheter-related bloodstream infections by 66%.
The World Health Organization has published a sheet demonstrating standard hand-washing and hand-rubbing in health-care sectors. The draft guidance of hand hygiene by the organization can also be found at its website for public comment. A relevant review was conducted by Whitby et al. Commercial devices can measure and validate hand hygiene, if demonstration of regulatory compliance is required.
The World Health Organization has "Five Moments" for washing hands:
The addition of antiseptic chemicals to soap ("medicated" or "antimicrobial" soaps) confers killing action to a hand-washing agent. Such killing action may be desired before performing surgery or in settings in which antibiotic-resistant organisms are highly prevalent.
To 'scrub' one's hands for a surgical operation, it is necessary to have a tap that can be turned on and off without touching it with the hands, some chlorhexidine or iodine wash, sterile towels for drying the hands after washing, and a sterile brush for scrubbing and another sterile instrument for cleaning under the fingernails. All jewelry should be removed. This procedure requires washing the hands and forearms up to the elbow, usually 2–6 minutes. Long scrub-times (10 minutes) are not necessary. When rinsing, water on the forearms must be prevented from running back to the hands. After hand-washing is completed, the hands are dried with a sterile cloth and a surgical gown is donned.
To reduce the spread of pathogens, it is better to wash the hands or use a hand antiseptic before and after tending to a sick person.
For control of staphylococcal infections in hospitals, it has been found that the greatest benefit from hand-cleansing came from the first 20% of washing, and that very little additional benefit was gained when hand cleansing frequency was increased beyond 35%. Washing with plain soap results in more than triple the rate of bacterial infectious disease transmitted to food as compared to washing with antibacterial soap.
Comparing hand-rubbing with alcohol-based solution with hand washing with antibacterial soap for a median time of 30 seconds each showed that the alcohol hand-rubbing reduced bacterial contamination 26% more than the antibacterial soap. But soap and water is more effective than alcohol-based hand rubs for reducing H1N1 influenza A virus and Clostridium difficile spores from hands.
Interventions to improve hand hygiene in healthcare settings can involve education for staff on hand washing, increasing the availability of alcohol-based hand rub, and written and verbal reminders to staff. There is a need for more research into which of these interventions are most effective in different healthcare settings.
In developing countries, hand washing with soap is recognized as a cost-effective, essential tool for achieving good health, and even good nutrition. However, a lack of reliable water supply, soap or hand washing facilities in people's homes, at schools and the workplace make it a challenge to achieve universal hand washing behaviors. For example, in most of rural Africa hand washing taps close to every private or public toilet are scarce, even though cheap options exist to build hand washing stations. However, low hand washing rates can also be the result of engrained habits rather than due to a lack of soap or water.
Hand washing at a global level has its own indicator within Sustainable Development Goal 6, Target 6.2 which states "By 2030, achieve access to adequate and equitable sanitation and hygiene for all and end open defecation, paying special attention to the needs of women and girls and those in vulnerable situations. The corresponding Indicator 6.2.1 is formulated as follows: "Proportion of population using (a) safely managed sanitation services and (b) a hand-washing facility with soap and water" (see map to the right with data worldwide from 2017)."
The promotion and advocacy of hand washing with soap can influence policy decisions, raise awareness about the benefits of hand washing and lead to long-term behavior change of the population. For this to work effectively, monitoring and evaluation are necessary. A systematic review of 70 studies found that community-based approaches are effective at increasing hand washing in LMICs, while social marketing campaigns are less effective.
One example for hand washing promotion in schools is the "Three Star Approach" by UNICEF that encourages schools to take simple, inexpensive steps to ensure that students wash their hands with soap, among other hygienic requirements. When minimum standards are achieved, schools can move from one to ultimately three stars. Building hand washing stations can be a part of hand washing promotion campaigns that are carried out to reduce diseases and child mortality.
Global Handwashing Day is another example of an awareness-raising campaign that is trying to achieve behavior change.
As a result of the ongoing COVID-19 pandemic, UNICEF promoted the adoption of a hand washing emoji.
Designing hand washing facilities that encourage use can use the following aspects:
Few studies have considered the overall cost effectiveness of hand washing in developing countries in relationship to DALYs averted. However, one review suggests that promoting hand washing with soap is significantly more cost-effective than other water and sanitation interventions.
The importance of hand washing for human health – particularly for people in vulnerable circumstances like mothers who had just given birth or wounded soldiers in hospitals – was first recognized in the mid 19th century by two pioneers of hand hygiene: the Hungarian physician Ignaz Semmelweis who worked in Vienna, Austria and Florence Nightingale, the English "founder of modern nursing". At that time most people still believed that infections were caused by foul odors called miasmas.
In the 1980s, foodborne outbreaks and healthcare-associated infections led the United States Centers for Disease Control and Prevention to more actively promote hand hygiene as an important way to prevent the spread of infection. The outbreak of swine flu in 2009 and the COVID-19 pandemic in 2020 led to increased awareness in many countries of the importance of washing hands with soap to protect oneself from such infectious diseases. For example, posters with "correct hand washing techniques" were hung up next to hand washing sinks in public toilets and in the toilets of office buildings and airports in Germany.
The phrase "washing one's hands of" something, means declaring one's unwillingness to take responsibility for the thing or share complicity in it. It originates from the bible passage in Matthew where Pontius Pilate washed his hands of the decision to crucify Jesus Christ, but has become a phrase with a much wider usage in some English communities.
In Shakespeare's Macbeth, Lady Macbeth begins to compulsively wash her hands in an attempt to cleanse an imagined stain, representing her guilty conscience regarding crimes she had committed and induced her husband to commit.
It has also been found that people, after having recalled or contemplated unethical acts, tend to wash hands more often than others, and tend to value hand washing equipment more. Furthermore, those who are allowed to wash their hands after such a contemplation are less likely to engage in other "cleansing" compensatory actions, such as volunteering.
Steps and duration[edit]
Poster about when to wash hands to raise awareness about hygiene. This poster can be used to raise awareness on that topic amongst school children.
The United States Centers for Disease Control and Prevention (CDC) recommends the following steps when washing one's hands for the prevention of transmission of disease:
Wet hands with warm or cold running water. Running water is recommended because standing basins may be contaminated, while the temperature of the water does not seem to make a difference, however some experts suggest warm, tepid water may be superior.
Lather hands by rubbing them with a generous amount of soap, including the backs of hands, between fingers, and under nails. Soap lifts pathogens from the skin, and studies show that people tend to wash their hands more thoroughly when soap is used rather than water alone.
Scrub for at least 20 seconds. Scrubbing creates friction, which helps remove pathogens from skin, and scrubbing for longer periods removes more pathogens.
Rinse well under running water. Rinsing in a basin can recontaminate hands.
Dry with a clean towel or allow to air dry. Wet and moist hands are more easily recontaminated.
The most commonly missed areas are the thumb, the wrist, the areas between the fingers, and under fingernails. Artificial nails and chipped nail polish may harbor microorganisms.
When it is recommended[edit]
There are five critical times during the day where washing hands with soap is important to reduce fecal-oral transmission of disease: after using the toilet (for urination, defecation, menstrual hygiene), after cleaning a child's bottom (changing diapers), before feeding a child, before eating and before/after preparing food or handling raw meat, fish, or poultry. Other occasions when correct handwashing technique should be practiced in order to prevent the transmission of disease include before and after treating a cut or wound; after sneezing, coughing, or blowing your nose; after touching animal waste or handling animals; and after touching garbage.
Public health[edit]
Health benefits[edit]
Building a culture of handwashing with children can create a change in culture with widespread public health benefits.
Hand washing has many significant health benefits, including minimizing the spread of influenza, COVID-19, and other infectious diseases; preventing infectious causes of diarrhea; decreasing respiratory infections;
and reducing infant mortality rate at home birth deliveries. A 2013 study showed that improved hand washing practices may lead to small improvements in the length growth in children under five years of age. In developing countries, childhood mortality rates related to respiratory and diarrheal diseases can be reduced by introducing simple behavioral changes, such as hand washing with soap. This simple action can reduce the rate of mortality from these diseases by almost 50%. Interventions that promote hand washing can reduce diarrhoea episodes by about a third, and this is comparable to providing clean water in low income areas. 48% of reductions in diarrhoea episodes can be associated with hand washing with soap.
Handwashing with soap is the single most effective and inexpensive way to prevent diarrhea and acute respiratory infections (ARI), as automatic behavior performed in homes, schools, and communities worldwide. Pneumonia, a major ARI, is the number one cause of mortality among children under five years old, taking the lives of an estimated 1.8 million children per year. Diarrhea and pneumonia together account for almost 3.5 million child deaths annually. According to UNICEF, turning handwashing with soap before eating and after using the toilet into an ingrained habit can save more lives than any single vaccine or medical intervention, cutting deaths from diarrhea by almost half and deaths from acute respiratory infections by one-quarter. Hand washing is usually integrated with other sanitation interventions as part of water, sanitation, and hygiene (WASH) programmes. Hand washing also protects against impetigo which is transmitted through direct physical contact.
Adverse effects[edit]
A small detrimental effect of handwashing is that frequent hand washing can lead to skin damage due to the drying of the skin. A 2012 Danish study found that excessive hand washing can lead to an itchy, flaky skin condition known as contact dermatitis, which is especially common among health-care workers.
Behavior change[edit]
Hand cleaning station at the entrance of the Toronto General Hospital, Canada
In many countries, there is a low rate of hand washing with soap. A study of hand washing in 54 countries in 2015 found that on average, 38.7% of households practiced hand washing with soap.
A 2014 study showed that Saudi Arabia had the highest rate of 97%; the United States near the middle with 77%; and China with the lowest rate of 23%.
Several behavior change methodologies now exist to increase uptake of the behavior of hand washing with soap at the critical times.
Group hand washing for school children at set times of the day is one option in developing countries to engrain hand washing in children's behaviors. The "Essential Health Care Program" implemented by the Department of Education in the Philippines is an example of at scale action to promote children's health and education. Deworming twice a year, supplemented with washing hands daily with soap, brushing teeth daily with fluoride, is at the core of this national program. It has also been successfully implemented in Indonesia.
Substances used[edit]
Soap and detergents[edit]
Removal of microorganisms from skin is enhanced by the addition of soaps or detergents to water. Soap and detergents are surfactants that kill microorganisms by disorganizing their membrane lipid bilayer and denaturing their proteins. It also emulsifies oils, enabling them to be carried away by running water.
Solid soap[edit]
Solid soap, because of its reusable nature, may hold bacteria acquired from previous uses. A small number of studies which have looked at the bacterial transfer from contaminated solid soap have concluded transfer is unlikely as the bacteria are rinsed off with the foam. The CDC still states "liquid soap with hands-free controls for dispensing is preferable".
Antibacterial soap[edit]
Antibacterial soaps have been heavily promoted to a health-conscious public. To date, there is no evidence that using recommended antiseptics or disinfectants selects for antibiotic-resistant organisms in nature. However, antibacterial soaps contain common antibacterial agents such as triclosan, which has an extensive list of resistant strains of organisms. So, even if antibiotic resistant strains are not selected for by antibacterial soaps, they might not be as effective as they are marketed to be. Besides the surfactant and skin-protecting agent, the sophisticated formulations may contain acids (acetic acid, ascorbic acid, lactic acid) as pH regulator, antimicrobially active benzoic acid and further skin conditioners (aloe vera, vitamins, menthol, plant extracts).
A 2007 meta-analysis from the University of Oregon School of Public Health indicated that plain soaps are as effective as consumer-grade anti-bacterial soaps containing triclosan in preventing illness and removing bacteria from the hands. Dissenting, a 2011 meta-analysis in the Journal of Food Protection argued that when properly formulated, triclosan can grant a small but detectable improvement, as can chlorhexidine gluconate, iodophor, or povidone.
Warm water[edit]
Hot water that is still comfortable for washing hands is not hot enough to kill bacteria. Bacteria grow much faster at body temperature (37 °C). WHO considers warm soapy water to be more effective than cold, soapy water at removing natural oils which hold soils and bacteria. But CDC mentions that warm water causes skin irritations more often and its ecological footprint is more significant. Water temperatures from 4 to 40 °C do not differ significantly regarding removal of microbes. The most important factor is proper scrubbing.
Contrary to popular belief, scientific studies have shown that using warm water has no effect on reducing the microbial load on hands. Using hot water for handwashing can even be regarded as a waste of energy.
Antiseptics (hand sanitizer)[edit]
Hand disinfection procedure according to the German standard DIN EN 1500
Main article: Hand sanitizer
In situations where hand washing with soap is not an option (e.g., when in a public place with no access to wash facilities), a waterless hand sanitizer such as an alcohol hand gel can be used. They can be used in addition to hand washing to minimize risks when caring for "at-risk" groups. To be effective, alcohol hand gels should contain not less than 60%v/v alcohol. Enough hand antiseptic or alcohol rub must be used to thoroughly wet or cover both hands. The front and back of both hands and between and the ends of all fingers must be rubbed for approximately 30 seconds until the liquid, foam or gel is dry. Finger tips must be washed well too, rubbing them in both palms.
A hand sanitizer or hand antiseptic is a non-water-based hand hygiene agent. In the late 1990s and early part of the 21st century, alcohol rub non-water-based hand hygiene agents (also known as alcohol-based hand rubs, antiseptic hand rubs, or hand sanitizers) began to gain popularity. Most are based on isopropyl alcohol or ethanol formulated together with a thickening agent such as Carbomer (polymer of acrylic acid) into a gel, or a humectant such as glycerin into a liquid, or foam for ease of use and to decrease the drying effect of the alcohol. Adding diluted hydrogen peroxide increases further the antimicrobial activity.
Hand sanitizers are most effective against bacteria and less effective against some viruses. Alcohol-based hand sanitizers are almost entirely ineffective against norovirus (or Norwalk) type viruses, the most common cause of contagious gastroenteritis.
US Centers for Disease Control and Prevention recommend hand washing with soap over hand sanitizer rubs, particularly when hands are visibly dirty. The increasing use of these agents is based on their ease of use and rapid killing activity against micro-organisms; however, they should not serve as a replacement for proper hand washing unless soap and water are unavailable. Despite their effectiveness, non-water agents do not cleanse the hands of organic material, but simply disinfect them. It is for this reason that hand sanitizers are not as effective as soap and water at preventing the spread of many pathogens, since the pathogens remain on the hands.
Wipes[edit]
Hand washing using hand sanitizing wipes is an alternative during traveling in the absence of soap and water. Alcohol-based hand sanitizer should contain at least 60% alcohol.
Ash or mud[edit]
Many people in low-income communities cannot afford soap and use ash or soil instead. The World Health Organization recommended ash or sand as an alternative to soap when soap is not available. Use of ash is common in rural areas of developing countries and has in experiments been shown at least as effective as soap for removing pathogens. However, evidence to support the use of ash to wash hands is of poor quality. It is not clear if washing hands with ash is effective at reducing viral or bacterial spreading compared to washing with mud, not washing, or with washing with water alone. One concern is that if the soil or ash is contaminated with microorganisms it may increase the spread of disease rather than decrease it, however, there is also no clear evidence to determine the level of risk. Like soap, ash is also a disinfecting agent because in contact with water, it forms an alkaline solution.
Technologies and design aspects[edit]
Low-cost options when water is scarce[edit]
A school girl using a Veronica Bucket in Ghana for handwashing
Various low-cost options can be made to facilitate hand washing where tap-water and/or soap is not available e.g. pouring water from a hanging jerrycan or gourd with suitable holes and/or using ash if needed in developing countries.
In situations with limited water supply (such as schools or rural areas in developing countries), there are water-conserving solutions, such as "tippy-taps" and other low-cost options. A tippy-tap is a simple technology using a jug suspended by a rope, and a foot-operated lever to pour a small amount of water over the hands and a bar of soap.
Low-cost hand washing technologies for households may differ from facilities for multiple users. For households, options include tippy taps, bucket/container with tap (such as a Veronica Bucket), conventional tap with/without basin, valve/tap fitted to bottles, bucket and cup, camp sink. Options for multiple users include: adapting household technologies for multiple users, water container fitted to a pipe with multiple taps, water container fitted to a pipe with holes.
Advanced technologies[edit]
Several companies around the globe have developed technologies that aim to improve the hand washing process. Among the different inventions, there are eco-friendly devices that use 90% less
water and 60% less soap compared to hand washing under a faucet. Another device uses
light-based rays to detect contaminants on the hands after they have been washed.
Certain environments are especially sensitive to the transmission of pathogenic microorganisms, like health care and food production. Organizations attempting to prevent infection transmission in these environments have started using programmed washing cycles that provide sufficient time for scrubbing the hands with soap and rinsing them with water. Combined with AI-powered software, these technological advancements turn the hand-washing process into digital data, allowing individuals to receive insights and improve their hand hygiene practices.
A nurse uses a smart hand washing device.
Drying with towels or hand driers[edit]
Further information: Hand dryer
Effective drying of the hands is an essential part of the hand hygiene process. Therefore, the proper drying of hands after washing should be an integral part of the hand hygiene process in health care.
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) are clear and straightforward concerning hand hygiene, and recommend paper towels and hand dryers equally. Both have stressed the importance of frequent and thorough hand washing followed by their complete drying as a means to stop the spread of pathogens, like COVID-19. Specifically, the World Health Organization recommends that everyone "frequently clean [their] hands..." and "dry [them] thoroughly by using paper towels or a warm air dryer." The CDC report that, "Both [clean towels or air hand dryers] are effective ways to dry hands."
A study in 2020 found that hand dryers and paper towels were both found to be equally hygienic hand-drying solutions.
However, there is some debate over the most effective form of drying in public toilets. A growing volume of research suggests paper towels are much more hygienic than the electric hand dryers found in many public toilets. A review in 2012 concluded that "From a hygiene standpoint, paper towels are superior to air dryers; therefore, paper towels should be recommended for use in locations in which hygiene is paramount, such as hospitals and clinics."
Jet-air dryers were found to be capable of blowing micro-organisms from the hands and the unit and potentially contaminating other users and the environment up to 2 metres (6.6 feet) away. In the same study in 2008 (sponsored by the paper-towel industry the European Tissue Symposium), use of a warm-air hand dryer spread micro-organisms only up to 0.25 metres (0.82 feet) from the dryer, and paper towels showed no significant spread of micro-organisms. No studies have found a correlation to hand dryers and human health, however, making these findings inconsequential.
Accessibility[edit]
A community handwashing facility in Rwanda with sinks for people of different heights. During the COVID-19 pandemic in Rwanda handwashing was part of a system of public health measures encouraged to reduce transmission.
Making hand washing facilities accessible (inclusive) to everyone is crucial to maintain hand washing behavior. Considerations for accessibility include age, disability, seasonality (with rains and muddiness), location and more. Important aspects for good accessibility include: Placement of the technology, paths, ramps, steps, type of tap, soap placement.
Medical use[edit]
Medical hand-washing became mandatory long after Hungarian physician Ignaz Semmelweis discovered its effectiveness (in 1846) in preventing disease in a hospital environment. There are electronic devices that provide feedback to remind hospital staff to wash their hands when they forget. One study has found decreased infection rates with their use.
Method[edit]
Medical hand-washing is for a minimum of 15 seconds, using generous amounts of soap and water or gel to lather and rub each part of the hands. Hands should be rubbed together with digits interlocking. If there is debris under fingernails, a bristle brush may be used to remove it. Since pathogens may remain in the water on the hands, it is important to rinse well and wipe dry with a clean towel. After drying, the paper towel should be used to turn off the water (and open any exit door if necessary). This avoids re-contaminating the hands from those surfaces.
The purpose of hand-washing in the health-care setting is to remove pathogenic microorganisms ("germs") and avoid transmitting them. The New England Journal of Medicine reports that a lack of hand-washing remains at unacceptable levels in most medical environments, with large numbers of doctors and nurses routinely forgetting to wash their hands before touching patients, thus transmitting microorganisms. One study showed that proper hand-washing and other simple procedures can decrease the rate of catheter-related bloodstream infections by 66%.
Video demonstration on hand washing
The World Health Organization has published a sheet demonstrating standard hand-washing and hand-rubbing in health-care sectors. The draft guidance of hand hygiene by the organization can also be found at its website for public comment. A relevant review was conducted by Whitby et al. Commercial devices can measure and validate hand hygiene, if demonstration of regulatory compliance is required.
The World Health Organization has "Five Moments" for washing hands:
before patient care
after environmental contact
after exposure to blood/body fluids
before an aseptic task, and
after patient care.
The addition of antiseptic chemicals to soap ("medicated" or "antimicrobial" soaps) confers killing action to a hand-washing agent. Such killing action may be desired before performing surgery or in settings in which antibiotic-resistant organisms are highly prevalent.
To 'scrub' one's hands for a surgical operation, it is necessary to have a tap that can be turned on and off without touching it with the hands, some chlorhexidine or iodine wash, sterile towels for drying the hands after washing, and a sterile brush for scrubbing and another sterile instrument for cleaning under the fingernails. All jewelry should be removed. This procedure requires washing the hands and forearms up to the elbow, usually 2–6 minutes. Long scrub-times (10 minutes) are not necessary. When rinsing, water on the forearms must be prevented from running back to the hands. After hand-washing is completed, the hands are dried with a sterile cloth and a surgical gown is donned.
Further information: Jewelry hygiene
Effectiveness in healthcare settings[edit]
Microbial growth on a cultivation plate without procedures (A), after washing hands with soap (B) and after disinfection with alcohol (C)
To reduce the spread of pathogens, it is better to wash the hands or use a hand antiseptic before and after tending to a sick person.
For control of staphylococcal infections in hospitals, it has been found that the greatest benefit from hand-cleansing came from the first 20% of washing, and that very little additional benefit was gained when hand cleansing frequency was increased beyond 35%. Washing with plain soap results in more than triple the rate of bacterial infectious disease transmitted to food as compared to washing with antibacterial soap.
Comparing hand-rubbing with alcohol-based solution with hand washing with antibacterial soap for a median time of 30 seconds each showed that the alcohol hand-rubbing reduced bacterial contamination 26% more than the antibacterial soap. But soap and water is more effective than alcohol-based hand rubs for reducing H1N1 influenza A virus and Clostridium difficile spores from hands.
Interventions to improve hand hygiene in healthcare settings can involve education for staff on hand washing, increasing the availability of alcohol-based hand rub, and written and verbal reminders to staff. There is a need for more research into which of these interventions are most effective in different healthcare settings.
Developing countries[edit]
World map for SDG 6 Indicator 6.2.1b in 2017: "Share of the population with basic handwashing facilities on premises"
In developing countries, hand washing with soap is recognized as a cost-effective, essential tool for achieving good health, and even good nutrition. However, a lack of reliable water supply, soap or hand washing facilities in people's homes, at schools and the workplace make it a challenge to achieve universal hand washing behaviors. For example, in most of rural Africa hand washing taps close to every private or public toilet are scarce, even though cheap options exist to build hand washing stations. However, low hand washing rates can also be the result of engrained habits rather than due to a lack of soap or water.
Hand washing at a global level has its own indicator within Sustainable Development Goal 6, Target 6.2 which states "By 2030, achieve access to adequate and equitable sanitation and hygiene for all and end open defecation, paying special attention to the needs of women and girls and those in vulnerable situations. The corresponding Indicator 6.2.1 is formulated as follows: "Proportion of population using (a) safely managed sanitation services and (b) a hand-washing facility with soap and water" (see map to the right with data worldwide from 2017)."
Promotion campaigns[edit]
The promotion and advocacy of hand washing with soap can influence policy decisions, raise awareness about the benefits of hand washing and lead to long-term behavior change of the population. For this to work effectively, monitoring and evaluation are necessary. A systematic review of 70 studies found that community-based approaches are effective at increasing hand washing in LMICs, while social marketing campaigns are less effective.
Poster used in Africa for raising awareness about hand washing after using the toilet with simple low-cost hand washing device
One example for hand washing promotion in schools is the "Three Star Approach" by UNICEF that encourages schools to take simple, inexpensive steps to ensure that students wash their hands with soap, among other hygienic requirements. When minimum standards are achieved, schools can move from one to ultimately three stars. Building hand washing stations can be a part of hand washing promotion campaigns that are carried out to reduce diseases and child mortality.
Global Handwashing Day is another example of an awareness-raising campaign that is trying to achieve behavior change.
As a result of the ongoing COVID-19 pandemic, UNICEF promoted the adoption of a hand washing emoji.
Designing hand washing facilities that encourage use can use the following aspects:
Nudges, cues and reminders
Hand washing facilities should be placed at convenient locations to encourage people to use them regularly and at the right times; they should be attractive and well maintained.
Cost effectiveness[edit]
Hand washing stands at a school in Mysore district, Karnataka, India
Few studies have considered the overall cost effectiveness of hand washing in developing countries in relationship to DALYs averted. However, one review suggests that promoting hand washing with soap is significantly more cost-effective than other water and sanitation interventions.
Cost-Effectiveness of Water Supply, Sanitation and Hygiene Promotion
Intervention
Costs (US$/DALY)
Hand-pump or standpost
94
House water connection
223
Water sector regulation
47
Basic sanitation – construction and promotion
≤270
Sanitation promotion only
11.2
Hygiene promotion
3.4
History[edit]
Further information: Ignaz Semmelweis
Electronic sign inside a Washington Metro station during the COVID-19 pandemic
The importance of hand washing for human health – particularly for people in vulnerable circumstances like mothers who had just given birth or wounded soldiers in hospitals – was first recognized in the mid 19th century by two pioneers of hand hygiene: the Hungarian physician Ignaz Semmelweis who worked in Vienna, Austria and Florence Nightingale, the English "founder of modern nursing". At that time most people still believed that infections were caused by foul odors called miasmas.
In the 1980s, foodborne outbreaks and healthcare-associated infections led the United States Centers for Disease Control and Prevention to more actively promote hand hygiene as an important way to prevent the spread of infection. The outbreak of swine flu in 2009 and the COVID-19 pandemic in 2020 led to increased awareness in many countries of the importance of washing hands with soap to protect oneself from such infectious diseases. For example, posters with "correct hand washing techniques" were hung up next to hand washing sinks in public toilets and in the toilets of office buildings and airports in Germany.
Society and culture[edit]
Moral aspects[edit]
The phrase "washing one's hands of" something, means declaring one's unwillingness to take responsibility for the thing or share complicity in it. It originates from the bible passage in Matthew where Pontius Pilate washed his hands of the decision to crucify Jesus Christ, but has become a phrase with a much wider usage in some English communities.
In Shakespeare's Macbeth, Lady Macbeth begins to compulsively wash her hands in an attempt to cleanse an imagined stain, representing her guilty conscience regarding crimes she had committed and induced her husband to commit.
It has also been found that people, after having recalled or contemplated unethical acts, tend to wash hands more often than others, and tend to value hand washing equipment more. Furthermore, those who are allowed to wash their hands after such a contemplation are less likely to engage in other "cleansing" compensatory actions, such as volunteering.
See also[edit]
Viruses portal
Antibiotic resistance
Didier Pittet, an infectious diseases expert
Food safety
Bactericide
Global Handwashing Day
Nosocomial infection
Occupational biosafety
Public health
Patient safety
Rubbing alcohol
Virucide | biology | 721753 | https://sv.wikipedia.org/wiki/Handhygien | Handhygien | Att tvätta händerna eller två sina händer innebär att rengöra händerna, ofta med tvål och vatten eller på annat sätt med motsvarande verkan. Syftet med handtvätten är att avlägsna jord, smuts och mikroorganismer, och på så sätt hålla god handhygien. Allmän handhygien förhindrar eller minimerar sjukdomar och spridning av sjukdomar.
Syfte
För att minimera smittspridning är det viktigt att både vuxna och barn alltid tvättar händerna efter toalettbesök, efter utomhusvistelse, innan hantering av livsmedel och före måltid. Det främsta medicinska syftet med handtvättning är att rengöra händerna från smittämnen (inklusive bakterier och virus) och kemikalier som kan orsaka personlig skada eller sjukdom. Människor kan till exempel smittas med luftvägssjukdomar som influensa eller förkylning, om de inte tvättar händerna innan de rör ögonen, näsan eller munnen. Centers for Disease Control and Prevention (CDC) hävdar: "Det är väldokumenterat att en av de viktigaste åtgärderna för att förhindra spridning av smittämnen är effektiv handtvättning". Handtvättning skyddar bäst mot sjukdomar som överförs genom fekal-orala vägar (som många former av magsjuka) och direkt fysisk kontakt (till exempel svinkoppor), men minskar också risken för spridning via droppsmitta. Alkoholgeler kan användas som komplement till handtvätt som ett sätt att döda vissa typer av smittämnen.
Historik
Handtvättning i sjukvården introducerades av den ungerske läkaren Ignaz Semmelweis, som på 1840-talet upptäckte och dokumenterade statistiskt att detta drastiskt kunde minska dödligheten i barnsängsfeber. Vid denna tid var bakterieteorin ännu inte känd, och det dröjde ytterligare några decennier innan Semmelweiss rön och råd blev mer allmänt accepterade.
Utförande
För att handtvättningen ska ha fullgod rengörande effekt och minimera smittspridning är det viktigt att tvättningen utförs noggrant. Avlägsna först eventuella smycken. Vid tvätt med tvål och vatten sköljs händerna först enbart i rinnande vatten. Sedan tvålas hela händerna in (alla fingrarna, handflatorna, ovansidan av händerna, mellan fingrarna, naglarna och handlederna) ordentligt med tvål i minst 15–20 sekunder. Vårdguiden rekommenderar omkring 30 sekunder. En rekommenderad metod för att hålla ordning på tiden är att nynna en sång med samma längd. Sedan sköljs händerna ordentligt i vatten så att skummet avlägsnas. Ett annat viktigt moment är att torka händerna helt torra efteråt och att eventuell handduk som används är ren. Helst bör alla personer använda en separat handduk. En textilhandduk behöver bytas ut och tvättas regelbundet. När många är sjuka rekommenderas engångshanddukar istället. Om handsprit används sker det vanligen efter den vanliga handtvättningen med tvål och vatten. Den kan även användas utan tvätt med tvål och vatten, men vissa virus är resistenta mot handsprit.
Ämnen som används och effekt
Vatten
Fingervarmt vatten är inte tillräckligt hett för att döda bakterier. Tvålvatten är mer effektivt för att ta bort de naturliga oljorna på händerna som innehåller smuts och bakterier. Fram till 2016 rekommenderades allmänt att tvätta händerna i fingervarmt (37,8 grader Celsius eller 100 grader Fahrenheit) vatten, men 2017 visade omfattande forskning från Rutgers-New Brunswick att lägre vattentemperatur inte avlägsnade färre bakterier. Svenska Folkhälsomyndigheten har däremot kvar sin rekommendation om varmt vatten.
Tvål och rengöringsmedel
Bara vatten är ineffektivt för att rengöra huden. Därför kräver avlägsnandet av mikroorganismer tvål eller rengöringsmedel i kombination med vatten. Antingen fast eller flytande tvål kan användas beroende på vilken man föredrar. Tvålen tar bort fett, oljor och proteiner som finns i organisk smuts.
Handsprit
Korrekt handtvättning med tvål och vatten ger i de flesta fall bra effekt både vad gäller avlägsnande av smuts och minskad smittspridning. Desinfektionssprit, så kallad handsprit, brukar främst rekommenderas till särskilt bakteriekänsliga eller bakterieutsatta miljöer där händerna tvättas ofta, exempelvis sjukhus och förskolor. Handsprit kan även användas när möjligheter till handtvätt är begränsade. Det finns dock virus som är resistenta mot handspriten, exempelvis sådana som sprider vinterkräksjuka.
Återfuktning av händer
Det finns handtvål som återfuktar händerna och vid högfrekvent handtvättning kan handsprit ibland motverka torra händer, men främst används handkräm för ändamålet, särskilt för personer med torra händer.
Symbolisk handtvagning
Handtvagning i religiösa sammanhang förstås som en symbol för själens rening liksom är fallet med all rituell tvagning i alla religioner. I den kristna gudstjänsten, mässan, förekommer rituell handtvagning, lavabo, som en del av offertoriet, då prästen tillreder nattvardsgåvorna.
Två sina händer är ett begrepp som betyder att man fritager sig från ansvar, efter Nya testamentet (Matt. 27:24), där det omtalas hur Pilatus "lät han hämta vatten och tvådde sina händer i folkets åsyn" för att symboliskt framhålla att han var "oskyldig till denne mans blod".
Se även
Fottvagning
Internationella handtvättsdagen
Referenser
Noter
Vidare läsning
Tvagning | swedish | 0.617499 |
hot_water_bacteria/49833116TheEffectofH.txt |
ArticlePDF Available
The Effect of Handwashing with Water or Soap on Bacterial Contamination of Hands
MDPI
December 2011International Journal of Environmental Research and Public Health (IJERPH) 8(1):97-104
DOI:10.3390/ijerph8010097
SourcePubMed
LicenseCC BY 3.0
Authors:
Maxine Burton
Emma Cobb
Peter Donachie
Gaby Judah
Imperial College London
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Citations (315)
References (22)
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Abstract and Figures
Handwashing is thought to be effective for the prevention of transmission of diarrhoea pathogens. However it is not conclusive that handwashing with soap is more effective at reducing contamination with bacteria associated with diarrhoea than using water only. In this study 20 volunteers contaminated their hands deliberately by touching door handles and railings in public spaces. They were then allocated at random to (1) handwashing with water, (2) handwashing with non-antibacterial soap and (3) no handwashing. Each volunteer underwent this procedure 24 times, yielding 480 samples overall. Bacteria of potential faecal origin (mostly Enterococcus and Enterobacter spp.) were found after no handwashing in 44% of samples. Handwashing with water alone reduced the presence of bacteria to 23% (p < 0.001). Handwashing with plain soap and water reduced the presence of bacteria to 8% (comparison of both handwashing arms: p < 0.001). The effect did not appear to depend on the bacteria species. Handwashing with non-antibacterial soap and water is more effective for the removal of bacteria of potential faecal origin from hands than handwashing with water alone and should therefore be more useful for the prevention of transmission of diarrhoeal diseases.
Effect of handwashing with water alone or soap and water compared to no handwashing. P-values derived from logistic regression adjusted for within-person correlation, except * where p-value was derived from Fishers exact test ignoring within-person correlation. The design effect due to within-person clustering was low (around 1.2–1.3). Note different y-axis scales in top vs. bottom panels.
Effect of handwashing with water alone or soap and water compared to no handwashing. P-values derived from logistic regression adjusted for within-person correlation, except * where p-value was derived from Fishers exact test ignoring within-person correlation. The design effect due to within-person clustering was low (around 1.2–1.3). Note different y-axis scales in top vs. bottom panels.
…
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Int. J. Environ. Res. Public Health 2011, 8, 97-104; doi:10.3390/ijerph8010097 International Journal of Environmental Research and Public Health ISSN 1660-4601 www.mdpi.com/journal/ijerph Article The Effect of Handwashing with Water or Soap on Bacterial Contamination of Hands Maxine Burton, Emma Cobb, Peter Donachie, Gaby Judah, Val Curtis and Wolf-Peter Schmidt * Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK; E-Mails: [email protected] (M.B.); [email protected] (E.C.); [email protected] (P.D.); [email protected] (G.J.); [email protected] (V.C.) * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +44-20-7927-2461; Fax: +44-20-7636-7843. Received: 24 November 2010; in revised form: 30 December 2010 / Accepted: 31 December 2010 / Published: 6 January 2011 Abstract: Handwashing is thought to be effective for the prevention of transmission of diarrhoea pathogens. However it is not conclusive that handwashing with soap is more effective at reducing contamination with bacteria associated with diarrhoea than using water only. In this study 20 volunteers contaminated their hands deliberately by touching door handles and railings in public spaces. They were then allocated at random to (1) handwashing with water, (2) handwashing with non-antibacterial soap and (3) no handwashing. Each volunteer underwent this procedure 24 times, yielding 480 samples overall. Bacteria of potential faecal origin (mostly Enterococcus and Enterobacter spp.) were found after no handwashing in 44% of samples. Handwashing with water alone reduced the presence of bacteria to 23% (p < 0.001). Handwashing with plain soap and water reduced the presence of bacteria to 8% (comparison of both handwashing arms: p < 0.001). The effect did not appear to depend on the bacteria species. Handwashing with non-antibacterial soap and water is more effective for the removal of bacteria of potential faecal origin from hands than handwashing with water alone and should therefore be more useful for the prevention of transmission of diarrhoeal diseases. Keywords: hygiene; trial; infection OPEN ACCESS
Citations (315)
References (22)
... Thus, hands serve as the vehicle of infectious disease transmission, especially amongst people living and working in close proximity to one another, such as dormitories, classrooms, camps etc. Close environments, doorknobs and other inanimate objects serving as resting vehicles of transmission all contribute to increased infection rates among these groups [14]. Human hands usually constitute microorganisms both as part of the body's normal flora and transient microorganisms contracted from the environment [15]. Although it is nearly impossible for the hands to be free of microorganisms and usually harbour microorganisms both as residents and transients, the presence and transfer of pathogenic microorganisms could occur between people who access the same areas or surfaces may lead to chronic or acute illnesses [15,16]. ...
... Human hands usually constitute microorganisms both as part of the body's normal flora and transient microorganisms contracted from the environment [15]. Although it is nearly impossible for the hands to be free of microorganisms and usually harbour microorganisms both as residents and transients, the presence and transfer of pathogenic microorganisms could occur between people who access the same areas or surfaces may lead to chronic or acute illnesses [15,16]. Therefore, the study aimed to investigate the microorganisms isolated from the hands of students of the Federal University of Lafia, Nasarawa State, Nigeria. ...
... Additionally, these microorganisms, being opportunistic human pathogens, pose implications for food safety, particularly in the case of enterotoxin-producing strains of staphylococci linked to food poisoning [27]. Bacillus spp, known for bearing resistant spores, was also prevalent and has implications for human pathogenesis and food spoilage [15]. The presence of Klebsiella spp, Escherichia coli, Salmonella spp, and Enterococcus faecalis might suggest compromised personal and domestic hygiene, especially concerning hand contamination after restroom visits, thereby potentially predisposing individuals to diseases [15]. ...
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... It has been mentioned transmission of bacteria occur from the handler by direct contact with the fresh produce without proper hand washing [75]. Research found approximately 44 % of the bacteria presence from bare-handed without hand washing and shows hand washing able to reduce around 23 % of the bacteria by hand washing with water alone [87]. Besides that, the preparation of fresh produce from cultivating, harvesting, and within marketplaces also can lead to biological contamination even at the last stages in the kitchen of the consumer [88]. ...
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| biology | 1385201 | https://no.wikipedia.org/wiki/Hydrophilus | Hydrophilus | Hydrophilus er en slekt av biller som hører til familien vannkjær (Hydrophilidae).
Utseende
Store (gjerne 4-5 centimeter), avlangt ovale, svarte biller. De er blant de største billene i Europa. Antennene er korte og klubbeformede, palpene noe lengre enn antennene, kraftige. Dekkvingene er uten punktrader. Beina er forholdsvis lange, med hårfrynser som er til hjelp ved svømmingen.
Hos hannene er forføttene utvidete.
Levevis
Hydrophilus-artene lever i vegetasjonsrike ferskvann. De voksne billene er forholdsvis trege svømmere, ulikt de store vannkalv-artene som de overflatisk kan ligne noen på. De har et variert kosthold, men spiser mye plantemateriale og alger. Disse billene puster ved hjelp av et plastron, en tynn hinne av luft som sitter fast på billenes hårete underside. De tar opp luft i overgangen mellom pronotum og dekkvingene.
Systematisk inndeling
Artslisten følger og
Ordenen biller, Coleoptera
Underordenen Polyphaga
Overfamilien vannkjær, Hydrophiloidea
Familien vannkjær, Hydrophilidae
Underfamilien vannkjær, Hydrophilinae
Stamme vannkjær, Hydrophilini
Slekten Hydrophilus Geoffroy, 1762
Underslekten Hydrophilus (i snever forstand)
Hydrophilus acuminatus Motschulsky, 1854
Hydrophilus aterrimus Eschscholtz, 1822
Hydrophilus bilineatus (MacLeay, 1825)
Hydrophilus cavisternum (Bedel, 1891)
Hydrophilus dauricus Mannerheim, 1852
Hydrophilus hastatus (Herbst, 1779)
Hydrophilus indicus (Bedel, 1891)
Hydrophilus mesopotamiae Kniž, 1914
Hydrophilus olivaceus Fabricius, 1781
Hydrophilus piceus (Linnaeus, 1758) - funnet noen få steder i Sørøst-Norge
Hydrophilus pistaceus Laporte, 1840
Hydrophilus rufocinctus (Bedel, 1891)
Hydrophilus senegalensis (Percheron, 1835)
Hydrophilus sternitalis Reitter, 1906
Underslekten Temnopterus Solier, 1834
Hydrophilus aculeatus (Solier, 1834)
Referanser
Kilder
Hansen, M. 1987. The Hydrophiloidea (Coleoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica 18. E.J. Brill/Scandinavian Science Press Ltd.
Eksterne lenker
Vannkjær
Biller formelt beskrevet i 1762
Dyr formelt beskrevet av Étienne Louis Geoffroy | norwegian_bokmål | 1.048432 |
hot_water_bacteria/PMC3037063.txt | Skip to main content
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Int J Environ Res Public Health. 2011 Jan; 8(1): 97–104.
Published online 2011 Jan 6. doi: 10.3390/ijerph8010097
PMCID: PMC3037063
PMID: 21318017
The Effect of Handwashing with Water or Soap on Bacterial Contamination of Hands
Maxine Burton, Emma Cobb, Peter Donachie, Gaby Judah, Val Curtis, and Wolf-Peter Schmidt*
Author information Article notes Copyright and License information PMC Disclaimer
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Abstract
Handwashing is thought to be effective for the prevention of transmission of diarrhoea pathogens. However it is not conclusive that handwashing with soap is more effective at reducing contamination with bacteria associated with diarrhoea than using water only. In this study 20 volunteers contaminated their hands deliberately by touching door handles and railings in public spaces. They were then allocated at random to (1) handwashing with water, (2) handwashing with non-antibacterial soap and (3) no handwashing. Each volunteer underwent this procedure 24 times, yielding 480 samples overall. Bacteria of potential faecal origin (mostly Enterococcus and Enterobacter spp.) were found after no handwashing in 44% of samples. Handwashing with water alone reduced the presence of bacteria to 23% (p < 0.001). Handwashing with plain soap and water reduced the presence of bacteria to 8% (comparison of both handwashing arms: p < 0.001). The effect did not appear to depend on the bacteria species. Handwashing with non-antibacterial soap and water is more effective for the removal of bacteria of potential faecal origin from hands than handwashing with water alone and should therefore be more useful for the prevention of transmission of diarrhoeal diseases.
Keywords: hygiene, trial, infection
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1. Introduction
Diarrhoeal diseases are one of the leading causes of child death around the world [1]. The World Health Organisation (WHO) recognises the spread of diarrhoeal diseases as a serious global problem [2] and estimates that each year, there are more than 2.2 million lives lost due to these infections, more than from malaria, HIV/AIDS and measles combined [1]. The majority of these deaths are in children under 5 years of age [3]. It has been suggested that handwashing may substantially reduce the risk of diarrhoeal diseases [4].
Promotion of improved hand hygiene has been recognised as an important public health measure but it is unclear how much hand hygiene is required to interrupt transmission of diarrhoea pathogens. In particular it has not been conclusively shown whether use of soap is essential to remove pathogens from hands. Recent hygiene promotion campaigns especially in low income settings have not been unanimous in recommending soap use [4].
A number of studies have compared different hand hygiene methods in hospital settings [5]. In contrast, few studies have been published on the effect of hand hygiene on bacterial contamination of hands in the community. Hoque and colleagues found that a wide variety of hand cleansing means in poor settings (soap, ash, mud) are effective in reducing the contamination with coliform bacteria on hands [6,7]. In a small randomised trial the same author reported that soap may be more effective than water in reducing the presence of coliform bacteria on hands [6].
Luby and colleagues found that a simple microbiological method with three fingers directly imprinting a MacConkey agar for thermotolerant coliforms was unable to distinguish between households who were given soap during a large randomized handwashing trial and control households [8]. They concluded that the method was unsuitable for the evaluation of handwashing practices. However, the lack of difference in bacterial contamination may have been due to lack of compliance with the intervention. We thought that a proof-of-principle trial was needed where participants would be given specific tasks to contaminate their hands in a naturalistic setting and where handwashing was done under supervision.
We conducted a randomised controlled trial to determine whether non-antibacterial soap is better at reducing bacteria of potential faecal origin than water only. A further goal was to clarify whether a simple microbiological test that can be applied to large groups in a relatively short time [9,10] would be able to distinguish people who practice handwashing from those who don’t.
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2. Experimental Section
This study was carried out between July and August 2009. Overall, 20 volunteers were taken to a large, frequently visited British museum, or asked to travel on a bus or the underground. They were asked to deliberately wipe their hands over hand contact surfaces such as handrails, door handles and seats with the aim of contaminating their hands with whatever bacteria were present. Using a pre-determined random sequence, not known to the participants during self-contamination, participants were then asked to wash their hands with soap, to use water only or not to wash at all. Each volunteer underwent this sequence 24 times, 8 times for each of the three hand hygiene approaches (soap, water, no handwash). Participants assigned to handwashing were asked to wash their hands as they would normally do, without instructions on length of time or thoroughness. The volunteers allocated to handwashing were then provided with a paper towel to dry their hands. A wet NaCl-soaked charcoal swab was then wiped across the fingers of the dominant hand of the participant. The participants were finally given an alcohol gel to clean their hands (78% total alcohol content, Ethanol 71% / Propanol 29%, Softalind Viscorub, Braun-Melsungen). The swabs were returned to the laboratory within 5 hours of being taken. In total, 480 samples were collected; 160 after handwashing with plain soap, 160 after handwashing with water alone and 160 with no handwashing. During the experimental phase we measured the amount of time taken to conduct handwashing with and without soap, once for each volunteer.
Upon arrival at the laboratory the swabs were immediately cut into a universal tube containing 10 mL of Purple MacConkey broth using aseptic techniques. The swabs were incubated at 35 °C for 48 hours. All samples were then streaked onto the MacConkey agar No.3 and Bile Aesculin agar. MacConkey agar No. 3 is a selective media which can differentiate between coliforms and non-lactose fermenters, whilst inhibiting gram-positive cocci. These plates were incubated for 18–24 hours at 35 °C. For all other colonies produced on MacConkey agar No. 3 and those which were spot indole negative, a gram stain, catalase and oxidase test was carried out followed by an API 20E biochemical test to determine the identity of the bacteria. Bile Aesculin agar is a differential medium for the isolation of Enterococcus spp. and group D Streptococcus and inhibition of other gram positive bacteria. These plates were incubated at 37 °C for 18–24 hours. Enterococcus and Group D Streptococcus spp. are able to hydrolyse the aesculin to form aesculetin, producing a brown/black complex. Any white colonies on Bile Aesculin agar were presumed to be Staphylococcus spp. and any black colonies were tested with Lancefield group D antisera. Agglutination indicated a positive result for Enterococcus spp.
The prevalence of bacterial contamination in the three study arms (soap, water, no handwash) was compared using logistic regression. Since the same volunteers repeatedly underwent testing, within-subject correlation was accounted for by the use of generalised estimating equations (GEE) with robust standard errors. If the cell numbers were too low for conducting regression analysis, Fishers exact test was used instead, ignoring clustering (the design effect was found to be low, see results).
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3. Results and Discussion
Table 1 shows the different organisms isolated in the three study arms. Enterococcus spp. were the most common bacteria found, followed by Enterobacter spp. Figure 1 shows the effect of handwashing with soap or water only on contamination, compared to no handwashing. Overall, handwashing with water alone reduced the prevalence of bacteria substantially. Handwashing with soap was more effective in reducing the prevalence of contamination and specifically of Enterococcus spp. There was a trend that handwashing with soap was also more effective in reducing the prevalence of other species and of multiple isolates, but the statistical support was low (Figure 1).
An external file that holds a picture, illustration, etc.
Object name is ijerph-08-00097f1.jpg
Figure 1
Effect of handwashing with water alone or soap and water compared to no handwashing. P-values derived from logistic regression adjusted for within-person correlation, except * where p-value was derived from Fishers exact test ignoring within-person correlation. The design effect due to within-person clustering was low (around 1.2–1.3). Note different y-axis scales in top vs. bottom panels.
Table 1
Organisms found after self-contamination of hands, and handwashing with either soap, water only, or no handwashing.
Faecal Bacteria No Handwashing Water only Soap and water
Enterococcus spp. 46 (29%) 24 (15%) 4 (3%)
Enterobacter amnigenus 14 (9%) 4 (3%) 4 (3%)
Enterobacter cloacae 13 (8%) 5 (3%) 2 (1%)
Shigella spp. 2 (1%) 1 (1%) 0 (0%)
Klebsiella spp. 5 (3%) 2 (1%) 1 (1%)
E. coli spp. 0 (0%) 0 (0%) 1 (1%)
Pantoea spp. 0 (0%) 2 (1%) 1 (1%)
Multiple isolations 10 (6%) 2 (1%) 0 (0%)
Any bacteria 70 (44%) 36 (23%) 13 (8%)
Total 160 (100%) 160 (100%) 160 (100%)
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The effect of repeated measurements in the same individual was low: the design effect (the factor by which a sample size needs to be increased to achieve the same statistical power as an unclustered study) ranged from 1.2 to 1.3 (depending on the comparison group).
Participants were asked to wash their hands as long and as thorough as they would normally do. The length of time required to carry out handwashing was measured once for each method in all volunteers. Participants took on average 12 seconds (standard deviation 2.8) to wash their hands with water alone, and 14 seconds (standard deviation 2.3) to wash their hands with water and soap (p = 0.02).
Thus, handwashing with soap took them only slightly longer than handwashing with water alone. It seems unlikely that this small difference can explain the large difference in the removal of bacteria. Soap on its own appears to have an effect on the removal of bacteria of potential faecal origin, independent of the possibility that soap use may cause people to wash their hands longer.
Unlike the study by Hoque and colleagues our trial was conducted in an experimental (albeit naturalistic) setting, where volunteers deliberately contaminated their hands. Additional testing showed that this approach increased the prevalence of contamination from around 10% to over 40% of individuals. It also improved control over the conduct of the experiment, but may affect generalisability, as the study primarily aimed at providing a proof of principle. However, we believe that the superior effect of soap on the removal of bacteria compared to water alone as the principal finding of our study is unlikely to depend on the setting.
Not all of the bacteria isolated in our study are known to cause disease in humans. Surprisingly, we found few E. coli on hands which may be due to their short survival time in the environment. Overall, the effect of soap appeared to be independent of the type of bacteria (Figure 1), a view which is supported by the study by Hoque and colleagues who found a similar effect of hand hygiene on unspecified faecal coliform bacteria [6]. However, the power of our study to detect differences between species was low.
We used plain non-antibacterial soap for the experiment. Future studies could address whether antibacterial soap is more effective in removing pathogens from hands. However, Luby and colleagues conducted a large double-blind randomised trial in Pakistan and found antibacterial soap no more effective in reducing diarrhoea than normal soap [11]. It is still not clear whether or in what circumstances anti-bacterial soaps offer a health advantage [12].
The bacteriological methods used in this study provide no quantification of bacterial load, unlike a study by Hoque and colleagues [7]. Quantifying the effect of different hand washing procedures on bacterial load may be particularly helpful for studies in poor settings with poor sanitation facilities, where the environmental contamination with faecal organisms is much higher [13–15]. We also tested a semi-quantitative finger-print method used previously in Thailand [15] not unsimilar to the method used by Luby and colleagues [8] but found that contamination levels were too low to provide consistent results. Therefore we decided to use a qualitative method.
It seems reasonable to assume that handwashing with soap is also more effective in reducing bacterial load compared to water alone. Future studies could address the effect of different hand hygiene procedures on removing gastro-intestinal or respiratory viruses such as influenza A. Hands have been implicated especially in the spread of Norovirus [16]. Viral studies are more difficult to conduct as viruses may not be as present in the environment as often as are bacteria of faecal origin, but they may be possible for example if patients with laboratory confirmed infection are recruited as volunteers. Alternatively, healthy volunteers may experimentally contaminate their hands with cultured viruses before undergoing different hand hygiene regimes, as was done in a recent study on influenza A H1N1 [17]. This study found that handwashing with soap was better at removing influenza A H1N1 than several hand sanitizers. Handwashing with water alone was not tested.
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4. Conclusions
The results demonstrate that handwashing with non-antibacterial soap is much more effective in removing bacteria from hands than handwashing with water only. Although handwashing with water alone reduced the presence of bacteria on hands substantially, the study supports the policy of many current hand hygiene campaigns promoting the use of soap [18,19]. The strong association between hand hygiene method and bacterial contamination of hands found in our study suggests that the prevalence of faecal indicator bacteria may also be used to monitor changes in hygiene behaviour in the general population, for example following hygiene promotion campaigns.
Hygiene behaviour is difficult to measure because people tend to change their behaviour under observation or over-report desired practices [15,20]. We have previously shown that our test kit can be used to study associations between hygiene relevant behaviours and hand contamination [9]. We found that test results positive for bacteria of potential faecal origin were more common in people frequently shaking hands, reporting soil contact or those scoring low on a hygiene score based on self-report [9]. The microbiological method used in this and our earlier studies [9,10] is relatively simple and of low cost (around $3.80). Its suitability for large scale use in the evaluation of handwashing campaigns in low income settings where handwashing should be most beneficial remains to be investigated. A sophisticated laboratory infrastructure may not be required to conduct testing. However, modifying the method to allow semi-quantitative or quantitative analysis may be necessary if contamination rates are high [15].
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References
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| biology | 1773312 | https://sv.wikipedia.org/wiki/Hyphoderma%20microcystidium | Hyphoderma microcystidium | Hyphoderma microcystidium är en svampart som beskrevs av Sheng H. Wu 1990. Hyphoderma microcystidium ingår i släktet Hyphoderma och familjen Meruliaceae. Inga underarter finns listade i Catalogue of Life.
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The handiwork of good health
January 1, 2007
Alcohol-based hand sanitizers are more effective than antibacterial soaps, but don't give up on plain soap and water.
That our hands are crawling with germs is old, old news. Adults have hectored children about the dangers of unwashed hands for generations. Over a century ago, a few pioneering doctors (Holmes, Semmelweis, Lister) figured out that physicians' hands were infecting patients and making many people sick.
What is new, though, is the range of organisms you might find on even a seemingly clean pair of hands.
It's pretty normal to have staph germs living on your skin (and in your nose): About 25%–30% of us are "colonized" with no ill effects — unless the bacteria get into a break in the skin. But a new version is increasingly prevalent: methicillin-resistant Staphylococcus aureus (MRSA), a bacterium that resists not only methicillin but many other antibiotics. MRSA was once almost exclusively found in hospitals. Now outbreaks are occurring at schools, in jails, and among sports teams. Members of the Boston Celtics pro basketball team were infected in the fall of 2006
Clostridium difficile, a bacterium found in feces, is another hospital germ that's flown the health care coop. Hands are often the middleman in the fecal-oral transmission route: C. difficile gets on people's hands when they come in contact with a contaminated surface or object, and they inadvertently infect themselves when their hands touch their mouths.
Our hands are much more hospitable to bacteria than to viruses, but you'll find a few of the latter. Most flu is transmitted through the air in virus-laden droplets propelled by coughs and sneezes. But our hands can pick up those droplets from any number of surfaces, so they're often an important link in the chain of transmission. Hand washing is a standard item on flu-prevention lists, and health officials are putting special emphasis on it now because of the bird flu epidemic.
Americans say they wash their hands. Over 90% of those questioned in a telephone survey said they washed up after using a public bathroom. But when the American Society of Microbiology and a trade association group observed people in public restrooms (in stadiums, train stations, etc.), they found that only 75% of men washed their hands. Women weren't perfect, but at 90%, did better than the men. This Mars-Venus disparity extends to those with medical degrees. In one study, female physicians washed their hands 88% of the time after seeing a patient; their male colleagues did so only 54% of the time.
Overkill overdoes it
There are those, both men and women, who overdo the hand washing. Our hands weren't meant to be sterile objects. Having some bacteria on the skin is perfectly natural, and "resident flora," as the experts call it, is probably healthful — unless you're a surgeon about to put your hands inside someone's body. Frequent hand washing, even with mild soap, can damage skin, worsening cuts and causing cracks that can harbor even more bacteria. Dry, damaged skin may also spread germs more easily because it flakes off, taking bacteria with it.
How often should you wash your hands? There's no set frequency; it really depends on your activities. Must-wash occasions include after using the bathroom, before eating or preparing food, and after being with someone who's ill, particularly if he or she has a respiratory or gastrointestinal infection.
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Lathering up
New products clamor for our attention, but plain old soap and water is still a good way to clean your hands. In studies, washing hands with soap and water for 15 seconds (about the time it takes to sing one chorus of "Happy Birthday to You") reduces bacterial counts by about 90%. When another 15 seconds is added, bacterial counts drop by close to 99.9% (bacterial counts are measured in logarithmic reductions). Few of us wash our hands that long — 5 seconds is more like it. One reason you're supposed to use cool or lukewarm water is to increase the chances you'll wash them a little longer. Hot water is also more damaging to skin.
Soap and water don't kill germs; they work by mechanically removing them from your hands. Running water by itself does a pretty good job of germ removal, but soap increases the overall effectiveness by pulling unwanted material off the skin and into the water. In fact, if your hands are visibly dirty or have food on them, soap and water are more effective than the alcohol-based "hand sanitizers" because the proteins and fats in food tend to reduce alcohol's germ-killing power. This is one of the main reasons soap and water is still favored in the food industry.
Even people who are conscientious about washing their hands make the mistake of not drying them properly. Wet hands are more likely to spread germs than dry ones. It takes about 20 seconds to dry your hands well if you're using paper or cloth towels and 30–45 seconds under an air dryer.
Antibacterial soap
By some accounts, almost half of the hand soaps on the market have an antibacterial additive. Many brands are in liquid form, so they're less messy than a traditional bar of soap, but you can, of course, buy plain soap in liquid form, too.
The active ingredient in most antibacterial soaps is a chemical called triclosan. Triclosan in the amounts used in soap doesn't kill many bacteria (concentrations of 0.2% or less), but it keeps the counts down partly because it has residual activity.
The big question has been whether widespread use of antibacterial soaps will worsen the problem of antibiotic resistance. Doctors have worried that bacteria exposed to low levels of triclosan aren't killed outright so much as given an opportunity to mutate so their offspring are more resistant to triclosan and, ultimately, to antibiotics as well. In the lab, that's how it has played out: Bacteria that become less susceptible to triclosan show indications of developing "cross-resistance" to antibiotics.
But what happens outside the lab is less clear. In the biggest study of its kind, researchers recruited about 240 households in upper Manhattan to participate in a "real-world" hand washing study. Half were randomized to use 0.2% triclosan soap; half, to plain soap. After a year, the researchers tested the hands of the primary caregivers in the households for antibiotic-resistant bacteria. The result: no statistically significant difference between antibacterial and plain-soap households. The researchers offered several possible explanations for their findings (resistance may not develop in a year; high antibiotic use may make it difficult to detect small changes), so the case isn't closed, but their findings do counter the lab research.
Even if antibiotic resistance weren't an issue, results from this study (and others) make you wonder if the antibacterial soaps available to consumers add much to hand hygiene. In the Manhattan households, a year of washing with an antibacterial soap didn't lower bacterial counts on hands any more than a year of washing with plain soap. Nor did the antibacterial soap households experience fewer cold-like symptoms. That's not surprising: Colds are caused by viruses, not bacteria. Still, the finding is a useful reminder that the antibacterial soaps aren't the all-purpose germ fighters that many people expect them to be.
Four dos and don'ts
Don't scrub. Scrubbing can damage skin, especially if you do it a lot. The resulting cracks and small cuts give pathogens a place to grow.
Keep your fingernails short. Bacteria like the area under our fingernails. Long nails make it more difficult to keep those areas clean.
Use hand lotions, especially during the winter. Keeping the skin of your hands intact is essential to good hand hygiene.
Don't be in such a hurry. It takes about a minute to properly wash and dry your hands.
Rubbing it in
The hot new products in hand hygiene are alcohol-based rubs, sold as "hand sanitizers." Purell is the most popular brand-name product, but you'll pay considerably less if you buy a store-brand version. The big advantage of the alcohol-based cleansers is that you don't need water (you just rub the stuff on your hands) or a towel, so they can be used anywhere, not just in the bathroom. Politicians use them on the campaign trail (see box), and we've spotted bottles on people's desks and in their cars. Although many surgeons still scrub in the way seen on television, some have switched to an alcohol-based foam, transforming that iconic image of hand hygiene.
Can we shake on that?
Who touches more dirty hands than a politician on the campaign trail?
In his book, Sen. Barack Obama says President Bush is an enthusiastic user of hand sanitizers. Obama describes a brief conversation he had with the president during a visit to the White House. "Good stuff, keeps you from getting colds," Bush told the Illinois senator before offering him a squirt, which the Democrat says he accepted because he "did not want to appear unhygienic."
Perhaps this is one area of bipartisan agreement. According to The New York Times, Obama now keeps his own bottle of an alcohol-based cleanser in his travel bag.
Alcohol's killing power comes from its ability to change the shape of (denature) proteins crucial to the survival of bacteria and viruses. In the United States, most of the alcohol-based hand cleansers sold to consumers are 62% alcohol. By itself, alcohol would completely dry out people's hands, so various skin conditioners are added. Alcohol does a superb job of getting rid of bacteria and even some viruses. In all but a few trials, alcohol-based cleaners have reduced bacterial counts on hands better than plain soap, several kinds of antibacterial soap, and even iodine.
But alcohol doesn't kill everything: bacterial spores, some protozoa, and certain "nonenveloped" viruses aren't affected. That's why it shouldn't be the only cleaner available in hospitals or other health care settings, according to Dr. Duncan Macdonald, a surgeon in Glasgow, Scotland, who has studied hand hygiene. Dr. Macdonald says hospitals where he has worked go back to soap and water during "winter vomiting outbreaks" caused by nonenveloped viruses.
To be effective, the alcohol-based rubs need to come into contact with all the surfaces of your hands — back, front, in between the fingers, and so forth. For that reason, studies have shown that using small amounts — 0.2 milliliters (ml) to 0.5 ml — is really no better than washing with plain soap and water. Dr. Macdonald reported study results in 2005 that showed coverage with an alcohol-based gel improved considerably when he had hospital staff members double the amount they used from 1.75 ml to 3.5 ml. In another study, Dr. Macdonald found that coverage also improved if staff members saw the areas they missed under an ultraviolet light and were then shown the six hand washing steps designed to maximize coverage, regardless of the type of cleanser (see illustration).
Six steps to super-clean hands
six-steps-to-super-clean-hands
At the Health Letter, when we measured a squirt from a bottle of Purell hand sanitizer, it was 0.5 ml at most, which would suggest that a single squirt isn't much better than washing hands the old-fashioned way. So keep in mind that the way we actually use alcohol-based products may not be leaving our hands quite as germ-free as we suppose. On the other hand (pun intended), their convenience may mean people will clean their hands more often, especially if they're on the go, so hand hygiene might improve over all.
Dr. Macdonald sees no need to use alcohol rubs at home: "I use regular soap and hot water and have no intention of throwing out my pleasant-smelling lotions for alcohol rubs. Most of the germs around the home have come from us and live with us in perfect harmony." The exception, he adds, might be if you are caring for someone who's at high risk for infection.
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This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. | biology | 721753 | https://sv.wikipedia.org/wiki/Handhygien | Handhygien | Att tvätta händerna eller två sina händer innebär att rengöra händerna, ofta med tvål och vatten eller på annat sätt med motsvarande verkan. Syftet med handtvätten är att avlägsna jord, smuts och mikroorganismer, och på så sätt hålla god handhygien. Allmän handhygien förhindrar eller minimerar sjukdomar och spridning av sjukdomar.
Syfte
För att minimera smittspridning är det viktigt att både vuxna och barn alltid tvättar händerna efter toalettbesök, efter utomhusvistelse, innan hantering av livsmedel och före måltid. Det främsta medicinska syftet med handtvättning är att rengöra händerna från smittämnen (inklusive bakterier och virus) och kemikalier som kan orsaka personlig skada eller sjukdom. Människor kan till exempel smittas med luftvägssjukdomar som influensa eller förkylning, om de inte tvättar händerna innan de rör ögonen, näsan eller munnen. Centers for Disease Control and Prevention (CDC) hävdar: "Det är väldokumenterat att en av de viktigaste åtgärderna för att förhindra spridning av smittämnen är effektiv handtvättning". Handtvättning skyddar bäst mot sjukdomar som överförs genom fekal-orala vägar (som många former av magsjuka) och direkt fysisk kontakt (till exempel svinkoppor), men minskar också risken för spridning via droppsmitta. Alkoholgeler kan användas som komplement till handtvätt som ett sätt att döda vissa typer av smittämnen.
Historik
Handtvättning i sjukvården introducerades av den ungerske läkaren Ignaz Semmelweis, som på 1840-talet upptäckte och dokumenterade statistiskt att detta drastiskt kunde minska dödligheten i barnsängsfeber. Vid denna tid var bakterieteorin ännu inte känd, och det dröjde ytterligare några decennier innan Semmelweiss rön och råd blev mer allmänt accepterade.
Utförande
För att handtvättningen ska ha fullgod rengörande effekt och minimera smittspridning är det viktigt att tvättningen utförs noggrant. Avlägsna först eventuella smycken. Vid tvätt med tvål och vatten sköljs händerna först enbart i rinnande vatten. Sedan tvålas hela händerna in (alla fingrarna, handflatorna, ovansidan av händerna, mellan fingrarna, naglarna och handlederna) ordentligt med tvål i minst 15–20 sekunder. Vårdguiden rekommenderar omkring 30 sekunder. En rekommenderad metod för att hålla ordning på tiden är att nynna en sång med samma längd. Sedan sköljs händerna ordentligt i vatten så att skummet avlägsnas. Ett annat viktigt moment är att torka händerna helt torra efteråt och att eventuell handduk som används är ren. Helst bör alla personer använda en separat handduk. En textilhandduk behöver bytas ut och tvättas regelbundet. När många är sjuka rekommenderas engångshanddukar istället. Om handsprit används sker det vanligen efter den vanliga handtvättningen med tvål och vatten. Den kan även användas utan tvätt med tvål och vatten, men vissa virus är resistenta mot handsprit.
Ämnen som används och effekt
Vatten
Fingervarmt vatten är inte tillräckligt hett för att döda bakterier. Tvålvatten är mer effektivt för att ta bort de naturliga oljorna på händerna som innehåller smuts och bakterier. Fram till 2016 rekommenderades allmänt att tvätta händerna i fingervarmt (37,8 grader Celsius eller 100 grader Fahrenheit) vatten, men 2017 visade omfattande forskning från Rutgers-New Brunswick att lägre vattentemperatur inte avlägsnade färre bakterier. Svenska Folkhälsomyndigheten har däremot kvar sin rekommendation om varmt vatten.
Tvål och rengöringsmedel
Bara vatten är ineffektivt för att rengöra huden. Därför kräver avlägsnandet av mikroorganismer tvål eller rengöringsmedel i kombination med vatten. Antingen fast eller flytande tvål kan användas beroende på vilken man föredrar. Tvålen tar bort fett, oljor och proteiner som finns i organisk smuts.
Handsprit
Korrekt handtvättning med tvål och vatten ger i de flesta fall bra effekt både vad gäller avlägsnande av smuts och minskad smittspridning. Desinfektionssprit, så kallad handsprit, brukar främst rekommenderas till särskilt bakteriekänsliga eller bakterieutsatta miljöer där händerna tvättas ofta, exempelvis sjukhus och förskolor. Handsprit kan även användas när möjligheter till handtvätt är begränsade. Det finns dock virus som är resistenta mot handspriten, exempelvis sådana som sprider vinterkräksjuka.
Återfuktning av händer
Det finns handtvål som återfuktar händerna och vid högfrekvent handtvättning kan handsprit ibland motverka torra händer, men främst används handkräm för ändamålet, särskilt för personer med torra händer.
Symbolisk handtvagning
Handtvagning i religiösa sammanhang förstås som en symbol för själens rening liksom är fallet med all rituell tvagning i alla religioner. I den kristna gudstjänsten, mässan, förekommer rituell handtvagning, lavabo, som en del av offertoriet, då prästen tillreder nattvardsgåvorna.
Två sina händer är ett begrepp som betyder att man fritager sig från ansvar, efter Nya testamentet (Matt. 27:24), där det omtalas hur Pilatus "lät han hämta vatten och tvådde sina händer i folkets åsyn" för att symboliskt framhålla att han var "oskyldig till denne mans blod".
Se även
Fottvagning
Internationella handtvättsdagen
Referenser
Noter
Vidare läsning
Tvagning | swedish | 0.617499 |
hot_water_bacteria/Water.txt |
Water is an inorganic compound with the chemical formula H2O. It is a transparent, tasteless, odorless, and nearly colorless chemical substance, and it is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vital for all known forms of life, despite not providing food energy or organic micronutrients. Its chemical formula, H2O, indicates that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°. In liquid form, H2O is also called "Water" at standard temperature and pressure.
Because Earth's environment is relatively close to water's triple point, water exists on Earth as a solid, a liquid, and a gas. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor.
Water covers about 71% of the Earth's surface, with seas and oceans making up most of the water volume (about 96.5%). Small portions of water occur as groundwater (1.7%), in the glaciers and the ice caps of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (consisting of ice and liquid water suspended in air), and precipitation (0.001%). Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.
Water plays an important role in the world economy. Approximately 70% of the fresh water used by humans goes to agriculture. Fishing in salt and fresh water bodies has been, and continues to be, a major source of food for many parts of the world, providing 6.5% of global protein. Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) is transported by boats through seas, rivers, lakes, and canals. Large quantities of water, ice, and steam are used for cooling and heating in industry and homes. Water is an excellent solvent for a wide variety of substances, both mineral and organic; as such, it is widely used in industrial processes and in cooking and washing. Water, ice, and snow are also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, diving, ice skating, snowboarding, and skiing.
The word water comes from Old English wæter, from Proto-Germanic *watar (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, vatn, Gothic 𐍅𐌰𐍄𐍉 (wato)), from Proto-Indo-European *wod-or, suffixed form of root *wed- ('water'; 'wet'). Also cognate, through the Indo-European root, with Greek ύδωρ (ýdor; from Ancient Greek ὕδωρ (hýdōr), whence English 'hydro-'), Russian вода́ (vodá), Irish uisce, and Albanian ujë.
Water (H2O) is a polar inorganic compound. At room temperature it is a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life": indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically pure water. Water is the only common substance to exist as a solid, liquid, and gas in normal terrestrial conditions.
Along with oxidane, water is one of the two official names for the chemical compound H2O; it is also the liquid phase of H2O. The other two common states of matter of water are the solid phase, ice, and the gaseous phase, water vapor or steam. The addition or removal of heat can cause phase transitions: freezing (water to ice), melting (ice to water), vaporization (water to vapor), condensation (vapor to water), sublimation (ice to vapor) and deposition (vapor to ice).
Water differs from most liquids in that it becomes less dense as it freezes. In 1 atm pressure, it reaches its maximum density of 999.972 kg/m (62.4262 lb/cu ft) at 3.98 °C (39.16 °F), or almost 1,000 kg/m (62.43 lb/cu ft) at almost 4 °C (39 °F). The density of ice is 917 kg/m (57.25 lb/cu ft), an expansion of 9%. This expansion can exert enormous pressure, bursting pipes and cracking rocks.
In a lake or ocean, water at 4 °C (39 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter.
Water is a diamagnetic material. Though interaction is weak, with superconducting magnets it can attain a notable interaction.
At a pressure of one atmosphere (atm), ice melts or water freezes (solidifies) at 0 °C (32 °F) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface by evaporation (vaporization throughout the liquid is known as boiling). Sublimation and deposition also occur on surfaces. For example, frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus. In the process of freeze-drying, a food is frozen and then stored at low pressure so the ice on its surface sublimates.
The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius–Clapeyron relation:
d
T
d
P
=
T
(
v
L
−
v
S
)
L
f
{\displaystyle {\frac {dT}{dP}}={\frac {T\left(v_{\text{L}}-v_{\text{S}}\right)}{L_{\text{f}}}}}
where
v
L
{\displaystyle v_{\text{L}}}
and
v
S
{\displaystyle v_{\text{S}}}
are the molar volumes of the liquid and solid phases, and
L
f
{\displaystyle L_{\text{f}}}
is the molar latent heat of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases. In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes.
The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure. Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in Old Faithful, a geyser in Yellowstone National Park. In hydrothermal vents, the temperature can exceed 400 °C (752 °F).
At sea level, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters. High-altitude cooking takes longer than sea-level cooking. For example, at 1,524 metres (5,000 ft), cooking time must be increased by a fourth to achieve the desired result. Conversely, a pressure cooker can be used to decrease cooking times by raising the boiling temperature. In a vacuum, water will boil at room temperature.
On a pressure/temperature phase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the triple point, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C; 32.02 °F) and a pressure of 611.657 pascals (0.00604 atm; 0.0887 psi); it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the Kelvin temperature scale.
The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm). This is known as the critical point. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a supercritical fluid. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can mix freely with nonpolar compounds, including most organic compounds. This makes it useful in a variety of applications including high-temperature electrochemistry and as an ecologically benign solvent or catalyst in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.
The normal form of ice on the surface of Earth is ice Ih, a phase that forms crystals with hexagonal symmetry. Another with cubic crystalline symmetry, ice Ic, can occur in the upper atmosphere. As the pressure increases, ice forms other crystal structures. As of 2019, seventeen have been experimentally confirmed and several more are predicted theoretically. The eighteenth form of ice, ice XVIII, a face-centred-cubic, superionic ice phase, was discovered when a droplet of water was subject to a shock wave that raised the water's pressure to millions of atmospheres and its temperature to thousands of degrees, resulting in a structure of rigid oxygen atoms in which hydrogen atoms flowed freely. When sandwiched between layers of graphene, ice forms a square lattice.
The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behaviour is due to the existence of two liquid states.
Pure water is usually described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, and frogs are known to be able to smell it. However, water from ordinary sources (including mineral water) usually has many dissolved substances that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water in order to avoid water that is too salty or putrid.
Pure water is visibly blue due to absorption of light in the region c. 600–800 nm. The color can be easily observed in a glass of tap-water placed against a pure white background, in daylight. The principal absorption bands responsible for the color are overtones of the O–H stretching vibrations. The apparent intensity of the color increases with the depth of the water column, following Beer's law. This also applies, for example, with a swimming pool when the light source is sunlight reflected from the pool's white tiles.
In nature, the color may also be modified from blue to green due to the presence of suspended solids or algae.
In industry, near-infrared spectroscopy is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass cuvettes with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3,500 cm (2.85 μm) a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm and insoluble in water; calcium fluoride is one material that is in common use for the cuvette windows with aqueous solutions.
The Raman-active fundamental vibrations may be observed with, for example, a 1 cm sample cell.
Aquatic plants, algae, and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them.
Practically no sunlight reaches the parts of the oceans below 1,000 meters (3,300 ft) of depth.
The refractive index of liquid water (1.333 at 20 °C (68 °F)) is much higher than that of air (1.0), similar to those of alkanes and ethanol, but lower than those of glycerol (1.473), benzene (1.501), carbon disulfide (1.627), and common types of glass (1.4 to 1.6). The refraction index of ice (1.31) is lower than that of liquid water.
In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are lone pairs of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms. The O–H bond length is about 0.096 nm.
Other substances have a tetrahedral molecular structure, for example, methane (CH4) and hydrogen sulfide (H2S). However, oxygen is more electronegative than most other elements, so the oxygen atom retains a negative charge while the hydrogen atoms are positively charged. Along with the bent structure, this gives the molecule an electrical dipole moment and it is classified as a polar molecule.
Water is a good polar solvent, dissolving many salts and hydrophilic organic molecules such as sugars and simple alcohols such as ethanol. Water also dissolves many gases, such as oxygen and carbon dioxide—the latter giving the fizz of carbonated beverages, sparkling wines and beers. In addition, many substances in living organisms, such as proteins, DNA and polysaccharides, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape protein folding, DNA base pairing, and other phenomena crucial to life (hydrophobic effect).
Many organic substances (such as fats and oils and alkanes) are hydrophobic, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal oxides, sulfides, and silicates.
Because of its polarity, a molecule of water in the liquid or solid state can form up to four hydrogen bonds with neighboring molecules. Hydrogen bonds are about ten times as strong as the Van der Waals force that attracts molecules to each other in most liquids. This is the reason why the melting and boiling points of water are much higher than those of other analogous compounds like hydrogen sulfide. They also explain its exceptionally high specific heat capacity (about 4.2 J/(g·K)), heat of fusion (about 333 J/g), heat of vaporization (2257 J/g), and thermal conductivity (between 0.561 and 0.679 W/(m·K)). These properties make water more effective at moderating Earth's climate, by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent.
These bonds are the cause of water's high surface tension and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.
Water is a weak solution of hydronium hydroxide—there is an equilibrium 2H2O ⇌ H3O + OH, in combination with solvation of the resulting hydronium and hydroxide ions.
Pure water has a low electrical conductivity, which increases with the dissolution of a small amount of ionic material such as common salt.
Liquid water can be split into the elements hydrogen and oxygen by passing an electric current through it—a process called electrolysis. The decomposition requires more energy input than the heat released by the inverse process (285.8 kJ/mol, or 15.9 MJ/kg).
Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10 Pa in ordinary conditions. Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.
The viscosity of water is about 10 Pa·s or 0.01 poise at 20 °C (68 °F), and the speed of sound in liquid water ranges between 1,400 and 1,540 meters per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03 dB/km for 1 kHz), a property that is exploited by cetaceans and humans for communication and environment sensing (sonar).
Metallic elements which are more electropositive than hydrogen, particularly the alkali metals and alkaline earth metals such as lithium, sodium, calcium, potassium and cesium displace hydrogen from water, forming hydroxides and releasing hydrogen. At high temperatures, carbon reacts with steam to form carbon monoxide and hydrogen.
Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in the focus of ecohydrology.
The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles).
Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is seawater. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.
Water is important in many geological processes. Groundwater is present in most rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes at subduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic record of Earth history.
The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.
Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes:
Most water vapors found mostly in the ocean returns to it, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 Tt per year whilst evaporation and transpiration happening in land masses also contribute another 72 Tt per year. Precipitation, at a rate of 119 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew. Dew is small drops of water that are condensed when a high density of water vapor meets a cool surface. Dew usually forms in the morning when the temperature is the lowest, just before sunrise and when the temperature of the earth's surface starts to increase. Condensed water in the air may also refract sunlight to produce rainbows.
Water runoff often collects over watersheds flowing into rivers. Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water which occurs when a river overflows its banks or a storm surge happens. On the other hand, drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation either due to its topography or due to its location in terms of latitude.
Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. Water occurs as both "stocks" and "flows". Water can be stored as lakes, water vapor, groundwater or aquifers, and ice and snow. Of the total volume of global freshwater, an estimated 69 percent is stored in glaciers and permanent snow cover; 30 percent is in groundwater; and the remaining 1 percent in lakes, rivers, the atmosphere, and biota. The length of time water remains in storage is highly variable: some aquifers consist of water stored over thousands of years but lake volumes may fluctuate on a seasonal basis, decreasing during dry periods and increasing during wet ones. A substantial fraction of the water supply for some regions consists of water extracted from water stored in stocks, and when withdrawals exceed recharge, stocks decrease. By some estimates, as much as 30 percent of total water used for irrigation comes from unsustainable withdrawals of groundwater, causing groundwater depletion.
Seawater contains about 3.5% sodium chloride on average, plus smaller amounts of other substances. The physical properties of seawater differ from fresh water in some important respects. It freezes at a lower temperature (about −1.9 °C (28.6 °F)) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing. The salinity of water in major seas varies from about 0.7% in the Baltic Sea to 4.0% in the Red Sea. (The Dead Sea, known for its ultra-high salinity levels of between 30 and 40%, is really a salt lake.)
Tides are the cyclic rising and falling of local sea levels caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.
From a biological standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g., glucose, fatty acids, and amino acids to be used for fuels for energy use or other purposes). Without water, these particular metabolic processes could not exist.
Water is fundamental to both photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. In the presence of sunlight, hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration).
Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7.
Earth's surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.
Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see insect and mollusc siphons) and gills (Carcinus). However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.
Civilization has historically flourished around rivers and major waterways; Mesopotamia, one of the so-called cradles of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. The early Indus Valley civilization (c. 3300 BCE – c. 1300 BCE) developed along the Indus River and tributaries that flowed out of the Himalayas. Rome was also founded on the banks of the Italian river Tiber. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.
Water fit for human consumption is called drinking water or potable water. Water that is not potable may be made potable by filtration or distillation, or by a range of other methods. More than 660 million people do not have access to safe drinking water.
Water that is not fit for drinking but is not harmful to humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water). Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as chlorine or ozone or by the use of ultraviolet light.
Water reclamation is the process of converting wastewater (most commonly sewage, also called municipal wastewater) into water that can be reused for other purposes. There are 2.3 billion people who reside in nations with water scarcities, which means that each individual receives less than 1,700 cubic metres (60,000 cu ft) of water annually. 380 billion cubic metres (13×10^ cu ft) of municipal wastewater are produced globally each year.
Freshwater is a renewable resource, recirculated by the natural hydrologic cycle, but pressures over access to it result from the naturally uneven distribution in space and time, growing economic demands by agriculture and industry, and rising populations. Currently, nearly a billion people around the world lack access to safe, affordable water. In 2000, the United Nations established the Millennium Development Goals for water to halve by 2015 the proportion of people worldwide without access to safe water and sanitation. Progress toward that goal was uneven, and in 2015 the UN committed to the Sustainable Development Goals of achieving universal access to safe and affordable water and sanitation by 2030. Poor water quality and bad sanitation are deadly; some five million deaths a year are caused by water-related diseases. The World Health Organization estimates that safe water could prevent 1.4 million child deaths from diarrhoea each year.
In developing countries, 90% of all municipal wastewater still goes untreated into local rivers and streams. Some 50 countries, with roughly a third of the world's population, also suffer from medium or high water scarcity and 17 of these extract more water annually than is recharged through their natural water cycles. The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
The most substantial human use of water is for agriculture, including irrigated agriculture, which accounts for as much as 80 to 90 percent of total human water consumption. In the United States, 42% of freshwater withdrawn for use is for irrigation, but the vast majority of water "consumed" (used and not returned to the environment) goes to agriculture.
Access to fresh water is often taken for granted, especially in developed countries that have built sophisticated water systems for collecting, purifying, and delivering water, and removing wastewater. But growing economic, demographic, and climatic pressures are increasing concerns about water issues, leading to increasing competition for fixed water resources, giving rise to the concept of peak water. As populations and economies continue to grow, consumption of water-thirsty meat expands, and new demands rise for biofuels or new water-intensive industries, new water challenges are likely.
An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population. It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity. It found that a fifth of the world's people, more than 1.2 billion, live in areas of physical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today's food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently.
Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.
On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one-hundredth of a meter, and at the temperature of melting ice". For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C (32 °F)—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).
The Kelvin temperature scale of the SI system was based on the triple point of water, defined as exactly 273.16 K (0.01 °C; 32.02 °F), but as of May 2019 is based on the Boltzmann constant instead. The scale is an absolute temperature scale with the same increment as the Celsius temperature scale, which was originally defined according to the boiling point (set to 100 °C (212 °F)) and melting point (set to 0 °C (32 °F)) of water.
Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes oxygen-18, oxygen-17, and hydrogen-2 (deuterium). The percentage of the heavier isotopes is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less heavy isotopes than seawater. Therefore, standard water is defined in the Vienna Standard Mean Ocean Water specification.
The human body contains from 55% to 78% water, depending on body size. To function properly, the body requires between one and seven liters (0.22 and 1.54 imp gal; 0.26 and 1.85 U.S. gal) of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though the British Dietetic Association advises that 2.5 liters of total water daily is the minimum to maintain proper hydration, including 1.8 liters (6 to 7 glasses) obtained directly from beverages. Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.
Healthy kidneys can excrete 0.8 to 1 liter of water per hour, but stress such as exercise can reduce this amount. People can drink far more water than necessary while exercising, putting them at risk of water intoxication (hyperhydration), which can be fatal. The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science. Studies have shown that extra water intake, especially up to 500 milliliters (18 imp fl oz; 17 U.S. fl oz) at mealtime, was associated with weight loss. Adequate fluid intake is helpful in preventing constipation.
An original recommendation for water intake in 1945 by the Food and Nutrition Board of the U.S. National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." The latest dietary reference intake report by the U.S. National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters (0.81 imp gal; 0.98 U.S. gal) for men and 2.7 liters (0.59 imp gal; 0.71 U.S. gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.
Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The US Institute of Medicine recommends that, on average, men consume 3 liters (0.66 imp gal; 0.79 U.S. gal) and women 2.2 liters (0.48 imp gal; 0.58 U.S. gal); pregnant women should increase intake to 2.4 liters (0.53 imp gal; 0.63 U.S. gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.
Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead, and harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.
The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.
Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as ammonia and compounds closely related to water. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.
Water and steam are a common fluid used for heat exchange, due to its availability and high heat capacity, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It is especially effective to transport heat through vaporization and condensation of water because of its large latent heat of vaporization. A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam. In almost all thermal power stations, water is used as the working fluid (used in a closed-loop between boiler, steam turbine, and condenser), and the coolant (used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower). In the United States, cooling power plants is the largest use of water.
In the nuclear power industry, water can also be used as a neutron moderator. In most nuclear reactors, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down. However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling.
Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid.
Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal, or coke graphite, decompose the water, producing water gas.
The power of such explosions was seen in the Chernobyl disaster, although the water involved in this case did not come from fire-fighting but from the reactor's own water cooling system. A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of a reaction between steam and hot zirconium.
Some metallic oxides, most notably those of alkali metals and alkaline earth metals, produce so much heat in reaction with water that a fire hazard can develop. The alkaline earth oxide quicklime, also known as calcium oxide, is a mass-produced substance that is often transported in paper bags. If these are soaked through, they may ignite as their contents react with water.
Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice. Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other flowing water structures are popular decorations. Some keep fish and other flora and fauna inside aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports such as skiing, sledding, snowmobiling or snowboarding, which require the water to be at a low temperature either as ice or crystallized into snow.
The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells, cisterns for rainwater harvesting, water supply networks, and water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development.
Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve the removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid climates.
The distribution of drinking water is done through municipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge.
Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, seawater is extensively used for flushing toilets citywide in order to conserve freshwater resources.
Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market cannot account. Thus other people pay the price of water pollution, while the private firms' profits are not redistributed to the local population, victims of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.
Municipal and industrial wastewater are typically treated at wastewater treatment plants. Mitigation of polluted surface runoff is addressed through a variety of prevention and treatment techniques.
Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances, or to wash products or process equipment. Processes such as mining, chemical pulping, pulp bleaching, paper manufacturing, textile production, dyeing, printing, and cooling of power plants use large amounts of water, requiring a dedicated water source, and often cause significant water pollution.
Water is used in power generation. Hydroelectricity is electricity obtained from hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the motion of water. Typically a dam is constructed on a river, creating an artificial lake behind it. Water flowing out of the lake is forced through turbines that turn generators.
Pressurized water is used in water blasting and water jet cutters. High pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating.
Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and uses a variety of purification techniques both in water supply and discharge.
Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam. Water is also used for dishwashing. Water also plays many critical roles within the field of food science.
Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well as air pressure, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure that occurs at higher elevations. One mole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C (0.918 °F), and one mole of salt per kg raises the boiling point by 1.02 °C (1.836 °F); similarly, increasing the number of dissolved particles lowers water's freezing point.
Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food. Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water. Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity. Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.
Water hardness is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system. It can dramatically affect the quality of a product, as well as playing a role in sanitation. Water hardness is classified based on concentration of calcium carbonate the water contains. Water is classified as soft if it contains less than 100 mg/L (UK) or less than 60 mg/L (US).
According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand liters (3.3×10^ imp gal; 4.0×10^ U.S. gal) of water; however, the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production.
Water for injection is on the World Health Organization's list of essential medicines.
Much of the universe's water is produced as a byproduct of star formation. The formation of stars is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.
On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing "140 trillion times more water than all of Earth's oceans combined" around a quasar located 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence".
Water has been detected in interstellar clouds within the Milky Way. Water probably exists in abundance in other galaxies, too, because its components, hydrogen, and oxygen, are among the most abundant elements in the universe. Based on models of the formation and evolution of the Solar System and that of other star systems, most other planetary systems are likely to have similar ingredients.
Water is present as vapor in:
Liquid water is present on Earth, covering 71% of its surface. Liquid water is also occasionally present in small amounts on Mars. Scientists believe liquid water is present in the Saturnian moons of Enceladus, as a 10-kilometre thick ocean approximately 30–40 kilometres below Enceladus' south polar surface, and Titan, as a subsurface layer, possibly mixed with ammonia. Jupiter's moon Europa has surface characteristics which suggest a subsurface liquid water ocean. Liquid water may also exist on Jupiter's moon Ganymede as a layer sandwiched between high pressure ice and rock.
Water is present as ice on:
And is also likely present on:
Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper still as superionic water in which the oxygen crystallizes, but the hydrogen ions float about freely within the oxygen lattice.
The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the Solar System; if it were slightly closer to or farther from the Sun (about 5%, or about 8 million kilometers), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.
Earth's gravity allows it to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in polar ice caps (as on Mars).
The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.
The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanets Gliese 436 b and GJ 1214 b.
Water politics is politics affected by water and water resources. Water, particularly fresh water, is a strategic resource across the world and an important element in many political conflicts. It causes health impacts and damage to biodiversity.
Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.
1.6 billion people have gained access to a safe water source since 1990. The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970 to 71% in 1990, 79% in 2000, and 84% in 2004.
A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption. In addition, global initiatives to improve the efficiency of aid delivery, such as the Paris Declaration on Aid Effectiveness, have not been taken up by water sector donors as effectively as they have in education and health, potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act.
The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context. Mistakes have sometimes been made by trying to apply 'blueprints' that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken. They also discovered that Cambodia's draft water law was much more complex than it needed to be.
In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases, which are often tied to a lack of adequate sanitation.
Since 2003, the UN World Water Development Report, produced by the UNESCO World Water Assessment Programme, has provided decision-makers with tools for developing sustainable water policies. The 2023 report states that two billion people (26% of the population) do not have access to drinking water and 3.6 billion (46%) lack access to safely managed sanitation. People in urban areas (2.4 billion) will face water scarcity by 2050. Water scarcity has been described as endemic, due to overconsumption and pollution. The report states that 10% of the world's population lives in countries with high or critical water stress. Yet over the past 40 years, water consumption has increased by around 1% per year, and is expected to grow at the same rate until 2050. Since 2000, flooding in the tropics has quadrupled, while flooding in northern mid-latitudes has increased by a factor of 2.5. The cost of these floods between 2000 and 2019 was 100,000 deaths and $650 million.
Organizations concerned with water protection include the International Water Association (IWA), WaterAid, Water 1st, and the American Water Resources Association. The International Water Management Institute undertakes projects with the aim of using effective water management to reduce poverty. Water related conventions are United Nations Convention to Combat Desertification (UNCCD), International Convention for the Prevention of Pollution from Ships, United Nations Convention on the Law of the Sea and Ramsar Convention. World Day for Water takes place on 22 March and World Oceans Day on 8 June.
Water is considered a purifier in most religions. Faiths that incorporate ritual washing (ablution) include Christianity, Hinduism, Islam, Judaism, the Rastafari movement, Shinto, Taoism, and Wicca. Immersion (or aspersion or affusion) of a person in water is a central Sacrament of Christianity (where it is called baptism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after washing certain parts of the body using clean water (wudu), unless water is unavailable (see Tayammum). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of misogi).
In Christianity, holy water is water that has been sanctified by a priest for the purpose of baptism, the blessing of persons, places, and objects, or as a means of repelling evil.
In Zoroastrianism, water (āb) is respected as the source of life.
The Ancient Greek philosopher Empedocles saw water as one of the four classical elements (along with fire, earth, and air), and regarded it as an ylem, or basic substance of the universe. Thales, whom Aristotle portrayed as an astronomer and an engineer, theorized that the earth, which is denser than water, emerged from the water. Thales, a monist, believed further that all things are made from water. Plato believed that the shape of water is an icosahedron – flowing easily compared to the cube-shaped earth.
The theory of the four bodily humors associated water with phlegm, as being cold and moist. The classical element of water was also one of the five elements in traditional Chinese philosophy (along with earth, fire, wood, and metal).
Some traditional and popular Asian philosophical systems take water as a role-model. James Legge's 1891 translation of the Dao De Jing states, "The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the Tao" and "There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed." Guanzi in the "Shui di" 水地 chapter further elaborates on the symbolism of water, proclaiming that "man is water" and attributing natural qualities of the people of different Chinese regions to the character of local water resources.
"Living water" features in Germanic and Slavic folktales as a means of bringing the dead back to life. Note the Grimm fairy-tale ("The Water of Life") and the Russian dichotomy of living [ru] and dead water [ru]. The Fountain of Youth represents a related concept of magical waters allegedly preventing aging.
Painter and activist Fredericka Foster curated The Value of Water, at the Cathedral of St. John the Divine in New York City, which anchored a year-long initiative by the Cathedral on our dependence on water. The largest exhibition to ever appear at the Cathedral, it featured over forty artists, including Jenny Holzer, Robert Longo, Mark Rothko, William Kentridge, April Gornik, Kiki Smith, Pat Steir, Alice Dalton Brown, Teresita Fernandez and Bill Viola. Foster created Think About Water, an ecological collective of artists who use water as their subject or medium. Members include Basia Irland, Aviva Rahmani, Betsy Damon, Diane Burko, Leila Daw, Stacy Levy, Charlotte Coté, Meridel Rubenstein, and Anna Macleod.
To mark the 10th anniversary of access to water and sanitation being declared a human right by the UN, the charity WaterAid commissioned ten visual artists to show the impact of clean water on people's lives.
'Water' is technically correct but rarely used chemical name, dihydrogen monoxide, has been used in a series of hoaxes and pranks that mock scientific illiteracy. This began in 1983, when an April Fools' Day article appeared in a newspaper in Durand, Michigan. The false story consisted of safety concerns about the substance.
The word "Water" has been used by many Florida based rappers as a sort of catchphrase or adlib. Rappers who have done this include BLP Kosher and Ski Mask the Slump God. To go even further some rappers have made whole songs dedicated to the water in Florida, such as the 2023 Danny Towers song "Florida Water". Others have made whole songs dedicated to water as a whole, such as XXXTentacion, and Ski Mask the Slump God with their hit song "H2O".
Etymology
The word water comes from Old English wæter, from Proto-Germanic *watar (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, vatn, Gothic 𐍅𐌰𐍄𐍉 (wato)), from Proto-Indo-European *wod-or, suffixed form of root *wed- ('water'; 'wet'). Also cognate, through the Indo-European root, with Greek ύδωρ (ýdor; from Ancient Greek ὕδωρ (hýdōr), whence English 'hydro-'), Russian вода́ (vodá), Irish uisce, and Albanian ujë.
History
Main articles: Origin of water on Earth § History of water on Earth, and Properties of water § History
On Earth
This section is an excerpt from Origin of water on Earth § History of water on Earth.[edit]
One factor in estimating when water appeared on Earth is that water is continually being lost to space. H2O molecules in the atmosphere are broken up by photolysis, and the resulting free hydrogen atoms can sometimes escape Earth's gravitational pull. When the Earth was younger and less massive, water would have been lost to space more easily. Lighter elements like hydrogen and helium are expected to leak from the atmosphere continually, but isotopic ratios of heavier noble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses. In particular, xenon is useful for calculations of water loss over time. Not only is it a noble gas (and therefore is not removed from the atmosphere through chemical reactions with other elements), but comparisons between the abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water early in its history, between the Hadean and Archean eons.
Any water on Earth during the latter part of its accretion would have been disrupted by the Moon-forming impact (~4.5 billion years ago), which likely vaporized much of Earth's crust and upper mantle and created a rock-vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majority carbon dioxide atmosphere with hydrogen and water vapor. Afterward, liquid water oceans may have existed despite the surface temperature of 230 °C (446 °F) due to the increased atmospheric pressure of the CO2 atmosphere. As the cooling continued, most CO2 was removed from the atmosphere by subduction and dissolution in ocean water, but levels oscillated wildly as new surface and mantle cycles appeared.
This pillow basalt on the seafloor near Hawaii was formed when magma extruded underwater. Other, much older pillow basalt formations provide evidence for large bodies of water long ago in Earth's history.
Geological evidence also helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption) was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence has yet to be discovered (which may be because such potential evidence has been destroyed by geological processes like crustal recycling). More recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.
Unlike rocks, minerals called zircons are highly resistant to weathering and geological processes and so are used to understand conditions on the very early Earth. Mineralogical evidence from zircons has shown that liquid water and an atmosphere must have existed 4.404 ± 0.008 billion years ago, very soon after the formation of Earth. This presents somewhat of a paradox, as the cool early Earth hypothesis suggests temperatures were cold enough to freeze water between about 4.4 billion and 4.0 billion years ago. Other studies of zircons found in Australian Hadean rock point to the existence of plate tectonics as early as 4 billion years ago. If true, that implies that rather than a hot, molten surface and an atmosphere full of carbon dioxide, early Earth's surface was much as it is today (in terms of thermal insulation). The action of plate tectonics traps vast amounts of CO2, thereby reducing greenhouse effects, leading to a much cooler surface temperature and the formation of solid rock and liquid water.
Properties
Main article: Properties of water
See also: Water (data page) and Water model
A water molecule consists of two hydrogen atoms and one oxygen atom.
Water (H2O) is a polar inorganic compound. At room temperature it is a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life": indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically pure water. Water is the only common substance to exist as a solid, liquid, and gas in normal terrestrial conditions.
States
The three common states of matter
Along with oxidane, water is one of the two official names for the chemical compound H2O; it is also the liquid phase of H2O. The other two common states of matter of water are the solid phase, ice, and the gaseous phase, water vapor or steam. The addition or removal of heat can cause phase transitions: freezing (water to ice), melting (ice to water), vaporization (water to vapor), condensation (vapor to water), sublimation (ice to vapor) and deposition (vapor to ice).
Density
See also: Frost weathering
Water differs from most liquids in that it becomes less dense as it freezes. In 1 atm pressure, it reaches its maximum density of 999.972 kg/m (62.4262 lb/cu ft) at 3.98 °C (39.16 °F), or almost 1,000 kg/m (62.43 lb/cu ft) at almost 4 °C (39 °F). The density of ice is 917 kg/m (57.25 lb/cu ft), an expansion of 9%. This expansion can exert enormous pressure, bursting pipes and cracking rocks.
In a lake or ocean, water at 4 °C (39 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter.
Magnetism
Water is a diamagnetic material. Though interaction is weak, with superconducting magnets it can attain a notable interaction.
Phase transitions
At a pressure of one atmosphere (atm), ice melts or water freezes (solidifies) at 0 °C (32 °F) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface by evaporation (vaporization throughout the liquid is known as boiling). Sublimation and deposition also occur on surfaces. For example, frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus. In the process of freeze-drying, a food is frozen and then stored at low pressure so the ice on its surface sublimates.
The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius–Clapeyron relation:
d
T
d
P
=
T
(
v
L
−
v
S
)
L
f
{\displaystyle {\frac {dT}{dP}}={\frac {T\left(v_{\text{L}}-v_{\text{S}}\right)}{L_{\text{f}}}}}
where
v
L
{\displaystyle v_{\text{L}}}
and
v
S
{\displaystyle v_{\text{S}}}
are the molar volumes of the liquid and solid phases, and
L
f
{\displaystyle L_{\text{f}}}
is the molar latent heat of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases. In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes.
The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure. Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in Old Faithful, a geyser in Yellowstone National Park. In hydrothermal vents, the temperature can exceed 400 °C (752 °F).
At sea level, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters. High-altitude cooking takes longer than sea-level cooking. For example, at 1,524 metres (5,000 ft), cooking time must be increased by a fourth to achieve the desired result. Conversely, a pressure cooker can be used to decrease cooking times by raising the boiling temperature. In a vacuum, water will boil at room temperature.
Triple and critical points
Phase diagram of water (simplified)
On a pressure/temperature phase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the triple point, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C; 32.02 °F) and a pressure of 611.657 pascals (0.00604 atm; 0.0887 psi); it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the Kelvin temperature scale.
The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm). This is known as the critical point. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a supercritical fluid. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can mix freely with nonpolar compounds, including most organic compounds. This makes it useful in a variety of applications including high-temperature electrochemistry and as an ecologically benign solvent or catalyst in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.
Phases of ice and water
Main article: Ice
The normal form of ice on the surface of Earth is ice Ih, a phase that forms crystals with hexagonal symmetry. Another with cubic crystalline symmetry, ice Ic, can occur in the upper atmosphere. As the pressure increases, ice forms other crystal structures. As of 2019, seventeen have been experimentally confirmed and several more are predicted theoretically. The eighteenth form of ice, ice XVIII, a face-centred-cubic, superionic ice phase, was discovered when a droplet of water was subject to a shock wave that raised the water's pressure to millions of atmospheres and its temperature to thousands of degrees, resulting in a structure of rigid oxygen atoms in which hydrogen atoms flowed freely. When sandwiched between layers of graphene, ice forms a square lattice.
The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behaviour is due to the existence of two liquid states.
Taste and odor
Pure water is usually described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, and frogs are known to be able to smell it. However, water from ordinary sources (including mineral water) usually has many dissolved substances that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water in order to avoid water that is too salty or putrid.
Color and appearance
Main article: Color of water
See also: Electromagnetic absorption by water
Pure water is visibly blue due to absorption of light in the region c. 600–800 nm. The color can be easily observed in a glass of tap-water placed against a pure white background, in daylight. The principal absorption bands responsible for the color are overtones of the O–H stretching vibrations. The apparent intensity of the color increases with the depth of the water column, following Beer's law. This also applies, for example, with a swimming pool when the light source is sunlight reflected from the pool's white tiles.
In nature, the color may also be modified from blue to green due to the presence of suspended solids or algae.
In industry, near-infrared spectroscopy is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass cuvettes with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3,500 cm (2.85 μm) a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm and insoluble in water; calcium fluoride is one material that is in common use for the cuvette windows with aqueous solutions.
The Raman-active fundamental vibrations may be observed with, for example, a 1 cm sample cell.
Aquatic plants, algae, and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them.
Practically no sunlight reaches the parts of the oceans below 1,000 meters (3,300 ft) of depth.
The refractive index of liquid water (1.333 at 20 °C (68 °F)) is much higher than that of air (1.0), similar to those of alkanes and ethanol, but lower than those of glycerol (1.473), benzene (1.501), carbon disulfide (1.627), and common types of glass (1.4 to 1.6). The refraction index of ice (1.31) is lower than that of liquid water.
Molecular polarity
Tetrahedral structure of water
In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are lone pairs of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms. The O–H bond length is about 0.096 nm.
Other substances have a tetrahedral molecular structure, for example, methane (CH4) and hydrogen sulfide (H2S). However, oxygen is more electronegative than most other elements, so the oxygen atom retains a negative charge while the hydrogen atoms are positively charged. Along with the bent structure, this gives the molecule an electrical dipole moment and it is classified as a polar molecule.
Water is a good polar solvent, dissolving many salts and hydrophilic organic molecules such as sugars and simple alcohols such as ethanol. Water also dissolves many gases, such as oxygen and carbon dioxide—the latter giving the fizz of carbonated beverages, sparkling wines and beers. In addition, many substances in living organisms, such as proteins, DNA and polysaccharides, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape protein folding, DNA base pairing, and other phenomena crucial to life (hydrophobic effect).
Many organic substances (such as fats and oils and alkanes) are hydrophobic, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal oxides, sulfides, and silicates.
Hydrogen bonding
See also: Chemical bonding of water
Model of hydrogen bonds (1) between molecules of water
Because of its polarity, a molecule of water in the liquid or solid state can form up to four hydrogen bonds with neighboring molecules. Hydrogen bonds are about ten times as strong as the Van der Waals force that attracts molecules to each other in most liquids. This is the reason why the melting and boiling points of water are much higher than those of other analogous compounds like hydrogen sulfide. They also explain its exceptionally high specific heat capacity (about 4.2 J/(g·K)), heat of fusion (about 333 J/g), heat of vaporization (2257 J/g), and thermal conductivity (between 0.561 and 0.679 W/(m·K)). These properties make water more effective at moderating Earth's climate, by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent.
These bonds are the cause of water's high surface tension and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.
Specific heat capacity of water
Self-ionization
Main article: Self-ionization of water
Water is a weak solution of hydronium hydroxide—there is an equilibrium 2H2O ⇌ H3O + OH, in combination with solvation of the resulting hydronium and hydroxide ions.
Electrical conductivity and electrolysis
Pure water has a low electrical conductivity, which increases with the dissolution of a small amount of ionic material such as common salt.
Liquid water can be split into the elements hydrogen and oxygen by passing an electric current through it—a process called electrolysis. The decomposition requires more energy input than the heat released by the inverse process (285.8 kJ/mol, or 15.9 MJ/kg).
Mechanical properties
Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10 Pa in ordinary conditions. Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.
The viscosity of water is about 10 Pa·s or 0.01 poise at 20 °C (68 °F), and the speed of sound in liquid water ranges between 1,400 and 1,540 meters per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03 dB/km for 1 kHz), a property that is exploited by cetaceans and humans for communication and environment sensing (sonar).
Reactivity
Metallic elements which are more electropositive than hydrogen, particularly the alkali metals and alkaline earth metals such as lithium, sodium, calcium, potassium and cesium displace hydrogen from water, forming hydroxides and releasing hydrogen. At high temperatures, carbon reacts with steam to form carbon monoxide and hydrogen.
On Earth
Main articles: Hydrology and Water distribution on Earth
Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in the focus of ecohydrology.
The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles).
Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is seawater. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.
Water is important in many geological processes. Groundwater is present in most rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes at subduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic record of Earth history.
Water cycle
Main article: Water cycle
Water cycle
The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.
Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes:
evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air.
precipitation, from water vapor condensing from the air and falling to the earth or ocean.
runoff from the land usually reaching the sea.
Most water vapors found mostly in the ocean returns to it, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 Tt per year whilst evaporation and transpiration happening in land masses also contribute another 72 Tt per year. Precipitation, at a rate of 119 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew. Dew is small drops of water that are condensed when a high density of water vapor meets a cool surface. Dew usually forms in the morning when the temperature is the lowest, just before sunrise and when the temperature of the earth's surface starts to increase. Condensed water in the air may also refract sunlight to produce rainbows.
Water runoff often collects over watersheds flowing into rivers. Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water which occurs when a river overflows its banks or a storm surge happens. On the other hand, drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation either due to its topography or due to its location in terms of latitude.
Water resources
Main article: Water resources
Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. Water occurs as both "stocks" and "flows". Water can be stored as lakes, water vapor, groundwater or aquifers, and ice and snow. Of the total volume of global freshwater, an estimated 69 percent is stored in glaciers and permanent snow cover; 30 percent is in groundwater; and the remaining 1 percent in lakes, rivers, the atmosphere, and biota. The length of time water remains in storage is highly variable: some aquifers consist of water stored over thousands of years but lake volumes may fluctuate on a seasonal basis, decreasing during dry periods and increasing during wet ones. A substantial fraction of the water supply for some regions consists of water extracted from water stored in stocks, and when withdrawals exceed recharge, stocks decrease. By some estimates, as much as 30 percent of total water used for irrigation comes from unsustainable withdrawals of groundwater, causing groundwater depletion.
Seawater and tides
Main articles: Seawater and Tides
Seawater contains about 3.5% sodium chloride on average, plus smaller amounts of other substances. The physical properties of seawater differ from fresh water in some important respects. It freezes at a lower temperature (about −1.9 °C (28.6 °F)) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing. The salinity of water in major seas varies from about 0.7% in the Baltic Sea to 4.0% in the Red Sea. (The Dead Sea, known for its ultra-high salinity levels of between 30 and 40%, is really a salt lake.)
Tides are the cyclic rising and falling of local sea levels caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.
The Bay of Fundy at high tide and low tide
High tide
Low tide
Effects on life
Overview of photosynthesis (green) and respiration (red)
From a biological standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g., glucose, fatty acids, and amino acids to be used for fuels for energy use or other purposes). Without water, these particular metabolic processes could not exist.
Water is fundamental to both photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. In the presence of sunlight, hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration).
Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7.
Aquatic life forms
Further information: Hydrobiology, Marine life, and Aquatic plant
Earth's surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.
Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see insect and mollusc siphons) and gills (Carcinus). However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.
Some of the biodiversity of a coral reef
Some marine diatoms – a key phytoplankton group
Squat lobster and Alvinocarididae shrimp at the Von Damm hydrothermal field survive by altered water chemistry.
Effects on human civilization
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Water fountain
Civilization has historically flourished around rivers and major waterways; Mesopotamia, one of the so-called cradles of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. The early Indus Valley civilization (c. 3300 BCE – c. 1300 BCE) developed along the Indus River and tributaries that flowed out of the Himalayas. Rome was also founded on the banks of the Italian river Tiber. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.
Health and pollution
An environmental science program – a student from Iowa State University sampling water
Water fit for human consumption is called drinking water or potable water. Water that is not potable may be made potable by filtration or distillation, or by a range of other methods. More than 660 million people do not have access to safe drinking water.
Water that is not fit for drinking but is not harmful to humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water). Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as chlorine or ozone or by the use of ultraviolet light.
Water reclamation is the process of converting wastewater (most commonly sewage, also called municipal wastewater) into water that can be reused for other purposes. There are 2.3 billion people who reside in nations with water scarcities, which means that each individual receives less than 1,700 cubic metres (60,000 cu ft) of water annually. 380 billion cubic metres (13×10^ cu ft) of municipal wastewater are produced globally each year.
Freshwater is a renewable resource, recirculated by the natural hydrologic cycle, but pressures over access to it result from the naturally uneven distribution in space and time, growing economic demands by agriculture and industry, and rising populations. Currently, nearly a billion people around the world lack access to safe, affordable water. In 2000, the United Nations established the Millennium Development Goals for water to halve by 2015 the proportion of people worldwide without access to safe water and sanitation. Progress toward that goal was uneven, and in 2015 the UN committed to the Sustainable Development Goals of achieving universal access to safe and affordable water and sanitation by 2030. Poor water quality and bad sanitation are deadly; some five million deaths a year are caused by water-related diseases. The World Health Organization estimates that safe water could prevent 1.4 million child deaths from diarrhoea each year.
In developing countries, 90% of all municipal wastewater still goes untreated into local rivers and streams. Some 50 countries, with roughly a third of the world's population, also suffer from medium or high water scarcity and 17 of these extract more water annually than is recharged through their natural water cycles. The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
Human uses
Further information: Water supply
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m) per year in 2010
Agriculture
The most substantial human use of water is for agriculture, including irrigated agriculture, which accounts for as much as 80 to 90 percent of total human water consumption. In the United States, 42% of freshwater withdrawn for use is for irrigation, but the vast majority of water "consumed" (used and not returned to the environment) goes to agriculture.
Access to fresh water is often taken for granted, especially in developed countries that have built sophisticated water systems for collecting, purifying, and delivering water, and removing wastewater. But growing economic, demographic, and climatic pressures are increasing concerns about water issues, leading to increasing competition for fixed water resources, giving rise to the concept of peak water. As populations and economies continue to grow, consumption of water-thirsty meat expands, and new demands rise for biofuels or new water-intensive industries, new water challenges are likely.
An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population. It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity. It found that a fifth of the world's people, more than 1.2 billion, live in areas of physical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today's food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently.
Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.
Water requirement per tonne of food product
Water distribution in subsurface drip irrigation
Irrigation of field crops
As a scientific standard
On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one-hundredth of a meter, and at the temperature of melting ice". For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C (32 °F)—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).
The Kelvin temperature scale of the SI system was based on the triple point of water, defined as exactly 273.16 K (0.01 °C; 32.02 °F), but as of May 2019 is based on the Boltzmann constant instead. The scale is an absolute temperature scale with the same increment as the Celsius temperature scale, which was originally defined according to the boiling point (set to 100 °C (212 °F)) and melting point (set to 0 °C (32 °F)) of water.
Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes oxygen-18, oxygen-17, and hydrogen-2 (deuterium). The percentage of the heavier isotopes is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less heavy isotopes than seawater. Therefore, standard water is defined in the Vienna Standard Mean Ocean Water specification.
For drinking
Main article: Drinking water
A young girl drinking bottled water
Water availability: the fraction of the population using improved water sources by country
Roadside fresh water outlet from glacier, Nubra
The human body contains from 55% to 78% water, depending on body size. To function properly, the body requires between one and seven liters (0.22 and 1.54 imp gal; 0.26 and 1.85 U.S. gal) of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though the British Dietetic Association advises that 2.5 liters of total water daily is the minimum to maintain proper hydration, including 1.8 liters (6 to 7 glasses) obtained directly from beverages. Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.
Healthy kidneys can excrete 0.8 to 1 liter of water per hour, but stress such as exercise can reduce this amount. People can drink far more water than necessary while exercising, putting them at risk of water intoxication (hyperhydration), which can be fatal. The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science. Studies have shown that extra water intake, especially up to 500 milliliters (18 imp fl oz; 17 U.S. fl oz) at mealtime, was associated with weight loss. Adequate fluid intake is helpful in preventing constipation.
Hazard symbol for non-potable water
An original recommendation for water intake in 1945 by the Food and Nutrition Board of the U.S. National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." The latest dietary reference intake report by the U.S. National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters (0.81 imp gal; 0.98 U.S. gal) for men and 2.7 liters (0.59 imp gal; 0.71 U.S. gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.
Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The US Institute of Medicine recommends that, on average, men consume 3 liters (0.66 imp gal; 0.79 U.S. gal) and women 2.2 liters (0.48 imp gal; 0.58 U.S. gal); pregnant women should increase intake to 2.4 liters (0.53 imp gal; 0.63 U.S. gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.
Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead, and harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.
The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.
Washing
This section is an excerpt from Washing.[edit]
A woman washes her hands with soap and water.
Washing is a method of cleaning, usually with water and soap or detergent. Washing and then rinsing both body and clothing is an essential part of good hygiene and health.
Often people use soaps and detergents to assist in the emulsification of oils and dirt particles so they can be washed away. The soap can be applied directly, or with the aid of a washcloth.
People wash themselves, or bathe periodically for religious ritual or therapeutic purposes or as a recreational activity.
In Europe, some people use a bidet to wash their external genitalia and the anal region after using the toilet, instead of using toilet paper. The bidet is common in predominantly Catholic countries where water is considered essential for anal cleansing.
More frequent is washing of just the hands, e.g. before and after preparing food and eating, after using the toilet, after handling something dirty, etc. Hand washing is important in reducing the spread of germs. Also common is washing the face, which is done after waking up, or to keep oneself cool during the day. Brushing one's teeth is also essential for hygiene and is a part of washing.
'Washing' can also refer to the washing of clothing or other cloth items, like bedsheets, whether by hand or with a washing machine. It can also refer to washing one's car, by lathering the exterior with car soap, then rinsing it off with a hose, or washing cookware.
A private home washing machine
Excessive washing may damage the hair, causing dandruff, or cause rough skin/skin lesions.
Transportation
These paragraphs are an excerpt from Maritime transport.[edit]
Maritime transport (or ocean transport) or more generally waterborne transport, is the transport of people (passengers) or goods (cargo) via waterways. Freight transport by sea has been widely used throughout recorded history. The advent of aviation has diminished the importance of sea travel for passengers, though it is still popular for short trips and pleasure cruises. Transport by water is cheaper than transport by air or ground, but significantly slower for longer distances. Maritime transport accounts for roughly 80% of international trade, according to UNCTAD in 2020.
Maritime transport can be realized over any distance by boat, ship, sailboat or barge, over oceans and lakes, through canals or along rivers. Shipping may be for commerce, recreation, or military purposes. While extensive inland shipping is less critical today, the major waterways of the world including many canals are still very important and are integral parts of worldwide economies. Particularly, especially any material can be moved by water; however, water transport becomes impractical when material delivery is time-critical such as various types of perishable produce. Still, water transport is highly cost effective with regular schedulable cargoes, such as trans-oceanic shipping of consumer products – and especially for heavy loads or bulk cargos, such as coal, coke, ores, or grains. Arguably, the industrial revolution had its first impacts where cheap water transport by canal, navigations, or shipping by all types of watercraft on natural waterways supported cost-effective bulk transport.
Containerization revolutionized maritime transport starting in the 1970s. "General cargo" includes goods packaged in boxes, cases, pallets, and barrels. When a cargo is carried in more than one mode, it is intermodal or co-modal.
Chemical uses
Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as ammonia and compounds closely related to water. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.
Heat exchange
Water and steam are a common fluid used for heat exchange, due to its availability and high heat capacity, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It is especially effective to transport heat through vaporization and condensation of water because of its large latent heat of vaporization. A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam. In almost all thermal power stations, water is used as the working fluid (used in a closed-loop between boiler, steam turbine, and condenser), and the coolant (used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower). In the United States, cooling power plants is the largest use of water.
In the nuclear power industry, water can also be used as a neutron moderator. In most nuclear reactors, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down. However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling.
Fire considerations
Water is used for fighting wildfires.
Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid.
Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal, or coke graphite, decompose the water, producing water gas.
The power of such explosions was seen in the Chernobyl disaster, although the water involved in this case did not come from fire-fighting but from the reactor's own water cooling system. A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of a reaction between steam and hot zirconium.
Some metallic oxides, most notably those of alkali metals and alkaline earth metals, produce so much heat in reaction with water that a fire hazard can develop. The alkaline earth oxide quicklime, also known as calcium oxide, is a mass-produced substance that is often transported in paper bags. If these are soaked through, they may ignite as their contents react with water.
Recreation
Main article: Water sport (recreation)
San Andrés island, Colombia
Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice. Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other flowing water structures are popular decorations. Some keep fish and other flora and fauna inside aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports such as skiing, sledding, snowmobiling or snowboarding, which require the water to be at a low temperature either as ice or crystallized into snow.
Water industry
The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells, cisterns for rainwater harvesting, water supply networks, and water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development.
Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve the removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid climates.
The distribution of drinking water is done through municipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge.
Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, seawater is extensively used for flushing toilets citywide in order to conserve freshwater resources.
Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market cannot account. Thus other people pay the price of water pollution, while the private firms' profits are not redistributed to the local population, victims of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.
Municipal and industrial wastewater are typically treated at wastewater treatment plants. Mitigation of polluted surface runoff is addressed through a variety of prevention and treatment techniques.
A water-carrier in India, 1882. In many places where running water is not available, water has to be transported by people.
A manual water pump in China
Water purification facility
Reverse osmosis (RO) desalination plant in Barcelona, Spain
Industrial applications
Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances, or to wash products or process equipment. Processes such as mining, chemical pulping, pulp bleaching, paper manufacturing, textile production, dyeing, printing, and cooling of power plants use large amounts of water, requiring a dedicated water source, and often cause significant water pollution.
Water is used in power generation. Hydroelectricity is electricity obtained from hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the motion of water. Typically a dam is constructed on a river, creating an artificial lake behind it. Water flowing out of the lake is forced through turbines that turn generators.
Three Gorges Dam is the largest hydro-electric power station in the world.
Pressurized water is used in water blasting and water jet cutters. High pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating.
Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and uses a variety of purification techniques both in water supply and discharge.
Food processing
Water can be used to cook foods such as noodles.
Sterile water for injection
Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam. Water is also used for dishwashing. Water also plays many critical roles within the field of food science.
Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well as air pressure, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure that occurs at higher elevations. One mole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C (0.918 °F), and one mole of salt per kg raises the boiling point by 1.02 °C (1.836 °F); similarly, increasing the number of dissolved particles lowers water's freezing point.
Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food. Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water. Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity. Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.
Water hardness is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system. It can dramatically affect the quality of a product, as well as playing a role in sanitation. Water hardness is classified based on concentration of calcium carbonate the water contains. Water is classified as soft if it contains less than 100 mg/L (UK) or less than 60 mg/L (US).
According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand liters (3.3×10^ imp gal; 4.0×10^ U.S. gal) of water; however, the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production.
Medical use
Water for injection is on the World Health Organization's list of essential medicines.
Distribution in nature
In the universe
Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.
Much of the universe's water is produced as a byproduct of star formation. The formation of stars is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.
On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing "140 trillion times more water than all of Earth's oceans combined" around a quasar located 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence".
Water has been detected in interstellar clouds within the Milky Way. Water probably exists in abundance in other galaxies, too, because its components, hydrogen, and oxygen, are among the most abundant elements in the universe. Based on models of the formation and evolution of the Solar System and that of other star systems, most other planetary systems are likely to have similar ingredients.
Water vapor
Water is present as vapor in:
Atmosphere of the Sun: in detectable trace amounts
Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere
Atmosphere of Venus: 0.002%
Earth's atmosphere: ≈0.40% over full atmosphere, typically 1–4% at surface; as well as that of the Moon in trace amounts
Atmosphere of Mars: 0.03%
Atmosphere of Ceres
Atmosphere of Jupiter: 0.0004% – in ices only; and that of its moon Europa
Atmosphere of Saturn – in ices only; Enceladus: 91% and Dione (exosphere)
Atmosphere of Uranus – in trace amounts below 50 bar
Atmosphere of Neptune – found in the deeper layers
Extrasolar planet atmospheres: including those of HD 189733 b and HD 209458 b, Tau Boötis b, HAT-P-11b, XO-1b, WASP-12b, WASP-17b, and WASP-19b.
Stellar atmospheres: not limited to cooler stars and even detected in giant hot stars such as Betelgeuse, Mu Cephei, Antares and Arcturus.
Circumstellar disks: including those of more than half of T Tauri stars such as AA Tauri as well as TW Hydrae, IRC +10216 and APM 08279+5255, VY Canis Majoris and S Persei.
Liquid water
Liquid water is present on Earth, covering 71% of its surface. Liquid water is also occasionally present in small amounts on Mars. Scientists believe liquid water is present in the Saturnian moons of Enceladus, as a 10-kilometre thick ocean approximately 30–40 kilometres below Enceladus' south polar surface, and Titan, as a subsurface layer, possibly mixed with ammonia. Jupiter's moon Europa has surface characteristics which suggest a subsurface liquid water ocean. Liquid water may also exist on Jupiter's moon Ganymede as a layer sandwiched between high pressure ice and rock.
Water ice
Water is present as ice on:
South polar ice cap of Mars during Martian south summer 2000
Mars: under the regolith and at the poles.
Earth–Moon system: mainly as ice sheets on Earth and in Lunar craters and volcanic rocks NASA reported the detection of water molecules by NASA's Moon Mineralogy Mapper aboard the Indian Space Research Organization's Chandrayaan-1 spacecraft in September 2009.
Ceres
Jupiter's moons: Europa's surface and also that of Ganymede and Callisto
Saturn: in the planet's ring system and on the surface and mantle of Titan and Enceladus
Pluto–Charon system
Comets and other related Kuiper belt and Oort cloud objects
And is also likely present on:
Mercury's poles
Tethys
Exotic forms
Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper still as superionic water in which the oxygen crystallizes, but the hydrogen ions float about freely within the oxygen lattice.
Water and planetary habitability
Further information: Water distribution on Earth and Planetary habitability
The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the Solar System; if it were slightly closer to or farther from the Sun (about 5%, or about 8 million kilometers), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.
Earth's gravity allows it to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in polar ice caps (as on Mars).
The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.
The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanets Gliese 436 b and GJ 1214 b.
Law, politics, and crisis
Main articles: Water law, Water right, and Water scarcity
This section needs to be updated. Please help update this article to reflect recent events or newly available information. (June 2022)
An estimate of the proportion of people in developing countries with access to potable water 1970–2000
Water politics is politics affected by water and water resources. Water, particularly fresh water, is a strategic resource across the world and an important element in many political conflicts. It causes health impacts and damage to biodiversity.
Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.
1.6 billion people have gained access to a safe water source since 1990. The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970 to 71% in 1990, 79% in 2000, and 84% in 2004.
A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption. In addition, global initiatives to improve the efficiency of aid delivery, such as the Paris Declaration on Aid Effectiveness, have not been taken up by water sector donors as effectively as they have in education and health, potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act.
The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context. Mistakes have sometimes been made by trying to apply 'blueprints' that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken. They also discovered that Cambodia's draft water law was much more complex than it needed to be.
In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases, which are often tied to a lack of adequate sanitation.
Since 2003, the UN World Water Development Report, produced by the UNESCO World Water Assessment Programme, has provided decision-makers with tools for developing sustainable water policies. The 2023 report states that two billion people (26% of the population) do not have access to drinking water and 3.6 billion (46%) lack access to safely managed sanitation. People in urban areas (2.4 billion) will face water scarcity by 2050. Water scarcity has been described as endemic, due to overconsumption and pollution. The report states that 10% of the world's population lives in countries with high or critical water stress. Yet over the past 40 years, water consumption has increased by around 1% per year, and is expected to grow at the same rate until 2050. Since 2000, flooding in the tropics has quadrupled, while flooding in northern mid-latitudes has increased by a factor of 2.5. The cost of these floods between 2000 and 2019 was 100,000 deaths and $650 million.
Organizations concerned with water protection include the International Water Association (IWA), WaterAid, Water 1st, and the American Water Resources Association. The International Water Management Institute undertakes projects with the aim of using effective water management to reduce poverty. Water related conventions are United Nations Convention to Combat Desertification (UNCCD), International Convention for the Prevention of Pollution from Ships, United Nations Convention on the Law of the Sea and Ramsar Convention. World Day for Water takes place on 22 March and World Oceans Day on 8 June.
In culture
Religion
Main article: Water and religion
See also: Sacred waters
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water.
Water is considered a purifier in most religions. Faiths that incorporate ritual washing (ablution) include Christianity, Hinduism, Islam, Judaism, the Rastafari movement, Shinto, Taoism, and Wicca. Immersion (or aspersion or affusion) of a person in water is a central Sacrament of Christianity (where it is called baptism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after washing certain parts of the body using clean water (wudu), unless water is unavailable (see Tayammum). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of misogi).
In Christianity, holy water is water that has been sanctified by a priest for the purpose of baptism, the blessing of persons, places, and objects, or as a means of repelling evil.
In Zoroastrianism, water (āb) is respected as the source of life.
Philosophy
Icosahedron as a part of Spinoza monument in Amsterdam
The Ancient Greek philosopher Empedocles saw water as one of the four classical elements (along with fire, earth, and air), and regarded it as an ylem, or basic substance of the universe. Thales, whom Aristotle portrayed as an astronomer and an engineer, theorized that the earth, which is denser than water, emerged from the water. Thales, a monist, believed further that all things are made from water. Plato believed that the shape of water is an icosahedron – flowing easily compared to the cube-shaped earth.
The theory of the four bodily humors associated water with phlegm, as being cold and moist. The classical element of water was also one of the five elements in traditional Chinese philosophy (along with earth, fire, wood, and metal).
Some traditional and popular Asian philosophical systems take water as a role-model. James Legge's 1891 translation of the Dao De Jing states, "The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the Tao" and "There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed." Guanzi in the "Shui di" 水地 chapter further elaborates on the symbolism of water, proclaiming that "man is water" and attributing natural qualities of the people of different Chinese regions to the character of local water resources.
Folklore
"Living water" features in Germanic and Slavic folktales as a means of bringing the dead back to life. Note the Grimm fairy-tale ("The Water of Life") and the Russian dichotomy of living [ru] and dead water [ru]. The Fountain of Youth represents a related concept of magical waters allegedly preventing aging.
Art and activism
Painter and activist Fredericka Foster curated The Value of Water, at the Cathedral of St. John the Divine in New York City, which anchored a year-long initiative by the Cathedral on our dependence on water. The largest exhibition to ever appear at the Cathedral, it featured over forty artists, including Jenny Holzer, Robert Longo, Mark Rothko, William Kentridge, April Gornik, Kiki Smith, Pat Steir, Alice Dalton Brown, Teresita Fernandez and Bill Viola. Foster created Think About Water, an ecological collective of artists who use water as their subject or medium. Members include Basia Irland, Aviva Rahmani, Betsy Damon, Diane Burko, Leila Daw, Stacy Levy, Charlotte Coté, Meridel Rubenstein, and Anna Macleod.
To mark the 10th anniversary of access to water and sanitation being declared a human right by the UN, the charity WaterAid commissioned ten visual artists to show the impact of clean water on people's lives.
Dihydrogen monoxide parody
Main article: Dihydrogen monoxide parody
'Water' is technically correct but rarely used chemical name, dihydrogen monoxide, has been used in a series of hoaxes and pranks that mock scientific illiteracy. This began in 1983, when an April Fools' Day article appeared in a newspaper in Durand, Michigan. The false story consisted of safety concerns about the substance.
Music
The word "Water" has been used by many Florida based rappers as a sort of catchphrase or adlib. Rappers who have done this include BLP Kosher and Ski Mask the Slump God. To go even further some rappers have made whole songs dedicated to the water in Florida, such as the 2023 Danny Towers song "Florida Water". Others have made whole songs dedicated to water as a whole, such as XXXTentacion, and Ski Mask the Slump God with their hit song "H2O".
See also
Oceans portalWater portal
Outline of water – Overview of and topical guide to water
Water (data page) – Chemical data page for water is a collection of the chemical and physical properties of water.
Aquaphobia – Persistent and abnormal fear of water
Human right to water and sanitation – Human right recognized by the United Nations General Assembly in 2010
Hydroelectricity – Electricity generated by hydropower
Marine current power – Extraction of power from ocean currents
Marine energy – Energy stored in the waters of oceans
Mpemba effect – Natural phenomenon that hot water freezes faster than cold
Oral rehydration therapy – Type of fluid replacement used to prevent and treat dehydration
Osmotic power – Energy available from the difference in the salt concentration between seawater and river water
Properties of water – Physical and chemical properties of pure water
Thirst – Craving for potable fluids experienced by animals
Tidal power – Technology to convert the energy from tides into useful forms of power
Water pinch analysis
Wave power – Transport of energy by wind waves, and the capture of that energy to do useful work
Catchwater – Runoff catching or channeling device
Notes
^
A commonly quoted value of 15.7 used mainly in organic chemistry for the pKa of water is incorrect.
^ Vienna Standard Mean Ocean Water (VSMOW), used for calibration, melts at 273.1500089(10) K (0.000089(10) °C, and boils at 373.1339 K (99.9839 °C). Other isotopic compositions melt or boil at slightly different temperatures.
^ see the taste and odor section
^ Other substances with this property include bismuth, silicon, germanium and gallium. | biology | 6633 | https://sv.wikipedia.org/wiki/Vatten | Vatten | Vatten är en på jorden allmänt förekommande kemisk förening, bestående av väte och syre, som är nödvändig för allt känt liv. Det vetenskapliga namnet är divätemonoxid eller diväteoxid (se även diväteoxidbluffen). Det latinska namnet aqua används ofta i bland annat innehållsförteckningar till kemiska och kosmetiska produkter.
Till vardags menar man med "vatten" bara dess flytande aggregationstillstånd, men vatten förekommer även i fast form, som is, och i gasform, som vattenånga. Vatten täcker 70 % av jordytan. På jorden återfinns den största delen i akviferer och 0,001 % i atmosfären som ånga, moln (består av fasta och flytande vattenpartiklar), och nederbörd. Oceanerna innehåller 97 % av ytvattnet, glaciärer och polarisar 2,4 % och andra ytvattensamlingar, som floder, sjöar och dammar 0,6 %.
Vattnet på jorden rör sig kontinuerligt genom ett vattenkretslopp som består av avdunstning eller transpiration (evapotranspiration), nederbörd och ytavrinning, som vanligtvis når havet.
Rent, färskt dricksvatten är nödvändigt för människan och andra livsformer. Tillgången till säkert dricksvatten har ökat stadigt och avsevärt de senaste decennierna i nästan alla världens delar. Det finns ett tydligt samband mellan tillgång till rent vatten och BNP per capita. Några observatörer har dock beräknat att mer än hälften av jordens folkmängd kommer att drabbas av vattenbaserad sårbarhet år 2025. En rapport från november 2009 menar att vattenbehovet kommer överstiga tillgången med 50 % i några utvecklingsregioner år 2030. Vatten spelar en viktig roll i världsekonomin. Det fungerar som ett lösningsmedel för ett antal olika kemikalier och underlättar industriell nedkylning och transport. Omkring 70 procent av färskvattnet går till jordbruket.
Kemiska och fysikaliska egenskaper
Vatten är en kemisk förening med den kemiska formeln H2O. En vattenmolekyl består sålunda av två väteatomer i kovalent bindning till en syreatom. Inom kärnkraftsindustrin kallas vanligt vatten lättvatten för att skilja det från tungt och halvtungt vatten. Vatten förekommer på jorden i alla de tre vanliga aggregationstillstånden: vattenånga och moln i himlen, havsvatten och isberg i polarhaven, glaciärer och floder i bergen, och vätska i akviferen i marken.
De viktigaste kemiska och fysikaliska egenskaperna hos vatten är:
Vatten är en lukt- och smaklös vätska i standardtryck och -temperatur. Is och vattens färg har i sig självt en mycket svagt blå färgton, även om vattnet verkar färglöst i små mängder. Is verkar också färglöst, och vattenånga är i huvudsak osynlig som gas.
Vatten är transparent och således kan vattenväxter leva i vattnet eftersom solljuset kan nå dem. Bara starka ultravioletta strålar blir obetydligt absorberade.
Då vattenmolekylen inte är linjär och syreatomen har en högre elektronegativitet än väteatomer har syreatomen något större negativ laddning, medan väteatomerna är något positiva. Som ett resultat av detta är vatten en polär molekyl med ett elektriskt dipolmoment. Nätväxelverkan mellan dipolerna på varje molekyl kan orsaka en effektiv skineffekt på vattnets yta med andra substanser, eller luft vid ytan, den senare har gett upphov till vattnets höga ytspänning. Ytspänningen är temperaturberoende och minskar vid högre temperatur (se figur). Varmvatten väter bättre än kallvatten. Vattnets dipolära natur bidrar till vattenmolekylens tendens att forma vätebindningar, vilka bidrar till vattnets speciella egenskaper. Den polära naturen favoriserar även adhesion till andra material.
Varje vätekärna är bunden till den centrala syreatomen genom ett elektronpar som delas mellan dem. Kemister kallar det delade elektronparet för en kovalent kemisk bindning. I H2O används bara två av de sex elektronerna på det yttre skalet av syreatomen till det här syftet, vilket lämnar fyra elektroner organiserade i två obundna par. De fyra elektronparen som omger syret tenderar arrangera sig själva så långt bort från varandra som möjligt för att minimera bortstötningarna mellan dessa negativt laddade skaror. Det leder normalt till en tetraedrisk geometri i vilken vinkeln mellan elektronparen (och därför H-O-H-bindningsvinkeln) är 109,5°. Då de två obundna paren orienterar sig närmare syreatomen, har dessa en starkare bortstötning mot de två kovalent bundna paren, som effektivt trycker de två väteatomerna närmare varandra. Det leder till en förvrängd tetraedrisk disposition där H-O-H-vinkeln är 104,5°.
Som ett resultat av samspelet mellan dessa egenskaper avser kapillärkraft vattnets tendens att röra sig uppför ett smalt rör mot gravitationskraften. Den egenskapen utnyttjar alla kärlväxter såsom träd.
Vatten är ett bra lösningsmedel och kallas ofta ”det universella lösningsmedlet”. Ämnen som löser sig i vatten, exempelvis salter, sockerarter, syror, alkalimetaller och några gaser, speciellt syre och koldioxid, är kända som hydrofila ämnen, medan de som inte löser upp sig i vatten, exempelvis fetter och oljor, är kända som hydrofoba ämnen. Inom kemin anger en förkortning aq att ett ämne är löst i vatten, till exempel
Alla större komponenter i celler, protein, DNA och polysackarider löser sig också i vatten.
Rent vatten har en låg konduktivitet, vilken dock ökar påtagligt om man löser en liten mängd jonföreningar i vattnet, till exempel natriumklorid.
Vattnets kokpunkt beror (likt alla andra vätskors) på lufttrycket. Exempelvis kokar vatten på Mount Everests topp vid 68 °C, jämfört med 100 °C vid havsytan. Omvänt kan vatten på stora djup i oceanerna, nära geotermiska ventiler, uppnå temperaturer på flera hundra grader och ändå förbli flytande.
Vattnets volym expanderar ungefär 1650 gånger när det övergår från vätskefas till ångfas vid normalt tryck. (Vattenånga har specifik volym 1,694 m3/kg vid 1 bar.)
Vatten har den näst högsta värmekapacitiviteten av alla kända ämnen, efter ammoniak, och också hög ångbildningsvärme (40,65 kJ·mol−1. Det är ett resultat av vätebindningarna mellan dess molekyler. Dessa två ovanliga egenskaper gör att vatten kan moderera jordens klimat genom att buffra stora temperaturskillnader.
Vattnets maximala densitet uppnås vid 3,98 °C. Vatten blir mindre tätt vid fryspunkten, och har då expanderat med 9 %. Det resulterar i ett ovanligt fenomen, nämligen att vattnets fasta form, is, flyter ovanpå vatten, vilket gör att varelser kan leva i en delvis fryst vattenkropp då vattnet på botten har en temperatur på runt 4 °C.
Vatten är blandbart med många vätskor, såsom etanol, i alla proportioner vilket gör att det är en homogen vätska. Å andra sidan är vatten och de flesta oljor oblandbara, vilket gör att det vanligtvis skapas lager med en ökande densitet mot botten. Som gas är vattenångan blandbar med luften.
Vatten bildar en azeotrop med många andra ämnen.
Vatten kan genom elektrolys sönderdelas till väte och syre.
Som en oxid av väte skapas vatten när väte eller väteinnehållande föreningar bränner eller reagerar med syre eller syreinnehållande föreningar. Vatten är inte ett bränsle, utan en slutprodukt av förbränningen av väte. Energin som krävs för att sönderdela vatten till väte och syre genom elektrolys är större än energin som släpps när väte och syre återförenas.
Ämnen som är mer elektropositiva än väte såsom litium, natrium, kalcium, kalium och cesium förskjuter väte från vattnet vilket skapar hydroxider och vätgas. Vätgas är lättantändlig, så när vatten reagerar med mer elektropositiva ämnen kan reaktionen bli våldsamt explosiv.
Smak och lukt
Vatten kan lösa många olika ämnen, som ger vattnet olika smaker och lukter. Människor och djur har utvecklat smak- och luktsinnen som gör det möjligt för dem att utvärdera dricksvattnets drickbarhet och undvika vatten som är alltför salt eller smutsigt. Människor har en tendens att föredra kallt vatten före ljummet vatten då kallt vatten förmodligen innehåller färre mikroorganismer. Smaken som annonseras på källvatten eller mineralvatten kommer från de mineraler som är upplösta i det. Rent vatten är emellertid smak- och luktlöst. Den annonserade renheten på käll- och mineralvatten åsyftar frånvaron av toxiner, föroreningar och mikrober.
Etymologi
Ordet 'vatten' är ett urgemanskt arvord, från roten *wintru, som ytterst kan komma från den urindoeuropeiska roten *uendru. Från denna rot kan möjligen svenskans vinter ha kommit (kunde ha betytt "regntid"), engelskans water, wash med flera, tyskans Wasser, ryskans voda och vodka ("litet vatten"). Från den urindoeuropeiska avledningen *wed igenkänner man ord som grekiskans hydro (vatten) och hydra och svenskans utter (från urindoeuropeiska *udroz). Från den urindoeuropeiska roten *akwa- känner man igen latinets aqua, besläktat med svenskans å.
Vattnets fördelning
Vatten i universum
En stor del av universums vatten kan skapas som en biprodukt av stjärnbildning. När stjärnor föds ackompanjeras deras födsel av en stark utåtgående vind av gas och damm. När materialutflödet slutligen påverkar den omgivande gasen komprimeras chockvågorna som skapas och värmer gasen. Vattnet produceras snabbt i den varma, täta gasen.
Vatten har upptäckts i interstellära moln i vår galax, Vintergatan. Vatten existerar förmodligen i andra galaxer med, då dess komponenter, väte och syre, är bland de mest förekommande ämnena i universum. Interstellära moln kondenseras slutligen till nebulosor och solsystem såsom vårt.
Vattenånga finns i:
Merkurius atmosfär: 3,4 % (dock är atmosfären extremt tunn varför den totala mängden vattenånga är liten)
Venus atmosfär: 0,002 %
Jordens atmosfär: ~0,55 % i övre atmosfären, vanligtvis 1–4 % vid ytan
Mars atmosfär: 0,03 %
Jupiters atmosfär: 0,0004 %
Enceladus atmosfär: 91 ±3 % (atmosfären är dock extremt tunn)
Exoplaneterna HD 189733 b och HD 209458 b:s atmosfärer.
Flytande vatten finns i:
Jorden - 71 % av ytan
Månen – små mängder vatten påvisades 2008 inne i vulkaniska glaspärlor som togs från månen till jorden av Apollo 15-teamet 1971.
Vissa bevis talar för att flytande vatten finns precis under ytan på Saturnus måne Enceladus och på Jupiters måne Europa, där det kan finnas en 100 km djup ocean som täcker hela månen vilket skulle bli mer vatten än i alla jordens oceaner.
Vattenis finns i:
Jorden - huvudsakligen som inlandsisar
Polarisar på Mars
Månen
Titan
Europa
Saturnus ringar
Enceladus
Pluto och Charon
Kometer
Vattenis kan finnas på Ceres och Tethys.
Vatten och beboeliga områden
Det flytande vattnets existens, och i mindre grad dess gas- och fasta former är på jorden vitala för allt jordens liv. Jorden ligger i solsystemets beboeliga zon. Om den var något närmare eller längre bort från solen (runt 5 % eller runt 8 miljoner kilometer) skulle förhållandena som gör att alla tre formerna kan existera vara betydligt mindre gynnsamma.
Jordens gravitation gör att den har en atmosfär. Vattenånga och koldioxid i atmosfären möjliggör tillsammans med ozonskiktet växthuseffekten, som hjälper att bibehålla en relativt stadig yttemperatur. Om jordens massa hade varit mindre skulle en tunnare atmosfär leda till stora temperaturskillnader mellan ekvatorn och polerna varpå vatten bara skulle existera i form av is vid polerna som på planeten Mars.
Yttemperaturen på jorden har hållit sig relativt stadig genom de geologiska perioderna trots olika nivåer av inkommande solstrålning (solinstrålning). Det kan indikera att en dynamisk process styr jordens temperatur via en kombination av växthusgaser och den atmosfäriska albedons yta. Teorin är känd som gaiateorin.
Vattnets tillstånd på en planet beror på omgivningens tryck, som bestäms av planetens gravitation. Om en planet är tillräckligt stor kan vattnet på den vara fast även vid höga temperaturer, på grund av det höga trycket som orsakas av gravitationen.
Det finns olika teorier om vattnets ursprung på jorden.
Vatten på jorden
Läran om vattens rörelse, fördelning och kvalitet på jorden kallas hydrologi. Läran om vattnets fördelning kallas hydrografi. Läran om grundvattnets rörelse kallas hydrogeologi, läran om glaciärer heter glaciologi, om inlandsvatten limnologi, samt om fördelningen av oceaner oceanografi. Ekologiska processer med hydrologi studeras inom ekohydrologin.
Vattnets kollektiva massa ovan, under och på en planets yta kallas hydrosfären. Jordens ungefärliga vattenvolym, världens totala vattenmängd, är . Grundvatten och färskvatten är användbara, eller potentiellt användbara, för människor som vattenresurser. Flytande vatten finns i vattensamlingar såsom oceaner, hav, sjöar, floder, strömmar, kanaler och dammar. Majoriteten av världens vatten är havsvatten. Vatten finns även i atmosfären i fast, flytande och gasform. Det finns även grundvatten i akviferer.
Vatten är viktigt i många geologiska processer. Grundvatten är allestädes närvarande i jordskorpan, och trycket på detta grundvattnet påverkar förkastningsmönster. Vatten i manteln är ansvarigt för smältandet som skapar vulkaner på subduktionszoner. På jordens yta är vatten viktigt i både kemiska och fysikaliska vittringsprocesser. Vatten och – till en mindre men fortfarande märkbar grad – is är även ansvariga för en stor mängd sedimentförflyttning som sker på jordens yta. Avlagring av förflyttat sediment formar många sorters sedimentära bergarter, som skapar det geologiska registrerandet av jordens historia.
Under vissa ljusförhållanden kan regn ge upphov till en regnbåge.
Jordens vatten ur ett astronomiskt perspektiv
Endast i det yttre planetsystemet, där jätteplaneterna nu finns, var temperaturen och tätheten i solnebulosan lämplig för att planeterna skulle få stora mängder vatten. Allt vatten samlades dock inte i dessa jätteplaneter, utan många mindre kroppar rika på is bildades också (se Kuiperbältet). Jordens vatten har möjligtvis delvis ett ursprung från dessa små kroppar, och har tillförts jorden i form av nedslag av kometer.
Det har stor betydelse för livet på jorden att vatten finns i fast och flytande form och som gas. Jordens massa, som den största av stenplaneterna i det inre planetsystemet, är här av stor betydelse. Jordens massa ger ett tyngdkraftsfält som är tillräckligt starkt för att hålla kvar en atmosfär, vilket är förutsättningen för en jämn yttemperatur.
Även avståndet mellan jorden och solen är lagom för att vatten ska kunna förekomma i flytande form. Om jorden skulle ligga längre bort från solen skulle den vara kallare och allt vatten skulle vara is. Om jorden låg närmare solen skulle dess högre yttemperatur förhindra isbildningen vid polerna eller orsaka att vatten bara existerade som ånga. I det förra fallet skulle oceanernas låga albedo göra att jorden absorberade mer energi från solen. I båda fallen skulle jorden bli lika ogästvänlig som planeten Venus. (Se även antropiska principen.)
Vattnets kretslopp
Vattnet cirkulerar i ett ständigt utbyte mellan atmosfär, markvatten, dagvatten, grundvatten och växter. Alla områden som vattnet rör sig i kallas tillsammans för hydrosfären.
Följande processer överför vatten mellan olika regioner:
avdunstning från oceaner och andra vattensamlingar till luften och transpiration från landväxter och djur till luften.
nederbörd, från vattenånga som kondenseras från luften och som faller till marken eller havet.
ytavrinning från marken som vanligtvis når havet.
Den största delen av den vattenånga som befinner sig ovanför oceanerna återvänder till dessa, men vindar bär vattenånga över marken till samma grad som ytavrinning till havet, runt 10 biljoner ton om året. Ovan land bidrar avdunstning och transpiration med ytterligare 71 biljoner ton per år. Nederbörd, med 107 biljoner ton per år, har flera olika former: oftast regn, snö och hagel, samt i mindre mängder från dimma och dagg. Kondenserat vatten i luften kan även bryta solstrålar för att bilda regnbågar.
Ytavrinning ansamlas i avrinningsområden som flyter till ned i floder. En matematisk modell som används för att simulera vatten eller strömflöden och räkna ut parametrar på vattenkvalitet kallas på engelska hydrological transport model, fritt översatt "hydrologisk transportmodell". En del av vattnet används för konstbevattning i jordbruket. Floder och hav gör det möjligt att resa och handla. Genom erosion formar ytavrinningen omgivningen och skapar dalar och floddeltan som ger bördig jord och jämnt underlag för att etablera befolkningscentra. En översvämning inträffar när ett landområde som ofta ligger lågt täcks med vatten, när en flod översvämmar dess flodbankar eller översvämningar från havet. Torka är en förlängd period i månader eller år när en region får vattenbrist. Det inträffar när en region under en längre period får under genomsnittet i nederbörd.
Sötvattenslagring
120pxHögvatten (vänster) och ebb (höger).
En del avrinningsvatten blir i perioder kvar, exempelvis i sjöar. På hög höjd, under vintern, och långt i norr och syd, samlas snö i isar, snötäcken och glaciärer. Vatten infiltrerar även marken och går in i akviferer. Grundvattnet flyter senare tillbaka till ytan i vattenkällor, eller mer spektakulärt i heta källor och gejsrar. Grundvatten extraheras även artificiellt i brunnar. Vattenförvaringen är viktig, eftersom rent, färskt vatten är nödvändigt för människor och annat landbaserat liv. I många delar av världen finns det ont om färskvatten.
Havsvatten
Havsvatten innehåller 3,51 % salt i genomsnitt, och mindre mängder av andra substanser. De fysikaliska egenskaperna hos havsvatten skiljer sig från färskvatten i några viktiga aspekter. Det fryser vid en lägre temperatur (runt −1,9 °C) och dess densitet ökar med minskande temperatur ner till fryspunkten, istället för att nå maximal densitet vid en temperatur ovan fryspunkten (3,9 °C). Salthalten i de större havens vatten varierar från nästan sötvatten i norra Östersjön till 4 % i Röda havet.
Tidvatten
Tidvatten är det cykliska stigandet och fallandet av jordens oceanytor som orsakas av tidvattenkrafter från månen och solen. Tidvatten orsakar förändringar i marina och estuarierelaterade vattensamlingars djup och orsakar oscillerande strömmar kända som tidvattensströmmar. Förändringarna i tidvattnet på en given plats är resultatet av månens och solens förändrade positioner i förhållande till jorden tillsammans med effekterna av jordens rotation och den lokala batymetrin. Havsstränder som hamnar under vatten vid högvatten och som åter kommer fram vid ebb, i tidvattenszonen, är en viktig ekologisk miljö som tidvattnet skapat.
Vattnets biologiska roll
Från en biologisk synvinkel har vatten många speciella egenskaper som är nödvändiga för liv som särskiljer det från andra ämnen. Exempelvis tillåter vatten kolföreningar att reagera på sätt som gör reproducering möjligt, löser lätt andra ämnen och har hög ytspänning. Alla kända former av liv är beroende av vatten. Vatten är vitalt både som ett lösningsmedel i vilka många av kroppens ämnen löser sig och är en essentiell del av många metaboliska processer i kroppen. Metabolism är summan av anabolism och katabolism. I anabolism tas vatten bort från molekyler (genom energi som kräver kemiska enzymreaktioner) för att odla större molekyler (såsom stärkelse, triglycerider och proteiner för lagring av bränslen och information). I katabolism används vatten för att bryta band för att generera mindre molekyler (såsom glukos, fettsyror och aminosyror att använda som bränslen för energi eller andra syften). Vatten är essentiellt och centralt i dessa metaboliska processer. Dessa metaboliska processer skulle utan vatten inte kunna fungera.
Vatten är även centralt i fotosyntesen och cellandningen. Fotosyntetiska celler använder solens energi för att skilja vattnets väte från syre. Väte kombineras med koldioxid (absorberas från luft eller vatten) för att bilda glukos, varvid syre frigörs. Alla levande celler använder sådana bränslen och oxiderar vätet och kolet som innehåller fångad solenergi och ombildar vatten och koldioxid i processen (cellandning).
Vatten är även centralt för syrabaserad neutralitet och enzymfunktioner. En syra, en vätejondonator (H+, som är en proton) kan neutraliseras av en bas, en protonacceptor såsom hydroxidjoner (OH−) och bilda vatten. Vatten anses vara neutralt, med ett pH på 7. Vattenlösningar av syror har pH-värden under 7 medan de med baser har värden över 7.
Magsyra (HCl) används i matspjälkningen. Dess frätande effekter på matstrupen under återinflödet kan temporärt neutraliseras av intagandet av en bas såsom aluminiumhydroxid för att bilda de neutrala molekylerna vatten och saltet aluminiumklorid.
Exempelvis innehåller en escherichia coli-cell 70 procent vatten, människokroppen 55–60 procent (kvinnor respektive män), växter upp till 90 procent och en färdigbildad manet utgörs av 94–98 procent vatten.
Hydrofoba ämnen, som till exempel oljor, passar inte ihop med vatten. Detta, tillsammans med vattnets ytspänning, utnyttjas i cellernas membran, som består av lipider och proteiner, för att styra kemiska processer. Vattnets ytspänning gör små vattendroppar stabila vilket är avgörande för växternas transpiration.
Livet på jorden har utvecklats med och anpassat sig till vattnets egenskaper. Lika överraskande som vattnets egenskaper kan tyckas vara är livets förmåga att anpassa sig till de ibland mycket extrema miljöer som vattnet ger upphov till. Djur och växter som endast lever i vatten kallas akvatiska.
Akvatiska livsformer
Jordens vatten är fyllda av liv. De tidigaste livsformerna uppkom i vattnet. Nästan alla fiskar lever uteslutande i vatten, och det finns många sorters marina däggdjur, såsom delfiner och valar som också lever i vatten. Några sorters djur, såsom amfibier, tillbringar delar av sina liv i vatten och delar på land. Växter såsom kelp och alger växer i vattnet och är bas för några viktiga undervattenbaserade ekosystem. Plankton är basen i oceaners näringskedjor.
Akvatiska djur måste få syrgas för att överleva, och det sker på olika sätt. Fiskar har gälar istället för lungor, även om några fiskarter, såsom lungfiskar, har både och. Marina däggdjur, såsom delfiner, valar, uttrar och sälar har lungor och behöver därför gå upp till ytan emellanåt för att andas. Mindre livsformer kan absorbera syre genom skinnet.
Vatten och människan
Civilisationen har historiskt sett blomstrat runt floder och större vattensamlingar; Mesopotamien, som kallats "civilisationens vagga", låg mellan de två större floderna Tigris och Eufrat. Det egyptiska antika samhället var helt beroende av Nilen.
Stora metropoler som Rotterdam, London, Montréal, Paris, New York, Buenos Aires, Shanghai, Tokyo, Chicago och Hongkong har sin framgång i den nära tillgången till vatten och den av det resulterande handelsexpansionen. Öar med säkra vattenhamnar, som Singapore, har blomstrat av samma anledning. Ställen där vattentillgången är knappare, som Nordafrika och Mellanöstern, är tillgången till rent dricksvatten en viktig faktor för utvecklingen.
Alla former av liv på jorden är beroende av vatten. Vatten har en viktig roll i kroppens metabolism. Stora mängder vatten går åt till matspjälkningen. Vissa bakterier och växter kan dock inta anabiotiska tillstånd under mycket långa perioder då de helt torkar ut för att sedan leva upp igen när vatten åter finns att tillgå.
Till skillnad från många andra djur har människan låg tolerans mot uttorkning. Redan tio procents vätskebrist kan vara livshotande. Kamelen och dromedaren tål upp till 30 procents uttorkning, björndjur (phylum Tardigrada, knappt millimeterstora organismer) tål i ännu högre grad uttorkning.
Det kan även vara farligt att dricka för mycket vatten. En överkonsumtion av vatten kan leda till hyponatremi.
All inlagring av energi i musklerna sker med vatten. 1 gram kolhydrat, eller glykogen, lagras med 2,7 gram vatten, som sedan frigörs då energin förbrukas.
Hälsa och förorening
Vatten som är lämpligt för mänsklig konsumtion kallas dricksvatten. Vatten som inte är drickbart kan bli det genom filtrering eller destillering, eller genom andra metoder (kemiska metoder eller värmebehandling som dödar bakterier). Emellanåt används termen "säkert vatten" för att beskriva dricksvatten med lägre kvalitetströskel (det vill säga, som kan användas av människor som har sämre tillgång till vattenreningsprocesser, och som gör mer nytta än skada). Vatten som inte är lämpligt för förtäring men som inte är direkt skadligt för människor för simning eller bad kallas emellanåt också säkert vatten, eller "badsäkert". Klor är ett hud- och slemhinneirriterande ämne som vanligtvis används för att göra vatten bad- och drickssäkert. Dess användning övervakas ofta av statliga förordningar. Vanligtvis används 1 del per miljon för dricksvatten, och 1–2 delar per miljon för badvatten.
Förekomsten av vatten som naturresurs är knapp i vissa områden på vår planet, och dess tillgänglighet blir då av stor social och ekonomisk angelägenhet. För närvarande dricker ungefär en miljard människor regelbundet ohälsosamt vatten. De flesta länder accepterade målet att halvera mängden personer över hela världen som inte har tillgång till säkert vatten och rening under G8-mötet 2003 till 2015. Även om det svåra målet skulle uppnås, kommer det fortfarande att finnas drygt en halv miljard människor utan tillgång till säkert dricksvatten och över en miljard utan tillgång till adekvat rening. Dålig vattenkvalitet och dålig rening är dödlig; ungefär fem miljoner dödsfall om året orsakas av förorenat dricksvatten. WHO uppskattar att säkert vatten skulle förebygga 1,4 miljoner barndödsfall från diarré varje år.
I utvecklingsländerna går fortfarande 90 procent av allt avloppsvatten obehandlat ut i floder och andra vattendrag. Runt 50 länder, med drygt en tredjedel av världens befolkning, har ont om vatten, vissa av dessa i hög grad, och 17 av dessa länder använder mer vatten årligen än vad som kommer tillbaka genom vattnets naturliga kretslopp. Belastningen påverkar inte bara ytliga färskvattentäkter som floder och sjöar, utan bryter också ner grundvattensresurserna.
Organiska mikroföroreningar är föroreningar som förekommer i den akvatiska miljön i låga halter, ofta i mikro- eller nanogram per liter. Utsläpp från reningsverk benämns ofta som en källa till förekomsten av dessa ämnen. Organiska mikroföroreningar kan delas upp i olika kategorier baserat på deras ursprung. Till exempel läkemedelsrester, rester från hygien- och kosmetikaprodukter (bland andra mikroplaster), pesticider, flamskyddsmedel (bland andra perfluorerade alkylsyror PFAS) och industrikemikalier.
Förekomsten av organiska mikroföroreningar i den akvatiska miljön kan få olika betydelse beroende på ämnesspecifika egenskaper, i vilken koncentration ämnet förekommer och vilken organism som exponeras för vattnet. För olika typer av vatten finns etablerade toleransnivåer eller gränsvärden för olika ämnen och vilka koncentrationer av dessa som kan accepteras som säkra i miljön eller i dricksvatten.
Vatten som strategisk och ekonomisk tillgång
Dricksvattentillgång är framför allt ett problem i torra och fattiga områden, men även i rikare och regnigare områden. I sistnämnda områden kan problemet lösas till höga kostnader. Bolmentunneln, en 82 km lång tunnel byggdes för att säkra Skånes tillgång till bra vatten. I Saudiarabien och Arabemiraten avsaltas havsvatten till dricksvatten, en mycket energikrävande och kostsam process.
Samtidigt har andelen människor med tillgång till vatten kraftigt ökat under 1900-talet och i industriländer finns ingen reell vattenbrist, vilken antyder att vattenproblemet framför allt är en fråga om ekonomi. En FN-rapport fastslog att det "finns tillräckligt med vatten för alla".
Generellt kan man säga att Amerika (speciellt Sydamerika) har mer dricksvatten per invånare än Eurasien. För specifika regioner gäller exempelvis:
Asien har 60 procent av världens befolkning och 36 procent av världens vattentillgångar.
Europa har 13 procent av världens befolkning och 8 procent av världens vattentillgångar.
Afrika har 13 procent av världens befolkning och 11 procent av världens vattentillgångar.
Nordamerika har 8 procent av världens befolkning och 15 procent av världens vattentillgångar.
Sydamerika har 6 procent av världens befolkning och 26 procent av världens vattentillgångar.
Även inom turistindustrin är vatten en utomordentlig viktig tillgång , inte bara som vatten utan även som snö och is. En stor andel av turistresorna går till orter vid hav och sjöar eller till skidorter. I många kustländer och öriken utgör turismen en viktig inkomstkälla. Värdet på fritidsbostäder är betydligt högre om bostaden är sjö- eller havsnära.
Vatten i katastrofer
Vatten orsakar också många människors död, i flodvågor och översvämningar. Då vatten väller fram i stora mängder kan det krossa allt i sin väg och spola bort även grundfasta hus. Flodvågor och översvämningar orsakas ofta av orkaner, jordbävning, eller i mindre skala av våldsamma skyfall.
Jordskred är en annan typ av naturkatastrof som ofta uppstår genom att sluttande lager av lera eller annan finkornig jordart mättats med vatten och därefter genomgått en drastisk minskning av sin stabilitet. Jordskred kan även utlösas då sluttande mark fått sin växtlighet borttagen, så att växternas rötter inte längre förmår ”armera” jorden.
Poröst och vittrat berg kan utsättas för frostsprängning vintertid, så att stenblock lossnar och faller ner på vägar och hus.
Varje år sker många dödsolyckor vid laviner. Även hela byar har krossats och begravts vid sådana katastrofer vid ogynnsam väderlek som utlöst en lavin.
Vidare dör många genom drunkning, vilket naturligtvis inte är att räkna som en naturkatastrof. Vid båt- och fartygshaverier drunknar ofta människor; människor faller överbord; andra drunknar under bad och simning.
Av de 10 naturkatastroferna med flest antal döda spelade vatten en stor roll i 7 av dem.
Mänskliga användningsområden
Jordbruk
Jordbrukets viktigaste användningsområde för vatten är konstbevattning som är viktigt för att producera tillräckligt med mat. Konstbevattning upptar 90 procent av det använda vattnet i flera utvecklingsländer och en stor del även i mer ekonomiskt utvecklade länder (USA, 30 procent av färskvattenanvändandet är konstbevattning).
Vatten som en vetenskaplig standard
Den 7 april 1795 definierades 1 gram i Frankrike att vara samma som ”den absoluta vikten av en volym av rent vatten till samma mängd som en kub av en hundradels meter, och till temperaturen av smältande is.” För praktiska syften krävdes dock en metallisk referensstandard som var tusen gånger tyngre, det vill säga kilogramet. Ansträngningar gjordes därför att precist bestämma massan av en liter vatten. Trots den förordade definitionen av gramspecificerat vatten vid 0 °C – en väldigt reproducerbar temperatur – valde vetenskapsmännen att omdefiniera standarden och att göra mätningarna vid den temperatur då vatten har högst densitet, det vill säga 4 °C.
Internationella måttenhetssystemets Kelvinskala är baserad på vattnets trippelpunkt, definierat som exakt 273,16 K eller 0,01 °C. Skalan är en mer exakt utveckling av Celsius-skalan, som ursprungligen definierades enligt vattnets kokpunkt (100 °C) och smältpunkt (0 °C).
Naturligt vatten består huvudsakligen av isotoperna väte-1 och syre-16, men det finns även små mängder av tyngre isotoper såsom väte-2 (deuterium) och väte-3 (tritium). Mängden deuteriumoxid eller tungt vatten är väldigt liten, men påverkar ändå vattnets egenskaper. Vatten från floder och sjöar tenderar innehålla mindre deuterium än havsvatten. Därför är standardvatten definierat enligt Vienna Standard Mean Ocean Water-specifikationen.
Dricksvatten
Människokroppen består till mellan 55 och 78 procent av vatten, beroende på kroppsstorleken. För att fungera ordentligt behöver kroppen tillföras mellan en och sju liter vatten per dag för att undvika uttorkning (dehydrering). Den exakta mängden beror på hur aktiv man är, temperatur, luftfuktighet och andra faktorer. Mängden vatten i kroppen styrs av osmoregleringen.
Den största delen vatten får man i sig genom mat och dryck. Det går inte exakt att fastställa hur mycket vatten en välmående person behöver, även om en vanlig uppskattning är att sex till sju glas (runt 2 liter) dagligen är minimum för att hydreringen skall fungera ordentligt. Medicinska skrifter förespråkar en mindre mängd, vanligtvis 1 liter vatten för en genomsnittlig man, oräknat extra behov beroende på vätskeförlust vid varmt väder eller träning.
För den som har friska njurar är det svårt att dricka för mycket vatten, men speciellt i varmt fuktigt väder och vid träning är det farligt att dricka för lite. Personer kan dricka betydligt mer vatten än vad som behövs under träning vilket i förlängningen ger en viss risk för vattenförgiftning, som kan vara dödligt. Rekommendationen att en person borde dricka åtta glas vatten om dagen saknar vetenskapligt stöd.
En äldre rekommendation för vattenintag, från 1945 av "Food and Nutrition Board" av United States National Research Council säger: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." (Fritt översatt: En vanlig standard för olika personer är en milliliter vatten för varje kalori mat. Den största delen av detta kommer från tillagad mat.) De senaste dietiska referenserna för intag av vatten av dem är allmänt rekommenderat (inklusive från mat): 2,7 liter vatten för kvinnor och 3,7 liter för män. Speciellt gravida och ammande kvinnor behöver mer vätska för att inte bli dehydrerade. Enligt Institute of Medicine - som rekommenderar att kvinnor i genomsnitt får i sig 2,2 liter och män 3 liter, rekommenderas det vara 2,4 liter för gravida kvinnor och 3 liter för ammande kvinnor då en speciellt stor mängd vätska förloras under amning. Noterbart är att normalt sett kommer runt 20 procent av vattenintaget från mat, medan resten kommer från att dricka vatten och drycker. Vatten lämnar kroppen på flera sätt; genom urin och avföring, svettning, och utandning av vattenånga när man andas. Med fysisk ansträngning och värmeexponering ökar vätskeförlusten och det dagliga behovet av vätskeintag ökar.
Människor behöver relativt rent vatten. Vanliga orenheter är bland annat metallsalter och oxider (däribland koppar, järn, kalcium och bly) och/eller skadliga bakterier såsom Vibrio. Några lösningar är accepterade och till och med önskade för att förhöja smaken och tillföra kroppen behövda elektrolyter.
Den enskilt största färskvattenkällan som innehåller drickbart vatten är Bajkalsjön i Sibirien, som har väldigt låg salt- och kalciumhalt och därför är väldigt ren.
Hygien
Vattnets förmåga att göra solvatiseringar och emulsioner används vid tvättning. Många industriella processer använder reaktioner där i vatten upplösta kemikalier används, suspension av fasta ämnen i vattenslam eller att använda vatten för att lösa upp och extrahera ämnen.
Kemiska användningsområden
Vatten används ofta i kemiska reaktioner som ett lösningsmedel eller reaktant och mer sällan som löst ämne eller katalysator. I oorganiska reaktioner är vatten ett vanligt lösningsmedel, som löser upp många jonföreningar. I organiska reaktioner är vatten mindre vanligt som reagerande lösningsmedel, då det inte löser reaktanterna så bra och är amfolytiskt och nukleofilt. Icke desto mindre är dessa egenskaper emellanåt önskvärda. Likväl har en ökning av Diels–Alderreaktioner av vatten observerats. Superkritisk vätska har nyligen blivit ett ämne att forska i. Syremättat superkritiskt vatten förbränner organiska föroreningar effektivt.
Som en värmeutbytesvätska
Vatten och ånga används som medel för värmeutbyte i olika värmeutbytessystem, på grund av tillgängligheten och den höga värmekapaciteten, både för nedkylning och upphettning. Kallt vatten kan även vara naturligt tillgängligt från en sjö eller från havet. Att kondensera ånga är ett speciellt effektivt upphettningssystem på grund av den höga värmen vid förångning. En nackdel är att vatten och ånga är relativt frätande. I nästan alla elektriska kraftverk används vatten för nedkylning, vilket förångar och driver ångturbiner. I USA är nedkylande kraftverk ett stort användningsområde för vatten.
Inom kärnkraftsindustrin används vatten som moderator. I en tryckvattenreaktor är vatten både nedkylare och moderator. Det ger ett passivt säkerhetsmått, eftersom borttagning av vatten från reaktorn även saktar ner kärnreaktionen.
Vatten som konstnärlig inspiration
Människan har sannolikt alltid haft en stark dragning till vatten. För att ha god tillgång på dricksvatten, vatten till matlagning och rengöring, och för att få tag i fisk, har det varit bekvämt att bo nära vatten. Floder, sjöar och hav har dessutom erbjudit människan ett bekvämt sätt att transportera både sig själv och sina tillhörigheter.
Poeter har i alla tider skrivit och besjungit vatten, såväl källor, bäckar, sjöar och hav som regn, dimma, moln och regnbågar; konstnärer har målat vatten; musiker har komponerat med vatten som inspiration. I nutid är det dessutom exklusivt att bo strandnära, för att det är rofyllt att se ut över vatten och vågors spel.
Färg på vatten
Rent vatten ser färglöst ut i små mängder. Att havet ser blått ut har framförallt två orsaker, som bidrar i olika mån beroende på omständigheterna. Den ena faktorn är reflekterat ljus från en blå himmel. Den andra faktorn är vattnets egen färg, som är svagt blå. En liten mängd vatten ser färglös ut, men tittar man genom många meter vatten syns den blå färgen. Den blå färgen hos vattnet beror på att rött ljus absorberas av vibrationer i vattenmolekylerna, till skillnad från de flesta andra färger vi ser som beror ljusets växelverkan med elektroners excitation. I tropikerna där vattnet är klart syns vattnets färg speciellt tydligt på sandstränder där vattnet är grunt och sanden är vit. Anledningen till att havsvatten kan ha andra färger är att vattnet inte är rent eller att det är bemängt med plankton. Den grönbruna färg som havet har i till exempel Nordatlanten beror på att alger ger vattnet denna nyans.
Vatten i kulturen
Religion
Flera skapelsemyter låter själva skapelsen föregås av ett världshav, en "urocean", däribland den bibliska i Moseboken. Även syndaflod är ett i många föreställningar återkommande tema.
Vatten anses vara en renare i de flesta religioner. Större religioner som innehåller rituell tvagning är bland andra kristendom, hinduism, rastafari, islam, shinto, daoism och judendom. Nedsänkning av en person i vatten är ett centralt sakrament i kristendomen (där det kallas dop). Det är det även i fler religioner, däribland judendomen (mikvah) och sikhismen (Amrit Sanskar). Dessutom förekommer rituella bad i rent vatten för de döda i flera religioner, till exempel i judendomen och islam.
I islam görs de fem dagliga bönerna i många fall efter att ha tvättat delar av kroppen med rent vatten (wudu). I shinto används vatten i nästan alla ritualer för att rengöra en person eller ett område (exempelvis i ritualen misogi). Vatten omnämns 442 gånger i Bibeln i New International Version och 363 gånger i King James Bible. I Andra Petrusbrevets tredje kapitel vers 5 (2 Peter 3:5) står det "De bortser från att det för länge sedan fanns himlar och en jord som hade uppstått ur vatten och genom vatten i kraft av Guds ord."
Filosofi
Den antike grekiske filosofen Empedokles menade att vatten är ett av de fyra klassiska elementen tillsammans med eld, jord och luft, och ansåg det vara universums grundämne. Vatten ansågs vara kallt och fuktigt. Inom humoralpatologin associerades vatten med flegma. Vatten var också ett av de fem elementen inom kinesisk filosofi, tillsammans med jord, eld, trä och metall.
Vatten är även använt som en förebild i vissa delar av traditionell och populär asiatisk filosofi. James Legges översättning av Tao Te Ching från 1891 fastslår att ”Den högsta förträffligheten är liksom vatten. Vattnets förträfflighet visar sig i att det gynnar alla ting, och att det intar, utan att sträva (efter motsatsen), den låga ställning som alla människor ogillar. Därför är dess väg nära Tao”, och ”Det finns ingenting i världen mjukare och svagare än vatten, och ändå, när det kommer till att attackera saker som är fasta och starka finns det inget som kan överträffa det – för det finns inget (så verkningsfullt) som kan ersätta [vattnet]."
Litteratur
Vatten används inom litteraturen som en symbol för rening. Ett enkelt exempel är en flods avgörande betydelse i As I Lay Dying av William Faulkner och dränkandet av Ofelia i Hamlet. Sherlock Holmes konstaterade att "från en droppe vatten kan en logiker dra slutsatsen om Atlanten eller Niagarafallen, utan att ha sett eller hört av den ena eller den andre."
”Vattnet är ett farligt gift, vilket omger Visby stift” enligt boken En hvar sin egen professor av Falstaff, fakir (Axel Wallengren, 1865–1896).
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Vattenrätt
Tritierat vatten
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Vattenkraft
Referenser
Externa länkar
Fysikum om Vatten den märkligaste vätskan
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Wikipedia:Basartiklar | swedish | 0.401925 |
accelerate_plants_growth/Circadian_rhythm.txt | A circadian rhythm (/sərˈkeɪdiən/), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., endogenous) and responds to the environment (is entrained by the environment). Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
The term circadian comes from the Latin circa, meaning "around", and dies, meaning "day". Processes with 24-hour cycles are more generally called diurnal rhythms; diurnal rhythms should not be called circadian rhythms unless they can be confirmed as endogenous, and not environmental.
Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called zeitgebers (from German Zeitgeber (German: [ˈtsaɪtˌɡeːbɐ]; lit. 'time giver')), which include light, temperature and redox cycles. In clinical settings, an abnormal circadian rhythm in humans is known as a circadian rhythm sleep disorder.
History[edit]
The earliest recorded account of a circadian process is credited to Theophrastus, dating from the 4th century BC, probably provided to him by report of Androsthenes, a ship's captain serving under Alexander the Great. In his book, 'Περὶ φυτῶν ἱστορία', or 'Enquiry into plants', Theophrastus describes a "tree with many leaves like the rose, and that this closes at night, but opens at sunrise, and by noon is completely unfolded; and at evening again it closes by degrees and remains shut at night, and the natives say that it goes to sleep." The tree mentioned by him was much later identified as the tamarind tree by the botanist, H Bretzl, in his book on the botanical findings of the Alexandrian campaigns.
The observation of a circadian or diurnal process in humans is mentioned in Chinese medical texts dated to around the 13th century, including the Noon and Midnight Manual and the Mnemonic Rhyme to Aid in the Selection of Acu-points According to the Diurnal Cycle, the Day of the Month and the Season of the Year.
In 1729, French scientist Jean-Jacques d'Ortous de Mairan conducted the first experiment designed to distinguish an endogenous clock from responses to daily stimuli. He noted that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica persisted, even when the plants were kept in constant darkness.
In 1896, Patrick and Gilbert observed that during a prolonged period of sleep deprivation, sleepiness increases and decreases with a period of approximately 24 hours. In 1918, J.S. Szymanski showed that animals are capable of maintaining 24-hour activity patterns in the absence of external cues such as light and changes in temperature.
In the early 20th century, circadian rhythms were noticed in the rhythmic feeding times of bees. Auguste Forel, Ingeborg Beling, and Oskar Wahl conducted numerous experiments to determine whether this rhythm was attributable to an endogenous clock. The existence of circadian rhythm was independently discovered in fruit flies in 1935 by two German zoologists, Hans Kalmus and Erwin Bünning.
In 1954, an important experiment reported by Colin Pittendrigh demonstrated that eclosion (the process of pupa turning into adult) in Drosophila pseudoobscura was a circadian behaviour. He demonstrated that while temperature played a vital role in eclosion rhythm, the period of eclosion was delayed but not stopped when temperature was decreased.
The term circadian was coined by Franz Halberg in 1959. According to Halberg's original definition:
The term "circadian" was derived from circa (about) and dies (day); it may serve to imply that certain physiologic periods are close to 24 hours, if not exactly that length. Herein, "circadian" might be applied to all "24-hour" rhythms, whether or not their periods, individually or on the average, are different from 24 hours, longer or shorter, by a few minutes or hours.
In 1977, the International Committee on Nomenclature of the International Society for Chronobiology formally adopted the definition:
Circadian: relating to biologic variations or rhythms with a frequency of 1 cycle in 24 ± 4 h; circa (about, approximately) and dies (day or 24 h). Note: term describes rhythms with an about 24-h cycle length, whether they are frequency-synchronized with (acceptable) or are desynchronized or free-running from the local environmental time scale, with periods of slightly yet consistently different from 24-h.
Ron Konopka and Seymour Benzer identified the first clock mutation in Drosophila in 1971, naming the gene "period" (per) gene, the first discovered genetic determinant of behavioral rhythmicity. The per gene was isolated in 1984 by two teams of researchers. Konopka, Jeffrey Hall, Michael Roshbash and their team showed that per locus is the centre of the circadian rhythm, and that loss of per stops circadian activity. At the same time, Michael W. Young's team reported similar effects of per, and that the gene covers 7.1-kilobase (kb) interval on the X chromosome and encodes a 4.5-kb poly(A)+ RNA. They went on to discover the key genes and neurones in Drosophila circadian system, for which Hall, Rosbash and Young received the Nobel Prize in Physiology or Medicine 2017.
Joseph Takahashi discovered the first mammalian circadian clock mutation (clockΔ19) using mice in 1994. However, recent studies show that deletion of clock does not lead to a behavioral phenotype (the animals still have normal circadian rhythms), which questions its importance in rhythm generation.
The first human clock mutation was identified in an extended Utah family by Chris Jones, and genetically characterized by Ying-Hui Fu and Louis Ptacek. Affected individuals are extreme 'morning larks' with 4-hour advanced sleep and other rhythms. This form of familial advanced sleep phase syndrome is caused by a single amino acid change, S662➔G, in the human PER2 protein.
Criteria[edit]
To be called circadian, a biological rhythm must meet these three general criteria:
The rhythm has an endogenous free-running period that lasts approximately 24 hours. The rhythm persists in constant conditions, i.e. constant darkness, with a period of about 24 hours. The period of the rhythm in constant conditions is called the free-running period and is denoted by the Greek letter τ (tau). The rationale for this criterion is to distinguish circadian rhythms from simple responses to daily external cues. A rhythm cannot be said to be endogenous unless it has been tested and persists in conditions without external periodic input. In diurnal animals (active during daylight hours), in general τ is slightly greater than 24 hours, whereas, in nocturnal animals (active at night), in general τ is shorter than 24 hours.
The rhythms are entrainable. The rhythm can be reset by exposure to external stimuli (such as light and heat), a process called entrainment. The external stimulus used to entrain a rhythm is called the zeitgeber, or "time giver". Travel across time zones illustrates the ability of the human biological clock to adjust to the local time; a person will usually experience jet lag before entrainment of their circadian clock has brought it into sync with local time.
The rhythms exhibit temperature compensation. In other words, they maintain circadian periodicity over a range of physiological temperatures. Many organisms live at a broad range of temperatures, and differences in thermal energy will affect the kinetics of all molecular processes in their cell(s). In order to keep track of time, the organism's circadian clock must maintain roughly a 24-hour periodicity despite the changing kinetics, a property known as temperature compensation. The Q10 temperature coefficient is a measure of this compensating effect. If the Q10 coefficient remains approximately 1 as temperature increases, the rhythm is considered to be temperature-compensated.
Origin[edit]
This section is missing information about independently evolved four times [PMID 11533719]. Please expand the section to include this information. Further details may exist on the talk page. (September 2021)
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. They thus enable organisms to make better use of environmental resources (e.g. light and food) compared to those that cannot predict such availability. It has therefore been suggested that circadian rhythms put organisms at a selective advantage in evolutionary terms. However, rhythmicity appears to be as important in regulating and coordinating internal metabolic processes, as in coordinating with the environment. This is suggested by the maintenance (heritability) of circadian rhythms in fruit flies after several hundred generations in constant laboratory conditions, as well as in creatures in constant darkness in the wild, and by the experimental elimination of behavioral—but not physiological—circadian rhythms in quail.
What drove circadian rhythms to evolve has been an enigmatic question. Previous hypotheses emphasized that photosensitive proteins and circadian rhythms may have originated together in the earliest cells, with the purpose of protecting replicating DNA from high levels of damaging ultraviolet radiation during the daytime. As a result, replication was relegated to the dark. However, evidence for this is lacking: in fact the simplest organisms with a circadian rhythm, the cyanobacteria, do the opposite of this: they divide more in the daytime. Recent studies instead highlight the importance of co-evolution of redox proteins with circadian oscillators in all three domains of life following the Great Oxidation Event approximately 2.3 billion years ago. The current view is that circadian changes in environmental oxygen levels and the production of reactive oxygen species (ROS) in the presence of daylight are likely to have driven a need to evolve circadian rhythms to preempt, and therefore counteract, damaging redox reactions on a daily basis.
The simplest known circadian clocks are bacterial circadian rhythms, exemplified by the prokaryote cyanobacteria. Recent research has demonstrated that the circadian clock of Synechococcus elongatus can be reconstituted in vitro with just the three proteins (KaiA, KaiB, KaiC) of their central oscillator. This clock has been shown to sustain a 22-hour rhythm over several days upon the addition of ATP. Previous explanations of the prokaryotic circadian timekeeper were dependent upon a DNA transcription/translation feedback mechanism.
A defect in the human homologue of the Drosophila "period" gene was identified as a cause of the sleep disorder FASPS (Familial advanced sleep phase syndrome), underscoring the conserved nature of the molecular circadian clock through evolution. Many more genetic components of the biological clock are now known. Their interactions result in an interlocked feedback loop of gene products resulting in periodic fluctuations that the cells of the body interpret as a specific time of the day.
It is now known that the molecular circadian clock can function within a single cell. That is, it is cell-autonomous. This was shown by Gene Block in isolated mollusk basal retinal neurons (BRNs). At the same time, different cells may communicate with each other resulting in a synchronised output of electrical signaling. These may interface with endocrine glands of the brain to result in periodic release of hormones. The receptors for these hormones may be located far across the body and synchronise the peripheral clocks of various organs. Thus, the information of the time of the day as relayed by the eyes travels to the clock in the brain, and, through that, clocks in the rest of the body may be synchronised. This is how the timing of, for example, sleep/wake, body temperature, thirst, and appetite are coordinately controlled by the biological clock.
Importance in animals[edit]
Circadian rhythmicity is present in the sleeping and feeding patterns of animals, including human beings. There are also clear patterns of core body temperature, brain wave activity, hormone production, cell regeneration, and other biological activities. In addition, photoperiodism, the physiological reaction of organisms to the length of day or night, is vital to both plants and animals, and the circadian system plays a role in the measurement and interpretation of day length. Timely prediction of seasonal periods of weather conditions, food availability, or predator activity is crucial for survival of many species. Although not the only parameter, the changing length of the photoperiod (day length) is the most predictive environmental cue for the seasonal timing of physiology and behavior, most notably for timing of migration, hibernation, and reproduction.
Effect of circadian disruption[edit]
Mutations or deletions of clock genes in mice have demonstrated the importance of body clocks to ensure the proper timing of cellular/metabolic events; clock-mutant mice are hyperphagic and obese, and have altered glucose metabolism. In mice, deletion of the Rev-ErbA alpha clock gene can result in diet-induced obesity and changes the balance between glucose and lipid utilization, predisposing to diabetes. However, it is not clear whether there is a strong association between clock gene polymorphisms in humans and the susceptibility to develop the metabolic syndrome.
Effect of light–dark cycle[edit]
The rhythm is linked to the light–dark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a free-running rhythm. Their sleep cycle is pushed back or forward each "day", depending on whether their "day", their endogenous period, is shorter or longer than 24 hours. The environmental cues that reset the rhythms each day are called zeitgebers. Totally blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Although they lack image-forming eyes, their photoreceptors (which detect light) are still functional; they do surface periodically as well.
Free-running organisms that normally have one or two consolidated sleep episodes will still have them when in an environment shielded from external cues, but the rhythm is not entrained to the 24-hour light–dark cycle in nature. The sleep–wake rhythm may, in these circumstances, become out of phase with other circadian or ultradian rhythms such as metabolic, hormonal, CNS electrical, or neurotransmitter rhythms.
Recent research has influenced the design of spacecraft environments, as systems that mimic the light–dark cycle have been found to be highly beneficial to astronauts. Light therapy has been trialed as a treatment for sleep disorders.
Arctic animals[edit]
Norwegian researchers at the University of Tromsø have shown that some Arctic animals (e.g., ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets. In one study of reindeer, animals at 70 degrees North showed circadian rhythms in the autumn, winter and spring, but not in the summer. Reindeer on Svalbard at 78 degrees North showed such rhythms only in autumn and spring. The researchers suspect that other Arctic animals as well may not show circadian rhythms in the constant light of summer and the constant dark of winter.
A 2006 study in northern Alaska found that day-living ground squirrels and nocturnal porcupines strictly maintain their circadian rhythms through 82 days and nights of sunshine. The researchers speculate that these two rodents notice that the apparent distance between the sun and the horizon is shortest once a day, and thus have a sufficient signal to entrain (adjust) by.
Butterflies and moths[edit]
The navigation of the fall migration of the Eastern North American monarch butterfly (Danaus plexippus) to their overwintering grounds in central Mexico uses a time-compensated sun compass that depends upon a circadian clock in their antennae. Circadian rhythm is also known to control mating behaviour in certain moth species such as Spodoptera littoralis, where females produce specific pheromone that attracts and resets the male circadian rhythm to induce mating at night.
In plants[edit]
Sleeping tree by day and night
Plant circadian rhythms tell the plant what season it is and when to flower for the best chance of attracting pollinators. Behaviors showing rhythms include leaf movement (Nyctinasty), growth, germination, stomatal/gas exchange, enzyme activity, photosynthetic activity, and fragrance emission, among others. Circadian rhythms occur as a plant entrains to synchronize with the light cycle of its surrounding environment. These rhythms are endogenously generated, self-sustaining and are relatively constant over a range of ambient temperatures. Important features include two interacting transcription-translation feedback loops: proteins containing PAS domains, which facilitate protein-protein interactions; and several photoreceptors that fine-tune the clock to different light conditions. Anticipation of changes in the environment allows appropriate changes in a plant's physiological state, conferring an adaptive advantage. A better understanding of plant circadian rhythms has applications in agriculture, such as helping farmers stagger crop harvests to extend crop availability and securing against massive losses due to weather.
Light is the signal by which plants synchronize their internal clocks to their environment and is sensed by a wide variety of photoreceptors. Red and blue light are absorbed through several phytochromes and cryptochromes. Phytochrome A, phyA, is light labile and allows germination and de-etiolation when light is scarce. Phytochromes B–E are more stable with phyB, the main phytochrome in seedlings grown in the light. The cryptochrome (cry) gene is also a light-sensitive component of the circadian clock and is thought to be involved both as a photoreceptor and as part of the clock's endogenous pacemaker mechanism. Cryptochromes 1–2 (involved in blue–UVA) help to maintain the period length in the clock through a whole range of light conditions.
Graph showing timeseries data from bioluminescence imaging of circadian reporter genes. Transgenic seedlings of Arabidopsis thaliana were imaged by a cooled CCD camera under three cycles of 12h light: 12h dark followed by 3 days of constant light (from 96h). Their genomes carry firefly luciferase reporter genes driven by the promoter sequences of clock genes. The signals of seedlings 61 (red) and 62 (blue) reflect transcription of the gene CCA1, peaking after lights-on (48h, 72h, etc.). Seedlings 64 (pale grey) and 65 (teal) reflect TOC1, peaking before lights-off (36h, 60h, etc.). The timeseries show 24-hour, circadian rhythms of gene expression in the living plants.
The central oscillator generates a self-sustaining rhythm and is driven by two interacting feedback loops that are active at different times of day. The morning loop consists of CCA1 (Circadian and Clock-Associated 1) and LHY (Late Elongated Hypocotyl), which encode closely related MYB transcription factors that regulate circadian rhythms in Arabidopsis, as well as PRR 7 and 9 (Pseudo-Response Regulators.) The evening loop consists of GI (Gigantea) and ELF4, both involved in regulation of flowering time genes. When CCA1 and LHY are overexpressed (under constant light or dark conditions), plants become arrhythmic, and mRNA signals reduce, contributing to a negative feedback loop. Gene expression of CCA1 and LHY oscillates and peaks in the early morning, whereas TOC1 gene expression oscillates and peaks in the early evening. While it was previously hypothesised that these three genes model a negative feedback loop in which over-expressed CCA1 and LHY repress TOC1 and over-expressed TOC1 is a positive regulator of CCA1 and LHY, it was shown in 2012 by Andrew Millar and others that TOC1, in fact, serves as a repressor not only of CCA1, LHY, and PRR7 and 9 in the morning loop but also of GI and ELF4 in the evening loop. This finding and further computational modeling of TOC1 gene functions and interactions suggest a reframing of the plant circadian clock as a triple negative-component repressilator model rather than the positive/negative-element feedback loop characterizing the clock in mammals.
In 2018, researchers found that the expression of PRR5 and TOC1 hnRNA nascent transcripts follows the same oscillatory pattern as processed mRNA transcripts rhythmically in A. thaliana. LNKs binds to the 5'region of PRR5 and TOC1 and interacts with RNAP II and other transcription factors. Moreover, RVE8-LNKs interaction enables a permissive histone-methylation pattern (H3K4me3) to be modified and the histone-modification itself parallels the oscillation of clock gene expression.
It has previously been found that matching a plant's circadian rhythm to its external environment's light and dark cycles has the potential to positively affect the plant. Researchers came to this conclusion by performing experiments on three different varieties of Arabidopsis thaliana. One of these varieties had a normal 24-hour circadian cycle. The other two varieties were mutated, one to have a circadian cycle of more than 27 hours, and one to have a shorter than normal circadian cycle of 20 hours.
The Arabidopsis with the 24-hour circadian cycle was grown in three different environments. One of these environments had a 20-hour light and dark cycle (10 hours of light and 10 hours of dark), the other had a 24-hour light and dark cycle (12 hours of light and 12 hours of dark),and the final environment had a 28-hour light and dark cycle (14 hours of light and 14 hours of dark). The two mutated plants were grown in both an environment that had a 20-hour light and dark cycle and in an environment that had a 28-hour light and dark cycle. It was found that the variety of Arabidopsis with a 24-hour circadian rhythm cycle grew best in an environment that also had a 24-hour light and dark cycle. Overall, it was found that all the varieties of Arabidopsis thaliana had greater levels of chlorophyll and increased growth in environments whose light and dark cycles matched their circadian rhythm.
Researchers suggested that a reason for this could be that matching an Arabidopsis's circadian rhythm to its environment could allow the plant to be better prepared for dawn and dusk, and thus be able to better synchronize its processes. In this study, it was also found that the genes that help to control chlorophyll peaked a few hours after dawn. This appears to be consistent with the proposed phenomenon known as metabolic dawn.
According to the metabolic dawn hypothesis, sugars produced by photosynthesis have potential to help regulate the circadian rhythm and certain photosynthetic and metabolic pathways. As the sun rises, more light becomes available, which normally allows more photosynthesis to occur. The sugars produced by photosynthesis repress PRR7. This repression of PRR7 then leads to the increased expression of CCA1. On the other hand, decreased photosynthetic sugar levels increase PRR7 expression and decrease CCA1 expression. This feedback loop between CCA1 and PRR7 is what is proposed to cause metabolic dawn.
In Drosophila[edit]
Main article: Drosophila circadian rhythm
Key centers of the mammalian and Drosophila brains (A) and the circadian system in Drosophila (B)
The molecular mechanism of circadian rhythm and light perception are best understood in Drosophila. Clock genes are discovered from Drosophila, and they act together with the clock neurones. There are two unique rhythms, one during the process of hatching (called eclosion) from the pupa, and the other during mating. The clock neurones are located in distinct clusters in the central brain. The best-understood clock neurones are the large and small lateral ventral neurons (l-LNvs and s-LNvs) of the optic lobe. These neurones produce pigment dispersing factor (PDF), a neuropeptide that acts as a circadian neuromodulator between different clock neurones.
Molecular interactions of clock genes and proteins during Drosophila circadian rhythm
Drosophila circadian rhythm is through a transcription-translation feedback loop. The core clock mechanism consists of two interdependent feedback loops, namely the PER/TIM loop and the CLK/CYC loop. The CLK/CYC loop occurs during the day and initiates the transcription of the per and tim genes. But their proteins levels remain low until dusk, because during daylight also activates the doubletime (dbt) gene. DBT protein causes phosphorylation and turnover of monomeric PER proteins. TIM is also phosphorylated by shaggy until sunset. After sunset, DBT disappears, so that PER molecules stably bind to TIM. PER/TIM dimer enters the nucleus several at night, and binds to CLK/CYC dimers. Bound PER completely stops the transcriptional activity of CLK and CYC.
In the early morning, light activates the cry gene and its protein CRY causes the breakdown of TIM. Thus PER/TIM dimer dissociates, and the unbound PER becomes unstable. PER undergoes progressive phosphorylation and ultimately degradation. Absence of PER and TIM allows activation of clk and cyc genes. Thus, the clock is reset to start the next circadian cycle.
PER-TIM model[edit]
This protein model was developed based on the oscillations of the PER and TIM proteins in the Drosophila. It is based on its predecessor, the PER model where it was explained how the PER gene and its protein influence the biological clock. The model includes the formation of a nuclear PER-TIM complex which influences the transcription of the PER and the TIM genes (by providing negative feedback) and the multiple phosphorylation of these two proteins. The circadian oscillations of these two proteins seem to synchronise with the light-dark cycle even if they are not necessarily dependent on it. Both PER and TIM proteins are phosphorylated and after they form the PER-TIM nuclear complex they return inside the nucleus to stop the expression of the PER and TIM mRNA. This inhibition lasts as long as the protein, or the mRNA is not degraded. When this happens, the complex releases the inhibition. Here can also be mentioned that the degradation of the TIM protein is sped up by light.
In mammals[edit]
A variation of an eskinogram illustrating the influence of light and darkness on circadian rhythms and related physiology and behavior through the suprachiasmatic nucleus in humans
The primary circadian clock in mammals is located in the suprachiasmatic nucleus (or nuclei) (SCN), a pair of distinct groups of cells located in the hypothalamus. Destruction of the SCN results in the complete absence of a regular sleep–wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eye contains "classical" photoreceptors ("rods" and "cones"), which are used for conventional vision. But the retina also contains specialized ganglion cells that are directly photosensitive, and project directly to the SCN, where they help in the entrainment (synchronization) of this master circadian clock. The proteins involved in the SCN clock are homologous to those found in the fruit fly.
These cells contain the photopigment melanopsin and their signals follow a pathway called the retinohypothalamic tract, leading to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external cues.
The SCN takes the information on the lengths of the day and night from the retina, interprets it, and passes it on to the pineal gland, a tiny structure shaped like a pine cone and located on the epithalamus. In response, the pineal secretes the hormone melatonin. Secretion of melatonin peaks at night and ebbs during the day and its presence provides information about night-length.
Several studies have indicated that pineal melatonin feeds back on SCN rhythmicity to modulate circadian patterns of activity and other processes. However, the nature and system-level significance of this feedback are unknown.
The circadian rhythms of humans can be entrained to slightly shorter and longer periods than the Earth's 24 hours. Researchers at Harvard have shown that human subjects can at least be entrained to a 23.5-hour cycle and a 24.65-hour cycle.
Humans[edit]
When eyes receive light from the sun, the pineal gland's production of melatonin is inhibited, and the hormones produced keep the human awake. When the eyes do not receive light, melatonin is produced in the pineal gland and the human becomes tired.
See also: Sleep § Circadian clock, and Phase response curve § Light
Early research into circadian rhythms suggested that most people preferred a day closer to 25 hours when isolated from external stimuli like daylight and timekeeping. However, this research was faulty because it failed to shield the participants from artificial light. Although subjects were shielded from time cues (like clocks) and daylight, the researchers were not aware of the phase-delaying effects of indoor electric lights. The subjects were allowed to turn on light when they were awake and to turn it off when they wanted to sleep. Electric light in the evening delayed their circadian phase. A more stringent study conducted in 1999 by Harvard University estimated the natural human rhythm to be closer to 24 hours and 11 minutes: much closer to the solar day. Consistent with this research was a more recent study from 2010, which also identified sex differences, with the circadian period for women being slightly shorter (24.09 hours) than for men (24.19 hours). In this study, women tended to wake up earlier than men and exhibit a greater preference for morning activities than men, although the underlying biological mechanisms for these differences are unknown.
Biological markers and effects[edit]
The classic phase markers for measuring the timing of a mammal's circadian rhythm are:
melatonin secretion by the pineal gland,
core body temperature minimum, and
plasma level of cortisol.
For temperature studies, subjects must remain awake but calm and semi-reclined in near darkness while their rectal temperatures are taken continuously. Though variation is great among normal chronotypes, the average human adult's temperature reaches its minimum at about 5:00 a.m., about two hours before habitual wake time. Baehr et al. found that, in young adults, the daily body temperature minimum occurred at about 04:00 (4 a.m.) for morning types, but at about 06:00 (6 a.m.) for evening types. This minimum occurred at approximately the middle of the eight-hour sleep period for morning types, but closer to waking in evening types.
Melatonin is absent from the system or undetectably low during daytime. Its onset in dim light, dim-light melatonin onset (DLMO), at roughly 21:00 (9 p.m.) can be measured in the blood or the saliva. Its major metabolite can also be measured in morning urine. Both DLMO and the midpoint (in time) of the presence of the hormone in the blood or saliva have been used as circadian markers. However, newer research indicates that the melatonin offset may be the more reliable marker. Benloucif et al. found that melatonin phase markers were more stable and more highly correlated with the timing of sleep than the core temperature minimum. They found that both sleep offset and melatonin offset are more strongly correlated with phase markers than the onset of sleep. In addition, the declining phase of the melatonin levels is more reliable and stable than the termination of melatonin synthesis.
Other physiological changes that occur according to a circadian rhythm include heart rate and many cellular processes "including oxidative stress, cell metabolism, immune and inflammatory responses, epigenetic modification, hypoxia/hyperoxia response pathways, endoplasmic reticular stress, autophagy, and regulation of the stem cell environment." In a study of young men, it was found that the heart rate reaches its lowest average rate during sleep, and its highest average rate shortly after waking.
In contradiction to previous studies, it has been found that there is no effect of body temperature on performance on psychological tests. This is likely due to evolutionary pressures for higher cognitive function compared to the other areas of function examined in previous studies.
Outside the "master clock"[edit]
More-or-less independent circadian rhythms are found in many organs and cells in the body outside the suprachiasmatic nuclei (SCN), the "master clock". Indeed, neuroscientist Joseph Takahashi and colleagues stated in a 2013 article that "almost every cell in the body contains a circadian clock". For example, these clocks, called peripheral oscillators, have been found in the adrenal gland, oesophagus, lungs, liver, pancreas, spleen, thymus, and skin. There is also some evidence that the olfactory bulb and prostate may experience oscillations, at least when cultured.
Though oscillators in the skin respond to light, a systemic influence has not been proven. In addition, many oscillators, such as liver cells, for example, have been shown to respond to inputs other than light, such as feeding.
Light and the biological clock[edit]
Further information: Light effects on circadian rhythm
Light resets the biological clock in accordance with the phase response curve (PRC). Depending on the timing, light can advance or delay the circadian rhythm. Both the PRC and the required illuminance vary from species to species, and lower light levels are required to reset the clocks in nocturnal rodents than in humans.
Enforced longer or shorter cycles[edit]
Various studies on humans have made use of enforced sleep/wake cycles strongly different from 24 hours, such as those conducted by Nathaniel Kleitman in 1938 (28 hours) and Derk-Jan Dijk and Charles Czeisler in the 1990s (20 hours). Because people with a normal (typical) circadian clock cannot entrain to such abnormal day/night rhythms, this is referred to as a forced desynchrony protocol. Under such a protocol, sleep and wake episodes are uncoupled from the body's endogenous circadian period, which allows researchers to assess the effects of circadian phase (i.e., the relative timing of the circadian cycle) on aspects of sleep and wakefulness including sleep latency and other functions - both physiological, behavioral, and cognitive.
Studies also show that Cyclosa turbinata is unique in that its locomotor and web-building activity cause it to have an exceptionally short-period circadian clock, about 19 hours. When C. turbinata spiders are placed into chambers with periods of 19, 24, or 29 hours of evenly split light and dark, none of the spiders exhibited decreased longevity in their own circadian clock. These findings suggest that C. turbinata do not have the same costs of extreme desynchronization as do other species of animals.
How humans can optimize their circadian rhythm in terms of ability to achieve proper sleep
Human health[edit]
A short nap during the day does not affect circadian rhythms.
Foundation of circadian medicine[edit]
The leading edge of circadian biology research is translation of basic body clock mechanisms into clinical tools, and this is especially relevant to the treatment of cardiovascular disease. Timing of medical treatment in coordination with the body clock, chronotherapeutics, may also benefit patients with hypertension (high blood pressure) by significantly increasing efficacy and reduce drug toxicity or adverse reactions. 3) "Circadian Pharmacology" or drugs targeting the circadian clock mechanism have been shown experimentally in rodent models to significantly reduce the damage due to heart attacks and prevent heart failure. Importantly, for rational translation of the most promising Circadian Medicine therapies to clinical practice, it is imperative that we understand how it helps treats disease in both biological sexes.
Causes of disruption to circadian rhythms[edit]
Indoor lighting[edit]
Lighting requirements for circadian regulation are not simply the same as those for vision; planning of indoor lighting in offices and institutions is beginning to take this into account. Animal studies on the effects of light in laboratory conditions have until recently considered light intensity (irradiance) but not color, which can be shown to "act as an essential regulator of biological timing in more natural settings".
Blue LED lighting suppresses melatonin production five times more than the orange-yellow high-pressure sodium (HPS) light; a metal halide lamp, which is white light, suppresses melatonin at a rate more than three times greater than HPS. Depression symptoms from long term nighttime light exposure can be undone by returning to a normal cycle.
Airline pilots and cabin crew[edit]
Due to the work nature of airline pilots, who often cross several time zones and regions of sunlight and darkness in one day, and spend many hours awake both day and night, they are often unable to maintain sleep patterns that correspond to the natural human circadian rhythm; this situation can easily lead to fatigue. The NTSB cites this as contributing to many accidents, and has conducted several research studies in order to find methods of combating fatigue in pilots.
Effect of drugs[edit]
Studies conducted on both animals and humans show major bidirectional relationships between the circadian system and abusive drugs. It is indicated that these abusive drugs affect the central circadian pacemaker. Individuals with substance use disorder display disrupted rhythms. These disrupted rhythms can increase the risk for substance abuse and relapse. It is possible that genetic and/or environmental disturbances to the normal sleep and wake cycle can increase the susceptibility to addiction.
It is difficult to determine if a disturbance in the circadian rhythm is at fault for an increase in prevalence for substance abuse—or if other environmental factors such as stress are to blame.
Changes to the circadian rhythm and sleep occur once an individual begins abusing drugs and alcohol. Once an individual chooses to stop using drugs and alcohol, the circadian rhythm continues to be disrupted.
The stabilization of sleep and the circadian rhythm might possibly help to reduce the vulnerability to addiction and reduce the chances of relapse.
Circadian rhythms and clock genes expressed in brain regions outside the suprachiasmatic nucleus may significantly influence the effects produced by drugs such as cocaine. Moreover, genetic manipulations of clock genes profoundly affect cocaine's actions.
Consequences of disruption to circadian rhythms[edit]
Disruption[edit]
Further information: Circadian rhythm sleep disorder
Disruption to rhythms usually has a negative effect. Many travelers have experienced the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia.
A number of other disorders, such as bipolar disorder and some sleep disorders such as delayed sleep phase disorder (DSPD), are associated with irregular or pathological functioning of circadian rhythms.
Disruption to rhythms in the longer term is believed to have significant adverse health consequences for peripheral organs outside the brain, in particular in the development or exacerbation of cardiovascular disease.
Studies have shown that maintaining normal sleep and circadian rhythms is important for many aspects of brain and health. A number of studies have also indicated that a power-nap, a short period of sleep during the day, can reduce stress and may improve productivity without any measurable effect on normal circadian rhythms. Circadian rhythms also play a part in the reticular activating system, which is crucial for maintaining a state of consciousness. A reversal in the sleep–wake cycle may be a sign or complication of uremia, azotemia or acute kidney injury. Studies have also helped elucidate how light has a direct effect on human health through its influence on the circadian biology.
Relationship with cardiovascular disease[edit]
One of the first studies to determine how disruption of circadian rhythms causes cardiovascular disease was performed in the Tau hamsters, which have a genetic defect in their circadian clock mechanism. When maintained in a 24-hour light-dark cycle that was "out of sync" with their normal 22 circadian mechanism they developed profound cardiovascular and renal disease; however, when the Tau animals were raised for their entire lifespan on a 22-hour daily light-dark cycle they had a healthy cardiovascular system. The adverse effects of circadian misalignment on human physiology has been studied in the laboratory using a misalignment protocol, and by studying shift workers. Circadian misalignment is associated with many risk factors of cardiovascular disease. High levels of the atherosclerosis biomarker, resistin, have been reported in shift workers indicating the link between circadian misalignment and plaque build up in arteries. Additionally, elevated triacylglyceride levels (molecules used to store excess fatty acids) were observed and contribute to the hardening of arteries, which is associated with cardiovascular diseases including heart attack, stroke and heart disease. Shift work and the resulting circadian misalignment is also associated with hypertension.
Obesity and diabetes[edit]
Obesity and diabetes are associated with lifestyle and genetic factors. Among those factors, disruption of the circadian clockwork and/or misalignment of the circadian timing system with the external environment (e.g., light–dark cycle) can play a role in the development of metabolic disorders.
Shift work or chronic jet lag have profound consequences for circadian and metabolic events in the body. Animals that are forced to eat during their resting period show increased body mass and altered expression of clock and metabolic genes. In humans, shift work that favours irregular eating times is associated with altered insulin sensitivity, diabetes and higher body mass.
Cancer[edit]
Circadian misalignment has also been associated with increased risk of cancer. In mice, the disruption to the essential clock genes, Period genes (Per2, Per1) caused by circadian misalignment was found to accelerate the growth of cancer cells in mice. However, the link between these genes and cancer is dependent on type pathways and genes involved. Significant evidence exists that correlates shift work and therefore circadian misalignment with breast and prostate cancer in humans.
Cognitive effects[edit]
Reduced cognitive function has been associated with circadian misalignment. Chronic shift workers display increased rates of operational error, impaired visual-motor performance and processing efficacy which can lead to both a reduction in performance and potential safety issues. Increased risk of dementia is associated with chronic night shift workers compared to day shift workers, particularly for individuals over 50 years old.
Society and Culture[edit]
In 2017, Jeffrey C. Hall, Michael W. Young, and Michael Rosbash were awarded Nobel Prize in Physiology or Medicine "for their discoveries of molecular mechanisms controlling the circadian rhythm".
Circadian rhythms was taken as an example of scientific knowledge being transferred into the public sphere.
See also[edit]
Actigraphy (also known as actimetry)
ARNTL
ARNTL2
Bacterial circadian rhythms
Circadian rhythm sleep disorders, such as
Advanced sleep phase disorder
Delayed sleep phase disorder
Non-24-hour sleep–wake disorder
Chronobiology
Chronodisruption
CLOCK
Circasemidian rhythm
Circaseptan, 7-day biological cycle
Cryptochrome
CRY1 and CRY2: the cryptochrome family genes
Diurnal cycle
Light effects on circadian rhythm
Light in school buildings
PER1, PER2, and PER3: the period family genes
Photosensitive ganglion cell: part of the eye which is involved in regulating circadian rhythm.
Polyphasic sleep
Rev-ErbA alpha
Segmented sleep
Sleep architecture (sleep in humans)
Sleep in non-human animals
Stefania Follini
Ultradian rhythm | biology | 8507823 | https://sv.wikipedia.org/wiki/Cirkadiskt%20ljus | Cirkadiskt ljus | Cirkadiskt ljus är en term för ljusets effekter på den cirkadiska rytmen. Mer specifikt används termen för ljus som anpassar sig efter dygnsrytmen.
Cirkadiska rytmen, även kallat dygnsrytm, är en biologisk klocka som återfinns i hjärnan hos ett stort antal djur och organismer. Den biologiska klockan reglerar det dagliga beteendet och styr ett antal processer/kroppsfunktioner som ämnesomsättning, hormonnivå, födointag, kroppstemperatur och växling mellan vila och aktivitet. Den mänskliga cirkadiska rytmen förhåller sig naturligt till naturens 24-timmars dag-/nattcykel. Den genomsnittliga dygnsrytmen har en periodlängd på 24.18 timmar, men varierar beroende på individ och anpassas bland annat efter intryck från omgivningen, även kallat zeitgebers.
Ljus är kanske den zeitgeber som har störst effekt på den cirkadiska rytmen. Människan är en dagsaktiv art och ljus hjälper till att synkronisera den naturliga dygnsrytmen i kroppen. Ljus stimulerar ljuskänsliga nervceller i näthinnan som skickar signaler/information genom tractus retino hypothalamicus till dygnsrytmskärnan. Dygnsrytmkärnan, nucleus suprachiasmaticus (SCN), påverkar talgkörtelns utsöndring av melatonin, vilket styr kroppens vakenhetsnivå och gör att människan känner sig sömnig.
Cirkadiskt ljus påverkan på sömn
Sömnmönster är direkt kopplade till människans cirkadiska rytm. Flera studier visar att ljus kan korrigera en störd dygnsrytm. Exponering av ljus på kväll/tidig natt förskjuter melatoninutsöndringen en timme nästkommande natt, vilket gör att människan upplever trötthet en timme senare. Exponering av ljus tidig morgon flyttar fram melatoninutsöndringen en timme tidigare kommande natt, vilket gör att människan upplever trötthet tidigare. Styrkan av synkroniseringen beror på distributionen och tiden av ljusexponeringen. Senare forskning har visar hur en förbättrad cirkadisk rytm är kopplad till förbättrad sömn och reducerar depressiva symptom.
Cirkadiskt ljus och psykiskt välmående
Flera studier visar att exponeringen av ljus har indirekta effekter på människan. Forskning har konstaterat att dagsljus innehåller naturliga antidepressiva beståndsdelar som hjälper oss människor att synkronisera med den naturliga livsrytmen. Det finns forskningsunderlag som stödjer att man genom att exponera sig för direkt dagsljus kan minska risken för Årtidsburen depression (SAD), som uppkommer med minskat dagsljus.
Ny teknik korrigerar dygnsrytmen
Idag tillbringar den genomsnittliga befolkningen 90% av sin tid inomhus. Detta har lett till att dagsljus fått en större roll och mer påverkan på våra inomhusmiljöer. Inomhusljus har vanligtvis inte samma intensitet och variation i färgspektra som dagsljus och ger därför inte samma effekt. Med ett större fokus på dagsljusets betydelse för välmående har många parter börjat arbeta för ny teknik som stärker den naturliga dygnsrytmen genom belysning som återskapar och imiterar naturligt dagsljus. Exempel på företag som idag utvecklar teknik för att stärka den naturliga cirkadiska rytmen med ljus är Fagerhult och BrainLit.
Referenser
Den här artikeln är helt eller delvis baserad på material från engelskspråkiga Wikipedia, Light effects on circadian rhythm, 2 december 2020
Sömn
Kronobiologi | swedish | 0.570398 |
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Elsevier
Current Opinion in Plant Biology
Volume 60, April 2021, 101986
Current Opinion in Plant Biology
Need for speed: manipulating plant growth to accelerate breeding cycles
Author links open overlay panelMadhav Bhatta 1 2, Pablo Sandro 1, Millicent R Smith 3 4, Oscar Delaney 4, Kai P Voss-Fels 4, Lucia Gutierrez 1, Lee T Hickey 4
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To develop more productive and resilient crops that are capable of feeding 10 billion people by 2050, we must accelerate the rate of genetic improvement in plant breeding programs. Speed breeding manipulates the growing environment by regulating light and temperature for the purpose of rapid generation advance. Protocols are now available for a range of short-day and long-day species and the approach is highly compatible with other cutting-edge breeding tools such as genomic selection. Here, we highlight how speed breeding hijacks biological processes for applied plant breeding outcomes and provide a case study examining wheat growth and development under speed breeding conditions. The establishment of speed breeding facilities worldwide is expected to provide benefits for capacity building, discovery research, pre-breeding, and plant breeding to accelerate the development of productive and robust crops.
Introduction
The year 2050 is fast approaching and we must increase farm productivity by 60% in order to feed a population of 10 billion [1, 2, 3]. To develop the required crop varieties with enhanced yield and climate resilience, the rate of genetic gain in crop breeding programs must be doubled [1, 2, 3]. Technologies that reduce the length of the breeding cycle are critical to help achieve this goal.
A major bottleneck of plant breeding programs is the length of the breeding cycle. In a breeding program focused on line development, once parents have been selected and intermated, 4–6 plant generations are required to generate genetically stable homozygous lines for field evaluation. The time taken to identify parents for the next breeding cycle directly impacts the rate of genetic gain and time required to release improved cultivars to farmers. To short-cut this process, plant breeders have adopted different strategies such as doubled haploid technology [4,5] and shuttle breeding [6]. Gaining traction among modern plant breeding programs is ‘Speed Breeding’ (SB) technology, which involves growing plant populations under environmental conditions that are conducive for early flowering to accelerate generation time [7•,8••,9,10].
In this review, we highlight the underlying biological processes that are fundamentally influenced by SB environments and the potential to refine SB protocols. To demonstrate the changes in crop growth and development under SB, we present a case study of wheat. We discuss the opportunities to integrate SB technology with predictive breeding approaches and enhance training capabilities.
Section snippets
Speed breeding technology exploits plant processes
SB manipulates the growing environment by regulating light and temperature [8••], hijacking biological processes for the purpose of rapid generation advance. Plant growth and development is regulated by many internal and external signals particularly, photoperiod, temperature, light quality and intensity, and planting density [11, 12, 13]. Knowledge of fundamental plant growth and development processes is critical to effectively design and optimize SB protocols for a given species.
In many
A case study: wheat growth and development under speed breeding conditions
Many wheat breeding programs have recently established SB facilities to accelerate genetic gain. Typically, these are indoor or glasshouse growth facilities designed to control light and temperature. To highlight changes in growth and development, we studied wheat grown in a controlled SB growth facility (protocol as per Ghosh et al. [7•]) compared to glasshouse conditions. We tracked phenological development and crop growth rate, and used a portable photosynthesis system (LI-6800, LI-COR
Opportunities and challenges in speed breeding techniques
SB protocols for LDP and DNPs require continuous light or prolonged photoperiods which may result in negative effects such as chlorosis, leaf injury, and limited plant growth and productivity. Deleterious effects on plant growth may be associated with high starch production, photooxidation, and production of stress hormones [30]. Therefore, SB protocols need to be optimized to accelerate development whilst avoiding deleterious effects on plant growth. For example, in spring bread wheat (
Establishing cost-effective operations and facilities
Streamlining operations and automating processes (such as water and nutrient delivery), are key to improving efficiencies and reducing costs. SB is a flexible technology and facilities can be designed considering the tradeoffs between the degree of environmental control, the subsequent impact on generation time and economic cost. The cost of running SB facilities may be high especially in areas with extreme winters and/or very hot summers. Energy costs in SB facilities are reported to be
Integration of speed breeding in a modern plant breeding program
Genotyping a plant in the 90s was extremely expensive and low throughput. However, the advent of next-generation sequencing technologies helped to revolutionize genotyping for plant breeding applications — providing genome-wide marker coverage at low cost. This opened the door for genomics-assisted breeding approaches, which are now widely adopted by modern crop improvement programs. Plant breeders can now cost-effectively select for key genes or traits using forward-breeding approaches and
Accelerating research, pre-breeding and training the next generation
SB technology provides an avenue to support training, discovery research, pre-breeding, and breeding activities of students and early career scientists by reducing the time required to complete plant breeding activities. By implementing SB in their research and training, students are able to gain hands-on experience crossing and developing their own population for quantitative trait loci (QTL) mapping or introgression, which is otherwise difficult to achieve within a 3–4 year program.
Conclusions
The concept of integrating SB into a crop improvement program is simple — ‘grow plants fast and cheap’. Plant growth and development processes are critical for crop performance and adaptation to changing environments. While SB technology artificially manipulates plant growth environments to accelerate crop breeding and builds on relatively straightforward biological processes, in reality the underlying physiological and genetic mechanisms are complex. Further insight into processes underpinning
Conflict of interest statement
Nothing declared.
Acknowledgement
We apologize to colleagues whose important work was not cited due to the brevity of this format.
References (61)
H. Li et al.
Fast-forwarding genetic gain
Trends Plant Sci
(2018)
B.P. Forster et al.
The resurgence of haploids in higher plants
Trends Plant Sci
(2007)
T. Draeger et al.
Short periods of high temperature during meiosis prevent normal meiotic progression and reduce grain number in hexaploid wheat (Triticum aestivum L.)
Theor Appl Genet
(2017)
A. Sharma et al.
Recent advances in developing disease resistance in plants
F1000 Res
(2019)
J.M. Hickey et al.
Genomic prediction unifies animal and plant breeding programs to form platforms for biological discovery
Nat Genet
(2017)
D. Tilman et al.
Global food demand and the sustainable intensification of agriculture
Proc Nat Acad Sci U S A
(2011)
P.G. Pardey et al.
A bounds analysis of world food futures: global agriculture through to 2050
Aust J Agric Resour Econ
(2014)
M. Maluszynski et al.
Published doubled haploid protocols in plant species
R. Ortiz et al.
High yield potential, shuttle breeding, genetic diversity, and a new international wheat improvement strategy
Euphytica
(2007)
S. Ghosh et al.
Speed breeding in growth chambers and glasshouses for crop breeding and model plant research
Nat Protoc
(2018)
View more references
Cited by (36)
CRISPR/Cas9-mediated genome editing techniques and new breeding strategies in cereals – current status, improvements, and perspectives
2023, Biotechnology Advances
Show abstract
Pyramiding of multiple genes generates rapeseed introgression lines with clubroot and herbicide resistance, high oleic acid content, and early maturity
2023, Crop Journal
Citation Excerpt :
However, it is still time-consuming to pyramid multiple desirable genes into elite varieties using only MAS. To cope with this problem, the speed breeding methodology [54] was introduced in some crops and accelerates generation turnover by shortening the growth cycle. In our previous study [29], a CSB system was proposed as a fast and efficient crop improvement method.
Show abstract
Speed breeding—A powerful tool to breed more crops in less time accelerating crop research
2023, Abiotic Stresses in Wheat: Unfolding the Challenges
Show abstract
A protocol for increased throughput phenotyping of plant resistance to the pollen beetle
2024, Pest Management Science
Genetic biofortification: advancing crop nutrition to tackle hidden hunger
2024, Functional and Integrative Genomics
A comprehensive review on speed breeding methods and applications
2024, Euphytica
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View full text
© 2020 Elsevier Ltd. All rights reserved.
Part of special issue
Plant biotechnology
Edited by Yiping Qi, Jing-Ke Weng
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Feedback | biology | 4692552 | https://sv.wikipedia.org/wiki/Hygrophila%20polysperma | Hygrophila polysperma | Hygrophila polysperma är en akantusväxtart som först beskrevs av William Roxburgh, och fick sitt nu gällande namn av John Smith. Hygrophila polysperma ingår i släktet Hygrophila, och familjen akantusväxter. IUCN kategoriserar arten globalt som livskraftig. Inga underarter finns listade i Catalogue of Life.
Hygrophila polysperma används som akvarieväxt och anses vara relativt lättskött. Det finns också en variant med rosanerviga blad.
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Källor
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Akantusväxter
polysperma | swedish | 1.151412 |
accelerate_plants_growth/accelerate20growthpd.txt | 38 APRIL 2018 GPNMAG.COM
BY ERIK RUNKLE
A constant challenge for producers of floriculture crops
is to have them at the desired stage of development on predetermined dates. Oftentimes, this means that plants are
starting to flower on the date they marketed. To accomplish
this, advanced planning is required, young plants need to arrive
on time and the desired environmental conditions need to be
delivered. Unfortunately, it is not uncommon for plants to be
behind or ahead
of schedule, so
adjustments need
to be made to get
the plants back on
track. This article
summarizes what
can — and can
not — be done to
accelerate growth and
development to meet
your marketing date.
Temperature.
The most effective
way growers can
accelerate plant
development is to increase the
greenhouse air temperature.
The average temperature,
not just the day or night
temperature, is what controls
crop timing. A few words of caution, however. When light is
limiting, such as when the daily light integral (DLI) is less than
10 mol·m–2·d–1, the combination of a high temperature and
low light can lead to poor plant quality. In addition, a high
temperature during the night can delay flowering of at least
some short-day plants, such as chrysanthemum and poinsettia.
For these crops, a maximum night temperature is around 70° F.
Light intensity. Increasing the amount of light available
to plants increases photosynthesis and increases plant
temperature. An exception to this rule is light from LEDs, which
does not substantially increase plant temperature. Therefore,
when the DLI is low, providing plants with more light can
directly and indirectly accelerate plant development. An added
benefit is that for most high-light (shade-avoiding) crops, plant
quality also increases with DLI.
Light can be limiting in greenhouses, even when we receive
ample quantities of sunlight. This happens when plants are
excessively shaded from hanging baskets above and/or when
too high of a shading factor is delivered by whitewash or shade
curtains. It’s useful to continuously monitor the DLI where plants
are growing to ensure plants receive a sufficient amount of light.
Photoperiod. If plants have a photoperiodic flowering
response, delivering the most inductive day length will
initiate flowers earlier. Many bedding plants and herbaceous
perennials have a long-day flowering response, which means
that plants flower earliest when the nights are short (the
days are long). For most of these crops, long days are already
naturally occurring in April, in which case delivering lowintensity lighting during the
night will have no benefits.
If plants have a short-day
response, then shortening
the days by totally excluding
light from the plants for 12
hours per day will accelerate
flowering.
Gibberellic acid.
Gibberellic acid (GA) is a
plant hormone that regulates
the elongation of different
plant tissues, including
leaves and stems. The
common GA products labeled
for use on floriculture crops
are Fascination and Fresco.
These products, when
applied as a foliar spray
and/or substrate drench,
primarily increase the size
of cells and thus, plant height. However, these products usually
have no effect on flowering time. In other words, plants may
appear to grow quicker following an application, but they just
increase in size and don’t accelerate maturity.
There are a few cases, however, when GA can hasten
flowering. One of them is when plants have received an
overdose of a growth retardant, which stunts growth and
can delay flowering. In this case, an application of GA can
get plants to grow again and at least partly overcome the
flowering delay.
Nutrition. Fertility rarely influences flowering time, so
increasing the amount of fertilizer is not an effective method
to accelerate flowering. However, when plants are grown with
inadequate feed and are experiencing nutritional deficiencies,
a corrective application of micro- and/or macro-nutrients can
alleviate any flowering delays caused by inadequate nutrition.
In summary, if plants are behind schedule, increase the
temperature and provide high light intensities. If plants are
photoperiodic, ensure they are receiving the most inductive day
length. Application of Fascination or Fresco, or increasing the
rate of fertility, usually has no effect on crop timing.
technically speaking
Accelerating Growth: What
Works and What Does Not
The most effective way
growers can accelerate
plant development is to
increase the greenhouse
air temperature.
Erik Runkle is
professor and
floriculture
Extension specialist
in the department
of horticulture at
Michigan State
University. He
can be reached at
[email protected]. | biology | 762145 | https://no.wikipedia.org/wiki/Sagopalme | Sagopalme | Sagopalme (Cycas revoluta), av noen kalt kongepalme, er en av de mest populære plantene i konglepalmeslekten, og kommer opprinnelig fra sørlige Japan. På tross av navnet, er planten ingen palme.
Beskrivelse
Det er en saktevoksende plante som i løpet av 50-100 år blir inntil 6-7 meter høy. Planten har en symmetrisk bladkrone bestående av mørkegrønne blader, og en stammediameter på 20cm.
Sagopalmen er svært populær som stueplante i kjøligere klima, men kan plantes utendørs i et varmt temperert eller subtropisk klima. Den liker sandholdig jord og trenger god drenering, tåler tørke bra og kan vokse utendørs i full sol eller skygge. Som stueplante bør planten stå lyst.
Planten tåler en del kulde, men trenger vanligvis varme fuktige somrer for å vokse bra. Frostskade på blader kan forekomme ved temperaturer ned mot -10 grader celcius; ved lavere temperaturer hvor bladene visner ned vil planten vanligvis overleve og sende ut et nytt sett med blader følgende vår/sommer.
Smarte triks
Hvis planten ikke har sendt ut nye bladsett på noen år, eller hvis bladene har fått store vinterskader, kan man simulere en monsun ved å sette plantens rotklump under vann i tre sammenhengende døgn. Når planten har stått relativt tørt over lang tid og opplever å få røttene dynket med vann vil den tro det er regntid.
I sitt opprinnelige element er planten avhengig av monsunen for å ha rikelig tilgang på vann for å kunne produsere nye blader. Skal man lure planten til å produsere nye blader bør dette gjøres tidlig på sommeren mens solen er sterkest (medio juni) og temperaturene er gode. I mangel på tilstrekkelig sol og varme vil ikke bladene herdes i tide til vinteren, og vil lettere ta skade fra vær og vind.
Toksisitet
Planten er svært gifitg for både mennesker og dyr hvis den konsumeres. Man bør derfor vise stor aktsomhet når man berører planten, og plantestedet bør tenkes nøye igjennom slik at ikke husdyr lar seg friste av planten.
Eksterne lenker
Nakenfrøede planter | norwegian_bokmål | 0.602223 |
accelerate_plants_growth/PMC6745571.txt | Back to TopSkip to main content
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Journal List Physiol Mol Biol Plants v.25(5); 2019 Sep PMC6745571
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Physiol Mol Biol Plants. 2019 Sep; 25(5): 1107–1119.
Published online 2019 Aug 21. doi: 10.1007/s12298-019-00699-9
PMCID: PMC6745571
PMID: 31564775
Magnetic field regulates plant functions, growth and enhances tolerance against environmental stresses
Ramalingam Radhakrishnancorresponding author
Author information Article notes Copyright and License information PMC Disclaimer
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Abstract
Global climatic fluctuations and the increasing population have been responsible for the decline in the crop productivity. The chemical fertilizers, pesticides, and suitable genetic resources are commonly used for improving the crop yield. Magnetic field (MF) therapy for plants and animals has been found to be an effective and emerging tool to control diseases and increase tolerance against the adverse environment. Very limited studies have been attempted to determine the role of MF on plant tolerance against various stress conditions. This review aims to highlight the mitigating effect of MF on plants against abiotic and biotic stresses. MF interacts with seeds and plants and accelerates metabolism, which leads to an improved germination. The primary and secondary metabolites, enzyme activities, uptake of nutrient and water are reprogrammed to stimulate the plant growth and yield under favorable conditions. During adverse conditions of abiotic stress such as drought, salt, heavy metal contamination in soil, MF mitigates the stress effects by increasing antioxidants and reducing oxidative stress in plants. The stunted plant growth under different light and temperature conditions can be overcome by the exposure to MF. An MF treatment lowers the disease index of plants due to the modulation of calcium signaling, and proline and polyamines pathways. This review explores the basic and recent information about the impact of MF on plant survival against the adverse environment and emphasizes that thorough research is required to elucidate the mechanism of its interaction to protect the plants from biotic and abiotic stresses.
Keywords: Diseases, Drought, Heavy metals, Magnetic field, Pant growth, Salt
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Introduction
The earth is a giant magnet and its geomagnetic field (GMF) has a huge impact on the productivity of crops. Specifically, the electromagnetic radiations coming from the sun stimulate the growth and development of plants through the process of photosynthesis. The other possibility to increase plant growth could be a alteration in electrostatic balance of the plant system at the cell membrane level, as it is the primary of plant growth. The GMF can influence basic biological functions such as rhythmicity (Wever 1968), orientation (Brown 1962), and development (Asashima et al. 1991). The effects of the magnetic field (MF) on plants, fungi, and microbes can be elucidated by ion-cyclotron-resonance (ICR) and the radical-pair model. These two mechanisms also play an essential role in the magneto-reception of organisms.
Many scientists have proposed various theories about the biological effects of MF, these are as follows: a moving electric charge generates an MF around it (like an electron, ion or polarized particle). The organic material, constituting living organisms, has a polar structure due to various polarized chemical bonds, which may be linked to water molecules and dissociated mineral salts conferring magnetic properties (Chepts et al. 1985). The hypothetical interaction of weak magnetic field (WMF) and the living organism has been proposed by Binhi (2001). The experimental analysis of electromagnetic fields (EMF) applied to biological systems has gained a rapid interest in the past few years. The applications of MF are being explored in several areas, particularly in the agricultural science. The effects of MF on seed germination, biochemical, hormonal changes, plant growth, and yield have been subject to several investigations. The enhancement of growth in crops under precise magnetic conditions has been confirmed but a systematic and extensive study is still necessary to delineate the mechanisms of magnetic action in cells and tissues. Although attempts have been made to understand the mechanisms of action of extremely low-frequency EMFs in biological systems, still more detailed studies need to be undertaken (Belyavskaya 2004).
An application of 20–30 mT of MF on crop plants revealed an enhancement in their growth. The plant cells contain ferritin and each cell has about 4500 iron atoms involved in growth and metabolism. The magnetic rotator moment of ultimate iron atoms creates an external MF, and collectively generates oscillations, which generate energy and finally re-position the atoms in the direction of MF. This increases the temperature in plants, which depends upon the duration and the frequency of MF treatment (Vaezzadeh et al. 2006). WMF modulates cryptochrome and phytochrome mediated plant responses in plants (Dhiman and Galland 2018). Very limited information is available on the molecular basis and the function of the putative WMF receptors and their activation by physiological signals, therefore their involvement in directing the overall response in different plant organs is yet to be determined.
Savostin (1930) first reported a two-fold increase in wheat seedling elongation under MF. Murphy (1942) observed the positive effects of MF on seed germination. Audus (1960) and Pittman (1965) also studied a strong magnetotropic effect on root development. MF influences the normal tendency of Fe and Co atoms and utilizes their energies to continue the translocation of microelements in root meristems, which leads to an increased plant growth (Mericle et al. 1964). The different dosage of MF alters the root biomass, stems girth, and leaf size. Further, the root growth is more sensitive than shoots to MF (Kato 1988; Kato et al. 1989; Smith et al. 1993). The pretreatment of seeds by MF resulted in seedling growth, seed vigor, and increased crop yield (Pieturszewski 1993). MF accelerates growth by triggering the protein synthesis and activates the root tropism by altering the intracellular movement of amyloplasts in the statocyst of root cap cells (Kuznetsov et al. 1999; Pieturszewski 1999). A positive effect on seed germination, uptake of nutrients, flowering, and crop yield can be achieved by applying MF (Duarte-Diaz et al. 1997; Samy 1998; Souza-Torres et al. 1999). MF treatments also affect the plant metabolisms that involve free radicals and stimulate the activity of proteins and enzymes to enhance seed vigor (Morar et al. 1993).
The effects of continuous as well as pulsed MF on plant growth and development have been investigated in a large number of plant species (Yano et al. 2001). Aladjadjiyan (2002) revealed that the exposure of MF (150 mT) stimulated shoot development which led to an increase in the germination, fresh weight, and shoot length in maize. The mechanism of action of MF on plant growth promotion is still not very clearly understood, therefore an optimal external EMF may accelerate the plant growth, especially seed germination (Esitken and Turan 2004). Yinan et al. (2005) observed a positive effect of MF pretreatment on cucumber seedlings by stimulating seedling growth and development. The promotion of seed germination and the growth of plants depend on the magnetic flux densities, frequencies, and pretreatment of the plant material (Davies 1996).
Several harsh environmental conditions such as drought, salinity, low or high temperatures, flood, pollution, radiation, and diseases are the important stress factors that adversely affect the growth, metabolism, and the yield of plants and thereby limit the productivity of crops (Lawlor 2002).The productivity of plants can be increased by the application of plant growth promoting substances, microbial inoculation to the soil, organic and inorganic manure and several other non-conventional approaches such as plant breeding and genetic engineering (Radhakrishnan and Lee 2013; Radhakrishnan et al. 2014; Radhakrishnan et al. 2015). The application of MF is a novel approach to improve plant growth and the overall productivity (Radhakrishnan and Ranjitha-Kumari 2012; Maffei 2014).
Plant growth promoting effect of MF on plant physiology under favorable condition: seed germination
Many researchers reported an increase in seed germination under MF exposure. MF stimulates the initial growth stages and early sprouting of seeds (Carbonell et al. 2000). Recently, Radhakrishnan and Ranjitha-Kumari (2012) observed an increased rate of seed germination in soybean under pulsed MF. Morar et al. (1993) also reported that MF influences the free radical formation and stimulates the activity of proteins and enzymes to enhance the seed vigor. The paramagnetic properties of plastid may be responsible for the enhanced seed vigor. MF increases the energy in plants and disperses this energy to biomolecules, which in turn stimulates the metabolism to enhance the seed germination. A metabolically active plant cell contains free radicals that play a vital role in electron transfer and the kinetics of biochemical reactions. These free radicals possess non-paired electrons with magnetic activities that can be oriented under an external MF. The microwave energy is absorbed as a result of the interaction between the external MF and the magnetic action of unpaired electrons. Finally, this energy is converted into a chemical form and accelerates the fundamental processes in seeds (Commoner et al. 1954). The overall effects of MF on crop plants are summarized in Fig. 1 and Table 1.
An external file that holds a picture, illustration, etc.
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Fig. 1
Effect of magnetic field on functional changes in plants for their growth improvement. Magnetic field (MF+) treatment triggers seed germination, plant growth, water and nutrient uptake, pigments synthesis, protein and enzyme activities as compared to the control (MF−)
Table 1
MF induced biochemical and physiological changes improve crop production at different environmental conditions
MF treatments Crops Plant functions References
Plant growth promoting activity
150 mT- 250 mT of SMF Oryza sativa L. Improve seed germination Carbonell et al. (2000)
1500 nTat 10.0 Hz of PMF Glycine max L.
Increase plant height, biomass, number of leaves, pods, seeds, weight of seeds, proteins, β-amylase, acid phosphatase, polyphenol oxidase, catalase, Fe, Cu, Mn, Zn, Mg, K and Na contents
Decrease α-amylase, alkaline phosphatase, protease and nitrate reductase activities and Ca content
Radhakrishnan and Ranjitha-Kumari (2012)
500 gauss -1550 gauss MF Lycopersicum esculentum L. Increase branches of shoots Dayal and Singh (1986)
125 mT-250 mT SMF Zea mays L. Faster seed germination, increase length and biomass of plants Florez et al. (2007)
7 T EMF Zea mays L Accelerate meristem activity and cell division in roots Bitonti et al. (2006)
20 µT at 16 2/3 Hz SSMF Helianthus annuusL. and Triticum aestivumL. Increase germination rate and growth of plants Fischer et al. (2004)
100 mT -170 mT SSMF Lycopersicum esculentum L. Enhance plant growth, pigments synthesis and fruit yield Souza-Torres et al. (1999, 2006)
1500 nT at 100 Hz SSMF Gossypium species Increase germination percentage, growth, pigments synthesis and yield Leelapriya et al. (2003)
0.096 T-0.384 T AMF Fragaria × ananassa cv. camarosa
Increase fruit yield, N, K, Ca, Mg, Cu, Fe, Mn, Na and Zn in plants
Reduce P and S content
Esitken and Turan (2004)
403 A/m WMF Allium cepa L. Increase chlorophylls, proteins and enzyme activities in plants Novitsky et al. (2001)
Drought tolerance
Magnetic funnel Lycopersicum esculentum L. Stimulate plant growth, cambium differentiation activity, thickness of mesophyll tissue, water uptake, proline concentration and photosynthetic pigments Selim and El-Nady (2011)
100 mT-150 mT EMF Zea mays L. Improve plant growth, chlorophyll, photosynthesis rate, transpiration rate, stomatal conductance, substomatal CO2 concentration, photochemical quenching and nonphotochemical quenching reactions Javed et al. (2011)
100 mT-200 mT SMF Zea mays L.
Increase plant growth, leaf water potential, turgor potential, water content, photosynthesis and stomatal conductance
Decrease H2O2, POX,CAT and SOD activities
Anand et al. (2012)
2.9 mT-4.7 mT SMF Triticum aestivum L.
Increase chlorophyll and carotenoids
Decrease SOD, POX, APX and CAT activities
Sen and Alikamanoglu (2014)
Salinity tolerance
4 mT-7mT SMF Triticum aestivum L. and Phaseolus vulgaris L. Increase seed germination, biomass and growth of plants Cakmak et al. (2010)
1500 nT at 0.1,1.0,10.0 and 100.0 Hz PMF Glycine max L. Enhance the frequency of shoot and root regeneration, length and number of roots Radhakrishnan and Ranjitha-Kumari (2013)
200 mT SMF Glycine max L. and Zea mays L. Increase seed germination, seedling growth, α-amylase, protease and free-radicals Kataria et al. (2017)
200 mT SMF Glycine max L. Enhance root nodules, biomass, yield, pigments synthesis, photosynthetic rate, stomatal conductance, transpiration, internal CO2 concentration, carbon metabolism, nitrogen metabolism, leghemoglobin and hemechrome content in root nodules Baghel et al. (2016)
1500 nT at 1.0 Hz PMF Glycine max L.
Increase callus biomass, sugars, proteins, phenols, flavonoids, flavonoles, alkaloids and saponins
Decrease lipid peroxidation and CAT activity
Radhakrishnan et al. (2012)
Heavy metal tolerance
600 mT MF Vigna radiata L.
Increase plant growth, photosynthesis, nitric oxide synthase and nitric oxide
Decrease lipid peroxidation, H2O2, O2−and electrolyte leakage
Chen et al. (2011)
Temperature and light stress tolerance
150 mT MF Zea maysL.
Increase chilling tolerance, plant growth, chlorophyll, total phenolics, gaseous exchange, seed protein, and oil
Reduce membrane permeability
Afzal et al. (2015)
400 A/m WMF Raphanus sativus L. Increase polar lipids at light and chilling stresses Novitskaya et al. (2010)
Biotic stress resistance
10 kHz WMF Citrus aurantifoliaL.
Increase biomass of leaves, MDA, proline and protein content
Decrease H2O2 and carbohydrates
Abdollahi et al. (2012)
-17 to 13 µT (SMF) + 10 Hz at 25.6 to 28.9 µT (SSMT) Nicotiana tabacumL.
Decrease number and area of lesions
Increase ODC and PAL activities
Trebbi et al. (2007)
Open in a separate window
AMF alternative magnetic field, EMF electro magnetic field, MF magnetic field, PMF pulsed magnetic field, SMF static magnetic field, SSMF sinusoidal magnetic field, T tesla
Vegetative growth phase
MF positively influences the growth of plants by increasing shoot and root length (Dayal and Singh 1986; Florez et al. 2007). Root growth depends upon the cell division in the root meristems and subsequent differentiation and elongation of the descendant cells (Beemster and Baskin 1998). The root cap cells were notably larger and the metaxylem cells became significantly longer starting from the quiescent center to periphery in MF treated plants. The induction of metaxylem cells by EMF is an important component of the increase in the rate of root elongation (Bitonti et al. 2006). MF exposure to seeds accelerates their growth, activates protein formation and the root growth (Pieturszewski 1999). In an experiment, sunflower seedlings exposed to MF showed a substantial increase in the shoot and root fresh weight (Fischer et al. 2004). MF treated plants also showed, at the vegetative stage, a significantly larger leaf area and higher leaf dry weight than the controls. This effect may be attributed to the increased photosynthetic rates due to the better perception of light and nutrients available for vegetative growth (Souza-Torres et al. 1999, 2006).
Reproductive growth phase
Very limited studies have documented the effect of MF on reproductive development in crops. Matsuda et al. (1993) reported that MF enhanced the yield in strawberry. Similar effects were also witnessed for flax, buckwheat, pea, wheat, tomato, pepper, soybean and cotton by Gubbels (1982), Grabrielian (1996), Phirke and Umbarkar (1998), Pieturszewski (1993), Ogolnej et al. (2002), Vasilevski (2003), Leelapriya et al. (2003) and Esitken and Turan (2004), respectively, and it was suggested that the enhancement in growth and yield of the tomato plants may be attributed to an MF-induced energetic excitement of cellular proteins and carbohydrates and/or water inside the dry seeds.
Endogenous bio-molecular changes
The plant growth is regulated by various biochemical processes. MF may cause changes in one or more parameters that affect the enzymatic activity, the transportation of metabolites, growth regulators, ions, and water, thereby regulating the overall plant growth (Leelapriya et al. 2003). The transport of carbohydrate and plant growth hormones from the site of synthesis to the distant growth zones (fruits) could be stimulated at lower MF intensity (Esitken and Turan 2004). Hirano et al. (1998) also observed that the increase in MF intensity from 0.0005 to 0.1 T showed a positive effect on the growth and photosynthesis in Spirulina platensis. MF showed an increase in the chlorophyll content in onion (Novitsky et al. 2001), cotton (Leelapriya et al. 2003), potato and wild Solanum species (Tican et al. 2005).
The GMF may affect a variety of enzymes in many living organisms. The activity of Ca2+/calmodulin dependent cyclic nucleotide phosphodiesterase at 20 μT (Liboff et al. 2003) and cytochrome C oxidase at 50 Hz (Nossol et al. 1993) were altered by MF. It is well known that MF can influence biological processes involving photochemical reactions (Boxer et al. 1982), the biological effects of MF are still debatable (Azanza and Del-Moral 1994; Grissom 1995). However, the mechanisms of some of the alterations in enzyme activity during MF exposure have been identified (Grissom 1995). MF effects are exerted by the inter-conversion of singlet and triplet rotatory states of the radical pair of bio-molecules (Salikhov et al. 1984). Some enzyme reactions are sensitive and their kinetics are affected by MF.
MF treatments are expected to enhance seed vigor by influencing activity of proteins and enzymes and the biochemical processes that involve free radicals (Jia-Ming 1988; Kurinobu and Okazaki 1995; Morar et al. 1993), auxin content (Mitrov et al. 1988), nutrient (Duarte-Diaz et al. 1997), and water uptake (Reina et al. 2001). Auxin is a signaling molecule, present in root apices, which manages the activities of adjacent cells via electrochemical signaling. The transport of auxin in plants is associated with environmental factors such as gravity, MF, and light (Baluska et al. 2005). MF increases the auxin content as well as enzymes activities that regulate the elongation of the plant cell wall (Mitrov et al. 1988). The studies on the influence of MF on the modifications in protein profile and enzyme activity are scarce and no information is available on its chemical constituents so far (Novitsky et al. 2001). The total protein contents of onion leaves were increased in MF treated plants. MF at different levels altered distribution of polypeptide in eukaryotic and bacterial cells (Blank et al. 1994; Goodman et al. 1994; Radhakrishnan and Ranjitha-Kumari 2012).
Xiao-ju and Guo (1999) found an increase in the activity of catalase and peroxidase enzymes in tomato seeds pretreated with MF. The amplitude, gradient and high frequency of the non-uniform MF together cause a combined effect on dry seeds and induced the changes in living matter and was called as “ponderomotive effects”. This effect reprograms the enzymatic activity, transport of the metabolites including growth regulators, and also the transport of charged solutes possibly through “Hall” effect for plant growth improvement (Balcavage et al. 1996; Souza-Torres et al. 2006). The stationary MF (150 and 200 mT) stimulates reactive oxygen species in germinating seeds to enhance plant growth (Shine et al. 2012). The changes in amylase and nitrate reductase activities were detected in germinating seeds treated with different levels of EMF (Levedev et al. 1975; Bathnagar and Deb 1978) and many authors have reported the effect of static MF on the metabolism and growth of different plants (Kato 1988; Kato et al. 1989; Peteiro-Cartelle and Cabezas-Cerato 1989). An extremely low MF (0.2–0.3μT) stimulates the activity of Na and K-ATPases (Blank and Soo 1996), whereas a weak and moderate MF influences the redox activity of cytochrome C oxidase (Nossol et al. 1993). A treatment of 30 mT increased the esterase activity in Triticum aestivum (Aksenov et al. 2000) and 1 mT influenced the activity of horseradish peroxidase (Portaccio et al. 2005). Strong MF (6 T) reduced L-glutamate dehydrogenase and catalase activity (Haberditzl 1967), but 2 T substantially enhanced the activity of carboxydismutase in Spinacia oleracea (Akoyunoglou 1964). The strong MF also enhanced the activity of trypsin (Cook and Smith 1964) and ornithine decarboxylase (Mullins et al. 1999); so that the changes in the enzyme activity may depend on strength, the frequency of the MF and the plant species.
A study on tomato plants showed that the irrigation water exposed to MF increases the nutrient uptake in plants (Duarte-Diaz et al. 1997). Radhakrishnan and Ranjitha-Kumari (2012) reported that the MF increases the Fe, Cu, Mn, Zn, Mg, K, and Na content and decreases the Ca content in soybean seedlings. Another study showed that the levels of N, K, Ca, Mg, Fe, Mn, and Zn significantly increased but Cu and Na remained unchanged in the leaves of MF treated strawberry plants (Esitken and Turan 2004). MF affects the membranes and Ca2+ signaling in plant cells, and many magnetic effects in living organisms are probably due to the alterations in membrane-associated Ca2+ flux (Galland and Pazur 2005). Na-channels are less affected than Ca2+ channels (Rosen 2003) and due to the changes of Ca2+ channels, the Ca content might be reduced in MF treated plants. However, MF treatment in seeds induces the changes in protein and lipid profile in harvested seeds (Radhakrishnan 2018).
Mitigation effect of MF on crops against unfavorable environments
The adverse environmental conditions including drought, salinity and heavy metal accumulation in soil, and light, temperature, insects, and pathogens affect the growth and yield of agricultural crops. MF induced changes in the metabolism of plants during those unfavorable environments are given in Fig. 2 and Table 1.
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Fig. 2
Magnetic field induced metabolic alteration and tolerance of plants against adverse environmental conditions. Adverse stress conditions including drought, salinity, heavy metals, high/low temperatures, high/low light and pathogens infections reduce seed germination, plant growth and yield due to the molecular and physiological changes in plants. MF treatment reduces the ROS production in plants at stress conditions, and enhances cambium differentiation, photosynthesis, stomatal conductance, water and nutrient uptake in drought affected plants. MF induced salinity tolerance is achieved by an increase of photosynthesis, stomatal conductance, transpiration, water uptake, carbon, nitrogen, amylase and protease activities and while reducing the DPPH activity, CAT, proline and some secondary metabolites. Cadmium (Cd) and Arsenic (As) affected plants are possibly recovered by promoting photosynthesis, stomatal conductance, transpiration, water use efficiency (WUE), carbon, nitrogen, amylase activities due to the treatment of MF. Whereas plants that suffered at temperature and light stresses are mitigated by MF treatment, which accelerate photosynthesis, stomatal conductance, transpiration and polar lipids. In addition, MF recovers the pathogen infected plants by increasing protein, proline, putrescine synthesis and disease index
Drought
Drought is a very serious problem in agriculture. Few researchers have studied the application of MF to overcome the detrimental effect of drought stress (Vashisth and Nagarajan 2010; Javed et al. 2011; Selim and El-Nady 2011; Anand et al. 2012; Karimi et al. 2012; Sen and Alikamanoglu 2014). The drought-induced reduction in plant growth can be mitigated by the application of MF as it stimulates cambium differentiation activity to form more xylem and phloem tissues for improving the absorption and transport of water and nutrients to enhance plant growth under drought condition (Selim and El-Nady 2011). The plant cell membrane permeability and free water flow are increased in MF pretreated seeds (Bondarenko et al. 1996). Owing to the variability in ionic flow through the cell membrane, the osmotic potential is changed under drought condition. In MF treated plants, Ca2+ enhancement is found to play a significant role in plant drought tolerance, it prevents the impairment of plasma membrane and photosynthetic apparatus and regulates the hormonal metabolism in drought affected plants (Blum 1993; Song et al. 2008, Selim and El-Nady 2011). MF enhanced the chlorophyll and carotenoid synthesis in leaves, which might be due to the increase in proline and GA3, which trigger the accumulation of Mg2+ for chlorophyll synthesis (Shaddad 1990) and K+ to increase the number of chloroplasts (Garcia-Reina and Arza-Pascual 2001). This might eventually lead to increase in the thickness of mesophyll tissue (Selim and El-Nady 2011). In addition, it also increases stomatal conductance, sub-stomatal CO2 concentration, and photochemical and non-photochemical reducing reactions to moderate the effect of drought in plants (Javed et al. 2011). MF prevents oxidative stress damage in drought affected plants by reducing H2O2, SOD, POD and CAT activities and, the metabolic energy used for scavenging the free radicals and ultimately improves the plant growth (Anand et al. 2012; Sen and Alikamanoglu 2014).
Soil salinity
About one-third of the agricultural land is affected by salinity (Flowers and Yeo 1995) due to in appropriate irrigation practices and natural factors (Chinnusamy and Zhu 2003). A high salt content in soil disrupts the homeostasis in water potential and ion distribution in plant cells (Zhu 2001; Munns et al. 2002). An excessive accumulation of Na+ and Cl–ions changes the protein structures, which lead to the loss of turgidity of the cell (Chinnusamy and Zhu 2003). MF pretreatment enhances the water absorption in seeds and promotes the seed germination and growth of plants in saline or non-saline soil conditions (Cakmak et al. 2010; Radhakrishnan and Ranjitha-Kumari 2013; Karimi et al. 2017). In addition, α-amylase and protease activities are also increased in MF treated seeds due to the faster utilization of reserve materials required for a higher rate of germination (Kataria et al. 2017). MF treated seeds absorb water faster due to the electrophysiological changes in cells (Reina et al. 2001) and may help to alleviate the salt stress. Nevertheless, the photosynthetic rate, stomatal conductance, transpiration, and internal CO2 concentrations were enhanced in salt affected plants pretreated with MF (Baghel et al. 2016; Rathod and Anand 2016). To achieve salt tolerance, plant cells have evolved several biochemical and physiological pathways, which include the exclusion of Na+ and their trans-localization into vacuoles, and also the accumulation of compatible solutes such as proline, glycine, betaine, and polyols (Kameli and Losel 1996; Hasegawa et al. 2000; Chinnusamy and Zhu 2003; Parida and Das 2005). However, the precise mechanism underlying these effects has not yet been fully understood because salinity tolerance is a multigenic trait (Parida and Das 2005). MF exposure increases the sugar and protein content in salt affected calli to overcome the stress effects (Radhakrishnan et al. 2012). These compounds accumulate in high volumes in the cytoplasm of stressed cells without interfering with other macromolecules and act as osmoprotectants (Yancey 1994). It has been shown that proline plays a key role in stabilizing the cellular membrane and proteins (Rudolph et al. 1986; Yancey 1994). The higher proline accumulation in roots may be due to the increased rate of inhibition of proline dehydrogenase and proline oxidase (Veeranjaneyullu and Ranjitha-Kumari 1989). The production, along with accumulation, of proline in plant tissue during salt stress is an adaptive response and it has been proposed as a stress-related metabolic marker (Burton 1991). The osmotic potential in the cytoplasm is adjusted by proline which acts as a compatible solute (Bartels and Sunkar 2006). It signals protein synthesis immediately after the salt stress that protects the plasma membrane (Santoro et al. 1992). Ahmad and Wyn Jones (1979) reported that during recovery period, tissue rehydration is associated with decline. Hence, subsequent to relief of stress, it acts as reserve of organic nitrogen for maintaining amino acid and protein synthesis (Trotel et al. 1996; Sairam and Tygai 2004). MF ameliorates the salt effects by reducing the overproduction of proline (Radhakrishnan et al. 2012).
According to Mittler (2002) high level of H2O2 accelerates the Haber–Weiss reaction and results in OH· formation and consequently lipid peroxidation. Several studies showed that the lipid peroxidation activity is enhanced during high salinity (Hernandez et al. 2000; Davenport et al. 2003). MF also increased lipid peroxidation in tobacco cell suspension cultures (Sahebjamei et al. 2007). On the contrary, during a salt stress condition, MF pretreatment resulted in the decline of lipid peroxidation in soybean callus culture (Radhakrishnan et al. 2012). Salt stress increases catalase (CAT) in plants (Manchandia et al. 1999), but MF pretreated seeds showed resistance toward the salinity and decreased the CAT and DPPH scavenging activity due to the reduction of oxidative stress (Radhakrishnan et al. 2012; Roshandel and Azimian 2015).
Alkaloids, saponins, flavonoids, flavones, and flavonols are generally increased in salt affected cells, while MF exposure reduced the accumulation of these secondary metabolites and alleviated the salt stress (Radhakrishnan et al. 2012). Saponins are glycosides occurring commonly in plants, which are derived from tri-terpenoids and exhibit a wide range of biological functions (Osborn 2003). The decrease in saponins at high Cu concentration provides an intrinsic defense to resist Cu-induced oxidative damage in Panax ginseng (Ali et al. 2006). Russo et al. (2002) reported that flavones and flavonols have antioxidant property, and isoflavones also possess antioxidant and antifungal activities that protect the plant against insect attack (Burden and Norris 1992). The salt stress induces the accumulation of isoflavones such as genistein and daidzein, while MF pretreatment resulted in the lowering of their levels. The high amount of total polyphenols increases the antioxidant potential in plants and MF results in the enhancement of total polyphenol in callus tissue grown under saline condition (Radhakrishnan et al. 2012).
Heavy metals
The heavy metals from the industry, fertilizers, and pesticides enter the water bodies and soil and subsequently reach to humans through the food chain (Wagner 1993; Pinto et al. 2014). The excessive deposition of heavy metals in soil limits the plant productivity. Recently, Chen et al. (2011) and Flores-Tavizon et al. (2012) reported that the toxic effects of cadmium (Cd) and arsenic (As) in plants were mitigated by an MF exposure. Due to the heavy metal toxicity, plants produce reactive oxygen species (ROS), which damage the cellular membranes and inhibit the photosynthesis and other metabolic processes (Prasad 1995). MF triggers nitric oxide (NO) signaling, which activates cell division, photosynthesis, and growth of Cd affected plants. The mung-bean seedlings treated with MF (600 mT) showed a lower level of ROS such as H2O2, O2−, and malondialdehyde (MDA) but a higher level of total chlorophyll, photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO2 concentration, and water use efficiency in Cd stress conditions. In addition, MF increased the C and N concentrations in Cd-stressed plants (Chen et al. 2011). Another toxic metal, As is a non-essential metal for plant growth and inhibits enzyme activities in plants (Liu et al. 2005). MF pretreatment increased resistance towards As toxicity in the plants by the regulation of ionic flow in plant cell membranes (Galland and Pazur 2005). The seed germination, growth, amylolytic activity, and As uptake was increased in As stressed plants treated with MF (Flores-Tavizon et al. 2012).
Temperature and light stresses
Crop productivity is affected by a wide range of temperature and light regimes. MF exposure alleviates the inhibitory effect of heat shock by eliciting heat shock proteins under thermal stress (Goodman and Blank 1998; Ruzic and Jerman 2002). Low temperature (cold) stress limits the yield and geographical distribution of several crops (Gai et al. 2008). Afzal et al. (2015) proved that chilling stress reduces the seed germination in maize, but MF treatment stabilizes the membrane permeability and regulates ion transport in stressed seeds to alleviate the chilling stress. In addition, MF accelerates the primary metabolic process such as photosynthesis, transpiration, and stomatal conductance during chilling injury in maize plants. The increased synthesis of chlorophylls and phenolics due to the effect of MF in stressed plants could be the reason for averting the ROS production. Similarly, the harvest index, weight, yield, and protein content in grains were significantly higher but the oil contents were lower in MF treated plants than untreated plants.
The role of MF against thermal stress varies under light or dark conditions. At low temperature, cell membranes change the lipid composition by promoting the conversion of unsaturated fatty acids to saturated ones (Kreps 1981). The fatty acids, especially erucic acid, are enhanced by 25% in light and dark grown plants pretreated with MF at 20 °C and declined at 10 °C in the light (Novitskaya et al. 2010). At 20 °C, MF decreased the synthesis of polar lipids (18%) in radish seedlings grown under thelight but it was about 80% higher than non-treated seedlings. MF exposure increased the polar lipid content during chilling (10 °C) temperature and light but had no effects in the plants grown in dark plants. The breakdown process of lipids in germinating seeds is a critical element that provides energy for growing cells (Bewley and Black 1994). The MF treatment can modulate the lipid metabolism and synthesis in plants at the exposure of light and temperature (Novitskaya et al. 2010). The strong light enhances the singlet oxygen production in chloroplast by photosystem II (Telfer 2014) but disrupts the cellular activities and is harmful to plant growth. MF inhibits the formation of singlet oxygen, which reduces the metabolic energy available to the chloroplast (Hakala-Yatkin et al. 2011). The light wavelengths significantly influence the growth and flowering in plants, MF suppresses the flowering in white and blue light but did not affect the flowering in the red light (Xu et al. 2015).
Biotic stresses
The application of MF can reduce the detrimental effect of pathogenic microbes and increase the growth and yield of plants (Galland and Pazur 2005). For example, citrus plants intermittently exposed to 10 Hz MF showed a substantial enhancement in fresh and dry leaf weight in healthy as well as Phytoplasma aurantifolia infected plants (Abdollahi et al. 2012). It proved that MF could also increase the resistance against pathogens. Biochemical analysis revealed that the accumulation of proteins was higher but carbohydrates were lesser in infected plants treated with MF. The synthesis of proline (a protective osmolyte) is notably activated by MF thus supporting cellular structures (Resenburg et al. 1993). The biotic stress alleviation mechanism of MF was determined by reduced H2O2 production in infected plants exposed to MF. On the other hand, scavenging enzymes control the free radicals, which alter membrane integrity and increase the resistance in plants against pathogen infection. However, Trebbi et al. (2007) studied the hypersensitive response (HR) in tobacco mosaic virus infected tobacco plants during the MF exposure and proved that MF treatment decreases the number and area of lesions in the diseased plants and it also regulates the calcium (Ca2+) signaling pathway in the cell. During the HR, the Ca2+ influx into the cytosol is stimulated that increases the resistance (Baureus-Koch et al. 2003). Similarly, MF influences the polyamine pathway enzymes such as ornithine decarboxylase (ODC) and phenylalanine ammonia lyase (PAL). The ODC and PAL activities enhanced by an MF exposure during infection suggest that putrescine synthesis helps the plant withstand the biotic stress (Trebbi et al. 2007).
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Conclusion
Magnetic field (MF) therapy has been claimed to be effective for human ailments. Very few studies have been undertaken to understand the positive effect of MF on crop plants during environmental stress conditions. This review explores the current knowledge and future prospects of MF-induced physiological changes in plants toward enhancing the growth and yield under favorable and adverse conditions. The application of MF accelerates the seed germination, vegetative as well as reproductive growth in plants due to an increase in energy and its distribution to biomolecules in the cell. The enhancement of water and nutrient uptake, photosynthesis, carbohydrates, protein and enzyme metabolisms would impact the promotion of plant growth and yield. Unfavorable environments such as drought, salinity, heavy metal contamination in soil, cold and/or hot conditions drastically decrease the crop productivity. MF exposed plants tolerate these adverse environments by reducing oxidative stresses. MF treatment can enhance plants drought tolerance by stimulating water and Ca2+ uptake, cell membrane permeability, cambial differentiation, pigment synthesis, stomatal conductance. Similarly, MF protects the plants against salinity by increasing water uptake, stomatal conductance, sugar, and protein synthesis, and also by regulating the antioxidants and defense metabolites. Heavy metals in soil suppress the plant growth but MF treatment alleviates these metal stresses through the increased water flow, nitrogen, carbon, endogenous NO accumulation, photosynthesis, stomatal conductance, transpiration, and cell division. In addition, the production of heat shock proteins in MF exposed plants confers protection against the hyperthermic stresses. During low temperature, MF triggers ion transport, membrane permeability, photosynthesis, stomatal conductance, and transpiration, and regulates the polar lipids and erucic acids, irrespective of the presence or absence of light conditions to enhance the plant tolerance against temperature stresses. However, a reduced area of infection in leaves showed the control of plant diseases by MF exposure and this resistance may be due to the accumulation of Ca2+, proteins, and proline in plants.
Future prospectus
The MF-induced changes in the fundamental physiological process of crop plants against adverse environmental conditions have been investigated by only few researchers. A comprehensive bio-stimulatory activity of MF in several cellular metabolisms and their subsequent effects on tissue proliferation and organization need to be elucidated to decipher the mitigation mechanism of MF and plant interaction under stress environments. The future studies are required to confirm the positive effects of MF on crop yield by answering the following: (1) Whether MF treatment influences the next generation of crop growth and yield? (2) Is there any toxicity due to the consumption of MF treated foods? (3) Does it affect the micro and macro flora of soil during plant growth? In addition, the comprehensive genomic and proteomic analyses in MF treated plants would also bridge the space between current understanding and future perspective of biological effects of the magnetic field in plants.
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Acknowledgements
I thank Karpagam Academy of Higher Education, Coimbatore, India for providing financial support through Seed money project.
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Compliance with ethical standards
Conflict of interest
The author has no conflict of interest to declare.
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Footnotes
Publisher's Note
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References
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| biology | 4660641 | https://sv.wikipedia.org/wiki/Syzygium%20camptophyllum | Syzygium camptophyllum | Syzygium camptophyllum är en myrtenväxtart som först beskrevs av Murray Ross Henderson, och fick sitt nu gällande namn av Ian Mark Turner. Syzygium camptophyllum ingår i släktet Syzygium och familjen myrtenväxter. IUCN kategoriserar arten globalt som akut hotad. Inga underarter finns listade i Catalogue of Life.
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and 3 more
* [ Organic Manipulation ](/wiki/Category:Organic_Manipulation "Category:Organic Manipulation")
* [ Plant-based Powers ](/wiki/Category:Plant-based_Powers "Category:Plant-based Powers")
* [ Earth Powers ](/wiki/Category:Earth_Powers "Category:Earth Powers")
# Plant Growth
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## Plant Growth
[ 
](https://static.wikia.nocookie.net/powerlisting/images/1/1b/Te_Fiti.gif/revision/latest?cb=20180323202625
"Te Fiti")
## Te Fiti (Moana)
### Power/Ability to:
Accelerate plant growth.
The power to **influence the growth of plant life.** Sub-power of [ Plant
Manipulation ](/wiki/Plant_Manipulation "Plant Manipulation") and [ Plant
Enhancement ](/wiki/Plant_Enhancement "Plant Enhancement") .
## Contents
* 1 Also Called
* 2 Capabilities
* 3 Applications
* 4 Techniques
* 5 Associations
* 6 Limitations
* 7 Known Users
* 8 Known Objects
* 9 Gallery
* 10 Videos
## Also Called [ ]
* Accelerated Plant Growth
* Plant Fertility Manipulation
* Plant Growth Acceleration
* Plant Size Alteration/Enhancement
## Capabilities [ ]
The user can influence and accelerate the growth of plants causing flowers and
other plants to bloom instantaneously, causing them to mature with
supernatural speed, grow to unusual size, and produce in abundance. The user
can cause plants to grow from seeds to mature plants in moments, cause them to
flower and produce fruits, seeds, etc. outside season, cause a cut plant to
grow roots and other similar feats.
## Applications [ ]
* [ Accelerated Growth ](/wiki/Accelerated_Growth "Accelerated Growth")
## Techniques [ ]
* [ Planet Sustaining ](/wiki/Planet_Sustaining "Planet Sustaining")
## Associations [ ]
* [ Fertility Inducement ](/wiki/Fertility_Inducement "Fertility Inducement")
* [ Food Generation ](/wiki/Food_Generation "Food Generation")
* [ Plant Enhancement ](/wiki/Plant_Enhancement "Plant Enhancement")
* [ Plant Manipulation ](/wiki/Plant_Manipulation "Plant Manipulation")
## Limitations [ ]
* User cannot _create_ plants, so they need seeds and maybe fertile soil.
* May be limited to the user's emotional state.
* May be unable to manipulate plant-life that isn't native to the area they are.
* May be unable to manipulate plant-life that isn't native to them.
* Weak against [ Growth Negation ](/wiki/Growth_Negation "Growth Negation") .
* Opposed by and sometimes highly vulnerable against [ Pollution Manipulation ](/wiki/Pollution_Manipulation "Pollution Manipulation") .
## Known Users [ ]
* Yi ( _Abominable_ ); via violin magics
* Twillerbees ( _Barbie Thumbelina_ )
* Gwen Tennyson ( _Ben 10_ ); via a spell
* Charmcaster ( _Ben 10_ ); via a spell
* Toa of Plant Life ( _Bionicle_ )
* Makuta species ( _Bionicle_ )
* Obyn Greenfoot ( _Bloons_ )
* [ Rose Lily Kikunojo/Wild Wister ](https://bobobo.fandom.com/wiki/Rose_Lily_Kikunojo "w:c:bobobo:Rose Lily Kikunojo") ( _Bobobo-bo Bo-bobo_ )
* Willow Rosenberg ( _Buffy the Vampire Slayer_ )
* Hikari Sakurada ( _Castle Town Dandelion_ )
* Wood Nymphs ( _Charmed_ )
* [ Botan the Plant-Man ](https://dozerfleet.wikia.com/wiki/Botan_the_Plant-Man) ( _Ciem_ )
* Fairy Godmother ( _Cinderella_ )
* Le Selvasa ( _Combo Ninos_ )
* Bushroot ( _Darkwing Duck_ )
* Pamela Isley/Poison Ivy ( _DC Comics_ )
* Chlorophyll Kid ( _DC Comics_ )
* Rosetta ( _Disney Fairies_ )
* Garden Fairies ( _Disney Fairies_ )
* Lola ( _Deer Squad_ )
* Sinder ( _Gone_ )
* Gaia ( _Greek Mythology_ )
* [ Au Co ](http://heroeswiki.com/Au_Co) ( _Heroes_ )
* [ Ian Michaels ](http://heroeswiki.com/Ian_Michaels) ( _Heroes_ )
* Sadida God ( _Dofus/Wakfu_ )
* Sadida Class ( _Dofus/Wakfu_ )
* Isabela Madrigal ( _Encanto_ )
* Warrod Sequen ( _Fairy Tail_ )
* Aldoron ( _Fairy Tail: The 100 Years Quest_ )
* Archetype ( _Godzilla: Singular Point_ )
* Andy ( _Heart of Darkness_ )
* Mystique Sonia ( _Hero 108_ ); via her Saliva in order to instantly grow various types of bun
* Bianka Ataegina ( _Honkai impact 3rd_ )
* Mirai ( _Jibaku Shounen Hanako-kun_ ); via [ Time Acceleration ](/wiki/Time_Acceleration "Time Acceleration")
* [ Reagan Sinclair ](https://herokiller.fandom.com/wiki/Reagan_Sinclair "w:c:herokiller:Reagan Sinclair") ( _Hero Killer_ )
* [ Raxfer Sinclair ](https://herokiller.fandom.com/wiki/Raxfer_Sinclair "w:c:herokiller:Raxfer Sinclair") ( _Hero Killer_ )
* [ Rachel Sinclair ](https://herokiller.fandom.com/wiki/Rachel_Sinclair "w:c:herokiller:Rachel Sinclair") ( _Hero Killer_ )
* Hamon/Ripple Users ( _JoJo's Bizarre Adventure_ )
* Giorno Giovanna ( _JoJo's Bizarre Adventure Part V: Golden Wind/Vento Aureo_ ); via Gold Experience
* Koyo Aoba ( _Katekyo Hitman Reborn!_ )
* Zyra, the Rise of the Thorns ( _League of Legends_ )
* Koroks ( _The Legend of Zelda: The Wind Waker_ )
* Bolobo ( _Lego Ninjago: Masters of Spinjitzu_ )
* Dr Potter ( _Luigi's Mansion 3_ )
* Jack ( _Marchen Awakens Romance_ )
* Jake ( _Marchen Awakens Romance_ )
* Weasel ( _Marchen Awakens Romance_ )
* Users of Quan Quan ( _Mairimashita! Iruma-Kun_ )
* [ Klara Prast ](https://marvel.fandom.com/Klara_Prast_\(Earth-616\)) ( _Marvel Comics_ )
* [ Callie Betto/Dryad ](https://marvel.fandom.com/Callie_Betto_\(Earth-616\)) ( _Marvel Comics_ )
* [ Lin Li/Nature Girl ](https://marvel.fandom.com/Lin_Li_\(Earth-616\)) ( _Marvel Comics_ )
* Mukae Emukae ( _Medaka Box_ )
* [ Te Fiti ](https://moana.fandom.com/wiki/Te_Fiti) ( _Moana_ )
* Toshiki Minegishi ( _Mob Psycho 100_ )
* Shigeo Kageyama ( _Mob Psycho 100_ )
* Venus McFlytrap ( _Monster High_ )
* Mother ( _Mother!_ )
* Mistmane ( _My Little Pony: Friendship is Magic_ )
* Discord ( _My Little Pony series_ ); via [ Chaos Magic ](/wiki/Chaos_Magic "Chaos Magic")
* Earth ponies ( _My Little Pony: A New Generation_ )
* Cloud Galaxy ( _Nature Wolf Spirits_ )
* [ Aramaki ](https://onepiece.fandom.com/wiki/Aramaki "w:c:onepiece:Aramaki") ( _One Piece_ )
* [ Usopp ](https://onepiece.fandom.com/wiki/Usopp "w:c:onepiece:Usopp") ( _One Piece_ )
* [ Binz ](https://onepiece.fandom.com/wiki/Binz "w:c:onepiece:Binz") ( _One Piece_ )
* Willow Park ( _The Owl House_ )
* Luz Noceda ( _The Owl House_ )
* Leafspeakers ( _Wings of Fire_ )
* Hawthorn
* Sundew
* [ Demeter ](https://riordan.fandom.com/wiki/Demeter "w:c:riordan:Demeter") ( _Percy Jackson_ )
* [ Children of Demeter ](https://riordan.fandom.com/wiki/Demeter%27s_Cabin "w:c:riordan:Demeter's Cabin") ( _Percy Jackson_ )
* [ Katie Gardner ](https://riordan.fandom.com/wiki/Katie_Gardner "w:c:riordan:Katie Gardner")
* [ Miranda Gardiner ](https://riordan.fandom.com/wiki/Miranda_Gardiner "w:c:riordan:Miranda Gardiner")
* [ Meg McCaffrey ](https://riordan.fandom.com/wiki/Meg_McCaffrey "w:c:riordan:Meg McCaffrey")
* Calyrex ( _Pokémon_ )
* Pokémon that can use Grass-Type moves ( _Pokémon_ )
* Mike ( _Power Rangers Samurai_ )
* E. Aster Bunnymund/The Easter Bunny ( _Rise of the Guardians_ )
* Kusano ( _Sekirei_ )
* Perfuma ( _She-Ra and the Princesses of Power_ )
* Camo ( _Skylanders_ )
* Dark Oak, Black Narcissus and Pale Bayleaf ( _Sonic X_ ); in Final Mova transformation
* Thorn Rose ( _Sonic Prime_ ); via her hammer and a Prism Shard
* Cosmo ( _Sonic X_ ); via a unnamed jungle planet's Planet Egg
* Maleficent ( _Sleeping Beauty_ )
* [ Filforth, Defender of the Natural Order ](https://dozerfleet.wikia.com/wiki/Filforth) ( _Stationery Voyagers_ )
* Vida Calavera ( _Super Monsters_ )
* Satan ( _The Adventures of Mark Twain_ )
* Yarrow ( _Thea Stilton: The Land of Flowers_ ); via Absolute Elixir
* Yuuka Kazami ( _Touhou_ )
* Amalia Sheran Sharm ( _Wakfu Animated Series_ )
* Gardener ( _Wild Cards_ )
* Flora ( _Winx Club_
* Kurama ( _Yu Yu Hakusho_ )
* Alexstrasza ( _Warcraft_ )
* Rosey ( _Sofia the First_ )
* [ Plant grower ](https://the-nevers.fandom.com/wiki/Plant_grower "w:c:the-nevers:Plant grower") ( _The Nevers_ )
## Known Objects [ ]
* [ Pop Greens ](https://onepiece.fandom.com/wiki/Pop_Greens "w:c:onepiece:Pop Greens") ( _One Piece_ )
* [ Mosa Mosa no Mi ](https://onepiece.fandom.com/wiki/Mosa_Mosa_no_Mi "w:c:onepiece:Mosa Mosa no Mi") ( _One Piece_ )
* [ Mori Mori no Mi ](https://onepiece.fandom.com/wiki/Mori_Mori_no_Mi "w:c:onepiece:Mori Mori no Mi") ( _One Piece_ )
* Unnanmed jungle planet's Planet Egg ( _Sonic X_ )
* Green Prism Shard ( _Sonic Prime_ )
## Gallery [ ]
[  
](/wiki/File:Charmcaster_plants.gif "Charmcaster plants.gif \(6.03 MB\)")
Charmcaster (Ben10) using a [ magic ](/wiki/Magic "Magic") spell to control
the seeds.
[  
](/wiki/File:Gwen_Tennyson_Flower_Magic_\(Ben_10\).gif "Gwen Tennyson Flower
Magic \(Ben 10\).gif \(7.97 MB\)")
Gwen Tennyson (Ben 10)
[  
](/wiki/File:Green_Magic.gif "Green Magic.gif \(229 KB\)")
Warrod Sequen (Fairy Tail) using _Green Magic_ to grow a flower.
[  
](/wiki/File:Jonathan_Joestar_\(JoJo\)_grow_plant.gif "Jonathan Joestar
\(JoJo\) grow plant.gif \(9.41 MB\)")
Jonathan Joestar (JoJo's Bizarre Adventure)…
[  
](/wiki/File:Joseph_Joestar_\(JoJo\)_grow_plant.gif "Joseph Joestar \(JoJo\)
grow plant.gif \(7.77 MB\)")
...and his grandson, Joseph Jostar demonstrates with _Ripple/Hamon_ .
[  
](/wiki/File:Giorno%27s_Gold_Experience_powa!!!.gif "Giorno's Gold Experience
powa!!!.gif \(8.76 MB\)")
Similar to his relatives' Hamon/Ripple, Giorno Giovanna's Stand, _Gold
Experience_ (JoJo's Bizarre Adventure Part V/5: Golden Wind/Vento Aureo) can
grow plants with its life energy.
[  
](/wiki/File:Shin.gif "Shin.gif \(734 KB\)")
Shin (Pretear) showing his powers of growing plants quickly.
[  
](/wiki/File:Flora_Winx.png "Flora Winx.png \(148 KB\)")
Flora (Winx Club)
[  
](/wiki/File:Ian_Michaels_\(Heroes\)_Plant_growth.jpg "Ian Michaels \(Heroes\)
Plant growth.jpg \(127 KB\)")
Ian Michaels (Heroes) accelerates the growth of grass.
[  
](/wiki/File:Sonic_X_ep_77_042.png "Sonic X ep 77 042.png \(599 KB\)")
Final Mova (Sonic X) emitting energy waves to accelerate plant growth.
[  
](/wiki/File:Sonic_X_Cosmo_unlock_the_Planet_Egg%27s_power_to_grow_vines_ep_58.gif
"Sonic X Cosmo unlock the Planet Egg's power to grow vines ep 58.gif \(3.28
MB\)")
Cosmo (Sonic X) unlock a Planet Egg's power to grow vines.
[  
](/wiki/File:Green_Prism_Shard.png "Green Prism Shard.png \(1.03 MB\)")
Green Prism Shard (Sonic Prime)
[ 
](/wiki/File:Ezgif.com-resize_18.gif "Ezgif.com-resize 18.gif \(580 KB\)")
Thorn Rose (Sonic Prime) with the shard.
[  
](/wiki/File:God_Hand.png "God Hand.png \(1.45 MB\)")
Hikari Sakurada (Castle Town Dandelion) using _God Hand_ to accelerate a
tree's growth.
[  
](/wiki/File:My_Little_Pony_Series_Discord_Plant_Growth.gif "My Little Pony
Series Discord Plant Growth.gif \(1.11 MB\)")
Discord (My Little Pony series) is also capable of using this power.
[  
](/wiki/File:Pcontrol.jpg "Pcontrol.jpg \(23 KB\)")
Kurama (Yu Yu Hakusho) accelerating plant growth.
[  
](/wiki/File:Callie_Betto_\(Earth-616\)_from_New_X-
Men_Yearbook_Special_Vol_1_1_0001.png "Callie Betto \(Earth-616\) from New
X-Men Yearbook Special Vol 1 1 0001.png \(246 KB\)")
Callie Betto/Dryad (Marvel Comics) could accelerate, decelerate, or reverse
plant growth in a twenty-foot radius.
[  
](/wiki/File:Meg_McCaffrey-RR.jpg "Meg McCaffrey-RR.jpg \(29 KB\)")
As a daughter of Demeter, Meg McCaffrey (Trials of Apollo) can make plants,
crops, fruits and vegetables grow more faster than normal or in enormous
proportions.
[  
](/wiki/File:ObynGreenFootPortrait.png "ObynGreenFootPortrait.png \(84 KB\)")
Obyn Greenfoot (Bloons)
[  
](/wiki/File:Mistmane_ID_S7E16.png "Mistmane ID S7E16.png \(747 KB\)")
Mistmane (My Little Pony: Friendship is Magic)
[  
](/wiki/File:1000px-Bunnymund_\(Poster_2\).jpg "1000px-Bunnymund \(Poster
2\).jpg \(214 KB\)")
E. Aster Bunnymund/The Easter Bunny (Rise of the Guardians) has the power to
control flora growth, sometimes making a flower grow whenever his tunnels
close up.
[  
](/wiki/File:Earthcorn_.gif "Earthcorn .gif \(591 KB\)")
Cornelia Hale (W.I.T.C.H), as the Guardian of Earth, can control plants and
their growth and structure.
[  
](/wiki/File:Sofia_the_First_-_Rosey.jpg "Sofia the First - Rosey.jpg \(22
KB\)")
Rosey (Sofia the First)
[  
](/wiki/File:C6B7300B-36F6-4435-8236-0153F4ADF70F.webp
"C6B7300B-36F6-4435-8236-0153F4ADF70F.webp \(60 KB\)")
As a leafspeaker, Sundew (Wings of Fire) can make plants, crops, fruits and
vegetables grow more faster than normal or in enormous proportions.
## Videos [ ]
[ 
](/wiki/File:Yavanna_Kement%C3%A1ri,_Queen_of_the_Earth_-_Tolkien_Explained
"Yavanna Kementári, Queen of the Earth - Tolkien Explained \(36 KB\)")
Yavanna Kementári, Queen of the Earth - Tolkien Explained
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| biology | 4438552 | https://sv.wikipedia.org/wiki/Dracophyllum%20scoparium | Dracophyllum scoparium | Dracophyllum scoparium är en ljungväxtart som beskrevs av Joseph Dalton Hooker.
Dracophyllum scoparium ingår i släktet Dracophyllum och familjen ljungväxter. Inga underarter finns listade i Catalogue of Life.
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# Auditory Signal Processing Laboratory
##
Auditory Signal Processing Laboratory
The Auditory Signal Processing (ASP) Lab has three primary goals:
* Understanding the scientific basis of signal processing in the human peripheral auditory system
* Develop innovative methods for the clinical assessment of hearing loss
* Develop signal-processing strategies inspired by the auditory system for the remediation of hearing deficits
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Omaha, NE 68131).
This laboratory has two sound-treated booths, each with a clinical audiometer
and tympanometer. The lab is equipped with specialized hardware used for the
measurement of electrophysiological responses, otoacoustic emissions, acoustic
reflectance, speech perception, and psychoacoustic procedures, run by custom-
designed software.
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The Auditory Signal Processing Lab is directed by Stephen Neely, D.Sc. , and
is supported by funding from the National Institutes of Health, National
Institute for Deafness and Communication Disorders (NIDCD). Sara Harris, Au.D.
manages laboratory operations. The lab benefits from internal collaborations
with Lori Leibold Ph.D. and Gabrielle Merchant Au.D., Ph.D.
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| biology | 1801997 | https://no.wikipedia.org/wiki/George%20Anthony%20Giannoumis | George Anthony Giannoumis | Dr. George Anthony Giannoumis (Dr. Philos) (født i 1979) er en norsk-amerikansk forsker og førsteamanuensis ved Kristiania Høyskole . Han er også anerkjent som medgrunnlegger og styreleder i Inclusive Creation , et IT-rådgivningsfirma basert i Norge. Dr. Giannoumis ble født i Charlotte, Nord-Carolina., USA.
Hans hovedinteresser innen forskning omfatter universell utforming av informasjons- og kommunikasjonsteknologi, universell e-tilgjengelighet, teknologilovgivning, bærekraftig utvikling og inkluderende ledelse. Dr. Giannoumis er kjent for sine engasjerende og innflytelsesrike keynote-taler om inkluderende ledelse .
Utdanning og yrkeskarriere
Giannoumis har en mastergrad i global helse fra Temple University i Philadelphia. Tittelen på masteroppgaven var A Systematic Review of the Unintended Effects of Legislation on Population Health. Giannoumis har dessuten en doktorgrad i komparativ europeisk og internasjonal rett fra Universitetet i Bergen. Temaet for doktoravhandlingen var IKT-hjelpemidler for personer med funksjonsnedsettelser, og hadde tittelen Implementing Web Accessibility Policy: A comparative case study of the United Kingdom, Norway and the United States.
Giannoumis har blant annet arbeidet som vitenskapelig assistent ved Guru Charitable Foundation og som gjesteforsker ved Burton Blatt Institute ved Syracuse University. I 2011 ble Giannoumis tildelt et stipend fra EU-programmet Marie Skłodowska-Curie Actions (MSCA). Stipendet førte ham til Velferdsforskningsinstituttet NOVA, der han forsket på overvåking, gjennomføring og håndheving av lover og politikk forbundet med universell e-tilgjengelighet. 2014 ble han ansatt som førsteamanuensis ved Institutt for informasjonsteknologi ved Oslomet – storbyuniversitetet.
Giannoumis har også vært gjesteforsker og gjesteforeleser ved National University of Ireland, Galway, Maynooth University, Communication University of China, Sapienza-universitetet og Universitetet i Padua. Han har dessuten deltatt i Mozambique Norway Accessibility Project (MAP) - et samarbeidsprosjekt mellom Oslomet og Eduardo Mondlane University, ment å styrke forskningssamarbeid og studentutveksling innenfor områdene universell utforming og IKT-tilgjengelighet.
Giannoumis er viserapportør for FN-organet Den internasjonale telekommunikasjonsunion, i spørsmål vedrørende teknologitilgjengelighet og digital likestilling. Han er også medlem av underutvalget i organisasjonen EQUALS Global Partnership for Gender Equality in the Digital Age og tenketanken MyGoverNext Oslo. Han er også styremedlem i studentorganisasjonen Gender Equality in Technology. Giannoumis har tidligere vært medlem av Association for Computing Machinerys (ACM) ekspertutvalg for mangfold og inkludering.
Forskningsprosjekter
Giannoumis har deltatt i flere store forskningsprosjekter. Blant dem er to EU-finansierte prosjekter:
DISCIT - making persons with disabilities full citizens. Prosjektets formål var å innhente ny kunnskap for å sette EU, medlemsstatene og assosierte land i stand til å oppnå full økonomisk og samfunnsmessig deltakelse fra personer med nedsatt funksjonsevne. Giannoumis deltok som forsker og var prosjektets kommunikasjonsleder. Prosjektet ble ferdigstilt i 2016.
Cloud4All. Et prosjekt for å utvikle teknologisk infrastruktur til automatisk personalisering av produkter og tjenester for alle typer apparater og plattformer, for personer med funksjonsnedsettelser. Giannoumis deltok som etisk og juridisk rådgiver.
Giannoumis deltar nå i følgende forskningsprosjekter:
Demokratisk byutvikling i den digitale tidsalderen - DEMUDIG. Forskningsprosjektet skal undersøke hvordan bruk av digitale plattformer fremmer deltakerdemokrati, ved å sammenligne byutviklingsprosesser i Oslo, Madrid og Melbourne. Prosjektet ferdigstilles i desember 2021.
RELINK - Forsterking av det svake leddet. Utforsking, intervensjon og samskapte løsninger for å bygge robuste digitale hushold. Forskningsprosjektet skal kartlegge digitale sårbarheter i dagens husholdninger, og utvikle verktøy og løsninger som kan gjøre fremtidens oppkoplede hus mer robuste mot digitale sårbarheter. Prosjektet avsluttes i juli 2023.
Vitenskapelige publikasjoner
Et utvalg av Giannoumis' publikasjoner:
Giannoumis, George Anthony; Gjøsæter, Terje; Paupini, Cristina (2020). Towards an Indoor Navigation Application for Emergency Evacuations and Persons with Visual Impairments – Experiences from First Responders and End Users. IFIP Advances in Information and Communication Technology. Vol. 575.
Giannoumis, G. Anthony; Stein, Michael Ashley (2019). Conceptualizing universal design for the information society through a universal human rights lens. International Human Rights Law Review. Vol. 8.
Giannoumis, G. Anthony; Gjøsæter, Terje; Radianti, Jaziar; Paupini, Cristina (2019). Universally Designed Beacon-Assisted Indoor Navigation for Emergency Evacuations. Information Technology in Disaster Risk reduction - Third IFIP TC5 DCITDRR International Conference ITDRR 2018 Held at the 24th IFIP World Computer Congress, WCC 2018 Poznan, Poland, September 20-21, 2018 Revised Selected Papers. 9. s. 120-129. Springer Nature.
Frey, Elsebeth; Olsen, Ragnhild; Giannoumis, G. Anthony (2019). Exploring Journalism and Computer Science Student Collaboration A Norwegian case study. Nordicom Review. Vol. 40.
Paupini, Cristina; Giannoumis, G. Anthony (2019). Applying Universal Design Principles in Emergency Situations: An Exploratory Analysis on the Need for Change in Emergency Management. Lecture Notes in Computer Science (LNCS). Vol. 11573 LNCS.
Giannoumis, G. Anthony (2018). Regulatory Intermediaries: The Role of Interest Organizations in Supporting Web Accessibility Policy Implementation. Studies in Health Technology and Informatics.
Ahmad, Faizan; Beyene, Wondwossen; Giannoumis, G. Anthony (2018). Comparative Evaluation of Accessibility and Learnability of Learning Management Systems: Case of Fronter and Canvas. Communications in Computer and Information Science. Vol. 851.
Giannoumis, G. Anthony; Pandya, Umesh; Ferati, Mexhid; Krivonos, Daria; Pey, Tom (2018). Usability of Indoor Network Navigation Solutions for Persons with Visual Impairments. Usability of Indoor Network Navigation Solutions for Persons with Visual Impairments.
Giannoumis, G. Anthony (2018). Accessibility of anonymity networks: How can Web accessibility policies promote the usability of darknets for persons with disabilities?. First Monday. Vol. 23.
Ferati, Mexhid; Murano, Pietro; Giannoumis, G. Anthony (2017). Universal Design of User Interfaces in Self-driving Cars. Di Bucchianico, Giuseppe; Kercher, Peter (Red.). Advances in Design for Inclusion. Kapittel. s. 220-228. Springer Publishing Company.
Hagerup, Nina; Giannoumis, G. Anthony; Haakonsen, Peter; Øyan, Petter (2017). CHALLENGING THE AUDITORIUM. HOW TO FLIP A CLASSROOM IN A ROOM THAT CANNOT BE FLIPPED?. Proceedings of E&PDE 2017 - International Conference on Engineering and Product Design Education. Building Community: Design Education for a Sustainable Future. Section: Ethics and Social Issues in Design Education. s. 580-584. The Design Society.
Cibulka, Jaroslav; Giannoumis, G. Anthony (2017). Augmented and Virtual Reality for Engineering Education. Jonsson, Magnus (Red.). Proceedings of the 58th Conference on Simulation and Modelling (SIMS 58) Reykjavik, Iceland, September 25th – 27th, 2017. Article No.: 29. Linköping University Electronic Press.
Giannoumis, G. Anthony; Nthenge, Mirriam; Manhique, Jorge (2017). Pivot Model of Policy Entrepreneurship: an application of European ideas in the Global South. Lazar, Jonathan; Stein, Michael Ashley (Red.). Disability, Human Rights, and Information Technology. Chapter 14. University of Pennsylvania Press.
Thapa, Ratan Bahadur; Ferati, Mexhid; Giannoumis, G. Anthony (2017). Using non-speech sounds to increase web image accessibility for screen-reader users. Andersen, Rebekka (Red.). Proceedings of the 35th ACM International Conference on the Design of Communication. Article No.:19. Association for Computing Machinery (ACM).
Yao, Ding; Giannoumis, G. Anthony (2017). Information and Communications Technology and Social Media Accessibility in China -A peep at a Leopard through a Tube?. Kent, Mike; Ellis, Katie; Xu, Jian (Red.). Chinese Social Media: Social, Cultural, and Political Implications. Part III: Chapter 10. Routledge.
Giannoumis, G. Anthony; Land, Molly; Beyene, Wondwossen; Blanck, Peter (2017). Web accessibility and technology protection measures: Harmonizing the rights of persons with cognitive disabilities and copyright protections on the web. 19 s. Cyberpsychology : Journal of Psychosocial Research on Cyberspace. Vol. 11.
Tatara, Naoe; Giannoumis, G. Anthony (2017). Cultivating a Universal Design Mindset in Young Students. Proceedings of E&PDE 2017 - International Conference on Engineering and Product Design Education. Building Community: Design Education for a Sustainable Future. Chapter 1 - Design Education Practice. s. 62-67. The Design Society.
Bøhler, Kjetil Klette; Giannoumis, G. Anthony (2017). Technologies for Active Citizenship and the Agency of Objects. Halvorsen, Rune; Hvinden, Bjørn; Beadle-Brown, Julie; Biggeri, Mario; Tøssebro, Jan; Waldschmidt, Anne (Red.). Understanding the Lived Experiences of Persons with Disabilities in Nine Countries : Active Citizenship and Disability in Europe Volume 2. 12. s. 167-201. Routledge.
Skjerve, Rannveig Alette; Giannoumis, G. Anthony; Naseem, S (2016). An Intersectional Perspective on Web Accessibility. Langdon, Pat; Lazar, Jonathan; Heylighen, Ann; Dong, Hua (Red.). An Intersectional Perspective on Web Accessibility. Kapittel. s. 13-22. Springer.
Giannoumis, G. Anthony (2016). Framing the universal design of information and communication technology: An interdisciplinary model for research and practice. Studies in Health Technology and Informatics. Vol. 229.
En fullstendig liste over Giannoumis' publikasjoner ligger på Oslomets ansattside.
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Anatomy Head and neck Ear Auditory pathway
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Anatomy Head and neck Ear Auditory pathway
# Auditory pathway
Author: Shahab Shahid, MBBS • Reviewer: Jerome Goffin
Last reviewed: July 27, 2023
Reading time: 15 minutes
Hearing is an essential process. It enables us to understand and communicate
with our fellow human beings using our ears , and also experience the
outside world. The auditory pathway is more complex than the visual and
the olfactory pathways. It is composed of a number of nuclei and is
dependent on a range of functional areas .
This article will explore the anatomy , function and clinical relevance
of the auditory pathway.
Contents
1. Outer ear
2. Middle ear
1. Malleus
2. Incus
3. Stapes
4. Chorda tympani
3. Inner ear
4. Auditory pathway
5. Clinical aspects
6. Sources
\+ Show all
## Outer ear
Ear (ventral view)
The outer ear /visible ear is referred to as the pinna. It collects
omnidirectional sound waves and transforms them into a unidirectional
source of information. By funneling the sound waves in this way, it is able to
direct them into the auditory canal and amplify them.
The pinna has a number of features on its surface, which we will now discuss.
The external auditory canal is the opening of the ear . The helix is the
folded outer edge of the ear. The antihelix is a y-shaped region of ear
cartilage. It has an inferior and superior crus that lie either side of the
fossa triangularis. The groove between the helix and anti-helix is called the
scapha. The tragus and antitragus are the cartilaginous prominences that lie
anterior and inferior respectively to the external auditory opening.
The space between the tragus and antitragus is called the incisura anterior
auris. The lobe is either attached or free (genetic determination). The concha
is the hollow region that lies adjacent to the external ear opening. Finally
the auricular sulcus is the depression that lies posterior to the ear.
## Middle ear
Malleus (ventral view)
### Malleus
The malleus , or hammer in Latin, develops from the first pharyngeal arch
cartilage, like the mandible and maxilla jawbones. This small bone is
connected with the tympanic membrane via its manubrium and with the incus
via its articulating facet. The lateral process of the malleus is attached to
the upper part of the tympanic membrane. The lower part of the malleus is
attached to the tympanic membrane at the umbo, and is a strong connection. The
anterior process is attached to the petrotympanic fissure.
There are anterior, lateral and superior malleal ligaments, which maintain the
position of the malleus at the level of the head, neck and head of the malleus
respectively, dampen the response of the ossicles to excessively loud
sounds, and also reduce the displacement of the ossicles when middle ear
pressure changes .
The tensor tympani muscle attaches onto the neck of the malleus, and its
role is to dampen sounds. It arises from the greater wing of sphenoid and
auditory canal and can be voluntarily controlled. However its involuntary
function is most important.
Incus (ventral view)
### Incus
The incus is shaped like an anvil . It is attached to the malleus via a
facet, and to the stapes via its lenticular process located at the end of
the long crus . It also has a short crus and its body lies mainly in the
epitympanic recess. The posterior incudal ligament as well as the anterior
malleal ligament give the ossicles their axis of rotation.
Stapes (ventral view)
### Stapes
This is the smallest bone in the human body. It develops from the second
pharyngeal arch, and is the last ossicle of the middle ear . Its footplate
articulates with the oval window via the annular ligament.
The stapedius is the smallest skeletal muscle in the human body, and is just
over a millimeter in length. It stabilizes the stapes , and is innervated by
the facial nerve ( cranial nerve 7). Hence in facial nerve palsy (usually
a lower motor neuron i.e. Bell’s palsy), one of the symptoms is pain on
hearing noises (especially loud noises ) on the affected side, due to a lack
of innervation of the stapedius. It arises from the cone shaped eminence in
the posterior part of the tympanic cavity known as pyramidal eminence, and
inserts onto the neck of the stapes.
### Chorda tympani
This nerve provides taste to the anterior two thirds of the tongue, and is
a branch of the facial nerve (cranial nerve 7). It passes through the middle
ear on its way to the tongue.
## Inner ear
Cochlea (ventral view)
This region is found within the bony labyrinth . The cochlea (the region
responsible for hearing) is a spiral shaped hollow organ. The cochlear duct
is the triangular shaped section of the cochlea, which contains the organ of
Corti . The oval window is quite simply an oval shaped window that is moved
inwards by the movement of the stapes footplate .
The scala vestibuli is the semicircle shaped region above the scala media
and contains perilymph . It is separated from the scala media by Reissner’s
membrane . It receives the sound waves from the oval window, and sends them
up to the apex of the cochlea (the helicotrema ). Here the sound wave
vibrations continue and head back down the cochlea via the scala tympani .
The scala media lies between the scala vestibuli and the scala tympani and
contains endolymph .
The organ of Corti lies within the scala media. The scala tympani lies below
the scala media, and is separated from the scala media by the basilar
membrane . The round window is a circular window that moves out upon sound
transmission .
It is essential for sound transmission in the inner ear , as perilymph is a
fluid, and fluids are essentially non-compressible. Without the round window,
the compression of the stapes footplate would not transmit the vibrations from
the tympanic membrane.
## Auditory pathway
The external ear/pinna funnels sound waves into a unidirectional wave , and
is able to direct it into the auditory canal . This sound then reaches the
tympanic membrane , and causes it to vibrate . The louder the sound the
bigger the vibration , the lower pitch the sound the slower the vibration.
The handle of the malleus articulates with the tympanic membrane , and the
malleus also has an articulating facet for the Incus . The axis of rotation
is maintained by two ligaments (the anterior malleal and posterior incudal
ligaments). The incus lies in the epitympanic area, and is shaped like an
anvil. It articulates with the stapes via its lenticular process.
The stapes is shaped like a stirrup, and impacts onto the oval window .
The stapes moves like a piston, and causes the oval window to move in and out
with sounds. There is a round window located below the oval window that
moves out when the oval window moves in.
Without it, there would be no transmission of the sound waves into vibrations
in the inner ear . The sound waves are sent up the scala vestibuli to the
apex of the cochlear duct (the helicotrema). Here it continues back down the
spiral shaped cochlear organ in the scala tympani. The scala vestibuli and
scala media are separated by Reissner’s membrane. Scala media and scala
tympani below are separated by the basilar membrane.
When these waves move up and down the perilymph in the scala vestibuli and
scala tympani, the vibrations move the basilar membrane . The organ of
Corti lies on the basilar membrane, and is the organ responsible for
converting these vibrations into electrochemical signals . There are
stereocilia that lie on the organ of Corti. Their tips go into a gel like
layer called the tectorial membrane . When vibrations move the basilar
membrane, these hair cells bend, and potassium channels open.
Organ of Corti (histological slide)
The influx of potassium causes the generation of a local current and then an
action potential that is sent up the cochlear division of the
vestibulocochlear nerve (cranial nerve 8). This nerve then sends the signal
to nuclei in the brainstem .
These include the cochlear nuclei . The information from the cochlear nerve
passes to the ventral and dorsal cochlear nuclei . These nuclei are the
first connection with the auditory information. The three major outputs of
these nuclei are to the superior olivary complex (via the trapezoid body).
The other half of the information is sent to the contralateral superior
olivary complex . The second order neurons are sent via the lateral
lemniscus to the inferior colliculus , which receives connections from from
the superior olivary complex. The majority of these connections will
ultimately terminate in the auditory cortex .
Inferior colliculi (cranial view)
The superior olivary complex \- This is a cluster of nuclei found in the
brainstem. It has a number of roles in the process of hearing. These include
detection of the time difference between sound reaching each ear, and hence
localization of where the sound is coming from. The lateral superior olive
has a role in detecting the differences in sound intensity between both ears
. The medial superior olive will locate which angle the sound is coming
from.
The inferior colliculus \- This is the ultimate end point of many of the
brainstem nuclei outputs. Vertical and horizontal sound location information
synapses in the inferior colliculus and localizes where the sound is coming
from. It functions as the switchboard and as the convergence of many pathways.
The medial geniculate nucleus \- This is the nucleus of the thalamus that
acts as the relay point between the inferior colliculus and the auditory
cortex . The lateral geniculate nucleus (involved in the visual pathway) lies
adjacent to it.
The primary auditory cortex \- This is located in the temporal lobe and has
a role in the processing of auditory information. It lies in the superior
temporal gyrus of the lobe, and extends as far as the transverse temporal
gyri. The frontal and parietal lobes are responsible for the final elements of
sound processing (secondary auditory cortex). The primary auditory cortex is
tonotopically organised , meaning that the cells within the cortex, will
receive inputs from cells in the inner ear that respond to specific
frequencies.
Wernicke’s area \- This is a region on the temporal-parietal junction and on
the left side of the brain , which is responsible for understanding of
speech . The primary auditory cortex will signal next to this area.
Broca’s area \- This is a region within the inferior frontal gyrus of the
frontal lobe . On the left side it is responsible for generating speech .
Arcuate fasciculus \- This is a white matter tract that connects
Wernicke’s area to Broca’s area .
## Clinical aspects
Tinnitus \- Tinnitus is a ringing sound in the ears without actual sound
coming from the environment. It usually occurs after hearing loss, when the
inner hair cells become highly sensitised.
Presbyacusis \- This is defined as age related hearing loss. It is
progressive and irreversible , and mainly affects high-pitched sounds. It is
the commonest cause of hearing loss. Sounds appeared muffled, or dull. Causes
include damage to the organ of Corti, basilar membrane stiffening, vascular
degeneration, and spiral ganglion cell degeneration.
Wernicke’s aphasia \- Wernicke's aphasia is a type of aphasia where the
patient is unable to understand their usual language in its spoken or
written form. Wernicke’s area on the left side enables us to understand
speech, and a stroke affecting the area causes word salad or nonsense
sentences or random words. The patient will not be aware of this defect when
they speak.
Meniere’s disease \- This is a disease caused by a build up of endolymph
fluid in the inner earcausing dizziness, vertigo , tinnitus and balance
issues . It can be caused by infection or scar tissue following surgery.
Vestibular schwannoma \- Vestibular schwannoma is a tumor of the schwann
cells of the vestibulocochlear nerve. Symptoms include hearing loss,
tinnitus, balance issues, a feeling of pressure in the ears, and rarely a
headache with larger tumors. If the tumor is large it can also compress the
facial nerve (which also leaves the skull via the internal acoustic meatus
) or the trigeminal nerve, causing facial weakness or tingling respectively.
Otitis media \- This is an infection of the middle ear , most commonly
following an upper respiratory tract infection. The auditory (a.k.a.
Eustachian) tube opens into the middle ear and auditory tube dysfunction
promotes viral or bacterial colonisation of the middle ear. Treatment is
conservative. If children have this repeatedly, they get a condition called
glue ear (otitis media with effusion), which requires a tympanostomy tube
(grommet) to perforate the eardrum and ventilate the middle ear. If bacteria
cause an infection then the disease may become suppurative, in which case
antibiotics are required.
Otosclerosis \- This is defined as abnormal growth of bone in the middle
ear , which results in the fixation of the footplate of the stapes The
patient will experience increasing deafness as the condition worsens. It is an
inherited condition, and is an example of conductive hearing loss. There is
evidence that the condition can be triggered by a viral infection.
## Sources
All content published on Kenhub is reviewed by medical and anatomy experts.
The information we provide is grounded on academic literature and peer-
reviewed research. Kenhub does not provide medical advice. You can learn
more about our content creation and review standards by reading our content
quality guidelines .
References:
* Frank H. Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and Neck.
* Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
* Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
* Elliiot L.Manchell: Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience.
* The Definitive Neurological Surgery Board Review By Shawn P. Moore, 2005.
* Human Neuroanatomy By James R. Augustine, 2008.
* Surgical anatomy of the Ear and Temporal Bone By Bruce Proctor, 1989.
Illustrators:
* Malleus (ventral view) - Paul Kim
* Incus (ventral view) - Paul Kim
* Stapes (ventral view) - Paul Kim
* Cochlea (ventral view) - Paul Kim
* Inferior colliculi (cranial view) - Paul Kim
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| biology | 52311 | https://no.wikipedia.org/wiki/%C3%98re | Øre | Øret (latin: auris) er en av kroppens legemsdeler og dets hovedfunksjon er å oppfatte (høre) lyd.
Ører finnes hos de aller fleste dyr.
Vanligvis er det to ører. Fordi det er to ører (stereofoni) kan en retningsbestemme hvor lydkilden befinner seg.
Det er vanlig å inndele pattedyrs ører i en indre, midtre og en ytre del.
Det ytre øre (latin: pinna) består stort sett av hud og brusk. Det har til oppgave å lede lyden inn i øregangen, og beskytte det indre øret mot vann og andre fremmedelementer. I tillegg endrer foldene i det ytre øret frekvensspekteret på den innkommende lyden, alt etter hvor lyden kommer fra. Dette skjer for at individet lettere skal kunne retningsbestemme lyden.
Mellomøre inneholder en knokkelkjede bestående av hammeren (lat. malleus), ambolten (lat. incus) og stigbøylen (lat. stapes). Stigbøylen er koblet til en membran som kler det ovale vindu som grenser til sneglehuset (se under).
Det indre øre inneholder blant annet sneglehuset som omdanner vibrasjoner til nervesignaler, og labyrinten som hjelper individet å holde balansen.
Menneskets øre
Det ytre øret, Auris externa
Øremuslingen, auricula: omgir åpningen til ytre øregang og består av en hudkledd bruskplate. Har liten betydning for hørselen, men kosmetisk viktig.
Ytre øregang, meatus acusticus externa: 3-4cm lang hudkledd kanal. Små kjertler produserer ørevoks.
Trommehinnen, membrana tympani: Spent opp i enden av ytre øregang. Vibrerer ved påvirkning av lyd. Består av løvtynn bindevevsplate (ca, 0,1mm tykk), dannet av konsentrisk og radielt anordnede kollagenfibrer. Trommehinnens ytre flate er kledd av et tynt hudlag, den indre flate er dekket av luftveisepitel
Mellomøret, Auris media
En liten luftfylt grotte i tinningbensklippen, pars petrose ossis temporalis, avgrenset fra det ytre øret av trommehinnen. På motsatt side er det to små åpninger; det ovale vindu (lat. fenestra vestibuli) og det runde vindu (lat. fenestra cochlea). Det ovale vindu er helt dekket av basis stapedis, (dvs stigbøylens bunn) og det er her lyden ledes over i det indre øre.
Mellomøreknoklene
Mellomøreknoklene danner et mekanisk system som overfører lydimpulser fra trommehinnen til det ovale vindu. To ørsmå tverrstripete muskler går fra veggen i mellomøret, den ene til hammeren, den andre til stigbøylen. Sammentrekning av disse musklene hindrer lydoverføringen fra trommehinnen og beskytter sansecellene i indre øret mot støyskade.
Det ovale vindu Dekket av tynn bindevevsmembran.
Stigbøylen (lat. Stapes) Kroppens minste knokkel. Fotplaten dekker det ovale vindu som et tett lokk. Andre enden danner en leddforbindelse med ambolten (lat. Incus) som på andre side står i forbindelse med hammeren (lat. Malleus); den tredje og største mellomøreknokkelen. Skaftet på hammeren er sammenvokst med trommehinnen.
Øretrompeten (lat. tuba auditiva). En tynn kanal til svelget som utligner lufttrykket i øret. Dette for at trommehinnen skal kunne vibrere uhindret. Er blokkert av en slimhinne, men når vi svelger eller beveger kjevene oppstår et mekanisk drag som åpner kanalen og luft kan strømme fritt mellom svelg og mellomøret.
Mastoidcellene Finnes rett bak øremuslingen kan en kjenne et tydelig knokkelfremspring. Dette er øreknuten (lat. processus mastoideus). På innsiden er det tallrike små luftfylte hulrom i beinvevet, som står i forbindelse med mellomøret. Ingen kjent betydning.
Det indre øret, Auris interna
Det indre øret består av et komplisert system av væskefylte kanaler i tinningsbensklippen, også kalt labyrinten. Alle delene står i forbindelse med hverandre, men delt i tre hoveddeler:
Sneglehuset (lat.cochlea) – ivaretar hørselssansen
Buegangene – ivaretar likevektssansen
Vestibulum – ivaretar likevektssansen
Sneglehuset Tynn spiralformet kanal, delt på langs av to bindevevsmenbraner som gir tre parallelle kanalløp. På den ene av disse membranene, basilarmembranen sitter sansecellene.
Buegangene Tre halvsirkelformede rør som står vinkelrett på hverandre i tre plan, og vestibulum består av to mindre hulrom; sacculus og utriculus. Alle disse strukturene inneholder sanseceller som forteller om hodet og kroppens stilling og bevegelse. Afferente signaler fra indre øret formidles gjennom den indre øregangen. Her passeres nervus vestibulocochlearis, som formidler de afferente sansesignalene fra likevektsorganet og hørselsorganet. Sammen med denne nerven går små arterier fra en av de store arteriene til lillehjernen.
Nervus facialis går først sammen med nervus vestibulocochlearisi den indre øregangen, og deretter alene i en slynget kanal før den kommer ut av kraniet rett bak øreknuten (processus mastoideus).
Lydbølger med ulik frekvens skaper svingninger i ulike deler av basilarmembranen. Høy frekvens (lyst) – langt nede, lav frekvens (mørk) – i toppen. Her er grunnen til at vi kan skille mellom mørke og lyse toner. svingninger i basilarmembranen fører til at hårene på hårcellene bøyer seg og fører til dannelse av afferente sensoriske nerveimpulser. Disse impulsene blir ledet videre til kjerner i hjernestammen, thalamus, ved hjelp av nervus vestibulocochlearis, som på sin side formidler signalene videre til andre deler av sentralnervesystemet.
Hørselsbarken i temporallappen ivaretar bevisst lydopplevelse og står i forbindelse med språkområdene og har stor betydning for språkfunksjonen. Wernickes område i venstre hemisfære er f.eks. spesielt viktig for forståelsen av språk. Ved ødeleggelse her, for eksempel i forbindelse med et hjerneslag, vil pasienten utvikle sensorisk afasi – kan uttale ord, men ordene har ingen mening.
En liten utvidet del av hver buegang, samt sacculus og utriculus, inneholder hårceller. De stikker inn i en geléaktig masse. I sacculus og utriculus inneholder denne massen små saltkrystaller som kalles otolitter. Når man dreier på hodet blir væsken i buegangene ”hengende igjen” i forhold til hodebevegelsen. Dermed ”dytter” væsken på den geléaktige massen over hårcellene slik at hårcellene bøyes, som igjen forårsaker afferente nerveimpulser i tilhørende sensoriske nevroner. Buegangene registrerer altså rotasjon av hodet. Ulike rotasjoner stimulerer de tre buegangene på ulike måter ettersom de står i hvert sitt plan. Dermed får hjernen presis informasjon om hvilke bevegelse som har funnet sted. Enten man beveger seg eller står stille virker tyngdekraften på otolittene i sacculus og utriculus, slik at hårene alltid blir trukket i en bestemt retning.
De sensoriske nervene fra likevektsorganet går i nervus vestibulocochlearis til hjernestammen, der de ender i flere store kjerner, vestibulariskjernene. Herfra går de i motonevronene i ryggmargen til lillehjernen. Samlet bidrar disse til overordnet kontroll over muskler for at vi kan opprettholde balansen.
Et samarbeid mellom flere deler av nervesystemet er avgjørende for at vi skal kunne gå og stå uanstrengt:
Synssansen registrerer hvordan kroppen er plassert i forhold til omgivelsene
Ulike mekanoreseptorer i bevegelsesapperatet forteller om leddenes stilling og bevegelse
Trykkreseptorer i huden under føttene registrerer kroppens vektfordeling i forhold til underlaget
Områder i hjernebarken setter sammen denne sanseinformasjonen sammen med sanseimpulsene fra likevektsorganet.
Nedstigende baner til motonevronene i ryggmargen sørger deretter, i samarbeid med lillehjernen, for å kontrollere muskulaturen vi bruker for å holde oss oppreiste.
Svimmelhet ved for eksempel piruetter skyldes uoverensstemmelse mellom sanseinformasjon fra likevektsorganene og andre kilder. Når vi plutselig stopper opp, så fortsetter væsken i buegangene å bevege seg en stund etterpå. Hjernen tolker dette som at hodet fortsatt roterer, men motsatt av først. Annen sanseinformasjon forteller at kroppen faktisk står stille. Dermed oppfattes en illusjon om at rommet snurrer rundt oss.
Mennesker kan oppfatte frekvenser fra ca. 30 Hz og helt opp mot 15-20 000 Hz.
Virvelløse dyr
Sanseorganer som kan oppfatte lyder hos virvelløse dyr er små akustiske hår på hudskjelettet (kutikula) eller noen organ som ligner litt på et øre. Disse kalles tympanalorganer og er plassert på forskjellige steder på kroppen. Løvgresshopper og sirisser har de på frambeina, litt høyt oppe på leggen. Ved å snu på seg kan de også rettningsbestemme hvor lyden kommer fra. Andre har slike hørselorgan på bakkroppen.
Insekter kan oppfatte frekvenser, helt opp mot 200 kHz., det er langt høyere enn det mennesker kan oppfatte (15-20 kHz).
Det å kunne høre er nyttig for å finne en partner (forplantning), for å unngå fiender og oppdage fare. Noen nattaktive insekter, blant annet sommerfugler i gruppen nattfly, har evnen til å høre lyden fra flaggermus som er på jakt. Like før flaggermusen angriper, slipper sommerfuglen seg ned, og unngår å bli spist.
Galleri
Øre
1000 artikler enhver Wikipedia bør ha | norwegian_bokmål | 0.635031 |
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# Hearing
Your hearing system has many working parts. Your outer ear directs sound waves
to your eardrum and causes it to vibrate. These vibrations move through your
middle ear and into your inner ear. Finally, these signals travel to your
brain, which translates them into what you hear.
### What is hearing (auditory processing)?
Hearing — or auditory processing — refers to the awareness of sounds and
placing meaning to those sounds. It involves a complex series of steps in
which several parts of your ear and auditory nervous system work together
harmoniously.
#### What are the parts of my auditory system?
Your auditory system (hearing system) consists of many different parts,
including your:
* Outer ear.
* Middle ear.
* Inner ear.
* Auditory nervous system.
Successful hearing requires all of these parts to function properly.
##### Outer ear
Your outer ear consists of your pinna and your ear canal. Your pinna is the
visible, external part of your ear. It funnels sound into your ear canal like
a reverse megaphone.
##### Middle ear
Your middle ear consists of your eardrum (tympanic membrane) and your
ossicles (tiny, sound-conducting bones called the malleus, incus and stapes).
Your eardrum sits at the very end of your ear canal. Your ossicles — located
on the other side of your eardrum — carry sound vibrations to your inner ear.
##### Inner ear
Your inner ear contains a spiral-shaped structure called the cochlea (which
means snail shell). Tiny hair cells line the inside of your cochlea. When
sound vibrations reach these hair cells, they transmit signals to your
auditory nerve.
##### Auditory nervous system
Your auditory nerve runs from your cochlea to a station in your brain stem
(known as the nucleus). From that station, neural impulses travel to your
temporal lobe — where your brain attaches sound to meaning.
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### How does hearing work?
Your hearing process involves all of the auditory system parts mentioned
above. Here’s a step-by-step guide to this complex process:
1. Sound waves travel through your ear canal to your eardrum and cause it to vibrate.
2. The vibrations travel from your eardrum to your ossicles (tiny bones in your middle ear).
3. Your ossicles send the vibrations to your cochlea (a spiral cavity in your inner ear that’s lined with hair cells).
4. The tiny hair cells vibrate and send messages to your auditory nerve (the nerve that connects your ears to your brain ).
5. Your brain receives this information and translates it into sound. In other words, your brain is where your sense of hearing comes to life.
### What conditions can impact my ability to hear?
Many conditions, illnesses and diseases can affect your hearing, including:
* Aging : Hearing naturally weakens as you grow older. Noise exposure, illnesses and certain medications can all contribute to age-related hearing loss .
* Ear trauma : Pushing cotton swabs or other objects into your ear can result in a ruptured eardrum . A hard slap on your ear can cause trauma, and head trauma can cause fractures within your ear.
* Disease : Cardiovascular diseases and diabetes can increase your risk for hearing issues by decreasing the blood supply to your ear and your auditory system.
* Medication : Some medications, such as cancer treatment drugs, can contribute to hearing loss .
* Sound exposure : Long-term exposure to excessively loud sounds will damage the structures in your inner ear and cause hearing loss. It can happen gradually over time (for example, working for many years in a factory), or it can happen instantly (when using things like firearms or firecrackers). The greater the exposure, the greater the hearing loss. Noise-induced hearing loss , however, is 100% preventable by using hearing protection devices like earplugs or earmuffs.
* Earwax : Earwax (cerumen) in your ear canal is normal and healthy. But sometimes too much earwax can build up and block sound from getting to your eardrum. Eventually, this can result in hearing loss. Professional earwax removal by a healthcare provider can help restore hearing in these instances.
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### When should I call my healthcare provider?
Visit a hearing care provider immediately if you experience sudden hearing
loss, even if it’s only in one ear. Seeking medical attention within the first
72 hours is essential to reduce your risk of complications, including
permanent hearing loss.
Hearing care specialists are different from your primary care physician (PCP)
. They include:
* Audiologist : A healthcare provider trained to diagnose and treat nonmedical hearing and balance problems.
* Otolaryngologist (ENT): A physician who treats problems with your ears, nose and throat .
* Otologist: A specialist who focuses on ear health and the medical and surgical management of ear or hearing issues.
If you notice a change in your ability to hear or understand, or if it seems
like everyone is mumbling, schedule an appointment with a hearing care
specialist. Hearing loss can occur gradually so it’s good practice to have
your hearing tested on a regular basis. This is especially true if you have a
family history of hearing loss.
### How do hearing care specialists check for hearing loss?
A hearing care specialist will give you a hearing test called an audiogram.
During this test, your provider plays sounds through headphones. You’ll press
a button when you hear a sound. The results measure your ability to hear.
Tests take place in your provider’s or audiologist’s office in a soundproof
booth.
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### How can I keep my hearing healthy?
To protect your hearing, you should:
* Use hearing protection (earplugs or earmuffs) during loud activities such as concerts, riding motorcycles or snowmobiles, or working with loud machinery.
* When listening to music through headphones or earbuds, keep the volume level low enough that you can hear people speaking around you. Another good rule is not to exceed 80% volume for more than 90 minutes a day.
* Don’t stick anything into your ear canal, including cotton swabs or hairpins. These objects could become lodged in your ear canal or cause an eardrum rupture.
* Avoid smoking , which can impair circulation and harm your hearing.
* Get regular exercise to help prevent health issues like diabetes or high blood pressure that can cause hearing problems.
* Manage any chronic illnesses to prevent further damage.
### What is auditory perception?
Auditory perception is the ability to identify and interpret sounds — and
attach meaning to them.
### What is the purpose of hearing?
Hearing helps you stay aware of your surroundings and connect to the world
around you.
A note from Cleveland Clinic
Hearing is one of the five basic human senses. It’s a complex process that you
use every day but probably don’t think about too often. Many people have
hearing difficulties. In fact, more than 37 million adults in the U.S. have
some degree of hearing loss. Today, there are many treatments and devices that
can improve your hearing, such as hearing aids, cochlear implants and bone
anchored implants . There are also resources to help people with profound
hearing loss communicate effectively. If you have difficulty hearing, ask a
healthcare provider about your options.
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Medically Reviewed
Last reviewed by a Cleveland Clinic medical professional on 02/21/2023.
Learn more about our editorial process .
#### References
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site helps support our mission. We do not endorse non-Cleveland Clinic
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| biology | 197959 | https://da.wikipedia.org/wiki/Apd | Apd | (Central) Auditory Perception Disorder (APD) (også kaldet CAPD) er samlebetegnelsen for tilstande, hvor hjernen har svært ved at bearbejde høreindtryk, selvom hørelsen som sådan fungerer normalt. Patienter med APD har således et normalt lydinput fra det indre øre og videre til hørenerven, men centralnervesystemet har problemer med at opfatte og bearbejde lydindtrykket i de centrale hørebaner, der inkluderer hørecenteret, som ligger i hjernebarkens tindingelap.
Diagnose
Der findes ikke diagnostiske tests, der med sikkerhed kan afgøre, hvorvidt et barn/en patient har APD. Børn med APD kan have problemer med taleforståelse, når der er baggrundsstøj, med at opfatte en besked, specielt hvis den er flerleddet, og ofte også med retningshørelsen. Ifølge Dansk Medicinsk Audiologisk Selskab har patienter med APD symptomer, der viser sig som vanskeligheder med et eller flere af følgende områder:
Lokalisation og lateralisation af lyd (retningsbestemmelse)
Auditiv diskrimination (høre forskel på ord, der ligner hinanden)
Auditiv mønstergenkendelse
Temporale aspekter af hørelsen
Talegenkendelse i baggrundsstøj (forstå tale i støj)
Auditive færdigheder ved konkurrerende akustiske signaler (f.eks. dikotisk lytning) (høre i støj)
Auditive færdigheder ved forringede akustiske signaler
Huske mundtlige beskeder
Klare telefonsamtaler
Læse og/eller stave
Følge instruktioner med flere led
Lære fremmedsprog og vanskelige ord
Behandling
Børn, der er er blevet diagnosticeret med APD, bør behandles på samme måde som de behandler børn, der er blevet diagnosticeret med sprog- og indlæringsproblemer. Tidlig auditiv træning (høretræning) øger muligheden for at udnytte hjernens plasticitet. Høretræningen kan finde sted i form af leg og øvelser og kan også inkludere træning på musikinstrument. Behandlingen tilrettelægges af en tale/hørepædagog og udføres i samarbejde med forældre, lærere og pædagoger.
Referencer
Eksterne kilder
Christian Worsøe: Når hjernen ikke kan høre. I: Psykolog Nyt nr. 6 – 2004. En artikel som for en stor del er baseret på Teri James Bellis: When the Brain Can’t Hear. New York: Simon & Schuster, Pocket Books, 2002.
APD Auditory Processing Disorder: Når hjernen ikke forstår hvad ørerne hører. www.apd.dk Hentet 3. oktober 2021.
Udviklingsforstyrrelser
Indlæringsvanskeligheder | danish | 0.649585 |
fake_auditory_signal/Cochlear_implant.txt | A cochlear implant (CI) is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. With the help of therapy, cochlear implants may allow for improved speech understanding in both quiet and noisy environments. A CI bypasses acoustic hearing by direct electrical stimulation of the auditory nerve. Through everyday listening and auditory training, cochlear implants allow both children and adults to learn to interpret those signals as speech and sound.
The implant has two main components. The outside component is generally worn behind the ear, but could also be attached to clothing, for example, in young children. This component, the sound processor, contains microphones, electronics that include digital signal processor (DSP) chips, battery, and a coil that transmits a signal to the implant across the skin. The inside component, the actual implant, has a coil to receive signals, electronics, and an array of electrodes which is placed into the cochlea, which stimulate the cochlear nerve.
The surgical procedure is performed under general anesthesia. Surgical risks are minimal and most individuals will undergo outpatient surgery and go home the same day. However, some individuals will experience dizziness, and on rare occasions, tinnitus or facial nerve bruising.
From the early days of implants in the 1970s and the 1980s, speech perception via an implant has steadily increased. More than 200,000 people in the United States had received a CI through 2019. Many users of modern implants gain reasonable to good hearing and speech perception skills post-implantation, especially when combined with lipreading. One of the challenges that remain with these implants is that hearing and speech understanding skills after implantation show a wide range of variation across individual implant users. Factors such as age of implantation, parental involvement and education level, duration and cause of hearing loss, how the implant is situated in the cochlea, the overall health of the cochlear nerve, but also individual capabilities of re-learning are considered to contribute to this variation.
History[edit]
1994 body-worn Cochlear Spectra processor. Early cochlear implant users utilized body-worn processors like this one
Cochlear implant recipient utilizing a behind-the-ear processor
André Djourno and Charles Eyriès invented the original cochlear implant in 1957. Their design distributed stimulation using a single channel.
William House also invented a cochlear implant in 1961. In 1964, Blair Simmons and Robert J. White implanted a single-channel electrode in a patient's cochlea at Stanford University. However, research indicated that these single-channel cochlear implants were of limited usefulness because they cannot stimulate different areas of the cochlea at different times to allow differentiation between low and mid to high frequencies as required for detecting speech.
NASA engineer Adam Kissiah started working in the mid-1970s on what would become the modern cochlear implant. Kissiah used his knowledge learned while working as an electronics instrumentation engineer for NASA. This work took place over three years, when Kissiah would spend his lunch breaks and evenings in Kennedy's technical library, studying the impact of engineering principles on the inner ear. In 1977, NASA helped Kissiah obtain a patent for the cochlear implant; Kissiah later sold the patent rights.
The modern multi-channel cochlear implant was independently developed and commercialized by two separate teams—one led by Graeme Clark in Australia and another by Ingeborg Hochmair and her future husband, Erwin Hochmair in Austria, with the Hochmairs' device first implanted in a person in December 1977 and Clark's in August 1978.
Parts[edit]
Cochlear implants bypass most of the peripheral auditory system which receives sound and converts that sound into movements of hair cells in the cochlea; the deflection of stereocilia causes an influx of potassium ions into the hair cells, and the depolarisation in turn stimulates calcium influx, which increases release of the neurotransmitter, glutamate. Excitation of the cochlear nerve by the neurotransmitter sends signals to the brain, which creates the experience of sound. With an implant, instead, the devices pick up sound and digitize it, convert that digitized sound into electrical signals, and transmit those signals to electrodes embedded in the cochlea. The electrodes electrically stimulate the cochlear nerve, causing it to send signals to the brain.
There are several systems available, but generally they have the following components:
External:
one or more microphones that pick up sound from the environment
a speech processor which selectively filters sound to prioritize audible speech
a transmitter that sends power and the processed sound signals across the skin to the internal device by radio frequency transmission
Internal:
a receiver/stimulator, which receives signals from the speech processor and converts them into electric impulses
an electrode array embedded in the cochlea
A totally implantable cochlear implant (TICI) is currently in development. This new type of cochlear implant incorporates all the current external components of an audio processor into the internal implant. The lack of external components makes the implant invisible from the outside and also means it is less likely to be damaged or broken.
Assistive listening devices[edit]
Most modern cochlear implants can be used with a range of assistive listening devices (ALDs), which help people to hear better in challenging listening situations. These situations could include talking on the phone, watching TV or listening to a speaker or teacher. With an ALD, the sound from devices including mobile phones or from an external microphone is sent to the audio processor directly, rather than being picked up by the audio processor's microphone. This direct transmission improves the sound quality for the user, making it easier to talk on the phone or stream music.
ALDs come in many forms, such as neckloops, pens, and specialist battery pack covers. Modern ALDs are usually able to receive sound from any Bluetooth device, including phones and computers, before transmitting it wirelessly to the audio processor. Most cochlear implants are also compatible with older ALD technology, such as a telecoil.
Surgical procedure[edit]
Surgical techniques[edit]
Implantation of children and adults can be done safely with few surgical complications and most individuals will undergo outpatient surgery and go home the same day.
Occasionally, the very young, the very old, or patients with a significant number of medical diseases at once may remain for overnight observation in the hospital. The procedure can be performed in an ambulatory surgery center in healthy individuals.
The surgical procedure most often used to implant the device is called mastoidectomy with facial recess approach (MFRA).
The procedure is usually done under general anesthesia. Complications of the procedure are rare, but include mastoiditis, otitis media (acute or with effusion), shifting of the implanted device requiring a second procedure, damage to the facial nerve, damage to the chorda tympani, and wound infections.
Cochlear implantation surgery is considered a clean procedure with an infection rate of less than 3%. Guidelines suggest that routine prophylactic antibiotics are not required. However, the potential cost of a postoperative infection is high (including the possibility of implant loss); therefore, a single preoperative intravenous injection of antibiotics is recommended.
The rate of complications is about 12% for minor complications and 3% for major complications; major complications include infections, facial paralysis, and device failure.
Although up to 20 new cases of post-CI bacterial meningitis occur annually worldwide, data demonstrates a reducing incidence. To avoid the risk of bacterial meningitis, the CDC recommends that adults and children undergoing CI receive age-appropriate vaccines that generate antibodies to Streptococcus pneumoniae.
The rate of transient facial nerve palsy is estimated to be approximately 1%. Device failure requiring reimplantation is estimated to occur 2.5–6% of the time. Up to one-third of people experience disequilibrium, vertigo, or vestibular weakness lasting more than one week after the procedure; in people under 70 these symptoms generally resolve over weeks to months, but in people over 70 the problems tend to persist.
In the past, cochlear implants were only approved for people who were deaf in both ears; as of 2014 a cochlear implant had been used experimentally in some people who had acquired deafness in one ear after they had learned how to speak, and none who were deaf in one ear from birth; clinical studies as of 2014 had been too small to draw generalizations.
Alternative surgical technique[edit]
Other approaches, such as going through the suprameatal triangle, are used. A systematic literature review published in 2016 found that studies comparing the two approaches were generally small, not randomized, and retrospective so were not useful for making generalizations; it is not known which approach is safer or more effective.
Endoscopic cochlear implantation[edit]
With the increased utilization of endoscopic ear surgery as popularized by professor Tarabichi, there have been multiple published reports on the use of endoscopic technique in cochlear implant surgery. However, this has been motivated by marketing and there is clear indication of increased morbidity associated with this technique as reported by the pioneer of endoscopic ear surgery.
Complications of cochlear implant surgery[edit]
As cochlear implant surgical techniques have advanced over the last four decades, the global complication rate for CI surgery in both children and adults has decreased from >35% in 1991 to less than 10% at present. The risk of postoperative facial nerve injury has also decreased over the last several decades to less than 1%, most of which demonstrated complete return of function within six months. The rate of permanent paralysis is approximately 1 per 1,000 surgeries and likely less than that in experienced CI centers.
The majority of complications following CI surgery are minor requiring only conservative medical management or prolongation of hospital stay. Less than 5% of all complications are major resulting in surgical intervention or readmission to the hospital. Reported rates of revision cochlear implant surgery vary in adults and children from 3.8% to 8% with the most common indications being device failure, infection, and migration of the implant or electrode. Disequilibrium and vertigo after CI surgery can occur but the symptoms tend to be mild and short-lived. CI rarely results in significant or persistent adverse effects on the vestibular system when hearing conservation surgical techniques are practiced. Moreover, gait and postural stability may actually improve post-implantation.
Outcomes[edit]
Cochlear implant outcomes can be measured using speech recognition ability and functional improvements measured using patient reported outcome measures. While the degree of improvement after cochlear implantation may vary, the majority of patients who receive cochlear implants demonstrate a significant improvement in speech recognition ability compared to their preoperative condition.
Multiple meta-analyses of the literature from 2018 showed that CI users have large improvements in quality of life after cochlear implantation. This improvement occurs in many different facets of life that extends beyond communication including improved ability to engage in social activities; decreased mental effort from listening; and improved environmental sound awareness. Deaf adolescents with cochlear implants attending mainstream educational settings report high levels of scholastic self-esteem, friendship self-esteem, and global self-esteem. They also tend to hold mostly positive attitudes towards their cochlear implants, and as a part of their identity, a majority either do "not really think about" their hearing loss, or are "proud of it." Though advancements in cochlear implant technology have helped patients in their understanding of language, users are still unable to understand suprasegmental portions of language, which includes pitch.
A study by Johns Hopkins University determined that for a three-year-old child who receives them, cochlear implants can save $30,000 to $50,000 in special-education costs for elementary and secondary schools as the child is more likely to be mainstreamed in school and thus use fewer support services than similarly deaf children.
Efficacy[edit]
A 2019 study found that bilateral cochlear implantation was widely regarded as the most beneficial hearing intervention for acceptable candidates, although it is more likely to be performed and reimbursed in children than adults. The study also found that the efficacy of bilateral implantation could be improved by enhancing communication between the two implants and by developing sound coding strategies specifically for bilateral users.
Early research reviews found that the ability to communicate in spoken language was better the earlier the implantation was performed. The reviews also found that, overall, while cochlear implants provide open-set speech understanding for the majority of implanted profoundly hearing-impaired children, it was not possible to accurately predict the specific outcome of the given implanted child. Research since then has reported long-term socio-economic benefits for children as well as audiological outcomes including improved sound localization and speech perception. A consensus statement from the European Bilateral Pediatric Cochlear Implant Forum also confirmed the importance of bilateral cochlear implantation in children. In adults, new research shows that bilateral implantation can improve quality of life and speech intelligibility in quiet and noise.
A 2015 review examined whether CI implantation to treat people with bilateral hearing loss had any effect on tinnitus. This review found the quality of evidence to be poor and the results variable: overall total tinnitus suppression rates for patients who had tinnitus prior to surgery varied from 8% to 45% of people who received CI; decrease of tinnitus was seen in 25% to 72%, of people; for 0% to 36% of the people there was no change; increase of tinnitus occurred in between 0% to 25% of patients; and, in between 0 and 10% of cases, people who did not have tinnitus before the procedure, got it. Further research found that the electrical stimulation of the CI is at least partly responsible for the general reduction in symptoms. A 2019 study found that although tinnitus suppression in patients with CIs is multifactorial, simply having the CI switched on without any audiological input (while standing alone in a soundproof booth) reduced the symptoms of tinnitus. This would suggest that it is the electrical stimulation that explains the decrease in tinnitus symptoms for many patients, and not only the increased access to sound.
A 2015 literature review on the use of CI for people with auditory neuropathy spectrum disorder found that, as of that date, description and diagnosis of the condition was too heterogeneous to make clear claims about whether CI is a safe and effective way to manage it.
The data for cochlear implant outcomes in older adults differs. A 2016 research study found that age at implantation was highly correlated with post-operative speech understanding performance for various test measures. In this study, people who were implanted at age 65 or older performed significantly worse on speech perception testing in quiet and in noisy conditions compared to younger CI users. Other studies have shown different outcomes, with some reporting that adults implanted at the age of 65 and older showed audiological and speech discrimination outcomes similar to younger adults. While cochlear implants demonstrate substantial benefit across all age groups, results will depend on cognitive factors that are ultimately highly age dependent. However, studies have documented the benefit of cochlear implants in octogenarians.
The effects of aging on central auditory processing abilities are thought to play an important role in impacting an individual's speech perception with a cochlear implant. The Lancet reported that untreated hearing loss in adults is the number one modifiable risk factor for dementia. In 2017, a study also reported that adults using a cochlear implant had significantly improved cognitive outcomes including working memory, reaction time, and cognitive flexibility compared to people who were waiting to receive a cochlear implant.
Prolonged duration of deafness is another factor that is thought to have a negative impact on overall speech understanding outcomes for CI users. However, a study found no statistical difference in the speech understanding abilities of CI patients over 65 who had been hearing impaired for 30 years or more prior to implantation. In general, outcomes for CI patients are dependent upon the individual's level of motivation, expectations, exposure to speech stimuli and consistent participation in aural rehabilitation programs.
A 2016 systematic review of CI for people with unilateral hearing loss (UHL) found that of the studies conducted and published, none were randomized, only one evaluated a control group, and no study was blinded. After eliminating multiple uses of the same subjects, the authors found that 137 people with UHL had received a CI. While acknowledging the weakness of the data, the authors found that CI in people with UHL improves sound localization compared with other treatments in people who lost hearing after they learned to speak; in the one study that examined this, CI did improve sound localization in people with UHL who lost hearing before learning to speak. It appeared to improve speech perception and to reduce tinnitus.
In terms of quality of life, several studies have shown that cochlear implants are beneficial in many aspects of quality of life, including communication improvements and positive effects on social, emotional, psychological and physical well-being. A 2017 narrative review also concluded that the quality of life scores of children using cochlear implants were comparable to those of children without hearing loss. Studies involving adults of all ages reported significant improvement in QoL after implantation when compared to adults with hearing aids. This was often independent of audiological performance.
Society and culture[edit]
Usage[edit]
As of October 2010, approximately 188,000 individuals had been fitted with cochlear implants. As of December 2012, the same publication cited approximately 324,000 cochlear implant devices having been surgically implanted. In the U.S., roughly 58,000 devices were implanted in adults and 38,000 in children. As of 2016, the Ear Foundation in the United Kingdom, estimates the number of cochlear implant recipients in the world to be about 600,000. The American Cochlear Implant Alliance estimates that 217,000 people received CIs in the United States through the end of 2019.
Cost and insurance[edit]
Cochlear implantation includes the medical device as well as related services and procedures including pre-operative testing, the surgery, and aftercare that includes audiology and speech language pathology services. These are provided over time by a team of clinicians with specialized training. All of these services, as well as the cochlear implant device and related peripherals, are part of the medical intervention and are typically covered by health insurance in the United States and many areas of the world. These medical services and procedures include candidacy evaluation, hospital services inclusive of supplies and medications used during surgery, surgeon and other physicians such as anesthesiologists, the cochlear implant device and system kit, and programming and (re)habilitation following the surgery. In many countries around the world, the cost of cochlear implantation and aftercare is covered by health insurance. However, financial factors impact the evaluation selection process. Children with public health insurance or no health insurance are less likely to receive the implant before 2 years old.
In the USA, as cochlear implants have become more commonplace and accepted as a valuable and cost effective health intervention, insurance coverage has expanded to include private insurance, Medicare, Tricare, the VA System, other federal health plans, and Medicaid. In September 2022 the Centers for Medicare & Medicaid Services expanded coverage of cochlear implants for appropriate candidates under Medicare. Candidates must demonstrate limited benefit with appropriately fit hearing aids but with criteria now defined by test scores of less than or equal to 60% correct in the best-aided listening condition on recorded tests of open-set sentence recognition. Just as there is with any medical procedure, there are typically co-pays which vary depending upon the insurance plan.
In the United Kingdom, the NHS covers cochlear implants in full, as does Medicare in Australia, and the Department of Health in Ireland, Seguridad Social in Spain, Sistema Sanitario Nazionale in Italy, Sécurité Sociale in France and Israel, and the Ministry of Health or ACC (depending on the cause of deafness) in New Zealand. In Germany and Austria, the cost is covered by most health insurance organizations.
Public health[edit]
6.1% of the world population live with hearing loss, and it is predicted that by 2050, more than 900 million people around the globe will have a disabling hearing loss. According to a WHO report, unaddressed hearing loss costs the world 980 billion dollars annually. Particularly hard hit are the healthcare and educational sectors, as well as societal costs. 53% of these costs are attributable to low- and middle-income countries.
The WHO reports that cochlear implants have been shown to be a cost-effective way to mitigate the challenges of hearing loss. In a low-to-middle-income setting, every dollar invested in unilateral cochlear implants has a return on investment of 1.46 dollars. This rises to a return on investment of 4.09 dollars in an upper-middle-income setting. A study in Colombia assessed the lifetime investments made in 68 children who received cochlear implants at an early age. Taking into account the cost of the device and any other medical costs, follow-up, speech therapy, batteries and travel, each child required an average investment of US$99 000 over the course of their life (assuming a life span of 78 years for women and 72 years for men). The study concluded that for every dollar invested in rehabilitation of a child with a cochlear implant, there was a return on investment of US$2.07.
Manufacturers[edit]
As of 2021, four cochlear implant devices approved for use in the United States are manufactured by Cochlear Limited, the Advanced Bionics division of Sonova, MED-EL, and Oticon Medical.
In Europe, Africa, Asia, South America, and Canada, an additional device manufactured by Neurelec (later acquired by Oticon Medical) was available. A device made by Nurotron (China) was also available in some parts of the world. Each manufacturer has adapted some of the successful innovations of the other companies to its own devices. There is no consensus that any one of these implants is superior to the others. Users of all devices report a wide range of performance after implantation.
Criticism and controversy[edit]
Much of the strongest objection to cochlear implants has come from within the deaf community, some of whom are pre-lingually deaf people whose first language is a sign language. Some in the deaf community call cochlear implants audist and an affront to their culture, which, as they view it, is a minority threatened by the hearing majority. This is an old problem for the deaf community, going back as far as the 18th century with the argument of manualism vs. oralism. This is consistent with medicalisation and the standardisation of the "normal" body in the 19th century when differences between normal and abnormal began to be debated. It is important to consider the sociocultural context, particularly in regards to the deaf community, which has its own unique language and culture. This accounts for the cochlear implant being seen as an affront to their culture, as many do not believe that deafness is something that needs to be cured. However, it has also been argued that this does not necessarily have to be the case: the cochlear implant can act as a tool deaf people can use to access the "hearing world" without losing their deaf identity.
Cochlear implants for congenitally deaf children are most effective when implanted at a young age. Children who have had confirmed severe hearing loss can receive the implant as young as 9 months old. Evidence shows that deaf children of deaf parents (or with fluent signers as daily caregivers) learn signed language as effectively as hearing peers. Some deaf-community advocates recommend that all deaf children should learn sign language from birth, but more than 90% of deaf children are born to hearing parents. Since it takes years to become fluent in sign language, deaf children who grow up without amplification such as hearing aids or cochlear implants will not have daily access to fluent language models in households without fluent signers.
Critics of cochlear implants from deaf cultures also assert that the cochlear implant and the subsequent therapy often become the focus of the child's identity at the expense of language acquisition and ease of communication in sign language and deaf identity. They believe that measuring a child's success only by their mastery of speech will lead to a poor self-image as "disabled" (because the implants do not produce normal hearing) rather than having the healthy self-concept of a proudly deaf person. However, these assertions are not supported by research. The first children to receive cochlear implants as infants are only in their 20s (as of 2020), and anecdotal evidence points to a high level of satisfaction in this cohort, most of whom don't consider their deafness their primary identity.
Children with cochlear implants are most likely to be educated with listening and spoken language, without sign language and are often not educated with other deaf children who use sign language. Cochlear implants have been one of the technological and social factors implicated in the decline of sign languages in the developed world. Some Deaf activists have labeled the widespread implantation of children as a cultural genocide.
As the trend for cochlear implants in children grows, deaf-community advocates have tried to counter the "either or" formulation of oralism vs. manualism with a "both and" or "bilingual-bicultural" approach; some schools are now successfully integrating cochlear implants with sign language in their educational programs. However, there is disagreement among researchers about the effectiveness of methods using both sign and speech as compared to sign or speech alone.
Another point of controversy made by advocates are that there are racial disparities in the cochlear implantation evaluation process. Data taken from 2010-2020 showed that 68.5% of patients referred for evaluation were White, 18.5% were Black, and 12.3% were Asian, however the institution's main service area was 46.9% White, 42.3% Black, and 7.7% Asian. It was also shown that the Black patients who were referred for evaluation to receive the implants had greater hearing loss compared to White patients who were also referred. Based on this study, it is shown that Black patients receive cochlear implants at a disproportionally lower rate than White patients.
Notable recipients (partial list)[edit]
Jack Ashley, Baron Ashley of Stoke - British MP
Michael Chorost - American writer
Dorinda Cox - Australian politician
Lou Ferrigno - bodybuilder and actor
Rush Limbaugh - American conservative radio host
Heather Whitestone - 1995 Miss America
Malala Yousafzai - Nobel peace prize recipient
Millicent Simmonds - American actress
Daisy Kent - American TV personality
Elena LaQuatra - WTAE-TV news anchor
See also[edit]
3D Printing
Auditory brainstem response
Auditory brainstem implant
Bone-anchored hearing aid
Bone conduction
Brain implant
Ear trumpet
Electric Acoustic Stimulation
Electrophonic hearing
Neuroprosthetics
Noise health effects
Visual prosthesis
Language deprivation § Deaf and Hard of Hearing Children | biology | 5180106 | https://sv.wikipedia.org/wiki/Misofoni | Misofoni | Misofoni (eller selektivt ljudkänslighetssyndrom, eller på engelska selective sound sensitivity syndrome), är ett sällan diagnosticerat tillstånd som många tror har sin grund i neurologi. Misofoni innebär nedsatt tolerans för specifika ljud eller deras associerade stimuli, eller signaler. Dessa signaler, som kallas "triggers", upplevs som obehagliga eller plågsamma och tenderar att framkalla starka negativa emotionella, fysiologiska och beteendemässiga reaktioner som inte ses hos de flesta andra människor.
Misofoni och misofoniska symtom kan negativt påverka förmågan att uppnå livsmål och njuta av sociala situationer. Det uppmärksammades först 2001, diagnosen finns dock inte med i varken DSM-5 eller ICD-10, men det har föreslagits att tillståndet ska klassas som en fristående psykisk sjukdom.
Reaktionerna på utlösande ljud varierar från irritation till ilska, med möjlig aktivering av flykt- och kampresponsen. Misofoni verkar inte framkallas av ljudets styrka, utan snarare av dess specifika mönster eller betydelse för den som lyssnar. Triggers är ofta repetitiva stimuli och är främst, men inte uteslutande, relaterade till människokroppen, såsom att tugga, äta, smacka med läpparna, slurpa, hosta, rensa halsen och svälja. När ett trigger-stimulus har upptäckts kan personer med misofoni ha svårt att distrahera sig från stimulus och kan uppleva lidande, ångest och/eller försämrad social, yrkesmässig eller akademisk funktion. Uttrycket av misofonisymtomen varierar, liksom svårighetsgraden, som varierar från mild till svår. Vissa personer med misofoni är medvetna om att deras reaktioner på misofoniska triggers är oproportionerliga i förhållande till omständigheterna. Symtom på misofoni uppträder vanligtvis först i barndomen eller tidiga tonåren.
Termens ursprung
Termen myntades 2001 av professor Pawel Jastreboff och doktor Margaret M. Jastreboff, med hjälp av klassicisten Guy Lee, som introducerade den i sin artikel "Hyperacusis".
Termen användes för första gången i en expertgranskad tidskrift 2002.
"Misofoni" kommer från de forngrekiska orden μῖσος, "hat", och φωνή, "ljud", kan översättas till "hata ljud" och myntades för att skilja tillståndet från andra former av nedsatt ljudtolerans såsom hyperakusi (överkänslighet mot vissa frekvenser och volymintervall) och fonofobi (rädsla för ljud).
Tecken och symtom
Fram till 2016 var litteraturen om misofoni begränsad. Några inledande små studier visade att personer med misofoni i allmänhet har starka negativa känslor, tankar och fysiska reaktioner på specifika ljud, som i litteraturen kallas "triggerljud". Dessa ljud verkar vanligtvis tysta för andra, men kan verka höga för personen med misofoni, som om de inte kan höra något annat än ljudet. En studie visade att cirka 80 % av ljuden var relaterade till munnen (t.ex. äta, slurpa, tugga eller poppa tuggummi, viska, vissla, snyta sig) och cirka 60 % var repetitiva. Men nyare forskning ger neurala bevis för triggers som inte har med mun och ansikte att göra. En visuell trigger kan utvecklas i samband med triggerljudet, och en misofonisk reaktion kan uppstå i frånvaro av ett ljud (exempel inkluderar bengungande, hårsnurrande och fingerpekning).
Reaktioner på utlösande faktorer kan variera från milda (ångest, obehag och/eller avsky) till allvarliga (raseri, ilska, hat, panik, rädsla och/eller känslomässigt lidande). Reaktioner på utlösande faktorer kan omfatta aggression mot ljudets ursprung, att lämna det, stanna kvar i dess närvaro men lida, försöka blockera det eller försöka härma ljudet. Reaktioner kan också omfatta fysiska reaktioner som ökad hjärtfrekvens, tryck över bröst och huvud samt högt blodtryck.
Den första misofoniska reaktionen kan inträffa när en person är ung, ofta mellan 9 och 13 år, och kan komma från någon i en nära relation eller från ett husdjur.
Rädsla och ångest i samband med triggerljud kan leda till att personen undviker viktiga sociala och andra interaktioner som kan utsätta dem för dessa ljud. Detta undvikande och andra beteenden kan göra det svårare för personer med detta tillstånd att uppnå sina mål och njuta av interpersonella interaktioner. Det kan också ha en betydande negativ effekt på deras karriärer och relationer.
Mekanism
Misofonins mekanism är ännu inte helt klarlagd, men det verkar som om den kan orsakas av en dysfunktion i det centrala nervsystemet i hjärnan och inte i öronen. Ljudets upplevda ursprung och sammanhang verkar spela en viktig roll för att utlösa en reaktion.
En studie från 2017 visade att den främre insulära hjärnbarken (som spelar en roll både för känslor som ilska och för att integrera input utifrån, t.ex. ljud, med input från organ som hjärta och lungor) orsakar mer aktivitet i andra delar av hjärnan som svar på triggers, särskilt i de delar som ansvarar för långtidsminnen, rädsla och andra känslor. Studien visade också att personer med misofoni har högre halter av myelin (en fet substans som omsluter nervceller i hjärnan för att ge elektrisk isolering). Det är oklart om myelin är en orsak till eller en effekt av misofoni och dess utlösning av andra hjärnområden.
En studie från 2021 visade att motorbarken, en del av hjärnan som representerar läpp-, käk- och munrörelser, har ökad aktivering för typiska triggerljud mycket mer än för aversiva eller neutrala ljud hos personer som lider av misofoni. Man fann också förbättrad funktionell konnektivitet mellan motorbarken och hörselbarken under ljudperception för alla ljud. Vidare rapporterades funktionell fMRI-konnektivitet i viloläge mellan motorbarken och sekundära auditiva och visuella hjärnområden samt sekundär interoceptiv cortex (vänster anterior insula). Detta tyder på att misofoni, som vanligtvis betraktas som en störning i ljudkänslobearbetningen, är ett resultat av överaktivering av det motoriska spegelneuronsystemet som är involverat i att producera de rörelser som associeras med dessa triggerljud eller bilder.
Diagnos
År 2022 samlades kliniska och vetenskapliga ledare för att skapa en konsensusdefinition av misofoni, där man enades om att det är en störning som innebär minskad tolerans för specifika ljud och deras associerade stimuli. Innan denna konsensusdefinition nåddes diskuterade forskare och kliniker hur misofoni skulle beskrivas och definieras, vilket har begränsat jämförelsen av kohortstudier och hindrat utvecklingen av standarddiagnostiska kriterier.
Misofoni skiljer sig från hyperakusi, som inte är specifikt för ett visst ljud och inte innebär en liknande stark reaktion, och från fonofobi, som är en rädsla för höga ljud, men alla tillstånd kan förekomma. Det finns inga standardiserade diagnostiska kriterier, och många läkare är omedvetna om störningen.
Studier visar att misofoni ofta har relaterade samsjuklighetstillstånd, inklusive humörstörningar, ångeststörningar, ADHD, OCD, affektiva störningar och autism. Forskning har visat att misofoni kan vara genetiskt betingat, men det behövs mer forskning för att bekräfta detta. Det verkar som om misofoni kan förekomma ensamt eller tillsammans med andra hälso-, utvecklings- och psykiatriska problem. När läkare försöker diagnostisera en patient med misofoni förväxlar de ibland symptomen med ångestsyndrom, bipolär sjukdom eller tvångssyndrom.
Klassificering
Diagnosen misofoni erkänns inte i DSM-IV eller ICD-11, och den klassificeras inte som en hörsel- eller psykiatrisk störning. Det kan vara en form av ljudkänselsynestesi och har paralleller med vissa ångeststörningar. En strukturerad studie från 2022 av framstående forskare resulterade i en konsensusdefinition av misofoni, som fastställde att misofoni bör klassificeras som en störning och inte ett symptom på ett annat tillstånd eller syndrom. Under den tidiga fasen av forskningen om misofoni definierades det av olika kriterier med varierande metoder för diagnos och bedömning av symptomens svårighetsgrad. Som ett resultat av bristen på konsensus om hur misofoni ska definieras och utvärderas var det svårt att jämföra olika studiegrupper, mätverktygen var inte psykometriskt väl validerade och fältet kunde inte rigoröst utvärdera effekten av olika behandlingsmetoder. Definitionen ligger till grund för framtida diagnostiska kriterier och validerade diagnostiska verktyg, och ger sammanhållning åt de olika och tvärvetenskapliga forskargrupperna inom misofoni och klinik.
Hantering
Vårdgivare försöker i allmänhet hjälpa människor att hantera misofoni genom att erkänna vad personen upplever och arbeta med livshanteringsstrategier. En majoritet av de mindre studier som gjorts i ämnet har fokuserat på användning av tinnitus retraining therapy (TRT), kognitiv beteendeterapi och exponeringsterapi, som antas minska personens medvetenhet om sina triggerljud. Dessa behandlingsmetoder har inte studerats tillräckligt för att fastställa deras effektivitet. Andra möjliga behandlingsalternativ har teoretiserats av forskare, inklusive acceptansbaserade metoder och mindfulness. I slutändan spekuleras det i att behandlingsmetoderna kan variera avsevärt i effektivitet från patient till patient.
Minimalt med forskning har genomförts om de möjliga effekterna av neuromodulering och farmakologiska behandlingar. En studie som publicerades 2022 tyder på att vissa former av misofonibehandling kan variera i effektivitet baserat på varje patients preferenser, särskilt när det gäller föräldrar med barn som har misofoni.
Även om storskalig forskning ännu inte har genomförts, har observation av livshanteringsstrategier som används av personer med misofoni visat på vissa konsekventa metoder för att hantera tillståndet. Dessa inkluderar användning av öronproppar och hörlurar, efterliknande av triggerljud, och musik.
Epidemiologi
Forskning pågår fortfarande om misofonis globala prevalens, men en studie från 2023 visade att prevalensen i Storbritannien var cirka 18 %. Denna studie har citerats i populära medier, inklusive BBC, Medscape, och Medical Xpress. Studier av misofonis globala prevalens har visat att den är så låg som 5 % och så hög som 20 %. Förekomsten och svårighetsgraden verkar vara liknande oavsett kön.
Associerade symtom
Det finns flera anekdotiska rapporter om människor som säger sig ha både misofoni och autonomous sensory meridian response (ASMR). Gemensamt för dessa rapporter är upplevelsen av ASMR som svar på vissa ljud och misofoni som svar på andra ljud.
Samhälle och kultur
Människor som upplever misofoni har bildat stödgrupper online.
År 2016 släpptes en dokumentär om tillståndet, Quiet Please.
År 2020 fick en grupp misofoni-forskare Ig Nobelpriset i medicin "för att ha diagnostiserat ett länge okänt medicinskt tillstånd".
I filmen Tár från 2022 porträtteras en dirigent med misofoni.
Säsong 1, avsnitt 4 av Hulus The Old Man har en kort diskussion om misofoni.
Anmärkningsvärda fall
Richard E. Grant
Barron H. Lerner
Melanie Lynskey
Kelly Osbourne
Kelly Ripa
Sarah Silverman
Lisa Loeb
Se även
Stimiluskontroll
Referenser
Noter
Sensoriska störningar
Öronsjukdomar | swedish | 0.761933 |
fake_auditory_signal/Auditory_Signal_Processing.txt | # Sensory Systems/Auditory Signal Processing
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< Sensory Systems
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## Contents
* 1 Auditory Signal Processing
* 1.1 Effect of the head
* 1.2 Sound reception at the pinna
* 1.3 Sound conduction to the cochlea
* 1.4 Frequency analysis in the cochlea
* 1.5 Sensory transduction in the cochlea
* 1.6 Auditory pathway of nerve impulses
* 1.6.1 Superior olivary complex: Sound localization
* 1.7 Primary auditory cortex and higher order auditory areas
## Auditory Signal Processing [ edit | edit source ]
Now that the anatomy of the auditory system has been sketched out, this topic
goes deeper into the physiological processes which take place while perceiving
acoustic information and converting this information into data that can be
handled by the brain. Hearing starts with pressure waves hitting the auditory
canal and is finally perceived by the brain. This section details the process
transforming vibrations into perception.
### Effect of the head [ edit | edit source ]
Sound waves with a wavelength shorter than the head produce a sound shadow on
the ear further away from the sound source. When the wavelength is longer than
the head, diffraction of the sound leads to approximately equal sound
intensities on both ears.
Difference in loudness and timing help us to localize the source of a sound
signal.
### Sound reception at the pinna [ edit | edit source ]
The pinna collects sound waves in air affecting sound coming from behind and
the front differently with its corrugated shape. The sound waves are reflected
and attenuated or amplified. These changes will later help sound localization.
In the external auditory canal, sounds between 3 and 12 kHz - a range crucial
for human communication - are amplified. It acts as resonator amplifying the
incoming frequencies.
### Sound conduction to the cochlea [ edit | edit source ]
Sound that entered the pinna in form of waves travels along the auditory canal
until it reaches the beginning of the middle ear marked by the tympanic
membrane (eardrum). Since the inner ear is filled with fluid, the middle ear
is kind of an impedance matching device in order to solve the problem of sound
energy reflection on the transition from air to the fluid. As an example, on
the transition from air to water 99.9% of the incoming sound energy is
reflected. This can be calculated using:
I r I i = ( Z 2 − Z 1 Z 2 \+ Z 1 ) 2 {\displaystyle {\frac {I_{r}}{I_{i}}}=\left({\frac {Z_{2}-Z_{1}}{Z_{2}+Z_{1}}}\right)^{2}}
with I r the intensity of the reflected sound, I i the intensity of the
incoming sound and Z k the wave resistance of the two media ( Z air = 414
kg m -2 s -1 and Z water = 1.48*10 6 kg m -2 s -1 ). Three factors
that contribute the impedance matching are:
* the relative size difference between tympanum and oval window
* the lever effect of the middle ear ossicles and
* the shape of the tympanum.
Mechanics of the amplification effect of the middle ear.
The longitudinal changes in air pressure of the sound-wave cause the tympanic
membrane to vibrate which, in turn, makes the three chained ossicles malleus,
incus and stirrup oscillate synchronously. These bones vibrate as a unit,
elevating the energy from the tympanic membrane to the oval window. In
addition, the energy of sound is further enhanced by the areal difference
between the membrane and the stapes footplate. The middle ear acts as an
impedance transformer by changing the sound energy collected by the tympanic
membrane into greater force and less excursion. This mechanism facilitates
transmission of sound-waves in air into vibrations of the fluid in the
cochlea. The transformation results from the pistonlike in- and out-motion by
the footplate of the stapes which is located in the oval window. This movement
performed by the footplate sets the fluid in the cochlea into motion.
Through the stapedius muscle , the smallest muscle in the human body, the
middle ear has a gating function: contracting this muscle changes the
impedance of the middle ear, thus protecting the inner ear from damage through
loud sounds.
### Frequency analysis in the cochlea [ edit | edit source ]
The three fluid-filled compartements of the cochlea (scala vestibuli, scala
media, scala tympani) are separated by the basilar membrane and the Reissner’s
membrane. The function of the cochlea is to separate sounds according to their
spectrum and transform it into a neural code. When the footplate of the stapes
pushes into the perilymph of the scala vestibuli, as a consequence the
membrane of Reissner bends into the scala media. This elongation of Reissner’s
membrane causes the endolymph to move within the scala media and induces a
displacement of the basilar membrane. The separation of the sound frequencies
in the cochlea is due to the special properties of the basilar membrane. The
fluid in the cochlea vibrates (due to in- and out-motion of the stapes
footplate) setting the membrane in motion like a traveling wave. The wave
starts at the base and progresses towards the apex of the cochlea. The
transversal waves in the basilar membrane propagate with
c t r a n s = μ ρ {\displaystyle c_{trans}={\sqrt {\frac {\mu }{\rho }}}}
with μ the shear modulus and ρ the density of the material. Since width and
tension of the basilar membrane change, the speed of the waves propagating
along the membrane changes from about 100 m/s near the oval window to 10 m/s
near the apex.
There is a point along the basilar membrane where the amplitude of the wave
decreases abruptly. At this point, the sound wave in the cochlear fluid
produces the maximal displacement (peak amplitude) of the basilar membrane.
The distance the wave travels before getting to that characteristic point
depends on the frequency of the incoming sound. Therefore each point of the
basilar membrane corresponds to a specific value of the stimulating frequency.
A low-frequency sound travels a longer distance than a high-frequency sound
before it reaches its characteristic point. Frequencies are scaled along the
basilar membrane with high frequencies at the base and low frequencies at the
apex of the cochlea.
The position x of the maximal amplitude of the travelling wave corresponds in
a 1-to-1 way to a stimulus frequency.
Identifying frequency by the location of the maximum displacement of the
basilar membrane is called tonotopic encoding of frequency. It automatically
solves two problems:
* It automatically parallelizes the subsequent processing of frequency. This tonotopic encoding is maintained all the way up to the cortex.
* Our nervous system transmits information with action potentials, which are limited to less than 500 Hz. Through tonotopic encoding, also higher frequencies can be accurately represented.
Action potentials have a stereotyped shape. And since during the refractive
period Na-ion channels are actively blocked, the maximum frequency of action
potentials is about 500 Hz - significantly lower than the frequencies required
for human speach.
### Sensory transduction in the cochlea [ edit | edit source ]
Most everyday sounds are composed of multiple frequencies. The brain processes
the distinct frequencies, not the complete sounds. Due to its inhomogeneous
properties, the basilar membrane is performing an approximation to a Fourier
transform. The sound is thereby split into its different frequencies, and each
hair cell on the membrane corresponds to a certain frequency. The loudness of
the frequencies is encoded by the firing rate of the corresponding afferent
fiber. This is due to the amplitude of the traveling wave on the basilar
membrane, which depends on the loudness of the incoming sound.
Transduction mechanism in auditory or vestibular hair cell. Tilting the hair
cell towards the kinocilium opens the potassium ion channels. This changes the
receptor potential in the hair cell. The resulting emission of
neurotransmitters can elicit an action potential (AP) in the post-synaptic
cell. Auditory haircells are very similar to those of the vestibular system.
Here an electron microscopy image of a frog's sacculus haircell. Additional
example of the hair cells of a frog.
The sensory cells of the auditory system, known as hair cells, are located
along the basilar membrane within the organ of Corti. Each organ of Corti
contains about 16,000 such cells, innervated by about 30,000 afferent nerve
fibers. There are two anatomically and functionally distinct types of hair
cells: the inner and the outer hair cells. Along the basilar membrane these
two types are arranged in one row of inner cells and three to five rows of
outer cells. Most of the afferent innervation comes from the inner hair cells
while most of the efferent innervation goes to the outer hair cells. The inner
hair cells influence the discharge rate of the individual auditory nerve
fibers that connect to these hair cells. Therefore inner hair cells transfer
sound information to higher auditory nervous centers. The outer hair cells, in
contrast, amplify the movement of the basilar membrane by injecting energy
into the motion of the membrane and reducing frictional losses but do not
contribute in transmitting sound information. The motion of the basilar
membrane deflects the stereocilias (hairs on the hair cells) and causes the
intracellular potentials of the hair cells to decrease (depolarization) or
increase (hyperpolarization), depending on the direction of the deflection.
When the stereocilias are in a resting position, there is a steady state
current flowing through the channels of the cells. The movement of the
stereocilias therefore modulates the current flow around that steady state
current.
Let's look at the modes of action of the two different hair cell types
separately:
* Inner hair cells:
The deflection of the hair-cell stereocilia opens mechanically gated ion
channels that allow small, positively charged potassium ions (K \+ ) to
enter the cell and causing it to depolarize. Unlike many other electrically
active cells, the hair cell itself does not fire an action potential. Instead,
the influx of positive ions from the endolymph in scala media depolarizes the
cell, resulting in a receptor potential. This receptor potential opens voltage
gated calcium channels; calcium ions (Ca 2+ ) then enter the cell and
trigger the release of neurotransmitters at the basal end of the cell. The
neurotransmitters diffuse across the narrow space between the hair cell and a
nerve terminal, where they then bind to receptors and thus trigger action
potentials in the nerve. In this way, neurotransmitter increases the firing
rate in the VIIIth cranial nerve and the mechanical sound signal is converted
into an electrical nerve signal.
The repolarization in the hair cell is done in a special manner. The perilymph
in Scala tympani has a very low concentration of positive ions. The
electrochemical gradient makes the positive ions flow through channels to the
perilymph. (see also: Wikipedia Hair cell )
* Outer hair cells:
In humans' outer hair cells, the receptor potential triggers active vibrations
of the cell body. This mechanical response to electrical signals is termed
somatic electromotility and drives oscillations in the cell’s length, which
occur at the frequency of the incoming sound and provide mechanical feedback
amplification. Outer hair cells have evolved only in mammals. Without
functioning outer hair cells the sensitivity decreases by approximately 50 dB
(due to greater frictional losses in the basilar membrane which would damp the
motion of the membrane). They have also improved frequency selectivity
(frequency discrimination), which is of particular benefit for humans, because
it enables sophisticated speech and music. (see also: Wikipedia Hair cell )
With no external stimulation, auditory nerve fibres discharge action
potentials in a random time sequence. This random time firing is called
spontaneous activity. The spontaneous discharge rates of the fibers vary from
very slow rates to rates of up to 100 per second. Fibers are placed into three
groups depending on whether they fire spontaneously at high, medium or low
rates. Fibers with high spontaneous rates (> 18 per second) tend to be more
sensitive to sound stimulation than other fibers.
### Auditory pathway of nerve impulses [ edit | edit source ]
Lateral lemniscus in red, as it connects the cochlear nucleus, superior
olivary nucleus and the inferior colliculus. Seen from behind.
So in the inner hair cells the mechanical sound signal is finally converted
into electrical nerve signals. The inner hair cells are connected to auditory
nerve fibres whose nuclei form the spiral ganglion. In the spiral ganglion the
electrical signals (electrical spikes, action potentials) are generated and
transmitted along the cochlear branch of the auditory nerve (VIIIth cranial
nerve) to the cochlear nucleus in the brainstem.
From there, the auditory information is divided into at least two streams:
* Ventral Cochlear Nucleus:
One stream is the ventral cochlear nucleus which is split further into the
posteroventral cochlear nucleus (PVCN) and the anteroventral cochlear nucleus
(AVCN). The ventral cochlear nucleus cells project to a collection of nuclei
called the superior olivary complex.
#### Superior olivary complex: Sound localization [ edit | edit source ]
The superior olivary complex - a small mass of gray substance - is believed to
be involved in the localization of sounds in the azimuthal plane (i.e. their
degree to the left or the right). There are two major cues to sound
localization: Interaural level differences (ILD) and interaural time
differences (ITD). The ILD measures differences in sound intensity between the
ears. This works for high frequencies (over 1.6 kHz), where the wavelength is
shorter than the distance between the ears, causing a head shadow - which
means that high frequency sounds hit the averted ear with lower intensity.
Lower frequency sounds don't cast a shadow, since they wrap around the head.
However, due to the wavelength being larger than the distance between the
ears, there is a phase difference between the sound waves entering the ears -
the timing difference measured by the ITD. This works very precisely for
frequencies below 800 Hz, where the ear distance is smaller than half of the
wavelength. Sound localization in the median plane (front, above, back, below)
is helped through the outer ear, which forms direction-selective filters.
There, the differences in time and loudness of the sound information in each
ear are compared. Differences in sound intensity are processed in cells of the
lateral superior olivary complexm and timing differences (runtime delays) in
the medial superior olivary complex. Humans can detect timing differences
between the left and right ear down to 10 μs, corresponding to a difference in
sound location of about 1 deg. This comparison of sound information from both
ears allows the determination of the direction where the sound came from. The
superior olive is the first node where signals from both ears come together
and can be compared. As a next step, the superior olivary complex sends
information up to the inferior colliculus via a tract of axons called lateral
lemniscus. The function of the inferior colliculus is to integrate information
before sending it to the thalamus and the auditory cortex. It is interesting
to know that the superior colliculus close by shows an interaction of
auditory and visual stimuli.
* Dorsal Cochlear Nucleus:
The dorsal cochlear nucleus (DCN) analyzes the quality of sound and projects
directly via the lateral lemnisucs to the inferior colliculus.
From the inferior colliculus the auditory information from ventral as well as
dorsal cochlear nucleus proceeds to the auditory nucleus of the thalamus which
is the medial geniculate nucleus. The medial geniculate nucleus further
transfers information to the primary auditory cortex, the region of the human
brain that is responsible for processing of auditory information, located on
the temporal lobe. The primary auditory cortex is the first relay involved in
the conscious perception of sound.
### Primary auditory cortex and higher order auditory areas [ edit | edit source ]
Sound information that reaches the primary auditory cortex (Brodmann areas 41
and 42). The primary auditory cortex is the first relay involved in the
conscious perception of sound. It is known to be tonotopically organized and
performs the basics of hearing: pitch and volume. Depending on the nature of
the sound (speech, music, noise), is further passed to higher order auditory
areas. Sounds that are words are processed by Wernicke’s area (Brodmann area
22). This area is involved in understanding written and spoken language
(verbal understanding). The production of sound (verbal expression) is linked
to Broca’s area (Brodmann areas 44 and 45). The muscles to produce the
required sound when speaking are contracted by the facial area of motor cortex
which are regions of the cerebral cortex that are involved in planning,
controlling and executing voluntary motor functions.
Lateral surface of the brain with Brodmann's areas numbered.
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| biology | 31458 | https://da.wikipedia.org/wiki/Auditiv%20perception | Auditiv perception | Auditiv perception betyder bredt hørelse, dvs. sansning af lyd. Ofte hentyder ordet kun til den proces, der følger efter selve sansningen. Sansningen der foregår i øret består af opfangelsen af lydbølger.
Lydperception består i fortolkning og bearbejdning af sansedata, ud fra såkaldte cues. Ud fra sansesdata foretages differentiering og lokalisering af lydkilder. Der er mange forskellige cues.
Et af de cues der hjælper ved lokalisering er interaurale forskelle i amplitude og tid. Det øre der er tættest på lydkilden rammes først og dette giver hjernen information om stedet. Samtidig falder amplituden inden den rammer det andet øre. Men er kilden lige bag ved eller foran er der ikke interaurale forskelle. Der hjælper så et andet cue: Lydbølgerne ændres når de rammer torso og hoved og herved kan hjernen skelne bølger, der kommer bagfra og bølger der kommer forfra. Denne spektrale transformation af lyden kaldes Head related transfer function.
De simpleste cues, der bruges for at adskille lydkilder fra hinanden er spatial og temporal separation, altså lydkilderne befinder sig forskellige steder, og giver lyd på forskellige tidspunkter. Andre cues er modulation, frekvens, harmonicitet og intensitet.
Se også
Akustik
Kognitionspsykologi
Psykologi | danish | 0.547476 |
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##### TABLE OF CONTENTS
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## SYSTEMATIC REVIEW article
Front. Oral. Health, 10 June 2022
Sec. Oral Epidemiology
Volume 3 - 2022 | [ https://doi.org/10.3389/froh.2022.916372
](https://doi.org/10.3389/froh.2022.916372)
# Fluoride Intake Through Dental Care Products: A Systematic Review
Hanan Saad 1,2
Raphaëlle Escoube 3 [
 Sylvie Babajko
](https://www.frontiersin.org/people/u/67189) 1 *
Sophia Houari 1,2
* 1 Laboratory of Molecular Oral Physiopathology, Centre de Recherche des Cordeliers, INSERM, Université Paris Cité, Sorbonne Université, Paris, France
* 2 AP-HP, Dental Medicine Department, Pitié-Salpétrière Hospital, GHN-Université Paris Cité, Paris, France
* 3 Laboratoire de Géologie de Lyon, UM R5276, CNRS, Université Lyon 1, École Normale Supérieure de Lyon 46, Lyon, France
Fluoride (F) is added to many dental care products as well as in drinking
water to prevent dental decay. However, recent data associating exposure to F
with some developmental defects with consequences in many organs raise
concerns about its daily use for dental care. This systematic review aimed to
evaluate the contribution of dental care products with regard to overall F
intake through drinking water and diet with measurements of F excretion in
urine used as a suitable biomarker. According to the Preferred Reporting Items
for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using keywords
related to chronic exposure to F in the human population with measurements of
F levels in body fluids, 1,273 papers published between 1995 and 2021 were
screened, and 28 papers were finally included for data extraction concerning
daily F intake. The contribution of dental care products, essentially by
toothbrushing with kinds of toothpaste containing F, was 38% in the mean
regardless of the F concentrations in drinking water. There was no correlation
between F intake through toothpaste and age, nor with F levels in water
ranging from 0.3 to 1.5 mg/L. There was no correlation between F intake and
urinary F excretion levels despite an increase in its content in urine within
hours following exposure to dental care products (toothpastes, varnishes, or
other dental care products). The consequences of exposure to F on health are
discussed in the recent context of its suspected toxicity reported in the
literature. The conclusions of the review aim to provide objective messages to
patients and dental professionals worried about the use of F-containing
materials or products to prevent initial caries or hypomineralized enamel
lesions, especially for young children.
## Introduction
Fluoride (F) is the lighter halogen element and is largely present in food and
drinking water with levels depending on the geological environment of the
area. It is also added to dental care products used for oral hygiene and
dentistry to prevent dental decay. It is admitted that tooth brushing with
fluoridated toothpaste is a fundamental cornerstone for the prevention of
early childhood caries [ 1 ]. It protects against caries by generating
fluoridated apatite more resistant to acids produced by oral bacteria,
increasing the remineralization process, and inhibiting bacterial enolase
activity [ 2 , 3 ]. However, limits to the prescription of F have been
repeatedly advised, mostly because of the narrow safety range for its use.
According to the European Food and Safety Authority (EFSA), the recommended
doses to prevent caries have been evaluated approximately 0.05–0.07 mg/kg/day,
which is close to the amount that may cause enamel hypomineralization, called
dental fluorosis (>0.1 mg/kg/day) [ 4 ].
The main sources of F intake are fluoridated drinking water, dietary F, infant
formulas, and F-containing dental care products, especially toothpaste. Some
foods and beverages contain high levels of F, such as tea [ 5 ]. The
increased prevalence of dental fluorosis indicates that some young children
are exposed to F from sources other than drinking water, essentially the
F-containing toothpaste they may swallow. F can substitute hydroxyl of the
hydroxyapatite containing matrices, to form fluorapatite, underlying its
extracellular effects in enamel, dentin, and bone [ 6 ]. F tropism for
apatite explains its expected reinforced effects on enamel as well as dental
and bone fluorosis when absorbed in excess [ 7 ]. Besides biomineralized
matrices, many experimental studies report F effects on cell differentiation,
proliferation, and apoptosis that may explain its toxic effects on the
development and the physiology of many other tissues and organs when ingested
at high doses [ 8 – 11 ]. The severity of F effects is related to the dose
and duration of exposure as well as to its combination with other
environmental factors as suggested by experimental studies on rodents and
zebrafish [ 7 , 12 , 13 ]. The severity of F effects also appears to be
contingent on the genetic background in rodents and humans and renal function
[ 8 , 14 – 17 ]. Once absorbed, F travels throughout the body _via_ the
blood circulation before being filtered by the kidney and excreted in urine,
which thus ensures the majority of F removal from the body. Approximately 60%
of ingested F by healthy adults are excreted in the urine, but only 45% for
children, with the rest re-circulating into the plasma or deposited into the
bone [ 18 ]. As a consequence, plasma and urinary excretion reflect a
physiologic homeostasis determined by previous F intake, rate of F uptake and
removal from bone, and the efficiency with which the kidneys excrete F.
Dental fluorosis and other F side effects on health may occur due to F
overload from a combination of various sources, such as drinking water, dental
care products used for caries prevention, medication with fluoridated
products, and anesthetics, each source being innocent alone but with an
unclear dose-response relationship when combined [ 19 ]. Due to the general
awareness of relations between human environment and health, many patients are
currently questioning their physicians and dentists about the safety of the
prescribed treatments. Dentists strongly advice to brush teeth at least two
times a day with fluorinated toothpastes, preconize fluorinated varnishes to
protect children's teeth from caries, and higher fluorinated gels for specific
patients and use biomaterials, such as adhesives or ionomer cements, for
conservative dentistry and orthodontic treatments that may contain F.
The aim of this study is to provide a qualitative and descriptive analysis of
the numerical data to evaluate the contribution of dental care products in the
total daily fluoride intake (TDFI) based on urine monitoring and regarding the
literature from 1995 to 2021. In the light of these results, dentists will be
able to qualify the place that F takes in prevention and treatment programs in
the overall systemic exposure of patients.
## Methods
This systematic review is conducted according to the Preferred Reporting Items
for Systematic Reviews and Meta-Analyses (PRISMA) guidelines ( Figure 1 ).
FIGURE 1
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-g001.jpg)
**Figure 1** . The Preferred Reporting Items for Systematic Reviews and Meta-
Analyses (PRISMA) flowchart for the systematic review. From the 1,273 articles
found in PubMed included in the search, 46 studies were included and 28
selected in this review for their analyses. Among the 28 articles, 19 only
listed the estimated total daily fluoride intake (TDFI) ( Table 1 ). The
other nine articles had information regarding both the TDFI and the daily
urinary fluoride excretion (DUFE) ( Table 2 ).
TABLE 1
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-t001.jpg)
**Table 1** . Number of participants, their mean age and country of residence,
with the associated F concentration in tap water (mg/L) in articles with only
estimation of F intake in our Excel database.
TABLE 2
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-t002.jpg)
**Table 2** . Number of participants, their mean age and country of residence,
with the associated F concentration in tap water (mg/L) in articles regarding
estimated F intake and urine monitoring in our Excel database.
### Search Strategy
The following search equation was entered in PubMed/Medline using the
Booleans: (((dent * ) OR (mouth * ) OR (teeth) OR (tooth * ) OR
(enamel)) OR ((resin?) OR (“glass ionomer * ”) OR (“bioactive glass * ”)
OR (composite?)) AND ((urin * fluori * ) OR (plasma * fluori * ) OR
(“blood fluori * ”) OR (“saliva fluori * ”) OR (“bone fluori * ”) OR
(“hair fluori * ”) OR (“nail fluori * ”)) AND ((1995/1/1:2021/12/31[pdat])
AND (english[Filter] OR french[Filter]))) OR (((dent * ) OR (mouth * ) OR
(teeth) OR (tooth * ) OR (enamel)) OR ((resin?) OR (“glass ionomer * ”) OR
(“bioactive glass * ”) OR (composite?)) AND ((“chronic fluoride”) OR
(“chronic exposure to fluoride”) OR (“chronic fluoride exposure”) OR
(“fluoride intake”) OR (“daily fluoride intake”) OR (“systemic fluoride”)) AND
((1995/1/1:2021/12/31[pdat]) AND (english[Filter] OR french [Filter]))).
Open access articles were retrieved and those with restricted access were
retrieved through institutional access. Only two articles were excluded
because the full-text was not accessible.
We checked that none of the included studies in this review were retracted due
to error or fraud.
### Eligibility Criteria
#### Inclusion Criteria
When establishing the search equation, language was limited to English and
French, and articles were restricted from 01/01/1995 to 31/12/2021. The
articles were selected taking into account the following inclusion criteria:
(1) studies with human participants, (2) studies involving topical use of
F-containing dental care products, (3) studies estimating the TDFI from water,
beverages, such as juices, milk and infant formulas, meals, and dental care
products which are mainly toothpastes in this review, and (4) studies
monitoring F exposure through urine as a contemporary biomarker.
#### Exclusion Criteria
The exclusion process consisted of two steps. The first was applied before the
inclusion of articles with the following criteria on title and abstract: (1)
studies conducted on animals, (2) studies _in vitro_ , (3) articles focusing
on inhaled F, which may be found in some anesthesia, (4) articles with no
related content to F exposure, and (5) reviews and case reports. The second
step consisted on excluding those that had the following criteria: (1) F
monitoring in other matrices than urine (plasma, saliva, nails, and hair), (2)
articles with no F quantification or estimation, (3) articles that were not
accessible, and (4) studies with missing data from at least one source of F
either from water, beverages, solid food, or dental care product.
### Process of Study Selection
First, all articles resulting of the search equation were entered in Zotero
software. Elimination of duplicates was performed. Then the screening of title
and abstract by two independent reviewers (HS et SH) was carried out according
to the first step of the exclusion process. The same reviewers proceeded to
select the articles by applying the inclusion criteria. The content of the
abstract of each study was analyzed and the articles with relevant information
regarding the subject of the current review were carefully chosen. Finally,
the selected articles were evaluated through full-text analysis to determine
which of them would be useful for the elaboration of the systematic review.
This second step of the exclusion process was performed independently and in
duplicate by each reviewer to compare the recorded information and correct the
differences that were found during this step. In the case of disagreement
between reviewers, a third reviewer (SB) was involved to resolve it.
### Data Charting Process
Among the articles included, those relating the daily F intake of each source
and monitoring the F in urine were selected. All data were entered in Excel
software and was sorted to identify the authors, year of publication, title of
article, country of study, number of participants, age and gender of
participants, sources of exposure to fluorides, F concentration in tap water,
and F monitoring in urine. Data extraction was performed by HS and RE.
### Data Synthesis
Studies' characteristics are as follows:
• Year: from 1995 to 2021. The year 1995 was selected because it was the last
recent date mentioned by Fejerskov et al. [ 48 ], which compiled all data
from the previous years.
• Country: Supplementary Figure 1 represents the Mondial geographical
repartition of the included articles in Excel. The percentage was calculated
by counting the number of studies conducted in a country and dividing it by
the total number of articles in Excel.
• Age: it was notified when it was presented ( Tables 1 , 2 ).
• Size of the cohort: the number of subjects was reported for each study when
available. Moreover, the number of participants using dental care products was
mentioned when it differed from the total number of participants ( Tables 1
, 2 ).
• Gender: proportion of men or women in participants was reported when data
were available.
• All the articles selected in Excel are listed in Table 1 for those
estimating F intake and in Table 2 for those estimating F intake and urine
monitoring with the number of subjects, their mean age, countries of
residence, and F concentration in tap water.
For outcome measures, we extracted information for the following parameters
when they were available:
• The concentration of F in tap water in the area was entered in Excel. From
our database, a range of F concentration was determined and quartiles were
calculated. We obtained different categories of water depending on F content:
poor (<0.3 mg/L), low (0.3–0.51 mg/L), medium (0.52–0.77 mg/L), and high
(0.77–1.5 mg/L).
• Estimated intakes of F sources were water, beverages, diet, dental products,
and supplements. Depending on the authors, the report of the sources may vary
by combination of the listed sources.
• Method of assessment of daily dietary F intake (DDFI): diet diary during 2–3
days, duplicate plate method, diet history, and food frequency questionnaire
(FFQ).
• Method of assessment of F intake from dental products: sample collection,
toothpaste applied/expectorate collected, toothbrushing questionnaire, and
toothpaste/toothbrush weighing before and after brushing.
• Contribution of dental care products to the TDFI: some values were easily
found in articles and others needed to be calculated, when possible, by taking
into account that not all participants had oral hygiene habits.
• Fluoride excretion: urine, or urine and feces (due to infant participants
wearing diapers).
• Kinetic studies: those studies were based on timeline variations of F
exposure depending on the dental care uses.
• Method of assessment of F in urine: urinary F concentration, urinary F
excretion (by collecting 24-h urine, or spot urine, or time-controlled urine).
Daily urinary fluoride excretion (DUFE) or F retention were reported when
presented in the article.
• Analytical method: F-ion selective electrode, hexamethyl-di-siloxane
diffusion, or not reported.
• Validity of data and methods: F intake, F excretion (urine collection), and
F analytical method, or not reported.
• Reporting of the investigation of any relationship between F-containing
dental products and F excretion.
### Data Reporting
All data were reported and homogenized for intercomparisons in μg/day or μg/kg
bw/day for F intake from diet and toothpaste, TDFI and DUFE, and in mg/L for F
concentration in tap water.
In some publications, the contribution of diet and toothpaste was not
reported. To be able to compare all the selected published data, we calculated
the percentage of contribution of diet and toothpaste to the mean TDFI. This
was based on the mean F intake extracted from the included articles regardless
of the availability of percentage data. Despite not being optimal, this
allowed to keep the maximum number of articles ( Figure 2 ).
FIGURE 2
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-g002.jpg)
**Figure 2** . Estimated F intake from diet (water, beverages, and solid
foods) (gray bars) and from toothpaste (black bars). F concentration in tap
water is represented by the gray line (mg/L). **(A)** Total daily fluoride
intake with dietary and toothpaste inputs (μg/day). **(B)** The contribution
of daily diet (water, beverages, and solid foods) and toothpaste (%) to the
estimated F intake in μg/day [based on **(A)** ]. **(C)** TDFI with dietary
and toothpaste inputs (μg/kg bw/day) with reference values of optimal daily F
intake [50–70 μg/kg bw/day, the European Food and Safety Authority (EFSA)].
**(D)** The contribution of daily diet (water, beverages, and solid foods) and
toothpaste (%) to the estimated F intake in μg/kg bw/day [based on **(C)** ].
*Diagonal hatched bars represent missing data of daily dietary F intake
(DDFI). **Horizontal hatched bars represent missing data of daily F intake
from toothpaste. # Optimal range of daily F intake reported in the
literature.
## Results
From our initial selection of 1,273 articles, 46 met the inclusion criteria
and only 28 were included in our systematic review as digital data concerning
the estimation of daily F intake was reported by authors ( Figure 1 ). Among
these 46 articles, 18 were used only for the discussion and were not included
into our database since they reported urine F excretion without any estimation
of the TDFI [ 49 – 66 ]. Concerning the 28 selected studies, they were
carried out in countries all over the world with almost half of the studies
(43%) carried out in Brazil ( Supplementary Figure 1 ) [ 20 – 47 ]. In
our database, we reported the estimated F intake and urinary F monitoring.
However, 19 publications only reported the estimated TDFI ( Table 1 ) and
the other nine reported both ( Table 2 ). The 28 selected articles can be
mentioned more than once depending on their categories of fluoridated tap
water (explained in methods). Only two studies were performed with adults
whose ages ranged from 20 to 35 years [ 28 , 47 ]. Some studies present a
high number of participants, however, in some of these publications, the
number of children using dental care products can narrow down to 5% of the
initial cohort [ 36 ]. In other publications, especially for urinary
measures, the number of subjects is about 18 children. To simplify the
figures, we compared the contribution of toothpaste only with dietary intake
(such as water, beverages, and food sources) without taking into account
supplements as only three studies mentioned them [ 20 , 22 , 41 ]. In
most studies, the dental care product was toothpaste. Only one study had
varnish in association with toothpaste [ 42 ]. F intake from the diet varied
depending on the F concentration in tap water, meals, and beverages. It should
be mentioned that local public water also affects the F content in meals (thus
in diet) during the cooking. This additional F input was included into the
diet.
In Figure 2 , the TDFI (reported in μg/day in Figure 2A and μg/kg bw/day
in Figure 2C ) and the fraction of diet or toothpaste exposures were
represented. Figures 2B,D showed the percentage of toothpaste in the total
exposure.
Without acknowledging age or F concentration in water, total F intake was
between 340 and 3,320 μg/day. Based on those concentrations, toothpaste F
represented 15–95% of the TDFI reported in μg/day ( Figures 2A,B ); in the
published percentages, its variation ranged from 19 to 84% (19 publications).
This discrepancy is caused by the fact that the authors did not calculate all
the toothpaste contribution percentages.
In Figure 2A , we can notice that the high F concentration in tap water was
not associated with a higher input of the diet in the TDFI [ 21 , 25 , 27
, 30 , 42 , 43 , 45 ]. In Figures 2C,D , the age of the children was
taken into consideration by dividing the body weight of the subjects. The TDFI
was driven to the optimal range (50–70 μg/kg bw/day) or above due to the F
intake from toothpaste ( Figure 2C ). The variations of F intake from diet
seemed to be less sensitive to the F concentrations in water than the
variations due to the concentrations and good practice of the use of dental
care products in the area. The F intake from toothpaste represented 3–90% of
the TDFI when reported to the body weight ( Figure 2D ), corresponding to
1–84% in published data, which discrepancy was due to the same reasons as
those cited above.
Extremely high F concentrations in the water (>1.5 mg/L) were associated with
a lower contribution of toothpaste, <20% of the total F intake. Among the
three measurements included in our database, one was measured on an adult
population supposed to have a better use of toothpaste (no swallowing) [ 47
]. Therefore, between the two studies carried out in extremely high-
fluoridated areas in children (>1.5 mg/L), only one reported an extremely high
daily dietary input ( Figure 2C ) [ 36 , 46 ].
When all the data were taken into consideration, the mean contribution of
dental care products to the total exposure was 38 ± 27%. The F exposure
through toothbrushing was thus significant when put into perspective with the
TDFI for children: 39–51%, regardless of the F concentration in water (0.3–1.5
mg/L) [ Table 3 , the values reported by [ 20 , 22 , 24 ] were
excluded]. However, in the case of extremely-fluoridated water (>1.5 mg/L),
the dental care products contribution was estimated approximately 3% in the
two studies carried out in children [ 36 , 46 ].
TABLE 3
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-t003.jpg)
**Table 3** . Contribution of dental care products in F exposure depending on
the F concentration in tap water for children and adults.
In adults, the mean contribution of dental care products to the total exposure
was 12% in poor, 95% in low, 53% in medium, and 3% in extremely-fluoridated
water ( Table 3 ) [ 28 , 47 ].
The contribution of toothpaste in different fluoridated areas according to the
mean age of participants was displayed in Figure 3 . As most of the articles
were kinetic studies, only values at peak-level were considered to evaluate
the maximum effect of dental care products on the daily intake. Only data
recorded 24 h after exposure have been reported for the kinetic studies. Data
reported by Levy et al. [ 20 , 22 , 24 ] were not included because the
different areas with different F concentrations could not be distinguished.
Calculated correlations ( _R_ 2 ) were all below 0.14 showing the absence of
correlation between daily F intake from toothpaste and the age of children
regardless of the tap water F concentrations ( Figure 3 ).
FIGURE 3
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-g003.jpg)
**Figure 3** . The contribution of daily toothpaste intake according to mean
age (years) of participants in areas with different F concentration in
drinking water (mg/L). **(A)** The contribution of toothpaste to the TDFI (%)
in poor fluoridated water (<0.3 mg/L). ¤ Gray arrow indicates the lowest value
from Abuhaloob et al. [ 36 ]: two toothpaste users among 81 participants.
**(B)** The contribution of toothpaste to the TDFI (%) in low fluoridated
water (0.3–0.51 mg/L). ¤ Gray arrow indicates the lowest value from Zohoori
and Rugg-Gunn [ 40 ]: 3 toothpaste users among 28 in Darab (not the same
region presented in Figure 2 ; Table 3 ). **(C)** The contribution of
toothpaste to the TDFI (%) in medium fluoridated water (0.52–0.77 mg/L).
**(D)** The contribution of toothpaste to the TDFI (%) in high fluoridated
water (>0.77 mg/L). ¤ Gray arrow indicates the lowest values from Abuhaloob et
al. [ 36 ]: nine toothpaste users among 135 participants.
Nevertheless, there was a tendency to present the highest estimation of daily
F intake from toothpaste for the youngest children (younger than 4 years old)
for all types of water ( Figure 3 ). This observation was even more
pronounced in poor-fluoridated areas, where the subjects under 4 years-old and
older children were exposed to F from toothpaste between 50–90% and 0.04–57%,
respectively ( Figure 3A ). The possible high contribution of toothpaste may
be explained by the swallowing behavior for children under 4 years old [ 21
, 25 , 29 , 30 , 44 ].
Due to their better practice, adults should not be exposed to F through dental
care products ( Supplementary Figure 2 ) [ 28 , 47 ]. However, Cardoso
et al. (2006) reported high percentage values of toothpaste contribution that
varied between 26 and 95% ( Supplementary Figure 2 ) [ 28 ]. This high
contribution for adult subjects was linked to their dental care practices. In
this study, the authors actually reported that some subjects brushed their
teeth three or four times a day. Another study also showed a non-negligible
contribution of toothpaste to the TDFI, with an F ingestion from toothpaste of
~12 and 3% for 31 and 29 adults in poor and high-fluoridated areas,
respectively [ 47 ].
To follow objectively the TDFI and to understand the capacity to eliminate
absorbed F, we searched if there was a relation between the DUFE and the TDFI
and the F intake from toothpaste ( Figure 4A ), as well as between the DUFE
and the percentage of daily F intake from toothpaste ( Figure 4B ). For
subjects living in high-fluoridated areas, data from Idowu et al. [ 46 , 47
] were removed.
FIGURE 4
[
](https://www.frontiersin.org/files/Articles/916372/froh-03-916372-HTML/image_m/froh-03-916372-g004.jpg)
**Figure 4** . Estimation of the mean DUFE (μg/day) in relation with the mean
TDFI (diet and toothpaste) or only daily F intake from toothpaste in
participants aged 1–7 years old and 20–35 years old [the highest dot in
**(A)** ]. **(A)** The mean DUFE (μg/day) in relation with TDFI and daily F
intake from toothpaste (μg/day). § Black arrow indicates the lowest value of F
intake from toothpaste from Zohoori and Rugg-Gunn [ 40 ]: three toothpaste
users among 28 in Darab (not the same region presented in Figure 2 ; Table
3 ). **(B)** The mean DUFE (μg/day) in relation with daily F intake from
toothpaste (%).
There was a similar tendency to increase DUFE with increased TDFI and F intake
through toothpaste ( Figures 4A,B ). However, with an _R_ 2 below 0.07,
there was no correlation between DUFE and TDFI or between DUFE and daily F
intake from toothpaste.
## Discussion
The present systematic review showed that the mean contribution of
F-containing dental care products, mainly toothpastes, is 38% regardless of
the age of children or F concentration in drinking water. These data are
slightly lower than those published earlier by Paiva et al. [ 26 ],
reporting a 65% contribution. The difference may be either due to the method
of collecting data or to evolution of the use of less fluoridated toothpastes.
The contribution of F intake was not correlated with the age of children.
However, children under 4 years old presented a very high TDFI as well as some
adults who did not respect the good practice of dental care uses. Those two
cases highlight the importance of: (i) dental products on the exposome, (ii)
the types of F, bio-assimilation, and concentrations in the dental care
products, and (iii) the importance of dental care products adapted to age, but
more importantly, the results show the importance of good dental care habits
(no swallowing, rinsing with water after toothbrushing, exposure to F after
meals, and use of appropriate amount of toothpaste). The variation of F intake
from the diet seemed to be less sensitive to the water concentration than the
variation due to the concentration and good use of dental care products in the
different areas. Therefore, despite the fact that studies in this field are
lacking especially for adults, impact of dental care products on TDFI for
adults should not be negligible. This requests to be further investigated in
the case of misconducted use as it can increase the risk of excessive F
intake.
The increase in F intake, especially due to dental care products did not
necessarily correlate with the amount of F excretion. This result can be
explained by the fact that we were looking at the reported means, which
smoothed the values. The lack of correlation between DUFE and TDFI can also be
due to (i) poor estimation of F inputs (additional sources and under or
overestimation), and/or (ii) bias of the methodological and/or analytical
quantification of urinary excretion (data were reported in means for each
publication, choice of collection, and measure of the F into the urine),
and/or (iii) variability of excretion capacity for each organism. In addition,
these data were based on nine publications which could be a limitation of the
study.
Urine is the only biomarker capable of measuring F excretion. However, urine
may not be the most pertinent biomarker for the estimation of TDFI especially
in children due to F accumulation during bone growth and mineralization.
Children can retain more F in their skeleton (~50%) than adults (approximately
36%), with inverse retention in bone with age of the children and with the
excess of F excreted in urine [ 67 ]. The absence of correlation between
DUFE and TDFI suggests that there is a variability but a non-negligible amount
of F was not eliminated from the organism. Our data showed a variation of DUFE
between 65.2 and 691 μg/day that may have informed on the F bioavailability,
its residence time (clearance), and its interactions with different tissues.
The majority of body F is bound in hard tissues, such as bones and teeth, and
<1% can be found in soft tissues [ 17 ].
Further investigation combining measures of F in plasma and urine could be
informative on the bioavailability of F and its interactions with different
organs. Once absorbed, F reaches peak serum concentrations after 20–60 min,
and then returns to the baseline after approximately 15 h suggesting that part
of the oral F passes through systemic route [ 56 , 57 , 68 , 69 ].
This is probably the reason why a relation has been reported between
supplement use or the amount of toothpaste used for brushing and child's
fluorosis scores [ 65 ]. Most pharmacokinetic analyses showed a transient
increase in the urinary F excretion approximately 1–3 h after topical
application of fluoridated varnishes in adults and in children, after the use
of a fluoridated mouthrinse solution, or after brushing with F-containing
toothpastes [ 42 , 56 – 58 , 60 , 64 , 66 ]. A return to baseline
is reported by all the studies 24–72 h after the end of the exposure,
irrespective of the source. The minimal recommended period of urine collection
is 24 h to obtain good estimations of the daily amount of F excretion. The
DUFE is the variable generally recommended for the estimation of the daily F
exposure. The amount of excreted F is obtained by multiplying the 24-h urinary
volume by its F concentration [ 18 ].
As a consequence, we have proposed an experimental model of cumulative F
exposure following the age of the individuals considering three different
thresholds of 30, 300, and 1,300 μg F/day ( Supplementary Figure 3 ) and a
model of mixed exposures (1,300 μg F/day until 4 years, then 300 μg F/day
until 8 years, and 30 μg F/day until 16 years). The thresholds have been
defined based on the estimated F retention. Those values were obtained by
subtracting the DUFE from the TDFI and were estimated between a few μg and
1,890 μg/day. Thus, this model is a cumulative representation, which includes
daily F bone retention to estimate the trapped F into the body over a span of
several years. According to this model, early age exposure could drastically
affect the total F retention into the organism. Even though the residence time
(i.e., half-life) of F into the different organs remains not well known, the
exposure to a high absorption of dental care products may print a high F
content over the years. In addition, bad habits of dental care products may
impact F exposure for the adults. Therefore, these data showing a non-
negligible contribution to daily F intake through toothbrushing using
F-containing toothpastes may be discussed in the light of the literature as F
was reported to pass through the blood-placental barrier and the blood-brain
barrier thus subsequently cause learning problems [ 70 ]. In fact, most of
studies on the safety of toothpastes and dental care products are short-term
pharmacokinetics studies that do not consider long-term effects, whereas F
accumulated in bone may be released in specific situations associated to
skeletal loss, such as lactation [ 71 ]. However, we found no study that has
explored the contribution of dental care products to total F exposure in
pregnant and lactating women nor studies taking into account the gender,
especially in young children. This concern is even more important considering
that recent studies reported a relation between prenatal F exposure and lower
performance intelligence quotient (IQ) in boys, but not in girls [ 72 ]. An
increase of 0.5 mg/L of F concentration in the water (approximately equal to
the difference between fluoridated and non-fluoridated regions) was associated
with a 7.9-point lower IQ score in formula-fed infants and 6.3-point lower IQ
score in breastfed children in both boys and girls, suggesting that postnatal
exposure to F may affect both sexes [ 73 ]. Sex-dependent susceptibility to
F may be due to multiple biological and behavioral reasons, they have also
been reported in several experimental studies in rodents, and more recently in
zebrafish [ 12 , 13 ].
In conclusion, our review highlights the major F contribution from dental care
products regardless of the area or F concentration in drinking water. This
additional source presents a large variability depending on the concentration,
chemical forms, and amount of the dental product used. However, the good usage
of these products also seems to be determinant for the contribution to TDFI.
Therefore, the contribution of F intake through toothpaste can be easily
controlled and adapted to the patient. Consequently, the future studies on F
exposure and toxicity need to take into consideration exposure to F-containing
dental care products, habits of use, and individual features (gender, age,
diet, caries, etc.). Furthermore, considering the contribution of dental care
products to the TDFI, the “optimal daily F intake” estimated approximately
50–70 μg/kg bw/day by EFSA could be reevaluated to determinate the optimal
DDFI depending on each individual. The contribution of ~39–51% due to dental
care products suggests that the optimal daily dietary F may be half of the
EFSA values.
## Data Availability Statement
The original contributions presented in the study are included in the article/
Supplementary Material , further inquiries can be directed to the
corresponding author.
## Author Contributions
HS and SH selected the papers and reviewed them independently. SB was the
third reviewer. HS and RE organized the data. HS, SH, and SB analyzed the data
and the discussion. SH and SB drafted the manuscript. All authors contributed
to the writing of the article and approved the final version.
## Funding
The study was funded by the French National Institute of Health and Medical
Research (INSERM), the Université Paris Cité (Idex Project FLUOREMAIL), and
the National Agency for Safety of Food and Environment (ANSES) (Grant
2019/1/230).
## Conflict of Interest
The authors declare that the research was conducted in the absence of any
commercial or financial relationships that could be construed as a potential
conflict of interest.
## Publisher's Note
All claims expressed in this article are solely those of the authors and do
not necessarily represent those of their affiliated organizations, or those of
the publisher, the editors and the reviewers. Any product that may be
evaluated in this article, or claim that may be made by its manufacturer, is
not guaranteed or endorsed by the publisher.
## Supplementary Material
The Supplementary Material for this article can be found online at: [
https://www.frontiersin.org/articles/10.3389/froh.2022.916372/full#supplementary-
material
](https://www.frontiersin.org/articles/10.3389/froh.2022.916372/full#supplementary-
material)
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Keywords: fluoride, drinking water, diet, toothpaste, dental products, urine
Citation: Saad H, Escoube R, Babajko S and Houari S (2022) Fluoride Intake
Through Dental Care Products: A Systematic Review. _Front. Oral. Health_
3:916372. doi: 10.3389/froh.2022.916372
Received: 09 April 2022; Accepted: 04 May 2022;
Published: 10 June 2022.
Edited by:
[ Rogelio González-González
](https://loop.frontiersin.org/people/626134/overview) , Juárez University of
the State of Durango, Mexico
Reviewed by:
[ Jesus Lavalle-Carrasco
](https://loop.frontiersin.org/people/1533158/overview) , Juárez University of
the State of Durango, Mexico
[ Omar Tremillo Maldonado
](https://loop.frontiersin.org/people/1526840/overview) , Juárez University of
the State of Durango, Mexico
Copyright © 2022 Saad, Escoube, Babajko and Houari. This is an open-access
article distributed under the terms of the [ Creative Commons Attribution
License (CC BY) ](http://creativecommons.org/licenses/by/4.0/) . The use,
distribution or reproduction in other forums is permitted, provided the
original author(s) and the copyright owner(s) are credited and that the
original publication in this journal is cited, in accordance with accepted
academic practice. No use, distribution or reproduction is permitted which
does not comply with these terms.
*Correspondence: Sylvie Babajko, [ [email protected] ](mailto:[email protected])
[
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| biology | 4965929 | https://sv.wikipedia.org/wiki/Kausticering | Kausticering | Kausticering kallas den process då natriumkarbonat omvandlas till natriumhydroxid. Kausticering utföres med hjälp av kalciumoxid (bränd kalk), som normalt erhålles genom ombränning av kalciumkarbonat (såsom kalksten):
CaCO3 (s) → CaO (s) + CO2 (g)
Kalciumoxiden kan också erhållas genom upphettning av både kalciumhydroxid och kalciumsulfat, som oftast ingår i mindre mängder i kalksten:
Ca(OH)2 (s) → CaO (s) + H2O (g)
2 CaSO4 (s) → 2 CaO (s) + 2 SO2 (g) + O2 (g)
Kausticeringen sker i två steg där man i första steget omvandlar kalciumoxid till kalciumhydroxid, vilket brukar kallas kalksläckning:
CaO (s) + H2O → Ca(OH)2 (s)
Släckningen är en relativt snabb reaktion. Kalciumhydroxiden kan därefter reagera med löst natriumkarbonat genom följande jämvikt (kausticeringsreaktionen):
Na2CO3 + Ca(OH)2 (s) ⇌ 2 NaOH + CaCO3 (s)
Denna reaktion är betydligt långsammare än släckningsreaktionen. Eftersom kalciumkarbonat har låg löslighet och faller ut förskjuts kausticeringsjämvikten åt höger, vilket gynnar bildningen av natriumhydroxid. Närvaro av hydroxid från annan källa, som t.ex. i sulfatmassabrukens grönlut där hydroxid bildas från sulfidjoner, motverkar å andra sidan kausticeringen.
Som mått på omvandlingen från natriumkarbonat till natriumhydroxid används följande begrepp, varvid cX betecknar molariteten [mol dm-3] för substansen X:
Kausticeringsjämvikten motverkas som nämnts av hög alkalihalt och normalt uppnås kausticeringsgrader på 80-85%.
Kaustik soda är en äldre benämning för natriumhydroxid och kaustik har betydelsen frätande, vilket gäller för koncentrerad natriumhydroxid (kaustik soda) till skillnad från natriumkarbonat (soda).
Kausticeringsprocessen utnyttjas i sulfatmassaindustrin då grönlut (huvudsakligen innehållande natriumkarbonat och natriumsulfid) omvandlas till vitlut (innehållande natriumhydroxid och natriumsulfid), där vitluten i sin tur används som reaktionskemikalie för att bryta ned och lösa ut ligninet från veden i kokprocesserna.
Källor
Hägg, Gunnar: Allmän och oorganisk kemi, 2:a upplagan, Almqvist & Wiksell, Stockholm, 1963.
Rydholm, Sven A.: Pulping Processes, Interscience Publishers (John Wiley & Sons), New York, 1965.
Macdonald, Ronald G. (Editor) and Franklin John N. (Technical Editor): Pulp and Paper Manufacture: Volume I - The Pulping of Wood, Second Edition, McGraw-Hill, New York, 1969.
Casey, James P. (Editor): Pulp and Paper: Volume I - Chemistry and Chemical Technology, Third Edition, Wiley-Interscience, New York, 1980.
Hough, Gerald: Chemical Recovery in the Alkaline Pulping Processes, Tappi Press, Atlanta, 1985.
Grace, Thomas M., Leopold, Bengt, and Malcolm, Earl W. (Technical Editors) and Kocurek, Michael J. (Series and Technical Editor): Pulp and Paper Manufacture: Volume 5 - Alkaline Pulping, Third Edition, TAPPI and CPPA, Atlanta and Montreal, 1989.
Smook, Gary: Handbook for Pulp and Paper Technologists, Angus Wilde Publications, Vancouver, 1992.
Bierman, Christopher J.: Handbook of Pulping and Papermaking, Second Edition, Academic Press, San Diego, 1996.
Tikka, Panu (Editor): Chemical Pulping Part 2, Recovery of Chemicals and Energy, ingående som Del 6 i Papermaking Science and Technology Book Series, Second Edition, Paper Engineers' Association/Paperi ja Puu, Helsinki, 2008.
Ek, Monica, Gellerstedt, Göran, and Henriksson, Gunnar (Editors): Pulp and Paper Chemistry and Technology: Volume 2 - Pulping Chemistry and Technology, Walter de Gruyter, Berlin, 2009.
Kemikalier i massa- och pappersindustrin
Pappersmassatillverkning | swedish | 1.173318 |
tooth_paste_teeth/Remineralisation_of_teeth.txt | Tooth remineralization is the natural repair process for non-cavitated tooth lesions, in which calcium, phosphate and sometimes fluoride ions are deposited into crystal voids in demineralised enamel. Remineralization can contribute towards restoring strength and function within tooth structure.
Demineralization is the removal of minerals (mainly calcium) from any of the hard tissues: enamel, dentine, and cementum. It begins at the surface, and may progress into either cavitation (tooth decay) or erosion (tooth wear). Tooth decay demineralization is caused by acids from bacteria in the dental plaque biofilm whilst tooth wear is caused by acids from non-bacterial sources. These can be extrinsic in source, such as carbonated drinks, or intrinsic acids, usually from stomach acid coming into the mouth. Both types of demineralization will progress if the acid attacks continue unless arrested or reversed by remineralization.
Tooth decay process[edit]
When food or drinks containing fermentable sugars enter the mouth, the bacteria in dental plaque rapidly feed on the sugars and produce organic acids as by-products. The glucose produced from starch by salivary amylase is also digested by the bacteria. When enough acid is produced so that the pH goes below 5.5, the acid dissolves carbonated hydroxyapatite, the main component of tooth enamel. The plaque can hold the acids in contact with the tooth for up to two hours, before it is neutralized by saliva. Once the plaque acid has been neutralized, the minerals can return from the plaque and saliva to the enamel surface.
However, the capacity for remineralization is limited, and if sugars enter the mouth too frequently then a net loss of minerals from enamel produces a cavity, through which bacteria can infect the inner tooth and destroy the latticework. This process requires many months or years.
Natural tooth remineralization[edit]
Role of saliva[edit]
Remineralization occurs on a daily basis after attack by acids from food, through the presence of calcium, phosphate and fluoride found in saliva.
Saliva also acts as a natural buffer to neutralize acid, preventing demineralization in the first place. If there is reduced saliva flow or reduced saliva quality, this will increase the risk of demineralization and create the need for treatment in order to prevent demineralization progression.
Saliva function can be organized into five major categories that serve to maintain oral health and create an appropriate ecologic balance:
Lubrication and protection
Buffering action and clearance
Maintenance of tooth integrity
Antibacterial activity
Taste and digestion.
As the demineralization process continues, the pH of the mouth becomes more acidic which promotes the development of cavities. Dissolved minerals then diffuse out of the tooth structure and into the saliva surrounding the tooth. The buffering capacity of saliva greatly impacts the pH of plaque surrounding the enamel, thereby inhibiting caries progression. Plaque thickness and the number of bacteria present determine the effectiveness of salivary buffers. The high salivary concentrations of calcium and phosphate which are maintained by salivary proteins may account for the development and remineralization of enamel. The presence of fluoride in saliva speeds up crystal precipitation forming a fluorapatite-like coating which will be more resistant to caries.
Treatment and prevention[edit]
Besides professional dental care, there are other ways for promoting tooth remineralization:
Fluoride[edit]
Fluoride therapy[edit]
Fluoride is a mineral found naturally in rock, air, soil, plants and water and may assist by:
Potentially repairing early white spot lesions found on the tooth surface that may develop into cavities.
And a reduction in cavities may result in the following downstream benefits:
Protecting children and adults against tooth decay
Helps prevent premature tooth loss of baby teeth due to decay and overall assists in guiding the adult teeth to correct tooth eruption.
Aids in the prevention of invasive dental treatment therefore reducing the amount of money spent on dental treatment
Provides an overall community advantage, especially individuals from low socioeconomic communities, who have less access to other forms of fluoride treatments
Evidence confirms that water fluoridation is a safe and effective way to help protect teeth against decay
The addition of fluoride to the water does not alter the taste or smell of the drinking water
Fluoride therapy is often used to promote remineralization. This produces the stronger and more acid-resistant fluorapatite, rather than the natural hydroxyapatite. Both materials are made of calcium. In fluorapatite, fluoride takes the place of a hydroxide.
Effect of fluoride[edit]
The presence of fluoride in saliva and plaque fluid interacts with remineralization process in many ways and thus exerts a topical or surface effect. A person living in an area with fluoridated water may experience rises of fluoride concentration in saliva to about 0.04 mg/L several times during a day. Technically, this fluoride does not prevent cavities but rather controls the rate at which they develop making them take a lot longer and making them easier to prevent via normal brushing as it will take a higher amount of acid, usually built up over a number of days, to destroy the created fluorapatite. When fluoride ions are present in plaque fluid along with dissolved hydroxyapatite, and the pH is higher than 4.5, a fluorapatite-like remineralised veneer is formed over the remaining surface of the enamel; this veneer is much more acid-resistant than the original hydroxyapatite, and is formed more quickly than ordinary remineralised enamel would be. The cavity-prevention effect of fluoride is partly due to these surface effects, which occur during and after tooth eruption. Fluoride interferes with the process of tooth decay as fluoride intake during the period of enamel development for up to 7 years of age; the fluoride alters the structure of the developing enamel making it more resistant to acid attack. In children and adults when teeth are subjected to the alternating stages of demineralisation and remineralization, the presence of fluoride intake encourages remineralization and ensures that the enamel crystals that are laid down are of improved quality. Fluoride is commonly found in toothpastes. Fluoride can be delivered to many parts of the oral cavity during brushing, including the tooth surface, saliva, soft tissues and remaining plaque biofilm. Some remineralization methods may work for "white spot lesions" but not necessarily "intact tooth surfaces".
Fluoridated toothpaste[edit]
Regular use of a fluoridated toothpaste has been shown to provide a significant source of fluoride to the mouth by the means of direct fluoride contact to tooth structure. The types of fluoride added to toothpaste include: sodium fluoride, sodium monofluorophosphate (MFP), and stannous fluoride.
As stated previously, fluoride has been proven to positively affect the remineralization process through fluorapatite-like veneer formation. Therefore, by using an adequately fluoridated toothpaste regularly, this assists the remineralization process of any hard tooth tissues.
Fluoride varnish[edit]
Fluoride varnishes were developed late 1960s and early 1970s and since then they have been used both as a preventative agent in public health programs and as a specific treatment for patients at risk of caries by the 1980s, mostly in European countries. Fluoride varnishes were developed primarily to overcome their shortcoming which is to prolong the contact time between fluoride and tooth surfaces. Furthermore, when compared to other existing topical fluoride the advantages of fluoride varnishes application are being a quick and easy procedure for the clinicians, reduced discomfort for the receiving patients, and greater acceptability by the patients. Fluoride varnishes are a concentrated topical fluoride containing 5% sodium fluoride (NaF) except the Fluor protector which contains difluorosilane. There are many types of fluoride varnishes and among them the popular brands are Duraphat and Fluor Protector. Currently, the anti-caries effect fluoride varnishes are backed up by Cochrane systematic reviews, 2002 which was updated in 2013 included 22 trials with 12,455 children aged 1–15 years old. The conclusion made is similar to its previous review, a 46% reduction in D(M)FS and 33% reduction in d (e/m)fs in permanent teeth and deciduous teeth respectively
Water fluoridation[edit]
Community water fluoridation is the addition of fluoride in the drinking water with the aim of reducing tooth decay by adjusting the natural fluoride concentration of water to that recommended for improving oral health. The NHMRC an Australian Government statutory body, released the public statement of efficacy and safety of fluoridation 2007 to set the recommended water fluoridation to the target range of 0.6 to 1.1 mg/L, depending on climate, to balance reduction of dental caries (tooth decay) and occurrence of dental fluorosis (mottling of teeth). Moreover the public statement states that the fluoridation of drinking water is an effective way to ensure the community is exposed to fluoride and can benefit from its preventative role in tooth decay.
Plaque control[edit]
Oral hygiene practices involve the mechanical removal of plaque from hard tissue surfaces Cariogenic bacteria levels in the plaque determine whether caries will occur or not, therefore, effective removal of plaque is paramount. The removal of plaque inhibits demineralisation of teeth, and increases opportunities for remineralization.
Diet[edit]
Demineralization is caused by bacteria excreting acids as a product of their metabolism of carbohydrates. By reducing the intake frequency of carbohydrates in an individual's diet, remineralization is increased and demineralization is decreased. Diet control is an important aspect in promoting remineralization to occur naturally. A loss of the tooth enamel structure and cavitation may occur if the demineralization phase continues for a long period of time. This disturbance of demineralisation caused by the presence of fermentable carbohydrates continues until the saliva has returned to a normal pH and had sufficient time to penetrate and neutralize the acids within any cariogenic biofilm present.
Increased sugar consumption in the means of foods and drinks containing high levels of sugar are known to be associated with high rates of dental decay. As a result, members of the dental team routinely assess patients' diets and highlight areas where this could be improved to reduce the risk of dental decay. A balanced diet is an important contributing factor towards oral health and general health. It is common knowledge that certain dietary habits contribute to disease, whether patients take note of advice which is given to them and change their diet as a result, is less certain.
Recent studies on diet and caries have been confounded by the widespread use of fluoride toothpastes. Studies have argued that with greater exposure to fluoride, the sugar consumption/caries relationship may be weaker in the modern age than previously thought, with fluoride raising the threshold of sugar intake at which caries progresses to cavitation. It has been concluded in modern societies that a significant relationship between sugars and caries persists despite the regular widespread use of fluoride toothpaste. Several reviews conclude that high sugar consumption continues to be the main threat for dental health of whole populations in some developed and many developing countries. Therefore, a key strategy to further reducing levels of caries in individuals as well as for populations, is by means of reducing the frequency of sugar intakes in the diet.
Foods high in refined carbohydrates, such as concentrated fruit snack bars, sweets, muesli bars, sweet biscuits, some breakfast cereals and sugary drinks including juices can contribute to dental decay, especially if eaten often and over long periods as the sugar nourishes the cariogenic bacteria in mouth. The bacteria produce acid, which destroys teeth. Highly refined packaged foods such as savory crackers and chips can also have high levels of carbohydrates. It is important to check the nutritional information panel on packaged foods to determine which foods and drinks have high carbohydrate concentrations.
To prevent demineralisation in the mouth, it is important for an individual to ensure they have a well-balanced diet, including foods containing calcium and foods that are low in acids and sugars. The individual should have a diet high in fresh fruits and vegetables, wholegrain cereals, legumes, seeds and nuts. Sugary snacks including lollies, fruit bars, muesli bars, biscuits, dried fruit, cordials, juices and soft drinks should be limited as they contribute to dental decay and dental erosion. Additionally, excessive starchy foods (such as bread, pasta, and crackers), fruits and milk products consumed frequently can cause the growth of dental plaque and bacteria. Therefore, a diet low in sugar and proper maintenance of oral hygiene is the best way to promote and maintain sound tooth structure for an individual.
Xylitol, Sorbitol, and Erythritol[edit]
Xylitol is a naturally-occurring sweetener that can be synthetically produced in bulk. It is classified as a sugar alcohol. Xylitol inhibits acid production by oral bacteria and promotes remineralization of the teeth. It can be found in various products which include chewing gums and lozenges. Xylitol has been found to reduce mutans streptococci in plaque and saliva and reduce the binding of these to the acquired enamel pellicle. This in turn leads to less adherent plaque and a decrease in acid production. In addition, chewing xylitol gum will stimulate increased salivary flow which in turn increases the amount of calcium in the saliva and enhances the oral clearance.
Additional saliva flow which includes chewing products such as gums that contain no fermentable carbohydrates can aid in the modulation of plaque pH. Xylitol is a sugar alcohol which provides the sensation of tasting sweetness in foods, particularly chewing gum, without providing sucrose which is the only sugar that S.mutans are capable of using to produce the polyacrylamide adhesive which allows them to bind to the teeth. Xylitol does not actively reduce or harm the presence or capacities of oral bacteria, but rather does not offer them the sustenance to propagate or function. There are often claims of significant dental benefits of Xylitol. These generally derive from the perspectives of; saliva production is increased during chewing and oral stimulation which can help to maintain a more adequate supply of saliva to support normal oral functioning. Also, the idea of Xylitol being a sweetener option which does not serve as fuel for oral bacteria is considered to be the healthier alternative than sucrose (table sugar), fructose, lactose, galactose products. While these considerations may not reverse any conditions in health, they are more so preventative, and do not further the consequential events such as dental caries, malodorous breath, excessive plaque and gingivitis conditions.
Erythritol may have greater protective action than xylitol and sorbitol. However, this research is industry funded and not as comprehensive as the research on xylitol.
Biomimetic glass and ceramics[edit]
Further information: Biomimetic material § Biomimetic mineralization
Biomimetic glass and ceramic particles, including amorphous calcium sodium phosphosilicate (CSPS, NovaMin) and amorphous calcium phosphate (ACP, Recaldent), are used in some toothpastes and topical preparations to promote remineralization of teeth. These particles have a structure mimicking hydroxyapatite, providing new sites for mineralisation to occur. Their binding to the teeth also occludes open dentin tubules, helping to reduce dentin hypersensitivity. Evidence is insufficient to recommend either for any indications, but the evidence for CSPS is stronger than that for ACP.
Oligopeptide P11-4[edit]
Main article: Oligopeptide P11-4
P11-4 (Ace-QQRFEWEFEQQ-NH2, Curolox) is a synthetic, pH controlled self-assembling peptide used for biomimetic mineralization e.g. for enamel regeneration or as an oral care agent. It has a high affinity to tooth mineral.
P11-4 is a self-assembling β-peptide. It builds a 3-D bio-matrix with binding sites for Calcium-ions serving as nucleation point for hydroxyapatite (tooth mineral) formation. The high affinity to tooth mineral is based on matching distances of Ca-ion binding sites on P11-4 and Ca spacing in the crystal lattice of hydroxyapatite. The matrix formation is pH controlled and thus allows control matrix activity and place of formation.
Self assembling properties of P11-4 are used to regenerate early caries lesions. By application of P11-4 on the tooth surface, the peptide diffuse through the intact hypomineralized plate into the early caries lesion body and start, due to the low pH in such a lesion, to self-assemble generating a peptide scaffold mimicking the enamel matrix. Around the newly formed matrix de-novo enamel-crystals are formed from calcium phosphate present in saliva. Through the remineralization caries activity is significantly reduced in comparison with a fluoride treatment alone. In aqueous oral care gels the peptide is present as matrix. It binds directly as matrix to the tooth mineral and forms a stable layer on the teeth. This layer does protect the teeth from acid attacks. It also occludes open dentin tubule and thus reduces the dental sensitivity.
See also[edit]
Medicine portal
Calcium lactate
Calcium phosphate
Tooth development
Toothpaste
Tooth enamel | biology | 17761 | https://da.wikipedia.org/wiki/Fosfor | Fosfor | Fosfor, også kendt som phosphor i fagsprog (på græsk betyder phôs lys og phoros betyder bærende, altså lys-bærende) er et grundstof med symbolet P og atomnummeret 15. Fosfor er meget reaktionsvilligt og findes ikke frit i naturen.
Fosfor er en vigtig brik i opbygningen af DNA og RNA og er desuden et essentielt stof for alle levende celler. Fosfor bruges også til fremstilling af gødning, hvilket er den vigtigste kommercielle anvendelse af grundstoffet.
Desuden finder man fosfor i sprængstoffer, nervegas, fyrværkeri, pesticider, tandpasta og vaskemidler.
Forbruget af fosfor er stærkt stigende og der forudses en global mangelsituation. Faktisk er det forkert at kalde det at forbruge fosfor, da fosfor stadig eksisterer som grundstof efter "brug". Noget fosfor bindes så stærkt i jordpartikler at planters rødder ikke kan optage dem, andet fosfor urineres til kloakken og sendes ud i havet. Mykorrhiza kan godt trække stærkt bundet fosfor ud af jordpartikler.
Forskellige kemiske grundstof gitterstrukturer (allotropi)
Grundstoffet fosfor kan danne flere forskellige kemiske grundstof-gitterstrukturer:
Hvidt fosfor, kaldes også gult fosfor - (P4) - opdaget af Hennig Brand i 1669 - eksisterer som molekyler dannet af fire atomer i en tetrahedral struktur. Hvidt fosfor kan selvantænde.
Rødt fosfor - opdaget af Anton von Schrötter i 1845 - er et amorft netværk. Rødt fosfor er rimeligt stabilt.
Violet fosfor - opfundet af Johann Wilhelm Hittorf i 1865. Fosforatomerne er på krystalformen monoklin eller rombohedral.
Sort fosfor (inklusiv fosforén) - først syntetiseret i 1914 - har en flad 2D-bikubestruktur. Sort fosfor er en smalbåndshalvleder med et båndgab på ca. 0,29 eV.
Blåt fosfor - bulet flad bikube gitterstruktur. Blåt fosfor blev opfundet i 2016 og bekræftet i 2018. Blåt fosfor er en halvleder med et båndgab på ca. 2 eV.
Historie
Den tyske alkymist Hennig Brand opdagede fosfor i 1669 under bearbejdelse af urin. Urin indeholder ved et normalt stofskifte opløst fosfor. Mens han arbejdede i Hamborg prøvede Brand at destillere nogle salte ved at inddampe urin. Processen resulterede i et hvidt stof som lyste i mørke og brændte med en flot flamme. Det fik navnet phosphorus mirabilis.
Fosfor blev først kommercielt anvendeligt for tændstikindustrien i det 19. århundrede ved at destillere fosfordampe fra bundfældet fosfat, opvarmet i en retort. Tændstikker fra den tid som blev lavet med fosfor, var giftige og derved farlige for mennesker, hvilket resulterede i mord, selvmord og uheld i form af forgiftninger.
Biologisk betydning
Stoffet indgår i dyrs celler og væv, fortrinsvis i form af fosfat (fosfolipider).
To helt væsentlige forhold er baseret på fosfor:
Energiformen ATP (adenosintrifosfat), hvor der foruden adenosin indgår tre energirige fosforbindinger, hvilket har betydning for leveringen af kemisk energi, som for eksempel ved funktionen af muskler
Arvematerialet DNA er bl.a. opbygget af fosforbindinger. Desuden er alle nukleinsyrerne opbygget tilsvarende med fosfat.
Cellulære processer reguleres ofte ved hjælp af de regulerende molekylers indhold af fosfat, bl.a. i tænder. Mange proteiner slukker for deres aktivitet via fosforylering og defosforylering, ligesom mange cofaktorer, toxiner og andre giftstoffer indeholder fosfatgrupper.
Mennesket
Fosfor er af helt afgørende betydning for mennesket, og kroppens behov for fosfor dækkes igennem føden, med en maksimal anbefalet mængde på 70 mg pr. kg kropsvægt dagligt. Menneskelegemet indeholder i alt 800-1.200 g fosfor, hvoraf det meste (80-85 %) findes i skelettet, fordi det sammen med calcium benyttes til opbygning af knoglemasse.
Fosfor findes især i mælk, nødder, frugt og grønt (bælgplanter), hvede og ris. Nyrerne regulerer fosformængden ved at udskille overskydende mængder af stoffet med urinen og ved at tilbageholde fosfor, hvis der er mangel på det.
Sygdomstilstande
Mangel på fosfor kan give muskelsvaghed, og knoglesvind kan optræde, hvis stoffet mangler i længere tid. Manglen kan optræde hos for tidligt fødte og hos personer, hvor en tarmsygdom forhindrer optagelsen.
For meget fosfor i kroppen er også farligt, fordi calciummængden i blodet vil stige. Symptomet herfor kan f.eks. være kramper.
Forholdsregler
Der findes mange organiske forbindelser, hvor fosfor indgår, og nogle af dem er meget giftige. Flourfosfat-estere er blandt de giftigste neurotoksiner, som man kender til. En stor del af de organiske fosfor-forbindelser er netop anvendt på grund af deres giftighed som i for eksempel pesticider og kemiske våben i form af neurotoksiner. De fleste uorganiske fosfatforbindelser er forholdsvis ugiftige og vigtige næringsstoffer for planter. En større tilstedeværelse af fosfater i miljøet kan medføre eutrofiering.
Den hvide fosfors allotropi bør altid opbevares i vand, da den udgør en alvorlig brandfare, fordi den ellers reagerer med ilten i luften. Ved håndtering bør man anvende en tang, for hvis fosfor kommer i kontakt med huden kan det forårsage alvorlige forbrændinger.
Når den hvide form af fosfor bliver udsat for sollys eller opvarmet i dens egen damp til 250oC, så transformerer den til den røde form af fosfor. Den røde form antænder ikke af sig selv og den er ikke ligeså farlig som den hvide form. Alligevel bør man håndtere det med forsigtighed, da den omdanner sig til den hvide form igen inden for nogle bestemte temperaturintervaller og udsender desuden giftige dampe bestående af fosforoxider, hvis man varmer det op.
Se også
Død zone
Fosfat
Fosfin
Fosfolipid
Fosforsyre
Fosforescens
Fosforkredsløb
Fosfofructokinase
Fosfatanalyse
Fosfoniumion
Fosforundersyrling
Eksterne links og henvisninger
Ikke-metaller | danish | 0.661125 |
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> Fluoride - Health Professional
# Fluoride
Fact Sheet for Health Professionals
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## Table of Contents
* Introduction
* Recommended Intakes
* Sources of Fluoride
* Fluoride Intakes and Status
* Fluoride and Health
* Health Risks from Excessive Fluoride
* Interactions with Fluoride
* Fluoride and Healthful Diets
* References
* Disclaimer
_This is a fact sheet intended for health professionals. For a general
overview, see our_ [ consumer fact sheet ](/factsheets/Fluoride-Consumer/) .
## Introduction
Fluoride, a mineral, is naturally present in many foods and available as a
dietary supplement. Fluoride is the ionic form of the element fluorine, and it
inhibits or reverses the initiation and progression of dental caries (tooth
decay) and stimulates new bone formation [ 1 ].
Soil, water, plants, and foods contain trace amounts of fluoride. Most of the
fluoride that people consume comes from fluoridated water, foods and beverages
prepared with fluoridated water, and toothpaste and other dental products
containing fluoride [ 2 , 3 ].
Approximately 80% or more of orally ingested fluoride is absorbed in the
gastrointestinal tract [ 1 ]. In adults, about 50% of absorbed fluoride is
retained, and bones and teeth store about 99% of fluoride in the body [ 1 ,
3 ]. The other 50% is excreted in urine [ 1 ]. In young children, up to 80%
of absorbed fluoride is retained because more is taken up by bones and teeth
than in adults [ 1 ].
Individual fluoride status is not typically assessed, although fluoride
concentrations can be measured in plasma, saliva, urine, bones, nails, hair,
and teeth [ 4 , 5 ]. Criteria for adequate, high, or low levels of
fluoride in the body have not been established.
## Recommended Intakes
Intake recommendations for fluoride and other nutrients are provided in the
Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board
(FNB) at the National Academies of Sciences, Engineering, and Medicine [ 1
]. DRI is the general term for a set of reference values used for planning and
assessing nutrient intakes of healthy people. These values, which vary by age
and sex, include the following:
* Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals
* Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA
* Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals
* Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects
The FNB found the data insufficient to derive EARs for fluoride. Therefore,
the board established AIs for all ages using estimated intakes shown to
maximize reductions in the incidence of dental caries without unwanted side
effects, such as dental fluorosis, a chronic condition resulting from the
consumption of too much fluoride when teeth are developing [ 1 ]. Table 1
lists the current AIs for fluoride for healthy individuals.
Table 1: Daily Adequate Intakes (AIs) for Fluoride [ 1 ] Age | Male |
Female | Pregnancy | Lactation
---|---|---|---|---
Birth to 6 months | 0.01 mg | 0.01 mg | |
7–12 months | 0.5 mg | 0.5 mg | |
1–3 years | 0.7 mg | 0.7 mg | |
4–8 years | 1 mg | 1 mg | |
9–13 years | 2 mg | 2 mg | |
14–18 years | 3 mg | 3 mg | 3 mg | 3 mg
19+ years | 4 mg | 3 mg | 3 mg | 3 mg
## Sources of Fluoride
### Food
Brewed tea typically contains higher levels of fluoride than most foods,
depending on the type of tea and its source, because tea plants take up
fluoride from soil [ 1 , 3 ]. Fluoride levels can range from 0.3 to 6.5
mg/L (0.07 to 1.5 mg/cup) in brewed tea made with distilled water [ 3 ].
Fluoride concentrations in breast milk are so low that they cannot always be
detected; when these levels can be measured, they range from less than 0.002
to 0.01 mg/L, even when mothers live in communities with fluoridated water [
3 ]. Fluoride concentrations in cow’s milk are also very low, ranging from
0.007 to 0.086 mg/L [ 3 ]. Fluoride levels in infant formulas in the United
States vary, depending on the type of formula and the fluoride content of the
water used to prepare the formula [ 3 ]. The typical fluoride concentration
is less than 0.2 mg/L in milk-based infant formula and 0.2 to 0.3 mg/L in soy-
based infant formula (not including contributions from tap water used to
prepare the formula).
Only trace amounts of fluoride are naturally present in most foods, and most
foods not prepared with fluoridated water provide less than 0.05 mg/100 g [ 1
, 6 ].
A variety of types of foods and their fluoride levels per serving are listed
in Table 2.
Table 2: Fluoride Content of Selected Foods [ 3 , 6 , 7 ] Food |
Milligrams per
Serving
---|---
Tea, black, brewed, 1 cup | 0.07 to 1.5*
Coffee, brewed, 1 cup | 0.22*
Shrimp, canned, 3 ounces | 0.17
Bottled water with added fluoride, 1 cup | ≤0.17
Raisins, ¼ cup | 0.08
Oatmeal, cooked, ½ cup | 0.08*
Grapefruit juice, ¾ cup | 0.08
Potatoes, russet, baked, 1 medium | 0.08
Rice, cooked, ½ cup | 0.04*
Cottage cheese, ½ cup | 0.04
Pork chop, baked, 3 ounces | 0.03
Yogurt, plain, low-fat, 1 cup | 0.03
Lamb chop, cooked, 3 ounces | 0.03
Tortilla, flour, 1 tortilla, approx. 10" diameter | 0.02
Corn, canned, ½ cup | 0.02
Beef, cooked, 3 ounces | 0.02
Tuna, light, canned in water, 3 ounces | 0.02
Cheese, cheddar, 1½ ounces | 0.01
Bread, white or whole wheat, 1 slice | 0.01
Asparagus, cooked, 4 spears | 0.01
Chicken, cooked, 3 ounces | 0.01
Milk, fat-free or 1%, 1 cup | 0.01
Apple, raw, with skin, 1 medium | 0.01
Avocado, raw, ½ cup sliced | 0.01
Macaroni, plain, cooked, ½ cup | 0.00*
Tomato, raw, 1 medium | 0.00
Banana, 1 medium | 0.00
Egg, cooked, 1 large | 0.00
Carrots, raw, 1 medium | 0.00
Peanut butter, 1 tbsp | 0.00
*Amounts of fluoride might vary by levels in the water used to prepare these foods and beverages.
### Fluoridated drinking water
Since 1962, the U.S. Public Health Service has recommended the addition of
fluoride to drinking (tap) water to reduce the risk and severity of dental
caries, one of the most common chronic diseases in children [ 8 ]. Many
countries around the world now adjust the fluoride concentration of community
drinking water supplies to the level recommended for the prevention of dental
caries [ 9 ].
Although the U.S. Public Health Service recommended fluoride concentrations of
0.7 in warmer climates (where children were expected to drink more water) to
1.2 mg/L in cooler climates to prevent dental caries in 1962, it amended its
recommended level in 2015 to 0.7 mg/L to maintain the ability to prevent
caries while minimizing the risk of dental fluorosis [ 8 , 10 ]. In 1986,
guidelines from the U.S. Environmental Protection Agency (EPA) established a
maximum allowable concentration of 4.0 mg/L fluoride in public drinking water
systems to prevent adverse effects from fluoride exposure (such as bone
disease) and a recommended maximum concentration of 2.0 mg/L to prevent dental
fluorosis [ 3 , 11 ]. A review of this regulation is a currently a low
priority for the EPA [ 12 ].
Fluoridated municipal drinking water—including water that people drink as well
as foods and beverages prepared using municipal drinking water—accounts for
about 60% of fluoride intakes in the United States [ 3 , 8 ]. In 2016,
62.4% of the U.S. population had access to a fluoridated community water
system [ 13 ]. The fluoride additives used to fluoridate drinking water in
the United States are fluosilicic acid, sodium fluosilicate, and sodium
fluoride [ 14 ]. The Centers for Disease Control and Prevention has a
webpage that lists fluoride levels in tapwater by county: [
https://nccd.cdc.gov/doh_mwf/Default/Default.aspx
](https://nccd.cdc.gov/doh_mwf/Default/Default.aspx) [  ](/About/exit_disclaimer.aspx
"External Website") [ 15 ]. Because of differences in amounts of fluoride in
groundwater, private water sources (including well water) have variable
fluoride concentrations [ 11 ].
Fluoride is not typically added to bottled drinking waters. However, when
fluoride is added, the U.S. Food and Drug Administration (FDA) stipulates that
the total amount of fluoride (added plus naturally occurring) cannot exceed
0.7 mg/L [ 7 ]. Previously allowable levels ranged from 0.8 to 1.7 mg/L. FDA
notes that this rule does not apply to bottled water without added fluoride
that contains fluoride naturally from its source water. The amount of fluoride
contained in bottled water is not required to be listed on the product label
unless the label makes a claim about the product’s fluoride content [ 16 ].
### Dietary supplements
Only a few dietary supplements contain fluoride, usually in the form of sodium
fluoride [ 17 ]. Most of these products are multivitamin/mineral
supplements, multivitamins plus fluoride, or supplements containing trace
minerals only. Some fluoride supplements, usually intended for children, are
in the form of drops. The most common amount of fluoride in supplements is
0.25 mg, although a few products contain 0.5 or 1 mg [ 17 ].
### Dental products
Most toothpaste sold in the United States contains fluoride in the form of
sodium fluoride or monofluorophosphate, most commonly at a level of 1,000 to
1,100 mg/L (about 1.3 mg in a quarter teaspoon, a typical amount of toothpaste
used for one brushing) [ 3 ]. The amount of fluoride ingested from
toothpaste depends on the amount used, the person’s swallowing control, and
how often the person uses toothpaste. Estimated typical amounts of fluoride
ingested daily from toothpaste are 0.1 mg to 0.25 mg for infants and children
age 0 to 5 years, 0.2 to 0.3 mg for children age 6–12 years, and 0.1 mg for
adults [ 3 ]. Fluoride in toothpaste, regardless of its form, is well
absorbed [ 1 ].
Other dental products that provide fluoride include mouth rinses for home use,
topical fluoride preparations applied in dentists’ offices or through school-
based programs, and dental devices (e.g., orthodontic bracket adhesives,
glass-ionomer and some composite resin dental restorative materials, and some
dental sealants and cavity liners) [ 3 , 18 ]. Gels used by dentists are
typically applied one to four times a year and can lead to ingestions of 1.3
to 31.2 mg fluoride each time; varnishes are least likely to produce a high
bolus of fluoride [ 3 ].
### Medications
Medications can contain fluoride. For example, voriconazole (VFEND or Vfend)
is an oral antifungal medication used to treat several infectious conditions,
including invasive aspergillosis, candidemia, and candidiasis [ 19 ].
Typical doses of voriconazole provide 65 mg/day fluoride. Long-term use (e.g.,
for 4 months or more) of this medication can lead to high fluoride
concentrations in serum [ 20 , 21 ]. The prescribing information for
voriconazole advises discontinuation of voriconazole if skeletal fluorosis and
periostitis (inflammation of the membrane surrounding and protecting the
bones) develop [ 19 ].
## Fluoride Intakes and Status
Most people in the United States consume adequate amounts of fluoride through
foods containing naturally occurring fluoride, fluoridated tap water, and food
products made with fluoridated tap water. According to the EPA, typical daily
fluoride intakes in the United States from foods and beverages (including
fluoridated drinking water) are 1.2 to 1.6 mg for infants and toddlers younger
than 4 years, 2.0 to 2.2 mg for children age 4–11 years, 2.4 mg for those age
11–14 years, and 2.9 mg for adults [ 10 ].
## Fluoride and Health
This section focuses on two conditions in which fluoride might play a role:
dental caries and bone fractures.
### Dental caries
Dental caries occurs when cariogenic bacteria in the mouth ferment foods and
produce acids that dissolve tooth mineral [ 22 ]. Over time, this tooth
decay can cause pain and tooth loss. Without treatment, dental caries can
cause infections, impair growth, lead to weight gain, affect school
performance, impair quality of life, and possibly result in death [ 23-26 ].
Adequate fluoride intakes reduce the risk of dental caries in its initial
stages by inhibiting demineralization and the activity of bacteria in dental
plaque and by enhancing tooth remineralization [ 24 ].
#### Impact of water fluoridation on dental caries
Water fluoridation protects teeth in two main ways—by preventing the
development of caries through ingestion of drinking water during the tooth-
forming years and through direct contact of fluoride with teeth throughout
life [ 27 , 28 ].
A 2015 Cochrane Review included 20 prospective observational studies (most
conducted before 1975) [ 8 ]. The results showed that water fluoridation
reduces the risk of decay and fillings, as well as of premature loss of
primary (baby) teeth, by 35% and loss of permanent (adult) teeth by 26% in
children receiving fluoridated water in comparison with children receiving
unfluoridated water. Fluoridation also increases the number of children with
no decay in their baby teeth by 15% and the number of children with no decay
in their permanent teeth by 14%. The authors concluded that water fluoridation
is effective for reducing dental caries rates in both primary and permanent
teeth in children. However, the reviewers were unable to assess the
effectiveness of water fluoridation for preventing caries in adults because no
evidence met the review’s inclusion criteria (which required studies to
include at least two groups, one receiving fluoridated water and one receiving
unfluoridated water).
The Cochrane Review’s findings were confirmed by a 2018 cross-sectional study
on the associations between fluoridated community water and dental caries in
the United States [ 29 ]. The authors analyzed data on 7,000 children age 2
to 8 years and 12,604 children and adolescents age 6 to 17 years who
participated in the National Health and Nutrition Examination Study (NHANES)
from 1999 to 2004 and 2011 to 2014, respectively. The results showed that
living in a county in which 75% or more of the drinking water contained at
least 0.7 mg/L fluoride was associated with a 30% reduction in the rate of
caries in primary teeth and a 12% reduction in the rate of caries in permanent
teeth.
Some evidence shows that the addition of fluoride to drinking water can also
prevent dental caries in adults. An observational study included 3,779
individuals in Australia age 15 and older who participated in the Australian
2004–2006 National Survey of Adult Oral Health [ 30 ]. In adults exposed to
fluoridated community water supplies for at least 14 years, rates of decayed,
missing, or filled teeth were 11%–12% lower than in adults whose drinking
water during this period had negligible amounts of fluoride. An earlier study
in 876 Australian Defence Force members age 17–56 years found that the average
rate of decayed, missing, and filled teeth was 24% lower in those with access
to water containing 0.5 to 1 mg/L fluoride for at least half of their lifetime
than in those exposed for less than 10% of their lifetime [ 31 ].
These findings show that fluoridated drinking water can prevent dental caries
in children and adults.
#### Impact of fluoride dietary supplements on dental caries in children
Some studies have assessed the impact of fluoride supplements on caries
development in children. For example, a 2011 Cochrane Review of 11 randomized
or quasi-randomized studies in a total of 7,196 children (most living in
communities lacking access to fluoridated drinking water) found that 0.25–1
mg/day supplemental fluoride for 24–55 months reduced rates of decayed,
missing, and filled tooth surfaces by 24% [ 32 ]. The authors concluded that
fluoride supplements were associated with a lower caries incidence rate in
permanent teeth. A 2013 systematic review found an even greater preventive
effect of fluoride supplements on the basis of one randomized and four
nonrandomized clinical trials in children [ 25 ]. The results showed that
0.25–1 mg/day fluoride supplementation reduced caries incidence rates in
primary teeth by 48%–72% in areas where water fluoridation levels were lower
than 0.6 mg/L. In two of these trials that monitored the children for 6–10
years, supplements were associated with a 33%–80% reduction in the incidence
of caries at age 7–10 years.
The U.S. Preventive Services Task Force (USPSTF) and the American Dental
Association have issued fluoride supplement recommendations for children whose
water supply contains little or no fluoride [ 23 ]. These recommendations
are summarized in Table 3.
Table 3: Expert Panel Recommendations for Fluoride Supplementation in Children
Source | Age Range | Recommendation
---|---|---
USPSTF [ 23 ] | 6 months and older | • Fluoride supplement (dose not
specified) for children whose water supply contains little or no fluoride*
American Dental Association [ 33 ]** | 6 months to 3 years | • Fluoride
supplement (0.25 mg/day) for children whose water supply contains less than
0.3 ppm (0.3 mg/L) fluoride
| 3–6 years | • Fluoride supplement (0.5 mg/day) for children whose water
supply contains less than 0.3 ppm (0.3 mg/L) fluoride
• Fluoride supplement (0.25 mg/day) for children whose water supply contains
0.3 to 0.6 ppm (0.3 to 0.6 mg/L) fluoride
| 6–16 years | • Fluoride supplement (1 mg/day) for children whose water
supply contains less than 0.3 ppm (0.3 mg/L) fluoride
• Fluoride supplement (0.5 mg/day) for children whose water supply contains
0.3 to 0.6 ppm (0.3 to 0.6 mg/L) fluoride
*No studies have addressed the dosage or duration of oral fluoride supplementation in this population.
**Recommended doses are based on poor-quality evidence.
Overall, the available evidence suggests that dietary supplements containing
fluoride can reduce rates of dental caries in children who lack access to
fluoridated drinking water. No studies have assessed the impact of fluoride
supplements on caries development in adults.
#### Fluoride dietary supplements in pregnant women
Like other nutrients, fluoride is transferred from a pregnant woman to her
fetus, so a few studies have evaluated the use of fluoride supplements by
pregnant women to prevent dental caries in their children. However, the
authors of a 2017 Cochrane Review found only one randomized controlled trial
published in 1997 that met the review’s inclusion criteria [ 34 ]. This
study assessed caries rates in 798 3-year-old children whose mothers had
received 1 mg/day fluoride during the last 6 months of pregnancy [ 35 ]. The
results showed no significant difference in the proportions of children who
had decayed or filled primary tooth surfaces or who had caries. The authors of
the Cochrane Review concluded that the 1997 study was of very low quality and
that no evidence shows that fluoride supplementation in pregnant women
prevents dental caries in their offspring.
### Bone fractures
Because fluoride helps stimulate the formation of new bone, researchers have
hypothesized that fluoride supplements might reduce bone fracture risk.
However, research to date has provided only limited evidence supporting this
hypothesis [ 36-38 ].
The findings of observational studies on the impact of fluoride levels in
water on bone mineral density (BMD) and fracture risk have been mixed. A study
of 7,129 white women found no significant differences in bone mineral density
or risk of hip, vertebral, wrist, or humerus fracture between those exposed
and those not exposed to fluoridated water between 1950 and 1994 [ 37 ]. In
contrast, in a study in 8,266 Chinese residents age 50 years or older, people
with access to water fluoride levels of approximately 1 mg/L had a lower
overall risk of fractures, but not of hip fractures, than those with access to
water containing negligible fluoride levels [ 38 ].
Clinical trials have also had conflicting findings about the efficacy of
fluoride dietary supplements to prevent bone fractures. For example, a meta-
analysis of 25 randomized controlled trials in a total of 954 participants
(four of the studies included people with osteoporosis) showed a significant
reduction in vertebral and nonvertebral fracture risk with daily doses of up
to 20 mg fluoride (in the form of monofluorophosphate or sodium fluoride), but
not with higher doses [ 39 ]. A more recent randomized controlled trial
found that 2.5, 5, or 10 mg/day fluoride for 1 year in 180 postmenopausal
women did not change BMD at any site assessed [ 40 ].
## Health Risks from Excessive Fluoride
Long-term ingestion of excess fluoride in infancy and childhood, when the
teeth are being formed, can lead to dental fluorosis [ 41 ]. The
characteristics of this chronic condition usually vary from almost
imperceptible white lines or flecks to white or brown stains on teeth [ 2 ].
Severe dental fluorosis can lead to pitting in tooth enamel. The risk of
dental fluorosis increases with fluoride intakes above recommended amounts [
42 ]. Severe enamel fluorosis is very rare, and no evidence indicates that
recommended levels of community water fluoridation lead to severe dental
fluorosis [ 3 , 28 ].
Analysis of 1999–2004 NHANES data showed that 22.8% of persons age 6–49 had
dental fluorosis, although less than 1% had severe fluorosis and less than 2%
had moderate fluorosis [ 41 ]. The prevalence rate of dental fluorosis was
highest, 41%, in adolescents and lowest, 8.7%, in those age 40–49. A more
recent analysis of NHANES data in 2001–2002 and 2011–2012 found that rates of
dental fluorosis (from very mild to severe) increased during this 10-year
period, from 29.7% to 61.3% [ 43 ].
High doses of fluoride (typically from rare accidents resulting in excessively
high levels of fluoridation of water, unintentional ingestion of fluoride
products intended for topical use in dentists’ offices, or fluoride
supplements inappropriately given to children) can result in nausea, vomiting,
abdominal pain, diarrhea, periostitis, and even death in rare cases [ 3 ,
19 , 44 ]. According to one estimate, the acute dose that could cause
serious systemic toxicity for fluoride is 5 mg/kg (e.g., 375 mg for someone
who weighs 75 kg [165 pounds]) [ 44 ]. This dose would be virtually
impossible to achieve from water or toothpaste containing standard levels of
added fluoride.
Chronic, excess intakes of fluoride are also associated with skeletal
fluorosis, although this condition is extremely rare in the United States. Its
effects can range from occasional joint pain or stiffness to osteoporosis,
muscle wasting, and neurological defects [ 1 , 45 ].
In addition to the potential to damage teeth and bones, some evidence suggests
that higher fluoride intakes during early development, including during
gestation, might be associated with a lower IQ and other cognitive impairments
(e.g., delays in cognitive development) in children [ 46-49 ]. However, many
experts, including the authors of a National Academies of Sciences,
Engineering, and Medicine review, consider this evidence to be weak and
methodologically flawed [ 50-60 ].
The FNB has established ULs for fluoride from all sources for healthy
individuals (Table 4) based on levels associated with dental and skeletal
fluorosis [ 1 ].
Table 4: Daily Tolerable Upper Intake Levels for
Fluoride [ 1 ] Age | Male | Female | Pregnancy | Lactation
---|---|---|---|---
Birth to 6 months | 0.7 mg | 0.7 mg | |
7–12 months | 0.9 mg | 0.9 mg | |
1–3 years | 1.3 mg | 1.3 mg | |
4–8 years | 2.2 mg | 2.2 mg | |
9–13 years | 10 mg | 10 mg | |
14–18 years | 10 mg | 10 mg | 10 mg | 10 mg
19–51 years | 10 mg | 10 mg | 10 mg | 10 mg
51+ years | 10 mg | 10 mg | |
## Interactions with Fluoride
Fluoride has no known, clinically relevant interactions with medications [ 61
].
## Fluoride and Healthful Diets
The federal government's 2020–2025 _Dietary Guidelines for Americans_ notes
that "Because foods provide an array of nutrients and other components that
have benefits for health, nutritional needs should be met primarily through
foods. ... In some cases, fortified foods and dietary supplements are useful
when it is not possible otherwise to meet needs for one or more nutrients
(e.g., during specific life stages such as pregnancy)."
For more information about building a healthy dietary pattern, refer to the _[
Dietary Guidelines for Americans ](https://www.dietaryguidelines.gov) [
](/About/exit_disclaimer.aspx "External Website") _ and the U.S. Department of
Agriculture's _[ MyPlate. ](https://www.choosemyplate.gov/) [  ](/About/exit_disclaimer.aspx
"External Website") _
The _Dietary Guidelines for Americans_ describes a healthy dietary pattern as
one that
* Includes a variety of vegetables; fruits; grains (at least half whole grains); fat-free and low-fat milk, yogurt, and cheese; and oils.
* Includes a variety of protein foods such as lean meats; poultry; eggs; seafood; beans, peas, and lentils; nuts and seeds; and soy products.
* Limits foods and beverages higher in added sugars, saturated fat, and sodium.
* Limits alcoholic beverages.
* Stays within your daily calorie needs.
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55. Gehani CP, Pollick H, Stevenson RA. Association Between Maternal Fluoride Exposure and Child IQ. JAMA Pediatrics 2020;174:215-6. [ [ PubMed abstract ](https://pubmed.ncbi.nlm.nih.gov/31886843/) ]
56. Gong CX, James NE. Association Between Maternal Fluoride Exposure and Child IQ. JAMA Pediatrics 2020;174:212-3. [ [ PubMed abstract ](https://pubmed.ncbi.nlm.nih.gov/31886860/) ]
57. Ritchie SJ, Morris AJ, McConway K. Association Between Maternal Fluoride Exposure and Child IQ. JAMA Pediatrics 2020;174:213-4. [ [ PubMed abstract ](https://pubmed.ncbi.nlm.nih.gov/31886842/) ]
58. Waugh D. Association Between Maternal Fluoride Exposure and Child IQ. JAMA Pediatrics 2020;174:211-2. [ [ PubMed abstract ](https://pubmed.ncbi.nlm.nih.gov/31886836/) ]
59. National Academies of Sciences, Engineering, and Medicine. [ Review of the Revised NTP Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects: A Letter Report ](https://doi.org/10.17226/26030) [  ](/About/exit_disclaimer.aspx "External Website") . Washington, DC: The National Academies Press. 2021.
60. American Dental Association. [ Re: State-of-the-Science Report on Fluoride Exposure ](https://www.ada.org/~/media/Project/ADA Organization/ADA/ADA-org/Files/Advocacy/220207_ntp_fluoride_report_nosig.pdf) [  ](/About/exit_disclaimer.aspx "External Website") . 2022
61. Natural Medicines. [ Fluoride. ](https://naturalmedicines.therapeuticresearch.com) [  ](/About/exit_disclaimer.aspx "External Website") 2019\.
## Disclaimer
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**Updated:** August 15, 2023 [ History of changes to this fact sheet
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# Fluoride toothpaste: Is it harmful?
Toothpaste with or without fluoride? This is the big question and a hotly
debated topic in the world of health. An increasing number of consumers are
reconsidering their choices and opting for zero fluoride toothpaste. Dentists,
medical associations and authorities advocate for fluoride, explicitly
endorsing its usage. Numerous studies have already demonstrated fluoride's
efficacy in preventing dental decay.
So, is there any truth behind the assumption that fluoride poses health risks?
By taking a closer look at the active ingredient, we will enable you to make
an informed choice with a clear conscience – using a toothpaste with or
without fluoride is then up to you.
__ min read
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* What is fluoride?
* Occurence
* Effectiveness against dental decay
* Side effects
* Zero fluoride toothpaste
* Selecting the right toothpaste
* Summary
* FAQs
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## What is fluoride?
Fluorides naturally arise from a compound containing fluorine gas. The element
with which fluorine binds determines whether sodium, amine or stannous
fluoride is formed. The compounds exhibit completely different properties than
fluorine. In fact, fluorides are salts with positive properties, while
fluorine is a toxic gas.
## Where is fluoride found?
Fluoride is a naturally occurring substance, not an artificial compound.
Fluorine salts are present not only in rock layers but also occur naturally in
the human body as essential components of our bones and teeth.
### Drinking water
Both mineral and tap water contain fluoride. How much fluoride depends on
where you live. In some countries, tap water is fluoridated as an extra
measure to safeguard the population against dental decay. However, this is not
the case in most European countries. Tap water in Germany, for example, is
considered low in fluoride, with a value of less than 0.3 mg per litre.
Fluoride levels in mineral water differ significantly depending on the water's
origin. Interesting fact: Seawater also contains fluoride – typically at an
average concentration of 1 mg per litre.
### Good to know:
Water with a fluoride content of up to 0.7 mg per litre is deemed appropriate
for preparing baby food.
**Digression: How is fluoride identified in drinking water?**
The German Federal Institute for Materials Research and Testing (BAM) has
developed a test strip for quickly determining the fluoride concentration in
water. This test strip works similar to a pH test strip, indicating the
fluoride concentration through a colour change.
In most European countries, however, this type of test is not necessary.
Fluoride detection is more useful in countries where water is fluoridated but
lacks consistent monitoring – for example, in certain regions of Asia and
Africa. If you want to know how much fluoride is in your tap water, simply get
in touch with your local water authority; there is no need to test the water
yourself.
### Fluoride in food
Trace amounts of fluoride are also found in food. Presented below is a list of
food products with the highest fluoride content – based on the Federal Food
Key of the the Max Rubner-Institut (MRI) (data in mg per 100 g):
* Fluoridated salt (47)
* White tea, dry (9.5)
* Mate tea, dry (9.5)
* Black tea, instant or dry (9.5)
* Green tea, dry (9.5)
* Peppermint tea and herbal tea, dry (7)
* Spirulina, powder or dried (0.92)
* Celery or sorrel, powder or dried (0.76)
* Seaweed powder (up to 0.69)
* Salmon (up to 0.69)
* Walnuts (up to 0.68)
* Sardines (up to 0.66)
* Brook trout (up to 0.648)
### Guide values for fluoride
How much fluoride is healthy? The German Nutrition Society (DGE) has
established recommended guide values for total fluoride consumption:
* Women: 3.1 mg per day
* Men: 3.8 mg per day
However, our typical dietary intake is notably lower: around 0.4 to 0.6 mg per
day.
### Fluoride in toothpaste and dental care products
Since 1850, the protective effects of fluoride-containing tooth enamel against
acids have been recognised. Consequently, scientists realised that fluoride
supplementation would help prevent dental decay. Fluoride has, therefore, been
recommended for protection against dental decay since 1874.
However, research did not stop there. Meanwhile, over 300,000 scientific
studies have explored fluoride's role in combating dental decay, resulting in
an abundance of dental care products like gels, varnishes, mouthwashes and, of
course, toothpaste containing sodium fluoride.
### Good to know:
Did you know that thoroughly rinsing your mouth with water after brushing your
teeth diminishes the effectiveness of fluoride in toothpaste? It is better to
just spit out the toothpaste and to not rinse your mouth with water. This
allows the fluoride to develop its full effect and optimally protect your
teeth.
## Effect: Fluoride in toothpaste - a key defence mechanism against dental
decay
How exactly does fluoride protect the teeth against dental decay? First, we
need to understand how dental decay initially develops.
### Digression: How does dental decay develop?
**The structure of tooth enamel**
Despite being the hardest material in the human body, tooth enamel is
remarkably sensitive. It consists of a super-fine crystalline lattice
structure of a mineral known as hydroxyapatite. Minerals such as magnesium,
sodium, calcium and phosphorus are bound within this crystalline lattice
structure.
**The mouth as a habitat**
Millions of bacteria live in the oral cavity. The majority of them are "good"
and essential for digestion. However, there are also "bad" cavity-causing
bacteria that attack the tooth enamel. And this is how it works: These
bacteria thrive on sugar, which they digest and excrete as acid. Thus, the pH
value in the mouth changes and becomes acidic.
### Good to know:
Cavity-causing bacteria thrive not only on sweets, cakes and chocolate. They
also love fructose and lactose, which are contained in healthy foods such as
fruit and dairy products.
**Demineralisation and remineralisation**
Upon acid secretion by bacteria, immediate neutralisation occurs, as minerals
like calcium and phosphorus are released directly from the crystalline lattice
structure of the tooth enamel. This process is referred to as
demineralisation.
The problem: The loosening of the minerals creates gaps in the crystalline
lattice structure of the tooth enamel that need to be filled. Saliva is
responsible for this task. As soon as the bacteria are done with their acid
attack, since the sugar has been digested and the oral pH value neutralised,
the saliva is able to re-close the open gaps in the tooth enamel. Because
besides water, saliva contains essential minerals such as calcium phosphates.
The crystalline lattice structure of the tooth enamel is replenished and the
actual tooth enamel becomes hard and durable again. This process of
replenishing mineral levels is also called remineralisation.
**The start of dental decay**
Serious problems only start to occur when demineralisation and
remineralisation are unbalanced. For instance, excessive sugar intake,
persistent acid secretion by bacteria and an unbalanced oral pH value may
overwhelm your saliva's capacity to replenish minerals. Bacteria can then
settle in the crystalline lattice structure of the tooth enamel and easily
multiply and spread. This is how dental decay develops.
### How does fluoride protect against dental decay?
Fluoride protects tooth enamel in three different ways:
**1\. Fluoride as a remineralisation accelerator**
With the help of fluorides, calcium phosphates can be absorbed more quickly in
the tooth enamel after teeth demineralisation caused by an "acid attack". This
helps to quickly close any weak spots in the crystalline lattice structure of
the tooth enamel, giving bacteria less time to settle in the gaps. The actual
fluorides are also stored in the tooth enamel. This means that the tooth
enamel is well prepared for efficient and rapid remineralisation after the
next acid attack.
**2\. Fluoride as a protective film against dental decay**
Regular use of fluoride toothpaste forms a kind of protective coating over the
teeth. Instead of neutralising the acidic pH value with minerals from the
tooth enamel, the protective layer is initially attacked, not the actual tooth
enamel. When brushing teeth, the fluoride is absorbed into the tooth enamel
and replaces hydroxide ions. This results in the formation of a wafer-thin
layer of a mineral called fluorapatite. In contrast to hydroxyapatite, which
makes up a large percentage of the foundation of our tooth enamel, it is
considerably stronger and more resilient. As such, fluoride protects the teeth
against acid attacks. Interesting fact: Shark teeth are made mostly of
fluorapatite and are, therefore, extremely strong.
**3\. Fluoride as a bacteria killer**
Fluoride has an antibacterial effect, which helps to combat bacteria already
on or in the tooth enamel. The fluoride penetrates the bacteria and
manipulates their metabolism. Consequently, fewer bacteria are able to produce
the acids that attack tooth enamel and, ultimately, cause dental decay.
### Scientific consensus on the effectiveness of fluoride
The world of dental health is in agreement: Fluoride offers effective
protection against dental decay. This is not only the view of the scientists
behind the more than 300,000 studies published on the subject of fluoride and
its impact on dental decay but also of official authorities and numerous
consumer protection organisations, such as Stiftung Warentest, Germany's
leading consumer testing organisation, all of whom recommend using fluoride
toothpaste.
In the world of dentistry, it is also an undeniable fact that the use of
fluoride toothpaste for brushing teeth is a primary reason for the drastic
reduction in dental decay in recent decades. A comprehensive oral health study
conducted by the German Dental Association in 2016 came to the conclusion that
there were twice as many caries-free teeth in 2014 as in 1997. Besides better
preventive dental care, fluoride toothpaste was also stated as one of reasons
for this improvement in oral health.
## Side effects: Is fluoride unhealthy?
So, if fluorides are so effective against dental decay and are recommended by
leading health institutions, why do doubts still remain? Terms such as "nerve
poison" or "neurotoxin" can frequently be heard. What effect does fluoride
have on the rest of the body? And what happens if you accidentally consume too
much fluoride?
Social media posts, internet forums and alternative health blogs are full of
content like: "The truth about fluoride". They tend to list the various
harmful side effects and use scare tactics to frighten consumers. Let us take
a closer look at the actual points of criticism.
### Result of overdosing: Fluorosis
Fluoride has been proven to effectively reduce dental decay, but you should
adhere to the "less is more" principle and never exceed the recommended
amounts. The exact recommendations for fluoride content in children's and
adult toothpaste can be found in the table below.
Children, in particular, should not exceed the prescribed daily fluoride
dosage. If children consume too much fluoride, they can develop what is known
as fluorosis – an overdose of fluoride that leads to white spots on their
teeth. This simply causes an excessive amount of minerals to be stored in the
tooth enamel.
An overdose may occur, for example, if fluoride tablets, fluoride toothpaste,
fluoridated salt and fluoridated drinking water are consumed at the same time
and over an extended period.
A mild form of dental fluorosis, which can also occur in Europe, is generally
harmless and merely an aesthetic "problem". In some regions of Africa and
India – where drinking water contains very high levels of fluoride – more
extreme forms of fluorosis are not uncommon. Sometimes, the spots on people's
teeth in these regions are even brownish in colour.
[ Fluorosis in children and babies: What to do?
](https://master.curaprox.com/blog/post/fluorosis-in-children-and-babies-what-
to-do)
### Good to know:
For a long time, scientists debated the question of whether it is better to
provide fluoride through toothpastes or tablets. Today, we know that
toothpaste is more effective due to its direct contact with the tooth enamel.
Fluoride tablets are not necessary if your child uses a fluoride toothpaste.
Important: Never give your child fluoride tablets and fluoride toothpaste at
the same time. Simply choose which option is best for your child.
**In case of extreme fluoride intake: Bone fluorosis**
If people ingest a particularly large amount of fluoride over a longer period
of time, it can lead to bone fluorosis, or skeletal fluorosis. In this case,
bone density is abnormally elevated. However, this results in bones losing
their natural elasticity, which can ultimately lead to restricted movement.
A report by the U.S. National Research Council indicated that crippling
skeletal fluorosis might occur in people who have ingested 10 to 20 mg of
fluoride per day for 10 to 20 years.
These values are very high and can only be achieved by drinking highly
fluoridated water. Seeing as most European countries do not fluoridate their
drinking water, you do not need to worry about skeletal fluorosis. This has
also been confirmed by Stiftung Warentest, Germany's leading consumer testing
organisation. According to the consumer protection organisation, products that
help prevent dental decay cannot damage your bones.
### Is fluoride toxic?
The dose makes the poison. The early modern physician Paracelsus came to this
conclusion as early as the 16th century, and it remains as relevant to
fluoride today as it did then. Yes, fluoride is poisonous, but only to a very
limited extent.
For someone weighing 70 kg, experiencing the initial symptoms of fluoride
poisoning, like nausea, abdominal pain, headache, diarrhoea, vomiting and
drowsiness, would require them ingesting at least 350 mg of fluoride. The
potentially toxic dose is 5 mg of fluoride per kilogram of body weight. In our
case, that would be the equivalent of consuming two to three tubes of
toothpaste.
A lethal dosage of fluoride would require the consumption of 33 to 67 tubes of
toothpaste by the same individual, with them likely falling into a coma or
suffering convulsions first.
But what about children? The German Federal Institute for Risk Assessment
(BfR) determined that a child may have an upset tummy at worst after consuming
a whole tube of children's toothpaste (with a fluoride concentration of 0.05
per cent). Poisoning by fluoride is therefore unlikely. Nevertheless, it is
advisable to restrict your child's access to fluoride toothpaste to prevent
any risks.
What we can say is that fluoride is poisonous when large amounts are ingested,
yet entirely harmless when used properly. In fact, according to the German
Dental Association, it is almost ten times less toxic than table salt.
### Good to know:
Often, the misconception that fluoride is detrimental to health or toxic comes
from it being confused with the genuinely toxic gas, fluorine. Fluoride, on
the other hand, is an entirely different substance with completely different
properties.
### Fluoride during pregnancy: Harmful to the brain?
A 2017 scientific study by the U.S. National Health Institute, various
universities and government health authorities raised concerns among expectant
parents. The study investigated whether heightened fluoride intake during
pregnancy has an impact on child IQ.
The result: Excessive fluoride intake can diminish a child's long-term IQ.
This study, however, did not refer to toothpaste but to drinking water in
Mexico characterised by significant and unregulated fluctuations in fluoride
content.
Expectant parents can therefore breathe a sigh of relief: The study subjects
consumed significantly higher levels of fluoride than typical in most European
countries. Brushing teeth with fluoride toothpaste during pregnancy is not
linked to any reduction in child IQ.
### Is fluoride harmful to the pineal gland?
Situated in the middle of the brain, the pineal gland, though tiny, plays a
significant role: It produces the sleep hormone melatonin, and its main job is
to help control important bodily functions, such as the circadian rhythm that
regulates the sleep-wake cycle and the onset of puberty.
Fluoride critics claim that fluoride triggers pineal gland calcification. In
fact, numerous studies have indeed discovered elevated fluoride concentrations
within the pineal gland. Nonetheless, the causative role of fluorides in
triggering calcification remains somewhat uncertain, as they might simply have
adhered to pre-existing calcification – similar to tooth enamel
remineralisation.
The important thing here, though, is: This criticism is founded on drinking
fluoridated water, not using fluoride toothpaste. Nonetheless, the potential
adverse impact of fluoridated water on the pineal gland and subsequent sleep
problems cannot be dismissed. That said, the amount of fluoride the body
absorbs through the use of toothpaste is extremely low, making it highly
unlikely that your fluoride toothpaste will cause you any sleepless nights.
### Is fluoride harmful to the thyroid gland?
In high doses, fluorides can indeed impede correct functioning of the thyroid
gland. However, the fluoride content in commercially available toothpaste is
so minimal that any concerns are completely unwarranted, particularly given
that the majority of toothpaste on the brush is not swallowed. A potential
link between fluoridated drinking water and hypothyroidism remains uncertain
and is a topic of ongoing scientific debate.
### Can fluoride cause a rash?
Perioral dermatitis is a red rash that appears around the mouth and on the
chin, resembling acne. It primarily affects women aged 16 to 50 and children.
The causes of this condition are unclear, but the suspected factors include
using fluoride toothpaste, drinking fluoridated water, taking the
contraceptive pill and applying oily facial creams. This fluoride intolerance
is harmless but profoundly discomforting for those affected.
If you suffer from a rash around your mouth, avoid using a toothpaste with
fluoride and oily facial products, at least temporarily, and seek medical
advice. Your doctor will probably also prescribe an antibiotic cream or
antibiotic tablets to treat the rash.
## Zero fluoride toothpastes: Yes or no?
Zero fluoride toothpastes are popular at present. But what is fuelling the
interest in them? Consumers are confused by rumours regarding fluoride's
adverse effects on the body. Are zero fluoride toothpastes really better and
healthier?
### Disadvantages of toothpastes without fluoride
The disadvantage of zero fluoride toothpastes is quite obvious: The three
protective effects of fluoride no longer apply. Zero fluoride toothpastes lack
the ability to coat the tooth enamel with a protective layer, to accelerate
remineralisation and to combat oral bacteria. Consequently, both Stiftung
Warentest and Öko-Test, two leading German consumer testing organisations,
consider zero fluoride toothpastes less effective in protecting against dental
decay.
### Advantages of toothpastes without fluoride
If you refrain from using a fluoride toothpaste, there is no risk of fluorosis
– at least not through the toothpaste. The fact is: There is no "fluoride
deficiency" in the human body as such. Fluoride is not essential for our
survival. Many consumers opt for a zero fluoride toothpaste as part of a
journey to embrace more natural products, devoid of the potentially
detrimental additives commonly found in conventional fluoride toothpastes.
### Good to know:
Even if you are a little worried about the harmful ingredients in your
toothpaste, you do not have to miss out on fluoride's efficacy in preventing
dental decay. Curaprox fluoride toothpastes are free from harmful substances
such as SLS, microplastics and triclosan.
We definitely agree with the proponents of zero fluoride toothpaste on another
aspect: Thorough mechanical cleaning with a [ toothbrush
](https://curaprox.us/toothbrushes) is much more important than the
composition of your toothpaste. Good and thorough dental care is also possible
using a zero fluoride toothpaste. Nonetheless, employing the correct
toothbrushing technique and maintaining a regular dental care routine are
crucial to preventing cavity-causing bacteria from colonising in your tooth
enamel.
### Who should use a zero fluoride toothpaste?
Zero fluoride toothpastes are particularly suitable for individuals who
already consume an ample amount of fluoride through alternative sources, such
as children taking fluoride tablets or people who live in areas with heavily
fluoridated drinking water. Children taking fluoride tablets can also use a [
special zero fluoride children's toothpaste
](https://curaprox.us/toothpaste/baby-kids-toothpaste/childrens-toothpaste-
kids-strawberry-zero-fluoride-60-ml-p522) .
### Good to know:
The zero fluoride toothpaste [ Enzycal zero from Curaprox
](https://curaprox.us/toothpaste/daily-toothpaste/enzycal-zero-
fluoride-75-ml-p121) contains three enzymes that are also found in saliva,
offering a natural and gentle approach to cleaning. This helps to stimulate
saliva production and thus also the remineralisation of tooth enamel. This
toothpaste is also ideal for individuals suffering from very sensitive teeth,
dry mouth, aphthae or irritation of the oral mucosa.
## Four factors for selecting the right toothpaste
Have you ever stood in the toothpaste section of a supermarket or pharmacy and
asked yourself the following question? Which product is the best one for me?
The choice of toothpaste often comes from more of a gut feeling, or you end up
buying the product with the most appealing packaging. The enormous choice is
overwhelming. After all, the question about "toothpaste with or without
fluoride" is not the only thing you need to consider when buying toothpaste.
Discover the four factors you should pay attention to for picking the right
toothpaste:
### 1\. Recommended amount of fluoride in toothpastes for babies, children
and adults
If you decide to buy a toothpaste with fluoride, the next question is: How
much fluoride should it contain? If you have children, even more questions
arise: When should you start brushing their teeth with fluoride? How much
fluoride may the toothpaste contain? And how much toothpaste should you
actually use for toddlers and babies? To answer these frequently asked
questions as clearly as possible, we have prepared a table showing the
recommended fluoride content in each case.
Based on the revised guidelines of the European Academy of Paediatric
Dentistry (EAPD), we recommend the following fluoride content when brushing
teeth:
Caution: The values for children only apply if you are not giving your child
fluoride tablets. If you are giving your child fluoride tablets and fluoride
toothpaste at the same time, there is a risk of fluorosis.
### 2\. RDA value
The RDA value (relative dentin abrasivity) indicates the extent to which a
toothpaste can wear away your tooth enamel. Some toothpastes contain abrasives
that can damage the enamel – similar to a skin peeling treatment, but with the
big difference that your tooth enamel will not grow back.
Evaluate the RDA values as follows:
* **Below 70:** Low abrasive effect; also suitable for sensitive teeth.
* **70 to 100:** Normal abrasive effect; suitable for daily use with healthy teeth.
* **Above 100:** High abrasive effect; not suitable for daily use.
Ideally, the RDA value should be between 40 and 80. Toothpastes with a
whitening effect usually have a much higher RDA value and thus a higher
abrasive effect. In this category, values of up to 100 are permitted. People
with particularly sensitive teeth should use a toothpaste with an abrasive
value of less than 50.
### Good to know:
Besides tasting exceptionally good, the [ Curaprox 'Be you' toothpastes
](https://curaprox.us/toothpaste/daily-toothpaste/toothpaste-be-you-
blackberry-60-ml-p514) whiten teeth naturally. Their RDA value of 50 is
particularly low for a whitening toothpaste, and they do not harm the tooth
enamel.
### 3\. Ingredients
Many people are worried about fluoride in toothpaste. However, it is not the
ingredient you should be concerned with the most:
* **SLS (sodium lauryl sulphate):** This active ingredient is responsible for the strong foaming effect of conventional toothpastes. Unfortunately, this gives us a misleading sense of cleanliness. Further, SLS attacks the oral mucosa and upsets the intestinal flora.
* **Microplastics:** The plastic particles, which are less than five millimetres in diameter, are a threat to both the environment and living organisms – despite this fact, they are used as abrasive microplastic beads in certain brands of toothpaste. Due to environmental pollution with plastic waste, microplastics have already been found in animals and drinking water. When it comes to cosmetics and care products, you should always opt for plastic-free ones whenever possible.
* **Triclosan:** Triclosan has an antibacterial effect and also helps to combat fungi. This active ingredient is often found in conventional toothpastes to help prevent gum inflammation. However, it makes the bacteria more resistant to our natural defences and is suspected of promoting cancer growth.
* **Bleaching agents:** Large quantities of aggressive bleaching agents can quickly have a whitening effect. However, they also attack the tooth enamel and result in a chemical imbalance, thereby making your teeth easy prey for cavity-causing bacteria.
* **Parabens:** Parabens are used to boost the shelf life of toothpaste. They help protect against microorganisms. However, they interfere with the body's hormones and are suspected of promoting breast cancer.
When choosing a toothpaste, make sure it does not contain any of the aforesaid
substances.
### Digression: Is titanium dioxide carcinogenic?
Due to genotoxicity concerns, titanium dioxide has been banned in food and
food supplements in the EU since August 2022. It was previously used as food
additive E 171 in chewing gum, coated tablets and baked goods.
The whitening and brightening agent fell into disrepute after studies with
rats showed that the agent could be carcinogenic if high concentrations of
titanium dioxide are inhaled. At one time, products containing titanium
dioxide in powder form had to display the warning label "possibly carcinogenic
to humans". However, the European Court of Justice (ECJ) has since declared
this regulation null and void.
For instance, titanium dioxide may still be used in cosmetic products, such as
sunscreens. Titanium dioxide is also used as a whitener in toothpastes. And
there is a risk of toothpaste being swallowed, especially by children.
Therefore, the [ Curaprox kids toothpastes
](https://curaprox.us/toothpaste/baby-kids-toothpaste) do not contain titanium
dioxide.
### 4\. Flavour and sensation of freshness
Even if you are not supposed to swallow toothpaste, its flavour is an
important criteria. After all, brushing your teeth should be fun, not a chore.
Toothpaste must taste delicious and leave a pleasant and long-lasting
refreshing taste in your mouth after brushing. If this is not the case with
your current toothpaste, try out a new one. It will make adhering to your
daily toothbrushing routine much easier.
### Good to know:
Fancy trying a gin tonic or apple flavoured toothpaste? The [ Curaprox 'Be
you' toothpastes ](https://curaprox.us/toothpaste/daily-toothpaste/toothpaste-
be-you-gin-and-tonic-60-ml-p517) come in six different flavours. The [ 'Be
you' Six Taste Pack from Curaprox ](https://curaprox.us/toothpaste/daily-
toothpaste/-be-you-six-taste-pack-p316) in a convenient travel size allows you
to sample the entire range and discover your favourite toothpaste.
## Summary: Are toothpastes with fluoride harmful?
No, toothpastes with fluoride are not harmful – provided you stick to the
recommended values and do not eat whole tubes of them. It is an undeniable
fact that fluoride serves to prevent dental decay and is a primary reason for
the drastic reduction in dental decay in recent decades. Dentists, consumer
protection organisations and public authorities all agree on this: The use of
toothpaste with fluoride is explicitly recommended.
Most of the criticism towards fluoride relates to fluoridated drinking water
and not to brushing teeth with a fluoride toothpaste. Since drinking water is
not usually fluoridated in Europe and tap water is low in fluoride, there is
no risk of overdosing as long as you do not give your child fluoride tablets
and fluoride toothpaste at the same time.
That said, if you give your child fluoride tablets and want to continue doing
so, or if you live in an area with fluoridated drinking water, it is probably
a good idea to switch to a zero fluoride toothpaste. Otherwise, a fluoride
toothpaste is the right choice to protect your teeth against dental decay. We
recommend using a fluoride toothpaste with natural ingredients.
## FAQs
Toothpaste with or without fluoride? A controversial topic. So, it is perhaps
not surprising that it throws up so many questions. Below we have provided
some frequently asked questions and answers:
### Who invented toothpaste without fluoride? __
Actually, zero fluoride toothpaste has been around longer than fluoride
toothpaste. The first toothpaste, resembling what we use today, was invented
by Washington W. Sheffield, an American dental surgeon, in 1850. He was the
first person to enrich the toothpaste powder, which was commonly used at the
time, with glycerine, thus creating a paste-like consistency. Initially, his
revolutionary invention was available in metal and ceramic tins and tin foil
bags. However, the toothpaste dried out very quickly. While studying dental
surgery in Paris, his son, Lucius, realised that the collapsible tubes used by
local artists to squeeze paint onto palettes would be ideal for his father's
toothpaste. Hence, the first tube of toothpaste was born.
The history of the toothbrush and toothbrushing
### Will fluoride toothpaste be banned? __
No, quite the contrary: Government authorities, scientists and medical
associations all agree that fluoride is an essential element in the fight
against dental decay and even expressly recommend its use.
### Is the fluoride in toothpaste carcinogenic? __
No, there is no evidence that fluoride in toothpaste could be carcinogenic.
According to Stiftung Warentest, Germany's leading consumer testing
organisation, there is also no increased risk of cancer in countries with
fluoridated drinking water.
### Which zero fluoride toothpaste should I buy? __
Seeing as zero fluoride toothpaste lacks the fluoride that serves to prevent
dental decay, it is best to choose a toothpaste that protects your teeth with
xylitol, hydroxyapatite or enzymes and that contains no harmful substances. To
find your ideal product, you can, for example, refer to various tests, take a
closer look at the toothpastes deemed the best and read what others have to
say about them. Your pharmacist will also be able to provide advice.
Our recommendation: The toothpaste [ Enzycal Zero from Curaprox
](https://curaprox.us/toothpaste/daily-toothpaste/enzycal-zero-
fluoride-75-ml-p121) contains three enzymes also found in saliva that
stimulate the flow of saliva. They, therefore, boost the antibacterial and
remineralising effect of saliva and protect your tooth enamel in a natural
fashion.
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Bashash, Morteza et al.: [ Prenatal Fluoride Exposure and Cognitive Outcomes
in Children at 4 and 6-12 Years of Age in Mexico
](https://pubmed.ncbi.nlm.nih.gov/28937959/) , in Environmental Health
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Birr, Cornelia: [ Hashimoto: Wenn die Schilddrüse sich selbst zerstört
](https://www.mdr.de/ratgeber/gesundheit/schilddruese-jod-hormone-hashimoto-
unterfunktion-100.html#:~:text=Dany%20Wiel%C3%A4nder:%20Fluoride%20in%20h%C3%B6herer,der%20Zahnpasta%20ja%20wieder%20ausgespuckt)
, at: mdr.de.
Federal Institute for Health Protection of Consumers and Veterinary Medicine
(BgVV): [ Verwendung fluoridierter Lebensmittel und die Auswirkung von Fluorid
auf die Gesundheit.
](https://www.bfr.bund.de/cm/343/verwendung_fluoridierter_lebensmittel_und_die_auswirkung_von_fluorid_auf_die_gesundheit.pdf)
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Kindern. ](https://www.bfr.bund.de/cm/350/risiko-vergiftungsunfaelle-bei-
kindern.pdf)
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Bundeslebensmittelschlüssel. ](https://www.blsdb.de/)
German Dental Association: [ Fünfte Deutsche Mundgesundheitsstudie (DMS V) –
Kurzfassung.
](https://www.bzaek.de/fileadmin/PDFs/dms/Zusammenfassung_DMS_V.pdf)
German Dental Association: [ Verwendung fluoridhaltiger Zahnpasta ist sicher
und schützt wirksam vor Karies. ](https://www.bzaek.de/service/positionen-
statements/einzelansicht/verwendung-fluoridhaltiger-zahnpasta-ist-sicher-und-
schuetzt-wirksam-vor-karies.html)
Chemie.de: [ Neuer Schnelltest für Fluorid-Nachweis im Trinkwasser.
](https://www.chemie.de/news/147508/neuer-schnelltest-fuer-fluorid-nachweis-
im-
trinkwasser.html#:~:text=%C3%84hnlich%20wie%20der%20Lackmustest%20zur,desto%20mehr%20Fluorid%20liegt%20vor)
The German Nutrition Society (DGE): [ Fluorid.
](https://www.dge.de/wissenschaft/referenzwerte/fluorid/)
Freund, Alexander: [ Wie gefährlich ist Titandioxid?
](https://www.dw.com/de/wie-gef%C3%A4hrlich-ist-titandioxid/a-48387575) , at:
dw.com
German National Association of Statutory Health Insurance Physicians (KZBV): [
Zahnschutz durch Fluoride. ](https://www.kzbv.de/zahnschutz-durch-
fluoride.63.de.html#)
Nährwertrechner.de: [ Suchergebnis (nach Fluorid absteigend)
](https://www.naehrwertrechner.de/naehrwerttabelle/suche.php?suchbegriff=&quelle=naehrwertrechner&rubrik=&aggregatszustand=&ernaehrungsform=&pref=MF&order=popularity&naehrwertampel=1&lowcarb=&lowfat=&highprotein=&konzentrate=&getrocknete=&gewuerze=&order=MF&reihenfolge=DESC)
.
Nguyen-Kim, Mai Thi: Komisch, alles chemisch! Handys, Kaffee, Emotionen – wie
man mit Chemie wirklich alles erklären kann. Droemer Verlag, Munich 2019.
O’Mullane, D.M. et al.: [ Fluoride and Oral Health
](https://eprints.whiterose.ac.uk/101379/1/Fluoride%20and%20oral%20health.pdf)
, in: Community Dental Health. 2016.
Quarks: [ Darum hilft Fluorid bei der Kariesvorsorge
](https://www.quarks.de/gesundheit/darum-solltest-du-es-mit-fluorid-nicht-
uebertreiben/) .
Raschke-Maas, Kathleen: [ Schutz oder Gift? Wieviel Fluorid brauchen wir?
](https://www.mdr.de/wissen/fluorid-gesund-oder-schaedlich-100.html) , at:
mdr.de.
Rehberg, Carina: [ Fluorid - Spurenelement oder Gift? ](https://www.zentrum-
der-gesundheit.de/bibliothek/umwelt/schaedliche-faktoren/fluorid) ,
at:zentrum-der-gesundheit.de.
Salz, Melanie: [ Fluoride: Wie Sie Mythen in der Beratung souverän begegnen
](https://www.coliquio.de/wissen/zahnmedizin-100/fluoride-3-behauptungen-
richtig-einordnen) , at: coliquio.de.
Sjögren, K. et al.: [ The influence of rinsing routines on fluoride retention
after toothbrushing ](https://pubmed.ncbi.nlm.nih.gov/11813383/) , in:
Gerodontology. 2001.
Steinert, Jürgen et al.: [ Macht uns Fluorid in Zahnpasta krank?
](https://www.oekotest.de/gesundheit-medikamente/Macht-uns-Fluorid-in-
Zahnpasta-krank_600876_1.html) , at: oekotest.de.
Stiftung Warentest: [ Das braucht es für gesunde Zähne
](https://www.test.de/FAQ-Zahnpflege-Ihre-Fragen-unsere-Antworten-4946155-0/)
.
Stiftung Warentest: [ Sind Fluorid, Zink und Titandioxid gefährlich?.
](https://www.test.de/Zahnpasta-im-Test-4607097-4723631/)
Tagesschau: [ Titandioxid zu Unrecht als krebserregend eingestuft.
](https://www.tagesschau.de/wissen/gesundheit/titandioxid-eugh-101.html)
Toumba, K.J. et al.: [ Guidelines on the use of fuoride for caries prevention
in children: an updated EAPD policy document
](https://www.eapd.eu/uploads/files/EAPD_Fluoride_Guidelines_2019.pdf) , in:
European Archives of Paediatric Dentistry. 2019.
Zm: [ Sieben Mythen über Fluorid auf den Zahn gefühlt. ](https://www.zm-
online.de/news/detail/sieben-mythen-ueber-fluorid-auf-den-zahn-gefuehlt)
All websites last accessed on 9 May 2023.
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### Oral health and individuals with disabilities
Maintaining oral health is crucial for our overall well-being, but individuals
with disabilities often face unique challenges in this area. From difficulties
with motor skills to cognitive...
[ Read more ](https://curaprox.us/blog/post/oral-health-and-individuals-with-
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](https://curaprox.us/blog/category/care) , [ Baby
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### How Do I Look After My Oral Health During Pregnancy – The Ultimate Guide
Learn about the risks to your oral health during pregnancy…… the best ways to
keep your teeth and gums clean and healthy…… and how this can help to give
your baby the best possible start in life.
[ Read more ](https://curaprox.us/blog/post/how-do-i-look-after-my-oral-
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](https://curaprox.us/blog/category/baby) , [ Kids
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Show kids that brushing is not just a necessary and annoying duty – it can
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children form important habits and...
[ Read more ](https://curaprox.us/blog/post/milk-teeth-are-as-important-as-
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| biology | 10011 | https://sv.wikipedia.org/wiki/Natriumhydroxid | Natriumhydroxid | Natriumhydroxid, NaOH, är ett vitt, fast ämne som är en Arrheniusbas, det vill säga ger ifrån sig hydroxidjoner (OH-) i vattenlösning. OH- är en stark Brønsted-Lowry-bas, så vattenlösningar av natriumhydroxid, som kallas natronlut eller bara lut, är starkt frätande. Natriumhydroxid är mycket lättlösligt i vatten. Det framställs genom elektrolytisk sönderdelning av natriumklorid i en delad cell.
Natriumhydroxid har många namn såsom kaustiksoda, kaustisk soda, kaustiskt natron, natron (vilket dock oftare används om natriumbikarbonat), natronhydrat, natriumhydrat, mineraliskt kali, alkali minerali eller etsnatron.
Egenskaper
Natriumhydroxid löser sig fullständigt i vatten. Basen löser sig även i etanol och metanol men inte lika bra som kaliumhydroxid. Natriumhydroxid är olösligt i opolära lösningsmedel som eter.
Bindningen mellan natrium och hydroxid i föreningen är fullständigt jonisk. Hydroxidjonen gör natriumhydroxid till en stark bas som reagerar med syror under bildning av vatten och ett korresponderande salt, till exempel vid reaktion med saltsyra bildas vatten och natriumklorid.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Oftast kan sådana neutraliseringsreaktioner sammanfattas med en nettojonformel:
OH−(aq) + H3O+(aq) → 2H2O
Denna typ av reaktion, med en stark syra, genererar värme, och kallas därför en exoterm reaktion. Sådana syrabasreaktioner kan också användas för titrering, en vanlig metod för att bestämma en syras koncentration. En annan typ av reaktion som natriumhydroxid kan vara inblandad i är med sura oxider. Till exempel så absorberar natriumhydroxid koldioxid från luften och måste därför förvaras i ett lufttätt kärl. Natriumhydroxid reagerar också fullständigt med svaveldioxid (SO2), och kan användas för att "skrubba" (från engelskan scrub, en process som avlägsnar en komponent i en gasblandning) bort giftiga sura gaser som SO2 och H2S så att de inte släpps ut i atmosfären.
2NaOH + CO2 → Na2CO3 + H2O
Natriumhydroxid reagerar långsamt med glas och bildar natriumsilikat, vilket kan påverka till exempel laboratoriekärl av glas. Glaskärl tar skada av långvarig kontakt med natriumhydroxid. Natriumhydroxid angriper inte järn eller koppar, men däremot andra metaller som aluminium, zink och titan. Aluminium får därför aldrig tvättas med natriumhydroxid.
2Al(s) + 6NaOH(aq) → 3H2(g) + 2Na3AlO3(aq)
Många icke-metaller reagerar också med natriumhydroxid under bildning av salter. Till exempel bildar fosfor natriumhypofosfit, medan kisel ger natriumsilikat.
Till skillnad från natriumhydroxid är de flesta metallers hydroxider olösliga i vatten, varför natirumhydroxid kan användas för att fälla ut metallhydroxider. En sådan metallhydroxid är aluminiumhydroxid som används som flockningsmedel för att filtrera bort partiklar vid vattenrening. Aluminiumhydroxid framställs vid reningsanläggningen från aluminiumsulfat genom att låta det reagera med natriumhydroxid NaOH:
6NaOH(aq) + Al2(SO4)3(aq) → 2Al(OH)3(s) + 3Na2SO4(aq)
Natriumhydroxid reagerar även med karboxylsyror under bildning av deras salter och är till och med tillräckligt starkt för att bilda salter med fenoler. Natriumhydroxid kan användas för basdriven hydrolys av estrar (såsom vid förtvålning), amider och alkylhalider.
Användning
Natriumhydroxid används som stark bas vid tillverkning av många kemikalier och andra produkter, såsom pappersmassa, textiler, dricksvatten, tvål och tvättmedel. Natriumhydroxid används även som propplösare. Speciellt inom massa- och pappersindustrin används enorma mängder natriumhydroxid. Vid massafabriker som utnyttjar sulfatprocessen både förbrukas och genereras stora mängder kontinuerligt - basen används för att lösa upp ligninet i ved, förbränns tillsammans med det utlösta materialet i en sodapanna och återskapas sedan i en så kallad kaustiseringsanläggning.
Som livsmedelstillsats har det E-nummer E 524, använd som surhetsreglerande medel i livsmedel. Det är dock inte kaustiksoda utan en vattenblandning med natriumkarbonat (soda) och kalciumhydroxid (släckt kalk) som används till lutvätskan i framställningen av lutfisk.
Natriumhydroxid förekommer också vid framställning av tvålprodukter. Om man får vattenlösning av natriumhydroxid på händerna känns det som tvålvatten eftersom lösningen omvandlar hudens eget fett till tvål. Detta bör dock undvikas eftersom lösningen är mycket skadlig för huden.
Hantering
Liksom andra frätande syror och baser kan droppar av natriumhydroxidlösningar lätt sönderdela proteiner och lipider i levande vävnader via amidhydrolys och esterhydrolys, vilket följaktligen orsakar kemiska brännskador och kan orsaka permanent blindhet vid kontakt med ögonen.
Således bör skyddsutrustning, som gummihandskar, säkerhetskläder och ögonskydd, alltid användas vid hantering av denna kemikalie eller dess lösningar. För mer ingående säkerhetsanvisningar se informationssidan på giftinformationscentralens hemsida.
För mer information om natriumhydroxid och dess risker se faktabladet "Varning för frätande propplösare" framtaget av giftinformationscentralen, arbetsmiljöverket och kemikalieinspektionen.
Se även
Kaliumhydroxid
Referenser
Rengöringsmedel
Natriumföreningar
Hydroxider
Torkmedel
Fotografiska kemikalier
Surhetsreglerande medel
Kemikalier i massa- och pappersindustrin | swedish | 1.00929 |
tooth_paste_teeth/PMC5651468.txt | Skip to main content
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Journal List Iran J Basic Med Sci v.20(8); 2017 Aug PMC5651468
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Iran J Basic Med Sci. 2017 Aug; 20(8): 841–848.
doi: 10.22038/IJBMS.2017.9104
PMCID: PMC5651468
PMID: 29085574
Potential fluoride toxicity from oral medicaments: A review
Rizwan Ullah,1 Muhammad Sohail Zafar,2,3,* and Nazish Shahani1
Author information Article notes Copyright and License information PMC Disclaimer
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Abstract
The beneficial effects of fluoride on human oral health are well studied. There are numerous studies demonstrating that a small amount of fluoride delivered to the oral cavity decreases the prevalence of dental decay and results in stronger teeth and bones. However, ingestion of fluoride more than the recommended limit leads to toxicity and adverse effects. In order to update our understanding of fluoride and its potential toxicity, we have described the mechanisms of fluoride metabolism, toxic effects, and management of fluoride toxicity. The main aim of this review is to highlight the potential adverse effects of fluoride overdose and poorly understood toxicity. In addition, the related clinical significance of fluoride overdose and toxicity has been discussed.
Keywords: Fluoridation, Fluoride, Oral health, Toxicity, Water fluoridation
Go to:
Introduction
Fluoride is the 13th most abundant element present in the earth’s crust. It belongs to the halogen group of elements and is found naturally in water, soil, animals, and plants (1). Fluoride is one of the most reactive and ubiquitously present in nature. It is present in trace amounts in all mineralized tissues of the body such as enamel, dentin, and bone. Fluoride is involved in a number of enzymatic reactions (2). In mineralized tissues and biomaterials, fluoride ions increase the stability of mineralized tissues and materials by decreasing the solubility of hydroxy-apatite mineral phase present in biomaterials and mineralized tissues (3). The protective effects of fluoride on dental health were first observed in 1930 as there was less tooth decay in communities consuming naturally fluoridated water compared to non-fluoridated areas (4). Due to these beneficial effects of fluoride, it was introduced into dentistry in 1940 and since then, it is being added to various consumer products. Water fluoridation is the most successfully adopted method (5-7). Fluoride delivery methods and related sources of dietary fluoride are:
Fluoridated water, beverages, and tea. Water is an important media for fluoride delivery. Fluoride exists either naturally or added during water fluoridation (8-11). Recommended optimal level of fluoride in drinking water is 0.7 mg/l; however, fluoride concentration in water varies based on geographical areas. For instance, fluoride content in drinking waters of Pakistan shows a large variation that ranges from < 0.1 ppm to >3 ppm (12). Another study demonstrated that natural water from certain geographical areas (e.g. Punjab, Pakistan) contains fluoride concentration of up to 21 ppm (13). Therefore, the data suggests a clear need for the careful selection of fluoride products to avoid toxic effects of fluoride (12).
Fluoride containing dentifrices such as tooth-paste, professionally used varnishes/gels, and mouth rinses. Fluoride tooth pastes are available as low fluoride (500 ppm), standard fluoride (1100-1500 ppm) and high fluoride toothpaste (>1500 ppm). Fluoride is added in different forms to toothpastes and mouth rinses such as sodium fluoride (NaF), mono-fluorophosphate (MFP), or stannous fluoride (SnF) (14, 15). The mouth rinses have an advantage over toothpastes because of their low viscosity that results in better delivery to least accessible areas of the teeth such as pits and fissures and interproximal areas (7, 16, 17).
Fluoridated milk including formula milk for infants and table salt fluoridation (7, 17). Fluoride delivery through milk fluoridation is not efficient as compared to other fluoride delivery methods. This is due to fluoride’s tendency to form insoluble complexes with calcium, which makes fluoride absorption difficult.
a) Fluoride releasing dental materials. Some of these biomaterials not only release fluoride but also have a property to recharge them with fluoride once fluoride from other sources is available into the oral cavity. Commonly available fluoride releasing mate-rials are glass ionomer cements (GICs), dental resin composites, compomers (modified dental composites), silicate cement, giomers, elastomeric rings and fluoride delivering mucoadhesive devices (18-21).
The suggestive mechanisms for the beneficial effects of fluoride include following mechanisms (22).
a) Fluorapatite (FA) formation on tooth surface by substitution of hydroxyl with fluoride ion in the hydroxyapatite (HA). FA decreases the solubility of HA and makes the dental enamel more resistant to dissolution from the acid that is produced by the pathogenic bacteria.
b) Inhibition of enzyme enolase, which results in a reduction in lactic acid formation.
Even though the beneficial effects of fluoride on dental health are well-established, it is very crucial to regulate the amount of fluoride intake. In addition to naturally or artificially fluoridated water, fluoride is available in a number of dental products and materials as mentioned earlier. Therefore, fluoride consumption at elevated levels may lead to a range of detrimental effects. The aim of this review is to highlight the potential adverse effects of fluoride overdose and poorly understood toxicity. In addition, the related clinical significance of fluoride overdose and toxicity has been discussed.
Fluoride absorption, metabolism, and excretion
Fluoride is consumed commonly through the oral cavity and absorbed through the gastrointestinal tract. Other less common routes of fluoride absorp-tion are inhalation and dermal absorption (23, 24). The principal sources of fluoride are fluoridated water and fluoride containing dental products.
The absorption of fluoride starts through the stomach and upper part of the small intestine (1, 25). In the stomach, the absorption of fluoride depends on the pH of the stomach while in the small intestine fluoride absorption is pH independent and absorp-tion is through facilitated diffusion (26). Fluoride absorption depends on numerous factors such as stomach pH, the chemical formula of consumed fluoride, presence of food in the stomach, interaction with other food ingredients present in gastrointestinal tract, aluminum, calcium, and magnesium compounds (23). The unabsorbed fluoride is defecated through feces while the absorbed fluoride is distributed rapidly through the circulation into the intracellular and extracellular fluids and is retained only in the mineralized tissues of the body.
The fluoride uptake by mineralized tissues is more efficient in growing children and progressively declines with age. Retention of fluoride in the mineralized tissues of the body is reversible; fluoride is released back slowly when the fluoride level in plasma falls (25, 27). Fluoride in the plasma is capable of crossing the placenta and is found in placental and fetal tissues. The placenta plays a regulatory role by the accumulation of excess fluoride, which protects the fetal tissues from excess fluoride intake (25). Absorbed fluoride is deposited from serum into mineralized tissues while the remaining is excreted primarily into the urine and to a lesser extent into feces, sweat, saliva, and breast milk. The excretion of fluoride through the urinary system depends upon several factors like plasma levels of fluoride, glomerular filtration rate (GFR), pH of the urine, and its flow (25, 28). The summary of the fluoride absorption, metabolism, and excretion is summarized in Figure 1.
An external file that holds a picture, illustration, etc.
Object name is IJBMS-20-841-g001.jpg
Figure 1
Summary of absorption, metabolism, and excretion of fluoride following oral intake
Toxic effects of fluoride
Excessive ingestion of fluoride may cause toxic and harmful effects. It is important to note that the major source of fluoride toxicity remains oral hygiene products. According to fluoride poisoning data collected by the American Association of Poison Control (AAPC), tooth paste ingestion remains the main source of toxicity followed by fluoride containing mouth washes and supplements (Table 1). The highest proportion (more than 80%) of the cases of fluoride toxicity was reported in children below the age of 6 (29).
Table 1
Percentage of reported cases of fluoride toxicity (29)
Cause of fluoride toxicity Percentage of cases
Toothpaste 68%
Mouth rinses 17%
Fluoride supplements 15%
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These reported toxicities are due to the fact that the swallowing reflex in children is not completely developed and fluoride toothpastes are flavored, which results in voluntary toothpaste swallowing (30). Alternatively, a variety of flavors added to toothpastes may inspire young children to ingest it. Chewing stick (miswak) is another option that is natural and there are no reports of fluoride toxicity from miswak (31). The optimum beneficial dose of fluoride and the fluoride minimal risk levels are summarized in Table 2. These given doses are based on limited data reported in the literature and even at lower than the mentioned doses there are reports of toxic and lethal effects.
Table 2
Summary of the important doses of fluoride (29, 30, 32)
Important doses of fluoride
Optimal dose of fluoride (for children & adults) 0.05 - 0.07 mg F/kg body weight
Toxic dose of fluoride (for children & adults) 5 mg F/kg body weight
Lethal dose of fluoride (children) 16 mg F/kg body weight
Lethal dose of fluoride (adults) 32 mg F/kg body weight
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The possible mechanisms of fluoride toxicity are (29):
(a) As the fluoride comes in contact with mois ture this results in the formation of hydrofluoric acid and this acid formation results in burning of tissues due to low pH.
(b) Inhibition of nerve impulse or nerve function is due to the fact that calcium forms chemical complexes with fluoride leading to hypocalcemia and ultimately results in inhibition of physiological nerve functioning.
(c) Cellular poisoning results due to inhibition of enzymes required for the physiological functioning of cells.
(d) Hypocalcemia and hyperkalemia result in elec-trolyte imbalance and eventually result in distur-bances in cardiac rhythm.
(e) Fluoride is one of the most reactive elements. In the case of a toxic amount of fluoride in the body, fluoride attacks oxygen and disrupt the metabolism resulting in the production of hydrogen peroxide as a product. In addition, fluoride results in excessive production of free radicles that disrupt the antioxidant formation (23).
The toxicity of fluoride due to excessive ingestion is classified into acute toxic effects and chronic effects (Figure 2).
An external file that holds a picture, illustration, etc.
Object name is IJBMS-20-841-g002.jpg
Figure 2
Classification of toxic effects due to excessive ingestion of fluoride
Acute toxic effects
Acute fluoride poisoning although occasionally reported, however, may be fatal. Acute fluoride toxicity usually occurs due to the accidental consumption of fluoride solution or fluoride salts wrongly perceived as sugar solution or powdered eggs (33). The symptoms of acute fluoride toxicity depend upon the type and chemical nature of the ingested compound, the age, and the elapsed time between exposure and the beginning of management (34). For instance, NaF is more toxic as it is more soluble and releases more amounts of fluoride compared to calcium fluoride (CaF) that is a less soluble compound (28). The acute toxic dose range is 5-8 mg/kg body weight. In the case of acute fluoride toxicity, one or a combination of the following symptoms such as gastric disturbances (nausea, vomiting occasionally with blood, abdominal pain, diarrhea, weakness, and hypocalcemia) are observed. These symptoms result in generalized or localized muscle tetany especially of hand and feet. In addition, hypotension, bronchospasm, fixed and dilated pupils, and hyperkalemia are also linked with fluoride toxicity, which may result in ventricular arrhythmias and cardiac arrest. Loss of body fluid contributes to an electrolyte imbalance, a state of hypovolemic shock, and decreased blood pressure. Acute fluoride poisoning may induce in some individuals a polyuria resembling diabetes insipidus, which may persist for days to months. In a few instances, the acute polyuric renal failure has terminated fatally (33). A progressive, mixed metabolic and respiratory acidosis may develop because of the failure of renal and respiratory systems, coma and convulsions terminating in death (28, 29).
Chronic toxic effects
Chronic toxicity of fluoride is more common than acute toxicity. The effects of chronic ingestion of fluoride depend not only on the duration and dose but also on several other factors such as nutritional status, renal function, and interactions with other trace elements (24, 28).
Dental fluorosis
The association between excessive ingestion of fluoride and dental mottling (fluorosis) was initially discovered over a century ago by Frederick Sumner McKay a practicing dentist in Colorado Springs area and G. V. Black (22). Dental fluorosis is the most sensitive and the earliest indicator of chronic fluoride toxicity (1). Although fluoride is an impor-tant element for caries prevention, the chronic intake of fluoride greater than 1 mg/l or 0.1 mg/kg daily during the period of tooth development interferes with the process of enamel and dentin formation and leads to dental fluorosis (1, 35, 36).
The mechanism of dental fluorosis is very complex and not fully understood. The excess amount of fluoride impedes normal enamel maturation and the dental enamel formed is hypomineralized with more surface and subsurface porosity in comparison with normal enamel. In dentine due to excessive fluoride during dentin formation, the dentinal tubules have an irregular distribution and the lumina of the tubules become narrow and disrupted (36, 37). Clinically, the appea-rance ranges from mild opaque white to brown mottling of enamel associated with pits and enamel fracture in both deciduous and permanent dentitions, and the lesions are generally symmetrical bilaterally (28, 38, 39). The severity of dental fluorosis not only depends on excessive consumption of fluoride but also on the timing and duration of excessive fluoride consumption, the plasma concentration of fluoride, type of fluoride consumed, renal function, and genetic factors (36).
Therefore, in order to prevent fluorosis the following measures should be instituted:
The fluoride level in the drinking water should be regulated between 0.5 to 1 ppm as suggested by the World Health Organization (5).
Low fluoride dentifrices (500 ppm) are indicated for children living in fluoridated areas (35).
Supervised brushing and a smear layer of low fluoride toothpaste should be applied on the brush (40).
Following these precautionary measurements, the chances of fluorosis and related lesions will be reduced.
Skeletal fluorosis
Chronic fluoride exposure at more than the recommended levels either by ingestion, inhalation, or a combination of both results in skeletal fluorosis. This condition is characterized by an increase in bone mass and density because of deposition of excess fluoride within the bone matrix (24). The primary phase of skeletal fluorosis is associated with symptoms such as sporadic pain, joints stiffness due to fluoride deposition with resultant difficulty in mobility, kyphosis of back bone, tingling sensation, muscle weakness, and fatigue. The advanced stage of skeletal fluorosis is linked with signs of arthritis and osteoporosis in long bones, spinal cord compression and calcification of ligaments with resulting neuro-logical defects and muscle wasting (41).
Radiographically, skeletal fluorosis may appear as osteosclerosis and calcification of ligaments (24, 27, 42, 43). The neurological symptoms that occur because of fluoride toxicity are due to abnormal bone outgrowths (1). Primary symptoms of skeletal fluorosis usually occur in fluoride doses greater than 4 mg/l. While the crippling skeletal fluorosis is rare and is associated with intake of water with fluoride level greater than 10 mg/l, it results in a remarkable limitation of joint movements, and deformities of major joints and spine leading to neurological problems (10, 27, 28). The severity of skeletal fluorosis depends on the amount of water intake, quality of water, renal disease, and dietary factors for instance calcium rich diet, which has a protective effect and prevents toxic effects of fluoride on bones (1, 27).
Renal effects
The kidney is the major organ that has a major role in fluoride excretion (50-60% excretion). It is the most commonly affected organ due to the uptake of fluoride within the kidney tubules (24). A prolonged exposure to concentrated fluoridated drinking water (8 ppm or higher) has been reported to increase renal diseases due to structural and functional changes in the kidney (23, 41). Structural changes due to fluoride toxicity include swelling, degeneration of tubular epithelium, fibrosis, atrophy of glomeruli, and tubular necrosis. All these structural changes result in increased serum creatinine and urea nitrogen (41).
Gastrointestinal tract (GIT)
High concentration fluoride reacts chemically with gastric acid (hydrochloric acid) in the stomach to form hydrogen fluoride. Gastric mucosa is irritated by this excessive formation of hydrofluoric acid (6). Non-ulcer dyspeptic symptoms have been observed in populations consuming high fluoride concentration (3.2 ppm) water. Animal studies reveal that fluoride has a potential to stimulate the secretion of gastric acids, diminish blood supply away from the stomach lining, and may result in the death of epithelial cells of GIT. The fluoride ingestion required to elicit such responses in humans could not be documented. For instance, adverse GIT symptoms are common in areas of endemic fluorosis where nutrition is generally poor or the individuals have gastrointestinal hypersensitivities (27).
Central nervous system
Fluoride can cross the blood brain barrier prior to birth and has been reported to affect mental development, learning disorders, and decrease intelligence and hyperactivity in children. In fetal brain, the levels of the neurotransmitters and the number of receptors are also reported to decrease in endemic fluoride areas (41). In addition, fluoride results in degenerative changes in neural tissues. These changes might account for neurological alterations (such as numbness, pain, and muscle spasm) and decreased memory and learning ability of the experimental animals (44). These neurological changes due to fluoride toxicity may be exacerbated by the deficiency of some other essential elements, for example, iodine or toxicity of other neurotoxic pollutants (41). A few studies have suggested that ingestion of dietary fluoride influences the intellectual capabilities of children. Children inges-ting high levels of fluoride (>2 mg/l) scored more poorly on intelligence tests compared with children ingesting lower amounts of fluoride (<1 mg/l). In addition, fluoride influences the reaction times and visuospatial capabilities, hence lowering the IQ scores during the time sensitive tests (27).
Fetal defects
Fluoride crosses the placental barrier and incorporates into the fetal tissues. This may lead to teratogenic effects. In addition, elevated fluoride exposures may result in disturbances in bone ossification (6). The genotoxic effects of fluoride are due to an aberration in chromosomes (41). These findings are suggestive of toxic effects of fluoride to fetal tissues hence extreme care required while prescribing to pregnant women. Any accidental ingestion of high amounts of dentifrices can lead to harmful effects on the fetus (45). The fetal brain is also susceptible to fluoride poisoning. Fluoride effects the fetal brain tissues and results in remark-able neurological damage, neuronal degeneration, and reduced secretion of neurotransmitters such as norepinephrine. In addition, fluoride disrupts the secretion of certain neurotransmitters and nerve cell receptors and results in neural dysplasia (46).
Table 3
Summary of treatment protocol for fluoride overdose (48)
Fluoride/kilogram body weight* Treatment
< 5.0 mg/kg
1.Oral administration of soluble calcium (milk) to relieve GIT symptoms
2.Observe for a few hours
3.Induced vomiting not required
> 5 mg/kg
1.Require hospital admission
2.Use emetic to empty the stomach. However, if the patient has depressed gag reflex for instance in the case of babies (<6 months old), Down’s syndrome, or mental retardation, endotracheal intubation should be performed before gastric lavage.
3.Oral administration of soluble calcium (e.g. milk, calcium lactate, or gluconate solution).
4. Keep under observation for a few hours.
>15 mg/kg
1.Immediate hospital admission
2.Immediate stomach emptying and gastric lavage
3.Begin cardiac monitoring and be prepared for cardiac arrhythmias
4.Intravenous administration of 10% calcium gluconate solution
5.Electrolytes (calcium and potassium) should be monitored and corrected as required
6.Maintenance of adequate urine output by diuretics if required
7.General supportive measures for shock
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*Average weight/age: 1–2 years= 10 kg; 2–4 years= 15 kg; 4–6 years= 20 kg; 6–8 years= 23 kg
Miscellaneous effects
Besides the adverse effects mentioned earlier, excessive fluoride ingestion affects multiple body systems with disturbances in respiratory functions, the gastrointestinal system, liver, and excretory system, causes hematological manifestations including red blood cell deformation, neurological manifestations such as depression, abnormal sensations in toes and fingers, excessive thirst, headache, and reduction in immune response (24). Key harmful effects are summarized below:
I. Fluoride level (greater than 3 ppm) affects the reproductive system resulting in a decrease in mean birth rates (6). In animal models, the male reproductive system is more susceptible to chronic fluoride toxicity because of the production of free radicals that result in histological and structural changes in the reproductive system that disturb sperm production and sexual functions (41, 47).
II. Higher fluoride level affects thyroid function due to rise in calcitonin activity. Excess fluoride also results in decreased glucose tolerance (1, 6).
III. Chronic fluoride toxicity adversely affects both cell mediated and humoral immunity, for instance, it destroys the white cell energy reservoirs that are required for phagocytosis of foreign agents and by inhibition of antibody formation (41).
All the above-reported toxicities may also be a result of the presence of heavy metals and other substances present in fluoridation chemicals added during fluoridation of water or related dental products. Therefore, it is important to purify fluoride from heavy metals and any impurities before adding it to the drinking water or other fluoride containing products (22).
Basis of the treatment
The management of fluoride toxicity consists of: i. The fluoride toxicity case must be evaluated immediately for the type and amount of ingested fluoride. The minimum optimal dose likely to cause toxicity and requiring therapeutic intervention has been set at 5 mg/kg of body weight. Regarding the chemical type, NaF and hydrogen fluoride are more soluble, resulting in faster absorption. On the other hand, CaF and magnesium fluoride are the less soluble fluoride compounds and absorption may be relatively slow (29).
ii. Milk has a proven role in reducing the absorption of fluoride (rich in calcium which has a fluoride binding effect). Further absorption can be minimized using, calcium gluconate, calcium lactate, or milk of magnesia and aluminum, which form insoluble complexes that decrease the absorption of fluoride. Therefore, calcium containing compounds are used in acute fluoride toxicity (25,40). Gastric lavage is recommended instead of an emetic agent because of the danger of aspiration of gastric contents and burning of the esophagus due to hydrofluoric acid present in the stomach (40).
iii. Alkalization of the body fluids results in the faster removal of the ingested fluoride from the body fluids because of the faster flux of fluoride out of the cells and its elimination into the urine (25).
iv. Supporting the vital signs by oxygen therapy, artificial respiration, and hemodialysis are highly recommended. These measures should be continued until the stabilization of vital signs and serum chemistry (25).
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Conclusion
The beneficial role of fluoride for the maintenance of good oral health has been known for many decades and strongly evidenced by scientific research. However, it must be emphasized that tooth decay (dental caries) is not caused by fluoride deficiency and fluoride supplementation will never reverse the active or gross carious lesions. Since the level of safety of fluoride is low, products that contain a high level of fluoride should be stored and used according to the recommend-dation and should be monitored by a qualified dental professional especially in children and pregnant women. In children, the swallowing reflex is not very well developed and the fluoride containing dental products are flavored hence increasing the possibility of a child to consume an excessive dose of fluoride. In areas with high fluoride levels in the drinking water, alternative dental products with low fluoride levels should be prescribed and monitored.
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Acknowledgment
We are grateful to Prof SM Kefi Iqbal, Dean Sindh Institute of Oral Health Sciences, Jinnah Sindh Medical University, Karachi, Pakistan for his valuable suggestions and guidance for the completion of this manuscript. This work did not receive any financial support.
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Conflicts of interest
The authors declared no conflicts of interest for conducting this research.
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| biology | 2862 | https://sv.wikipedia.org/wiki/Fluor | Fluor | Fluor (latin: Fluorum) är ett icke-metalliskt grundämne med atomnummer 9. Den har kemiskt tecken F och tillhör gruppen halogener. Fluor bildar en tvåatomig molekyl med sig själv i grundform, vilket resulterar i F2, fluorgas. Fluor är det mest reaktiva och elektronegativa av alla grundämnen. Till exempel antänds kolväten spontant och brinner i fluorgas till skillnad från förbränning av kolväten i luftens syre som kräver ett tillskott av energi för antändning - till exempel genom en gnista. Således är fluorgas mycket farligt – farligare än andra halogener såsom den giftiga klorgasen.
På grund av sin höga reaktivitet förekommer fluor inte fritt i naturen, utan alltid kemiskt bundet, vanligen som fluorid. Fluor är det 13:e vanligaste grundämnet på jordskorpan.
Fluor har högst elektronegativitet samt liten atomradie vilket ger unika egenskaper till många av dess föreningar. Till exempel bygger diffusionsmetoden för anrikning av uran på flyktigheten hos uranhexafluorid. Dessutom är kol–fluor-bindningen en av de starkaste bindningarna i organisk kemi. Detta leder till den höga stabiliteten och härdigheten hos fluororganiska föreningar, såsom (poly)tetrafluoreten (Teflon) och perfluoroktansulfonsyra. Kol–fluor-bindningens induktiva effekter leder till styrkan i många fluorhaltiga syror, såsom trifluormetansulfonsyra och trifluoretansyra. I mediciner substitueras ofta organiska föreningar med fluor på biologiskt reaktiva platser, för att förhindra deras metabolism och förlänga deras livslängd.
Karaktäristik
F2 är en frätande ljusgul eller brun gas och är ett kraftigt oxidationsmedel. Fluor är det mest reaktiva och mest elektronegativa av alla grundämnen på den klassiska Pauling-skalan (4,0), och bildar raskt föreningar med de flesta andra grundämnen. Fluor har ett oxidationstal på -1, förutom när den binder till en annan fluoratom i F2, då oxidationstalet är 0. Fluor bildar till och med föreningar med ädelgaserna argon, krypton, xenon och radon. Till och med i mörka, svala förhållanden, reagerar fluor explosivt med väte. Reaktionen med väte sker även vid extremt låga temperaturer, med flytande väte och fast fluor. Fluor är så pass reaktivt att metaller, och även vatten, samt andra substanser, brinner med en stark låga i en ström av fluor. I fuktig luft reagerar fluor med vatten och bildar den farliga gasen vätefluorid.
Fluorider är föreningar med fluor och en positivt laddad partikel. Dessa förekommer oftast som kristallina, joniska salter. Fluorföreningar med metaller är bland de mest stabila salterna.
Vätefluorid är en svag syra när den löses i vatten, men är ändock mycket frätande och angriper glas. Således bildar fluorider av alkalimetaller basiska lösningar. Till exempel, en enmolarig (1 mol/dm3) lösning av natriumfluorid i vatten har ett pH på 8,59, jämfört med en enmolarig lösning natriumhydroxid, en stark bas, som har ett pH på 14,00.
Isotoper
Trots att fluor har flera olika isotoper, är endast en av dessa (19F) stabil, och de övriga har kort halveringstid och återfinns ej naturligt. Fluor är således ett mononuklidiskt grundämne.
Nukliden 18F är radionukliden av fluor med längst halveringstid (ungefär 110 minuter = nästan 2 timmar), och är kommersiellt en viktig källa för positroner, vilket utnyttjas i positronemissionstomografi.
Historia
Mineralet flusspat (även kallat fluorit), vilket huvudsakligen består av kalciumfluorid, nämndes år 1530 av Georgius Agricola för sin användning som fluss. Fluss används för att främja sammansmältning av metaller eller mineraler. Namnet fluor kan härledas därifrån då ”fluere” på latin betyder ”att flöda”. År 1670 upptäckte Henrich Schwanhard att glas etsas vid kontakt med flusspat som hade behandlats med en syra. Carl Wilhelm Scheele, och senare andra forskare såsom Humphry Davy, Caroline Menard, Gay-Lussac, Antoine Lavoisier och Louis Jacques Thénard, har alla experimenterat med fluorvätesyra, som lätt framställdes genom att behandla fluorit med koncentrerad svavelsyra.
På grund av sin extrema reaktivitet så isolerades inte fluorgas förrän många år efter igenkännandet av fluorit. Utvecklingen i att isolera fluorgas gick långsamt på grund av att det endast kunde framställas elektrolytiskt och även under kontrollerade förhållanden angriper gasen många material. År 1886 rapporterades det att Henri Moissan hade lyckats isolera fluorgas efter nästan 74 år av insatser av andra kemister. Framställningen av fluorgas med fluorvätesyra som utgångspunkt är ytterst farligt, och förblindade eller dödade ett flertal kemister i tidiga försök att isolera denna halogen. Dessa individer kom att kallas fluormartyrer (eng. fluorine martyrs). Moissan fick Nobelpriset i kemi år 1906 för sin upptäckt. Den första storskaliga framställningen påbörjades till stöd för Manhattanprojektet, där föreningen uranhexafluorid hade valts till den form av uran som skulle möjliggöra separationen av dess isotoper 235U och 238U. I Manhattanprojektet upptäckte man att UF6 bryts ned till UF4 och F2. Korrosionsproblemet orsakat av F2 löstes till slut genom att elektrolytiskt täcka all UF6 med nickel, vilket bildar nickeldifluorid som inte angrips av fluorgas. Leder och flexibla delar var gjorda av teflon, en då väldigt nyupptäckt plast som inte heller angrips av F2.
Framställning
Industriell framställning av fluorgas medför elektrolys av vätefluorid i närheten av kaliumfluorid. Denna metod är baserad på pionjärstudierna av Moissan (se ovan). Fluorgas bildas vid anoden och vätgas vid katoden. Under dessa förhållanden omvandlas kaliumfluorid till kaliumvätefluorid, vilket är det egentliga elektrolytet. Kaliumvätefluorid understödjer elektrolysen genom att kraftigt öka konduktiviteten i lösningen.
HF + KF → KHF2
2KHF2 → 2 KF + H2 + F2
Den vätefluorid som krävs för elektrolysen skaffas som en biprodukt till framställning av fosforsyra. Mineraler som innehåller fosfatjoner innehåller stora mängder fluorit. Vid behandling med svavelsyra släpper dessa mineraler ifrån sig vätefluorid:
CaF2 + H2SO4 → 2 HF + CaSO4
År 1986, under förberedelserna inför en konferens för att fira upptäckten av fluors 100-årsjubileum, upptäckte Karl Christe ett rent kemisk sätt att framställa fluor med hjälp av vattenfri HF, kaliummangan(IV)hexafluorid och antimonpentafluorid vid 150 °C:
2K2MnF6 + 4SbF5 → 4KSbF6 + 2MnF3 + 2F2
Trots att detta inte är praktisk syntes på stor skala, så demonstrerar denna rapport att elektrolys inte är det enda sättet att utvinna fluorgas på.
Användningsområden
Fluorgas, F2, används huvudsakligen för att framställa två föreningar med kommersiellt intresse; uranhexafluorid och svavelhexafluorid.
Industriellt användande av fluorföreningar
Atomärt och molekylärt fluor används för plasmaetsning i tillverkandet av halvledare, tillverkning av plattskärmar och tillverkning av MEMS (mikroelektromekaniska system). Xenondifluorid används också för det sistnämnda.
Fluorvätesyra används för att etsa glas i glödlampor och andra produkter.
Tetrafluoreten och perfluoroktansyra används direkt i tillverkningen av plaster med låg friktionskoefficient såsom (poly)tetrafluoreten (PTFE; teflon).
Användning inom tandvård och medicin
Oorganiska föreningar med fluor, såsom natriumfluorid, tenn(II)fluorid och natriummonofluorfosfat, används i tandkräm och fluorsköljningar för att förhindra karies. Fluorpensling är ytterligare en metod som används för att minska förekomst av hål i tänderna.
Fludrokortison (9α-fluokortisol) är en av de vanligaste mineralkortikoiderna, en typ av läkemedel som härmar aldosterons verkan.
Biologisk roll
Även om F2 är för reaktivt för att ha någon naturlig biologisk roll, används fluor i föreningar med biologisk aktivitet. I denna form är Fluor starkt giftigt och ger svåra hud- och lungskador. Fluor i form av fluorid förekommer hos människan främst inlagrat i ben och tänder i form av fluorapatit.
Naturligt förekommande fluororganiska föreningar är ovanliga. Fluoretansyra används dock som skydd mot växtätare av minst 40 olika växter i Australien, Brasilien och Afrika.
Enzymet adenosylfluoridsyntas katalyserar bildningen av 5'-deoxy-5'-fluoradenosin enligt följande reaktion:
S-adenosyl-L-metionin + fluorid 5'-deoxi-5'-fluoradenosin + L-metionin
Fluor är inte ett essentiellt näringsämne, men dess betydelse i att förhindra karies är välkänt. Detta sker till övervägande del lokalt, men innan 1981 ansågs det i första hand vara enteralt (via matspjälkningssystemet).
Fluor har i djurförsök visat sig vara nödvändigt för normal tillväxt, men fluorbrist har inte kunnat påvisas hos människa.
Försiktighetsåtgärder
Fluorgas
F2 (fluorgas), är ett mycket giftigt, frätande oxidationsmedel, som kan antända organiska ämnen. Fluorgas har en karaktäristisk stickande lukt som kan upptäckas i koncentrationer så låga som 20 ppb. Eftersom det är så reaktivt så måste alla konstruktionsmaterial väljas noga och alla metallytor måste passiviseras.
Fluoridjon
Fluoridjoner är giftiga: den dödliga dosen för natriumfluorid för en människa på 70 kg uppskattas vara 5-10 g.
Vätefluorid och fluorvätesyra
Vätefluorid och fluorvätesyra (vattenlösningen av vätefluorid) är mycket farliga, mycket farligare än det relaterade ämnet saltsyra, eftersom odissocierade HF-molekyler penetrerar skinnet och biologiska membran, vilket orsakar djupa och smärtsamma brännskador, där dock smärtupplevelsen kan vara fördröjd. Den fria fluoridjonen, som bildas när en vätefluoridmolekyl dissocieras, kan orsaka död på grund av arytmi. Brännsår större än 160 cm2 kan leda till hypokalcemi.
Fluororganiska föreningar
Fluororganiska föreningar förekommer inte vanligtvis i naturen. De kan vara ogiftiga, som oktadekafluornaftalen, eller mycket giftiga som perfluorisobuten och fluoretansyra. Många läkemedel är fluororganiska föreningar, såsom den cancerförebyggande fluoruracil. Perfluoroktansulfonsyra är en långlivad organisk förorening.
Fluorets ursprung
Fluorets ursprung har i många år varit okänt. Ett forskarteam på Lunds universitet har undersökt det ljus som en stjärna sänder ut. Vilka grundämnen stjärnan innehåller har de kunnat räkna ut genom att jämföra ljusets våglängd. Innan stjärnan till slut brinner ut blir den en nebulosa och fluoren slungas ut och blandas upp med olika sorters gaser i nebulosans yttre. Nya stjärnor skapas när stjärnan dör. Fluoret fortsätter därmed sin vandring i det intergalaktiskt kretsloppet. Forskningen har publicerats i tidskriften Astrophysical Journal Letters. I framtiden skall forskarna undersöka om fluor kan skapas i andra sorters stjärnor, innan de blir röda jättar.
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Home / Blog / Five Breathing Tips for Open Water Swimming Five Breathing Tips for Open Water Swimming June 03, 2021 | 5 min read Link Copied Open water races require an extra level of effort. You’re battling waves, wind, currents, sun, and the flailing arms of a hundred other swimmers. With all these added stressors, being able to breathe consistently is more important than ever. But, breathing while open water swimming comes with its complications. If you’ve never swum outside the lane ropes of your local pool, you might be a little surprised by how different open water swimming is. The water is serene and calm at times, but it can also be stormy, unpredictable, and wavy. Here are five breathing tips to help you thrive during your next triathlon or open water swim race. Learn to breathe bilaterally. Bilateral breathing—or breathing on both sides—is one skill most swimmers learn at a young age. But, as years pass, many swimmers revert to breathing to one side. While it’s a good skill for all swimmers to feel comfortable breathing bilaterally, it’s especially beneficial for open water swimming. In open water races, some variables will force you to breathe on both sides. You might be next to a group of swimmers on one side, so you need to turn to the other side to avoid getting splashed whenever you come up for air. In other races, boats will come by, and you’ll need to breathe on the opposite side to avoid inhaling a swell. Additionally, by turning to both sides to breathe, you’ll get a better sense of the racers around you. Just because it’s essential to know how to breathe to both sides doesn’t mean you need to breathe every third stroke. There’s some debate over how often long-distance swimmers should breathe, but swimmers need to find the breathing pattern that’s right for them. Maybe it’s every third stroke or second or alternating between the two—as long as you’re getting the air you need to swim comfortably and smoothly. Try hypoxic breathing. The first 200 meters of any open water race or triathlon is always intense. The adrenaline and excitement levels are high. There will be high adrenaline levels, there will be flailing arms, there will be excessive splashing, and there won’t be many opportunities to breathe. Hypoxic breathing/training is a technique to help you get used to going further on fewer breaths. The best way to practice this is to find a section of open water that equates to around 50 meters. Swim the distance once, breathing every three strokes. Next, breathe once every five strokes. Then, every seven strokes. Eventually, try breathing once for the entire 50 meters. Work this drill into your triathlon or open water swim training. After a bit of practice, you’ll be ready to weather the first few minutes of your race, even if you can’t take as many breaths as you’d like. Techniques for breathing in choppy water. What makes open water so unique is its unpredictability. On race day, the water could be calm, peaceful, and glass-like; it could also be windy, choppy, and have the makings of a typhoon. It’s essential to know a few techniques to help get a full breath of air, no matter which scenario you face. Look to the sky. To remedy waves lapping into your mouth, turn your body slightly further than you usually would during a breath and look towards the sky. You shouldn’t completely turn on your back, but bring your shoulder back more and point your eyes and mouth up to make sure you inhale a good amount of air. Breathe in quickly. Whether the water is choppy or not, it’s always a good idea not to spend too much time on your side. When the conditions are stormy, it’s even more important to take a quick breath to minimize the potential of gulping in water. Lift your head slightly. Typically, you should always try to keep your head in line with the rest of your body. But desperate times call for clean breaths. When waves are high, lift your head slightly above the water, get a quick breath in, then return to your stroke. While most races won’t let you swim in extreme weather, they will continue in less-than-ideal situations. These tips should help you succeed, regardless of the conditions you’re facing. Practice creates confidence. Breathing techniques are mainly about confidence. When you’re swimming in open water and take in a mouthful of water, it can be scary for swimmers at any level. When you can’t breathe, you start to panic, which can lead to hyperventilation. Hyperventilation can stop even the most confident open water swimmer and force them to tread water or even pull out from a race. That’s why an essential way to get used to breathing in open water is to practice. Most open water is often a lot colder than your average pool, so you need to get your body used to the water before you start swimming. During your first few sessions in a lake or ocean, start by submerging your body entirely in a shallow area and splashing your face. This is also an excellent time to test out your wetsuit. Wetsuits can be restricting on your diaphragm, so it’s best to get a feel for what it’s like to breathe with one on in colder temperatures. Start by swimming a few hundred meters in a shallow area. Be careful not to breathe too much or too quickly; this can cause an imbalance of oxygen molecules in your lungs and lead to dizziness. If you ever find yourself hyperventilating during a race or workout, try slowing down and breathing every four or five strokes. It might seem counterintuitive to breathe less, but it helps you get your breathing back on track. Simulate Open Water Conditions in the Pool If you are restricted to only pool training before your race, consider mimicking open water race conditions. Grab a couple of friends, and line up two or three abreast and two deep. When you practice swimming in close quarters with other swimmers, the water will be choppy, just like open water. If you’re able to, another option is to remove lane lines and drop an empty gallon jug (attached to a weight) in the pool under the flags. You can practice racing your friends to the jug and turning around it as if it’s a buoy. You might be confident about breathing in the pool, but breathing in open water has its challenges. By practicing these skills, you’ll be able to power on during workouts and races, even when the water conditions are less than ideal. Open Water Swimming Triathlon FREE PERSONALIZED SWIM PLAN Take this 10 second quiz to find a free plan that matches your goals. Get Yours
Home / Blog / Five Breathing Tips for Open Water Swimming Five Breathing Tips for Open Water Swimming June 03, 2021 | 5 min read Link Copied Open water races require an extra level of effort. You’re battling waves, wind, currents, sun, and the flailing arms of a hundred other swimmers. With all these added stressors, being able to breathe consistently is more important than ever. But, breathing while open water swimming comes with its complications. If you’ve never swum outside the lane ropes of your local pool, you might be a little surprised by how different open water swimming is. The water is serene and calm at times, but it can also be stormy, unpredictable, and wavy. Here are five breathing tips to help you thrive during your next triathlon or open water swim race. Learn to breathe bilaterally. Bilateral breathing—or breathing on both sides—is one skill most swimmers learn at a young age. But, as years pass, many swimmers revert to breathing to one side. While it’s a good skill for all swimmers to feel comfortable breathing bilaterally, it’s especially beneficial for open water swimming. In open water races, some variables will force you to breathe on both sides. You might be next to a group of swimmers on one side, so you need to turn to the other side to avoid getting splashed whenever you come up for air. In other races, boats will come by, and you’ll need to breathe on the opposite side to avoid inhaling a swell. Additionally, by turning to both sides to breathe, you’ll get a better sense of the racers around you. Just because it’s essential to know how to breathe to both sides doesn’t mean you need to breathe every third stroke. There’s some debate over how often long-distance swimmers should breathe, but swimmers need to find the breathing pattern that’s right for them. Maybe it’s every third stroke or second or alternating between the two—as long as you’re getting the air you need to swim comfortably and smoothly. Try hypoxic breathing. The first 200 meters of any open water race or triathlon is always intense. The adrenaline and excitement levels are high. There will be high adrenaline levels, there will be flailing arms, there will be excessive splashing, and there won’t be many opportunities to breathe. Hypoxic breathing/training is a technique to help you get used to going further on fewer breaths. The best way to practice this is to find a section of open water that equates to around 50 meters. Swim the distance once, breathing every three strokes. Next, breathe once every five strokes. Then, every seven strokes. Eventually, try breathing once for the entire 50 meters. Work this drill into your triathlon or open water swim training. After a bit of practice, you’ll be ready to weather the first few minutes of your race, even if you can’t take as many breaths as you’d like. Techniques for breathing in choppy water. What makes open water so unique is its unpredictability. On race day, the water could be calm, peaceful, and glass-like; it could also be windy, choppy, and have the makings of a typhoon. It’s essential to know a few techniques to help get a full breath of air, no matter which scenario you face. Look to the sky. To remedy waves lapping into your mouth, turn your body slightly further than you usually would during a breath and look towards the sky. You shouldn’t completely turn on your back, but bring your shoulder back more and point your eyes and mouth up to make sure you inhale a good amount of air. Breathe in quickly. Whether the water is choppy or not, it’s always a good idea not to spend too much time on your side. When the conditions are stormy, it’s even more important to take a quick breath to minimize the potential of gulping in water. Lift your head slightly. Typically, you should always try to keep your head in line with the rest of your body. But desperate times call for clean breaths. When waves are high, lift your head slightly above the water, get a quick breath in, then return to your stroke. While most races won’t let you swim in extreme weather, they will continue in less-than-ideal situations. These tips should help you succeed, regardless of the conditions you’re facing. Practice creates confidence. Breathing techniques are mainly about confidence. When you’re swimming in open water and take in a mouthful of water, it can be scary for swimmers at any level. When you can’t breathe, you start to panic, which can lead to hyperventilation. Hyperventilation can stop even the most confident open water swimmer and force them to tread water or even pull out from a race. That’s why an essential way to get used to breathing in open water is to practice. Most open water is often a lot colder than your average pool, so you need to get your body used to the water before you start swimming. During your first few sessions in a lake or ocean, start by submerging your body entirely in a shallow area and splashing your face. This is also an excellent time to test out your wetsuit. Wetsuits can be restricting on your diaphragm, so it’s best to get a feel for what it’s like to breathe with one on in colder temperatures. Start by swimming a few hundred meters in a shallow area. Be careful not to breathe too much or too quickly; this can cause an imbalance of oxygen molecules in your lungs and lead to dizziness. If you ever find yourself hyperventilating during a race or workout, try slowing down and breathing every four or five strokes. It might seem counterintuitive to breathe less, but it helps you get your breathing back on track. Simulate Open Water Conditions in the Pool If you are restricted to only pool training before your race, consider mimicking open water race conditions. Grab a couple of friends, and line up two or three abreast and two deep. When you practice swimming in close quarters with other swimmers, the water will be choppy, just like open water. If you’re able to, another option is to remove lane lines and drop an empty gallon jug (attached to a weight) in the pool under the flags. You can practice racing your friends to the jug and turning around it as if it’s a buoy. You might be confident about breathing in the pool, but breathing in open water has its challenges. By practicing these skills, you’ll be able to power on during workouts and races, even when the water conditions are less than ideal. Open Water Swimming Triathlon
Open water races require an extra level of effort. You’re battling waves, wind, currents, sun, and the flailing arms of a hundred other swimmers. With all these added stressors, being able to breathe consistently is more important than ever. But, breathing while open water swimming comes with its complications.
If you’ve never swum outside the lane ropes of your local pool, you might be a little surprised by how different open water swimming is. The water is serene and calm at times, but it can also be stormy, unpredictable, and wavy.
Bilateral breathing—or breathing on both sides—is one skill most swimmers learn at a young age. But, as years pass, many swimmers revert to breathing to one side. While it’s a good skill for all swimmers to feel comfortable breathing bilaterally, it’s especially beneficial for open water swimming.
In open water races, some variables will force you to breathe on both sides. You might be next to a group of swimmers on one side, so you need to turn to the other side to avoid getting splashed whenever you come up for air. In other races, boats will come by, and you’ll need to breathe on the opposite side to avoid inhaling a swell. Additionally, by turning to both sides to breathe, you’ll get a better sense of the racers around you.
Just because it’s essential to know how to breathe to both sides doesn’t mean you need to breathe every third stroke. There’s some debate over how often long-distance swimmers should breathe, but swimmers need to find the breathing pattern that’s right for them. Maybe it’s every third stroke or second or alternating between the two—as long as you’re getting the air you need to swim comfortably and smoothly.
The first 200 meters of any open water race or triathlon is always intense. The adrenaline and excitement levels are high. There will be high adrenaline levels, there will be flailing arms, there will be excessive splashing, and there won’t be many opportunities to breathe. Hypoxic breathing/training is a technique to help you get used to going further on fewer breaths.
The best way to practice this is to find a section of open water that equates to around 50 meters. Swim the distance once, breathing every three strokes. Next, breathe once every five strokes. Then, every seven strokes. Eventually, try breathing once for the entire 50 meters.
Work this drill into your triathlon or open water swim training. After a bit of practice, you’ll be ready to weather the first few minutes of your race, even if you can’t take as many breaths as you’d like.
What makes open water so unique is its unpredictability. On race day, the water could be calm, peaceful, and glass-like; it could also be windy, choppy, and have the makings of a typhoon. It’s essential to know a few techniques to help get a full breath of air, no matter which scenario you face.
Look to the sky. To remedy waves lapping into your mouth, turn your body slightly further than you usually would during a breath and look towards the sky. You shouldn’t completely turn on your back, but bring your shoulder back more and point your eyes and mouth up to make sure you inhale a good amount of air.
Breathe in quickly. Whether the water is choppy or not, it’s always a good idea not to spend too much time on your side. When the conditions are stormy, it’s even more important to take a quick breath to minimize the potential of gulping in water.
Lift your head slightly. Typically, you should always try to keep your head in line with the rest of your body. But desperate times call for clean breaths. When waves are high, lift your head slightly above the water, get a quick breath in, then return to your stroke.
While most races won’t let you swim in extreme weather, they will continue in less-than-ideal situations. These tips should help you succeed, regardless of the conditions you’re facing.
Breathing techniques are mainly about confidence. When you’re swimming in open water and take in a mouthful of water, it can be scary for swimmers at any level. When you can’t breathe, you start to panic, which can lead to hyperventilation. Hyperventilation can stop even the most confident open water swimmer and force them to tread water or even pull out from a race. That’s why an essential way to get used to breathing in open water is to practice.
Breathing techniques are mainly about confidence. When you’re swimming in open water and take in a mouthful of water, it can be scary for swimmers at any level.
Most open water is often a lot colder than your average pool, so you need to get your body used to the water before you start swimming. During your first few sessions in a lake or ocean, start by submerging your body entirely in a shallow area and splashing your face. This is also an excellent time to test out your wetsuit. Wetsuits can be restricting on your diaphragm, so it’s best to get a feel for what it’s like to breathe with one on in colder temperatures.
Start by swimming a few hundred meters in a shallow area. Be careful not to breathe too much or too quickly; this can cause an imbalance of oxygen molecules in your lungs and lead to dizziness.
If you ever find yourself hyperventilating during a race or workout, try slowing down and breathing every four or five strokes. It might seem counterintuitive to breathe less, but it helps you get your breathing back on track.
If you are restricted to only pool training before your race, consider mimicking open water race conditions. Grab a couple of friends, and line up two or three abreast and two deep. When you practice swimming in close quarters with other swimmers, the water will be choppy, just like open water. If you’re able to, another option is to remove lane lines and drop an empty gallon jug (attached to a weight) in the pool under the flags. You can practice racing your friends to the jug and turning around it as if it’s a buoy.
You might be confident about breathing in the pool, but breathing in open water has its challenges. By practicing these skills, you’ll be able to power on during workouts and races, even when the water conditions are less than ideal.
FREE PERSONALIZED SWIM PLAN Take this 10 second quiz to find a free plan that matches your goals. Get Yours
FREE PERSONALIZED SWIM PLAN Take this 10 second quiz to find a free plan that matches your goals. Get Yours
FREE PERSONALIZED SWIM PLAN Take this 10 second quiz to find a free plan that matches your goals. Get Yours
FREE PERSONALIZED SWIM PLAN Take this 10 second quiz to find a free plan that matches your goals. Get Yours
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Learn More Goggles Premium Workouts & Plans Blog Custom Workout Builder Triathlon Open Water Swim Tracker Swim Tracking Heart Rate Reviews FAQ About Us Our Story Sustainability Careers Media & Press Ambassador Inquires Dealers & Distributors Accessibility Support Support Center Shipping Returns Replacement Parts Warranty Terms and Conditions Privacy Policy Contact Us
Goggles Premium Workouts & Plans Blog Custom Workout Builder Triathlon Open Water Swim Tracker Swim Tracking Heart Rate Reviews FAQ | biology | 988 | https://no.wikipedia.org/wiki/Sv%C3%B8mming | Svømming | Svømming er betegnelsen på hvordan mennesker og andre levende skapninger tar seg frem i vann. Svømming og bevegelse i vann kan brukes som en effektiv forflytning, i forbindelse med matauk, nedkjøling, vask, mosjon og rekreasjon. Svømming kan være livreddende der vann er en utvei ved fare og å kunne svømme kan være livreddende. Evnen til å svømme blir gjerne vurdert ut fra fart eller utholdenhet og konkurransesvømming foregår gjerne i et svømmeanlegg. Svømming nyttes som rekreasjon av en rekke ulike dyr, ikke minst av mennesker.
Konkurransesvømming
Svømming er en av verdens største sporter. Svømming er teknisk sett i hovedsak en individuell sport, der formålet er å bevege seg over ulike distanser i vann på kortest mulig tid. Det er flere ulike teknikker som kan nyttes i konkurranser, og konkurransesvømming er regulert i et internasjonalt regelverk bestemt av Federation Internationale de Natation Amateur (FINA). Svømming er først og fremst en utholdenhetsidrett, men hastigheten avhenger også av styrke i armer og bein, smidighet og koordinasjon.
Disipliner
Det konkurreres i følgende disipliner:
Medley (individuell og lagmedley)
Butterfly
Rygg
Bryst
Crawl (fristil)
Stafettøvelser
Svømming i åpent vann (sjøsvømming/havsvømming)
Svømming som en del av en triatlon.
I medley, består distansen av like lange strekninger med hver av de fire hovedsvømmeartene. En individuell medley består først av butterfly, rygg, bryst og til slutt crawl. En lagmedley har rekkefølgen rygg, bryst, butterfly og crawl. I fristil kan svømmeren selv velge svømmeart og det er færre regler for hvordan teknikken utføres. Crawl er den raskeste svømmearten vi kjenner til idag, tett fulgt av butterfly, rygg og bryst.
I alle svømmeartene bortsett fra rygg starter svømmerne på startpall på land. I ryggsvømming starter svømmerne i vann med føttene mot bassengveggen mens armene holder i et håndtak. Rett før start heiser svømmeren seg delvis opp av vannet, og når starten går kaster svømmeren seg bakover og stuper baklengs inn i vannet. En konkurranse deles først inn i øvelser og deretter flere heat. I noen konkurranser avanserer de beste utøverne videre til semifinaler og finaler.
Konkurranse
Sortering av svømmere
I hver øvelse på et svømmestevne er svømmerne sortert etter påmeldingstid. Svømmere uten påmeldningstid svømmer i de første heatene, etterfulgt av de med svakest påmeldingstid. De beste svømmerne svømmer i de siste heatene.
I hvert heat er også svømmerne sortert etter tid. De raskeste (best påmeldingstid) svømmerne svømmer i de midterste banene. De to midterste banene har gjerne annen farge på banetauene, f.eks. gult. De med svakest påmeldings i hvert heat svømmer nærmest bassengkanten.
Banetau
Banetaua er merket med forskjellige farger, symmetrisk delt på midten. Det kan være forskjellige farger på banetaua i forskjellige svømmeanlegg, men hvor tauene er merket er ikke tilfeldig. De første 5 meterne fra bassengkanten og ut skal ha sin farge på banetauet. Det er også et merke i banetauet 15 meter fra kanten. Noen banetau har merke på midten av bassenget.
Grunnen til at tauene har et 15-metersmerke er for at det skal være lettere for dommerne å se om svømmerne svømmer for langt under vann. Det er nemlig ikke lov å svømme mer enn 15 meter under vann.
Formater
Det konkurreres ulike formater i svømming basert på lengden på bassenget. Det mest vanlige er meter (brukes internasjonalt), som igjen deles inn i kortbane 25 og langbane 50 meter. Verdensmesterskap holdes i 25 meter og 50 meter. Olympiader holdes i 50-metersbassenger. For at en ny rekord skal være gyldig må lengden på bassenget være i nøyaktig lengde innenfor 1 cm og måles ut ifra bestemte kriterier.
I USA er de fleste svømmebassengene i yards, da spesielt 25 yards. Men nye langbanebassenger som bygges er som oftest i 50 meter, og noen ganger med mulighet til å justere ned til 50 yards. I Storbritannia er det fortsatt noen gamle svømmehaller som er i yards. Alle formatene har sine egne rekorder og ofte er det ulike rekordholdere i de forskjellige.
Distanser
I svømming konkurreres det for det meste over distanser på 50, 100 og 200 meter/yards. De vanligste distansene med tilhørende svømmestil er:
Medley: 100 (ved kortbane), 200 og 400 yards/meter.
Butterfly: 50, 100 og 200 yards/meter.
Rygg: 50, 100 og 200 yards/meter.
Bryst 50, 100 og 200 yards/meter.
Fristil: 50, 100, 200, 400, 800, 1500 meter
Organisering
Mesteparten av konkuranssesvømmingen i Norge organiseres i regi av Norges Svømmeforbund (NSF) som er Norges 8. største særforbund. NSF er medlem av FINA som gjør at bare NSF har mulighet til å organisere svømmeidrett innenfor FINAs idrettslige jurisdiksjon i Norge. I 2009 hadde NSF 49 119 aktive fordelt på 252 medlemsklubber.
Svømmetrening
Ved svømmetrening deler svømmerne seg inn i baner avhengig av nivå. I Norge svømmer man høyrekjøring og beveger seg til venstre side på slutten av hver vending. Svømmetrening består i for det meste av intervalltrening. Hoveddelene av et svømmeprogram består som oftest av oppvarming, teknikk, hovedsett, andresett og utsvømming. Elitesvømmere svømmer mellom 1000 til 2500 km året, avhengig av treningsbakgrunn, og konkurransedistanse.
Rekorder
Alexander Dale Oen satte i 2008-sesongen en rekke norges- og nordiske rekorder i svømming.
Norske utøvere
De mest kjente utøverne i norsk svømming var per 2012:
Aleksander Hetland
Anne-Mari Gulbrandsen
Sara Nordenstam
Ingvild Snildal
Alexander Dale Oen
Kjente paralympiske svømmere er:
Andreas Bjørnstad
Sarah Louise Rung
Etikette i svømmeanlegg
Det finnes generelle regler for oppførsel i svømmehaller som følges i de fleste land verden over . Det er både for å unngå smitte og sykdom og for å hindre unødvendig irritasjon. Svømmehaller kan være organisert svært effektivt, mens andre kan være organisert ineffektivt som kan føre til farlige situasjoner og kapasitetsproblemer.
Valg av bane
Man velger bane ut ifra hastigheten man selv realistisk sett svømmer. Så lenge hastigheten er den samme, kan mange svømme etter hverandre i en bane. Det kan være lurt å si ifra om at du legger deg i banen hvis det kun en person som svømmer der.
En utøver som trener mot en konkurranse har ofte større behov for færre forbikjøringer både for å opprettholde riktig intervallhastighet og for å kunne konsentrere seg om å holde riktig teknikk under anstrengelse. Raskere svømmere bør hvis mulig gi tregere svømmere et forsprang før de selv begynner. En saktere svømmer bør hvis mulig ikke starte å svømme rett før en raskere svømmer kommer inn for å vende , på samme måte som å hoppe ut i vannet rett foran en som svømmer er uheldig.
Små barn har mindre evne til å beregne hastigheten til de som svømmer fort og kan derfor plutselig prøve å krysse banen på et uheldig tidspunkt. Foreldre bør være oppmerksom på dette og fortelle barna at det kan være farlig.
Svømmeretning
Når det er flere enn tre i banen bør man svømme i sirkel. I Norge, som store deler av verden svømmer man høyrekjøring og man beveger seg til venstre side på slutten av hver vending, slik at man vender på venstre side av T-merket.
Når du skal stoppe, svømmer du til høyre siden av T-merket i en av endene av lengden, hvor du stopper. Dette er viktig for at det ikke skal oppstå farlige situasjoner, særlig når svømmere skyter seg ut fra veggen etter vending. Ofte ved crawlsvømming og ryggsvømming har svømmeren mindre mulighet til å se foran seg. Stå inn i et av hjørnene dersom du oppholder deg i vendeområdet. Banetauene bør ikke sittes på, det gjør at de blir slakke og til slutt blir ødelagt.
Forbikjøring
Vent på riktig anledning, så rører man en gang ved foten til vedkommende for å signalisere at du vil svømme forbi. Den som blir svømt forbi tar hensyn, og holder godt til høyre, mens den som skal forbi holder til venstre. Det kan være en god idé å gjøre forbipasseringen ved en vending; den som skal forbi rører ved beinet før en vending, betyr det at forbipasseringen skal skje ved vendingen. Den som skal forbi svømmer mot venstre i vendingen, mens den som blir forbigått vender på høyre side og bør ofte vente litt før skyver ifra.
Hygiene
Mangel på hygiene kan føre til smitte via vannet. Økt konsentrasjon av mikroorganismer og smuss gjør at man må bruke mer klor i vannet, noe som fører til økt klorlukt, uttørring av huden og på sikt astma. Det anbefales at man dusjer naken, og ikke legger badebuksa ned på gulvet der vannet ledes mot avløpet, og ikke svømmer når man har diaré, da man kan spre sykdom via vannet. Ikke svelg vannet i svømmebassenget. Foreldre bør passe på at barn har vært på do før de går ut i bassenget. At barn tisser utenfor toalettet kan være et problem, og foreldre bør følge med barna når de er i den alderen.
Referanser
Eksterne lenker
Norges Svømmeforbund
FINA
USA Swimming | norwegian_bokmål | 0.650505 |
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It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances. Follow Us Donate Contact Us About Us Privacy Policy Terms of Use Editorial Policy © Copyright 2024 American Academy of Pediatrics. All rights reserved. Back to Top
Our Sponsors Log in | Register Menu Log in | Register Home Our Sponsors Ages & Stages Ages & Stages Ages and Stages Your Child’s Checkups Prenatal Decisions to Make Delivery and Beyond Baby (0-12 mos.) Bathing ＆ Skin Care Breastfeeding Crying ＆ Colic Diapers ＆ Clothing Formula Feeding Nutrition Preemie Sleep Teething ＆ Tooth Care Toddler 1-3yrs. Fitness Nutrition Toilet Training Preschool 3-5yrs Nutrition ＆ Fitness Grade School 5-12yrs. Fitness Nutrition Puberty Teen 12-18yrs. Dating ＆ Sex Fitness Nutrition Young Adult 18-21yrs. Healthy Living Healthy Living Healthy Living Nutrition Fitness Sports Oral Health Emotional Wellness Building Resilience Growing Healthy Sleep Safety & Prevention Safety & Prevention Safety and Prevention Immunizations At Home Medication Safety At Play On The Go All Around Family Life Family Life Family Life Medical Home Pediatric Specialists Family Dynamics Communication ＆ Discipline Types of Families Media Getting Involved in Your Community Power of Play Work ＆ Child Care Health Issues Health Issues Health Issues Conditions Abdominal ADHD Autism Chest ＆ Lungs Chronic Conditions Cleft ＆ Craniofacial COVID-19 Developmental Disabilities Ear, Nose ＆ Throat Emotional Problems Eyes Fever Flu From Insects or Animals Genitals and Urinary Tract Head, Neck ＆ Nervous System Heart Infections Learning Disabilities Seizures Sexually Transmitted Infections Skin Conditions Treatments Vaccine Preventable Diseases Injuries ＆ Emergencies Sports Injuries News News Tips & Tools Tips & Tools Tips and Tools AAP Family Media Plan Motor Delay Tool Physical Activity Checker Symptom Checker HealthyChildren Texting Program Newsletters HealthyChildren Magazine Webinars Ask The Pediatrician Find a Pediatrician Our Mission Our Mission Our Mission AAP in Action Medical Editor & Contributors Sponsors Sponsorship Opportunities Spread the Word Shop AAP Find a Pediatrician Safety & Prevention Immunizations All Around At Home At Play On The Go In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know Safety & Prevention Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Menu Log in | Register Home Our Sponsors Ages & Stages Ages & Stages Ages and Stages Your Child’s Checkups Prenatal Decisions to Make Delivery and Beyond Baby (0-12 mos.) Bathing ＆ Skin Care Breastfeeding Crying ＆ Colic Diapers ＆ Clothing Formula Feeding Nutrition Preemie Sleep Teething ＆ Tooth Care Toddler 1-3yrs. Fitness Nutrition Toilet Training Preschool 3-5yrs Nutrition ＆ Fitness Grade School 5-12yrs. Fitness Nutrition Puberty Teen 12-18yrs. Dating ＆ Sex Fitness Nutrition Young Adult 18-21yrs. Healthy Living Healthy Living Healthy Living Nutrition Fitness Sports Oral Health Emotional Wellness Building Resilience Growing Healthy Sleep Safety & Prevention Safety & Prevention Safety and Prevention Immunizations At Home Medication Safety At Play On The Go All Around Family Life Family Life Family Life Medical Home Pediatric Specialists Family Dynamics Communication ＆ Discipline Types of Families Media Getting Involved in Your Community Power of Play Work ＆ Child Care Health Issues Health Issues Health Issues Conditions Abdominal ADHD Autism Chest ＆ Lungs Chronic Conditions Cleft ＆ Craniofacial COVID-19 Developmental Disabilities Ear, Nose ＆ Throat Emotional Problems Eyes Fever Flu From Insects or Animals Genitals and Urinary Tract Head, Neck ＆ Nervous System Heart Infections Learning Disabilities Seizures Sexually Transmitted Infections Skin Conditions Treatments Vaccine Preventable Diseases Injuries ＆ Emergencies Sports Injuries News News Tips & Tools Tips & Tools Tips and Tools AAP Family Media Plan Motor Delay Tool Physical Activity Checker Symptom Checker HealthyChildren Texting Program Newsletters HealthyChildren Magazine Webinars Ask The Pediatrician Find a Pediatrician Our Mission Our Mission Our Mission AAP in Action Medical Editor & Contributors Sponsors Sponsorship Opportunities Spread the Word Shop AAP Find a Pediatrician
Log in | Register Home Our Sponsors Ages & Stages Ages & Stages Ages and Stages Your Child’s Checkups Prenatal Decisions to Make Delivery and Beyond Baby (0-12 mos.) Bathing ＆ Skin Care Breastfeeding Crying ＆ Colic Diapers ＆ Clothing Formula Feeding Nutrition Preemie Sleep Teething ＆ Tooth Care Toddler 1-3yrs. Fitness Nutrition Toilet Training Preschool 3-5yrs Nutrition ＆ Fitness Grade School 5-12yrs. Fitness Nutrition Puberty Teen 12-18yrs. Dating ＆ Sex Fitness Nutrition Young Adult 18-21yrs. Healthy Living Healthy Living Healthy Living Nutrition Fitness Sports Oral Health Emotional Wellness Building Resilience Growing Healthy Sleep Safety & Prevention Safety & Prevention Safety and Prevention Immunizations At Home Medication Safety At Play On The Go All Around Family Life Family Life Family Life Medical Home Pediatric Specialists Family Dynamics Communication ＆ Discipline Types of Families Media Getting Involved in Your Community Power of Play Work ＆ Child Care Health Issues Health Issues Health Issues Conditions Abdominal ADHD Autism Chest ＆ Lungs Chronic Conditions Cleft ＆ Craniofacial COVID-19 Developmental Disabilities Ear, Nose ＆ Throat Emotional Problems Eyes Fever Flu From Insects or Animals Genitals and Urinary Tract Head, Neck ＆ Nervous System Heart Infections Learning Disabilities Seizures Sexually Transmitted Infections Skin Conditions Treatments Vaccine Preventable Diseases Injuries ＆ Emergencies Sports Injuries News News Tips & Tools Tips & Tools Tips and Tools AAP Family Media Plan Motor Delay Tool Physical Activity Checker Symptom Checker HealthyChildren Texting Program Newsletters HealthyChildren Magazine Webinars Ask The Pediatrician Find a Pediatrician Our Mission Our Mission Our Mission AAP in Action Medical Editor & Contributors Sponsors Sponsorship Opportunities Spread the Word Shop AAP Find a Pediatrician
Ages and Stages Your Child’s Checkups Prenatal Decisions to Make Delivery and Beyond Baby (0-12 mos.) Bathing ＆ Skin Care Breastfeeding Crying ＆ Colic Diapers ＆ Clothing Formula Feeding Nutrition Preemie Sleep Teething ＆ Tooth Care Toddler 1-3yrs. Fitness Nutrition Toilet Training Preschool 3-5yrs Nutrition ＆ Fitness Grade School 5-12yrs. Fitness Nutrition Puberty Teen 12-18yrs. Dating ＆ Sex Fitness Nutrition Young Adult 18-21yrs.
Healthy Living Nutrition Fitness Sports Oral Health Emotional Wellness Building Resilience Growing Healthy Sleep
Family Life Medical Home Pediatric Specialists Family Dynamics Communication ＆ Discipline Types of Families Media Getting Involved in Your Community Power of Play Work ＆ Child Care
Health Issues Conditions Abdominal ADHD Autism Chest ＆ Lungs Chronic Conditions Cleft ＆ Craniofacial COVID-19 Developmental Disabilities Ear, Nose ＆ Throat Emotional Problems Eyes Fever Flu From Insects or Animals Genitals and Urinary Tract Head, Neck ＆ Nervous System Heart Infections Learning Disabilities Seizures Sexually Transmitted Infections Skin Conditions Treatments Vaccine Preventable Diseases Injuries ＆ Emergencies Sports Injuries
Tips and Tools AAP Family Media Plan Motor Delay Tool Physical Activity Checker Symptom Checker HealthyChildren Texting Program Newsletters HealthyChildren Magazine Webinars Ask The Pediatrician Find a Pediatrician
Our Mission AAP in Action Medical Editor & Contributors Sponsors Sponsorship Opportunities Spread the Word
Safety & Prevention Immunizations All Around At Home At Play On The Go In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know Safety & Prevention Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know Safety & Prevention Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know Safety & Prevention Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know Safety & Prevention Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
In This Section Healthy Children > Safety & Prevention > At Play > Swim Lessons: When to Start & What Parents Should Know
Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Swim Lessons: When to Start & What Parents Should Know Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Page Content Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA Article Body Last Updated 5/25/2023 Source American Academy of Pediatrics (Copyright © 2019) The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun! Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program. When should my child learn to swim? Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind. The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1. Parent-child toddler & preschool swim classes: beneficial for many families Recent studies suggest that water survival skills training and swim lessons can help reduce drowning risk for children between ages 1-4. Classes that include both parents and their children also are a good way to introduce good water safety habits and start building swim readiness skills. If your child seems ready, it's a good idea to start lessons now. Swim lessons for children ages 4 and up: a must for most families By their 4th birthday, most children are ready for swim lessons. At this age, they usually can learn basic water survival skills such as floating, treading water and getting to an exit point. By age 5 or 6, most children in swim lessons can master the front crawl. If your child hasn't already started in a learn-to-swim program, now is the time! Does AAP recommend infant swim classes? No, because there is currently no evidence that infant swim programs for babies under 1 year old lower their drowning risk. Infants this age may show reflex "swimming" movements but can't yet raise their heads out of the water well enough to breathe. It's OK to enroll in a parent-child water play class to help your infant get used to being in the pool, though; this can be a fun activity to enjoy together. Remember, swim lessons don't make kids "drown proof." Always keep in mind that swim lessons are just one of several important layers of protection needed to help prevent drowning. Another layer includes constant, focused supervision when your child is in or near a pool or any body of water. It also is essential to block access to pools during non-swim time . The Consumer Product Safety Commission found that 69% of children under the age of 5 years were not expected to be in the water at the time of a drowning. What should I look for when choosing swim lessons? Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels. For children of all ages, look for programs that: Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification. Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake. Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help. Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable? Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills. In addition, for children under age 4, look for programs that: Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well. Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction. Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water. Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit. When the cost of swim lessons is a concern If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options. How to supervise your child in or near water Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers. To effectively supervise and keep your child safe during swim time, keep in mind: Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present. Avoid using alcohol or drugs around the water, especially when supervising others. For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you. Don't leave a baby or young child in or near any body of water under the care of another child. Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes). Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times. Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park. Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair! What to remember about swim lessons for kids Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family. More information Infant Water Safety: Protect Your New Baby from Drowning Drowning Prevention for Curious Toddlers: What Parents Need to Know Water Safety for Teens Pool Dangers and Drowning Prevention―When It's Not Swimming Time Keep Kids with Autism Safe from Wandering: Tips from the AAP Why Swimming Is the Best First Sport for Kids AAP Drowning Prevention Campaign Toolkit Water Safety USA
Learning to swim should be a priority for every family. It's an important life skill that can play a key role in helping to prevent drowning―a top cause of death among children. Children, and their parents, need to learn how to swim to help keep time in the water safe and fun!
Here are some tips from the American Academy of Pediatrics (AAP) on the best time to start swim lessons and what to look for in a quality learn-to-swim program.
Children develop at different rates, and not all are ready to begin swim lessons at exactly the same age. When making your decision, keep your child's emotional maturity, physical and developmental abilities and limitations, and comfort level in the water in mind.
The AAP recommends swim lessons as a layer of protection against drowning that can begin for many children starting at age 1.
Look for classes and instructors that follow guidelines focused not just on swim stroke techniques, but broader water survival competency skills . All children should learn how to get back to the surface from under water, propel themselves at least 25 yards, and get out of the water, for example. Instructors should evaluate children's progress and give ongoing feedback on their skill levels.
Have experienced, qualified instructors . Swim instructors should be trained and certified through a nationally recognized learn-to-swim curriculum. There should also be lifeguards on duty who have current CPR and First Aid certification.
Teach good safety habits in, on, and near water . Children should learn to never swim alone or without adult supervision. Instructors should teach children to always ask for permission from parents, lifeguards, or swimming instructors before they get into a pool or natural bodies of water like a lake.
Teach what to do if they end up in the water unexpectedly . This includes practicing water competency skills such as self-rescue. Lessons should provide training with a variety of realistic conditions, such as falling in and swimming in clothes. Older children also should learn what to do if they see someone else in the water who is struggling, and how to get help.
Let you watch a class first to see first-hand if it is right for your child . Not all swim lessons are created equal, and parents should investigate options to choose the best fit. Are they swimming most of the time, or are there long periods of inactivity where they are waiting for their turn? Do children get one-on-one attention? Are the instructors friendly and knowledgeable?
Require multiple sessions . Once children start lessons, you should be able to see gradual but consistent progress in their abilities over time. Continue lessons at least until your they master basic water competency skills.
Provide an age-appropriate atmosphere . Your child should feel safe and secure during lessons, with activities that support their social, intellectual, physical, and emotional development. However, children need to develop a healthy respect for water, as well.
Include "touch supervision." Whenever infants and toddlers are in or around water—even during swim lessons―an adult should be within arm's reach to provide "touch supervision." Parent participation should be encouraged, especially since it also helps families know what to practice in between classes. If you can't be in the water with your child, look for private classes that offer 1-on-1 instruction.
Maintain water purity . Young children are more likely to swallow or breathe in water, so water disinfection and maintaining proper chlorine levels is really important. A good program should also require the child to wear a swimsuit that is snug-fitting at the legs to help avoid spreading body waste into the water.
Keep the water warm . Hypothermia is a greater risk at this age. Ideally, swim and water safety classes for children age 3 and younger should be in water heated to 87 to 94 degrees Fahrenheit.
If you're worried your family can't afford swim lessons, check with your city government. Many towns have scholarship programs that help cover the cost of swim lessons held at public pools. Reach out to qualified instructors about possible payment plans or scholarship options.
Proper supervision in the water—even if your child is learning how to swim―is one of the most important ways to help prevent drowning. Drowning is quick, silent, and much more common than most families realize. It happens every day to children with loving, attentive parents and caregivers.
Pay close, constant attention. Do not get distracted with other activities (such as reading, playing games, using the cellphone, or mowing the lawn), even if lifeguards are present.
For younger children and weak swimmers, get in the water with them. "Touch supervision" is essential! Even if you are not swimming but there is a pool or body of water nearby, always keep children within arm's reach. If you must leave, take the child with you.
Especially during parties or picnics at the pool or lake, when it's easy to get distracted, assign a "water watcher" whose job is to constantly keep eyes on the child in or near the water. Take turns, passing along a water watcher card to the next responsible adult after a set time (such as 15 minutes).
Remember that the primary drowning risk for toddlers age 1-4 is unanticipated, unsupervised access to water. Children are naturally curious and commonly slip away unnoticed during non-swim times.
Always use life jackets when in, on or near natural bodies of water, such as lakes or rivers. Make sure they fit properly and are approved by the U.S. Coast Guard. Children. Weak swimmers should also wear life jackets when at a pool or water park.
Know how to recognize signs of distress and respond when there is trouble. Everyone, including parents, caregivers and older children, should learn CPR and safe rescue techniques to respond to a drowning incident. Water safety is a family affair!
Enrolling in quality swim lessons―once your child is ready for them―is one of several essential ways to help prevent drowning. And if you haven't learned to swim yet yourself , now is the perfect time for you to take lessons, too! Talk with your pediatrician if you have any questions about whether your child is developmentally ready for swim lessons and how to find a quality program for your family.
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Donate Contact Us About Us Privacy Policy Terms of Use Editorial Policy © Copyright 2024 American Academy of Pediatrics. All rights reserved. | biology | 396110 | https://da.wikipedia.org/wiki/Sv%C3%B8mmeb%C3%A6lte | Svømmebælte | Et svømmebælte er et redskab der bruges til begyndersvømning. Bæltet er beklædt med elementer (f.eks. af kork) som øger svømmerens flydeevne. Det bruges til både børn og voksne, der skal lære at svømme, og har brug for at kunne fokusere på at lære svømmebevægelser uden også at skulle koncentrere sig om at holde sig oven vande.
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water_enter_anus/.txt |
How to Breathe When Swimming The fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. Published Apr 17, 2023 Joel MacCaughey Facebook Icon Twitter Icon Email Icon Photo: Getty Images Photo: Getty Images New perk! Get after it with local recommendations just for you. Discover nearby events, routes out your door, and hidden gems when you sign up for the Local Running Drop . Inhale. Exhale. Repeat…right? Believe it or not, when it comes to learning how to breathe when swimming, there is more to optimal air exchange than those few words. Out of the water, breathing is basic; so effortless and fundamental that we rarely think about it. But in the water, gravity, buoyancy, propulsion, water resistance, and your own body join forces to shove water up your nose, down your lungs, and make breathing way more complicated than it should be. (Thanks a lot, physics.) Let’s explore the fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. RELATED: A Complete Guide to Triathlon Swimming Does it really matter how you breathe when swimming? Yes, it it matters – a lot. Bad breathing habits can undermine your swim and, even worse, they can set off a chain reaction that affects your overall race performance. If poor air exchange shoots your heart rate to Zone 5 and you’re redlining a few hundred meters into the swim, you have to ease off the pace or stop altogether until your heart rate returns to manageable levels. A setback like this can blow up plans for a PR, leaving you gasping for air and wondering how things went so wrong, so fast. The main considerations when learning how to breathe when swimming are effectiveness (getting enough oxygen) and efficiency (getting oxygen without impeding form or speed). Air exchange effectiveness is especially challenging for triathletes who are self-taught swimmers. It’s not just the rookies – high-performing athletes (the ones who easily hold sub-six-minute miles on the run) can also crack because of ineffective air exchange. But effectiveness alone won’t produce the results you want. Swimming breaststroke is a great way to enjoy effective air exchange…but you won’t enjoy your swim split. That’s where efficiency comes into play. You want to insert effective air exchange into your stroke seamlessly, without slowing down or disrupting your perfect and hard-earned technique. RELATED: Dear Coach: How is Breathing Related to Performance? Common misconceptions about breathing when swimming Inhaling water is inevitable. This may be the best news you hear all day: yes, you can avoid taking in water when you breathe. Adjusting body position, breathing to the side, relaxing your head and neck, and increasing the time spent swimming on your side will all contribute to gaining control of how and when you breathe. Always feeling winded is normal. It’s easy to mistake oxygen deprivation for real, honest, exertion. As you improve air exchange, you’ll begin to feel more relaxed and more in control of your swim. Don’t be surprised if you unlock new levels of stamina and speed in your swim. How to breathe when swimming: Inhale Inhale during the pull phase of your stroke. It’s usually better to start taking your breath early in the phase so you have enough time to breathe deep. As your body leans onto the side of your extended arm, rotate your head to the side just enough to inhale without taking in water through your mouth or nose. Keep your head in line with your body. Three good cues are: Make sure the head is in a neutral position, not straining your neck, or tilting your head up or down Keep one goggle in and one goggle out of the water Make sure your ear stays right against the shoulder of your extended arm Make the breath count; one full deep inhalation. If you feel the need to take multiple breaths during the pull phase, that’s a sign that you’re taking short, shallow breaths and aren’t getting enough air. Make the inhale count. You only want to take a single inhale per stroke, so this breath should be deep and full; at first, it will probably feel more exaggerated than what you’re used to on the bike or run. That’s normal, and you will get used to it. How to breathe when swimming: Exhale You should always exhale whenever you are face down in the water. You may think it’s smart to hold your breath, but don’t – it’s a trap! Holding your breath will throw off the timing of your stroke. If you wait until your lungs are screaming for oxygen to dump your ‘spent air’ in your lungs, you’re overdrawing from the bank. Exhale through all the other phases of your stroke, just do it face down. Limit the time your face is out of the water to inhaling, and nothing more. You can control the rate of exhalation to accommodate a breathing pattern that suits you, preferably one breath every three, four, or five strokes. Blow a steady stream of bubbles in the water as you count the strokes. This will help avoid breathing too often, which can lead to hyperventilation. It will also minimize excessive head movement, which can cause disorientation. You should be ready and hungry for your next breath. RELATED: A Beginner’s Guide to Learning How to Swim for Triathlon Tips and tricks for learning how to breathe when swimming Although not the hottest topic, perfecting air exchange can dramatically improve your swim and pay dividends on your overall race performance. The main goal is to gain more control over your swim. Below are a few key points, drills, and checklists you can reference for training purposes. Swimming mistakes to avoid Holding your breath while swimming . You wouldn’t hold your breath during your run, so don’t do it on the swim. Holding your breath disrupts a normal breathing pattern. Lifting your head out of the water to breathe. You may be tempted to lift your head up and away from the water for a clean breath, but it’s more efficient to turn to the side. The average human head weighs 10 to 11 pounds, so the instant you lift your noggin up, it loses the benefit of buoyancy. Now you’re hoisting a bowling ball above water while you swim. Breathing to the front. Can you see straight ahead while you breathe? If so, you’re swimming in a more vertically oriented position or “swimming uphill” and you are swimming flat and increasing your body’s drag resistance like a barge instead of a speed boat. Breathing too often. This might be contentious because some swimmers swear by a two-stroke breathing pattern. The main drawbacks are: such a short breathing interval can lead to hyperventilation, and the excessive head motion can throw off a good rhythm to your stroke and cause disorientation. RELATED: Now is the Time to Correct Your Biggest Swim Mistakes Breathing Drills for Swimmers Bobs Bobs are the best way to practice effective air exchange and become comfortable with your face underwater most of the time. and only come up for a single deep breath. Take one full inhalation and submerge. Stay submerged until you’ve exhaled almost all of the air in your lungs, then pop up briefly for another single full inhale and then back down you go. You should only come up to inhale otherwise, spend the rest of your time exhaling underwater. Do 10 bobs at the start of practice or whenever you feel like your stoke is getting out of control and you can’t catch your breath. Side kicking Begin streamline kicking on your front; maintain a steady kick and hold one arm fully extended out in front (12 o’clock) and lower the other arm down to your side (6 o’clock). Maintain a clean, straight body line. Lean onto the side of your outstretched arm – anywhere from a 45 to 90-degree lean is good. As you kick, position your head face down, toward the bottom of the pool, eyes looking past your armpit. Unless you are inhaling, your head should remain facedown. Whenever you need to breathe, roll and rotate your head face-up (toward the ceiling), get your air, then rotate back to the facedown position. Do not lift your head up. At first, you may feel off balance, like you are going to ‘fall.’ This feeling goes away as you strengthen your kick and gain balance. How to breathe when swimming: Air exchange checklist Inhale Maintain a long, straight body line during pull phase Lean to the side of the extended arm Ear rests against the shoulder of the extended arm One goggle in, one goggle out Rotate head enough that mouth and nose clear the water Looking out to the side during the inhale Breathe full and deep Rotate face down Exhale Neck relaxed and head in a ‘neutral’ position Force air out Eyes looking straight down Control rate of exhale to time the next inhale Lungs almost empty before inhale Joel MacCaughey has 14 years coaching experience in USA Masters swimming, age group and senior swimming, high school swimming and diving, and triathlon. Similar Reads 8-Week Sprint Triathlon Training Plan For Beginners The Complete Beginner’s Guide on How to Train For Your First Triathlon A Beginner’s Guide for Learning How to Swim for Triathlon 12 Week Super Simple Sprint Triathlon Training Plan Tags how to breathe when swimming triathlon swimming
How to Breathe When Swimming The fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. Published Apr 17, 2023 Joel MacCaughey Facebook Icon Twitter Icon Email Icon
How to Breathe When Swimming The fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. Published Apr 17, 2023 Joel MacCaughey Facebook Icon Twitter Icon Email Icon
The fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water.
New perk! Get after it with local recommendations just for you. Discover nearby events, routes out your door, and hidden gems when you sign up for the Local Running Drop . Inhale. Exhale. Repeat…right? Believe it or not, when it comes to learning how to breathe when swimming, there is more to optimal air exchange than those few words. Out of the water, breathing is basic; so effortless and fundamental that we rarely think about it. But in the water, gravity, buoyancy, propulsion, water resistance, and your own body join forces to shove water up your nose, down your lungs, and make breathing way more complicated than it should be. (Thanks a lot, physics.) Let’s explore the fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. RELATED: A Complete Guide to Triathlon Swimming Does it really matter how you breathe when swimming? Yes, it it matters – a lot. Bad breathing habits can undermine your swim and, even worse, they can set off a chain reaction that affects your overall race performance. If poor air exchange shoots your heart rate to Zone 5 and you’re redlining a few hundred meters into the swim, you have to ease off the pace or stop altogether until your heart rate returns to manageable levels. A setback like this can blow up plans for a PR, leaving you gasping for air and wondering how things went so wrong, so fast. The main considerations when learning how to breathe when swimming are effectiveness (getting enough oxygen) and efficiency (getting oxygen without impeding form or speed). Air exchange effectiveness is especially challenging for triathletes who are self-taught swimmers. It’s not just the rookies – high-performing athletes (the ones who easily hold sub-six-minute miles on the run) can also crack because of ineffective air exchange. But effectiveness alone won’t produce the results you want. Swimming breaststroke is a great way to enjoy effective air exchange…but you won’t enjoy your swim split. That’s where efficiency comes into play. You want to insert effective air exchange into your stroke seamlessly, without slowing down or disrupting your perfect and hard-earned technique. RELATED: Dear Coach: How is Breathing Related to Performance? Common misconceptions about breathing when swimming Inhaling water is inevitable. This may be the best news you hear all day: yes, you can avoid taking in water when you breathe. Adjusting body position, breathing to the side, relaxing your head and neck, and increasing the time spent swimming on your side will all contribute to gaining control of how and when you breathe. Always feeling winded is normal. It’s easy to mistake oxygen deprivation for real, honest, exertion. As you improve air exchange, you’ll begin to feel more relaxed and more in control of your swim. Don’t be surprised if you unlock new levels of stamina and speed in your swim. How to breathe when swimming: Inhale Inhale during the pull phase of your stroke. It’s usually better to start taking your breath early in the phase so you have enough time to breathe deep. As your body leans onto the side of your extended arm, rotate your head to the side just enough to inhale without taking in water through your mouth or nose. Keep your head in line with your body. Three good cues are: Make sure the head is in a neutral position, not straining your neck, or tilting your head up or down Keep one goggle in and one goggle out of the water Make sure your ear stays right against the shoulder of your extended arm Make the breath count; one full deep inhalation. If you feel the need to take multiple breaths during the pull phase, that’s a sign that you’re taking short, shallow breaths and aren’t getting enough air. Make the inhale count. You only want to take a single inhale per stroke, so this breath should be deep and full; at first, it will probably feel more exaggerated than what you’re used to on the bike or run. That’s normal, and you will get used to it. How to breathe when swimming: Exhale You should always exhale whenever you are face down in the water. You may think it’s smart to hold your breath, but don’t – it’s a trap! Holding your breath will throw off the timing of your stroke. If you wait until your lungs are screaming for oxygen to dump your ‘spent air’ in your lungs, you’re overdrawing from the bank. Exhale through all the other phases of your stroke, just do it face down. Limit the time your face is out of the water to inhaling, and nothing more. You can control the rate of exhalation to accommodate a breathing pattern that suits you, preferably one breath every three, four, or five strokes. Blow a steady stream of bubbles in the water as you count the strokes. This will help avoid breathing too often, which can lead to hyperventilation. It will also minimize excessive head movement, which can cause disorientation. You should be ready and hungry for your next breath. RELATED: A Beginner’s Guide to Learning How to Swim for Triathlon Tips and tricks for learning how to breathe when swimming Although not the hottest topic, perfecting air exchange can dramatically improve your swim and pay dividends on your overall race performance. The main goal is to gain more control over your swim. Below are a few key points, drills, and checklists you can reference for training purposes. Swimming mistakes to avoid Holding your breath while swimming . You wouldn’t hold your breath during your run, so don’t do it on the swim. Holding your breath disrupts a normal breathing pattern. Lifting your head out of the water to breathe. You may be tempted to lift your head up and away from the water for a clean breath, but it’s more efficient to turn to the side. The average human head weighs 10 to 11 pounds, so the instant you lift your noggin up, it loses the benefit of buoyancy. Now you’re hoisting a bowling ball above water while you swim. Breathing to the front. Can you see straight ahead while you breathe? If so, you’re swimming in a more vertically oriented position or “swimming uphill” and you are swimming flat and increasing your body’s drag resistance like a barge instead of a speed boat. Breathing too often. This might be contentious because some swimmers swear by a two-stroke breathing pattern. The main drawbacks are: such a short breathing interval can lead to hyperventilation, and the excessive head motion can throw off a good rhythm to your stroke and cause disorientation. RELATED: Now is the Time to Correct Your Biggest Swim Mistakes Breathing Drills for Swimmers Bobs Bobs are the best way to practice effective air exchange and become comfortable with your face underwater most of the time. and only come up for a single deep breath. Take one full inhalation and submerge. Stay submerged until you’ve exhaled almost all of the air in your lungs, then pop up briefly for another single full inhale and then back down you go. You should only come up to inhale otherwise, spend the rest of your time exhaling underwater. Do 10 bobs at the start of practice or whenever you feel like your stoke is getting out of control and you can’t catch your breath. Side kicking Begin streamline kicking on your front; maintain a steady kick and hold one arm fully extended out in front (12 o’clock) and lower the other arm down to your side (6 o’clock). Maintain a clean, straight body line. Lean onto the side of your outstretched arm – anywhere from a 45 to 90-degree lean is good. As you kick, position your head face down, toward the bottom of the pool, eyes looking past your armpit. Unless you are inhaling, your head should remain facedown. Whenever you need to breathe, roll and rotate your head face-up (toward the ceiling), get your air, then rotate back to the facedown position. Do not lift your head up. At first, you may feel off balance, like you are going to ‘fall.’ This feeling goes away as you strengthen your kick and gain balance. How to breathe when swimming: Air exchange checklist Inhale Maintain a long, straight body line during pull phase Lean to the side of the extended arm Ear rests against the shoulder of the extended arm One goggle in, one goggle out Rotate head enough that mouth and nose clear the water Looking out to the side during the inhale Breathe full and deep Rotate face down Exhale Neck relaxed and head in a ‘neutral’ position Force air out Eyes looking straight down Control rate of exhale to time the next inhale Lungs almost empty before inhale Joel MacCaughey has 14 years coaching experience in USA Masters swimming, age group and senior swimming, high school swimming and diving, and triathlon.
New perk! Get after it with local recommendations just for you. Discover nearby events, routes out your door, and hidden gems when you sign up for the Local Running Drop . Inhale. Exhale. Repeat…right? Believe it or not, when it comes to learning how to breathe when swimming, there is more to optimal air exchange than those few words. Out of the water, breathing is basic; so effortless and fundamental that we rarely think about it. But in the water, gravity, buoyancy, propulsion, water resistance, and your own body join forces to shove water up your nose, down your lungs, and make breathing way more complicated than it should be. (Thanks a lot, physics.) Let’s explore the fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water. RELATED: A Complete Guide to Triathlon Swimming Does it really matter how you breathe when swimming? Yes, it it matters – a lot. Bad breathing habits can undermine your swim and, even worse, they can set off a chain reaction that affects your overall race performance. If poor air exchange shoots your heart rate to Zone 5 and you’re redlining a few hundred meters into the swim, you have to ease off the pace or stop altogether until your heart rate returns to manageable levels. A setback like this can blow up plans for a PR, leaving you gasping for air and wondering how things went so wrong, so fast. The main considerations when learning how to breathe when swimming are effectiveness (getting enough oxygen) and efficiency (getting oxygen without impeding form or speed). Air exchange effectiveness is especially challenging for triathletes who are self-taught swimmers. It’s not just the rookies – high-performing athletes (the ones who easily hold sub-six-minute miles on the run) can also crack because of ineffective air exchange. But effectiveness alone won’t produce the results you want. Swimming breaststroke is a great way to enjoy effective air exchange…but you won’t enjoy your swim split. That’s where efficiency comes into play. You want to insert effective air exchange into your stroke seamlessly, without slowing down or disrupting your perfect and hard-earned technique. RELATED: Dear Coach: How is Breathing Related to Performance? Common misconceptions about breathing when swimming Inhaling water is inevitable. This may be the best news you hear all day: yes, you can avoid taking in water when you breathe. Adjusting body position, breathing to the side, relaxing your head and neck, and increasing the time spent swimming on your side will all contribute to gaining control of how and when you breathe. Always feeling winded is normal. It’s easy to mistake oxygen deprivation for real, honest, exertion. As you improve air exchange, you’ll begin to feel more relaxed and more in control of your swim. Don’t be surprised if you unlock new levels of stamina and speed in your swim. How to breathe when swimming: Inhale Inhale during the pull phase of your stroke. It’s usually better to start taking your breath early in the phase so you have enough time to breathe deep. As your body leans onto the side of your extended arm, rotate your head to the side just enough to inhale without taking in water through your mouth or nose. Keep your head in line with your body. Three good cues are: Make sure the head is in a neutral position, not straining your neck, or tilting your head up or down Keep one goggle in and one goggle out of the water Make sure your ear stays right against the shoulder of your extended arm Make the breath count; one full deep inhalation. If you feel the need to take multiple breaths during the pull phase, that’s a sign that you’re taking short, shallow breaths and aren’t getting enough air. Make the inhale count. You only want to take a single inhale per stroke, so this breath should be deep and full; at first, it will probably feel more exaggerated than what you’re used to on the bike or run. That’s normal, and you will get used to it. How to breathe when swimming: Exhale You should always exhale whenever you are face down in the water. You may think it’s smart to hold your breath, but don’t – it’s a trap! Holding your breath will throw off the timing of your stroke. If you wait until your lungs are screaming for oxygen to dump your ‘spent air’ in your lungs, you’re overdrawing from the bank. Exhale through all the other phases of your stroke, just do it face down. Limit the time your face is out of the water to inhaling, and nothing more. You can control the rate of exhalation to accommodate a breathing pattern that suits you, preferably one breath every three, four, or five strokes. Blow a steady stream of bubbles in the water as you count the strokes. This will help avoid breathing too often, which can lead to hyperventilation. It will also minimize excessive head movement, which can cause disorientation. You should be ready and hungry for your next breath. RELATED: A Beginner’s Guide to Learning How to Swim for Triathlon Tips and tricks for learning how to breathe when swimming Although not the hottest topic, perfecting air exchange can dramatically improve your swim and pay dividends on your overall race performance. The main goal is to gain more control over your swim. Below are a few key points, drills, and checklists you can reference for training purposes. Swimming mistakes to avoid Holding your breath while swimming . You wouldn’t hold your breath during your run, so don’t do it on the swim. Holding your breath disrupts a normal breathing pattern. Lifting your head out of the water to breathe. You may be tempted to lift your head up and away from the water for a clean breath, but it’s more efficient to turn to the side. The average human head weighs 10 to 11 pounds, so the instant you lift your noggin up, it loses the benefit of buoyancy. Now you’re hoisting a bowling ball above water while you swim. Breathing to the front. Can you see straight ahead while you breathe? If so, you’re swimming in a more vertically oriented position or “swimming uphill” and you are swimming flat and increasing your body’s drag resistance like a barge instead of a speed boat. Breathing too often. This might be contentious because some swimmers swear by a two-stroke breathing pattern. The main drawbacks are: such a short breathing interval can lead to hyperventilation, and the excessive head motion can throw off a good rhythm to your stroke and cause disorientation. RELATED: Now is the Time to Correct Your Biggest Swim Mistakes Breathing Drills for Swimmers Bobs Bobs are the best way to practice effective air exchange and become comfortable with your face underwater most of the time. and only come up for a single deep breath. Take one full inhalation and submerge. Stay submerged until you’ve exhaled almost all of the air in your lungs, then pop up briefly for another single full inhale and then back down you go. You should only come up to inhale otherwise, spend the rest of your time exhaling underwater. Do 10 bobs at the start of practice or whenever you feel like your stoke is getting out of control and you can’t catch your breath. Side kicking Begin streamline kicking on your front; maintain a steady kick and hold one arm fully extended out in front (12 o’clock) and lower the other arm down to your side (6 o’clock). Maintain a clean, straight body line. Lean onto the side of your outstretched arm – anywhere from a 45 to 90-degree lean is good. As you kick, position your head face down, toward the bottom of the pool, eyes looking past your armpit. Unless you are inhaling, your head should remain facedown. Whenever you need to breathe, roll and rotate your head face-up (toward the ceiling), get your air, then rotate back to the facedown position. Do not lift your head up. At first, you may feel off balance, like you are going to ‘fall.’ This feeling goes away as you strengthen your kick and gain balance. How to breathe when swimming: Air exchange checklist Inhale Maintain a long, straight body line during pull phase Lean to the side of the extended arm Ear rests against the shoulder of the extended arm One goggle in, one goggle out Rotate head enough that mouth and nose clear the water Looking out to the side during the inhale Breathe full and deep Rotate face down Exhale Neck relaxed and head in a ‘neutral’ position Force air out Eyes looking straight down Control rate of exhale to time the next inhale Lungs almost empty before inhale Joel MacCaughey has 14 years coaching experience in USA Masters swimming, age group and senior swimming, high school swimming and diving, and triathlon.
New perk! Get after it with local recommendations just for you. Discover nearby events, routes out your door, and hidden gems when you sign up for the Local Running Drop .
New perk! Get after it with local recommendations just for you. Discover nearby events, routes out your door, and hidden gems when you sign up for the Local Running Drop .
Believe it or not, when it comes to learning how to breathe when swimming, there is more to optimal air exchange than those few words. Out of the water, breathing is basic; so effortless and fundamental that we rarely think about it. But in the water, gravity, buoyancy, propulsion, water resistance, and your own body join forces to shove water up your nose, down your lungs, and make breathing way more complicated than it should be. (Thanks a lot, physics.)
Believe it or not, when it comes to learning how to breathe when swimming, there is more to optimal air exchange than those few words. Out of the water, breathing is basic; so effortless and fundamental that we rarely think about it. But in the water, gravity, buoyancy, propulsion, water resistance, and your own body join forces to shove water up your nose, down your lungs, and make breathing way more complicated than it should be. (Thanks a lot, physics.)
Let’s explore the fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water.
Let’s explore the fundamentals of how to breathe when swimming so you stay comfortable, relaxed, and fast in the water.
Yes, it it matters – a lot. Bad breathing habits can undermine your swim and, even worse, they can set off a chain reaction that affects your overall race performance. If poor air exchange shoots your heart rate to Zone 5 and you’re redlining a few hundred meters into the swim, you have to ease off the pace or stop altogether until your heart rate returns to manageable levels. A setback like this can blow up plans for a PR, leaving you gasping for air and wondering how things went so wrong, so fast.
Yes, it it matters – a lot. Bad breathing habits can undermine your swim and, even worse, they can set off a chain reaction that affects your overall race performance. If poor air exchange shoots your heart rate to Zone 5 and you’re redlining a few hundred meters into the swim, you have to ease off the pace or stop altogether until your heart rate returns to manageable levels. A setback like this can blow up plans for a PR, leaving you gasping for air and wondering how things went so wrong, so fast.
The main considerations when learning how to breathe when swimming are effectiveness (getting enough oxygen) and efficiency (getting oxygen without impeding form or speed).
The main considerations when learning how to breathe when swimming are effectiveness (getting enough oxygen) and efficiency (getting oxygen without impeding form or speed).
Air exchange effectiveness is especially challenging for triathletes who are self-taught swimmers. It’s not just the rookies – high-performing athletes (the ones who easily hold sub-six-minute miles on the run) can also crack because of ineffective air exchange.
Air exchange effectiveness is especially challenging for triathletes who are self-taught swimmers. It’s not just the rookies – high-performing athletes (the ones who easily hold sub-six-minute miles on the run) can also crack because of ineffective air exchange.
But effectiveness alone won’t produce the results you want. Swimming breaststroke is a great way to enjoy effective air exchange…but you won’t enjoy your swim split. That’s where efficiency comes into play. You want to insert effective air exchange into your stroke seamlessly, without slowing down or disrupting your perfect and hard-earned technique.
But effectiveness alone won’t produce the results you want. Swimming breaststroke is a great way to enjoy effective air exchange…but you won’t enjoy your swim split. That’s where efficiency comes into play. You want to insert effective air exchange into your stroke seamlessly, without slowing down or disrupting your perfect and hard-earned technique.
This may be the best news you hear all day: yes, you can avoid taking in water when you breathe. Adjusting body position, breathing to the side, relaxing your head and neck, and increasing the time spent swimming on your side will all contribute to gaining control of how and when you breathe.
This may be the best news you hear all day: yes, you can avoid taking in water when you breathe. Adjusting body position, breathing to the side, relaxing your head and neck, and increasing the time spent swimming on your side will all contribute to gaining control of how and when you breathe.
It’s easy to mistake oxygen deprivation for real, honest, exertion. As you improve air exchange, you’ll begin to feel more relaxed and more in control of your swim. Don’t be surprised if you unlock new levels of stamina and speed in your swim.
It’s easy to mistake oxygen deprivation for real, honest, exertion. As you improve air exchange, you’ll begin to feel more relaxed and more in control of your swim. Don’t be surprised if you unlock new levels of stamina and speed in your swim.
Inhale during the pull phase of your stroke. It’s usually better to start taking your breath early in the phase so you have enough time to breathe deep. As your body leans onto the side of your extended arm, rotate your head to the side just enough to inhale without taking in water through your mouth or nose. Keep your head in line with your body. Three good cues are:
Inhale during the pull phase of your stroke. It’s usually better to start taking your breath early in the phase so you have enough time to breathe deep. As your body leans onto the side of your extended arm, rotate your head to the side just enough to inhale without taking in water through your mouth or nose. Keep your head in line with your body. Three good cues are:
Make sure the head is in a neutral position, not straining your neck, or tilting your head up or down
Make the breath count; one full deep inhalation. If you feel the need to take multiple breaths during the pull phase, that’s a sign that you’re taking short, shallow breaths and aren’t getting enough air. Make the inhale count. You only want to take a single inhale per stroke, so this breath should be deep and full; at first, it will probably feel more exaggerated than what you’re used to on the bike or run. That’s normal, and you will get used to it.
If you feel the need to take multiple breaths during the pull phase, that’s a sign that you’re taking short, shallow breaths and aren’t getting enough air. Make the inhale count. You only want to take a single inhale per stroke, so this breath should be deep and full; at first, it will probably feel more exaggerated than what you’re used to on the bike or run. That’s normal, and you will get used to it.
You should always exhale whenever you are face down in the water. You may think it’s smart to hold your breath, but don’t – it’s a trap! Holding your breath will throw off the timing of your stroke. If you wait until your lungs are screaming for oxygen to dump your ‘spent air’ in your lungs, you’re overdrawing from the bank. Exhale through all the other phases of your stroke, just do it face down. Limit the time your face is out of the water to inhaling, and nothing more. You can control the rate of exhalation to accommodate a breathing pattern that suits you, preferably one breath every three, four, or five strokes. Blow a steady stream of bubbles in the water as you count the strokes. This will help avoid breathing too often, which can lead to hyperventilation. It will also minimize excessive head movement, which can cause disorientation. You should be ready and hungry for your next breath.
You should always exhale whenever you are face down in the water. You may think it’s smart to hold your breath, but don’t – it’s a trap! Holding your breath will throw off the timing of your stroke. If you wait until your lungs are screaming for oxygen to dump your ‘spent air’ in your lungs, you’re overdrawing from the bank. Exhale through all the other phases of your stroke, just do it face down. Limit the time your face is out of the water to inhaling, and nothing more. You can control the rate of exhalation to accommodate a breathing pattern that suits you, preferably one breath every three, four, or five strokes. Blow a steady stream of bubbles in the water as you count the strokes. This will help avoid breathing too often, which can lead to hyperventilation. It will also minimize excessive head movement, which can cause disorientation. You should be ready and hungry for your next breath.
Although not the hottest topic, perfecting air exchange can dramatically improve your swim and pay dividends on your overall race performance. The main goal is to gain more control over your swim. Below are a few key points, drills, and checklists you can reference for training purposes.
Although not the hottest topic, perfecting air exchange can dramatically improve your swim and pay dividends on your overall race performance. The main goal is to gain more control over your swim. Below are a few key points, drills, and checklists you can reference for training purposes.
You wouldn’t hold your breath during your run, so don’t do it on the swim. Holding your breath disrupts a normal breathing pattern.
You may be tempted to lift your head up and away from the water for a clean breath, but it’s more efficient to turn to the side. The average human head weighs 10 to 11 pounds, so the instant you lift your noggin up, it loses the benefit of buoyancy. Now you’re hoisting a bowling ball above water while you swim.
You may be tempted to lift your head up and away from the water for a clean breath, but it’s more efficient to turn to the side. The average human head weighs 10 to 11 pounds, so the instant you lift your noggin up, it loses the benefit of buoyancy. Now you’re hoisting a bowling ball above water while you swim.
Can you see straight ahead while you breathe? If so, you’re swimming in a more vertically oriented position or “swimming uphill” and you are swimming flat and increasing your body’s drag resistance like a barge instead of a speed boat.
This might be contentious because some swimmers swear by a two-stroke breathing pattern. The main drawbacks are: such a short breathing interval can lead to hyperventilation, and the excessive head motion can throw off a good rhythm to your stroke and cause disorientation.
Bobs are the best way to practice effective air exchange and become comfortable with your face underwater most of the time. and only come up for a single deep breath. Take one full inhalation and submerge. Stay submerged until you’ve exhaled almost all of the air in your lungs, then pop up briefly for another single full inhale and then back down you go. You should only come up to inhale otherwise, spend the rest of your time exhaling underwater.
Bobs are the best way to practice effective air exchange and become comfortable with your face underwater most of the time. and only come up for a single deep breath. Take one full inhalation and submerge. Stay submerged until you’ve exhaled almost all of the air in your lungs, then pop up briefly for another single full inhale and then back down you go. You should only come up to inhale otherwise, spend the rest of your time exhaling underwater.
Do 10 bobs at the start of practice or whenever you feel like your stoke is getting out of control and you can’t catch your breath.
Do 10 bobs at the start of practice or whenever you feel like your stoke is getting out of control and you can’t catch your breath.
Begin streamline kicking on your front; maintain a steady kick and hold one arm fully extended out in front (12 o’clock) and lower the other arm down to your side (6 o’clock). Maintain a clean, straight body line. Lean onto the side of your outstretched arm – anywhere from a 45 to 90-degree lean is good. As you kick, position your head face down, toward the bottom of the pool, eyes looking past your armpit. Unless you are inhaling, your head should remain facedown. Whenever you need to breathe, roll and rotate your head face-up (toward the ceiling), get your air, then rotate back to the facedown position. Do not lift your head up. At first, you may feel off balance, like you are going to ‘fall.’ This feeling goes away as you strengthen your kick and gain balance.
Begin streamline kicking on your front; maintain a steady kick and hold one arm fully extended out in front (12 o’clock) and lower the other arm down to your side (6 o’clock). Maintain a clean, straight body line. Lean onto the side of your outstretched arm – anywhere from a 45 to 90-degree lean is good. As you kick, position your head face down, toward the bottom of the pool, eyes looking past your armpit. Unless you are inhaling, your head should remain facedown. Whenever you need to breathe, roll and rotate your head face-up (toward the ceiling), get your air, then rotate back to the facedown position. Do not lift your head up. At first, you may feel off balance, like you are going to ‘fall.’ This feeling goes away as you strengthen your kick and gain balance.
Joel MacCaughey has 14 years coaching experience in USA Masters swimming, age group and senior swimming, high school swimming and diving, and triathlon.
Joel MacCaughey has 14 years coaching experience in USA Masters swimming, age group and senior swimming, high school swimming and diving, and triathlon.
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Industry athleteReg Bicycle Retailer & Industry News FinisherPix Nastar Outside Events Cycling Series Outside Shop | biology | 4200 | https://da.wikipedia.org/wiki/Crawl | Crawl | Crawl er en bestemt svømmestilart og er på visse distancer en olympisk disciplin. Crawl er den hurtigste af de traditionelle svømmemetoder og formodentlig også den mest anvendte blandt amatører. Ofte bruges definitionen fri svømning dog om løb, hvor der svømmes crawl, idet alle svømmearter som udgangspunkt kan anvendes.
Crawl
Crawl foregår på maven, og hovedet ligger stille, mens man bevæger arme og ben skiftevis. Kroppen roterer fra side til side. Armtaget hjælper til bedre rotation. Benene laver en opadgående bevægelse og et nedadgående spark. Armtaget starter, når armen er fremme foran hovedet. Der trækkes gennem vandet ned til hoften, hvor armen føres op over vandet og frem foran hovedet. Her sættes hånden først i vandet igen, og der kan tages et nyt armtag. Armene bevæger sig omtrent modsat hinanden.
Ved mindre stævner og turneringer konkurreres der på mange forskellige distancer. Ved store mesterskaber som EM, VM og OL svømmes der crawl på følgende distancer:
50 meter.
100 meter.
200 meter.
400 meter.
800 meter.
1500 meter.
4 ×100 meter fri.
4 ×200 meter fri.
Desuden indgår stilarten i følgende discipliner:
100 meter individuel medley.
200 meter individuel medley.
400 meter individuel medley.
4 ×100 meter holdmedley.
Diskvalifikation
I crawl/fri kan man blive diskvalificeret ved tyvstart, hvis der ingen berøring er ved vendingen, eller hvis man går på bunden.
Det er ikke tilladt at svømme mere end 15m ud under vandoverfladen. Efter hver vending skal man altså have brudt vandoverfladen inden 15 metermærket er nået
Fri svømning
Crawl den mest anvendte svømmeart under frisvømning (freestyle), da det for det meste er den hurtigste måde at svømme på.
Svømmestile | danish | 0.764422 |
water_enter_anus/Urethral_sphincters.txt | The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of these muscles contracts, the urethra is sealed shut.
The external urethral sphincter originates at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the other side. It is controlled by the deep perineal branch of the pudendal nerve. Activity in the nerve fibers constricts the urethra.
Function and sex differences[edit]
Main articles: External sphincter muscle of male urethra and External sphincter muscle of female urethra
In males and females, both internal and external urethral sphincters function to prevent the release of urine. The internal urethral sphincter controls involuntary urine flow from the bladder to the urethra, whereas the external urethral sphincter controls voluntary urine flow from the bladder to the urethra. Any damage to these muscles can lead to urinary incontinence. In males, the internal urethral sphincter has the additional function of preventing the flow of semen into the male bladder during ejaculation.
Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, the urethrovaginal muscle, and the compressor urethrae. The urethrovaginal muscle fibers wrap around the vagina and urethra and contraction leads to constriction of both the vagina and the urethra. The origin of the compressor urethrae muscle is the right and left inferior pubic ramus and it wraps anteriorly around the urethra so when it contracts, it squeezes the urethra against the vagina. The external urethrae, like in males, wraps solely around the urethra.
Congenital abnormalities of the female urethra can be surgically repaired with vaginoplasty.
Clinical significance[edit]
The urethral sphincter is considered an integral part of maintaining urinary continence, and it is important to understand its role in some conditions:
Stress urinary incontinence is a common problem related to the function of the urethral sphincter. Weak pelvic floor muscles, intrinsic sphincter damage, or damage to the surrounding nerves and tissue can make the urethral sphincter incompetent, and subsequently, it will not close fully, leading to stress urinary incontinence. In women, childbirth, obesity, and age can all be risk factors, especially by weakening the pelvic floor muscles. In men, prostate surgery (prostatectomy, TURP, etc) and radiation therapy can damage the sphincter and cause stress incontinence.
Neurogenic bladder dysfunction can involve a malfunctioning urethral sphincter.
Urge incontinence can happen when the urethra can't hold the urine in as the bladder contracts uncontrollably.
Retrograde ejaculation can occur when the urethral sphincter fails to adequately contract during ejaculation.
See also[edit]
Stress urinary incontinence
Membranous Urethra
Artificial Urinary Sphincter | biology | 4688088 | https://sv.wikipedia.org/wiki/Ranunculus%20pegaeus | Ranunculus pegaeus | Ranunculus pegaeus är en ranunkelväxtart som beskrevs av Hand.-mazz.. Ranunculus pegaeus ingår i släktet ranunkler, och familjen ranunkelväxter. Utöver nominatformen finns också underarten R. p. curvistylis.
Källor
Ranunkler
pegaeus | swedish | 1.27865 |
muscle_bigger/Hyperplasia.txt | Hyperplasia (from ancient Greek ὑπέρ huper 'over' + πλάσις plasis 'formation'), or hypergenesis, is an enlargement of an organ or tissue caused by an increase in the amount of organic tissue that results from cell proliferation. It may lead to the gross enlargement of an organ, and the term is sometimes confused with benign neoplasia or benign tumor.
Hyperplasia is a common preneoplastic response to stimulus. Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (hypertrophy). Hyperplasia is different from hypertrophy in that the adaptive cell change in hypertrophy is an increase in the size of cells, whereas hyperplasia involves an increase in the number of cells.
Causes[edit]
Hyperplasia may be due to any number of causes, including proliferation of basal layer of epidermis to compensate skin loss, chronic inflammatory response, hormonal dysfunctions, or compensation for damage or disease elsewhere. Hyperplasia may be harmless and occur on a particular tissue. An example of a normal hyperplastic response would be the growth and multiplication of milk-secreting glandular cells in the breast as a response to pregnancy, thus preparing for future breast feeding.
Perhaps the most interesting and potent effect insulin-like growth factor 1 (IGF) has on the human body is its ability to cause hyperplasia, which is an actual splitting of cells. By contrast, hypertrophy is what occurs, for example, to skeletal muscle cells during weight training and is simply an increase in the size of the cells. With IGF use, one is able to cause hyperplasia which actually increases the number of muscle cells present in the tissue. Weight training enables these new cells to mature in size and strength. It is theorized that hyperplasia may also be induced through specific power output training for athletic performance, thus increasing the number of muscle fibers instead of increasing the size of a single fiber.
Mechanism[edit]
Hyperplasia is considered to be a physiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. However, hyperplasia can also occur as a pathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled by growth hormones, and cease to proliferate if such stimuli are removed. This differs from neoplasia (the process underlying cancer and benign tumors), in which genetically abnormal cells manage to proliferate in a non-physiological manner which is unresponsive to normal stimuli. That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.
Role in disease[edit]
Hyperplasia of certain tissues may cause disease. Pathologic hyperplasia in these tissues may occur due to infection, physiological stress or trauma, or abnormal levels of particular hormones, such as estrogen, ACTH, or cortisol.
Types[edit]
Some of the more commonly known clinical forms of hyperplasia, or conditions leading to hyperplasia, include:
Benign prostatic hyperplasia, also known as prostate enlargement.
Cushing's disease – Physiopathology of hyperplasia of adrenal cortex due to increased circulating level of ACTH (adrenocorticotropic hormone).
Congenital adrenal hyperplasia – Inherited disorder of gland (adrenal).
Endometrial hyperplasia – Hyperproliferation of the endometrium, usually in response to unopposed estrogen stimulation in the setting of polycystic ovary syndrome or exogenous administration of hormones. Atypical endometrial hyperplasia may represent an early neoplastic process which can lead to endometrial adenocarcinoma. The development of endometrial adenocarcinoma from endometrial hyperplasia is a typical example of how the effects of pathologic hyperplasia can lead to neoplasia, and females who exhibit hyperplasia of the endometrium are indeed more likely to develop cancer of these cells.
Patient with hemihyperplasia involving the upper and lower left extremities. The leg length discrepancy can be noted by the pelvic tilt.
Hemihyperplasia – When only half (or one side) of the body is affected, sometimes generating limbs of different lengths.
Hyperplasia of the breast – "Hyperplastic" lesions of the breast include usual ductal hyperplasia, a focal expansion of the number of cells in a terminal breast duct, and atypical ductal hyperplasia, in which a more abnormal pattern of growth is seen, and which is associated with an increased risk of developing breast cancer.
Intimal hyperplasia – The thickening of the tunica intima of a blood vessel as a complication of a reconstruction procedure or endarterectomy. Intimal hyperplasia is the universal response of a vessel to injury and is an important reason of late bypass graft failure, particularly in vein and synthetic vascular grafts.
Focal epithelial hyperplasia (also known as Heck's disease) – This is a wart-like growth in the mucous tissues of the mouth or, rarely, throat that is caused by certain sub-types of the human papillomavirus (HPV). Heck's disease has not been known to cause cancer.
Myofibre hyperplasia (also known as double-muscling) – seen in cattle, genetic mutations cause large muscles due to increased proliferation of myofibres and decreased adipose tissue.
Sebaceous hyperplasia – In this condition, small yellowish growths develop on the skin, usually on the face. This condition is neither contagious nor dangerous.
Compensatory liver hyperplasia – The liver undergoes cellular division after acute injury, resulting in new cells that restore liver function back to baseline. Approximately 75% of the liver can be acutely damaged or resected with seemingly full regeneration through hepatocyte division, i.e., hyperplasia. This is what makes living-donor liver transplants possible.
Epidermal hyperplasia of the skin
See also[edit]
List of biological development disorders
Hyperplasia of midface | biology | 192087 | https://da.wikipedia.org/wiki/Hyperplasi | Hyperplasi | Hyperplasi (af gr: hyper, større/flere og plasía, forme/danne) er et lægeligt begreb, der betegner abnorm vækst af celler, væv eller organer, pga. øget celletal. Årsagen kan være mekanisk slid, sygdom, forgiftning eller alder.
Histologi
Ved hyperplasi stiger antallet af celler, mens cellestørrelsen normalt bevares. Hård eller fortykket hud er et resultat af at hudcellerne deler sig hurtigere, hvorved huden kommer til at bestå af flere cellelag. I endometriet i livmoderen kombineres hyperplasi og hypertrofi i proliferationsfasen af menstruationscyklusen.
Hyperplasi skal hverken forveksles med dysplasi: celleforandringer, der evt. kan blive til cancer
eller neoplasi: decideret nyvækst/tumor, der kan være malign (cancer) eller benign.
Se også
Atrofi
Dysplasi
Hypertrofi
Neoplasi
Histologi | danish | 0.352702 |
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Cell Cycle and Mitosis
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1. 1\. Description of the Cell Cycle and Mitosis
## 1\. Description of the Cell Cycle and Mitosis
**Why do cells divide?**
Cell divide so that organisms can grow. In order for organisms to grow, body
cells either have to increase their size or divide. Most cells divide, because
smaller is better when it comes to cells.
**Why do cells need to stay small? Why don't cells just keep getting bigger
instead of multiplying?**
Cells are limited in size because the outside (the plasma membrane) must
transport food and oxygen to the inside of the cell. This can be represented
by what is known as the surface to volume ratio. As a cell gets bigger, the
outside is unable to keep up with the inside, because the inside grows at a
faster rate than the outside. This is a problem because cells obtain nutrients
and get rid of wastes through a process called diffusion. Diffusion works
faster over short distances and takes longer over long distances. So if a cell
grows larger instead of dividing, diffusion will be too slow and the cell will
not be able to obtain nutrients and get rid of wastes efficiently, which
ultimately would kill the cell. Thus, cells divide so that an organism can get
bigger, despite the fact that cell size is limited.
Cells also divide to replace damaged or dying cells.
Figure \\(\PageIndex{1}\\). (CC BY-NC-SA)
**The Cell Cycle**
**Interphase** describes the period between cell divisions. Although it may
seem as though the cell is inactive during interphase, quite the opposite is
true. During this phase (the longest phase of the cell cycle) the cell grows,
DNA is replicated and the centrioles divide.
**Interphase is divided into the following three subphases:**
**G1 phase** or “first gap” is a growth phase for the cell.
**S phase** or “synthesis” is when the cell copies its chromosomes.
**G2 phase** or “second gap” is a second growth phase where further growth and
preparations for division occur.
**Mitosis (M Phase) is the process of nuclear division and is divided into the
following phases:**
**Prophase** is the first mitotic phase. During prophase the nucleoli
disappear and the chromatin (DNA and associated proteins) condenses into
discrete chromosomes that are observable with a light microscope. Each
replicated chromosome is composed of two sister chromatids, both containing
the same genetic information. The sister chromatids are joined together at
their centromeres. The mitotic spindle forms from the centrioles and begins to
elongate. As the centrioles reach opposite ends of the cell the spindle fibers
from each of the centrioles attach to each chromosome at a specialized protein
structure called the kinetochore. The kinetochore is located at the centromere
of each chromosome. Other spindle fibers elongate, but instead of attaching to
chromosomes, they interact with spindle from the opposite pole.
**
**
Figure \\(\PageIndex{2}\\). prophase (CC BY-NC-SA; _[ LadyofHats
](http://commons.wikimedia.org/wiki/File:MITOSIS_cells_secuence.svg) _ )
**
**
Figure \\(\PageIndex{3}\\). (CC BY-NC-SA)
**Metaphase** is the longest stage of mitosis. It is during this stage that
the tension applied by the mitotic spindle fibers aligns all of the
chromosomes along the metaphase plate, an imaginary line the divides the cell
in two. This organization is necessary to ensure that in the next phase, when
the chromosomes are separated, each new nucleus will receive one copy of each
chromosome.
**
**
Figure \\(\PageIndex{4}\\). metaphase (CC BY-NC-SA; _[ LadyofHats
](http://commons.wikimedia.org/wiki/File:MITOSIS_cells_secuence.svg) _ )
**Anaphase** is the shortest stage of mitosis. The spindle fibers shorten
during anaphase, pulling the sister chromatids apart towards opposite ends of
the cell.
**
**
Figure \\(\PageIndex{5}\\). anaphase (CC BY-NC-SA; _[ LadyofHats
](http://commons.wikimedia.org/wiki/File:MITOSIS_cells_secuence.svg) _ )
**Telophase** marks the stage where the daughter chromosomes arrive at the
poles and the spindle fibers begin to disperse. Two daughter nuclei form,
nuclear envelopes are constructed and the chromosomes become less condensed.
Mitosis, which describes the division of the nucleus, is now complete.
**
**
Figure \\(\PageIndex{6}\\). telophase (CC BY-NC-SA; _[ LadyofHats
](http://commons.wikimedia.org/wiki/File:MITOSIS_cells_secuence.svg) _ )
**Cytokinesis: The end of the Cell Cycle**
**Cytokinesis** describes the division of the cytoplasm and while it is not a
stage of mitosis (nuclear division), but does result in the completion of cell
division and the end of the cell cycle. In animal cells, cytokinesis involves
the formation of a cleavage furrow, which pinches the cell into two distinct
daughter cells.
Figure \\(\PageIndex{7}\\). cytokinesis (CC BY-NC-SA; _[ LadyofHats
](http://commons.wikimedia.org/wiki/File:MITOSIS_cells_secuence.svg) _ )
_[  ](http://creativecommons.org/licenses/by-nc-sa/3.0/) _
Cell Cycle and Mitosis Tutorial by _[ Dr. Katherine Harris
](https://www.hartnell.edu/mitosis.php) _ is licensed under a _[ Creative
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](http://creativecommons.org/licenses/by-nc-sa/3.0/) _ .
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# You Don’t Need To Lift Heavy Weights To Build Bigger Muscles
Just put in a good effort and do it regularly.
By [ Jennifer Heimlich ](/contributor/jennifer-heimlich)
February 12, 2024
Getty Images
When you see the biggest guy in the gym pull up to the weight room, you might
assume he’ll be reaching for the heaviest weights. You’ve gotta pump massive
iron to build massive muscles, right? Well, not really.
“There's a lot of lore around this routine or that routine, and a lot of it
comes from former Soviet bloc country training regimens where most people were
taking steroids,” says [ Stuart Phillips, PhD ](https://mira.mcmaster.ca/our-
faculty/stuart-phillips/) , a kinesiology professor and research director at
McMaster University. Some of it also comes from a misunderstood study from
1946: While rehabilitating soldiers from World War II, [ army physician Thomas
DeLorme argued ](https://pubmed.ncbi.nlm.nih.gov/22592167/) that heavy
resistance training was better at building muscle than, say, repetitive
activities like walking or biking, and for decades, many took that to mean
_only_ heavy weights were helpful, says Dr. Phillips.
Yet the more scientists look into it, the more they’re finding that heavy
lifting isn’t a prerequisite for growing muscle, or as the experts call it,
“hypertrophy.” Recently, Dr. Phillips led a [ network meta-analysis
](https://bjsm.bmj.com/content/57/18/1211.long) published in the _British
Journal of Sports Medicine_ that looked at 192 randomized, controlled studies
with a total sample size of more than 5,000 people to find the “optimal
prescription for hypertrophy.” What his team discovered shocked many. “You can
lift lighter weights, and as long as you lift them with a high degree of
effort, they're as good as heavier weights in making you bigger,” he says.
Even just using your own body weight, like with push-ups or lunges, works. The
key is simply to get pretty close to what personal trainers call “failure,” or
the point where you feel like you can’t keep going any longer. That could take
up to 25 to 30 reps, and you’ll still build muscle, says Dr. Phillips.
To understand the physiology at play, it helps to know the difference between
our two types of muscle fibers: fast twitch, or type II, produces force but
fatigues quickly (think sprinting), while slow twitch, or type I, gives us
endurance but aren’t super powerful (think marathon running). When you want to
get bigger, it’s the fast twitch you mostly want to target since those have
between 30 to 50 percent more growth potential than their slow counterparts,
says [ Bradley Schoenfeld, PhD ](https://www.lehman.edu/academics/health-
human-services-nursing/health-promotion-nutrition/fac-schoenfeld.php) ,
graduate director of the Human Performance and Fitness program at Lehman
College, who wrote the book [ _Science and Development of Muscle Hypertrophy_
. ](https://www.amazon.com/Science-Development-Muscle-Hypertrophy-
Schoenfeld/dp/1492597678)
While it used to be thought that only heavy loads—weights you can only lift
about three to five times—could activate the fast-twitch fibers, we now know
that’s not the case, Dr. Schoenfeld says. “Provided that you train with a lot
of effort where the last reps are difficult to complete, you will recruit the
majority of the fast-twitch muscle fibers,” he says. “Muscle growth tends to
be the same.”
That said, if your goals are more about strength than size, you’ll want to
keep reaching for the largest dumbbells. Our bodies get better at what we
practice, so if you want to be strong enough to lift heavy things, you have to
practice lifting heavy things, Dr. Phillips says.
But if getting big is primarily what you’re after, rather than worrying about
how much weight you’re hauling up and down, the key is to focus on doing
multiple sets. “There's a certain amount of work you need to do that signals
to your muscle to induce growth, to get bigger,” Dr. Phillips says. Exactly
how much volume you need to put in, however, is an ongoing debate. The _BJSM_
analysis found you need to complete at least two sets to near fatigue to grow
muscle and suggested that training twice a week is more effective than just
once. But doing more and more won’t make you bigger and bigger because, at a
certain point, the benefits plateau.
“My analogy is always, imagine if you dip a cloth in water and you're
squeezing the cloth. So you twist it once, that's one day a week. You twist it
twice and you get a little bit more water. You twist it a third time, and now
you're getting some water out, but it's much less than you got out on the
first and second twist,” says Dr. Phillips.
What the science is unequivocal about is that in order to make gains, you need
to be consistent—which is something that we know can be easy to make and
easier to break. To get yourself to hit the gym regularly, sport and
performance psychologist [ Marla Zucker, PhD, CMPC
](https://bostonsportpsych.com/about/) suggests strategies like reminding
yourself of the reasons why you work out, [ setting some short-term goals
](https://www.gq.com/story/tom-bosworth-goal-setting-podcast-interview) (ones
that you can actually accomplish), and working out with a coach or
accountability buddy to give you some camaraderie and help you enjoy the
process.
Because…you have to like your workout enough to do it over and over again.
Don’t make yourself suffer through it. “If you hate an exercise, there's no
exercise from a muscle growth standpoint that you _have_ to do,” says Dr.
Schoenfeld. “Different exercises can accomplish similar things, so pick
exercises that you like.” And do them with any weights you want as long as
they bring on that burn—even if that means that you’re doing more reps than
the guy grunting next to you.
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| biology | 313601 | https://no.wikipedia.org/wiki/PSTricks | PSTricks | PSTricks er et sett med utvidelser til LaTeX som gjør en i stand til å skrive grafikkode inni et TeX/LaTeX-miljø. Det ble opprinnelig utviklet av Timothy Van Zandt og har i de senere år blitt vedlikeholdt av Denis Girou, Sebastian Rahtz and Herbert Voss.
Det finnes en rekke ulike kommandoer som man bruker for å lage et bilde.
\begin{pspicture}(0,0)(6,6)
%\psgrid[gridcolor=lightgray,gridlabels=0pt]
\psline[linecolor=red](1,1)(5,1)(1,4)(1,1)
\pscurve[linecolor=green,linewidth=2pt,%
showpoints=true](5,5)(3,2)(4,4)(2,3)
\pscircle[linecolor=blue,linestyle=dashed](3,2.5){1}
\end{pspicture}
pst-plot lar en tegne grafen til matematiske funksjoner. Følgende kode vil generere bildet under:
\begin{pspicture*}(-7.5,-3)(7.5,3)
\psaxes[labels=none](0,0)(-7,-2)(7,2)
\psplot[linecolor=blue, linewidth=1.5pt]%
{-7}{7}{x 0.01745329252 div sin}
\uput[45](3.1415926,0){$\pi$}
\uput[90](-1.570796,0){$-\pi/2$}
\uput[-90](1.570796,0){$\pi/2$}
\uput[-135](-3.1415926,0){$-\pi$}
\psline[linewidth=1pt,linecolor=red,linestyle=dotted]%
(1.57079632,1)(1.57079632,0)
\psline[linewidth=1pt,linecolor=red,linestyle=dotted]%
(-1.57079632,-1)(-1.57079632,0)
\end{pspicture*}
Se også
LaTeX
Eksterne lenker
PSTricks dokumentasjon
PSTricks eksempler
LaTeXDraw
Fri_programvare
Linux-programmer | norwegian_bokmål | 0.74799 |
muscle_bigger/Muscle_hypertrophy.txt |
Muscle hypertrophy or muscle building involves a hypertrophy or increase in size of skeletal muscle through a growth in size of its component cells. Two factors contribute to hypertrophy: sarcoplasmic hypertrophy, which focuses more on increased muscle glycogen storage; and myofibrillar hypertrophy, which focuses more on increased myofibril size. It is the primary focus of bodybuilding-related activities.
Hypertrophy stimulation[edit]
A range of stimuli can increase the volume of muscle cells. These changes occur as an adaptive response that serves to increase the ability to generate force or resist fatigue in anaerobic conditions.
Strength training[edit]
Strength training is used to regulate muscle hypertrophy.
Main article: Strength training
Strength training (resistance training) causes neural and muscular adaptations which increase the capacity of an athlete to exert force through voluntary muscular contraction: After an initial period of neuro-muscular adaptation, the muscle tissue expands by creating sarcomeres (contractile elements) and increasing non-contractile elements like sarcoplasmic fluid.
Muscular hypertrophy can be induced by progressive overload (a strategy of progressively increasing resistance or repetitions over successive bouts of exercise to maintain a high level of effort). However, the precise mechanisms are not clearly understood; the current accepted theory is through the combination of mechanical tension, metabolic stress, and muscle damage. Although, there is insufficient evidence to suggest that metabolic stress has any significant effect on hypertrophy outcomes.
Muscular hypertrophy plays an important role in competitive bodybuilding and strength sports like powerlifting, American football, and Olympic weightlifting.
Anaerobic training[edit]
Main article: Anaerobic exercise
The best approach to specifically achieve muscle growth remains controversial (as opposed to focusing on gaining strength, power, or endurance); it was generally considered that consistent anaerobic strength training will produce hypertrophy over the long term, in addition to its effects on muscular strength and endurance. Muscular hypertrophy can be increased through strength training and other short-duration, high-intensity anaerobic exercises. Lower-intensity, longer-duration aerobic exercise generally does not result in very effective tissue hypertrophy; instead, endurance athletes enhance storage of fats and carbohydrates within the muscles, as well as neovascularization.
Temporary swelling[edit]
This section needs more reliable medical references for verification or relies too heavily on primary sources. Please review the contents of the section and add the appropriate references if you can. Unsourced or poorly sourced material may be challenged and removed. Find sources: "Muscle hypertrophy" – news · newspapers · books · scholar · JSTOR (May 2017)
During a workout, increased blood flow to metabolically active areas causes muscles to temporarily increase in size. This phenomenon is referred to as transient hypertrophy, or more commonly known as being "pumped up" or getting "a pump." About two hours after a workout and typically for seven to eleven days, muscles swell due to an inflammation response as tissue damage is repaired. Longer-term hypertrophy occurs due to more permanent changes in muscle structure.
Factors affecting hypertrophy[edit]
Biological factors (such as DNA and sex), nutrition, and training variables can affect muscle hypertrophy.
Individual differences in genetics account for a substantial portion of the variance in existing muscle mass. A classical twin study design (similar to those of behavioral genetics) estimated that about 53% of the variance in lean body mass is heritable, along with about 45% of the variance in muscle fiber proportion.
Testosterone helps to increase muscle hypertrophy.
During puberty in males, hypertrophy occurs at an increased rate. Natural hypertrophy normally stops at full growth in the late teens. As testosterone is one of the body's major growth hormones, on average, males find hypertrophy much easier (on an absolute scale) to achieve than females, and, on average, have about 60% more muscle mass than women. Taking additional testosterone, as in anabolic steroids, will increase results. It is also considered a performance-enhancing drug, the use of which can cause competitors to be suspended or banned from competitions. Testosterone is also a medically regulated substance in most countries, making it illegal to possess without a medical prescription. Anabolic steroid use can cause testicular atrophy, cardiac arrest, and gynecomastia.
In the long term, a positive energy balance, when more calories are consumed rather than burned, is helpful for anabolism and therefore muscle hypertrophy. An increased requirement for protein can help elevate protein synthesis, which is seen in athletes training for muscle hypertrophy. However, there is no scientific consensus on whether strength-training athletes have increased protein requirements.
Training variables, in the context of strength training, such as frequency, intensity, and total volume also directly affect the increase of muscle hypertrophy. A gradual increase in all of these training variables will yield muscular hypertrophy.
Changes in protein synthesis and muscle cell biology associated with stimuli[edit]
Protein synthesis[edit]
Main article: Protein biosynthesis
Protein biosynthesis starting with transcription and post-transcriptional modifications in the nucleus. Then the mature mRNA is exported to the cytoplasm where it is translated. The polypeptide chain then folds and is post-translationally modified.
The message filters down to alter the pattern of gene expression. The additional contractile proteins appear to be incorporated into existing myofibrils (the chains of sarcomeres within a muscle cell). There appears to be some limit to how large a myofibril can become: at some point, they split. These events appear to occur within each muscle fiber. That is hypertrophy results primarily from the growth of each muscle cell rather than an increase in the number of cells. Skeletal muscle cells are however unique in the body in that they can contain multiple nuclei, and the number of nuclei can increase.
Cortisol decreases amino acid uptake by muscle tissue, and inhibits protein synthesis. The short-term increase in protein synthesis that occurs subsequent to resistance training returns to normal after approximately 28 hours in adequately fed male youths. Another study determined that muscle protein synthesis was elevated even 72 hours following training.
A small study performed on young and elderly found that ingestion of 340 grams of lean beef (90 g protein) did not increase muscle protein synthesis any more than ingestion of 113 grams of lean beef (30 g protein). In both groups, muscle protein synthesis increased by 50%. The study concluded that more than 30 g protein in a single meal did not further enhance the stimulation of muscle protein synthesis in young and elderly. However, this study didn't check protein synthesis in relation to training; therefore conclusions from this research are controversial. A 2018 review of the scientific literature concluded that for the purpose of building lean muscle tissue, a minimum of 1.6 g protein per kilogram of body weight is required, which can for example be divided over 4 meals or snacks and spread out over the day.
It is not uncommon for bodybuilders to advise a protein intake as high as 2–4 g per kilogram of bodyweight per day. However, scientific literature has suggested this is higher than necessary, as protein intakes greater than 1.8 g per kilogram of body weight showed to have no greater effect on muscle hypertrophy. A study carried out by American College of Sports Medicine (2002) put the recommended daily protein intake for athletes at 1.2–1.8 g per kilogram of body weight. Conversely, Di Pasquale (2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight. However athletes involved in strength events (..) may need even more to maximize body composition and athletic performance. In those attempting to minimize body fat and thus maximize body composition, for example in sports with weight classes and in bodybuilding, it's possible that protein may well make up over 50% of their daily caloric intake."
Microtrauma[edit]
Main article: Microtrauma
Muscle fibres may be "microtorn" during microtrauma
Microtrauma is tiny damage to the muscle fibers. The precise relation between microtrauma and muscle growth is not entirely understood yet.
One theory is that microtrauma plays a significant role in muscle growth. When microtrauma occurs (from weight training or other strenuous activities), the body responds by overcompensating, replacing the damaged tissue and adding more, so that the risk of repeat damage is reduced. Damage to these fibers has been theorized as the possible cause for the symptoms of delayed onset muscle soreness (DOMS), and is why progressive overload is essential to continued improvement, as the body adapts and becomes more resistant to stress.
However, other work examining the time course of changes in muscle protein synthesis and their relationship to hypertrophy showed that damage was unrelated to hypertrophy. In fact, in one study the authors showed that it was not until the damage subsided that protein synthesis was directed to muscle growth.
Myofibrillar vs. sarcoplasmic hypertrophy[edit]
This article's factual accuracy is disputed. Relevant discussion may be found on the talk page. Please help to ensure that disputed statements are reliably sourced. (May 2017) (Learn how and when to remove this template message)
Hypertrophy of cell
In the bodybuilding and fitness community and even in some academic books skeletal muscle hypertrophy is described as being in one of two types: Sarcoplasmic or myofibrillar. According to this hypothesis, during sarcoplasmic hypertrophy, the volume of sarcoplasmic fluid in the muscle cell increases with no accompanying increase in muscular strength, whereas during myofibrillar hypertrophy, actin and myosin contractile proteins increase in number and add to muscular strength as well as a small increase in the size of the muscle. Sarcoplasmic hypertrophy is greater in the muscles of bodybuilders because studies suggest sarcoplasmic hypertrophy shows a greater increase in muscle size while myofibrillar hypertrophy proves to increase overall muscular strength making it more dominant in Olympic weightlifters. These two forms of adaptations rarely occur completely independently of one another; one can experience a large increase in fluid with a slight increase in proteins, a large increase in proteins with a small increase in fluid, or a relatively balanced combination of the two.
In sports[edit]
Examples of increased muscle hypertrophy are seen in various professional sports, mainly strength related sports such as boxing, olympic weightlifting, mixed martial arts, rugby, professional wrestling and various forms of gymnastics. Athletes in other more skill-based sports such as basketball, baseball, ice hockey, and football may also train for increased muscle hypertrophy to better suit their position of play. For example, a center (basketball) may want to be bigger and more muscular to better overpower his or her opponents in the low post. Athletes training for these sports train extensively not only in strength but also in cardiovascular and muscular endurance training.
Pathology[edit]
Main article: Pseudoathletic appearance
Some neuromuscular diseases result in true hypertrophy of one or more skeletal muscles, confirmed by MRI or muscle biopsy. As this muscle hypertrophy is not the result of resistance training nor heavy manual labour, this is why the muscle hypertrophy is described as a pseudoathletic appearance.
As muscle hypertrophy is a response to strenuous anaerobic activity, ordinary everyday activity would become strenuous in diseases that result in premature muscle fatigue (neural or metabolic), or disrupt the excitation-contraction coupling in muscle, or cause repetitive or sustained involuntary muscle contractions (fasciculations, myotonia, or spasticity). In lipodystrophy, an abnormal deficit of subcutaneous fat accentuates the appearance of the muscles, though the muscles are quantifiably hypertrophic (possibly due to a metabolic abnormality).
Diseases that result in true muscle hypertrophy include, but not limited to, select: muscular dystrophies, metabolic myopathies, endocrine myopathies, congenital myopathies, non-dystrophic myotonias and pseudomyotonias, denervation, spasticity, and lipodystrophy. The muscle hypertrophy may persist throughout the course of the disease, or may later atrophy, or become pseudohypertrophic (muscle atrophy with infiltration of fat or other tissue). For instance, Duchenne and Becker muscular dystrophy may start as true muscle hypertrophy, but later develop into pseudohypertrophy.
See also[edit]
Anabolism
Colorado Experiment
Davis' law
Follistatin
Lean body mass
Muscle atrophy
Muscle dystrophy
Myostatin
Pseudoathletic appearance
Pseudohypertrophy | biology | 585842 | https://no.wikipedia.org/wiki/Megalodon | Megalodon | Megalodon (gresk: μέγας (megas) «stor, mektig» og ὀδoύς (odoús), «tann»; i betydningen «stor tann») er en enorm, men nå utdødd art av hai som levde for cirka 28–1,5 millioner år siden; i tiden kenozoikum (midtre miocen fram til slutten av pliocen). Nyere forskning viser at monsterhaien trolig var varmblodig, og at dette kan ha medvirket til utryddelsen.
Det vitenskapelige navnet for denne arten er vanligvis forkortet til C. megalodon i litteraturen. Den er ansett som det største og mest kraftfulle rovdyret i virveldyrenes historie, og hadde sannsynlig en gjennomgripende virkning på strukturen i det maritime livet. Fossiler antyder at denne enorme haien nådde en maksimal lengde på opptil 18 meter, og at den hadde spredning over hele kloden. Megalodon hadde tenner som er blant de største noensinne, over 18 cm lange, og kunne veie over 100 tonn. Forskerne mener at megalodon var en tettbygd og stor versjon av dagens hvithai, Carcharodon carcharias.
Beskrivelse
Megalodon jaktet på store og mellomstore hvaler, og man spekulerer i at megalodon angrep fra dypet, lik dagens hvithai. I motsetning til den moderne hvithaien gikk den ikke etter de myke kjøttfulle delene av byttet for å blø den ihjel, men gikk heller etter de benete områdene, som brystkassen eller finnene, for å sette dyret ut av spill eller drepe det fort med et dødelig bitt mot brystregionen. Megalodon kunne bite med det hittil sterkeste bittet i dyrerikets historie.
Ungene ble født velutviklede, uten et ytre eggstadie. Beregninger antyder at de var rundt 2 meter ved fødselen. Dette antyder at de tok til seg næring under fosterutviklingen, trolig ved livmorkannibalisme.
Skjelettet på en megalodon var brusk, og det er derfor umulig å finne komplette rester av disse dyrene. Megalodons tenner er derimot vanlige funn og kan finnes i alle verdenshav, noe som støtter spekulasjonene om at haien fantes over hele kloden. Det er også funnet ryggvirvler.
Referanser
Eksterne lenker
Bruskfisker
Fisker formelt beskrevet i 1843
Dyr formelt beskrevet av Louis Agassiz | norwegian_bokmål | 1.27967 |
muscle_bigger/whydosomepeopleputon.txt | X
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# 5 Factors That Influence How Quickly You Build Muscle
There are good reasons that explain why you may have a hard time putting on
muscle.
Giselle Castro-Sloboda Fitness and Nutrition Writer
I'm a Fitness & Nutrition writer for CNET who enjoys reviewing the latest
fitness gadgets, testing out activewear and sneakers, as well as debunking
wellness myths. On my spare time I enjoy cooking new recipes, going for a
scenic run, hitting the weight room, or binge-watching many TV shows at once.
I am a former personal trainer and still enjoy learning and brushing up on my
training knowledge from time to time. I've had my wellness and lifestyle
content published in various online publications such as: Women's Health,
Shape, Healthline, Popsugar and more.
Expertise Fitness and Wellness
[ See full bio ](/)
Giselle Castro-Sloboda
Sept. 2, 2022 5:00 p.m. PT
7 min read
RLT_Images/Getty Images
Your body's ability to build muscle can be affected by many factors. These
include your genetics, diet, type of workouts you're doing, hormones, age and
even gender. More women are starting to lift weights and are no longer afraid
[ of getting "bulky" ](/health/fitness/does-lifting-weights-make-women-
bulky/) from strength training. They're also embracing the many health [
benefits that come from weight training ](/health/fitness/does-lifting-
weights-help-you-lose-weight-and-other-common-weightlifting-questions-
answered/) .
If your [ goal ](/health/fitness/7-fitness-goals-to-set-for-the-new-year/)
is to build more muscle and you're struggling to get there, you'll be glad to
know that there are many ways to improve your chances of gaining more muscle
and strength. It's important to understand what determines your muscle-
building ability.
We chatted with fitness experts and looked at scientific research to explain
why muscle growth varies per person and what changes you can make to get those
gains. Read on to find out what influences how quickly you build muscle and
how you can make them work in your favor.
## Genetics and hormones play a big role
![gettyimages-982409358]()
Westend61/Getty Images
Genetics play an important role in determining your body's ability to put on
muscle (and its limitations), partly by influencing your hormonal and muscular
make-up. But they're not the end-all, be-all.
### Hormones
Anabolic hormones -- consisting of [ growth hormone, estrogen, insulin and
testosterone ](https://www.healthline.com/health/catabolism-vs-
anabolism#hormones) \-- are key for muscle building. Contrary to popular
belief, estrogen and testosterone are both important for muscle structure and
function. Testosterone is responsible for muscle growth, while [ estrogen
improves muscle mass and strength
](https://www.frontiersin.org/articles/10.3389/fphys.2018.01834/full) , as
well as growing the collagen of connective tissues, such as your bones,
ligaments and tendons. Women typically produce more estrogen and less
testosterone than men, which is why men often have an easier time with visible
muscle growth. (The [ same seems to be true
](https://www.science.org/content/article/scientist-racing-discover-how-
gender-transitions-alter-athletic-performance-including) for transgender
people who take hormone replacement therapy.)
![gettyimages-1177357479]()
The molecular structure of testosterone, an important hormone for muscle
growth.
Evgeny Gromov/Getty Images
"Testosterone is an anabolic hormone and 10 times higher in men which can
benefit muscle growth goals," explains Ryan Turner, a registered dietitian,
certified specialist in sports dietetics and founder of Food is Fuel NYC. [
Testosterone helps release growth hormones
](https://www.precisionnutrition.com/anabolic-hormones-and-muscle) , which
stimulate tissue growth, and it connects with nuclear receptors in DNA, which
causes protein synthesis (or muscle growth).
Turner points out that as both men and women age, the reduction of both
testosterone and estrogen hormones can result in the breakdown of muscle.
Other aspects that can diminish your muscles are fluctuating hormones, such as
adrenaline, cortisol and glucagon, which prevent them from growing. That's why
it's important to monitor your day to day stress, sleep, and diet, since these
impact those hormones and in turn affect your ability to progress.
### Muscle fibers
Another thing that can influence how well you put on muscle are your fast-
twitch and slow-twitch muscle fibers. Skeletal muscles are composed of both of
these fibers, which serve different purposes and determine your potential
athletic ability. Fast-twitch muscle fibers are large and generate quick
bursts of energy that are good for exercises such as sprinting, jumping,
powerlifting and strength training. On the other hand, slow-twitch muscle
fibers are smaller and intended to help you sustain long periods of cardio
such as long distance running, swimming, cycling and any type of endurance
training.
![gettyimages-147218800]()
Anatomy of musculature in a cis male body.
Sciepro/Getty Images
We all have fast-twitch and slow-twitch muscle fibers, but genetically some
people may be predisposed to have more of one than the other. And fast-twitch
fibers are the ones that you need for sizable muscle growth.
"Different muscle fiber characteristics, Type I and II, slow and fast twitch
respectively can both increase in size, but the latter can have more growth
potential," explains Turner.
Research has found that two genes, [ known as the ACTN3 gene and the ACE gene
](https://medlineplus.gov/genetics/understanding/traits/athleticperformance/)
, heavily influence which muscle fibers we have more of. The ACTN3 gene helps
create a protein that is found in fast-twitch muscle fibers, for example,
while a genotype known as 577XX can occur across both genes, reducing fast-
twitch muscle fibers and increasing slow-twitch fibers. On the other hand, the
577RR genotype is linked to a greater presence of fast-twitch muscle fibers.
Tendon length can also determine how big your muscles get. Tendons vary per
person, but it's been found that having [ shorter tendons allow you to gain
bigger muscles
](https://www.sciencedaily.com/terms/tendon.htm#:~:text=Tendon%20length%20is%20practically%20the,man%20with%20a%20longer%20tendon.)
, while longer tendons make it harder to do so.
Still, it's not all about how you're born. "There is an upper limit to a
muscle's fiber size; however, don't forget that without proper and consistent
training the muscle's true potential won't be realized," Turner warns. So just
because your genetics say that you can put on muscle easier, if you don't put
in the work, there won't be anything to show for it.
## You are what you eat
![gettyimages-1211970540]()
MoMo Productions/Getty Images
It's impossible to ignore nutrition when discussing muscle mass. How you eat
can make a big difference on how well your body puts on and maintains muscle.
"Muscle is a very expensive tissue to maintain," explains Tami Smith, a
certified personal trainer and owner and CEO of Fit Healthy Momma. She says
you have to be intentional on not only putting it on, but also maintaining it.
Eating enough calories and protein helps with [ muscle recovery and growth
](https://www.healthline.com/nutrition/eat-after-workout#TOC_TITLE_HDR_3)
after a workout. Muscle is made up of protein, and eating adequate protein
after strength training is essential to [ limit muscle protein breakdown and
assist with muscle synthesis ](/health/nutrition/how-to-tell-if-you-eat-
enough-protein-and-how-to-get-more/) (growth of new muscle). Turner says that
individuals who strength train require more protein than their non-training
counterparts. Older adults will require more in general, but even more so if
they strength train. Similarly, if you want to put on muscle, you'll need to
add more calories to your diet.
"Well trained individuals consuming an additional 500 to 1,000 calories per
day, and untrained individuals, new to strength training, eating up to an
additional 2000 calories per day can show positive changes in muscle mass,"
says Turner. "In my day-to-day work with clients, in many cases 15 to 18
calories per pound has been supportive of client hypertrophy goals." (Muscular
hypertrophy refers to growing your muscles through exercise.)
**Read more:** [ Best Protein Powders for Your Muscle Gains in 2022
](/health/fitness/best-protein-powders/)
![gettyimages-1314742668]()
People who strength train need to consume more protein than those who don't.
VioletaStoimenova/Getty Images
Of the 20 amino acids found in protein, [ leucine is the most essential to
promote muscle growth ](https://www.healthline.com/nutrition/10-high-leucine-
foods) \-- and the body cannot produce it. "Three to four grams of leucine [or
6 to 8 ounces of animal protein] can promote maximal protein synthesis,"
explains Turner. If you're a vegetarian, you will need to strategically
prepare your meals ahead of time to achieve this, because plant based proteins
may only provide 25 to 60% of the recommended amount of leucine.
Some women who are having a hard time building muscle may be self-sabotaging
their potential without even realizing it. "Many women are caught in the
dieting mindset of always wanting to be smaller and weigh less on the scale,
which isn't conducive to building muscle," explains Smith. She says a lot of
women are scared to see the scale go up a bit, because adding muscle means
you're going to be adding weight. "I have so many clients that weigh more now
but look completely different with more muscle on their bodies," Smith says.
If you do allow yourself to gain that weight for muscle building, you can
change the look and feel of your body, and the number on the scale will become
irrelevant.
Turner says simple nutrition strategies such as meal planning, meal
scheduling, budgeting and supplementation can be implemented to overcome
challenges such as figuring out your food intake. If you aren't sure where to
begin, it's a good idea to consult with a sports dietitian who can set you on
the right path for your goals.
**Read more:** [ 7 Best Creatine Supplements to Build Strength
](/health/nutrition/7-best-creatine-supplements-to-build-strength/)
## The power of training (and rest)
![gettyimages-1056286622]()
svetikd/Getty Images
Once you have your nutrition in check and understand how your genetics
influence your muscle growth, strength training is another key player.
There are two types of muscular hypertrophy, known as [ myofibrillar
hypertrophy and sarcoplasmic hypertrophy
](https://www.healthline.com/health/muscular-hypertrophy#definition) .
Myofibrillar hypertrophy focuses on building strength, while sarcoplasmic
hypertrophy increases the volume of sarcoplasmic fluid within the muscle to
make it look bigger (think the "pump" you get after an arm workout).
Depending on your goals, the way you train will influence whether you get
stronger or have more defined muscles. Lifting lighter weights for higher
repetitions (ranges from six to 15 reps) will give you a defined look, but
often you'll lack strength -- bodybuilders use this method. To achieve
strength and up your muscle growth, you'll have to lift heavy weights for
fewer repetitions (six or fewer reps) and longer rest periods. Powerlifters
use this method.
Either way, you have to continue to challenge yourself to see continued growth
over time. "Using a program that implements some kind of progressive overload
to continue to build and challenge your muscles for growth is key," says
Smith. This means less cardio, HIIT and circuit-style training and more of a
focus on heavy lifting exercises.
Additionally, making sure you get a [ proper night's sleep
](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6988893/) (at least 7 to 9
hours) helps optimize recovery after a tough workout. While you're at rest,
your body is putting in the work to repair muscles and regulate your hormones,
which as you already know play a big part in muscle building. Lack of sleep
not only affects your ability to perform well, but also inhibits your growth
hormones.
There are so many [ benefits to strength training ](/health/fitness/does-
lifting-weights-help-you-lose-weight-and-other-common-weightlifting-questions-
answered/) aside from building muscle, such as increasing your metabolic rate,
improving your lean body mass which promotes blood sugar control, reducing
risk of injury, improving mental health, strengthening bone health and so much
more. Aiming to strength train two to three times a week is a good rule of
thumb, but if you'd like more guidance, consult with a personal trainer who
can create a personalized program that will help you achieve your goals.
## So what's the takeaway?
![gettyimages-1131209322-1]()
Corey Jenkins/Getty Images
Muscle-building abilities vary from person to person. That said, it's
important to understand the big picture, because it doesn't begin and end with
your genetics. You may have a genetic profile similar to that of an Olympic
athlete, but if you don't put in the work, you'll never learn your actual
potential. Likewise, if you are struggling to grow a certain muscle group with
ease, it doesn't mean you won't be able to achieve it with a little extra
work.
If stronger or bigger muscles are an important goal for you, dialing in on
your daily caloric intake, meeting your protein goals, and adhering to a
purposeful strength training program will help improve your chances.
The information contained in this article is for educational and informational
purposes only and is not intended as health or medical advice. Always consult
a physician or other qualified health provider regarding any questions you may
have about a medical condition or health objectives.
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| biology | 135266 | https://da.wikipedia.org/wiki/Bodytoning | Bodytoning | Bodytoning betyder opstramning af kroppen. Andre betegnelser er workout, bodysculpting, stram op o.l. Træningen er en variation af traditionel motionsgymnastik og er en af de mest udbredte træningsformer for motionshold.
Metode
Bodytoning er muskeltræning, styrke såvel som udholdenhed, med eller uden redskaber (elastikker, tubes, bånd, håndvægte, vægtstænger og træningsbolde) for store såvel som små muskler.
Hver øvelse udføres, som i styrketræning, 1-3 sæt á 8-16 gentagelser. En speciel form for muskeltræning i aerobicsalen er BodyPump, et konceptprogram (samme program i tre måneder) som er muskeludholdenhedstræning med mange gentagelser.
Et træningspas består af opvarmning (7-10 minutter), muskel- og balancetræning og nedkøling (20-40 minutter) og udstrækning (5-10 minutter).
Bodytoning findes i gymnastik- og idrætsforeninger og i kommercielle fitnesscentre.
Uddannelse
Bodytoning-/aerobicinstruktører uddannes på Trænerakademiet på Aalborg Sportshøjskole (1-årig), på idræts- og sportshøjskoler, via DGF, DGI og DFIF, og på kommercielle fitnesscentres uddannelser.
Litteratur
Aagaard, Marina, Workout – styrketræning og bodytoning med kropsvægt og redskaber, Aagaard, 2010.
Gymnastik
Motion | danish | 0.748125 |
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How to Get Bigger: 25 Ways to Get Big Muscles
Looking for bigger muscles? We’ve got 25 ways that’ll show you how to get bigger and stronger, faster so that you'll have your dream physique.
Michael Schletter, C.P.T.Oct 16, 2022 9:36 PM EDT
Every guy who walks into the gym has an aspiration to get bigger. That presents the gym-going guy with an age-old problem: How do you do it?
To help simplify the process, we've compiled a list of the 25 best ways to get big—and we've kept each method short and sweet, so you can get on to your workouts. For more in-depth information about each strategy, click through to the related article on our site.
1. Eat more
"Extra calories combined with training leads to growth," says Sean Hyson, C.S.C.S. It's really that cut and dry. More muscle comes from more food. The right kind of food, that is—like the 9 best foods for effective clean-bulking.
2. Power up with protein
Proteins are the building blocks of muscle. They assist with the rebuilding and recovery process. Shoot for 1-1.5 grams of protein per lean pound of body weight. We like these 12 protein-filled foods for your physique.
3. Don't cut carbs
Numerous studies have pointed to the benefit of protein supplements in muscle building, but many of them also mention carbohydrates as a hormone-balancing component that maximizes your gains after workouts. If you're looking to get bigger, here are 7 more reasons to keep the carbs.
4. Use dumbbells
Andrew Sakhrani, C.S.C.S., a Montreal-based strength coach, encourages occasionally swapping out barbell work with dumbbells. Why? "Dumbbell presses open up the chest and recruit more muscle fibers.” More muscle fibers = bigger muscles. This works for other exercises, too.
5. Work your back
It’s easy to focus on your arms and chest. However, too much training on those areas can lead to imbalances and injury, most of which can be avoided by doing plenty of rowing/pulling work.
6. Sleep
Getting bigger isn't just about what you do - it's also about rest. “Most of your growth hormone release in a day comes during sleep,” says Hyson. Stick with eight hours as a guideline. Here's everything an athlete needs to know about sleep and recovery.
7. Pump up the volume
Bodybuilders, widely known as the biggest guys on the planet, have an age-old training method that has withstood the test of time: volume training. They typically do five or more exercises per body part, four sets of 8-12 reps, amounting to approximately 200 reps per body part.
8. Go heavy
Circuits might get the blood flowing, but heavy lifting skyrockets testosterone levels throughout the body. Hyson recommends using the heaviest load possible for “sets of five or fewer reps.” This extra testosterone will help you get bigger quicker.
9. Move with multijoint exercises
The foundation of a big, muscular body comes from big, compound lifts, defined as motions that incorporate at least two joints. One example: the chinup/pullup. "The chinup is the original biceps curl," Sakhrani says. This principle holds true for all muscle groups, he adds.
10. Ease off your workload at times
Sometimes, the best way to increase your strength is to throttle back for a few days to give your body a chance to rebuild and recuperate. Decrease the weight, up the reps, and slash the last two sets. By scaling back occasionally in sequence with your workout routine, you allow for full recovery.
11. Change things up
Although we follow workout “routines,” there's always a need for variety. A workout shouldn't just be a weightlifting challenge—there should also be a level of complexity and variation to each move. Alternatively, try to work in a little bit of high-intensity interval training or cardio moves into each workout to make sure your body is constantly adjusting. Here are 11 reasons you're not breaking training plateaus.
12. Work your legs
Big powerlifting moves like squats and deadlifts stimulate your body to release high levels of testosterone, resulting in total-body growth. These two moves alone will add muscle everywhere.
13. Use your bodyweight
Remember, Bruce Lee was ripped and his muscles certainly weren’t small. He always touted the importance of body-weight exercises.
14. Train with a partner
“Competition in the weight room boosts testosterone and makes you enjoy your workouts more, so you’ll stick with them. You’ll also be forced to train harder,” says Hyson. So grab a buddy and get after it.
15. Take creatine
Creatine, when taken responsibly, has been linked to muscle gain in almost every study that has been performed on it. Don't believe us? We've got plenty of great reading material on the benefits of creatine.
16. Always focus on form
It sucks to sit out with an injury, especially because it kills your progress. Keep your form strict, and you’ll build more muscle while reducing the risk of getting hurt.
17. Be consistent
Going to the gym once a week won’t get you bigger. Pick a number of days to work out (3-4 is optimal), show up, and work hard, and you’ll see results quickly. Here's how to stay motivated to work out.
18. Chill out
Tension and stress stimulate your body to release cortisol, a stress hormone that inhibits muscle-building and promotes muscle breakdown. Try to breathe easy throughout the day, and practice mental exercises to keep stress at a minimum throughout the day. It'll maximize your muscle, and improve your overall sense of well-being.
19. Don't limit yourself
If you’re stuck at a weight and unsure if you can make that jump up to 225 from 215 on the bench press, don't just walk away from it. Grab a spotter who knows what they're doing, and give it a shot. Worst-case scenario? You fail, then you can try again next week. Best case? Boom—you've got a new PR.
20. Use a spotter
Spotters help you get that extra rep, and can help you keep an eye on your form and count reps when you're focused on moving a massive weight. Those extra reps and improved form will lead to muscle gains in the long run.
If your job is flexible and you can use your lunch break to get in a sweat session, try these weight-loss routines.
21. Consult a professional
There’s a reason that most trainers are muscular and fit—they know what they’re doing. Search out an educated trainer and have a session or two with him or her to learn some new moves or some new nutrition tricks to employ in your fit lifestyle.
22. Find your “zone”
Whether it takes a certain playlist on your iPod or you have to wear that weird pair of shoes, it’s important to have the right mindset when you enter the gym or you’ll be distracted and feel like you can’t get anything done.
23. Be intense
Joking around, texting, and being social are great—just not in the gym. Focus on your workout, that’s what you’re at the gym for. If you have to respond, keep it short and do it during your rest interval.
24. Always warm up properly
Every time you lift, you’re waging a war on the weights. However, you won’t see any benefit without preparing properly for that war. Take care of your joints, ligaments, tendons, and muscles. Warm up!
25. Experiment…
If you're following a program, be sure to give it at least 6-8 weeks. If you're not happy with your results, don't be afraid to try something completely different. Change the exercises, amount of weight, reps, rest periods, amount of days, you name it.
STRENGTH TRAININGBULK UPMASS BUILDING
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| biology | 1374865 | https://no.wikipedia.org/wiki/Kort%20forhudsstreng | Kort forhudsstreng | Kort forhudsstreng er når forhudsstrengen til penis er for kort, og dermed begrenser bevegelse av forhuden. Strengen bør normalt være lang og myk nok slik at forhuden kan trekkes fullt tilbake og legges jevnt rundt skaftet til penis i erigert tilstand.
Kjønnsorganer | norwegian_bokmål | 1.32015 |
parthenogenesis/human-egg-cell-explained.txt |
Call us today on +44 7897 035438 Why Apricity Treatments Pricing Resources Get in touch For employers Blog > The human egg cell explained for egg donors The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant. Medically verified Written by Apricity Team What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp Keep reading Written by Apricity Team i Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy Legal Notice T&Cs Refund Policies Privacy Cookies Ⓒ Apricity Fertility UK Limited. All rights reserved
Call us today on +44 7897 035438 Why Apricity Treatments Pricing Resources Get in touch For employers Blog > The human egg cell explained for egg donors The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant. Medically verified Written by Apricity Team What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp Keep reading Written by Apricity Team i Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy Legal Notice T&Cs Refund Policies Privacy Cookies Ⓒ Apricity Fertility UK Limited. All rights reserved
Blog > The human egg cell explained for egg donors The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant. Medically verified Written by Apricity Team What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant. Medically verified Written by Apricity Team What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant. Medically verified Written by Apricity Team
The human egg cell explained for egg donors The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant.
The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant.
The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant.
The egg cell, o ovum (plural ova), is the female reproductive cell, or gamete. During the egg donation process , egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant.
, egg donors donate their eggs cells for these to be fertilised by sperm from the male recipient; as a result, embryos usually develop. One (or possibly two) of these fresh embryos will then be placed into the recipient (the woman receiving the eggs), giving her a good chance of becoming pregnant.
What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released. How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later. What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest. Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
What is the structure of an egg cell? Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg. Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total. Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell. Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur. Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell. How big is a human egg? The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long. How are eggs produced? Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released.
Above you will see a diagram that labels the main parts of the human egg cell, together with an illustration of a real human egg.
Nucleus: the nucleus is the heart of the egg cell; it contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. So once an egg and sperm combine during fertilisation the resulting embryo will have the normal 46 chromosomes in total.
Cytoplasm: the cytoplasm is a gel-like substance that holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria, which supply most of the energy for the cell.
Zona Pellucida: the zona pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age – the reason that an egg does not fertilise. ‘Assisted hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall, allowing the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur.
Corona Radiata: the corona radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the zona pellucida – the outer protective layer of the egg – and their main purpose is to supply vital proteins to the cell.
The human egg, or ovum, is one of the largest cells in the human body. That said, it is still very small and measures approximately 0.12 mm in diameter. You would need 9 eggs to reach a millimetre in length, and if you laid 100 of them side by side they would sit on a line just 12 mm (1.2cm) long.
Eggs are produced in the ovaries, which are normally situated towards the back of a woman’s abdomen below the kidneys. The eggs develop from tiny cells inside the ovaries, going through various stages of development – known as oogenesis – until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if one ovary is absent or dysfunctional then the other ovary continues to provide eggs to be released.
How many eggs are there in an ovary? A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia. By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation. Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time. About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation. How does an egg develop? At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later.
A woman is born with approximately 500,000 potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more; in fact the number of eggs will steadily decline over her lifetime and be absorbed back into the body in a process known as atresia.
By the time a woman reaches puberty, the million original follicles will have reduced to roughly 300,000 ; they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is then released into the fallopian tube during ovulation.
Given an average span of 40 years between puberty and menopause, with one egg being released per month, only 400-500 eggs in total will actually be released . By the time a woman reaches the menopause, few or no follicles remain. Any that do are unlikely to mature and become viable eggs because of the hormonal changes that happen during this time.
About 1% of women will experience premature menopause (or premature ovarian failure), meaning that they will run out of eggs well before the normal age of menopause, sometimes when they are still teenagers. This is one of the reasons why otherwise healthy women need egg donation.
At the beginning of each menstrual cycle, a group of 10-20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around Day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately Day 14 of the cycle, a surge of Luteinising Hormone (LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later.
What’s different in an egg donation process? During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation. If you're interested in learning more about egg donation and becoming an egg donor, register your interest here . What is egg quality? Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health. Donate eggs in the UK When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete. If you think you could help someone with the altruistic act of egg donation in the UK, register your interest.
During egg donation, a donor is stimulated with a synthetic version of the naturally produced hormone Follicle Stimulating, in order to encourage the growth of the whole group of 10-20 follicles. This encourages all of the eggs to develop to the same stage of maturity as the one egg that would normally be released. Rather than let nature take its course, ovulation is triggered by medication and the eggs are surgically removed 36 hours later and placed in a dish in an incubator ready for fertilisation.
If you're interested in learning more about egg donation and becoming an egg donor, register your interest here .
Egg quality means how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. As both of these factors tend to reduce over time, age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years – the age when the egg quality begins to reduce. Other factors that affect egg quality are lifestyle issues such as smoking, drinking, drugs (medical or otherwise) and general health.
When trying to conceive, a lot of women and couples are heartbroken to find they can’t without the help of an egg donor. Altruistic egg donation is a wonderful, generous and selfless act. It allows a chance to make a real and meaningful difference in the life of another; to give hope to those who have none and offer a precious, life-changing gift that will help make another family complete.
If you think you could help someone with the altruistic act of egg donation in the UK, register your interest.
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Written by Apricity Team Helping you stay informed Written by our group of fertility experts and doctors consultants
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Written by Apricity Team i Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success Share this article Copy link Share on Whatsapp
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Get help now Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Book a call Speak with an advisor and get help Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Take the Fertility Predictor Quiz Try the fertility predictor for free and estimate your chance of success
Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy Legal Notice T&Cs Refund Policies Privacy Cookies Ⓒ Apricity Fertility UK Limited. All rights reserved
Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy Legal Notice T&Cs Refund Policies Privacy Cookies Ⓒ Apricity Fertility UK Limited. All rights reserved
Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols
Get in touch 07897 035438 New Patients: 9am - 5pm Mon-Fri Current Patient Care: 8am-8pm Mon-Fri & 9am-1pm Sat/Sun/Bank Hols
Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy
Why Apricity Success Rates Pricing At Home Care Technology About Us How It Works Team Careers Contact Feedback & Complaints Resources Blog Events Preserve Fertility Egg Freezing Sperm Freezing Embryo Freezing Fertility Treatments IVF IVF + ICSI Frozen Embryo Transfer IUI All treatments Egg Donation Donate Eggs Find an Egg Donor Surrogacy | biology | 87119 | https://no.wikipedia.org/wiki/Eggceller | Eggceller | Eggceller er de hunnlige kjønnscellene hos planter, dyr, sopp og enkelte protister, dannet ved meiose. Eggceller hører til de største av cellene til dyrene. Hos noen organismer kan eggcellen begynne cellekløyving og gjennomgå fosterutviklingen uten å bli befruktet, men i de fleste tilfeller vil en eggcelle måtte smelte sammen med en sædcelle for å kunne utvikle seg. En eggcelle som har smeltet sammen med en sædcelle kalles en zygote.
Genetikk
En eggcelle dannes ved meiose i nesten alle tilfeller. En slik eggcelle er haploid, og inneholde bare et kromosom fra hvert av kromosomparene. Får å få et fullt diploid kromosomsett må eggcellen ta opp i seg kjernen fra en sædcelle.
Noen eggceller vil imidlertid utvikle seg selv uten befruktnng. Hos mange encellede organismer vil en slik organisme gjennomføre et helt livsløp som haploid, og selv produsere sæd- og eggceller uten foregående meiose. Et slik system gir opphav til generasjonsveksling, der annenhver generasjon er haploid og annenhver diploid. Slike egg kalles gjerne sporer, og de diploide individene kalles gametofytter. Generasjonsveksling finnes hos mange alger, men også hos primitive landplanter som moser og karsporeplanter.
Hos en del dyr vil ubefruktede haploide eggceller gi opphav til hanner, mens befruktede egg gir opphav til hunner. Dette er særlig vanlig hos sosiale insekter som vepser og maur, der en hunn vil lagre større mengder spermier fra flere paringer og bruke disse til å lage arbeidere. Når sædlageret er tomt, vil det dannes haploide egg, som gir opphav til hanner. Dette systemet finnes hos alle vepser (veps, bier, maur), skallskjoldlus og trips, og finnes hos enkelte arter av barkebiller og hjuldyr.
Enkelte eggceller dannes uten at de gjennomgår meiose. Disse eggene vil ha morens fulle diploide kromosomsett og vil ikke trenge befruktning for å begynne fosterutviklingen. Dette fenomenet kalles partenogenese, og individer som vokser opp fra slike eggceller vil være naturlige kloner av moren. Dette systemet finnes hos flere grupper både hos insekter, krepsdyr, fisk, amfibier og krypdyr, men er ukjent hos pattedyr og fugler. I de fleste tilfellene vil artene veksle mellom generasjoner med kjønnet og ukjønnet formering.
Eggceller hos pattedyr
Pattedyrenes eggceller (herunder menneskets) er en kvinnelig kimcelle. Eggcellen dannes ved meiose der nesten all cytoplasma blir i den ene dattercellen. Den andre cellen kalles en «polcelle»og er svært mye mindre og går normalt i oppløsning. Deretter følger en ny celledeling, der hvert kromosom strippes ned til enkle DNA-tråder. Igjen vil det dannes en polcelle. Etter modning løsner eggcellen fra eggstokken og blir fanget opp av egglederen (ovulasjon, eggløsning). Hos de aller fleste pattedyr vil disse hormonene også være aktive i å bringe hunnen i løpetid, der kroppen hennes blir klargjort for paring. I egglederen blir eggcellen liggende i et par døgn, og kan da bli befruktet. Eggcellen gjennomgår en utvikling som er regulert av hormoner.
I ekstremt sjeldne tilfeller kan eggcellen befruktes av en av polcellene fra meiosen og gro fram til fødsel.
Se også
Egg
Referanser
Anatomi
Formering
Celler | norwegian_bokmål | 0.461383 |
parthenogenesis/Parthenogenesis.txt |
Parthenogenesis (/ˌpɑːrθɪnoʊˈdʒɛnɪsɪs, -θɪnə-/;
from the Greek παρθένος, parthénos, 'virgin' + γένεσις, génesis, 'creation')
is a natural form of asexual reproduction in which growth and development of an embryo occur directly from an egg, without need for fertilisation.
In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates (such as some fish, amphibians, reptiles,
and birds).
This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice.
Normal egg cells form in the process of meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles. In some types of parthenogenesis the offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring will get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation.
Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).
Parthenogenesis does not apply to isogamous species.
Life history types[edit]
Further information: Origin and function of meiosis
A young Komodo dragon, Varanus komodoensis, produced through parthenogenesis. Komodo dragons are an example of a species which can produce offspring both through sexual reproduction and parthenogenesis.
Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy or heterogony).
The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like Daphnia). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This is because in asexual reproduction a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who will not give birth. Some species can produce both sexually and through parthenogenesis, and offspring in the same clutch of a species of tropical lizard can be a mix of sexually produced offspring and parthenogenically produced offspring.
In California Condors facultative parthenogenesis can occur even when a male is present and available for a female to breed with.
In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions.
Many taxa with heterogony have within them species that have lost the sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis.
The production of female offspring by parthenogenesis is referred to as thelytoky (e.g., aphids) while the production of males by parthenogenesis is referred to as arrhenotoky (e.g., bees). When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky.
Types and mechanisms[edit]
Parthenogenesis can occur without meiosis through mitotic oogenesis. This is called apomictic parthenogenesis. Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother. Examples include aphids.
Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid (e.g., male ants). In other cases, collectively called automictic parthenogenesis, the ploidy is restored to diploidy by various means. This is because haploid individuals are not viable in most species. In automictic parthenogenesis, the offspring differ from one another and from their mother. They are called half clones of their mother.
Automictic [edit]
The effects of central fusion and terminal fusion on heterozygosity
Automixis is a term that covers several reproductive mechanisms, some of which are parthenogenetic.
Diploidy might be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed. This is referred to as an endomitotic cycle. This may also happen by the fusion of the first two blastomeres. Other species restore their ploidy by the fusion of the meiotic products. The chromosomes may not separate at one of the two anaphases (called restitutional meiosis) or the nuclei produced may fuse or one of the polar bodies may fuse with the egg cell at some stage during its maturation.
Some authors consider all forms of automixis sexual as they involve recombination. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined. The criterion for "sexuality" varies from all cases of restitutional meiosis, to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences.
The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosis or when central fusion occurs (restitutional meiosis of anaphase I or the fusion of its products), the offspring get all to more than half of the mother's genetic material and heterozygosity is mostly preserved (if the mother has two alleles for a locus, it is likely that the offspring will get both). This is because in anaphase I the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion. In the case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids.
If terminal fusion (restitutional meiosis of anaphase II or the fusion of its products) occurs, a little over half the mother's genetic material is present in the offspring and the offspring are mostly homozygous. This is because at anaphase II the sister chromatids are separated and whatever heterozygosity is present is due to crossing over. In the case of endomitosis after meiosis, the offspring is completely homozygous and has only half the mother's genetic material.
This can result in parthenogenetic offspring being unique from each other and from their mother.
Sex of the offspring[edit]
In apomictic parthenogenesis, the offspring are clones of the mother and hence (except for aphids) are usually female. In the case of aphids, parthenogenetically produced males and females are clones of their mother except that the males lack one of the X chromosomes (XO).
When meiosis is involved, the sex of the offspring will depend on the type of sex determination system and the type of apomixis. In species that use the XY sex-determination system, parthenogenetic offspring will have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), ZZ (male), or WW (non-viable in most species, but a fertile, viable female in a few, e.g., boas). ZW offspring are produced by endoreplication before meiosis or by central fusion. ZZ and WW offspring occur either by terminal fusion or by endomitosis in the egg cell.
In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female.
In many hymenopteran insects such as honeybees, female eggs are produced sexually, using sperm from a drone father, while the production of further drones (males) depends on the queen (and occasionally workers) producing unfertilized eggs. This means that females (workers and queens) are always diploid, while males (drones) are always haploid, and produced parthenogenetically.
Facultative[edit]
Facultative parthenogenesis is the term for when a female can produce offspring either sexually or via asexual reproduction. Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies; presumably, this is the default reproductive mode of all species in this insect order. Facultative parthenogenesis has generally been believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if a male is absent from the habitat or if it is unable to produce viable offspring. However, California condors and the tropical lizard Lepidophyma smithii both can produce parthenogenic offspring in the presence of males, indicating that facultative parthenogenesis may be more common than previously thought and is not simply a response to a lack of males.
In aphids, a generation sexually conceived by a male and a female produces only females. The reason for this is the non-random segregation of the sex chromosomess 'X' and 'O' during spermatogenesis.
Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals.
For example, many cases of spontaneous parthenogenesis in sharks, some snakes, Komodo dragons, and a variety of domesticated birds were widely attributed to facultative parthenogenesis.
These cases are examples of spontaneous parthenogenesis. The occurrence of such asexually produced eggs in sexual animals can be explained by a meiotic error, leading to eggs produced via automixis.
Obligate[edit]
Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means.
Many species have been shown to transition to obligate parthenogenesis over evolutionary time. Well documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms. These transitions often occur as a result of inbreeding or mutation within large populations.
There are a number of documented species, specifically salamanders and geckos, that rely on obligate parthenogenesis as their major method of reproduction. As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species), amphibians and fishes in nature for which males are no longer a part of the reproductive process.
A female will produce an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring.
Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been introduced.
Relying solely on parthenogenetic reproduction has several advantages for an invasive species: it obviates the need for individuals in a very sparse initial population to search for mates; and an exclusively female sex distribution allows a population to multiply and invade more rapidly (potentially twice as fast). Examples include several aphid species and the willow sawfly, Nematus oligospilus, which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.
Natural occurrence[edit]
Parthenogenesis is seen to occur naturally in aphids, Daphnia, rotifers, nematodes, and some other invertebrates, as well as in many plants. Among vertebrates, strict parthenogenesis is only known to occur in lizards, snakes,
birds,
and sharks,
with fish, amphibians, and reptiles exhibiting various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis).
The first all-female (unisexual) reproduction in vertebrates was described in the fish Poecilia formosa in 1932.
Since then at least 50 species of unisexual vertebrate have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders. Other usually sexual species may occasionally reproduce parthenogenetically; the Komodo dragon and hammerhead and blacktip sharks are recent additions to the known list of spontaneous parthenogenetic vertebrates. As with all types of asexual reproduction, there are both costs (low genetic diversity and therefore susceptibility to adverse mutations that might occur) and benefits (reproduction without the need for a male) associated with parthenogenesis.
Parthenogenesis is distinct from artificial animal cloning, a process where the new organism is necessarily genetically identical to the cell donor. In cloning, the nucleus of a diploid cell from a donor organism is inserted into an enucleated egg cell and the cell is then stimulated to undergo continued mitosis, resulting in an organism that is genetically identical to the donor. Parthenogenesis is different, in that it originates from the genetic material contained within an egg cell and the new organism is not necessarily genetically identical to the parent.
Parthenogenesis may be achieved through an artificial process as described below under the discussion of mammals.
Oomycetes[edit]
Apomixis can apparently occur in Phytophthora, an oomycete. Oospores from an experimental cross were germinated, and some of the progeny were genetically identical to one or other parent, implying that meiosis did not occur and the oospores developed by parthenogenesis.
Velvet worms[edit]
No males of Epiperipatus imthurni have been found, and specimens from Trinidad were shown to reproduce parthenogenetically. This species is the only known velvet worm to reproduce via parthenogenesis.
Rotifers[edit]
In bdelloid rotifers, females reproduce exclusively by parthenogenesis (obligate parthenogenesis), while in monogonont rotifers, females can alternate between sexual and asexual reproduction (cyclical parthenogenesis). At least in one normally cyclical parthenogenetic species obligate parthenogenesis can be inherited: a recessive allele leads to loss of sexual reproduction in homozygous offspring.
Flatworms[edit]
At least two species in the genus Dugesia, flatworms in the Turbellaria sub-division of the phylum Platyhelminthes, include polyploid individuals that reproduce by parthenogenesis. This type of parthenogenesis requires mating, but the sperm does not contribute to the genetics of the offspring (the parthenogenesis is pseudogamous, alternatively referred to as gynogenetic). A complex cycle of matings between diploid sexual and polyploid parthenogenetic individuals produces new parthenogenetic lines.
Snails[edit]
Several species of parthenogenetic gastropods have been studied, especially with respect to their status as invasive species. Such species include the New Zealand mud snail (Potamopyrgus antipodarum), the red-rimmed melania (Melanoides tuberculata), and the Quilted melania (Tarebia granifera).
Insects[edit]
Parthenogenesis in insects can cover a wide range of mechanisms. The offspring produced by parthenogenesis may be of both sexes, only female (thelytoky, e.g. aphids and some hymenopterans) or only male (arrhenotoky, e.g. most hymenopterans). Both true parthenogenesis and pseudogamy (gynogenesis or sperm-dependent parthenogenesis) are known to occur. The egg cells, depending on the species may be produced without meiosis (apomictically) or by one of the several automictic mechanisms.
A related phenomenon, polyembryony is a process that produces multiple clonal offspring from a single egg cell. This is known in some hymenopteran parasitoids and in Strepsiptera.
In automictic species the offspring can be haploid or diploid. Diploids are produced by doubling or fusion of gametes after meiosis. Fusion is seen in the Phasmatodea, Hemiptera (Aleurodids and Coccidae), Diptera, and some Hymenoptera.
In addition to these forms is hermaphroditism, where both the eggs and sperm are produced by the same individual, but is not a type of parthenogenesis. This is seen in three species of Icerya scale insects.
Parasitic bacteria like Wolbachia have been noted to induce automictic thelytoky in many insect species with haplodiploid systems. They also cause gamete duplication in unfertilized eggs causing them to develop into female offspring.
Honey bee on a plum blossom
Among species with the haplo-diploid sex-determination system, such as hymenopterans (ants, bees, and wasps) and thysanopterans (thrips), haploid males are produced from unfertilized eggs. Usually, eggs are laid only by the queen, but the unmated workers may also lay haploid, male eggs either regularly (e.g. stingless bees) or under special circumstances. An example of non-viable parthenogenesis is common among domesticated honey bees. The queen bee is the only fertile female in the hive; if she dies without the possibility of a viable replacement queen, it is not uncommon for the worker bees to lay eggs. This is a result of the lack of the queen's pheromones and the pheromones secreted by uncapped brood, which normally suppress ovarian development in workers. Worker bees are unable to mate, and the unfertilized eggs produce only drones (males), which can mate only with a queen. Thus, in a relatively short period, all the worker bees die off, and the new drones follow if they have not been able to mate before the collapse of the colony. This behavior is believed to have evolved to allow a doomed colony to produce drones which may mate with a virgin queen and thus preserve the colony's genetic progeny.
A few ants and bees are capable of producing diploid female offspring parthenogenetically. These include a honey bee subspecies from South Africa, Apis mellifera capensis, where workers are capable of producing diploid eggs parthenogenetically, and replacing the queen if she dies; other examples include some species of small carpenter bee, (genus Ceratina). Many parasitic wasps are known to be parthenogenetic, sometimes due to infections by Wolbachia.
The workers in five ant species and the queens in some ants are known to reproduce by parthenogenesis. In Cataglyphis cursor, a European formicine ant, the queens and workers can produce new queens by parthenogenesis. The workers are produced sexually.
In Central and South American electric ants, Wasmannia auropunctata, queens produce more queens through automictic parthenogenesis with central fusion. Sterile workers usually are produced from eggs fertilized by males. In some of the eggs fertilized by males, however, the fertilization can cause the female genetic material to be ablated from the zygote. In this way, males pass on only their genes to become fertile male offspring. This is the first recognized example of an animal species where both females and males can reproduce clonally resulting in a complete separation of male and female gene pools. As a consequence, the males will only have fathers and the queens only mothers, while the sterile workers are the only ones with both parents of both sexes.
These ants get both the benefits of both asexual and sexual reproduction—the daughters who can reproduce (the queens) have all of the mother's genes, while the sterile workers whose physical strength and disease resistance are important are produced sexually.
Other examples of insect parthenogenesis can be found in gall-forming aphids (e.g., Pemphigus betae), where females reproduce parthenogenetically during the gall-forming phase of their life cycle and in grass thrips. In the grass thrips genus Aptinothrips there have been, despite the very limited number of species in the genus, several transitions to asexuality.
Crustaceans[edit]
Crustacean reproduction varies both across and within species. The water flea Daphnia pulex alternates between sexual and parthenogenetic reproduction. Among the better-known large decapod crustaceans, some crayfish reproduce by parthenogenesis. "Marmorkrebs" are parthenogenetic crayfish that were discovered in the pet trade in the 1990s.
Offspring are genetically identical to the parent, indicating it reproduces by apomixis, i.e. parthenogenesis in which the eggs did not undergo meiosis. Spinycheek crayfish (Orconectes limosus) can reproduce both sexually and by parthenogenesis.
The Louisiana red swamp crayfish (Procambarus clarkii), which normally reproduces sexually, has also been suggested to reproduce by parthenogenesis,
although no individuals of this species have been reared this way in the lab. Artemia parthenogenetica is a species or series of populations of parthenogenetic brine shrimps.
Spiders[edit]
At least two species of spiders in the family Oonopidae (goblin spiders), Heteroonops spinimanus and Triaeris stenaspis, are thought to be parthenogenetic, as no males have ever been collected. Parthenogenetic reproduction has been demonstrated in the laboratory for T. stenaspis.
Sharks[edit]
Parthenogenesis in sharks has been confirmed in at least three species, the bonnethead, the blacktip shark,
and the zebra shark,
and reported in others.
A bonnethead, a type of small hammerhead shark, was found to have produced a pup, born live on December 14, 2001, at Henry Doorly Zoo in Nebraska, in a tank containing three female hammerheads, but no males. The pup was thought to have been conceived through parthenogenesis. The shark pup was apparently killed by a stingray within days of birth. The investigation of the birth was conducted by the research team from Queen's University Belfast, Southeastern University in Florida, and Henry Doorly Zoo itself, and it was concluded after DNA testing that the reproduction was parthenogenetic. The testing showed the female pup's DNA matched only one female who lived in the tank, and that no male DNA was present in the pup. The pup was not a twin or clone of her mother, but rather, contained only half of her mother's DNA ("automictic parthenogenesis"). This type of reproduction had been seen before in bony fish, but never in cartilaginous fish such as sharks, until this documentation.
In the same year, a female Atlantic blacktip shark in Virginia reproduced via parthenogenesis. On October 10, 2008, scientists confirmed the second case of a "virgin birth" in a shark. The Journal of Fish Biology reported a study in which scientists said DNA testing proved that a pup carried by a female Atlantic blacktip shark in the Virginia Aquarium & Marine Science Center contained no genetic material from a male.
In 2002, two white-spotted bamboo sharks were born at the Belle Isle Aquarium in Detroit. They hatched 15 weeks after being laid. The births baffled experts as the mother shared an aquarium with only one other shark, which was female. The female bamboo sharks had laid eggs in the past. This is not unexpected, as many animals will lay eggs even if there is not a male to fertilize them. Normally, the eggs are assumed to be inviable and are discarded. This batch of eggs was left undisturbed by the curator as he had heard about the previous birth in 2001 in Nebraska and wanted to observe whether they would hatch. Other possibilities had been considered for the birth of the Detroit bamboo sharks including thoughts that the sharks had been fertilized by a male and stored the sperm for a period of time, as well as the possibility that the Belle Isle bamboo shark is a hermaphrodite, harboring both male and female sex organs, and capable of fertilizing its own eggs, but that is not confirmed.
In 2008, a Hungarian aquarium had another case of parthenogenesis after its lone female shark produced a pup without ever having come into contact with a male shark.
The repercussions of parthenogenesis in sharks, which fails to increase the genetic diversity of the offspring, is a matter of concern for shark experts, taking into consideration conservation management strategies for this species, particularly in areas where there may be a shortage of males due to fishing or environmental pressures. Although parthenogenesis may help females who cannot find mates, it does reduce genetic diversity.
In 2011, recurring shark parthenogenesis over several years was demonstrated in a captive zebra shark, a type of carpet shark.
DNA genotyping demonstrated that individual zebra sharks can switch from sexual to parthenogenetic reproduction.
Rays[edit]
A female round stingray (Urobatis halleri) held in captivity from all males for eight years was reported pregnant in 2024.
Amphibians[edit]
Main article: Parthenogenesis in amphibians
Crocodiles[edit]
In June 2023, discovery was made at a zoo in Costa Rica, where researchers identified the first documented case of a self-pregnant crocodile. This female American crocodile, housed at Parque Reptilania, produced a genetically identical foetus, with a 99.9% similarity to herself. The scientists speculate that this unique ability might be inherited from an evolutionary ancestor, suggesting that even dinosaurs could have possessed the capability for self-reproduction. The 18-year-old crocodile laid the egg in January 2018, the fully formed foetus did not hatch and was stillborn. Notably, this crocodile had been kept separated from other crocodiles throughout her entire life since being acquired at the age of two.
Squamata[edit]
Main article: Parthenogenesis in squamata
Komodo dragon, Varanus komodoensis, rarely reproduces offspring via parthenogenesis.
Most reptiles of the squamatan order (lizards and snakes) reproduce sexually, but parthenogenesis has been observed to occur naturally in certain species of whiptails, some geckos, rock lizards,
Komodo dragons,
and snakes.
Some of these like the mourning gecko Lepidodactylus lugubris, Indo-Pacific house gecko Hemidactylus garnotii, the hybrid whiptails Cnemidophorus, Caucasian rock lizards Darevskia, and the brahminy blindsnake, Indotyphlops braminus are unisexual and obligately parthenogenetic. Other reptiles, such as the Komodo dragon, other monitor lizards,
and some species of boas,
pythons,
filesnakes,
gartersnakes,
and rattlesnakes
were previously considered as cases of facultative parthenogenesis, but may be cases of accidental parthenogenesis.
In 2012, facultative parthenogenesis was reported in wild vertebrates for the first time by US researchers amongst captured pregnant copperhead and cottonmouth female pit-vipers.
The Komodo dragon, which normally reproduces sexually, has also been found able to reproduce asexually by parthenogenesis.
A case has been documented of a Komodo dragon reproducing via sexual reproduction after a known parthenogenetic event, highlighting that these cases of parthenogenesis are reproductive accidents, rather than adaptive, facultative parthenogenesis.
Some reptile species use a ZW chromosome system, which produces either males (ZZ) or females (ZW). Until 2010, it was thought that the ZW chromosome system used by reptiles was incapable of producing viable WW offspring, but a (ZW) female boa constrictor was discovered to have produced viable female offspring with WW chromosomes.
Parthenogenesis has been studied extensively in the New Mexico whiptail in the genus Aspidoscelis of which 15 species reproduce exclusively by parthenogenesis. These lizards live in the dry and sometimes harsh climate of the southwestern United States and northern Mexico. All these asexual species appear to have arisen through the hybridization of two or three of the sexual species in the genus leading to polyploid individuals. The mechanism by which the mixing of chromosomes from two or three species can lead to parthenogenetic reproduction is unknown. Recently, a hybrid parthenogenetic whiptail lizard was bred in the laboratory from a cross between an asexual and a sexual whiptail.
Because multiple hybridization events can occur, individual parthenogenetic whiptail species can consist of multiple independent asexual lineages. Within lineages, there is very little genetic diversity, but different lineages may have quite different genotypes.
An interesting aspect to reproduction in these asexual lizards is that mating behaviors are still seen, although the populations are all female. One female plays the role played by the male in closely related species, and mounts the female that is about to lay eggs. This behaviour is due to the hormonal cycles of the females, which cause them to behave like males shortly after laying eggs, when levels of progesterone are high, and to take the female role in mating before laying eggs, when estrogen dominates. Lizards who act out the courtship ritual have greater fecundity than those kept in isolation, due to the increase in hormones that accompanies the mounting. So, although the populations lack males, they still require sexual behavioral stimuli for maximum reproductive success.
Some lizard parthenogens show a pattern of geographic parthenogenesis, occupying high mountain areas where their ancestral forms have an inferior competition ability.
In Caucasian rock lizards of genus Darevskia, which have six parthenogenetic forms of hybrid origin
hybrid parthenogenetic form D. "dahli" has a broader niche than either of its bisexual ancestors and its expansion throughout the Central Lesser Caucasus caused decline of the ranges of both its maternal and paternal species.
Birds[edit]
Parthenogenesis in birds is known mainly from studies of domesticated turkeys and chickens, although it has also been noted in the domestic pigeon. In most cases the egg fails to develop normally or completely to hatching.
The first description of parthenogenetic development in a passerine was demonstrated in captive zebra finches, although the dividing cells exhibited irregular nuclei and the eggs did not hatch.
Parthenogenesis in turkeys appears to result from a conversion of haploid cells to diploid; most embryos produced in this way die early in development. Rarely, viable birds result from this process, and the rate at which this occurs in turkeys can be increased by selective breeding,
however male turkeys produced from parthenogenesis exhibit smaller testes and reduced fertility.
In 2021, the San Diego Zoo reported that they had two unfertilized eggs from their California condor breeding program hatch. This is the first known example of parthenogenesis in this species, as well as one of the only known examples of parthenogenesis happening where males are still present.
Mammals[edit]
There are no known cases of naturally occurring mammalian parthenogenesis in the wild. Parthenogenetic progeny of mammals would have two X chromosomes, and would therefore be genetically female.
In 1936, Gregory Goodwin Pincus reported successfully inducing parthenogenesis in a rabbit.
In April 2004, scientists at Tokyo University of Agriculture used parthenogenesis successfully to create a fatherless mouse. Using gene targeting, they were able to manipulate two imprinted loci H19/IGF2 and DLK1/MEG3 to produce bi-maternal mice at high frequency and subsequently show that fatherless mice have enhanced longevity.
Induced parthenogenesis in mice and monkeys often results in abnormal development. This is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring in order for development to proceed normally. A mammal created by parthenogenesis would have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities. It has been suggested
that defects in placental folding or interdigitation are one cause of swine parthenote abortive development. As a consequence, research on human parthenogenesis is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy. In 2022, researchers reported that they have achieved parthenogenesis in mice for viable offspring born from unfertilized eggs, addressing the problems of genomic imprinting by "targeted DNA methylation rewriting of seven imprinting control regions".
Methods[edit]
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Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.
Induction of parthenogenesis in swine. Parthenogenetic development of swine oocytes. High metaphase promoting factor (MPF) activity causes mammalian oocytes to arrest at the metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations, and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis. To initiate parthenogenesis of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide, a non-specific protein synthesis inhibitor, enhances parthenote development in swine presumably by continual inhibition of MPF/cyclin B. As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote. Parthenotes can be surgically transferred to a recipient oviduct for further development, but will succumb by developmental failure after ≈30 days of gestation. The swine parthenote placentae often appears hypo-vascular and is approximately 50% smaller than biparental offspring placentae: see free image (Figure 1) in linked reference.
During oocyte development, high metaphase promoting factor (MPF) activity causes mammalian oocytes to arrest at the metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations, and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis.
To initiate parthenogenesis of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide, a non-specific protein synthesis inhibitor, enhances parthenote development in swine presumably by continual inhibition of MPF/cyclin B. As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote Parthenotes can be surgically transferred to a recipient oviduct for further development, but will succumb to developmental failure after ≈30 days of gestation. The swine parthenote placentae often appears hypo-vascular: see free image (Figure 1) in linked reference.
Humans[edit]
Reports of human parthenogenesis have famously existed since ancient times, featuring prominently in Christianity and various other religions. More recently, Helen Spurway, a geneticist specializing in the reproductive biology of the guppy (Lebistes reticulatus), claimed in 1955 that parthenogenesis, which occurs in the guppy in nature, may also occur (though very rarely) in the human species, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike. Sometimes an embryo may begin to divide without fertilisation, but it cannot fully develop on its own; so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes a type of benign tumor called an ovarian teratoma. Spontaneous ovarian activation is not rare and has been known about since the 19th century. Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs and other structures, but are non-viable.
In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as white blood cells) to be lacking in any genetic content from his father. Scientists believe that an unfertilised egg began to self-divide but then had some (but not all) of its cells fertilised by a sperm cell; this must have happened early in development, as self-activated eggs quickly lose their ability to be fertilised. The unfertilised cells eventually duplicated their DNA, boosting their chromosomes to 46. When the unfertilised cells hit a developmental block, the fertilised cells took over and developed that tissue. The boy had asymmetrical facial features and learning difficulties but was otherwise healthy. This would make him a parthenogenetic chimera (a child with two cell lineages in his body). While over a dozen similar cases have been reported since then (usually discovered after the patient demonstrated clinical abnormalities), there have been no scientifically confirmed reports of a non-chimeric, clinically healthy human parthenote (i.e. produced from a single, parthenogenetic-activated oocyte).
On June 26, 2007, the International Stem Cell Corporation (ISCC), a California-based stem cell research company, announced that their lead scientist, Dr. Elena Revazova, and her research team were the first to intentionally create human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way for creating stem cells that are genetically matched to a particular female for the treatment of degenerative diseases that might affect her. In December 2007, Dr. Revazova and ISCC published an article illustrating a breakthrough in the use of parthenogenesis to produce human stem cells that are homozygous in the HLA region of DNA. These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and have unique characteristics that would allow derivatives of these cells to be implanted into millions of people without immune rejection.
With proper selection of oocyte donors according to HLA haplotype, it is possible to generate a bank of cell lines whose tissue derivatives, collectively, could be MHC-matched with a significant number of individuals within the human population.
On August 2, 2007, after an independent investigation, it was revealed that discredited South Korean scientist Hwang Woo-Suk unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result later found to be fabricated. Further examination of the chromosomes of these cells show indicators of parthenogenesis in those extracted stem cells, similar to those found in the mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he contributed a major breakthrough to stem cell research by creating human embryos using parthenogenesis. The truth was discovered in 2007, long after the embryos were created by him and his team in February 2004. This made Hwang the first, unknowingly, to successfully perform the process of parthenogenesis to create a human embryo and, ultimately, a human parthenogenetic stem cell line.
Similar phenomena[edit]
Gynogenesis[edit]
See also: Gynogenesis and Parthenogenesis in amphibians § Gynogenesis
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some salamanders of the genus Ambystoma are gynogenetic and appear to have been so for over a million years. It is believed that the success of those salamanders may be due to rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million. In addition, the amazon molly is known to reproduce by gynogenesis.
Hybridogenesis[edit]
See also: Hybridogenesis in water frogs
Hybridogenesis is a mode of reproduction of hybrids. Hybridogenetic hybrids (for example AB genome), usually females, during gametogenesis exclude one of parental genomes (A) and produce gametes with unrecombined genome of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A) is restored by fertilization of these gametes with gametes from the first species (AA, sexual host, usually male).
So hybridogenesis is not completely asexual, but instead hemiclonal: half of genome is passed to the next generation clonally, unrecombined, intact (B), other half sexually, recombined (A).
This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from the father's side.
This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"):
P. kl. esculentus (edible frog): P. lessonae × P. ridibundus,
P. kl. grafi (Graf's hybrid frog): P. perezi × P. ridibundus
P. kl. hispanicus (Italian edible frog) – unknown origin: P. bergeri × P. ridibundus or P. kl. esculentus
and perhaps in P. demarchii.
Example crosses between pool frog (Pelophylax lessonae), marsh frog (P. ridibundus) and their hybrid – edible frog (P. kl. esculentus). First one is the primary hybridisation generating hybrid, second one is most widespread type of hybridogenesis.
Other examples where hybridogenesis is at least one of modes of reproduction include i.e.
Iberian minnow Tropidophoxinellus alburnoides (Squalius pyrenaicus × hypothetical ancestor related with Anaecypris hispanica)
spined loaches Cobitis hankugensis × C. longicorpus
Bacillus stick insects B. rossius × Bacillus grandii benazzii
See also[edit]
Crustaceans portal
Androgenesis - a form of quasi-sexual reproduction in which a male is the sole source of the nuclear genetic material in the embryo
Telescoping generations
Charles Bonnet – Genevan botanist (1720–1793) – conducted experiments that established what is now termed parthenogenesis in aphids
Jan Dzierżon – Polish apiarist (1811–1906)Pages displaying short descriptions of redirect targets – Polish apiarist and a pioneer of parthenogenesis among bees
Jacques Loeb – German-born American physiologist and biologist – caused the eggs of sea urchins to begin embryonic development without sperm
Miraculous births – Conceptions and births by miraculous circumstances
Parthenocarpy – Production of seedless fruit without fertilisation – plants with seedless fruit | biology | 998 | https://da.wikipedia.org/wiki/Art | Art | Arten (species, forkortet sp., flertal: spp.) er den grundlæggende systematiske enhed inden for biologien. Arten defineres ofte som en naturlig gruppe af populationer, hvor udveksling af gener finder sted (eller kan finde sted) og som i forhold til forplantning er isoleret fra andre grupper. Det vil sige at kun individer inden for samme art kan parre sig og få forplantningsdygtigt afkom. Dette kaldes det biologiske artsbegreb. For organismer, der formerer sig ukønnet eller ved selvbestøvning, må arter afgrænses ud fra ligheder og forskelle mellem forskellige individer. Nogle dyrearter kan i fangenskab hybridisere og få fertilt afkom, men da dette ikke vil ske i naturen, selv om de mødes her, betragtes de som forskellige arter.
Eksempel
To heste kan parre sig og få et føl, der igen kan få føl med andre heste – hestene tilhører derfor samme art. En hest og et æsel kan også parre sig og deres unger kaldes enten muldyr eller mulæsel, afhængig af hvem der er moren, men muldyret eller mulæselet kan (normalt) ikke få unger, da de oftest er sterile. Af den grund regnes hest og æsel som to forskellige arter. Det samme princip gælder også for planterne. Denne naturskabte afgrænsning mellem to arter kaldes en artsbarriere. Den kan af og til gennembrydes, når ellers sterile krydsninger spontant eller kunstigt får gennemført en kromosomfordobling. Se f.eks. Vadegræs (Spartina pectinata).
Arter over for hybrider
Man kan dog godt komme ud for, at arter kan krydses og får blandet afkom, men hybriden vil kun kunne bestå på steder, hvor ingen af forældrearterne kan klare sig. Dette er et særligt udpræget problem med Rododendron (Rhododendron) og Tjørn (Crataegus), fordi disse slægter breder sig voldsomt efter skovbrand eller stormfald. Da hybriderne bliver frugtbare i en yngre alder end arterne, kan de dominere i en periode, men når skoven lukker sig, så fortrænges hybriderne og kun de specialiserede arter kan overleve i skovens dybe skygge eller ude i lyset i sumpe, på ur og i kalksten, m.m.
Flere artsbegreber
Fordi det biologiske artsbegreb kan være besværligt at anvende i praksis, er der efterhånden skabt en række andre artsbegreber:
Morfologisk artsbegreb Arterne adskiller sig fra hinanden ved deres bygning. Dette begreb er blevet meget anvendt gennem tiden.
Økologisk artsbegreb Definerer en art som en gruppe af organismer, der udfylder samme niche. Krydsninger mellem to nærtstående arter vil ikke være optimalt tilpasset til forældrearternes nicher og vil ikke klare sig i konkurrencen.
Evolutionære artsbegreb Også kaldet det kladistiske eller fylogenetiske artsbegreb. Naturen er dynamisk, ikke statisk - alle arter ændrer sig med tiden og bliver, hvis de ikke uddør som følge af konkurrence, naturkatastrofer m.v., til én eller flere nye arter. Det evolutionære artsbegreb minder om det biologiske, men inddrager tidsdimensionen, det vil sige at en art udvikler sig over tid og at nye arter opstår ved artsdannelse. Individer der fylogenetisk har samme stamfader tilhører samme art.
Pluralistisk artsbegreb En art er et samfund af populationer, der formerer sig og lever inden for en bestemt niche i naturen.
Se også
Systematik
Evolutionsteori
Kilder
Lars Skipper: Hvad er en art? Citat: "...Arten er den eneste [klassifikations-kategori] der eksisterer i virkeligheden, alle andre (slægter, familier, ordener m.v.) er indført for overskuelighedens skyld..."
Eksterne henvisninger
2003-12-31, ScienceDaily: Working On The 'Porsche Of Its Time': New Model For Species Determination Offered Citat: "...two species of dinosaur that are members of the same genera varied from each other by just 2.2 percent. Translation of the percentage into an actual number results in an average of just three skeletal differences out of the total 338 bones in the body. Amazingly, 58 percent of these differences occurred in the skull alone. "This is a lot less variation than I'd expected," said Novak..."
2003-08-08, ScienceDaily: Cross-species Mating May Be Evolutionarily Important And Lead To Rapid Change, Say Indiana University Researchers Citat: "...the sudden mixing of closely related species may occasionally provide the energy to impel rapid evolutionary change..."
2004-01-09 ScienceDaily: Mayo Researchers Observe Genetic Fusion Of Human, Animal Cells; May Help Explain Origin Of AIDS Citat: "...The researchers have discovered conditions in which pig cells and human cells can fuse together in the body to yield hybrid cells that contain genetic material from both species..."What we found was completely unexpected," says Jeffrey Platt, M.D..."
2000-09-18, ScienceDaily: Scientists Unravel Ancient Evolutionary History Of Photosynthesis Citat: "...gene-swapping was common among ancient bacteria early in evolution..."
2004-06-07, Sciencedaily: Parting Genomes: University Of Arizona Biologists Discover Seeds Of Speciation Citat: "...There's a huge amount of biodiversity out there, and we don't know where it comes from. Evolutionary biologists are excited to figure out what causes what we see out there--the relative forces of selection and drift--whether things are adapting to their environment or variation is random..."
2005-07-05, Sciencedaily: Trees, Vines And Nets -- Microbial Evolution Changes Its Face Citat: "... EBI researchers have changed our view of 4 billion years of microbial evolution...In all, more than 600,000 vertical transfers are observed, coupled with 90,000 gene loss events and approximately 40,000 horizontal gene transfers...A few species, including beneficial nitrogen-fixing soil bacteria, appear to be 'champions'of horizontal gene transfer; "it's entirely possible that apparently harmless organisms are quietly spreading antibiotic resistance under our feet," concludes Christos Ouzounis..."
2005-11-11, Sciencedaily: Lateral Thinking Produces First Map Of Gene Transmission Citat: "...Their results clearly show genetic modification of organisms by lateral transfer is a widespread natural phenomenon, and it can occur even between distantly related organisms... it was assumed that transfer of genes could only be vertical, i.e. from parents to offspring..."
Økologi
Biologi | danish | 0.791178 |
parthenogenesis/difference-between-sperm-and-ovum.txt |
Courses Courses for Kids Free study material Offline Centres More Store Talk to our experts 1800-120-456-456 Sign In Biology Biology Difference Between Sperm and Ovum Difference Between Sperm and Ovum Biology Study Material Biology top 10 Important Topics Biology Syllabus Biology Question Papers Book online demo NCERT Solutions NCERT Solutions Class 12 Biology NCERT Solution Class 11 Biology NCERT Solutions for Class 10 Science NCERT Solutions for Class 9 Science NCERT Solutions for Class 8 Science NCERT Solutions for Class 7 Science NCERT Solutions for Class 6 Science NCERT Solutions for Class 5 EVS NCERT Solutions for Class 4 EVS NCERT Solutions for Class 3 EVS NCERT Notes Class 12 Biology Notes Class 11 Biology Notes Class 10 Science Notes Class 9 Science Notes Class 8 Science Notes Class 7 Science Notes Class 6 Science Notes NCERT Important Question Important Questions for Class 12 Science Important Questions for Class 11 Science Important Questions for Class 10 Science Important Questions for Class 9 Science Important Questions for Class 8 Science Important Questions for Class 7 Science Important Questions for Class 6 Science Difference Between Weather and Climate Scientific Names of Animals and Plants Bacterial Diseases in Humans Enzymes MCQs MCQs on Greenhouse Effect Deficiency Diseases Conservation of Biodiversity Difference Between Cyclic and Non Cyclic Photophosphorylation Conservation of Forest and Wildlife Difference Between National Park and Wildlife Sanctuary CBSE Class 12 Biology Syllabus CBSE Class 11 Biology Syllabus CBSE Class 10 Science Syllabus CBSE Class 9 Science Syllabus CBSE Class 8 Science Syllabus CBSE Class 7 Science Syllabus CBSE Class 6 Science Syllabus CBSE Class 5 EVS Syllabus CBSE Class 4 EVS Syllabus CBSE Class 3 EVS Syllabus ISC Class 12 Biology Syllabus ISC Class 11 Biology Syllabus ICSE Class 10 Biology Syllabus ICSE Class 9 Biology Syllabus ICSE Class 8 Biology Syllabus ICSE Class 7 Biology Syllabus ICSE Class 6 Biology Syllabus CBSE Class 12 Biology Question Papers CBSE Class 12 Biology Question Paper 2020 CBSE Class 12 Biology Question Paper 2019 CBSE Class 12 Biology Question Paper 2018 CBSE Class 12 Biology Question Paper 2017 CBSE Class 12 Biology Question Paper 2016 CBSE Class 12 Biology Question Paper 2015 CBSE Class 12 Biology Question Paper 2014 CBSE Class 12 Biology Question Paper 2013 CBSE Class 10 Science Question Papers CBSE Class 10 Science Question Paper 2020 CBSE Class 10 Science Question Paper 2019 CBSE Class 10 Science Question Paper 2018 CBSE Class 10 Science Question Paper 2017 CBSE Class 10 Science Question Paper 2016 CBSE Class 10 Science Question Paper 2015 CBSE Class 10 Science Question Paper 2014 CBSE Class 10 Science Question Paper 2013 CBSE Class 10 Science Question Paper 2012 CBSE Class 10 Science Question Paper 2011 CBSE Class 10 Science Question Paper 2010 CBSE Class 10 Science Question Paper 2009 CBSE Class 10 Science Question Paper 2008 CBSE Class 10 Science Question Paper 2007 ICSE Class 10 Biology Question Papers ICSE Class 10 Biology Question Paper 2020 ICSE Class 10 Biology Question Paper 2019 ICSE Class 10 Biology Question Paper 2018 ISC Class 12 Biology Question Papers ISC Class 12 Biology Question Paper 2020 ISC Class 12 Biology Question Paper 2019 ISC Class 12 Biology Question Paper 2018 Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future. 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Speak to an expert TOLL FREE: 1800-120-456-456 91 988-660-2456 (9 AM to 9:30 PM on all days) [email protected] Company About us Contact us Vedantu Blog News Child safety Why Vedantu Our results Careers Help india learn Other Links Free live classes Why teach with Vedantu Try WAVE Try Whiteboard Vedantu improvement promise VOLT Micro courses Maharastra Board Benefits Engineering Blog Courses CBSE Tuitions ICSE Tuitions JEE (Main & Advanced) NEET for Class 11 NEET for Class 12 Eklavya JEE Eklavya NEET Computer Science Vedantu Super Kids Coding for kids Spoken English Study material NCERT NCERT NCERT Solutions NCERT Solutions for Class 12 NCERT Solutions for Class 12 Maths NCERT Solutions for Class 12 Physics NCERT Solutions for Class 12 Chemistry NCERT Solutions for Class 12 Biology NCERT Solutions for Class 12 Business Studies NCERT Solutions for Class 12 Economics NCERT Solutions for Class 12 Accountancy NCERT Solutions for Class 12 English NCERT Solutions for Class 12 Hindi NCERT Solutions for Class 11 NCERT Solutions for Class 11 Maths NCERT Solutions for Class 11 Physics NCERT Solutions for Class 11 Chemistry NCERT Solutions for Class 11 Biology NCERT Solutions for Class 11 Business Studies NCERT Solutions for Class 11 Economics NCERT Solutions for Class 11 Accountancy NCERT Solutions for Class 11 English NCERT Solutions for Class 11 Hindi NCERT Solutions for Class 10 NCERT Solutions for Class 10 Maths NCERT Solutions for Class 10 Science NCERT Solutions for Class 10 English NCERT Solutions for Class 10 Social Science NCERT Solutions for Class 10 Hindi NCERT Solutions for Class 9 NCERT Solutions for Class 9 Maths NCERT Solutions for Class 9 Science NCERT Solutions for Class 9 English NCERT Solutions for Class 9 Social Science NCERT Solutions for Class 9 Hindi NCERT Solutions for Class 8 NCERT Solutions for Class 8 Maths NCERT Solutions for Class 8 Science NCERT Solutions for Class 8 English NCERT Solutions for Class 8 Social Science NCERT Solutions for Class 8 Hindi NCERT Books NCERT Books Class 12 NCERT Books Class 11 NCERT Books Class 10 NCERT Books Class 9 NCERT Books Class 8 Reference book solutions Reference Book Solutions HC Verma Solutions RD Sharma Solutions RS Aggarwal Solutions NCERT Exemplar Solutions Lakhmir Singh Solutions DK Goel Solutions TS Grewal Solutions Sandeep Garg Competitive Exams Competitive Exams JEE Main JEE Advanced NEET Olympiad Preparation NDA KVPY NTSE CBSE CBSE CBSE Syllabus CBSE Sample Paper CBSE Worksheets CBSE Important Questions CBSE Previous Year Question Papers Class 12 CBSE Previous Year Question Papers Class 10 CBSE Important Formulas ICSE ICSE ICSE Solutions ICSE Class 10 Solutions ICSE Class 9 Solutions ICSE Class 8 Solutions State boards State Boards AP Board Bihar Board Gujarat Board Karnataka Board Kerala Board Maharashtra Board MP Board Rajasthan Board Telangana Board TN Board UP Board WB Board Free Study Material Free Study Material Previous Year Question Papers Sample Papers JEE Main Study Materials JEE Advanced Study Materials NEET Study Materials Olympiad Study Materials Kids Learning Ask Questions Important Subjects Physics Biology Chemistry Maths English Commerce Geography Civics Revision Notes Revision Notes CBSE Class 12 Notes CBSE Class 11 Notes CBSE Class 10 Notes CBSE Class 9 Notes CBSE Class 8 Notes © 2024 .Vedantu.com. 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Courses Courses for Kids Free study material Offline Centres More Store Talk to our experts 1800-120-456-456 Sign In Biology Biology Difference Between Sperm and Ovum Difference Between Sperm and Ovum Biology Study Material Biology top 10 Important Topics Biology Syllabus Biology Question Papers Book online demo NCERT Solutions NCERT Solutions Class 12 Biology NCERT Solution Class 11 Biology NCERT Solutions for Class 10 Science NCERT Solutions for Class 9 Science NCERT Solutions for Class 8 Science NCERT Solutions for Class 7 Science NCERT Solutions for Class 6 Science NCERT Solutions for Class 5 EVS NCERT Solutions for Class 4 EVS NCERT Solutions for Class 3 EVS NCERT Notes Class 12 Biology Notes Class 11 Biology Notes Class 10 Science Notes Class 9 Science Notes Class 8 Science Notes Class 7 Science Notes Class 6 Science Notes NCERT Important Question Important Questions for Class 12 Science Important Questions for Class 11 Science Important Questions for Class 10 Science Important Questions for Class 9 Science Important Questions for Class 8 Science Important Questions for Class 7 Science Important Questions for Class 6 Science Difference Between Weather and Climate Scientific Names of Animals and Plants Bacterial Diseases in Humans Enzymes MCQs MCQs on Greenhouse Effect Deficiency Diseases Conservation of Biodiversity Difference Between Cyclic and Non Cyclic Photophosphorylation Conservation of Forest and Wildlife Difference Between National Park and Wildlife Sanctuary CBSE Class 12 Biology Syllabus CBSE Class 11 Biology Syllabus CBSE Class 10 Science Syllabus CBSE Class 9 Science Syllabus CBSE Class 8 Science Syllabus CBSE Class 7 Science Syllabus CBSE Class 6 Science Syllabus CBSE Class 5 EVS Syllabus CBSE Class 4 EVS Syllabus CBSE Class 3 EVS Syllabus ISC Class 12 Biology Syllabus ISC Class 11 Biology Syllabus ICSE Class 10 Biology Syllabus ICSE Class 9 Biology Syllabus ICSE Class 8 Biology Syllabus ICSE Class 7 Biology Syllabus ICSE Class 6 Biology Syllabus CBSE Class 12 Biology Question Papers CBSE Class 12 Biology Question Paper 2020 CBSE Class 12 Biology Question Paper 2019 CBSE Class 12 Biology Question Paper 2018 CBSE Class 12 Biology Question Paper 2017 CBSE Class 12 Biology Question Paper 2016 CBSE Class 12 Biology Question Paper 2015 CBSE Class 12 Biology Question Paper 2014 CBSE Class 12 Biology Question Paper 2013 CBSE Class 10 Science Question Papers CBSE Class 10 Science Question Paper 2020 CBSE Class 10 Science Question Paper 2019 CBSE Class 10 Science Question Paper 2018 CBSE Class 10 Science Question Paper 2017 CBSE Class 10 Science Question Paper 2016 CBSE Class 10 Science Question Paper 2015 CBSE Class 10 Science Question Paper 2014 CBSE Class 10 Science Question Paper 2013 CBSE Class 10 Science Question Paper 2012 CBSE Class 10 Science Question Paper 2011 CBSE Class 10 Science Question Paper 2010 CBSE Class 10 Science Question Paper 2009 CBSE Class 10 Science Question Paper 2008 CBSE Class 10 Science Question Paper 2007 ICSE Class 10 Biology Question Papers ICSE Class 10 Biology Question Paper 2020 ICSE Class 10 Biology Question Paper 2019 ICSE Class 10 Biology Question Paper 2018 ISC Class 12 Biology Question Papers ISC Class 12 Biology Question Paper 2020 ISC Class 12 Biology Question Paper 2019 ISC Class 12 Biology Question Paper 2018 Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future. Related articles Differences between Spermatogenesis and Oogenesis Biology • Class 12 Gametogenesis Biology • Class 12 Gametogenesis - Spermatogenesis and Oogenesis Biology • Class 12 Identification of Stages of Gamete Development Biology • Class 12 Effects of Radioactive Pollution Biology • Class 12 Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page More for class 10 NCERT Solutions Revision Notes Sample question papers NCERT Books Trending pages All About Renewable and Non-renewable Resources View page Living and Non-Living Things View page Aquatic Animals View page Difference Between Rabi and Kharif Crops View page Components of Food View page Saprophytes View page Heterotrophic Nutrition View page Weeding View page Binomial Nomenclature View page Study materials Live classes Explore Syllabus Explore Get link in sms to download the app + 91 Get the link Know more about our courses. Book a free counselling session. Speak to an expert TOLL FREE: 1800-120-456-456 91 988-660-2456 (9 AM to 9:30 PM on all days) [email protected] Company About us Contact us Vedantu Blog News Child safety Why Vedantu Our results Careers Help india learn Other Links Free live classes Why teach with Vedantu Try WAVE Try Whiteboard Vedantu improvement promise VOLT Micro courses Maharastra Board Benefits Engineering Blog Courses CBSE Tuitions ICSE Tuitions JEE (Main & Advanced) NEET for Class 11 NEET for Class 12 Eklavya JEE Eklavya NEET Computer Science Vedantu Super Kids Coding for kids Spoken English Study material NCERT NCERT NCERT Solutions NCERT Solutions for Class 12 NCERT Solutions for Class 12 Maths NCERT Solutions for Class 12 Physics NCERT Solutions for Class 12 Chemistry NCERT Solutions for Class 12 Biology NCERT Solutions for Class 12 Business Studies NCERT Solutions for Class 12 Economics NCERT Solutions for Class 12 Accountancy NCERT Solutions for Class 12 English NCERT Solutions for Class 12 Hindi NCERT Solutions for Class 11 NCERT Solutions for Class 11 Maths NCERT Solutions for Class 11 Physics NCERT Solutions for Class 11 Chemistry NCERT Solutions for Class 11 Biology NCERT Solutions for Class 11 Business Studies NCERT Solutions for Class 11 Economics NCERT Solutions for Class 11 Accountancy NCERT Solutions for Class 11 English NCERT Solutions for Class 11 Hindi NCERT Solutions for Class 10 NCERT Solutions for Class 10 Maths NCERT Solutions for Class 10 Science NCERT Solutions for Class 10 English NCERT Solutions for Class 10 Social Science NCERT Solutions for Class 10 Hindi NCERT Solutions for Class 9 NCERT Solutions for Class 9 Maths NCERT Solutions for Class 9 Science NCERT Solutions for Class 9 English NCERT Solutions for Class 9 Social Science NCERT Solutions for Class 9 Hindi NCERT Solutions for Class 8 NCERT Solutions for Class 8 Maths NCERT Solutions for Class 8 Science NCERT Solutions for Class 8 English NCERT Solutions for Class 8 Social Science NCERT Solutions for Class 8 Hindi NCERT Books NCERT Books Class 12 NCERT Books Class 11 NCERT Books Class 10 NCERT Books Class 9 NCERT Books Class 8 Reference book solutions Reference Book Solutions HC Verma Solutions RD Sharma Solutions RS Aggarwal Solutions NCERT Exemplar Solutions Lakhmir Singh Solutions DK Goel Solutions TS Grewal Solutions Sandeep Garg Competitive Exams Competitive Exams JEE Main JEE Advanced NEET Olympiad Preparation NDA KVPY NTSE CBSE CBSE CBSE Syllabus CBSE Sample Paper CBSE Worksheets CBSE Important Questions CBSE Previous Year Question Papers Class 12 CBSE Previous Year Question Papers Class 10 CBSE Important Formulas ICSE ICSE ICSE Solutions ICSE Class 10 Solutions ICSE Class 9 Solutions ICSE Class 8 Solutions State boards State Boards AP Board Bihar Board Gujarat Board Karnataka Board Kerala Board Maharashtra Board MP Board Rajasthan Board Telangana Board TN Board UP Board WB Board Free Study Material Free Study Material Previous Year Question Papers Sample Papers JEE Main Study Materials JEE Advanced Study Materials NEET Study Materials Olympiad Study Materials Kids Learning Ask Questions Important Subjects Physics Biology Chemistry Maths English Commerce Geography Civics Revision Notes Revision Notes CBSE Class 12 Notes CBSE Class 11 Notes CBSE Class 10 Notes CBSE Class 9 Notes CBSE Class 8 Notes © 2024 .Vedantu.com. 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Courses Courses for Kids Free study material Offline Centres More Store Talk to our experts 1800-120-456-456 Sign In Biology Biology Difference Between Sperm and Ovum Difference Between Sperm and Ovum Biology Study Material Biology top 10 Important Topics Biology Syllabus Biology Question Papers Book online demo NCERT Solutions NCERT Solutions Class 12 Biology NCERT Solution Class 11 Biology NCERT Solutions for Class 10 Science NCERT Solutions for Class 9 Science NCERT Solutions for Class 8 Science NCERT Solutions for Class 7 Science NCERT Solutions for Class 6 Science NCERT Solutions for Class 5 EVS NCERT Solutions for Class 4 EVS NCERT Solutions for Class 3 EVS NCERT Notes Class 12 Biology Notes Class 11 Biology Notes Class 10 Science Notes Class 9 Science Notes Class 8 Science Notes Class 7 Science Notes Class 6 Science Notes NCERT Important Question Important Questions for Class 12 Science Important Questions for Class 11 Science Important Questions for Class 10 Science Important Questions for Class 9 Science Important Questions for Class 8 Science Important Questions for Class 7 Science Important Questions for Class 6 Science Difference Between Weather and Climate Scientific Names of Animals and Plants Bacterial Diseases in Humans Enzymes MCQs MCQs on Greenhouse Effect Deficiency Diseases Conservation of Biodiversity Difference Between Cyclic and Non Cyclic Photophosphorylation Conservation of Forest and Wildlife Difference Between National Park and Wildlife Sanctuary CBSE Class 12 Biology Syllabus CBSE Class 11 Biology Syllabus CBSE Class 10 Science Syllabus CBSE Class 9 Science Syllabus CBSE Class 8 Science Syllabus CBSE Class 7 Science Syllabus CBSE Class 6 Science Syllabus CBSE Class 5 EVS Syllabus CBSE Class 4 EVS Syllabus CBSE Class 3 EVS Syllabus ISC Class 12 Biology Syllabus ISC Class 11 Biology Syllabus ICSE Class 10 Biology Syllabus ICSE Class 9 Biology Syllabus ICSE Class 8 Biology Syllabus ICSE Class 7 Biology Syllabus ICSE Class 6 Biology Syllabus CBSE Class 12 Biology Question Papers CBSE Class 12 Biology Question Paper 2020 CBSE Class 12 Biology Question Paper 2019 CBSE Class 12 Biology Question Paper 2018 CBSE Class 12 Biology Question Paper 2017 CBSE Class 12 Biology Question Paper 2016 CBSE Class 12 Biology Question Paper 2015 CBSE Class 12 Biology Question Paper 2014 CBSE Class 12 Biology Question Paper 2013 CBSE Class 10 Science Question Papers CBSE Class 10 Science Question Paper 2020 CBSE Class 10 Science Question Paper 2019 CBSE Class 10 Science Question Paper 2018 CBSE Class 10 Science Question Paper 2017 CBSE Class 10 Science Question Paper 2016 CBSE Class 10 Science Question Paper 2015 CBSE Class 10 Science Question Paper 2014 CBSE Class 10 Science Question Paper 2013 CBSE Class 10 Science Question Paper 2012 CBSE Class 10 Science Question Paper 2011 CBSE Class 10 Science Question Paper 2010 CBSE Class 10 Science Question Paper 2009 CBSE Class 10 Science Question Paper 2008 CBSE Class 10 Science Question Paper 2007 ICSE Class 10 Biology Question Papers ICSE Class 10 Biology Question Paper 2020 ICSE Class 10 Biology Question Paper 2019 ICSE Class 10 Biology Question Paper 2018 ISC Class 12 Biology Question Papers ISC Class 12 Biology Question Paper 2020 ISC Class 12 Biology Question Paper 2019 ISC Class 12 Biology Question Paper 2018 Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future. Related articles Differences between Spermatogenesis and Oogenesis Biology • Class 12 Gametogenesis Biology • Class 12 Gametogenesis - Spermatogenesis and Oogenesis Biology • Class 12 Identification of Stages of Gamete Development Biology • Class 12 Effects of Radioactive Pollution Biology • Class 12 Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page More for class 10 NCERT Solutions Revision Notes Sample question papers NCERT Books Trending pages All About Renewable and Non-renewable Resources View page Living and Non-Living Things View page Aquatic Animals View page Difference Between Rabi and Kharif Crops View page Components of Food View page Saprophytes View page Heterotrophic Nutrition View page Weeding View page Binomial Nomenclature View page Study materials Live classes Explore Syllabus Explore Get link in sms to download the app + 91 Get the link Know more about our courses. 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Biology Biology Difference Between Sperm and Ovum Difference Between Sperm and Ovum Biology Study Material Biology top 10 Important Topics Biology Syllabus Biology Question Papers Book online demo NCERT Solutions NCERT Solutions Class 12 Biology NCERT Solution Class 11 Biology NCERT Solutions for Class 10 Science NCERT Solutions for Class 9 Science NCERT Solutions for Class 8 Science NCERT Solutions for Class 7 Science NCERT Solutions for Class 6 Science NCERT Solutions for Class 5 EVS NCERT Solutions for Class 4 EVS NCERT Solutions for Class 3 EVS NCERT Notes Class 12 Biology Notes Class 11 Biology Notes Class 10 Science Notes Class 9 Science Notes Class 8 Science Notes Class 7 Science Notes Class 6 Science Notes NCERT Important Question Important Questions for Class 12 Science Important Questions for Class 11 Science Important Questions for Class 10 Science Important Questions for Class 9 Science Important Questions for Class 8 Science Important Questions for Class 7 Science Important Questions for Class 6 Science Difference Between Weather and Climate Scientific Names of Animals and Plants Bacterial Diseases in Humans Enzymes MCQs MCQs on Greenhouse Effect Deficiency Diseases Conservation of Biodiversity Difference Between Cyclic and Non Cyclic Photophosphorylation Conservation of Forest and Wildlife Difference Between National Park and Wildlife Sanctuary CBSE Class 12 Biology Syllabus CBSE Class 11 Biology Syllabus CBSE Class 10 Science Syllabus CBSE Class 9 Science Syllabus CBSE Class 8 Science Syllabus CBSE Class 7 Science Syllabus CBSE Class 6 Science Syllabus CBSE Class 5 EVS Syllabus CBSE Class 4 EVS Syllabus CBSE Class 3 EVS Syllabus ISC Class 12 Biology Syllabus ISC Class 11 Biology Syllabus ICSE Class 10 Biology Syllabus ICSE Class 9 Biology Syllabus ICSE Class 8 Biology Syllabus ICSE Class 7 Biology Syllabus ICSE Class 6 Biology Syllabus CBSE Class 12 Biology Question Papers CBSE Class 12 Biology Question Paper 2020 CBSE Class 12 Biology Question Paper 2019 CBSE Class 12 Biology Question Paper 2018 CBSE Class 12 Biology Question Paper 2017 CBSE Class 12 Biology Question Paper 2016 CBSE Class 12 Biology Question Paper 2015 CBSE Class 12 Biology Question Paper 2014 CBSE Class 12 Biology Question Paper 2013 CBSE Class 10 Science Question Papers CBSE Class 10 Science Question Paper 2020 CBSE Class 10 Science Question Paper 2019 CBSE Class 10 Science Question Paper 2018 CBSE Class 10 Science Question Paper 2017 CBSE Class 10 Science Question Paper 2016 CBSE Class 10 Science Question Paper 2015 CBSE Class 10 Science Question Paper 2014 CBSE Class 10 Science Question Paper 2013 CBSE Class 10 Science Question Paper 2012 CBSE Class 10 Science Question Paper 2011 CBSE Class 10 Science Question Paper 2010 CBSE Class 10 Science Question Paper 2009 CBSE Class 10 Science Question Paper 2008 CBSE Class 10 Science Question Paper 2007 ICSE Class 10 Biology Question Papers ICSE Class 10 Biology Question Paper 2020 ICSE Class 10 Biology Question Paper 2019 ICSE Class 10 Biology Question Paper 2018 ISC Class 12 Biology Question Papers ISC Class 12 Biology Question Paper 2020 ISC Class 12 Biology Question Paper 2019 ISC Class 12 Biology Question Paper 2018 Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future. Related articles Differences between Spermatogenesis and Oogenesis Biology • Class 12 Gametogenesis Biology • Class 12 Gametogenesis - Spermatogenesis and Oogenesis Biology • Class 12 Identification of Stages of Gamete Development Biology • Class 12 Effects of Radioactive Pollution Biology • Class 12 Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page More for class 10 NCERT Solutions Revision Notes Sample question papers NCERT Books Trending pages All About Renewable and Non-renewable Resources View page Living and Non-Living Things View page Aquatic Animals View page Difference Between Rabi and Kharif Crops View page Components of Food View page Saprophytes View page Heterotrophic Nutrition View page Weeding View page Binomial Nomenclature View page Study materials Live classes Explore Syllabus Explore
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Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future. Related articles Differences between Spermatogenesis and Oogenesis Biology • Class 12 Gametogenesis Biology • Class 12 Gametogenesis - Spermatogenesis and Oogenesis Biology • Class 12 Identification of Stages of Gamete Development Biology • Class 12 Effects of Radioactive Pollution Biology • Class 12 Recently Updated Pages Difference Between Afforestation and Deforestation View page rDNA and cDNA - Learn Important Terms and Concepts View page Coordination in Plants | Learn Important Terms and Concepts View page Water - A Wonder Liquid, Distribution, Importance and Pollution View page Study of Pollen Germination on a Slide - Working, Procedure and Observation View page Gram-Positive and Gram-Negative Bacteria | Learn Important Terms and Concepts View page
Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
Human Reproductive System The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised. Want to read offline? download full PDF here Download full PDF Is this page helpful? FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised.
The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised.
The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article. What is Sperm? It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm. Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen. Sperm Structure Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece. What is Ovum? Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae. Ovum Structure Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation. We will highlight the differences between sperm and ovum in a tabular chart as follows. Difference Between Ovum and Sperm Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes. Sperm vs Ovum Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes. In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have. Sperm Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids. These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body. Ovum Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised.
The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article.
The two important Cells of the Human Reproductive system are Sperm and Ovum, the former being male Reproductive Cell and the latter being a female Reproductive Cell. Both of these Cells are responsible to undergo Fertilisation through fusion and formation of zygote . However, you will learn about the difference between Ovum and Sperm related to certain characteristics, structure and functionalities in this article.
It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm.
It is the male gamete or reproductive cell that plays a major role in the reproduction process in humans and other animals. A motile sperm with a tail also called flagellum is produced by animals and it is known with the name spermatozoa whereas algae and fungi are known to produce non-motile sperm cells called spermatia. Talking about the plants, the flowering group contains non-motile sperm inside the pollen and some plants such as fern and gymnosperms consist of motile sperm.
Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen.
Human sperm cell is haploid and consists of 23 chromosomes which join with the 23 chromosomes of the female egg or ovum to form a diploid cell. Sperm is stored in the epididymis and during ejaculation, it is released from the penis along with a fluid called semen.
Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece.
Talking about the anatomy of a sperm cell, it can be divided into head and tail. The head contains a nucleus with densely coiled chromatin fibres and is anteriorly surrounded by a thin and flattened sac known as acrosome. Acrosome contains enzymes that help in the penetration into the female egg or ovum. The head portion of a sperm also contains vacuoles . On the other hand, the tail which is also known as flagellum is the longest part of a sperm and goes into a wave-like motion that helps the sperm to swim and penetrate the egg. The four parts of the tail include the connecting piece, principal piece, midpiece and the end piece.
Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae.
Also called the egg cell or ova in plural, it is the female gamete or reproductive cell present in humans and most of the animals. Ovum is non-motile and when the egg or ovum fuse with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. Mammals have numerous ova at birth and these mature through oogenesis. In all mammals including humans, the ovum is fertilised inside the female body. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Ovum is called the oosphere in algae.
Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation.
Ovum has a cell substance at its centre called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of developmental phase in mammals. On the other hand, birds contain egg nutritive yolk which is enough to supply its chick enough nutrients throughout the period of incubation.
Differences Sperm Ovum Definition It is the male gamete or male reproductive cell. It is a female gamete or female reproductive cell. Motility It is a motile cell having flagella that helps in its movement and penetration into ovum. It is non-motile and doesn’t possess any flagella. Size of cell It is the smallest cell in the human body. It is one of the largest cells in the human body. Location of mitochondria Mitochondria is centrally located in this cell. Mitochondria is scattered in the cytoplasm of the cell. Amount of Cytoplasm Cytoplasm is present in very small amounts in sperm cells. Cytoplasm is present in large amounts in the egg cell or the ovum. Nucleoplasm present/absent Nucleoplasm is absent in the cell. Nucleoplasm or the germinal vesicle is present in the egg cell. Type of Chromosomes Sperm cells contain X or Y chromosomes. Egg cells contain only X chromosomes. Centrioles present/absent Centrioles are present in the sperm cell. Centrioles are absent in the sperm cell. Where are they produced? Sperms are produced in the testes, male reproductive organ. Ovum is produced in the ovary which is a female reproductive organ. Segmentation A sperm is segmented into head, neck and tail. Ovum has no such segmentation or similar structure. Formation One spermatogonium results in the formation of four sperms. One oogonium results in the production of only one ovum. Surrounding A sperm cell is surrounded by a plasma membrane. An ovum cell is surrounded by egg envelopes.
Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes.
Human reproduction is a form of sexual reproduction which helps achieve Human Fertilization. Fertilisation is a process of Fusion of Male and Female gametes to give rise to a new individual Human being. Each gamete or Reproductive Cell carries half of the gene of an organism and when both of the gametes fuse the gene adds up to become complete. In Human beings, we have 46 Chromosomes and so to add up the number of Chromosomes after Fertilisation to be 46 each gamete should have 23 Chromosomes.
In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have.
In Sexual Reproduction there exists two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process it will always have half the number of genes that a parent Cell contains, for which they are called haploid. Let us take a look into both types of gamete and see what are the properties they have.
Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids.
Sperm are the male Reproductive Cells that help male organisms to pass down their genes to their offspring. Sperms are formed during the process of Spermatogenesis in the seminiferous tubules of the testes. The process starts with the creation of several successive Sperm Cell precursors which then are transferred into Spermatogonia and get differentiated into Spermatocytes. These Spermatocytes then undergo meiosis, which reduces the number of Chromosomes by half and produces Spermatids.
These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body.
These Spermatids then transform into mature motile Sperm Cells. This transformation includes the change in shape and size of the Cell. The biggest characteristic of Sperm is the ability to reach/travel to the Ovum. In animals, this is possible by the development of a tail-like structure called a filament. Sperms are the smallest of the Cells in the Human body.
Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised.
Ovum is the female Reproductive Cells that get fertilised by Sperm and create a zygote. Ovum is formed and released by the ovaries. The shape of the Ovum is spherical and non-motile. It usually is the largest Cell in the Human body. The majority of the Ovum is constituted by the cytoplasm. The formation of an Ovum in Human females is completed before birth and the ova are released on a cycled basis throughout their whole reproduction cycle. One Ovum is released by both ovaries on an alternate basis in the mid-day of the menstrual cycle. After that, the Ovum waits in the fallopian tube for the Sperm to reach there and get fertilised.
FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
FAQs on Difference Between Sperm and Ovum 1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism. 2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation. 3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote. 4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse. 5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male. 6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml. 7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum. 8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects. 9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
1. What is the difference between sperm and egg cells? Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism.
Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism.
Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism.
Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism.
Sperm are male reproductive cells or male gametes produced in the male reproductive organs known as the testes whereas egg cells are ovum (ova), female gametes produced in the female reproductive organs called ovaries. Both of them differ in their structure, however, these come together to fuse and form a zygote that results into a new organism.
2. What is fertilisation? It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation.
It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation.
It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation.
It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation.
It is the fusion of two gametes, one from male and another from female in humans that lead to the development of a new individual offspring or organism. In humans, sexual reproduction is the process where the cycle of fertilization and development of new offspring takes place. Other terms used for fertilisation in different organisms include insemination, pollination, syngamy, impregnation and generative fertilisation.
3. What is a diploid cell? A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote.
A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote.
A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote.
A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote.
A diploid cell is formed when the nucleus of both the sperm (haploid) and an egg (haploid) fuse. A diploid cell is also called zygote.
4. What is artificial insemination? It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse.
It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse.
It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse.
It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse.
It is the artificially done fertilisation process where introduction of sperm into a female's uterine cavity or female’s cervix is performed deliberately to achieve pregnancy. It is also in vivo fertilisation which is an alternative to achieve a new offspring other than sexual intercourse.
5. What is the genetic difference between sperm and ovum? The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male.
The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male.
The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male.
The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male.
The Human gene contains the Chromosomes in pairs and one pair of those Chromosomes is called sex Chromosomes. The sex Chromosomes have XX Chromosome for females and XY for males. Which makes it possible for Sperm to have either X or Y sex Chromosomes while the Ovum can only have an X Chromosome. If a Sperm with an X Chromosome fertilises the Ovum then the offspring will be a female else if it is fertilised by a Sperm with Y Chromosomes then it will be a male.
6. What does the male ejaculation consist of ? The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml.
The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml.
The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml.
The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml.
The male ejaculation fluid is called the semen and the Sperm only consists of 2-3% of the whole load amount. Some other components are water, fructose, protein, amino acids, vitamins, minerals and some acids. The semenal ejaculative fluids are not secreted only by testes but by many other glands like the prostate gland and bulbourethral gland. The whole constituents of semen help the Sperm to live and travel to the Ovum by providing a nurturing environment for it. The whole volume of semen is usually 2-3 ml.
7. What happens if the ovum is not fertilised? The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum.
The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum.
The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum.
The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum.
The ova are released by each ovary in each menstrual cycle into the fallopian tube. There the Ovum waits for the Sperm to get fertilised for around one day. If in that period the Sperm does not arrive and the Ovum is not fertilised then it is carried out to the uterus by the cilia where it will get discharged out through the vagina. It usually exits out along with mucus and blood Cells that develop on the wall lining of the uterus with every Ovum.
8. Where can I find the detailed concepts of Human reproduction? Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects.
Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects.
Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects.
Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects.
Our material on Human reproduction is created by the best of the faculty members from throughout the countries. Vedantu not only has detailed subject coverage in all subjects but also provides tailored solutions for each student so that it will be easy for everyone to understand. We insist on making the learning fun so that every student will enjoy their learning on our platform. Sign up today for the best materials available which will help you achieve your target in all subjects.
9. How important is the human reproductive system? The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
The chapter on the Human Reproductive system is very very important in the aspect of medical entrance examinations. The subject matter is repeated over multiple classes throughout the school education. It is not only important as a subject to score marks or crack entrance exams but for our better understanding of our own body. We should learn every detail about the Human Reproductive system as we will have to use it throughout our life. This will help us in planning our life in future.
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Revision Notes Revision Notes CBSE Class 12 Notes CBSE Class 11 Notes CBSE Class 10 Notes CBSE Class 9 Notes CBSE Class 8 Notes | biology | 4556022 | https://sv.wikipedia.org/wiki/Sematophyllum%20cellulosum | Sematophyllum cellulosum | Sematophyllum cellulosum är en bladmossart som beskrevs av William Russell Buck 1993. Sematophyllum cellulosum ingår i släktet Sematophyllum och familjen Sematophyllaceae. Inga underarter finns listade i Catalogue of Life.
Källor
Egentliga bladmossor
cellulosum | swedish | 0.989739 |
parthenogenesis/.txt |
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Sperm and ovum This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest. Table of Content Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids. Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes . Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all Related articles Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all Access more than 9,257+ courses for NEET UG Get subscription Trending Topics NEET Preparation Tips NEET 2024 Preparation Tips How to Prepare for NEET from Class 11? How to Prepare for NEET? 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Sperm and ovum This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest. Table of Content Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids. Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes . Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all Related articles Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all Access more than 9,257+ courses for NEET UG Get subscription Trending Topics NEET Preparation Tips NEET 2024 Preparation Tips How to Prepare for NEET from Class 11? How to Prepare for NEET? NEET 2024 NEET Syllabus 2024 NEET Question Paper NEET Exam Pattern NEET Notification NEET Exam Calendar NEET Results NEET Eligibility NEET Preparation Books NEET Previous Year Question Papers NEET 2022 Question Paper NEET 2021 Question Paper NEET 2020 Question Paper NEET 2019 Question Paper NEET 2018 Question Paper Related links NEET Study Materials How Many Attempts for NEET How Many Marks Are Required in NEET for MBBS Living World NEET Questions MBBS Full Form NEET Full Form Physics NEET Syllabus Download NEET 2023 question paper
Sperm and ovum This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest. Table of Content Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids. Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes . 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Sperm and ovum This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest.
Sperm and ovum This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest.
This article is about sexual reproduction. We discuss sperm and ovum in detail.Sperm and ovum are the gametes produced by vertebrates. More specifically, sperm is the male gamete while the ovum is the female gamete. These two cells also have contrasting sizes – for instance, the sperm is the smallest cell in the human body while the ovum is the largest.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism. What is sperm: In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa. Structure of Sperm: The sperm consists of a head, neck, middle piece, and tail. The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once. What is ovum? Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans. Structure of ovum: Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals. Fertilisation: Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation. In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy. Conclusion: In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents
Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism.
In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa.
The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once.
Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans.
Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals.
Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation.
In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy.
In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation. Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation.
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation.
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation.
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation.
Frequently asked questions Get answers to the most common queries related to the NEET UG Examination Preparation.
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full How do sperm get entry into the ovum? Ans. – The sperm immediately begin... Read full
Define fertilisation and where does it take place? Ans. Fertilisation is the fusion of male and female gametes to rise to a new i... Read full
What is the difference between sperm and egg cells? Ans. Sperm are male reproductive cells or male gametes in the male reproductiv... Read full
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing. Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries. Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.
Ans. Fertilisation is the fusion of male and female gametes to rise to a new individual. Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.
Fertilisation usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.
Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries.
Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries.
Ans. Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries.
Sperm are male reproductive cells or male gametes in the male reproductive organs known as testes whereas egg cells are ovum female gametes produced in female reproductive organs called ovaries.
Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
Ans. – The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes .
The sperm immediately begin swimming and some will find their way into the cervix. The sperm then begin their long journey towards the egg. Leaving the cervix they enter the womb. Here, they swim toward the Fallopian tubes
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all Related articles Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all Access more than 9,257+ courses for NEET UG Get subscription
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all Related articles Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all Access more than 9,257+ courses for NEET UG Get subscription
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Crack NEET UG with Unacademy Get subscription and access unlimited live and recorded courses from India’s best educators Structured syllabus Daily live classes Ask doubts Tests & practice Learn more
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Notifications Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc. Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc.
Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc.
Get all the important information related to the NEET UG Examination including the process of application, important calendar dates, eligibility criteria, exam centers etc.
Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
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Best Books for NEET 2023 – Physics, Chemistry & Biology How to Prepare for NEET 2024 at Home Without Coaching? Last 10 Years NEET Question Papers – Download NEET Previous Year Question Paper with Solutions PDFs NEET 2023 Counselling – Schedule, Dates, Fees, Seat Allotment NEET Answer Key 2021 – Download PDF NEET Eligibility Criteria 2024 – Age Limit, Qualifying Codes, Number of Attempt NEET Exam Calendar NEET Exam Information NEET Exam Pattern 2023 – Check Marking Scheme, Subject-wise Question Distribution – NEET Total Marks NEET Marking Scheme NEET Registration Date Extension NEET Registration Fees NEET Registration Process NEET Result 2023 (OUT): Download Link @neet.nta.nic.in, NEET Score card NEET Syllabus 2023 NEET Syllabus 2024 with Chapter-wise Weightage NEET UG Exam Analysis NEET UG Hall Ticket 2023 – Check Steps to Download NEET UG Previous Papers Analysis See all
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Related articles Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all
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Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all
Learn more topics related to Biology Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses. See all
Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic. Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans. Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more. Zinc In this article we were going to learn about the topic of Zinc in detail with examples and uses.
Zygote In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic.
In this chapter we will discuss zygote definition, formation of zygote, development of zygote and much more.At last we will discuss some important questions related to this topic.
Zoology Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans.
Zoology is the branch of biology that is concerned with the study of the animal kingdom. It is the scientific study of all of the species of the animal kingdom as a whole, including humans.
Zoological Park This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more.
This article gives you an insight into the zoological parks, the advantages and disadvantages of zoos and much more.
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Goals AFCAT AP EAMCET Bank Exam BPSC CA Foundation CAPF CAT CBSE Class 11 CBSE Class 12 CDS CLAT CSIR UGC GATE IIT JAM JEE Karnataka CET Karnataka PSC Kerala PSC MHT CET MPPSC NDA NEET PG NEET UG NTA UGC Railway Exam SSC TS EAMCET UPSC WBPSC CFA
Goals AFCAT AP EAMCET Bank Exam BPSC CA Foundation CAPF CAT CBSE Class 11 CBSE Class 12 CDS CLAT CSIR UGC GATE IIT JAM JEE Karnataka CET Karnataka PSC Kerala PSC MHT CET MPPSC NDA NEET PG NEET UG NTA UGC Railway Exam SSC TS EAMCET UPSC WBPSC CFA
Goals AFCAT AP EAMCET Bank Exam BPSC CA Foundation CAPF CAT CBSE Class 11 CBSE Class 12 CDS CLAT CSIR UGC GATE IIT JAM JEE Karnataka CET Karnataka PSC Kerala PSC MHT CET MPPSC NDA NEET PG NEET UG NTA UGC Railway Exam SSC TS EAMCET UPSC WBPSC CFA | biology | 29963 | https://sv.wikipedia.org/wiki/Befruktning | Befruktning | Befruktning, ibland konception, fertilisering, fekundation eller syngami, är den process då två könsceller (normalt manlig respektive kvinnlig) förenas och bildar en ny organism av samma art. Hos djur innefattar processen en spermies förening med en äggcell, med vardera hälften av antalet kromosomer en individ av arten innehar (hos människan har vardera gamet 23 av de 46 kromosomerna), och bildandet av en zygot, som sedermera utvecklas till ett embryo.
Störst chans för att en kvinnas äggcell ska bli befruktad är vid samlag vid eller upp till någon dag före tidpunkten för ägglossning. Ägglossning sker vanligen 12–16 dagar innan menstruationens första dag (med betydande individuella variationer). För att en kvinnas ägg ska kunna befruktas krävs att kvinnan har samlag med en man eller genomgår assisterad befruktning.
Mekanism hos däggdjur
Ett moget ägg som lossnat från äggstocken tas upp av äggledaren och fastnar normalt i ampulla uterus, en förträngning i äggledaren, strax innan det går in i livmodern. Ägget består av oocyten, som omges av ett lager av glykoproteiner kallat zona pellucida. Zona pellucida i sin tur består av fyra olika glykoproteiner, ZP1–4, som tillsammans utgör ett nätverk som omger äggcellen. Utanpå zona pellucida sitter dessutom ett lager av granulosaceller, kallat corona radiata. Dessa celler utgör den första barriären för spermier att passera. När spermiecellen når fram till corona radiata utsöndras ett enzym från spermiens akrosom kallat hyaluronidas, som bryter ner bindingarna mellan cellerna i corona radiata, så att spermierna når fram till zona pellucida. I zona pellucida finns receptorer, ZP3, dit spermiens huvud binder.
Vid inbindning till ZP3 utsöndras ytterligare hormoner från spermiens akrosom genom att den fuserar med spermiecellens yttre membran. Enzymerna bryter ner och ändrar strukturen hos zona pellucida så att enbart just ZP3-glykoproteinerna återstår. Det viktigaste av dessa enzymer är acrosin. Enzymatiska omstruktureringen av zona pellucida gör att spermien kan penetrera lagret genom fortsatta "simrörelser" mot äggcellens kärna.
När spermien jobbat sig in så att ungefär halva huvudet nått in i zona pellucida kommer plasmamembranet i den så kallade ekvatorialregionen på spermiens huvud att nå mikrovilliutskott på äggcellen. Genom ett antal molekyler på spermiecellens plasmamembran, däribland fertilin och cyritestin, binder till receptorer på äggcellens membran, däribland alfa-6-integriner och CD9-proteiner, så kan äggcellen och spermiecellen sammansmälta.
I samband med sammansmältningen stöter äggcellen ut en del av sitt genetiska material i en polkropp, den andra i ordningen. Äggcellen blir då haploid, så att den kan ta emot spermiecellens genetiska material utan att antalet kromosomer överstiger 46. Samtidigt triggas utsöndring av kalciumjoner i vågor inne i äggcellens cytosol, vilket bland annat triggar utsöndring av glykoproteiner som får zona pellucida att svälla, samt enzymer som hydrolyserar ZP3-glykoproteinerna. Detta kallas zona reaction, och är en viktig funktion för att förhindra polyspermi, det vill säga, att mer än en spermiecell lyckas ta sig in i ägget.
Även om spermiecellen har och behöver mitokondrier som driver dess "svans", som består av en stor cilie, så lämnas dessa utanför ägget. Endast moderns mitokondrier överförs till embryot. Spermien bidrar dock med en centrosom, som behövs för att utföra celldelningarna som följer.
Assisterad befruktning
Assisterad befruktning kan antingen ske genom In vitro-fertilisering eller genom insemination.
Dubbelbefruktning
Hos angiospermer är dubbelbefruktning ett utmärkande drag. Hanorganet, mikrogamofyten, mer känt som pollenkornet består hos angiospermerna av två celler: spermatogen cell och pollenslangscell. Den spermatogena cellen genomgår celldelning så att två spermieceller uppstår. Efter det att pollenslangen vuxit fram till mikropyle ("ingången" till honorganet makrogametofyten) befruktar den ena spermiecellen (haploid, n) äggcellen (n) så att den diploida zygoten (2n) bildas. Zygoten bildar sedan växtembryot. Den andra spermiecellen befruktar de bägge polkärnorna (3n + n) i mitten av makrogamofyten. Denna cell som alltså kommer att ha en pentaploid cellkärna (5n) och kommer att bilda det näringsrika endospermet (frövitan).
Även om dubbelbefruktning anses som en synapomorfi för angiospermerna, så har dubbelbefruktning även rapporterats hos vissa medlemmar av Gnetophyta.
Referenser
Fortplantning
Botanik | swedish | 0.500366 |
parthenogenesis/the-human-egg-cell-and-sperm-153m79.html.txt |
Phenomenology - Tom van Gelder Embryology Man does not become human, but is always human. Erich Blechschmidt Introduction Observing Making an observation Concluding or enriching Connecting observations Image and gesture First impressions Living in your own world? Different observations Magnifying and reducing The role of art Phenomenology Introduction The four elements Earth Water Metamorphosis Air Warmth The four ethers Warmth ether Light ether Tone ether Life ether Individual, specific action Literature Basic exercises The six basic exercises Control of thought Control of will Equanimity Positivity Open-mindedness Inner harmony The 12 senses The twelve senses Sense of touch Sense of life Sense of movement Sense of balance Sense of smell Sense of taste Sense of sight Sense of temperature Sense of hearing Sense of speech Sense of thought Sense of ego Using the senses together Literature Threefoldness Of man Of mouse - lion - cow Of horse - pig - cow Of odd-toed ungulates Of Suina Of dog and cat Embryology Introduction Plant and animal Egg cell and sperm The conception The first week The second week The third week The fourth week The fifth to eighth week Sources Evolution Introduction to evolution Evolution of the horse Evolution of Dinosaurs Man and the chimpanzee Evolution: a different view Service Tom van Gelder Books Links Contact De Javascript-functie van uw browser is uitgeschakeld. Daardoor kunt u maar beperkt gebruik maken van onze website. The human egg cell and sperm For a conception an egg cell and many sperm are needed. When the cells find each other, they fuse after a while and the chromosomes come together. Then the zygote (= fertilized egg) is formed and can begin to divide. Phenomenology gives us the characteristics of the ovum and sperm. There are no cells in humans that are so different and yet belong so much together. The ovum and sperm Size and shape The egg cell (or ovum, or oocyte) is the largest human cell. She measures 0.15 to 0.2 mm and is just visible to the naked eye. She is also the roundest cell, she is almost perfectly round (Fig. 4). She therefore has the largest volume in relation to her surface. The cell consists of a large amount of cytoplasm (= cell fluid) in which the nucleus is dissolved (and therefore invisible) until just before conception. Sperm cells are the smallest human cells. They are no more than a nucleus with a small amount of cytoplasm, some mitochondria (the energy suppliers of the cell) and a long tail. They have hardly any content and are the straightest cells. It is not strictly true that they are the largest and smallest cells. In the spinal cord there are larger cells, in the small brains smaller cells. This does not affect the principle. The difference between ovum and sperm remains enormous. Egg cell and sperm are each others opposite. Large versus small, round versus straight, cytoplasm versus nucleus. The differences are great, at the same time they belong together if we perceive the ovum as a sphere and the straight sperm as the corresponding radius. Figure 4. Spermatozoon (A) and ovum (C). B shows the sperm at the same scale as the ovum Mobility The cytoplasm of a normal body-cell is in movement, the nucleus is not. The two gametes (= germ cells) show different features. The egg cell consists primarily of cytoplasm, she is internally mobile. The nucleus is outspread, the chromosomes are unwound (not folded up). The cell is internally active and mobile. The sperm cells have hardly any cytoplasm and are concentrated in their nuclear DNA. They have a crystalline structure. These cells are internally structured and rigid. In contrast, the ovum is externally not active. After her release, she is passively moved by the fluid-flow in the oviduct (uterine tube), while the sperm cells are active, using their tails to swim against the stream of fluid in the oviduct. They are externally active and mobile. The ovum is internally mobile and externally passive, this is a polarity. The sperm shows the opposite: internally passive and externally mobile. Egg cell and sperm have a polarity and are opposite to each other, we see a double polarity. Metabolism An egg cell is a metabolically active cell; substances are absorbed and released. E.g. nutrients are absorbed, substances that affect the uterus and substances that attract the sperm are released. An egg cell lives only 12 to 24 hours in her own environment and cannot be preserved. The egg cell can easily be destroyed. She is an active cell and open to the environment. Sperm cells do not absorb or release substances. There is no interaction with the environment. They live about 3 to 5 days in the womb and can be preserved and frozen at temperatures below 60 °C. They are not easy to destroy. They are closed off from the environment and metabolically passive. The open and vulnerable state of the egg cell is polar to the closed and robust state of the sperm cells. Since several years an ovum can be frozen by vitrification, a process whereby water is removed and replaced by a concentrated liquid, leaving no freezing crystals, which can damage the chromosomes. Number For a conception one ovum and millions of sperm are required. The one ovum is worth as much as all those millions of sperm. A man with less than 20-40 million sperm in an ejaculation is barren. Such great numbers are necessary because most sperm do not reach the ovum. Also, for a conception more than one spermatozoon is necessary. See the page Conception. The ovum is alone and the sperm are with millions. One sperm cell is nothing, one ovum determines everything. One is polar to millions. One comprises everything, it is all there is, whereas the millions of sperm cells are infinitive, have no importance on their own. Location The egg cell develops in one of the two ovaries in the warm abdominal cavity, the sperm develop in the testicles just outside the body in a relatively cold environment. The ovum develops in warm- and sperm in relative cold conditions. Development Egg cells are produced well before birth in a huge number of so called primordial egg cells (primordial oocytes). From the beginning on, there is a continuous process of dying, so that at birth 2 million (!) are left. That process of dying goes on after birth. At the onset of puberty there remain about 40,000 ova. Then every four weeks a number of them begin a process of maturation. Of these, only one (sometimes two or three) ovum matures, the rest dies. In total about 400 ova mature (13 per year for 30 years). At menopause, no primordial egg cells are left. In men, a very different process is going on. The first sperm cells are formed only from puberty on, before that they are not produced. Then the production goes on and on and never stops, hundreds per second, millions each day. Sperm cells are constantly being newly formed. Egg cells are old cells that became mature. Primordial oocytes are in a process of dying. Sperm cells are newly formed and are young. The maturation process of ova is an expiring process, it stops. The formation of the sperm is a vital process, it never stops. Maturation From a primordial oocyte only one mature egg cell develops. During meiosis the rest of the mass of the nucleus is excreted as polar bodies. The cell grows during maturation, the amount of cytoplasm increases. During ripening the ovum moves from the centre of the ovary to the edge (Fig. 5). From a primordial spermcell four sperm cells develop. The cytoplasm is eliminated, the cell is getting smaller. When some cytoplasm stays behind, the sperm cell cannot swim well and cannot reach the egg cell. Sperm cells are produced at the edge of the testis and stored inside. At egg cell maturation the focus is on one cell, that expands in volume. Sperm cells show concentration of material and expansion of the number. Egg cells move from the inside to the outside, sperm cells from the outside to the inside. Conclusion In appearance and processes egg cell and sperm are mutually antagonistic, each others opposite. Large versus small, internally - versus externally active, old versus young, concentration versus expansion, etc. During maturation of these gametes two cells are formed which differ maximally and seem to go to extremes in their individuality. The development and maturation show increasing divergence, a process of polarization. When they are mature, ovum and sperm can come together and resolve the polarity in a conception, so that a new human being can be born, that has all the cell shapes that lie between the two extremes. If not, there is no viability, and then they die. egg cell sperm size largest cell smallest cell shape round straight inner mobility mobile cytoplasm rigid nuclear material outer mobility passive active metabolism active little activity openness yes no number one millions produced in the ovary, inside the body testes, outside the body temperature warm relatively cold when formed before birth from puberty age old young formed from - until before birth - menopause puberty - death maturation increasing volume decreasing volume life span short long storable no yes Table 2. Differences between an egg cell and sperm The development of the ovum Ova are created as primordial oocytes in million copies as early as in the embryonic stage and their number is gradually reduced. They lie separated from each other in follicles and are surrounded by a layer of nutritive, so called follicular cells. In the primordial follicles (= initial vesicles) they lead a passive existence. In Fig. 5 the development of the egg cell can be seen clockwise from the left (primordial follicles). The development begins with the thickening of the surrounding layer of nutritive cells, this is called the primary follicle (= first vesicle). This stage leads to the secondary follicle, because in the layer of nutritive cells an antrum (= cave) arises. The ovum grows and gets larger. The follicle produces oestrogen, a hormone that stimulates the wall of the uterus to thicken. The antrum grows larger. Around the ovum a layer is formed, called the zona pellucida (= translucent layer). Around it are the nutritive cells in the corona radiata (= radiating wreath). The growth of the ovum continues. The wall of the uterus continues to thicken. Then the ovum is shot away into the abdominal cavity. There is a moment when the ovum floats freely in the abdominal cavity. Then she will be collected by the fimbriae of the oviduct. The interception is an active process, the oviduct moves to the ovum. The remaining cavity in the ovary is called the corpus luteum (= yellow small body) that makes progesterone, which also plays a role in the thickening of the uterine wall, so that the fertilized ovum can implant. When a fertilization does not occur, then the thickened wall comes loose and menstruation occurs. Figure 5. Oogenesis, the development of the egg cell in the ovary (from the Internet) Konig (1986) gives a similarity between the development of the ovum and the evolution of the earth, as it is described by Rudolf Steiner in Anthroposophy: 1. The egg is surrounded for many years by tissue of the ovary. He compares this to the Warmth Stage of the earth, or the Saturn Stage. 2. The nutritive cells thicken, and the ovum increasingly stands on her own. He compares this to the Air or Sun Stage of the earth. 3. In the layer of nutritive cells the fluid-filled antrum is created. This is compared to the Water or Moon Stage of the earth. 4. The release of the ovum is compared with the (current) solid stage of the earth. The cell is completely on herself and will either develop or die. The development of sperm From a germ, four equal sperm cells are formed by division. Around the nucleus a hard cap is formed, the acrosome (acros = top, soma = body). Then the cytoplasm is ejected and the cell gets smaller. Mitochondria move to the beginning of the tail, that becomes thicker and longer. The cells are stored for about 60 days, after which they are resorbed. If a small cloud of cytoplasm remains with the nucleus, the sperm is badly damaged and will have trouble moving forward. Figure 6. Spermatogenesis, the development of sperm « 1 2 3 4 5 6 7 8 9 10 » Based on: Van der Wal, J., 2003. Dynamic morphology and embryology. In: Bie, van der G & M. Huber, Foundations of anthroposophical medicine. Floris books, Edinburgh. Bie, G van der, 2001. Embryology. Louis Bolk Institute, Driebergen. © Heirs Tom van Gelder - AntroVista Archief Netwerk
Phenomenology - Tom van Gelder Embryology Man does not become human, but is always human. Erich Blechschmidt Introduction Observing Making an observation Concluding or enriching Connecting observations Image and gesture First impressions Living in your own world? Different observations Magnifying and reducing The role of art Phenomenology Introduction The four elements Earth Water Metamorphosis Air Warmth The four ethers Warmth ether Light ether Tone ether Life ether Individual, specific action Literature Basic exercises The six basic exercises Control of thought Control of will Equanimity Positivity Open-mindedness Inner harmony The 12 senses The twelve senses Sense of touch Sense of life Sense of movement Sense of balance Sense of smell Sense of taste Sense of sight Sense of temperature Sense of hearing Sense of speech Sense of thought Sense of ego Using the senses together Literature Threefoldness Of man Of mouse - lion - cow Of horse - pig - cow Of odd-toed ungulates Of Suina Of dog and cat Embryology Introduction Plant and animal Egg cell and sperm The conception The first week The second week The third week The fourth week The fifth to eighth week Sources Evolution Introduction to evolution Evolution of the horse Evolution of Dinosaurs Man and the chimpanzee Evolution: a different view Service Tom van Gelder Books Links Contact
Phenomenology - Tom van Gelder Embryology Man does not become human, but is always human. Erich Blechschmidt
Introduction Observing Making an observation Concluding or enriching Connecting observations Image and gesture First impressions Living in your own world? Different observations Magnifying and reducing The role of art Phenomenology Introduction The four elements Earth Water Metamorphosis Air Warmth The four ethers Warmth ether Light ether Tone ether Life ether Individual, specific action Literature Basic exercises The six basic exercises Control of thought Control of will Equanimity Positivity Open-mindedness Inner harmony The 12 senses The twelve senses Sense of touch Sense of life Sense of movement Sense of balance Sense of smell Sense of taste Sense of sight Sense of temperature Sense of hearing Sense of speech Sense of thought Sense of ego Using the senses together Literature Threefoldness Of man Of mouse - lion - cow Of horse - pig - cow Of odd-toed ungulates Of Suina Of dog and cat Embryology Introduction Plant and animal Egg cell and sperm The conception The first week The second week The third week The fourth week The fifth to eighth week Sources Evolution Introduction to evolution Evolution of the horse Evolution of Dinosaurs Man and the chimpanzee Evolution: a different view Service Tom van Gelder Books Links Contact
De Javascript-functie van uw browser is uitgeschakeld. Daardoor kunt u maar beperkt gebruik maken van onze website. The human egg cell and sperm For a conception an egg cell and many sperm are needed. When the cells find each other, they fuse after a while and the chromosomes come together. Then the zygote (= fertilized egg) is formed and can begin to divide. Phenomenology gives us the characteristics of the ovum and sperm. There are no cells in humans that are so different and yet belong so much together. The ovum and sperm Size and shape The egg cell (or ovum, or oocyte) is the largest human cell. She measures 0.15 to 0.2 mm and is just visible to the naked eye. She is also the roundest cell, she is almost perfectly round (Fig. 4). She therefore has the largest volume in relation to her surface. The cell consists of a large amount of cytoplasm (= cell fluid) in which the nucleus is dissolved (and therefore invisible) until just before conception. Sperm cells are the smallest human cells. They are no more than a nucleus with a small amount of cytoplasm, some mitochondria (the energy suppliers of the cell) and a long tail. They have hardly any content and are the straightest cells. It is not strictly true that they are the largest and smallest cells. In the spinal cord there are larger cells, in the small brains smaller cells. This does not affect the principle. The difference between ovum and sperm remains enormous. Egg cell and sperm are each others opposite. Large versus small, round versus straight, cytoplasm versus nucleus. The differences are great, at the same time they belong together if we perceive the ovum as a sphere and the straight sperm as the corresponding radius. Figure 4. Spermatozoon (A) and ovum (C). B shows the sperm at the same scale as the ovum Mobility The cytoplasm of a normal body-cell is in movement, the nucleus is not. The two gametes (= germ cells) show different features. The egg cell consists primarily of cytoplasm, she is internally mobile. The nucleus is outspread, the chromosomes are unwound (not folded up). The cell is internally active and mobile. The sperm cells have hardly any cytoplasm and are concentrated in their nuclear DNA. They have a crystalline structure. These cells are internally structured and rigid. In contrast, the ovum is externally not active. After her release, she is passively moved by the fluid-flow in the oviduct (uterine tube), while the sperm cells are active, using their tails to swim against the stream of fluid in the oviduct. They are externally active and mobile. The ovum is internally mobile and externally passive, this is a polarity. The sperm shows the opposite: internally passive and externally mobile. Egg cell and sperm have a polarity and are opposite to each other, we see a double polarity. Metabolism An egg cell is a metabolically active cell; substances are absorbed and released. E.g. nutrients are absorbed, substances that affect the uterus and substances that attract the sperm are released. An egg cell lives only 12 to 24 hours in her own environment and cannot be preserved. The egg cell can easily be destroyed. She is an active cell and open to the environment. Sperm cells do not absorb or release substances. There is no interaction with the environment. They live about 3 to 5 days in the womb and can be preserved and frozen at temperatures below 60 °C. They are not easy to destroy. They are closed off from the environment and metabolically passive. The open and vulnerable state of the egg cell is polar to the closed and robust state of the sperm cells. Since several years an ovum can be frozen by vitrification, a process whereby water is removed and replaced by a concentrated liquid, leaving no freezing crystals, which can damage the chromosomes. Number For a conception one ovum and millions of sperm are required. The one ovum is worth as much as all those millions of sperm. A man with less than 20-40 million sperm in an ejaculation is barren. Such great numbers are necessary because most sperm do not reach the ovum. Also, for a conception more than one spermatozoon is necessary. See the page Conception. The ovum is alone and the sperm are with millions. One sperm cell is nothing, one ovum determines everything. One is polar to millions. One comprises everything, it is all there is, whereas the millions of sperm cells are infinitive, have no importance on their own. Location The egg cell develops in one of the two ovaries in the warm abdominal cavity, the sperm develop in the testicles just outside the body in a relatively cold environment. The ovum develops in warm- and sperm in relative cold conditions. Development Egg cells are produced well before birth in a huge number of so called primordial egg cells (primordial oocytes). From the beginning on, there is a continuous process of dying, so that at birth 2 million (!) are left. That process of dying goes on after birth. At the onset of puberty there remain about 40,000 ova. Then every four weeks a number of them begin a process of maturation. Of these, only one (sometimes two or three) ovum matures, the rest dies. In total about 400 ova mature (13 per year for 30 years). At menopause, no primordial egg cells are left. In men, a very different process is going on. The first sperm cells are formed only from puberty on, before that they are not produced. Then the production goes on and on and never stops, hundreds per second, millions each day. Sperm cells are constantly being newly formed. Egg cells are old cells that became mature. Primordial oocytes are in a process of dying. Sperm cells are newly formed and are young. The maturation process of ova is an expiring process, it stops. The formation of the sperm is a vital process, it never stops. Maturation From a primordial oocyte only one mature egg cell develops. During meiosis the rest of the mass of the nucleus is excreted as polar bodies. The cell grows during maturation, the amount of cytoplasm increases. During ripening the ovum moves from the centre of the ovary to the edge (Fig. 5). From a primordial spermcell four sperm cells develop. The cytoplasm is eliminated, the cell is getting smaller. When some cytoplasm stays behind, the sperm cell cannot swim well and cannot reach the egg cell. Sperm cells are produced at the edge of the testis and stored inside. At egg cell maturation the focus is on one cell, that expands in volume. Sperm cells show concentration of material and expansion of the number. Egg cells move from the inside to the outside, sperm cells from the outside to the inside. Conclusion In appearance and processes egg cell and sperm are mutually antagonistic, each others opposite. Large versus small, internally - versus externally active, old versus young, concentration versus expansion, etc. During maturation of these gametes two cells are formed which differ maximally and seem to go to extremes in their individuality. The development and maturation show increasing divergence, a process of polarization. When they are mature, ovum and sperm can come together and resolve the polarity in a conception, so that a new human being can be born, that has all the cell shapes that lie between the two extremes. If not, there is no viability, and then they die. egg cell sperm size largest cell smallest cell shape round straight inner mobility mobile cytoplasm rigid nuclear material outer mobility passive active metabolism active little activity openness yes no number one millions produced in the ovary, inside the body testes, outside the body temperature warm relatively cold when formed before birth from puberty age old young formed from - until before birth - menopause puberty - death maturation increasing volume decreasing volume life span short long storable no yes Table 2. Differences between an egg cell and sperm The development of the ovum Ova are created as primordial oocytes in million copies as early as in the embryonic stage and their number is gradually reduced. They lie separated from each other in follicles and are surrounded by a layer of nutritive, so called follicular cells. In the primordial follicles (= initial vesicles) they lead a passive existence. In Fig. 5 the development of the egg cell can be seen clockwise from the left (primordial follicles). The development begins with the thickening of the surrounding layer of nutritive cells, this is called the primary follicle (= first vesicle). This stage leads to the secondary follicle, because in the layer of nutritive cells an antrum (= cave) arises. The ovum grows and gets larger. The follicle produces oestrogen, a hormone that stimulates the wall of the uterus to thicken. The antrum grows larger. Around the ovum a layer is formed, called the zona pellucida (= translucent layer). Around it are the nutritive cells in the corona radiata (= radiating wreath). The growth of the ovum continues. The wall of the uterus continues to thicken. Then the ovum is shot away into the abdominal cavity. There is a moment when the ovum floats freely in the abdominal cavity. Then she will be collected by the fimbriae of the oviduct. The interception is an active process, the oviduct moves to the ovum. The remaining cavity in the ovary is called the corpus luteum (= yellow small body) that makes progesterone, which also plays a role in the thickening of the uterine wall, so that the fertilized ovum can implant. When a fertilization does not occur, then the thickened wall comes loose and menstruation occurs. Figure 5. Oogenesis, the development of the egg cell in the ovary (from the Internet) Konig (1986) gives a similarity between the development of the ovum and the evolution of the earth, as it is described by Rudolf Steiner in Anthroposophy: 1. The egg is surrounded for many years by tissue of the ovary. He compares this to the Warmth Stage of the earth, or the Saturn Stage. 2. The nutritive cells thicken, and the ovum increasingly stands on her own. He compares this to the Air or Sun Stage of the earth. 3. In the layer of nutritive cells the fluid-filled antrum is created. This is compared to the Water or Moon Stage of the earth. 4. The release of the ovum is compared with the (current) solid stage of the earth. The cell is completely on herself and will either develop or die. The development of sperm From a germ, four equal sperm cells are formed by division. Around the nucleus a hard cap is formed, the acrosome (acros = top, soma = body). Then the cytoplasm is ejected and the cell gets smaller. Mitochondria move to the beginning of the tail, that becomes thicker and longer. The cells are stored for about 60 days, after which they are resorbed. If a small cloud of cytoplasm remains with the nucleus, the sperm is badly damaged and will have trouble moving forward. Figure 6. Spermatogenesis, the development of sperm « 1 2 3 4 5 6 7 8 9 10 »
For a conception an egg cell and many sperm are needed. When the cells find each other, they fuse after a while and the chromosomes come together. Then the zygote (= fertilized egg) is formed and can begin to divide. Phenomenology gives us the characteristics of the ovum and sperm. There are no cells in humans that are so different and yet belong so much together.
The egg cell (or ovum, or oocyte) is the largest human cell. She measures 0.15 to 0.2 mm and is just visible to the naked eye. She is also the roundest cell, she is almost perfectly round (Fig. 4). She therefore has the largest volume in relation to her surface. The cell consists of a large amount of cytoplasm (= cell fluid) in which the nucleus is dissolved (and therefore invisible) until just before conception.
Sperm cells are the smallest human cells. They are no more than a nucleus with a small amount of cytoplasm, some mitochondria (the energy suppliers of the cell) and a long tail. They have hardly any content and are the straightest cells.
It is not strictly true that they are the largest and smallest cells. In the spinal cord there are larger cells, in the small brains smaller cells. This does not affect the principle. The difference between ovum and sperm remains enormous.
Egg cell and sperm are each others opposite. Large versus small, round versus straight, cytoplasm versus nucleus. The differences are great, at the same time they belong together if we perceive the ovum as a sphere and the straight sperm as the corresponding radius.
The cytoplasm of a normal body-cell is in movement, the nucleus is not. The two gametes (= germ cells) show different features. The egg cell consists primarily of cytoplasm, she is internally mobile. The nucleus is outspread, the chromosomes are unwound (not folded up). The cell is internally active and mobile. The sperm cells have hardly any cytoplasm and are concentrated in their nuclear DNA. They have a crystalline structure. These cells are internally structured and rigid.
In contrast, the ovum is externally not active. After her release, she is passively moved by the fluid-flow in the oviduct (uterine tube), while the sperm cells are active, using their tails to swim against the stream of fluid in the oviduct. They are externally active and mobile.
The ovum is internally mobile and externally passive, this is a polarity. The sperm shows the opposite: internally passive and externally mobile. Egg cell and sperm have a polarity and are opposite to each other, we see a double polarity.
An egg cell is a metabolically active cell; substances are absorbed and released. E.g. nutrients are absorbed, substances that affect the uterus and substances that attract the sperm are released. An egg cell lives only 12 to 24 hours in her own environment and cannot be preserved. The egg cell can easily be destroyed. She is an active cell and open to the environment.
Sperm cells do not absorb or release substances. There is no interaction with the environment. They live about 3 to 5 days in the womb and can be preserved and frozen at temperatures below 60 °C. They are not easy to destroy. They are closed off from the environment and metabolically passive.
The open and vulnerable state of the egg cell is polar to the closed and robust state of the sperm cells.
Since several years an ovum can be frozen by vitrification, a process whereby water is removed and replaced by a concentrated liquid, leaving no freezing crystals, which can damage the chromosomes.
For a conception one ovum and millions of sperm are required. The one ovum is worth as much as all those millions of sperm. A man with less than 20-40 million sperm in an ejaculation is barren. Such great numbers are necessary because most sperm do not reach the ovum. Also, for a conception more than one spermatozoon is necessary. See the page Conception.
The ovum is alone and the sperm are with millions. One sperm cell is nothing, one ovum determines everything. One is polar to millions. One comprises everything, it is all there is, whereas the millions of sperm cells are infinitive, have no importance on their own.
The egg cell develops in one of the two ovaries in the warm abdominal cavity, the sperm develop in the testicles just outside the body in a relatively cold environment.
Egg cells are produced well before birth in a huge number of so called primordial egg cells (primordial oocytes). From the beginning on, there is a continuous process of dying, so that at birth 2 million (!) are left. That process of dying goes on after birth. At the onset of puberty there remain about 40,000 ova. Then every four weeks a number of them begin a process of maturation. Of these, only one (sometimes two or three) ovum matures, the rest dies. In total about 400 ova mature (13 per year for 30 years). At menopause, no primordial egg cells are left.
In men, a very different process is going on. The first sperm cells are formed only from puberty on, before that they are not produced. Then the production goes on and on and never stops, hundreds per second, millions each day. Sperm cells are constantly being newly formed.
Egg cells are old cells that became mature. Primordial oocytes are in a process of dying. Sperm cells are newly formed and are young. The maturation process of ova is an expiring process, it stops. The formation of the sperm is a vital process, it never stops.
From a primordial oocyte only one mature egg cell develops. During meiosis the rest of the mass of the nucleus is excreted as polar bodies. The cell grows during maturation, the amount of cytoplasm increases. During ripening the ovum moves from the centre of the ovary to the edge (Fig. 5).
From a primordial spermcell four sperm cells develop. The cytoplasm is eliminated, the cell is getting smaller. When some cytoplasm stays behind, the sperm cell cannot swim well and cannot reach the egg cell. Sperm cells are produced at the edge of the testis and stored inside.
At egg cell maturation the focus is on one cell, that expands in volume. Sperm cells show concentration of material and expansion of the number. Egg cells move from the inside to the outside, sperm cells from the outside to the inside.
In appearance and processes egg cell and sperm are mutually antagonistic, each others opposite. Large versus small, internally - versus externally active, old versus young, concentration versus expansion, etc. During maturation of these gametes two cells are formed which differ maximally and seem to go to extremes in their individuality. The development and maturation show increasing divergence, a process of polarization.
When they are mature, ovum and sperm can come together and resolve the polarity in a conception, so that a new human being can be born, that has all the cell shapes that lie between the two extremes. If not, there is no viability, and then they die.
Ova are created as primordial oocytes in million copies as early as in the embryonic stage and their number is gradually reduced. They lie separated from each other in follicles and are surrounded by a layer of nutritive, so called follicular cells. In the primordial follicles (= initial vesicles) they lead a passive existence. In Fig. 5 the development of the egg cell can be seen clockwise from the left (primordial follicles).
Konig (1986) gives a similarity between the development of the ovum and the evolution of the earth, as it is described by Rudolf Steiner in Anthroposophy:
1. The egg is surrounded for many years by tissue of the ovary. He compares this to the Warmth Stage of the earth, or the Saturn Stage.
2. The nutritive cells thicken, and the ovum increasingly stands on her own. He compares this to the Air or Sun Stage of the earth.
3. In the layer of nutritive cells the fluid-filled antrum is created. This is compared to the Water or Moon Stage of the earth.
4. The release of the ovum is compared with the (current) solid stage of the earth. The cell is completely on herself and will either develop or die.
From a germ, four equal sperm cells are formed by division. Around the nucleus a hard cap is formed, the acrosome (acros = top, soma = body). Then the cytoplasm is ejected and the cell gets smaller. Mitochondria move to the beginning of the tail, that becomes thicker and longer. The cells are stored for about 60 days, after which they are resorbed. If a small cloud of cytoplasm remains with the nucleus, the sperm is badly damaged and will have trouble moving forward.
Based on: Van der Wal, J., 2003. Dynamic morphology and embryology. In: Bie, van der G & M. Huber, Foundations of anthroposophical medicine. Floris books, Edinburgh. Bie, G van der, 2001. Embryology. Louis Bolk Institute, Driebergen. | biology | 29963 | https://sv.wikipedia.org/wiki/Befruktning | Befruktning | Befruktning, ibland konception, fertilisering, fekundation eller syngami, är den process då två könsceller (normalt manlig respektive kvinnlig) förenas och bildar en ny organism av samma art. Hos djur innefattar processen en spermies förening med en äggcell, med vardera hälften av antalet kromosomer en individ av arten innehar (hos människan har vardera gamet 23 av de 46 kromosomerna), och bildandet av en zygot, som sedermera utvecklas till ett embryo.
Störst chans för att en kvinnas äggcell ska bli befruktad är vid samlag vid eller upp till någon dag före tidpunkten för ägglossning. Ägglossning sker vanligen 12–16 dagar innan menstruationens första dag (med betydande individuella variationer). För att en kvinnas ägg ska kunna befruktas krävs att kvinnan har samlag med en man eller genomgår assisterad befruktning.
Mekanism hos däggdjur
Ett moget ägg som lossnat från äggstocken tas upp av äggledaren och fastnar normalt i ampulla uterus, en förträngning i äggledaren, strax innan det går in i livmodern. Ägget består av oocyten, som omges av ett lager av glykoproteiner kallat zona pellucida. Zona pellucida i sin tur består av fyra olika glykoproteiner, ZP1–4, som tillsammans utgör ett nätverk som omger äggcellen. Utanpå zona pellucida sitter dessutom ett lager av granulosaceller, kallat corona radiata. Dessa celler utgör den första barriären för spermier att passera. När spermiecellen når fram till corona radiata utsöndras ett enzym från spermiens akrosom kallat hyaluronidas, som bryter ner bindingarna mellan cellerna i corona radiata, så att spermierna når fram till zona pellucida. I zona pellucida finns receptorer, ZP3, dit spermiens huvud binder.
Vid inbindning till ZP3 utsöndras ytterligare hormoner från spermiens akrosom genom att den fuserar med spermiecellens yttre membran. Enzymerna bryter ner och ändrar strukturen hos zona pellucida så att enbart just ZP3-glykoproteinerna återstår. Det viktigaste av dessa enzymer är acrosin. Enzymatiska omstruktureringen av zona pellucida gör att spermien kan penetrera lagret genom fortsatta "simrörelser" mot äggcellens kärna.
När spermien jobbat sig in så att ungefär halva huvudet nått in i zona pellucida kommer plasmamembranet i den så kallade ekvatorialregionen på spermiens huvud att nå mikrovilliutskott på äggcellen. Genom ett antal molekyler på spermiecellens plasmamembran, däribland fertilin och cyritestin, binder till receptorer på äggcellens membran, däribland alfa-6-integriner och CD9-proteiner, så kan äggcellen och spermiecellen sammansmälta.
I samband med sammansmältningen stöter äggcellen ut en del av sitt genetiska material i en polkropp, den andra i ordningen. Äggcellen blir då haploid, så att den kan ta emot spermiecellens genetiska material utan att antalet kromosomer överstiger 46. Samtidigt triggas utsöndring av kalciumjoner i vågor inne i äggcellens cytosol, vilket bland annat triggar utsöndring av glykoproteiner som får zona pellucida att svälla, samt enzymer som hydrolyserar ZP3-glykoproteinerna. Detta kallas zona reaction, och är en viktig funktion för att förhindra polyspermi, det vill säga, att mer än en spermiecell lyckas ta sig in i ägget.
Även om spermiecellen har och behöver mitokondrier som driver dess "svans", som består av en stor cilie, så lämnas dessa utanför ägget. Endast moderns mitokondrier överförs till embryot. Spermien bidrar dock med en centrosom, som behövs för att utföra celldelningarna som följer.
Assisterad befruktning
Assisterad befruktning kan antingen ske genom In vitro-fertilisering eller genom insemination.
Dubbelbefruktning
Hos angiospermer är dubbelbefruktning ett utmärkande drag. Hanorganet, mikrogamofyten, mer känt som pollenkornet består hos angiospermerna av två celler: spermatogen cell och pollenslangscell. Den spermatogena cellen genomgår celldelning så att två spermieceller uppstår. Efter det att pollenslangen vuxit fram till mikropyle ("ingången" till honorganet makrogametofyten) befruktar den ena spermiecellen (haploid, n) äggcellen (n) så att den diploida zygoten (2n) bildas. Zygoten bildar sedan växtembryot. Den andra spermiecellen befruktar de bägge polkärnorna (3n + n) i mitten av makrogamofyten. Denna cell som alltså kommer att ha en pentaploid cellkärna (5n) och kommer att bilda det näringsrika endospermet (frövitan).
Även om dubbelbefruktning anses som en synapomorfi för angiospermerna, så har dubbelbefruktning även rapporterats hos vissa medlemmar av Gnetophyta.
Referenser
Fortplantning
Botanik | swedish | 0.500366 |
trees_communicate/Mycorrhizal_network.txt | A mycorrhizal network (also known as a common mycorrhizal network or CMN) is an underground network found in forests and other plant communities, created by the hyphae of mycorrhizal fungi joining with plant roots. This network connects individual plants together. Mycorrhizal relationships are most commonly mutualistic, with both partners benefiting, but can be commensal or parasitic, and a single partnership may change between any of the three types of symbiosis at different times.
The formation and nature of these networks is context-dependent, and can be influenced by factors such as soil fertility, resource availability, host or mycosymbiont genotype, disturbance and seasonal variation. Some plant species, such as buckhorn plantain, a common lawn and agricultural weed, benefit from mycorrhizal relationships in conditions of low soil fertility, but are harmed in higher soil fertility. Both plants and fungi associate with multiple symbiotic partners at once, and both plants and fungi are capable of preferentially allocating resources to one partner over another.
Referencing an analogous function served by the World Wide Web in human communities, the many roles that mycorrhizal networks appear to play in woodland have earned them a colloquial nickname: the Wood Wide Web. Many of the claims made about common mycorrhizal networks, including that they are ubiquitous in forests, that resources are transferred between plants through them, and that they are used to transfer warnings between trees, have been criticised as being not strongly supported by evidence.
Types[edit]
There are two main types of mycorrhizal networks: arbuscular mycorrhizal networks and ectomycorrhizal networks.
Arbuscular mycorrhizal networks are formed between plants that associate with glomeromycetes. Arbuscular mycorrhizal associations (also called endomycorrhizas) predominate among land plants, and are formed with 150–200 known fungal species, although true fungal diversity may be much higher.
Ectomycorrhizal networks are formed between plants that associate with ectomycorrhizal fungi and proliferate by way of ectomycorrhizal extramatrical mycelium. In contrast to glomeromycetes, ectomycorrhizal fungal are a highly diverse and polyphyletic group consisting of 10,000 fungal species. These associations tend to be more specific, and predominate in temperate and boreal forests.
Communication[edit]
Reports discuss the ongoing debate within the scientific community regarding what constitutes communication, but the extent of communication influences how a biologist perceives behaviors. Communication is commonly defined as imparting or exchanging information. Biological communication, however, is often defined by how fitness in an organism is affected by the transfer of information in both the sender and the receiver. Signals are the result of evolved behavior in the sender and effect a change in the receiver by imparting information about the sender's environment. Cues are similar in origin but only effect the fitness of the receiver. Both signals and cues are important elements of communication, but workers maintain caution as to when it can be determined that transfer of information benefits both senders and receivers. Thus, the extent of biological communication can be in question without rigorous experimentation. It has, therefore, been suggested that the term infochemical be used for chemical substances which can travel from one organism to another and elicit changes. This is important to understanding biological communication where it is not clearly delineated that communication involves a signal that can be adaptive to both sender and receiver.
Behavior and information transfer[edit]
A morphological or physiological change in a plant due to a signal or cue from its environment constitutes behavior in plants, and plants connected by a mycorrhizal network have the ability to alter their behavior based on the signals or cues they receive from other plants. These signals or cues can be biochemical, electrical, or can involve nutrient transfer. Plants release chemicals both above and below the ground to communicate with their neighbors to reduce damage from their environment. Changes in plant behavior invoked by the transfer of infochemicals vary depending on environmental factors, the types of plants involved and the type of mycorrhizal network. In a study of trifoliate orange seedlings, mycorrhizal networks acted to transfer infochemicals, and the presence of a mycorrhizal network affected the growth of plants and enhanced production of signaling molecules. One argument in support of the claim mycorrhizal can transfer various infochemicals is that they have been shown to transfer molecules such as lipids, carbohydrates and amino acids. Thus, transfer of infochemicals via mycorrhizal networks can act to influence plant behavior.
There are three main types of infochemicals shown to act as response inducing signals or cues by plants in mycorrhizal networks, as evidenced by increased effects on plant behavior: allelochemicals, defensive chemicals and nutrients.
Allelopathic communication[edit]
Allelopathy is the process by which plants produce secondary metabolites known as allelochemicals, which can interfere with the development of other plants or organisms. Allelochemicals can affect nutrient uptake, photosynthesis and growth; furthermore, they can down regulate defense genes, affect mitochondrial function, and disrupt membrane permeability leading to issues with respiration.
Plants produce many types of allelochemicals, such as thiophenes and juglone, which can be volatilized or exuded by the roots into the rhizosphere. Plants release allelochemicals due to biotic and abiotic stresses in their environment and often release them in conjunction with defensive compounds. In order for allelochemicals to have a detrimental effect on a target plant, they must exist in high enough concentrations to be toxic, but, much like animal pheromones, allelochemicals are released in very small amounts and rely on the reaction of the target plant to amplify their effects. Due to their lower concentrations and the ease in which they are degraded in the environment, the toxicity of allelochemicals is limited by soil moisture, soil structure, and organic matter types and microbes present in soils. The effectiveness of allelopathic interactions has been called into question in native habitats due to the effects of them passing through soils, but studies have shown that mycorrhizal networks make their transfer more efficient. These infochemicals are hypothesized to be able to travel faster via mycorrhizal networks, because the networks protect them from some hazards of being transmitted through the soil, such as leaching and degradation. This increased transfer speed is hypothesized to occur if the allelochemicals move via water on hyphal surfaces or by cytoplasmic streaming. Studies have reported concentrations of allelochemicals two to four times higher in plants connected by mycorrhizal networks. Thus, mycorrhizal networks can facilitate the transfer of these infochemicals.
Studies have demonstrated correlations between increased levels of allelochemicals in target plants and the presence of mycorrhizal networks. These studies strongly suggest that mycorrhizal networks increase the transfer of allelopathic chemicals and expand the range, called the bioactive zone, in which they can disperse and maintain their function. Furthermore, studies indicate increased bioactive zones aid in the effectiveness of the allelochemicals because these infochemicals cannot travel very far without a mycorrhizal network. There was greater accumulation of allelochemicals, such as thiopenes and the herbicide imazamox, in target plants connected to a supplier plant via a mycorrhizal network than without that connection, supporting the conclusion that the mycorrhizal network increased the bioactive zone of the allelochemical. Allelopathic chemicals have also been demonstrated to inhibit target plant growth when target and supplier are connected via AM networks. The black walnut is one of the earliest studied examples of allelopathy and produces juglone, which inhibits growth and water uptake in neighboring plants. In studies of juglone in black walnuts and their target species, the presence of mycorrhizal networks caused target plants to exhibit reduced growth by increasing the transfer of the infochemical. Spotted knapweed, an allelopathic invasive species, provides further evidence of the ability of mycorrhizal networks to contribute to the transfer of allelochemicals. Spotted knapweed can alter which plant species a certain AM fungus prefers to connect to, changing the structure of the network so that the invasive plant shares a network with its target. These and other studies provide evidence that mycorrhizal networks can facilitate the effects on plant behavior caused by allelochemicals.
Defensive communication[edit]
Mycorrhizal networks can connect many different plants and provide shared pathways by which plants can transfer infochemicals related to attacks by pathogens or herbivores, allowing receiving plants to react in the same way as the infected or infested plants. A variety of plant derived substances act as these infochemicals.
When plants are attacked they can manifest physical changes, such as strengthening their cell walls, depositing callose, or forming cork. They can also manifest biochemical changes, including the production of volatile organic compounds (VOCs) or the upregulation of genes producing other defensive enzymes, many of which are toxic to pathogens or herbivores. Salicylic acid (SA) and its derivatives, like methyl salicylate, are VOCs which help plants to recognize infection or attack and to organize other plant defenses, and exposure to them in animals can cause pathological processes. Terpenoids are produced constituently in many plants or are produced as a response to stress and act much like methyl salicylate. Jasmonates are a class of VOCs produced by the jasmonic acid (JA) pathway. Jasmonates are used in plant defense against insects and pathogens and can cause the expression of proteases, which defend against insect attack. Plants have many ways to react to attack, including the production of VOCs, which studies report can coordinate defenses among plants connected by mycorrhizal networks.
Many studies report that mycorrhizal networks facilitate the coordination of defenses between connected plants using volatile organic compounds and other plant defensive enzymes acting as infochemicals.
Priming occurs when a plant's defenses are activated before an attack. Studies have shown that priming of plant defenses among plants in mycorrhizal networks may be activated by the networks, as they make it easier for these infochemicals to propagate among the connected plants. The defenses of uninfected plants are primed by their response via the network to the terpenoids produced by the infected plants. AM networks can prime plant defensive reactions by causing them to increase the production of terpenoids.
In a study of tomato plants connected via an AM mycorrhizal network, a plant not infected by a fungal pathogen showed evidence of defensive priming when another plant in the network was infected, causing the uninfected plant to upregulate genes for the SA and JA pathways. Similarly, aphid-free plants were shown to only be able to express the SA pathways when a mycorrhizal network connected them to infested plants. Furthermore, only then did they display resistance to the herbivore, showing that the plants were able to transfer defensive infochemicals via the mycorrhizal network.
Many insect herbivores are drawn to their food by VOCs. When the plant is consumed, however, the composition of the VOCs change, which can then cause them to repel the herbivores and attract insect predators, such as parasitoid wasps. Methyl salicylate was shown to be the primary VOC produced by beans in a study which demonstrated this effect. It was found to be in high concentrations in infested and uninfested plants, which were only connected via a mycorrhizal network. A plant sharing a mycorrhizal network with another that is attacked will display similar defensive strategies, and its defenses will be primed to increase the production of toxins or chemicals which repel attackers or attract defensive species.
In another study, introduction of budworm to Douglas fir trees led to increased production of defensive enzymes in uninfested ponderosa pines connected to the damaged tree by an ECM network. This effect demonstrates that defensive infochemicals transferred through such a network can cause rapid increases in resistance and defense in uninfested plants of a different species.
The results of these studies support the conclusion that both ECM and AM networks provide pathways for defensive infochemicals from infected or infested hosts to induce defensive changes in uninfected or uninfested conspecific and heterospecific plants, and that some recipient species generally receive less damage from infestation or infection.
Nutrient transfer[edit]
Numerous studies have reported that carbon, nitrogen and phosphorus are transferred between conspecific and heterospecific plants via AM and ECM networks. Other nutrients may also be transferred, as strontium and rubidium, which are calcium and potassium analogs respectively, have also been reported to move via an AM network between conspecific plants. Scientists believe that transfer of nutrients by way of mycorrhizal networks could act to alter the behavior of receiving plants by inducing physiological or biochemical changes, and there is evidence that these changes have improved nutrition, growth and survival of receiving plants.
Mechanisms[edit]
Several mechanisms have been observed and proposed by which nutrients can move between plants connected by a mycorrhizal network, including source-sink relationships, preferential transfer and kin related mechanisms.
Transfer of nutrients can follow a source–sink relationship where nutrients move from areas of higher concentration to areas of lower concentration. An experiment with grasses and forbs from a California oak woodland showed that nutrients were transferred between plant species via an AM mycorrhizal network, with different species acting as sources and sinks for different elements. Nitrogen has also been shown to flow from nitrogen-fixing plants to non-nitrogen fixing plants through a mycorrhizal network following a source-sink relationship.
It has been demonstrated that mechanisms exist by which mycorrhizal fungi can preferentially allocate nutrients to certain plants without a source–sink relationship. Studies have also detailed bidirectional transfer of nutrients between plants connected by a network, and evidence indicates that carbon can be shared between plants unequally, sometimes to the benefit of one species over another.
Kinship can act as another transfer mechanism. More carbon has been found to be exchanged between the roots of more closely related Douglas firs sharing a network than more distantly related roots. Evidence is also mounting that micronutrients transferred via mycorrhizal networks can communicate relatedness between plants. Carbon transfer between Douglas fir seedlings led workers to hypothesize that micronutrient transfer via the network may have increased carbon transfer between related plants.
These transfer mechanisms can facilitate movement of nutrients via mycorrhizal networks and result in behavioral modifications in connected plants, as indicated by morphological or physiological changes, due to the infochemicals being transmitted. One study reported a threefold increase in photosynthesis in a paper birch transferring carbon to a Douglas fir, indicating a physiological change in the tree which produced the signal. Photosynthesis was also shown to be increased in Douglas fir seedlings by the transport of carbon, nitrogen and water from an older tree connected by a mycorrhizal network. Furthermore, nutrient transfer from older to younger trees on a network can dramatically increase growth rates of the younger receivers. Physiological changes due to environmental stress have also initiated nutrient transfer by causing the movement of carbon from the roots of the stressed plant to the roots of a conspecific plant over a mycorrhizal network. Thus, nutrients transferred through mychorrhizal networks act as signals and cues to change the behavior of the connected plants.
Evolutionary and adaptational perspectives[edit]
It is hypothesized that fitness is improved by the transfer of infochemicals through common mycorrhizal networks, as these signals and cues can induce responses which can help the receiver survive in its environment. Plants and fungus have evolved heritable genetic traits which influence their interactions with each other, and experiments, such as one which revealed the heritability of mycorrhizal colonization in cowpeas, provide evidence. Furthermore, changes in behavior of one partner in a mycorrhizal network can affect others in the network; thus, the mycorrhizal network can provide selective pressure to increase the fitness of its members.
Adaptive mechanisms[edit]
Although they remain to be vigorously demonstrated, researchers have suggested mechanisms which might explain how transfer of infochemicals via mycorrhizal networks may influence the fitness of the connected plants and fungi.
A fungus may preferentially allocate carbon and defensive infochemicals to plants that supply it more carbon, as this would help to maximize its carbon uptake. This may happen in ecosystems where environmental stresses, such as climate change, cause fluctuations in the types of plants in the mycorrhizal network. A fungus might also benefit its own survival by taking carbon from one host with a surplus and giving it to another in need, thus it would ensure the survival of more potential hosts and leave itself with more carbon sources should a particular host species suffer. Thus, preferential transfer could improve fungal fitness.
Plant fitness may also be increased in several ways. Relatedness may be a factor, as plants in a network are more likely to be related; therefore, kin selection might improve inclusive fitness and explain why a plant might support a fungus that helps other plants to acquire nutrients. Receipt of defensive signals or cues from an infested plant would be adaptive, as the receiving plant would be able to prime its own defenses in advance of an attack by herbivores. Allelopathic chemicals transferred via CMNs could also affect which plants are selected for survival by limiting the growth of competitors through a reduction of their access to nutrients and light. Therefore, transfer of the different classes of infochemicals might prove adaptive for plants.
Seedling establishment[edit]
Mature Douglas fir
Seedling establishment research often is focused on forest level communities with similar fungal species. However mycorrhizal networks may shift intraspecific and interspecific interactions that may alter preestablished plants' physiology. Shifting competition can alter the evenness and dominance of the plant community. Discovery of seedling establishment showed seedling preference is near existing plants of conspecific or heterospecific species and seedling amount is abundant. Many believe the process of new seedlings becoming infected with existing mycorrhizae expedite their establishment within the community. The seedling inherit tremendous benefits from their new formed symbiotic relation with the fungi. The new influx of nutrients and water availability, help the seedling with growth but more importantly help ensure survival when in a stressed state. Mycorrhizal networks aid in regeneration of seedlings when secondary succession occurs, seen in temperate and boreal forests. Seedling benefits from infecting mycorrhizae include increased infectivity range of diverse mycorrhizal fungi, increased carbon inputs from mycorrhizal networks with other plants, increased area meaning greater access to nutrients and water, and increased exchange rates of nutrients and water from other plants.
Several studies have focused on relationships between mycorrhizal networks and plants, specifically their performance and establishment rate. Douglas fir seedlings' growth expanded when planted with hardwood trees compared to unamended soils in the mountains of Oregon. Douglas firs had higher rates of ectomycorrhizal fungal diversity, richness, and photosynthetic rates when planted alongside root systems of mature Douglas firs and Betula papyrifera than compared to those seedlings who exhibited no or little growth when isolated from mature trees. The Douglas fir was the focus of another study to understand its preference for establishing in an ecosystem. Two shrub species, Arctostaphylos and Adenostoma both had the opportunity to colonize the seedlings with their ectomycorrhizae fungi. Arctostaphylos shrubs colonized Douglas fir seedlings who also had higher survival rates. The mycorrhizae joining the pair had greater net carbon transfer toward the seedling. The researchers were able to minimize environmental factors they encountered in order to avoid swaying readers in opposite directions.
In burned and salvaged forest, Quercus rubrum establishment was facilitated when acorns were planted near Q. montana but did not grow when near arbuscular mycorrhizae Acer rubrum Seedlings deposited near Q. montana had a greater diversity of ectomycorrhizal fungi, and a more significant net transfer of nitrogen and phosphorus content, demonstrating that ectomycorrhizal fungi formation with the seedling helped with their establishment. Results demonstrated with increasing density; mycorrhizal benefits decrease due to an abundance of resources that overwhelmed their system resulting in little growth as seen in Q. rubrum.
Mycorrhizal networks decline with increasing distance from parents, but the rate of survival was unaffected. This indicated that seedling survival has a positive relation with decreasing competition as networks move out farther.
One study displayed the effects of ectomycorrhizal networks in plants which face primary succession. In an experiment, Nara (2006) transplanted Salix reinii seedlings inoculated with different ectomycorrhizal species. It was found that mycorrhizal networks are the connection of ectomycorrhizal fungi colonization and plant establishment. Results showed increased biomass and survival of germinates near the inoculated seedlings compared to inoculated seedlings.
Studies have found that association with mature plants correlates with higher survival of the plant and greater diversity and species richness of the mycorrhizal fungi.
Carbon transfer[edit]
Mycorrhizal networks can transfer carbon between plants in the network through the fungi linking them. Carbon transfer has been demonstrated by experiments using carbon-14 (C) isotopic labeling and following the pathway from ectomycorrhizal conifer seedlings to another using mycorrhizal networks. The experiment showed a bidirectional movement of the C within ectomycorrhizal species. Further investigation of bidirectional movement and the net transfer was analyzed using pulse labeling technique with C and C in ectomycorrhizal Douglas fir and Betula payrifera seedlings. Results displayed an overall net balance of carbon transfer between the two, until the second year where the Douglas fir received carbon from B. payrifera. Detection of the isotopes was found in receiver plant shoots, expressing carbon transfer from fungus to plant tissues.
The direction carbon resources flow through the mycorrhizal network has been observed to shift seasonally, with carbon flowing toward the parts of the network that need it the most. For example, in a network that includes Acer saccharinum (sugar maple) and Erythronium americanum (trout lily), carbon moves to young sugar maple saplings in spring when leaves are unfurling, and shifts to move to the trout lilies in fall when the lilies are developing their roots. A further study with paper birch and Douglas fir demonstrated that the flow of carbon shifts direction more than once per season: in spring, newly budding birch receives carbon from green Douglas fir, in summer, stressed Douglas fir in the forest understory receives carbon from birch in full leaf, and in fall, birch again receives carbon from Douglas fir as birch trees shed their leaves and evergreen Douglas firs continue photosynthesizing.
When the ectomycorrhizal fungus-receiving end of the plant has limited sunlight availability, there was an increase in carbon transfer, indicating a source–sink gradient of carbon among plants and shade surface area regulates carbon transfer.
Plants sense carbon through a receptor in their guard cells that measure carbon dioxide concentrations in the leaf and environment. Carbon information is integrated using proteins known as carbonic anhydrases, in which the plant then responds by utilizing or disregarding the carbon resources from the mycorrhizal networks. One case study follows a CMN shared by a paper birch and Douglas fir tree. By using radioactively-labeled carbon-13 and carbon-14, researchers found that both tree species were trading carbon–that is to say, carbon was moving from tree to tree in both directions. The rate of carbon transfer varied based on the physiological factors such as total biomass, age, nutrient status, and photosynthetic rate. At the end of the experiment, the Douglas fir was found to have a 2% to 3% net gain in carbon. This gain may seem small, but in the past a carbon gain of less than 1% has been shown to coincide with a four-fold increase in the establishment of new seedlings. Both plants showed a threefold increase in carbon received from the CMN when compared to the soil pathway. Bearing in mind that the paper birch and the Douglas fir also receive carbon from soil pathways, one can imagine a substantial disadvantage to plant competitors not in the CMN.
Importance[edit]
Mycorrhizal associations have profoundly impacted the evolution of plant life on Earth ever since the initial adaptation of plant life to land. In evolutionary biology, mycorrhizal symbiosis has prompted inquiries into the possibility that symbiosis, not competition, is the main driver of evolution.
Several positive effects of mycorrhizal networks on plants have been reported. These include increased establishment success, higher growth rate and survivorship of seedlings; improved inoculum availability for mycorrhizal infection; transfer of water, carbon, nitrogen and other limiting resources increasing the probability for colonization in less favorable conditions. These benefits have also been identified as the primary drivers of positive interactions and feedbacks between plants and mycorrhizal fungi that influence plant species abundance.
See also[edit]
Entangled Life (book)
Forest ecology
Symbiosis
Mutualism (biology)
Plant communication | biology | 867088 | https://da.wikipedia.org/wiki/Plantemorfologi | Plantemorfologi | Plantemorfologi eller fytomorfologi er studiet af planternes fysiske form og ydre opbygning. Dette ses oftest som adskilt fra planteanatomi, der er studiet af planternes indre opbygning, i særdeleshed på det mikroskopiske niveau. Planternes morfologi er især nyttig ved planters artsbestemmelse på baggrund af udseendet.
Arbejdsområder
[[Fil:Strom roka borovica velke borove 03.jpg|thumb|Et blik op i Skov-Fyrs (Pinus sylvestris) grenstruktur.]]
Plantemorfologi "repræsenterer et studie i udvikling, form og opbygning hos planterne og – som en logisk følge – et forsøg på at fortolke disse på baggrund af ligheder i i grundplan og oprindelse." Plantemorfologien har fire hovedområder, som hver især overlapper et andet felt inden for de biologiske videnskaber.
Udvikling og tilpasning
For det første er morfologi komparativ, dvs. at morfologen undersøger strukturer hos mange forskellige planter af den samme art eller blandt forskellige arter, for så at foretage sammenligninger og formulere tanker om lighederne. Når strukturer hos forskellige arter anses for at eksistere og udvikles som resultater af nogle fælles, arvemæssige mønstre, kaldes disse strukturer homologe. Denne side af plantemorfologien overlapper med studiet af planteevolution og palæobotanik.
Planternes strukturer
For det andet ser plantemorfologi både på de vegetative (somatiske) og de reproduktive strukturer hos planter. Karplanternes vegetative strukturer omfatter studiet af såvel skudsystemet (sammensat af af stængler og blade) som rodsystemet. De reproduktive strukturer er mere forskelligartede, og de er ofte særligt indrettede for hver enkelt plantegruppe, som f.eks. blomster og frø hos nåletræer og én- og tokimbladede planter, sori hos bregnerne og kapsler hos mosserne. Det indgående studium af planternes reproduktive strukturer førte til opdagelsen af generationsskiftet, som findes hos alle planter og de fleste alger. Dette område af plantemorfologien overlapper studiet af biodiversitet og plantesystematik.
Anatomi og vækstform
For det tredje undersøger plantemorfologien plantestruktur på en række forskellige niveauer. På det første niveau ser man på ultrastrukturen, cellernes generelle struktur, som kun er synlig ved hjælp af et elektronmikroskop, og på næste niveau drejer det sig om cytologi, undersøgelsen af celler ved hjælp af et optisk mikroskop. Derved overlapper plantemorfologien med planteanatomi. På det højeste niveau undersøger man plantens vækstform, dens overordnede arkitektur. Mønstret bag grenenes fordeling hos et træ vil være forskelligt fra art til art ganske som udseendet vil være det hos forskellige urter eller græsser.
Vækst og økologi
For det fjerde undersøger plantemorfologi mønstre i vækst, dvs. den proces, hvor strukturer opstår og modnes, mens planten vokser. Modsat dyrene, som tidligt i deres liv skaber alle de legemsdele, de nogensinde vil få, så producerer planterne konstant nyt væv og strukturer i løbet af deres liv. En levende plante har altid kimvæv til rådighed. Nye strukturer modnes i takt med, at de bliver dannet, men modningen kan både påvirkes af det tidspunkt i plantens liv, hvor strukturernes udvikling indledes, og af det miljø, som de bliver udsat for. En morfolog studerer denne proces, dens årsager og dens resultat, og derved overlapper dette område af plantemorfologien med plantefysiologi og økologi.
Komparativ videnskab
En plantemorfolog foretager sammenligninger mellem strukturer hos mange forskellige planter af samme eller forskellige arter. Når man sammenligner ensartede strukturer hos forskellige planter, forsøger man at besvare spørgsmålet om, hvorfor strukturerne ligner hinanden. Det er højst sandsynligt, at det er underliggende årsager af genetisk eller fysiologisk art eller måske i form af planternes svar på miljøbetingelserne, som har ført til denne lighed i udseende. Resultatet af en videnskabelig undersøgelse af disse årsager kan føre til én af to indsigter i den tilgrundliggende biologi:
Homologi – de to arters struktur ligner hinanden på grund af fælles ophav og ensartede arveanlæg.
Konvergens - de to arters struktur ligner hinanden på grund af uafhængige tilpasninger til det samme miljømæssige pres.
Det er vigtigt for at begribe planternes evolution, at man forstår hvilke kendetegn og strukturer, der skyldes hver af årsagerne. Evolutionsbiologen stoler på, at plantemorfologen kan fortolke strukturerne og skaffer på sin side den fylogenetiske forståelse af planternes slægtskabsforhold, som kan føre til ny, morfologisk indsigt.
Homologi
Når strukturer hos forskellige arter anses for at eksistere og udvikles som resultat af fælles nedarvede, genetiske spor, kalder man disse strukturer for homologe. Blade fra Fyr, Eg og Kål ser f.eks. meget forskellige ud, men de er fælles om visse basale strukturer og anbringelse af delene. Det er let at konkludere, at bladene er homologe. Plantemorfologen får videre og opdager, at kakturtornene også deler den samme basale struktur og udvikling som blade hos andre planter, og derfor er kaktustorne også homologe i forhold til blade.
Konvergens
Når strukturer hos forskellige arter anses for at eksistere og udvikles som resultater af ensartede, tilpasningssvar over for miljøpres, kaldes disse strukturer for [[Konvergens|konvergente]]. F.eks. har bladene hos Bryopsis plumosa og stænglerne hos Slør-Asparges (Asparagus setaceus den samme fjeragtige fordeling af forgreningerne, selv om den første er en alge, mens den anden er en frøplante. Lighederne i den overordnede struktur opstår uafhængigt af hinanden som et resultat af konvergens. Vækstformen hos mange Kaktus-arter og nogle arter i Vortemælk-slægten er meget lig hinanden, selv om de tilhører vidt adskilte familier. Lighederne skyldes fælles løsninger på problemet med at overleve i et varm og tørt miljø.
Vegetative og reproduktive karaktertræk
Plantemorfologien behandler både de vegetative og de reproduktive strukturer hos planterne.
De vegetative (somatiske) strukturer hos karplanterne omfatter to større organsystemer: 1) et skudsystem, der består af stængler og blade, og ) et rodsystem, der består af rødder og ofte også af jordstængler, løg eller knolde. Disse to systemer er fælles for næsten alle karplanter, og de er et samlende tema for studiet af plantemorfologi.
I modsætning hertil er de reproduktive strukturer varierede og sædvanligvis specielt byggede for hver enkelt, større gruppe af planter. Strukturer som blomster og frugter findes udelukkende hos de tokimbladede planter; sori kun hos bregnerne; og kogler kun hos nåletræer og andre nøgenfrøede. De reproduktive karaktertræk bliver derfor betragtet som mere nyttige end de vegetative træk, når det drejer sig om klassificering af planter.
Plantemorfologi og identificering
Planteforskere bruger planternes morfologiske træk, som kan sammenlignes, måles, tælles og beskrives, for at nå frem til forskelle og ligheder mellem plantegrupper, så disse træk kan bruges i identificering, klassificering og beskrivelse af planterne.
Når man bruger disse træk i beskrivelser eller ved identificering, bruger man dem som nøgle- eller diagnostiske træk, og de kan være enten kvalitetsmæssige eller mængdemæssige.
Mængdemæssige træk er de morfologiske særpræg, som kan tælles eller måles. F.eks. kan en planteart have kronblade, der er 10-12 mm brede.
Kvalitetsmæssige træk er morfologiske særpræg så som bladform, blomsterfarve eller behåring.
Begge typer træk kan være meget nyttige ved identificering af planter.
Generationsskifte
De detaljerede undersøgelser af de reproduktive strukturer hos planter førte frem til den tyske botaniker, Wilhelm Hofmeisters, opdagelsen af det generationsskifte, som findes hos alle planter og de fleste alger. Den opdagelse er én af de vigtigste, man har gjort inden for hele plantemorfologien, da den skaber en fælles ramme for forståelsen af alle planters livscyklus.
Farvethed hos planter
Den vigtigste funktion, som farve har for planterne, er knyttet til fotosyntesen, hvor det grønne farvestof, klorofyl bliver anvendt sammen med flere røde og gule farvestoffer til at opfange så meget lys som muligt. Farvestoffer har også et vigtigt element i det at tiltrække insekter og fugle for at opmuntre dem til at bestøve blomsten.
Plantefarver omfatter en mængde af forskellige slags molekyler som f.eks. porfyriner, karotenoider, antocyaniner og betalainer. Alle biologiske farvestoffer opsuger ganske bestemte bølgelængder af lys, mens de tilbagekaster andre. Lyset, som bliver opsuget, kan bruges af planten som drivkraft i kemiske reaktioner, mens de tilbagekastede bølgelængder af lys bestemmer den farve, som øjet vil opleve, at farvestoffet har.
Udvikling
Planternes udvikling er den proces, hvor strukturer opstår og modnes, mens planten vokser. Den er et emne for undersøgelser i planteanatomi og plantefysiologi og også i plantemorfologi.
Planternes udviklingsproces er grundlæggende forskellig fra den, man ser hos hvirveldyrene. Når et dyrefoster indleder sin udvikling, skaber det meget tidligt alle de kropsdele, som det nogensinde vil få senere i livet. Når et dyr fødes (eller udklækkes fra ægget), har det alle sine legemsdele, og fra det tidspunkt vil det kun vokse sig større og mere modent. Omvendt skaber planterne gennem hele deres liv uafbrudt nye væv og strukturer på grundlag af meristemer, der findes på spidserne af organerne eller inde mellem vævene. En levende plante har derfor altid nyt væv klar i kimstadiet.
De egenskaber, man ser hos en plante er opstående, dvs. mere end summen af enkeltdelene. "Sammenføjningen af disse væv og funktioner til en integreret, mangecellet organisme skaber ikke blot kendetegnene hos de enkelte dele og processer, men også et helt nyt sæt af kendetegn, som man ikke kunne have forudsagt ved at undersøge de enkelte dele." Med andre ord: det er ikke tilstrækkeligt at kende til molekylerne i en plante, når man skal forudsige, hvad der er karakteristisk for cellerne; og viden om cellernes egenskaber kan ikke forudsige alle egenskaber i plantens opbygning.
Vækst
En karplante vokser frem fra en enkelt celle, en zygote, der er opstået ved befrugtning af en ægcelle med en sædcelle. Fra det udgangspunkt begynder den at dele sig, sådan at der dannes et plantekim ved en proces, som kaldes embryogenese. Undervejs vil de dannede celler ordne sig sådan, at den ene ende bliver til den første rod, mens den anden ende udvikles til skudspidsen. Hos frøplanterne danner kimen et eller flere kimblade (også kaldet ’’kotyledoner’’). Ved afslutningen af kimdannelsen har den unge plante alle de dele, der er nødvendige for, at den kan begynde sit selvstændige liv.
Når kimen er spiret frem fra sit frø eller sin moderplante, begynder den at danne ekstra organer (blade, stængler og rødder) i den proces, som kaldes organogenese. Nye rødder vokser frem fra rodens meristemer, der findes ved rodspidsen, og stængler og blade vokser ud fra skudmeristemerne, der findes i skudspidsen. Forgreninger opstår, når små klumper af delingsdygtige celler, som er blevet efterladt af meristemet, endnu ikke har gennemgået celledifferentiering til specialiserede væv og begynder at vokse som en ny skudspids eller rodspids. Vækst fra ethvert af disse meristemer ved skud- eller rodspidserne kaldes primær vækst og fører til en forlængelse af samme skud eller rod. Sekundær vækst opstår ved fortykkelse af skud eller rod, opstået ved deling af celler i deres kambium.
Ud over den vækst, som skyldes celledeling, kan en plante vokse ved cellestrækning. Det sidste sker, når enkelte celler eller grupper af celler øger deres længde. Det er ikke alle planteceller, der vokser ud til samme. Når cellerne på den ene side af en stængel vokser hurtigere og mere end cellerne på den modsatte side, vil stænglen som en konsekvens deraf bøje sig over mod den side, hvor cellerne vokser mindst. Denne retningsbestemte vækst kan forekomme som et resultat af plantens reaktion på en bestemt påvirkning som f.eks. lys (fototropisme), tyngde (gravitropisme), vand (hydrotropism) og fysisk kontakt (tigmotropisme).
Planters vækst og udvikling reguleres af bestemte hormoner og vækstregulatorer (PGR’er) (Ross et al. 1983). De indre hormonniveauer er påvirkede af plantens alder, kuldetolerance, dvaleperiode og andre stofskiftevilkår: daglængde, tørke, temperatur og endnu flere udvendige miljøforhold så som ydre kilder til PGR, enten kunstigt tilførte eller optaget via rødderne.
Morfologisk variation
Planter har en naturlig variation i deres form og opbygning. Mens alle organismer varierer fra individ til individ, har planterne en ekstra variationsform. På det samme individ gentages dele, som kan være forskellige i form og struktur fra andre, tilsvarende dele. Denne variationsform ses lettest på plantens blade, selv om også andre organer som stængler og blomster kan vise lignende variation. Der er tre hovedårsager til denne variation: placeringens betydning, miljøpåvirkninger og ungdomsform (juvenilitet).
Placeringens betydning
Selv om en plante laver talløse kopier af det same organ i sin levetid, er det ikke alle kopierne af et givet organ, der bliver identiske. Der er en variation mellem en udvokset plantes enkelte dele, som skyldes stedet på planten, hvor organet blev skabt. For eksempel kan bladene variere på en ny gren i et fastholdt mønster ud langs grenen. Formen på de blade, der blev dannet nær grenens basis, er forskellig fra den, som ses på blade fra spidsen af plantens skud, og samme forskel går igen fra gren til gren på en given plante og en given art. Forskellen består, selv efter at bladene på begge ender af grenen er udvoksede, og den skyldes ikke, at nogle blade er yngre end andre.
Nye strukturer modnes på en bestemt måde, og den bliver ofte styret af det tidspunkt i plantens liv, hvor de begynder at udvikles og også af det miljø, som strukturerne bliver udsat for. Dette kan ses hos vandplanter og sumpplanter.
Temperatur
Temperaturen har et stort antal virkninger på planter, afhængigt af en mangfoldighed af faktorer, derunder plantens størrelse og tilstand samt temperaturens niveau og varigheden af påvirkningen. Jo mindre og jo mere sukkulent planten er, jo større er følsomheden overfor beskadigelse eller død på grund af temperaturer, der er for høje eller for lave. Temperaturen påvirker hastigheden i de biokemiske og fysiologiske processer, sådan at hastigheden generelt øges med stigende temperatur. Men van ’t Hoffs påstand angående monomolekylære reaktioner (som siger at reaktionernes hastighed fordobles eller tredobles med en forøgelse af temperature på 10 °C) holder ikke helt præcist for biologiske processer, i særdeleshed ved lave og høje temperaturer.
Når vand fryser i planter afhænger konsekvensen for planterne rigtigt meget af, om nedfrysningen sker intracellulært (inde i cellerne) eller extracellulært (i mellemrummene mellem dem). Intracellulær nedfrysning slår som regel cellen ihjel, uanset hårdførheden hos planten og dens væv. Intracellulær nedfrysning ses sjældent i naturen, men beskedne fald i temperaturen på f.eks. 1° C til 6° C pr. time fremmer dannelse af intracellulær is, og denne "is udenfor organerne" kan i visse tilfælde være dræbende, afhængigt af vævets hårdførhed.
Ved frostgrader er det vandet i plantevævenes intercellulære mellemrum, der fryser først, selv om vandet kan forblive i væsketilstand ned til en temperatur under ÷ 7° C. Efter den indledende dannelse af is mellem cellerne skrumper de, efterhånden som der tabes vand til den udskilte is. Cellerne underkastes frysetørring, og dehydreringen er den grundlæggende årsag til frostskaderne.
Man har bevist, at tempoet i nedkølingen påvirker vævenes hårdførhed overfor frost, men den faktiske nedfrysningsgrad afhænger ikke bare af afkølingstempoet, men også af en forudgående underafkøling og vævenes egenskaber. Sakai (1979a) påviste udskillelse af is i skuddenes vækstpunkter hos Hvid-Gran og Sort-Gran i Alaska, når de blev afkølet langsomt fra 30 °C til ÷ 40 °C. Disse frysetørrede knopper overlevede at blive nedsænket i flydende kvælstof, hvis de blev genopvarmet langsomt. Blomsteranlæg klarede sig på samme måde. Nedfrysning uden for vækstpunkternes organer forklarer den evne, de mest hårdføre nordlige arter har til at overleve vintre i egne, hvor lufttemperaturerne falder til ÷ 50° C eller lavere. Vinterknoppers hårdførhed hos disse nåletræer forøges af knoppernes ringe størrelse, udviklingen af en hurtigere vandtransport og en evne til at tåle intensiv frysetørring. Hos nordlige arter af Gran (Picea) og Fyr (Pinus) svarer frosthårdførheden hos ét år gamle frøplanter til den hos de voksne planter, når de er i den samme dvaletilstand.
Ungdomsformer
Organer og væv, som dannes af en unge plante, f.eks. En kimplante, afviger ofte fra dem, der bliver skabt af den samme plante, når den er ældre. Dette fænomen kaldes juvenilitet. Unge træer vil f.eks. danne længere og tyndere grene, som bøjer opad, til forskel fra de grene, de vil sætte som et fuldvoksent træ. Dertil kommer, at bladene i den tidlige vækstfase har tilbøjelighed til at være større, tyndere og mere uregelmæssige end bladene på den voksne plante. Eksemplarer af planter i ungdomsfasen kan se så komplet anderledes ud end de voksne planter, at æglæggende insekter ikke kan genkende planten som føde for sit afkom.
Man kan finde forskelle i evnen til at danne rødder og blomster på ét og samme træ. Stiklinger, der er skåret ved træets rodhals, vil lettere danne rødder end stiklinger, taget fra den midterste eller øverste del af kronen. Blomstring fra rodhalsen mangler helt eller er mindre rig end blomstring på højere grene, særligt når et ungt træ træder ind i blomstringsfasen for første gang.
Nyere opdagelser
Rolf Sattler har revideret grundlæggende opfattelser inden for sammenlignende homologi. Han understregede, at homologi også bør omfatte delvis homologi og kvantitativ homologi.R. Sattler: Homology, homeosis, and process morphology in plants i B.K. Hall (udg.) Homology: The hierarchical basis of comparative morphology, 1994, ISBN side 423-475. Det fører frem til en sammenhængende morfologi, som viser kontinuitet mellem de morfologiske kategorier rod, skud, stængel, blad og plantehår. Hvordan man bedst beskriver mellemformerne blev diskuteret hos Bruce K. Kirchoff m.fl.
Til ære for Agnes Arber, ophavskvinde til ”partial-shoot theory of the leaf”, kaldte Rutishauser og Isler kontinuumopfattelsen for ”Fuzzy Arberian Morphology” (FAM). “Fuzzy” henviser til den såkaldte fuzzy logic, mens “Arberian” sammenkæder udtrykket med Agnes Arber. Rutishauser og Isler understregede, at denne teori er underbygget ikke blot af mange morfologiske data, men også af molekylær genetik (dvs. DNA-undersøgelser). Nyere beviser fra molekylær genetik giver yderligere støtte til kontinuummorfologien. P.J. James konkluderede, at "det er nu bredt accepteret, at... mangesidethed [karakteristisk for de fleste skud] og tosidethed [karakteristisk for blade] kun er yderpunkter i et sammenhængende spektrum. I realiteten er det blot et spørgsmål om timing for aktivering af KNOX-proteinet!" Eckardt og Baum konkluderede, at "det er nu almindeligt accepteret, at sammensatte blade udtrykker både blad- og skudegenskaber”.
Procesorienteret morfologi (dynamisk morfologi) beskriver og analyserer det dynamiske kontinuum i planternes former. Ifølge denne tilgang opstår strukturer ikke af processer, for de er'' processer. På den måde kommer man om ved modsætningen struktur/proces gennem "en udvidelse af vores begreb om 'struktur', så det omfatter og anerkender, at i den levende organisme er det det ikke bare et spørgsmål om en rumlig struktur med en 'aktivitet' som noget udenfor eller imod den, men at den konkrete organisme er udtryk for en rumlig og tidsmæssig struktur, og at denne rum/tidsstruktur er selve aktiviteten."
For Jeune, Barabé og Lacroix, er den klassiske morfologi (dvs. den morfologiske hovedstrømning, der bygger på et koncept om kvalitativ homologi, som fører til gensidigt udelukkende kategorier) og kontinuummorfologien underklasser i den mere omfattende procesmorfologi (dynamisk morfologi).
Se også
Planteanatomi
Plantefysiologi
Planternes evolution
Noter
Eksterne henvisninger
Botanical Visual Glossary
Plant morphology: continuum and process morphology
Botanik
Haveplanter | danish | 0.567212 |
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Hidden Planet
# How plants communicate with each other when in danger
By Kasha Patel
October 21, 2023 at 7:00 a.m. EDT
(Illustration by Emily Sabens/The Washington Post; iStock)
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It sounds like fiction from “The Lord of the Rings.” An enemy begins attacking
a tree. The tree fends it off and sends out a warning message. Nearby trees
set up their own defenses. The forest is saved.
But you don’t need a magical Ent from J.R.R. Tolkien’s world to conjure this
scene. Real trees on our Earth can communicate and warn each other of danger —
and a new study explains how.
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| biology | 267970 | https://nn.wikipedia.org/wiki/Howarthbreen | Howarthbreen | Howarthbreen er ein liten isbre som flyt sør-søraust til Admirality Sound langs vestsida av The Watchtower, søraust på James Ross Island i Antarktis. Han vart namngjeven av UK Antarctic Place-Names Committee i 1995 etter Michael Kingsley Howarth som var Deputy Keeper of Paleontology ved British Museum (Natural History) i 1980–92, og forfattar av Falkland Islands Dependencies Survey Scientific Report Nr. 21 om Aleksanderøya.
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Isbrear på James Ross Island | norwegian_nynorsk | 1.153861 |
immortal_organisms/Organism.txt |
An organism (from Ancient Greek ὄργανον (órganon) 'instrument, implement, tool', and -ισμός (-ismós)) is any biological living system that functions as an individual life form. All organisms are composed of cells. The idea of organism is based on the concept of minimal functional unit of life. Three traits have been proposed to play the main role in qualification as an organism:
Organisms include multicellular animals, plants, and fungi; or unicellular microorganisms such as protists, bacteria, and archaea. All types of organisms are capable of reproduction, growth and development, maintenance, and some degree of response to stimuli. Most multicellular organisms differentiate into specialized tissues and organs during their development.
In 2016, a set of 355 genes from the last universal common ancestor (LUCA) of all organisms from Earth was identified.
Etymology[edit]
The term "organism" (from Greek ὀργανισμός, organismos, from ὄργανον, organon, i.e. "instrument, implement, tool, organ of sense or apprehension") first appeared in the English language in 1703 and took on its current definition by 1834 (Oxford English Dictionary). It is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to Immanuel Kant's 1790 Critique of Judgment.
Definitions[edit]
An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction". Many definitions exclude viruses and possible synthetic non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction. A superorganism is an organism consisting of many individuals working together as a single functional or social unit.
There has been controversy about the best way to define the organism, and from a philosophical point of view, whether such a definition is necessary. Problematic cases include colonial organisms: for instance, a colony of eusocial insects fulfils criteria such as adaptive organisation and germ-soma specialisation. If so, the same argument would include some mutualistic and sexual partnerships as organisms. If group selection occurs, then a group could be viewed as a superorganism, optimized by group adaptation. Another view is that attributes like autonomy, genetic homogeneity and genetic uniqueness should be examined separately rather than demanding that an organism should have all of them; if so, there are multiple dimensions to biological individuality, resulting in several types of organism.
Other views include the idea that an individual is distinguished by its immune response, separating self from foreign; that "anti-entropy", the ability to maintain order, is what distinguishes an organism; or that Shannon's information theory can be used to identify organisms as capable of self-maintaining their information content. Finally, it may be that the concept of the organism is inadequate in biology.
Viruses[edit]
Main article: Non-cellular life
Viruses are not typically considered to be organisms because they are incapable of autonomous reproduction, growth or metabolism. Although viruses have a few enzymes and molecules like those in living organisms, they have no metabolism of their own; they cannot synthesize the organic compounds from which they are formed. In this sense, they are similar to inanimate matter. Viruses have their own genes, and they evolve. Thus, an argument that viruses should be classed as living organisms is their ability to undergo evolution and replicate through self-assembly. However, some scientists argue that viruses neither evolve nor self-reproduce. Instead, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible. As for reproduction, viruses rely on hosts' machinery to replicate. The discovery of viruses with genes coding for energy metabolism and protein synthesis fuelled the debate about whether viruses are living organisms, but the genes have a cellular origin. Most likely, they were acquired through horizontal gene transfer from viral hosts.
Ancestry[edit]
Main article: Last universal common ancestor
Precambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, a paper in the scientific journal Nature suggested that these 3.5 Gya (billion years old) geological formations contain fossilized cyanobacteria microbes. This suggests they are evidence of one of the earliest known life forms on Earth.
There is strong evidence from genetics that all organisms have a common ancestor. In particular, every living cell makes use of nucleic acids as its genetic material, and uses the same twenty amino acids as the building blocks for proteins. All organisms use the same genetic code (with some extremely rare and minor deviations) to translate nucleic acid sequences into proteins. The universality of these traits strongly suggests common ancestry, because the selection of many of these traits seems arbitrary. Horizontal gene transfer makes it more difficult to study the last universal ancestor. However, the universal use of the same genetic code, same nucleotides, and same amino acids makes the existence of such an ancestor overwhelmingly likely. The first organisms were possibly anaerobic and thermophilic chemolithoautotrophs that evolved within inorganic compartments at geothermal environments.
The last universal common ancestor is the most recent organism from which all organisms now living on Earth descend. Thus, it is the most recent common ancestor of all current life on Earth. The last universal common ancestor lived some 3.5 to 3.8 billion years ago, in the Paleoarchean era. In 2016, a set of 355 genes considered likely to derive directly from the last universal common ancestor was identified.
Human intervention[edit]
Modern biotechnology is challenging traditional concepts of organisms and species. Cloning is the process of creating a new multicellular organism, genetically identical to another, with the potential of creating entirely new species of organisms. Cloning is the subject of ethical debate.
In 2008, the J. Craig Venter Institute assembled a synthetic bacterial genome, Mycoplasma genitalium, by using recombination in yeast of 25 overlapping DNA fragments in a single step. The use of yeast recombination greatly simplifies the assembly of large DNA molecules from both synthetic and natural fragments.
See also[edit]
Biology portal
Earliest known life forms | biology | 259293 | https://sv.wikipedia.org/wiki/Livscykel | Livscykel | För en produkttyps livscykel, se produktcykel. För en produktindivids livscykel, se livscykelanalys.''
En organisms livscykel är alla de förändringar som den genomgår från födelse till död. Hos en del organismer är livscykeln kort och innefattar endast ett fåtal olika stadier, medan andra organismer kan ha en lång och komplicerad livscykel som sträcker sig över flera år. Två viktiga steg i en organisms livscykel oberoende av dess längd är det stadium där organismen genomgår utveckling och tillväxt och det stadium som innefattar reproduktion.
En del organismer reproducerar sig endast en gång för att därefter dö. För sådana organismer markerar reproduktionen därmed fullbordan av livscykeln. Andra organismer har en livscykel med flera möjligheter att ge upphov till avkomma, genom att förmågan till reproduktion fortsätter, oftast genom hela livet.
Se även
Cellcykeln
Ekologi | swedish | 0.675465 |
immortal_organisms/Immortal_Technique.txt |
Felipe Andres Coronel (born February 19, 1978), better known by the stage name Immortal Technique, is an American rapper and activist. Most of his lyrics focus on controversial issues in global politics, from a radical left-wing perspective.
Immortal Technique seeks to retain control over his production, and has stated in his music that record companies, not artists themselves, profit the most from mass production and marketing of music. He claimed in an interview to have sold close to a combined total of 200,000 copies of his first three official releases.
Early life
Coronel was born in a military hospital in Lima. He is of mostly Amerindian descent, and also has Spanish, French and African ancestry. His family immigrated to Harlem, New York, in 1980 to escape the Peruvian Civil War. During his teenage years, he was arrested multiple times due in part to what he has said was "selfish and childish" behavior. He attended Hunter College High School on the Upper East Side of Manhattan, where his classmates included Chris Hayes and Lin-Manuel Miranda, whom he bullied, although the two later became friends. Shortly after enrolling in Pennsylvania State University, he was arrested and charged with assault-related offenses due to his involvement in an altercation between fellow students; the charges stemming from this incident led to him being incarcerated for a year.
After being paroled, he took political science classes at Baruch College in New York City for two semesters at the behest of his father, who allowed Coronel to live with him on the condition that he went to school. Honing his rapping skills in jail, and unable to find decent wage-paying employment after his release, he began selling his music on the streets of New York and battling with other MCs. This, coupled with his victories in numerous freestyle rap competitions of the New York underground hip hop scene such as Rocksteady Anniversary and Braggin Rites, led to his reputation as a ferocious Battle MC.
Musical career
2000–2005: Revolutionary Vol. 1 and Revolutionary Vol. 2
In 2001, Immortal Technique released his first album Revolutionary Vol. 1 without the help of a record label or distribution, instead using money earned from his rap battle triumphs. He also battled but lost to Posta Boy in 106 & Park's Freestyle Friday. Revolutionary Vol. 1 also contained the underground classic "Dance with the Devil". In November 2002, he was listed by The Source in its "Unsigned Hype" column, highlighting artists that are not signed to a record label. The following year, in September 2003, he received the coveted "Hip Hop Quotable" in The Source for a song entitled "Industrial Revolution" from his second album. Immortal Technique is the only rapper in history to have a "Hip Hop Quotable" while being unsigned. He released his second album Revolutionary Vol. 2 in 2003, which featured an intro and a spoken-word piece by death row inmate Mumia Abu-Jamal. In 2004 and 2005, Viper Records and Babygrande Records, respectively, re-released Immortal Technique's debut, Revolutionary Vol. 1, to make it available to a wider audience. "Point of No Return" from Revolutionary Vol 2 was used as the entrance theme for Rashad Evans during the UFC 88 Main Event between Chuck Liddell and Rashad Evans.
2005–present: The 3rd World, The Martyr and The Middle Passage
Immortal Technique performing in March 2006
Between 2005 and 2007 Immortal Technique began working on The Middle Passage and The 3rd World, the two albums that would serve a follow-up to Revolutionary Vol. 2. The 3rd World, produced by DJ Green Lantern, was released in 2008. Emilee Woods, writing for RapReviews.com, reviewed the album positively, praising its "earnestly and skillfully delivered" material, and claiming that Technique had "finally found a comfort zone in the balance between lyricism and message."
He was also featured on several movie soundtracks and video game soundtracks, all the while touring relentlessly. In October 2011, Immortal Technique released The Martyr, a free compilation album of previously unreleased material and new tracks.
In an interview in 2020 with Latino USA, Immortal Technique discussed that he was working on writing a book. He also mentioned that he was in the process of creating a new album, but had faced setbacks because of the Covid-19 Pandemic.
Collaborations
Immortal Technique (left) at the Roskilde Festival, 2006
The summer of 2005 saw the release of "Bin Laden", a vinyl single 12" featuring Mos Def and DJ Green Lantern. The single also contained a remix of the song featured Chuck D of Public Enemy and KRS-One. In early 2006, the song "Impeach the President", featuring Dead Prez and Saigon turned up in the mixtape "Alive on Arrival" DJ Green Lantern. This is a simple version of The Honeydrippers, 1973, in which Immortal Technique urged fans to organize a vote of censure against George W. Bush. In April 2009, a new song leaked on the internet named "Democratie Fasciste (Article 4)" by Brazilian-French rapper Rockin' Squat which featured Immortal Technique. The official release of the song and Rockin' Squat's album Confessions D'un Enfant Du Siècle Volume 2 was on May 12, 2009. The instrumental from the song was sampled from Wendy Rene's "After Laughter". The song expresses the inequalities of the Third World and revolutionary events throughout history against tyranny and oppression.
The song contains lyrics in English (Immortal Technique), French (Rockin' Squat) and brief shout outs in Spanish (Immortal Technique). This song is Immortal Technique's first official international collaboration. In early 2009, it was announced that there would be a collaboration between Technique and UK underground artist Lowkey, on a single called "Voices of the Voiceless". On September 11, 2009, a "snippet" of the song was released on YouTube. The preview was released ahead of its September 21 launch on iTunes, as part of a web-campaign that included updates, promotion and links on forums, E-Magazines and several social networking sites. The song's lyrics cover a broad range of issues that are familiar to listeners of both artists – racism, world revolution, war, socialism, government control, rape, famine, colonialism, Classism, self-determination and the war in Iraq.
Activism
Immortal Technique performing in March 2010
Immortal Technique visits prisons to speak to youth and working with immigrant-rights activists, and raising money for children's hospitals overseas. He created a writing grant program for high-school students as well.
In June 2008, Immortal Technique partnered with Omeid International, a non-profit human rights organization, and dubbed the work as "The Green Light Project". With the profits of the album The 3rd World, he traveled to Kabul, Afghanistan to help Omeid build an orphanage, the Amin Institute, without corporate or external funding.
Other work
Films
Immortal Technique featured in Ice-T's documentary Something from Nothing: The Art of Rap.
The (R)evolution of Immortal Technique
A documentary about Immortal Technique was released in September 2011 and premiered at the Harlem Film Festival. It was released on DVD on July 10, 2012.
This Revolution
Immortal Technique appeared as himself in a docudrama film entitled This Revolution, which was recorded during the 2004 Republican National Convention in New York. The tape contains the protests surrounding the convention in the form of a documentary. It also featured Viper Records affiliates Akir and producer SouthPaw in roles.
Since then, Immortal Technique has taken control of Viper Records and has signed a distribution deal with Babygrande Records / E1 Entertainment to vent to their next album. SouthPaw has managed to establish himself as A&R of Viper Records.
Discography
Studio albums
Title
Album details
Peak chart positions
US
USR&B
USRap
Revolutionary Vol. 1
Release Date: September 14, 2001
Label: Viper
Formats: CD, digital download
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—
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Revolutionary Vol. 2
Release Date: November 18, 2003
Label: Viper
Formats: CD, digital download, LP
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The 3rd World
Release Date: June 24, 2008
Label: Viper
Formats: CD, digital download, LP
99
36
12
Compilation album
Title
Album details
The Martyr
Release Date: October 27, 2011
Labels: Viper, Fontana
Formats: CD, digital download, cassette
Singles
Title
Year
Album
"Industrial Revolution"
2003
Revolutionary Vol. 2
"The Point of No Return"
2004
"Bin Laden" (with Mos Def and DJ Green Lantern)
2005
Non-album singles
"Bin Laden (Remix)" (with Chuck D and KRS-One)
"Caught in a Hustle"
BAADASSSSS! Soundtrack
"Stronghold Warriors" (with Poison Pen)
2007
Pick Your Poison (The Mark of the East)
"The 3rd World"
2008
The 3rd World
"Voices of the Voiceless"(with Lowkey)
2009
Soundtrack to the Struggle
"Political Prisoner (Remix)"
2020
Non-album single
"Civil War" (with Brother Ali, Killer Mike and Chuck D)
2022
Non-album single | biology | 582388 | https://sv.wikipedia.org/wiki/Lil%20Wayne | Lil Wayne | Dwayne Michael Carter, Jr., mer känd under sitt artistnamn Lil Wayne, föddes 27 september 1982 i New Orleans i Louisiana. Han är en amerikansk rappare, och redan vid nio års ålder blev han medlem i Cash Money Records som skivbolagets yngsta medlem och en av två medlemmar i duon The B.G.'z med B.G. 1997 gick Lil Wayne med i gruppen Hot Boys, som redan innehöll rapparna Juvenile, B.G. och Young Turk. Hot Boys debuterade med Get It How U Live! samma år. Lil Wayne fick stor framgång med gruppens storsäljande album Guerrilla Warfare, som släpptes 1999. Samma år släppte Lil Wayne sitt debutalbum Tha Block Is Hot, som sålde över en miljon exemplar i USA.
Hans två följande album Lights Out (2000) och 500 Degreez (2002) nådde endast guldstatus. Däremot nådde Lil Wayne stora framgångar 2004 med albumet Tha Carter, som innehöll singeln "Go D.J.". Wayne medverkade även på Destiny's Childs topp tio-singel "Soldier" samma år. 2005 släpptes uppföljaren till Tha Carter, Tha Carter II. Under 2006 och 2007 släppte Lil Wayne ett flertal mixtapes och medverkade på flera populära rap- och R&B-singlar. Hans mest framgångsrika album, Tha Carter III, släpptes 2008 och sålde över 1 miljon exemplar under sin första vecka. Den innehöll singeln och listettan "Lollipop" med Static Major. Den innehöll även singlarna "A Milli" och "Got Money" med T-Pain som vann Grammy Award för bästa rap-album.
Den 2 februari 2010 släppte Lil Wayne sitt första rockalbum, Rebirth, som möttes av mestadels negativa recensioner från kritiker. Albumet sålde emellertid guld i mars 2010 samt platina i september 2020. I mars 2010 började Lil Wayne avtjäna ett 8 månader långt fängelsestraff i New York efter att han blivit dömd för olaga vapeninnehav i och med en incident i juli 2007. I fängelset släppte han ännu ett album, med titeln I Am Not a Human Being, i september 2010 med artister som Drake, Nicki Minaj och Lil Twist. Hans nionde och första studioalbum sedan han släppts från fängelset, Tha Carter IV, släpptes den 29 augusti 2011. Albumet innehåller låtarna "6 Foot 7 Foot", "How to Love" och "She Will" med Drake och sålde 964 000 exemplar i USA första veckan.
Tidigt liv
Lil Wayne föddes som Dwayne (senare Wayne) Michael Carter Jr. och växte upp i Hollygrove, ett område i New Orleans. Hans mor var 19 år gammal när han föddes och två år senare skilde föräldrarna sig och pappan övergav familjen.
Wayne skrev sin första raplåt vid åtta års ålder. Under sommaren 1991 träffade han Bryan Williams, rappare och ägare av Cash Money Records. Wayne spelade in freestyle-rap på Williams telefonsvarare, vilket fick honom att ta den unge Wayne under sina vingar och inkludera honom i Cash Money-distribuerade låtar. Han spelade även in sitt första samarbetsalbum True Story med rapparen B.G. Vid tidpunkten var Wayne elva år och B.G. var fjorton år, och de fick namnet "The B.G.'z". När Wayne var tolv år spelade han Tin Man i en dramaklassversion av The Wiz.
Vid tolv års ålder försökte han att begå självmord genom att skjuta sig i bröstet med ett 9 mm handeldvapen som lämnats kvar hemma hos honom av en besökare kvällen innan. Skottet missade alla vitala organ och Wayne ringde själv ringa till larmcentralen. I flera decennier ljög han om att händelsen hade skett av misstag.
Wayne var en toppelev vid McMain Magnet School, men han hoppade av skolan vid 14 års ålder för att satsa på en karriär inom musiken.
Lil Wayne är även mentor till artister som Drake och Nicki Minaj genom sin musikgrupp Young Money.
Karriär
1997–1999: Hot Boys
1997 gick Lil Wayne med i Hot Boys tillsammans med rapparna Juvenile, B.G. och Turk. Endast 15 år gammal var han då gruppens yngste medlem. Debutalbumet Get It How U Live! släpptes samma år och följdes 1999 upp med Guerrilla Warfare som var gruppens första album på ett stort skivbolag. Guerrilla Warfare nådde förstaplatsen på Billboards Top R&B/Hip-Hop Albums Chart och plats fem på Billboard 200. Under sin karriär hade Hot Boys två låtar som lyckades ta sig in på topplistorna, "We on Fire" från Get It How U Live! och "I Need a Hot Girl" från Guerrilla Warfare. Wayne var även med på Juveniles singel "Back That Azz Up" som nådde förstaplatsen på Billboard Hot 100 samt plats fem på Hot R&B/Hip-Hop Singles & Tracks.
2003, flera år efter att gruppen splittrats, släpptes samlingsalbumet Let' Em Burn med tidigare osläppta låtar som var inspelade under 1999 och 2000. Det nådde plats tre på Billboards Top R&B/Hip-Hop Albums och fjortonde plats på Billboard 200.
Lil Wayne släppte sitt första soloalbum Tha Block Is Hot år 1999 vid 17 års ålder. Albumet innehöll betydande bidrag från Hot Boys, sålde platina och debuterade som nummer tre på Billboards album-lista. Albumet gav honom en nominering för "Best New Artist" av tidningen The Source 1999 och blev även en topp 10-hit. Huvudsingeln var Tha Block Is Hot.
Samma år medverkade Lil Wayne på singeln "Bling Bling" med B.G., Juvenile och Big Tymers. Hans vers fanns med på radioversionen och på album versionen, endast hans hook fanns med på singeln.
2000–2003: Lights Out och 500 Degreez
Hans uppföljare, 2000-albumet Lights Out, misslyckades med att uppnå samma framgångar som hans debutalbum, men certifierades som guld av RIAA. Kritiker pekade på bristen av samstämmiga berättelser i sina verser som bevis för att han mognadsmässigt ännu inte var på samma nivå som sina kollegor från Hot Boys. Huvudsingeln var "Get Off the Corner" som uppmärksammades för sin förbättring av textinnehåll och stil, och det gjordes även en musikvideo till låten. Den andra singeln "Shine", tillsammans med Hot Boys, fick mindre uppmärksamhet. Innan Lights Out släpptes var Lil Wayne med på singeln "1# Stunna", tillsammans med Big Tymers och Juvenile, som nådde plats 24 på Hot Rap Tracks-listan.
Lil Waynes tredje album, 500 Degreez, som släpptes 2002, följde samma linjer som hans två tidigare album, med bidrag från Hot Boys och Mannie Fresh. Trots att den certifierades guld, misslyckades även den med att matcha hans debutalbums framgångar. Titeln var en hänvisning till Hot Boys-medlemmen Juveniles album 400 Degreez. Huvudsingeln var "Way of Life" som, precis som albumet, misslyckades med att matcha hans tidigare singlars framgångar. Efter att 500 Degreez släppts, var han med på singeln "Neva Get Enuf" av 3LW.
2003–2005: Tha Carter och Tha Carter II
Sommaren 2004 släpptes Waynes album Tha Carter, som kritiker ansåg vara en förbättring gällande hans rappande och textteman. På albumets omslagsbild sågs han för första gången i sina nu välkända dreadlocks. Tha Carter gav Wayne mycket uppmärksamhet, och sålde 878 000 enheter i USA, medan singeln "Go DJ" blev en topp 5-hit på R&B/Hip-Hop-listan. Efter att Tha Carter släppts, var Wayne med på Destiny's Childs singel "Soldier" tillsammans med T.I. som nådde plats 3 på US Hot 100 och R&B-listan.
Tha Carter II, uppföljaren till Tha Carter, släpptes i december 2005, denna gång utan den tidigare Cash Money Records-producenten Mannie Fresh, som hade lämnat skivbolaget. Tha Carter II sålde mer än 238 000 enheter under sin första vecka och debuterade som nummer 2 på Billboard 200-listan och fortsatte att sälja 2 000 000 enheter världen över. Huvudsingeln, "Fireman", blev en stor hit i USA och nådde plats 32 på Billboard Hot 100. Andra singlar inkluderade "Grown Man", "Hustler Muzik", och "Shooter" (med R&B-sångaren Robin Thicke). Lil Wayne var även med på en remix av Bobby Valentinos "Tell Me" som nådde plats 13 på USA:s R&B-lista. 2005 blev Lil Wayne VD för Cash Money och samma år startade han Young Money Entertainment som ett imprint av Cash Money. Sent 2007 meddelade dock Lil Wayne att han avgått som VD för båda bolagen och har lämnat över ledningen av Young Money till Cortez Bryant.
2006–2008: Like Father, Like Son, Mixtapes och samarbeten
2006 samarbetade Lil Wayne med rapparen Birdman och gjorde albumet Like Father, Like Son, vars första singel "Stuntin' Like My Daddy" nådde plats 21 på Billboard Hot 100.
Istället för ett nytt soloalbum, släppte Lil Wayne en stor mängd mixtapes och gästspel på en del pop- och hiphop-singlar. Av hans många mixtapes fick Dedication 2 och Da Drought 3 mest uppmärksamhet i media. Dedication 2, som släpptes 2006, parade ihop Lil Wayne med DJ Drama och innehöll den hyllade och socialt medvetna låten "Georgia Bush", i vilken Lil Wayne kritiserar den tidigare USA-presidenten George W. Bushs svar, på effekterna av Orkanen Katrina som drabbade New Orleans. Da Drought 3 släpptes följande år och var tillgänglig för gratis nedladdning. Den innehöll Lil Wayne rappandes över en mängd beats från nya hits av andra musiker. Ett flertal tidningar såsom XXL och Vibe omfattade mixtapet. Christian Hoard från Rolling Stone ansåg Da Drought 3 och The Drought Is Over 2 vara två av de bästa albumen under 2007.
Trots att han inte släppt ett album på två år, var Lil Wayne med på ett flertal singlar, inklusive "Gimme That" av Chris Brown, Make It Rain av Fat Joe, You av Lloyd, We Takin' Over av DJ Khaled (tillsammans med Akon, T.I., Rick Ross, Fat Joe och Birdman), Duffle Bag Boy av Playaz Circle, Sweetest Girl (Dollar Bill) av Wyclef Jean (med Akon) och remixen till I'm So Hood DJ Khaled (tillsammans med T-Pain, Young Jeezy, Ludacris, Busta Rhymes, Big Boi, Fat Joe, Birdman och Rick Ross). Alla dessa singlar placerade sig bättre än plats 20 på Billboard Hot 100, Hot Rap Tracks och Hot R&B/Hip-Hop Songs. På Birdmans 2007-album 5 * Stunna är Lil Wayne med på singlarna 100 Million och I Run This bland flera andra spår. Wayne var även med på låtar från albumen Getback av Little Brother, American Gangster av Jay-Z, Graduation av Kanye West och Insomniac av Enrique Iglesias. "Make it Rain", en låt producerad av Scott Storch som nådde plats 13 på Hot 100 och plats två på Hot Rap Tracks-listan, nominerades till en Grammy för "Best Rap Performance by a Duo or Group, 2008.
Tidningen Vibe gjorde en lista över Lil Waynes 77 låtar under 2007 och rankade hans vers i DJ Khaleds "We Takin Over" som hans bästa 2007, med "Dough Is What I Got" (en freestyle över beatet från Jay-Z:s Show Me What You Got) på andra plats. I slutet av 2007 blev Lil Wayne vald som MTV:s "Hottest MC in the Game", The New Yorker rankade honom som "Rapper of the Year" och GQ gav honom titeln "Workaholic of the Year". 2008 blev han vald som "Best MC" av Rolling Stone.
2008–2010: Tha Carter III, We Are Young Money och Rebirth
Tha Carter III, som ursprungligen planerades att släppas under 2007, blev försenad efter att majoriteten av låtarna läckte ut och släpptes på mixtapes, såsom "The Drought Is Over Pt. 2" och "The Drought Is Over Pt. 4". Lil Wayne valde från början att använda de läckta låtarna, plus 4 nya låtar, till att göra ett separat album, kallat The Leak. The Leak skulle släppas den 18 december 2007, och det riktiga albumet försenades till 18 mars 2008. The Leak släpptes aldrig i det formatet, men en officiell EP kallad The Leak, innehållandes fem låtar släpptes digitalt den 25 december 2007. Tha Carter III släpptes den 10 juni 2008 och sålde mer än en miljon enheter första veckan, den första att göra det sedan 50 Cent The Massacre 2005. Den första singeln, "Lollipop", med Static Major blev hans mest kommersiellt framgångsrika låt vid tidpunkten och toppade Billboard Hot 100, vilket gjorde den till Lil Waynes första topp 10-singel som soloartist, såväl som hans första nummer 1-låt på listan. Hans tredje singel från Tha Carter III, "Got Money" med T-Pain, nådde plats 13 på Billboard 100. Tha Carter III vann även fyra Grammy Awards, bland annat för bästa rap-album och bästa rap-låt, som han vann med "Lollipop". Utöver sina album-singlar, medverkade Lil Wayne på R&B-singeln Girls Around the World av Lloyd, Love In This Club, Part II av Usher, Official Girl av Cassie, I'm So Paid av Akon, Turnin' Me On av Keri Hilson och Can't Believe It av T-Pain; rap-singlarna My Life av The Game, Shawty Say av David Banner, Swagga Like Us av T.I., Cutty Buddy av Mike Jones, All My Life (In the Ghetto) av Jay Rock och remixen av Certified av Glasses Malone; och pop-singlarna Let It Rock av nya Cash Money-artisten Kevin Rudolf. Den 14 juli certifierades Tha Carter III dubbelplatina av Recording Industry Association of America. I en intervju med MTV i oktober 2008 berättade Lil Wayne om planer att återutge albumet med enbart nya låtar, inklusive en duet med Ludacris och remixar på "A Milli".
Uppställningen till New Orleans Voodoo Experience-festival 2008, som hölls i oktober, innehöll Lil Wayne. Jonathan Cohen från tidningen Billboard skrev att händelsen skulle markera hans karriärs största uppträdande i sin hemstad. Lil Wayne sade att han skulle återförenas med Hot Boys, tillsammans med Juvenile, Turk, och B.G. De planerade att släppa ett album efter att B.G.:s soloalbum Too Hood 2 Be Hollywood var klart. Wayne uppträdde även på 2008 års Virgin Mobile Festival med Kanye West, där han framförde remixen av "Lollipop" med West och mimade till Whitney Houstons "I Will Always Love You". Lil Wayne uppträdde även på 2008 års MTV Video Music Awards med Kid Rock ("All Summer Long"), Leona Lewis ("DontGetIt") och T-Pain ("Got Money"). På säsongspremiären av Saturday Night Live framförde han "Lollipop" och "Got Money". Han uppträdde på 2008 års BET Hip Hop Awards, där han även var nominerad för 12 priser. Han vann "MVP"-titeln och sju andra priser. Den 11 november 2008 blev Wayne den första hiphop-artisten någonsin att uppträda på Country Music Association Awards. Han spelade tillsammans med Kid Rock och låten "All Summer Long", där Wayne inte rappade, utan istället spelade gitarr tillsammans med gitarristen i Kid Rocks band. Kort därefter nominerades Wayne till åtta Grammy Awards - flest av alla nominerade artister det året. Wayne utsågs sedan till den allra första MTV Man of the Year vid slutet av 2008. Han vann Grammy Award for Best Rap Solo Performance för "A Milli", Best Rap Performance by a Duo or Group för sitt medverkande i T.I.:s singel "Swagga Like Us" och Best Rap Song för "Lollipop". Tha Carter III vann priset för Best Rap Album.
MTV News listed Lil Wayne number two on their 2009 list of the Hottest MC:s In The Game.
Den 23 december 2009 släppte Wayne ett samarbetsalbum med Young Money, där den första singeln bekräftades vara "Every Girl". Den andra singeln, "BedRock", innehöll Lloyd Banks och den tredje singeln blev "Roger That". Den 24 maj 2010 certifierades albumet guld RIAA med över 500 000 enheter sålda. Wayne medverkar på låten "Revolver" tillsammans med Madonna på samlingsalbumet Celebration från 2009. Han medverkade även på en Weezer-låt, "Can't Stop Partying", på deras 2009-album Raditude. Sent 2008 sa Wayne att han skulle släppa om Tha Carter III med överblivna spår och kalla den Rebirth. Ett flertal månader senare meddelade han dock att Rebirth istället skulle släppas som hans första rockalbum. För att promota släppet av Rebirth och albumet tillsammans med Young Money Entertainment, headlineade Wayne "Young Money Presents: Americas Most Wanted Music Festival", en Nordamerikansk turné som började den 29 juli 2009. Rebirth-albumet var från början planerat att släppas den 7 april 2009, men efter ett flertal förseningar släpptes albumet den 2 februari 2010. I och med de stora förväntningarna på Rebirth, prydde Wayne omslaget till tidningen Rolling Stone. "Prom Queen", den första officiella singeln, debuterade den 27 januari 2009 omedelbart efter live-sändning på Ustream av hans konsert i San Diego. "Prom Queen" nådde plats 15 på Billboard Hot 100-listan. Den 3 december 2009 släpptes Lil Waynes andra singel, "On Fire", på iTunes. "On Fire" producerades av Cool & Dre.
2010–: I Am Not a Human Being och Tha Carter IV
Lil Wayne tänkte släppa en EP betitlad I Am Not a Human Being, men det bekräftades senare att det skulle bli ett fullängdsalbum. Albumet släpptes den 27 september 2010, på hans födelsedag. Albumet har sålt över 953 000 enheter i USA och den framgångsrika singeln "Right Above It" nådde plats 6 på Billboard Hot 100.
I en intervju med MTV nämnde Wayne att han möjligtvis skulle släppa Tha Carter IV.<ref>Lil Wayne Preps Mixtape And Tha Carter IV; Juelz Santana Plans Skull Gang Takeover: Mixtape Monday. MTV.com.'.' Retrieved September 15, 2008.</ref> Efter att Tha Carter III lyckats sälja över 3 miljoner enheter och bli 2008 års bäst säljande album, skrev Wayne ett nytt kontrakt med Cash Money Records. Wayne sade att Tha Carter IV skulle släppas 2009 precis innan jul.Lil Wayne Says Rebirth, Young Money LP May Be A Double Album. MTV News. Det bekräftades dock senare Rebirth och We Are Young Money skulle släppas separat och att Tha Carter IV skulle släppas under 2011. Han började om från början med Tha Carter IV efter att han släpptes ut från fängelset. Han spelade in sin första låt efter att han blivit frisläppt och den beskrevs som "en 2010 års version av A Milli på steroider." Den första singeln, "6 Foot 7 Foot", med Cory Gunz släpptes den 15 december 2010. Den gjordes tillgänglig som digital nedladdning på iTunes den 16 december 2010. Låten är producerad av Bangladesh, som också producerade Lil Waynes singel "A Milli", 2008. Den 8 mars 2011 släppte Wayne en annan låt, "We Back Soon". Låten producerades av den Grammy-vinnande producenten StreetRunner, men Wayne meddelade att låten inte skulle medverka på Tha Carter IV. Han släppte även den andra singeln till Tha Carter IV, "John", den 24 mars 2011. Rick Ross medverkar på låten och den producerades av Polow da Don. Den 20 april 2011 släpptes det officiella omslaget till Tha Carter IV. Tha Carter IV var tänkt att släppas den 16 maj 2011, men albumets exekutiva producent, Mack Maine, bekräftade att albumet skulle släppas den 21 juni 2011 istället, för att de behövde mer tid till att göra albumet perfekt. Den 26 maj släpptes den tredje singeln "How to Love". Tha Carter IV sköts även fram ännu en gång, till den 29 augusti 2011.
I väntan på Tha Carter IV släppte Wayne ett mixtape med namnet Sorry 4 the Wait. Han döpte mixtapet så som en ursäkt till sina fans för förseningarna av albumet. Den består av 12 låtar, där beaten kommer från andra artisters låtar, som på hans No Ceilings-mixtape.
I juli 2011, bekräftade Lil Wayne att Tha Carter IV var klar.Tha Carter IV debuterade som nummer 1 på Billboard 200 med 964 000 enheter sålda under första veckan, vilket gjorde det till hans tredje album att toppa Billboard-listan. Den 8 januari 2012 listades han som den sjunde bästsäljande artisten någonsin av digital musik, med 36 788 000 sålda album vid slutet av 2011.
Framtida projekt
Lil Wayne har utannonserat flera möjliga kommande projekt, inklusive ett samarbetsalbum betitlat I Can't Feel My Face med rapparen Juelz Santana som har varit under produktion under flera år. Han arbetade även med Tionne "T-Boz" Watkinsalbum Still Cool sent 2011. Han diskuterade ett möjlighet R&B-album Luv Sawngz, där han kommer använda sig av en vocoder. Han pratade även med sångaren Lloyd om att göra ett samarbetsalbum i framtiden. Den 19 juni 2008 bildade Lil Wayne och T-Pain en duo med namnet T-Wayne och planerade att släppa ett album. Enligt en intervju med Drake i 2011 års decemberupplaga av tidningen XXL har planerna för ett kommande album med Lil Wayne skrotas för nu, på grund av Jay-Z och Kanye Wests samarbete Watch the Throne. Lil Wayne och Birdman kommer släppa en uppföljare till deras album Like Father, Like Son. Det avslöjades av Mack Maine att Lil Wayne och Juelz Santana har gått tillbaka till att jobba med deras samarbetsalbum I Can't Feel My Face, som blivit försenad några år på grund av "skivbolagspolitik"..
I oktober 2011 rapporterades det att Lil Wayne jobbar på uppföljare till I Am Not a Human Being och Rebirth. Ett par månader senare berättade Birdman att I Am Not A Human Being 2 kommer att släppas innan sommaren 2012 och att han och Lil Wayne är klara med inspelningen av Like Father, Like Son 2.
Den 29 mars 2011, i en intervju med Hot 97s Angie Martinez, avslöjade Lil Wayne att han skulle gå i pension vid 35 års ålder, med motiveringen "Jag har fyra barn" och att "jag skulle känna mig självisk om jag fortfarande gick till studion när det är en så viktig del i deras liv."
Andra satsningar
TV- och filmkarriär
Lil Wayne bjöds in som gästdebattör mot Skip Bayless under "1st & 10"-segmentet av ESPN First Take, den 6 januari 2009. Den 10 februari 2010 medverkade han även i ESPN:s Around the Horn och slog ut veteran-sportkrönikörerna Woody Paige, Jay Mariotti samt New Orleans-reportern Michael Smith och vann det avsinttet av serien. Innan 2009 års Grammy Awards intervjuades Wayne av Katie Couric. Den 7 februari 2009 presenterade han The Top Ten List på CBS Late Show with David Letterman. Han medverkade sedan på The View, den 24 april 2009, där han pratade om sitt General Educational Development Test och sina beroenden. I september 2009 profilerades han i ett avsnitt av VH1:s Behind the Music samt var presentatör på 2009 års MTV Movie Awards.
Filmmässigt producerade och komponerade Wayne musik till och medverkade även i direkt till video-filmen Hurricane Season. En dokumentär om Lil Wayne betitlad Tha Carter släpptes under Sundance Film Festival.
Filantropi
Den 19 februari 2008 besökte Lil Wayne och Cortez Bryant sin gymnasieskola McMain Secondary School för att få studenter att designa en inbjudan till en gala som presenterade Lil Waynes ideella stiftelse One Family Foundation. Webbplatsen Change.org skriver "One Family Foundations uppdrag är att stärka ungdomar genom att ge dem möjligheter att odla sina talanger och färdigheter, utbilda dem att bli produktiva och ekonomiskt självförsörjande, samt motivera dem att drömma bortom sina förutsättningar."
Privatliv
Sport- och musikintressen
I en intervju med tidningen Blender, avslöjade Lil Wayne att ett av hans favoritband från hans barndom var rockgruppen Nirvana och nämner dem som en stor influens i hans musik.
Den 24 december 2008 publicerade Lil Wayne sin första blogg i ESPN The Magazine. Wayne avslöjade att var ett stort fan av tennis, Green Bay Packers, Boston Bruins, Los Angeles Lakers och Boston Red Sox. För att hylla att Packers tog sig till Super Bowl XLV gjorde han en remix av Wiz Khalifas hit-låt "Black and Yellow" (som var Pittsburgh Steelers, Packers motståndares, färger) betitlad "Green and Yellow". Wayne har fortsatt att skriva för ESPN och rapporterade från ESPN:s Super Bowl-fest.
Lil Wayne gjorde sin debut på ESPN:s dagliga program Around the Horn den 10 februari 2009.
Vid E3-mässan 2011 medverkade Lil Wayne i trailern till FIFA 12, tillsammans med Young Money-medlemmen Drake.
Religion och högre utbildning
Lil Wayne är kristen och läser bibeln regelbundet. Under ett uppträdande i Newark Symphony Hall bekände Lil Wayne sin tro "på Gud och hans son, Jesus." Även under sin 2011-turné i Australien med Eminem bekände han sin tro på Gud.
Efter att ha gjort ett GED-test (motsvarande högskoleprovet) skrev Wayne in sig på University of Houston i januari 2005, men hoppade av senare samma år på grund av andra åtaganden. På talkshowen The View uppgav han att han bytt till University of Phoenix där han läste psykologi som huvudämne, via online-kurser. Enligt tidningen Urb fick Wayne höga betyg i Houston.
Rättsliga frågor
Arresteringar och fängselse
Den 22 juli 2007 arresterades Lil Wayne i New York City efter att ha uppträtt på Beacon Theatre. New York City Police Department omhändertog Lil Wayne och en annan man efter att ha rökt marijuana vid en turnébuss. Efter häktningen hittade polisen en .40-kalibrig pistol. Vapnet, som stod skrivet i hans managers namn, hittades i en väska nära rapparen. Han åtalades för olaga vapeninnehav och innehav av marijuana. Den 22 oktober 2009 erkände sig Lil Wayne skyldig till olaga vapeninnehav. Han skulle ursprungligen få sin dom i februari 2010 och förväntades att få ett års fängelse, men den 9 februari 2010 meddelade Lil Waynes advokat att fängelsedomen skjutits upp till 2 mars på grund av en tandoperation, som ägde rum den 16 februari. Operationen omfattade åtta rotfyllningar, utbyte av flera tandimplantat, tillägg av ett par nya implantat och behandling av det som återstod av hans riktiga tänder. Den 2 mars 2010 sköts domen upp igen till följd av en brand i källaren på tingshuset. Den 8 mars 2010 dömdes slutligen Lil Wayne till ett års fängelse, som han avtjänade på Rikers Island. Hans advokat sade att rapparen skulle hållas i skyddsförvar, av säkerhetsskäl. I maj 2010 upptäckte personalen på Rikers Island att han hade otillåtna ägodelar i sin cell i form av hörlurar och en laddare till en MP3-spelare. Innan han började sitt straff hade han sagt att han tänkte ha en ipod med i fängelset. I april 2010 skapade Lil Waynes vänner en webbplats vid namn Weezy Thanx You, som publicerar brev skrivna av Wayne i fängelset. I det första brevet, betitlad "Gone 'til November", beskriver rapparen sina dagliga rutiner, och nämner att han tränar mycket och läser bibeln varje dag.
Efter ett uppträdande på Qwest Arena i Boise, Idaho, arresterades Lil Wayne den 5 oktober 2007 då myndigheterna i Georgia anklagade honom för att vara i besittning av en kontrollerad substans. Incidenten beskrevs senare som en förväxling och tog tillbaka anklagelserna.
Den 23 januari 2008 arresterades Lil Wayne tillsammans med två andra då hans turnébuss blev stoppad av en hundpatrull från gränspolisen nära Yuma, Arizona. I bussen fann man 105 gram marijuana, nästan 29 gram kokain, 41 gram ecstasy och 22 000 dollar i kontanter. Han åtalades för grovt narkotikabrott och olaga vapeninnehav, men tilläts att resa utanför staten, efter att han betalat borgen på 10 185 dollar. Den 6 maj 2008 återvände Wayne till Arizona och nekade till anklagelserna. En häktningsorder utfärdades den 17 mars 2010 när Lil Wayne inte dök upp till rättegången, men vid den tidpunkten satt han i fängelse på
Rikers Island och avtjänade ett ettårs fängelsestraff för vapenbrott. Den 22 juni 2010 erkände Wayne sig skyldig till anklagelserna och den 30 juni 2010 dömdes han till tre års skyddstillsyn.
Den 18 december 2009 stoppades Wayne och elva andra vid gränsbevakningens kontrollpunkt i Falfurrias, Texas, efter att en okänd mängd marijuana hittades i två av hans turnébussar.
Lil Wayne arresterades åter i december 2019 efter att polisen fått in tips om att det skulle finnas vapen och marijuana ombord på hans privata jetflygplan. Efter genomsöktning hittades flera olika sorters narkotika samt en pistol som inte var registrerad på Wayne. Lil Wayne riskerade ett fängelsestraff på tio år för olaga innehav av vapen och narkotika, men benådades av den amerikanska presidenten Donald Trump den 19 januari 2021 och fick därför inget straff.
Stämningar
Abkco Music Inc lämnade den 24 juli 2008 in en stämningsansökan mot Lil Wayne för upphovsrätts- och varumärkesintrång, med specifik hänvisning till Tha Carter III-låten "Playing with Fire". I Abkcos ansökan hävdar de att låten uppenbarligen är tagen från The Rolling Stones "Play with Fire", som Abkco äger rättigheterna till. Kort därefter togs låten bort från Tha Carter III på alla skivbutiker online och ersattes med den David Banner-producerade låten "Pussy Monster".
I februari 2009 stämde produktionsbolaget "RMF Productions" Wayne på 1,3 miljoner dollar, efter att de betalat 100 000 dollar i förskott för tre shower, som alla ställdes in av rapparen.
Diskografi
Studioalbum
1999: Tha Block Is Hot 2000: Lights Out 2002: 500 Degreez 2004: Tha Carter 2005: Tha Carter II 2008: Tha Carter III 2010: Rebirth 2010: I Am Not a Human Being 2011: Tha Carter IV 2013: I Am Not A Human Being 2''
2015: FWA
2018: Tha Carter V
2019: Welcome To The Concrete Jungle
2020: Funeral
2020: No Ceilings
2021: Trust Fund Babies (med Rich The Kid)
2022: Sorry 4 The Wait
Filmografi
Externa länkar
Lil' Wayne's officiella MySpace-sida
Cash Money Records officiella webbplats
Lil' Wayne's twitter
Svensk webbplats om Lil Wayne
Referenser
Amerikanska hiphopmusiker
Musiker från New Orleans
Födda 1982
Levande personer
Män | swedish | 0.392741 |
immortal_organisms/Immortality.txt |
Immortality is the concept of eternal life. Some species possess biological immortality.
Some scientists, futurists and philosophers have theorized about the immortality of the human body, with some suggesting that human immortality may be achievable in the first few decades of the 21st century with the help of certain technologies such as mind uploading (digital immortality). Other advocates believe that life extension is a more achievable goal in the short term, with immortality awaiting further research breakthroughs. The absence of aging would provide humans with biological immortality, but not invulnerability to death by disease or injury. Whether the process of internal immortality is delivered within the upcoming years depends chiefly on research (and in neuron research in the case of internal immortality through an immortalized cell line) in the former view and perhaps is an awaited goal in the latter case.
From at least the ancient Mesopotamians, there has been a conviction that gods may be physically immortal, and that this is also a state that the gods at times offer humans. For Christianity the conviction that God may offer physical immortality with the resurrection of the flesh at the end of time, has traditionally been at the very crux of its beliefs. What form an unending human life would take, or whether an immaterial soul exists and possesses immortality, has been a major point of focus of religion, as well as the subject of speculation and debate. In religious contexts, immortality is often stated to be one of the promises of divinities to human beings who perform virtue or follow divine law.
Definitions[edit]
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Scientific[edit]
Main article: Anti-aging movement
Life extension technologies claim to be developing a path to complete rejuvenation. Cryonics holds out the hope that the dead can be revived in the future, following sufficient medical advancements. While, as shown with creatures such as hydra and Planarian worms, it is indeed possible for a creature to be biologically immortal, these are animals which are physiologically very different from humans, and it is not known if something comparable will ever be possible for humans.
Religious[edit]
See also: Soul and Resurrection
Immortality in religion refers usually to either the belief in physical immortality or a more spiritual afterlife. In traditions such as ancient Egyptian beliefs, Mesopotamian beliefs and ancient Greek beliefs, the immortal gods consequently were considered to have physical bodies. In Mesopotamian and Greek religion, the gods also made certain men and women physically immortal, whereas in Christianity, many believe that all true believers will be resurrected to physical immortality. Similar beliefs that physical immortality is possible are held by Rastafarians or Rebirthers.
Physical immortality[edit]
Physical immortality is a state of life that allows a person to avoid death and maintain conscious thought. It can mean the unending existence of a person from a physical source other than organic life, such as a computer.
Pursuit of physical immortality before the advent of modern science included alchemists, who sought to create the Philosopher’s Stone, and various cultures’ legends such as the Fountain of Youth or the Peaches of Immortality inspiring attempts at discovering an elixir of life.
Modern scientific trends, such as cryonics, digital immortality, breakthroughs in rejuvenation, or predictions of an impending technological singularity, to achieve genuine human physical immortality, must still overcome all causes of death to succeed.
Causes of death[edit]
Main article: Death
There are three main causes of death: natural aging, disease, and injury. Such issues can be resolved with the solutions provided in research to any end providing such alternate theories at present that require unification.
Aging[edit]
Aubrey de Grey, a leading researcher in the field, defines aging as "a collection of cumulative changes to the molecular and cellular structure of an adult organism, which result in essential metabolic processes, but which also, once they progress far enough, increasingly disrupt metabolism, resulting in pathology and death." The current causes of aging in humans are cell loss (without replacement), DNA damage, oncogenic nuclear mutations and epimutations, cell senescence, mitochondrial mutations, lysosomal aggregates, extracellular aggregates, random extracellular cross-linking, immune system decline, and endocrine changes. Eliminating aging would require finding a solution to each of these causes, a program de Grey calls engineered negligible senescence. There is also a huge body of knowledge indicating that change is characterized by the loss of molecular fidelity.
Disease[edit]
Disease is theoretically surmountable by technology. In short, it is an abnormal condition affecting the body of an organism, something the body should not typically have to deal with its natural make up. Human understanding of genetics is leading to cures and treatments for a myriad of previously incurable diseases. The mechanisms by which other diseases do damage are becoming better understood. Sophisticated methods of detecting diseases early are being developed. Preventative medicine is becoming better understood. Neurodegenerative diseases like Parkinson’s and Alzheimer’s may soon be curable with the use of stem cells. Breakthroughs in cell biology and telomere research are leading to treatments for cancer. Vaccines are being researched for AIDS and tuberculosis. Genes associated with type 1 diabetes and certain types of cancer have been discovered, allowing for new therapies to be developed. Artificial devices attached directly to the nervous system may restore sight to the blind. Drugs are being developed to treat a myriad of other diseases and ailments.
Trauma[edit]
Physical trauma would remain as a threat to perpetual physical life, as an otherwise immortal person would still be subject to unforeseen accidents or catastrophes. The speed and quality of paramedic response remains a determining factor in surviving severe trauma. A body that could automatically repair itself from severe trauma, such as speculated uses for nanotechnology, would mitigate this factor. The brain cannot be risked to trauma if a continuous physical life is to be maintained. This aversion to trauma risk to the brain would naturally result in significant behavioral changes that would render physical immortality undesirable for some people.
Environmental change[edit]
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Organisms otherwise unaffected by these causes of death would still face the problem of obtaining sustenance (whether from currently available agricultural processes or from hypothetical future technological processes) in the face of changing availability of suitable resources as environmental conditions change. After avoiding aging, disease, and trauma, death through resource limitation is still possible, such as hypoxia or starvation.
If there is no limitation on the degree of gradual mitigation of risk then it is possible that the cumulative probability of death over an infinite horizon is less than certainty, even when the risk of fatal trauma in any finite period is greater than zero. Mathematically, this is an aspect of achieving 'actuarial escape velocity'.
Biological immortality[edit]
Human chromosomes (grey) capped by telomeres (white)
Main article: Biological immortality
Biological immortality is an absence of aging. Specifically it is the absence of a sustained increase in rate of mortality as a function of chronological age. A cell or organism that does not experience aging, or ceases to age at some point, is biologically immortal.
Biologists have chosen the word "immortal" to designate cells that are not limited by the Hayflick limit, where cells no longer divide because of DNA damage or shortened telomeres. The first and still most widely used immortal cell line is HeLa, developed from cells taken from the malignant cervical tumor of Henrietta Lacks without her consent in 1951. Prior to the 1961 work of Leonard Hayflick, there was the erroneous belief fostered by Alexis Carrel that all normal somatic cells are immortal. By preventing cells from reaching senescence one can achieve biological immortality; telomeres, a "cap" at the end of DNA, are thought to be the cause of cell aging. Every time a cell divides the telomere becomes a bit shorter; when it is finally worn down, the cell is unable to split and dies. Telomerase is an enzyme which rebuilds the telomeres in stem cells and cancer cells, allowing them to replicate an infinite number of times. No definitive work has yet demonstrated that telomerase can be used in human somatic cells to prevent healthy tissues from aging. On the other hand, scientists hope to be able to grow organs with the help of stem cells, allowing organ transplants without the risk of rejection, another step in extending human life expectancy. These technologies are the subject of ongoing research, and are not yet realized.
Biologically immortal species[edit]
See also: List of longest-living organisms
Life defined as biologically immortal is still susceptible to causes of death besides aging, including disease and trauma, as defined above. Notable immortal species include:
Bacteria – Bacteria reproduce through binary fission. A parent bacterium splits itself into two identical daughter cells which eventually then split themselves in half. This process repeats, thus making the bacterium essentially immortal. A 2005 PLoS Biology paper suggests that after each division the daughter cells can be identified as the older and the younger, and the older is slightly smaller, weaker, and more likely to die than the younger.
Turritopsis dohrnii, a jellyfish (phylum Cnidaria, class Hydrozoa, order Anthoathecata), after becoming a sexually mature adult, can transform itself back into a polyp using the cell conversion process of transdifferentiation. Turritopsis dohrnii repeats this cycle, meaning that it may have an indefinite lifespan. Its immortal adaptation has allowed it to spread from its original habitat in the Caribbean to "all over the world".
Hydra is a genus belonging to the phylum Cnidaria, the class Hydrozoa and the order Anthomedusae. They are simple fresh-water predatory animals possessing radial symmetry.
Evolution of aging[edit]
Main article: Evolution of aging
As the existence of biologically immortal species demonstrates, there is no thermodynamic necessity for senescence: a defining feature of life is that it takes in free energy from the environment and unloads its entropy as waste. Living systems can even build themselves up from seed, and routinely repair themselves. Aging is therefore presumed to be a byproduct of evolution, but why mortality should be selected for remains a subject of research and debate. Programmed cell death and the telomere "end replication problem" are found even in the earliest and simplest of organisms. This may be a tradeoff between selecting for cancer and selecting for aging.
Modern theories on the evolution of aging include the following:
Mutation accumulation is a theory formulated by Peter Medawar in 1952 to explain how evolution would select for aging. Essentially, aging is never selected against, as organisms have offspring before the mortal mutations surface in an individual.
Antagonistic pleiotropy is a theory proposed as an alternative by George C. Williams, a critic of Medawar, in 1957. In antagonistic pleiotropy, genes carry effects that are both beneficial and detrimental. In essence this refers to genes that offer benefits early in life, but exact a cost later on, i.e. decline and death.
The disposable soma theory was proposed in 1977 by Thomas Kirkwood, which states that an individual body must allocate energy for metabolism, reproduction, and maintenance, and must compromise when there is food scarcity. Compromise in allocating energy to the repair function is what causes the body gradually to deteriorate with age, according to Kirkwood.
Immortality of the germline[edit]
Individual organisms ordinarily age and die, while the germlines which connect successive generations are potentially immortal. The basis for this difference is a fundamental problem in biology. The Russian biologist and historian Zhores A. Medvedev considered that the accuracy of genome replicative and other synthetic systems alone cannot explain the immortality of germlines. Rather Medvedev thought that known features of the biochemistry and genetics of sexual reproduction indicate the presence of unique information maintenance and restoration processes at the different stages of gametogenesis. In particular, Medvedev considered that the most important opportunities for information maintenance of germ cells are created by recombination during meiosis and DNA repair; he saw these as processes within the germ cells that were capable of restoring the integrity of DNA and chromosomes from the types of damage that cause irreversible aging in somatic cells.
Prospects for human biological immortality[edit]
Life-extending substances[edit]
Some scientists believe that boosting the amount or proportion of telomerase in the body, a naturally forming enzyme that helps maintain the protective caps at the ends of chromosomes, could prevent cells from dying and so may ultimately lead to extended, healthier lifespans. A team of researchers at the Spanish National Cancer Centre (Madrid) tested the hypothesis on mice. It was found that those mice which were "genetically engineered to produce 10 times the normal levels of telomerase lived 50% longer than normal mice".
In normal circumstances, without the presence of telomerase, if a cell divides repeatedly, at some point all the progeny will reach their Hayflick limit. With the presence of telomerase, each dividing cell can replace the lost bit of DNA, and any single cell can then divide unbounded. While this unbounded growth property has excited many researchers, caution is warranted in exploiting this property, as exactly this same unbounded growth is a crucial step in enabling cancerous growth. If an organism can replicate its body cells faster, then it would theoretically stop aging.
Embryonic stem cells express telomerase, which allows them to divide repeatedly and form the individual. In adults, telomerase is highly expressed in cells that need to divide regularly (e.g., in the immune system), whereas most somatic cells express it only at very low levels in a cell-cycle dependent manner.
Technological immortality, biological machines, and "swallowing the doctor"[edit]
Main article: Molecular machine
Technological immortality is the prospect for much longer life spans made possible by scientific advances in a variety of fields: nanotechnology, emergency room procedures, genetics, biological engineering, regenerative medicine, microbiology, and others. Contemporary life spans in the advanced industrial societies are already markedly longer than those of the past because of better nutrition, availability of health care, standard of living and bio-medical scientific advances. Technological immortality predicts further progress for the same reasons over the near term. An important aspect of current scientific thinking about immortality is that some combination of human cloning, cryonics or nanotechnology will play an essential role in extreme life extension. Robert Freitas, a nanorobotics theorist, suggests tiny medical nanorobots could be created to go through human bloodstreams, find dangerous things like cancer cells and bacteria, and destroy them. Freitas anticipates that gene-therapies and nanotechnology will eventually make the human body effectively self-sustainable and capable of living indefinitely in empty space, short of severe brain trauma. This supports the theory that we will be able to continually create biological or synthetic replacement parts to replace damaged or dying ones. Future advances in nanomedicine could give rise to life extension through the repair of many processes thought to be responsible for aging. K. Eric Drexler, one of the founders of nanotechnology, postulated cell repair devices, including ones operating within cells and using as yet hypothetical biological machines, in his 1986 book Engines of Creation. Raymond Kurzweil, a futurist and transhumanist, stated in his book The Singularity Is Near that he believes that advanced medical nanorobotics could completely remedy the effects of aging by 2030. According to Richard Feynman, it was his former graduate student and collaborator Albert Hibbs who originally suggested to him (circa 1959) the idea of a medical use for Feynman’s theoretical micromachines (see biological machine). Hibbs suggested that certain repair machines might one day be reduced in size to the point that it would, in theory, be possible to (as Feynman put it) "swallow the doctor". The idea was incorporated into Feynman’s 1959 essay There's Plenty of Room at the Bottom.
Cryonics[edit]
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Main article: Cryonics
Cryonics, the practice of preserving organisms (either intact specimens or only their brains) for possible future revival by storing them at cryogenic temperatures where metabolism and decay are almost completely stopped, can be used to 'pause' for those who believe that life extension technologies will not develop sufficiently within their lifetime. Ideally, cryonics would allow clinically dead people to be brought back in the future after cures to the patients’ diseases have been discovered and aging is reversible. Modern cryonics procedures use a process called vitrification which creates a glass-like state rather than freezing as the body is brought to low temperatures. This process reduces the risk of ice crystals damaging the cell-structure, which would be especially detrimental to cell structures in the brain, as their minute adjustment evokes the individual’s mind.
Mind-to-computer uploading[edit]
Main article: Mind uploading
One idea that has been advanced involves uploading an individual’s habits and memories via direct mind-computer interface. The individual’s memory may be loaded to a computer or to a new organic body. Extropian futurists like Moravec and Kurzweil have proposed that, thanks to exponentially growing computing power, it will someday be possible to upload human consciousness onto a computer system, and exist indefinitely in a virtual environment.
This could be accomplished via advanced cybernetics, where computer hardware would initially be installed in the brain to help sort memory or accelerate thought processes. Components would be added gradually until the person’s entire brain functions were handled by artificial devices, avoiding sharp transitions that would lead to issues of identity, thus running the risk of the person to be declared dead and thus not be a legitimate owner of his or her property. After this point, the human body could be treated as an optional accessory and the program implementing the person could be transferred to any sufficiently powerful computer.
Another possible mechanism for mind upload is to perform a detailed scan of an individual’s original, organic brain and simulate the entire structure in a computer. What level of detail such scans and simulations would need to achieve to emulate awareness, and whether the scanning process would destroy the brain, is still to be determined.
It is suggested that achieving immortality through this mechanism would require specific consideration to be given to the role of consciousness in the functions of the mind. An uploaded mind would only be a copy of the original mind, and not the conscious mind of the living entity associated in such a transfer. Without a simultaneous upload of consciousness, the original living entity remains mortal, thus not achieving true immortality.
Research on neural correlates of consciousness is yet inconclusive on this issue. Whatever the route to mind upload, persons in this state could then be considered essentially immortal, short of loss or traumatic destruction of the machines that maintained them.
Cybernetics[edit]
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Main article: Cyborg
Transforming a human into a cyborg can include brain implants or extracting a human processing unit and placing it in a robotic life-support system. Even replacing biological organs with robotic ones could increase life span (e.g. pace makers) and depending on the definition, many technological upgrades to the body, like genetic modifications or the addition of nanobots would qualify an individual as a cyborg. Some people believe that such modifications would make one impervious to aging and disease and theoretically immortal unless killed or destroyed.
Digital immortality[edit]
Main article: Digital immortality
Religious views[edit]
Main articles: Afterlife and Soul
As late as 1952, the editorial staff of the Syntopicon found in their compilation of the Great Books of the Western World, that "The philosophical issue concerning immortality cannot be separated from issues concerning the existence and nature of man’s soul." Thus, the vast majority of speculation on immortality before the 21st century was regarding the nature of the afterlife.
Abrahamic religion[edit]
The viewpoints of Christianity, Islam, and Judaism regarding the concept of immortality diverge as each faith system encapsulates unique theological interpretations and doctrines on the enduring human nature soul or spirit.
Christianity[edit]
Main articles: Eternal life (Christianity), Christian conditionalism, Christian mortalism, and Universal resurrection
Adam and Eve condemned to mortality. Hans Holbein the Younger, Danse Macabre, 16th century
Christian theology holds that Adam and Eve lost physical immortality for themselves and all their descendants through the Fall, although this initial "imperishability of the bodily frame of man" was "a preternatural condition".
Christians who profess the Nicene Creed believe that every dead person (whether they believed in Christ or not) will be resurrected from the dead at the Second Coming; this belief is known as universal resurrection. Paul the Apostle, in following his past life as a Pharisee (a Jewish social movement that held to a future physical resurrection), proclaims an amalgamated view of resurrected believers where both the physical and the spiritual are rebuilt in the likeness of post-resurrection Christ, who "will transform our lowly body to be like his glorious body" (ESV). This thought mirrors Paul’s depiction of believers having been "buried therefore with him [that is, Christ] by baptism into death" (ESV).
N.T. Wright, a theologian and former Bishop of Durham, has said many people forget the physical aspect of what Jesus promised. He told Time: "Jesus' resurrection marks the beginning of a restoration that he will complete upon his return. Part of this will be the resurrection of all the dead, who will 'awake', be embodied and participate in the renewal. Wright says John Polkinghorne, a physicist and a priest, has put it this way: 'God will download our software onto his hardware until the time he gives us new hardware to run the software again for ourselves.' That gets to two things nicely: that the period after death (the Intermediate state) is a period when we are in God’s presence but not active in our own bodies, and also that the more important transformation will be when we are again embodied and administering Christ’s kingdom." This kingdom will consist of Heaven and Earth "joined together in a new creation", he said.
Christian apocrypha include immortal human figures such as Cartaphilus who were cursed with physical immortality for various transgressions against Christ during the Passion. The medieval Waldensians believed in the immortality of the soul. Leaders of sects such as John Asgill and John Wroe taught followers that physical immortality was possible.
Many Patristic writers have connected the immortal rational soul to the image of God found in Genesis 1:26. Among them is Athanasius of Alexandria and Clement of Alexandria, who say that the immortal rational soul itself is the image of God. Even Early Christian Liturgies exhibit this connection between the immortal rational soul and the creation of humanity in the image of God.
Islam[edit]
Islamic dogma bears the concept of spiritual immortality within it; following the death of a certain individual, it will be arbitrated consistent with its beliefs as well as actions and will embark on the ever-lasting place where they will abate.
The Muslim who holds the five pillars of Islam will make an entrance into the Jannah, where they will inhabit indefinitely.
Al-Baqarah (2:25):
"But give glad tidings to those who believe and work righteousness, that their portion is gardens, beneath which rivers flow. Every time they are fed with fruits therefrom, they say, 'Why, this is what we were fed with before,' for they are given things in similitude; and they have therein companions pure (and holy); and they abide therein forever."
In contrast, the kafir hold the contradictory notion that they abide in Jahannam perpetually.
Angels in Islam are reckoned as immortals from the perspective of Islam but most people believe is that the angels will die and that the Angel of Death will die, but there is no clear text concerning this. Rather there are texts which may indicate this, and there is the well known hadeeth (narration) about the ”trumpet”, which is a munkar hadeeth (rejected report). alternatively, Jinn have a long lifespan between 1000 and 1500. In some Muslim Sufi mystics, Khidr is given a long life but not immortality or there is more than a little argument stated about the demise of khidr; however, it is the matter of debate, and there is a fabrication point that goes around the Khidr drank from the fountain of Life, which is thoroughly invalid. Jesus in Islam was summoned to the sky by Allah's sanction to preserve him from the cross and endow him with long life until the advent of the Dajjal. Dijjal is, additionally, given a long life. Jesus Christ dispatches the Dajjal as he stays after 40 days, one like a year, one like a month, one like a week, and the rest of his days like normal days. The Qur’an repudiates rejuvenation and physical immortality, stating it is inconceivable for humans to attain genuine elixir of life.
كُلُّ نَفْسٍ ذَائِقَةُ الْمَوْتِ
Every soul will taste death
— Quran 3:185
It symbolize the transient nature of life and challenge the concept of immortality in the physical world. This phrase reflects the impermanence of all things.
Judaism[edit]
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The traditional concept of an immaterial and immortal soul distinct from the body was not found in Judaism before the Babylonian exile, but developed as a result of interaction with Persian and Hellenistic philosophies. Accordingly, the Hebrew word nephesh, although translated as "soul" in some older English-language Bibles, actually has a meaning closer to "living being". Nephesh was rendered in the Septuagint as ψυχή (psūchê), the Greek word for 'soul'.
The only Hebrew word traditionally translated "soul" (nephesh) in English language Bibles refers to a living, breathing conscious body, rather than to an immortal soul.
In the New Testament, the Greek word traditionally translated "soul" (ψυχή) has substantially the same meaning as the Hebrew, without reference to an immortal soul.
"Soul" may refer either to the whole person, the self, as in "three thousand souls" were converted in Acts 2:41 (see Acts 3:23).
The Hebrew Bible speaks about Sheol (שאול), originally a synonym of the grave – the repository of the dead or the cessation of existence, until the resurrection of the dead. This doctrine of resurrection is mentioned explicitly only in Daniel 12:1–4 although it may be implied in several other texts. New theories arose concerning Sheol during the intertestamental period.
The views about immortality in Judaism is perhaps best exemplified by the various references to this in Second Temple period. The concept of resurrection of the physical body is found in 2 Maccabees, according to which it will happen through recreation of the flesh. Resurrection of the dead is specified in detail in the extra-canonical books of Enoch, and in Apocalypse of Baruch. According to the British scholar in ancient Judaism P.R. Davies, there is "little or no clear reference ... either to immortality or to resurrection from the dead" in the Dead Sea scrolls texts.
Both Josephus and the New Testament record that the Sadducees did not believe in an afterlife,
but the sources vary on the beliefs of the Pharisees. The New Testament claims that the Pharisees believed in the resurrection, but does not specify whether this included the flesh or not. According to Josephus, who himself was a Pharisee, the Pharisees held that only the soul was immortal and the souls of good people will be reincarnated and "pass into other bodies", while "the souls of the wicked will suffer eternal punishment."
The Book of Jubilees seems to refer to the resurrection of the soul only, or to a more general idea of an immortal soul.
Rabbinic Judaism claims that the righteous dead will be resurrected in the Messianic Age, with the coming of the messiah. They will then be granted immortality in a perfect world. The wicked dead, on the other hand, will not be resurrected at all. This is not the only Jewish belief about the afterlife. The Tanakh is not specific about the afterlife, so there are wide differences in views and explanations among believers.
Dharmic religions[edit]
The perspectives on immortality within Hinduism and Buddhism exhibit nuanced differences, with each spiritual tradition offering distinctive theological interpretations and doctrines concerning the eternal essence of the human soul or consciousness.
Hinduism[edit]
See also: Chiranjivi and Naraka (Hinduism)
Representation of a soul undergoing punarjanma. Illustration from Hinduism Today, 2004
Hindus believe in an immortal soul which is reincarnated after death. According to Hinduism, people repeat a process of life, death, and rebirth in a cycle called samsara. If they live their life well, their karma improves and their station in the next life will be higher, and conversely lower if they live their life poorly. After many life times of perfecting its karma, the soul is freed from the cycle and lives in perpetual bliss. There is no place of eternal torment in Hinduism, although if a soul consistently lives very evil lives, it could work its way down to the very bottom of the cycle.
There are explicit renderings in the Upanishads alluding to a physically immortal state brought about by purification, and sublimation of the 5 elements that make up the body. For example, in the Shvetashvatara Upanishad (Chapter 2, Verse 12), it is stated "When earth, water, fire, air and sky arise, that is to say, when the five attributes of the elements, mentioned in the books on yoga, become manifest then the yogi’s body becomes purified by the fire of yoga and he is free from illness, old age and death."
Another view of immortality is traced to the Vedic tradition by the interpretation of Maharishi Mahesh Yogi:
That man indeed whom these (contacts)do not disturb, who is even-minded inpleasure and pain, steadfast, he is fitfor immortality, O best of men.
To Maharishi Mahesh Yogi, the verse means, "Once a man has become established in the understanding of the permanent reality of life, his mind rises above the influence of pleasure and pain. Such an unshakable man passes beyond the influence of death and in the permanent phase of life: he attains eternal life ... A man established in the understanding of the unlimited abundance of absolute existence is naturally free from existence of the relative order. This is what gives him the status of immortal life."
An Indian Tamil saint known as Vallalar claimed to have achieved immortality before disappearing forever from a locked room in 1874.
Buddhism[edit]
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One of the three marks of existence in Buddhism is anattā, "non-self". This teaching states that the body does not have an eternal soul but is composed of five skandhas or aggregates. Additionally, another mark of existence is impermanence, also called anicca, which runs directly counter to concepts of immortality or permanence. According to one Tibetan Buddhist teaching, Dzogchen, individuals can transform the physical body into an immortal body of light called the rainbow body.
Ancient religions[edit]
Within the intricate tapestry of ancient religious ideologies, delve into a profound contemplation of the concept of immortality. Simultaneously, broaden the expanse of this intellectual exploration, allowing for a more comprehensive examination of the subject matter.
Ancient Greek religion[edit]
Immortality in ancient Greek religion originally always included an eternal union of body and soul as can be seen in Homer, Hesiod, and various other ancient texts. The soul was considered to have an eternal existence in Hades, but without the body the soul was considered dead. Although almost everybody had nothing to look forward to but an eternal existence as a disembodied dead soul, a number of men and women were considered to have gained physical immortality and been brought to live forever in either Elysium, the Islands of the Blessed, heaven, the ocean or literally right under the ground.
Among those humans made immortal were Amphiaraus, Ganymede, Ino, Iphigenia, Menelaus, Peleus, and a great number of those who fought in the Trojan and Theban wars. Asclepius was killed by Zeus, and by Apollo's request, was subsequently immortalized as a star.
In ancient Greek religion a number of men and women have been interpreted as being resurrected and made immortal. Achilles, after being killed, was snatched from his funeral pyre by his divine mother Thetis and brought to an immortal existence in either Leuce, the Elysian plains or the Islands of the Blessed. Memnon, who was killed by Achilles, seems to have received a similar fate. Alcmene, Castor, Heracles, and Melicertes, are also among the figures interpreted to have been resurrected to physical immortality. According to Herodotus's Histories, the seventh century BC sage Aristeas of Proconnesus was first found dead, after which his body disappeared from a locked room. He would reappear alive years later. However, Greek attitudes towards resurrection were generally negative, and the idea of resurrection was considered neither desirable nor possible. For example, Asclepius was killed by Zeus for using herbs to resurrect the dead, but by his father Apollo's request, was subsequently immortalized as a star.
Writing his Lives of Illustrious Men (Parallel Lives) in the first century, the Middle Platonic philosopher Plutarch in his chapter on Romulus gave an account of the king's mysterious disappearance and subsequent deification, comparing it to Greek tales such as the physical immortalization of Alcmene and Aristeas the Proconnesian, "for they say Aristeas died in a fuller's work-shop, and his friends coming to look for him, found his body vanished; and that some presently after, coming from abroad, said they met him traveling towards Croton". Plutarch openly scorned such beliefs held in ancient Greek religion, writing, "many such improbabilities do your fabulous writers relate, deifying creatures naturally mortal." Likewise, he writes that while something within humans comes from the gods and returns to them after death, this happens "only when it is most completely separated and set free from the body, and becomes altogether pure, fleshless, and undefiled."
The parallel between these traditional beliefs and the later resurrection of Jesus was not lost on early Christians, as Justin Martyr argued:
"when we say ... Jesus Christ, our teacher, was crucified and died, and rose again, and ascended into heaven, we propose nothing different from what you believe regarding those whom you consider sons of Zeus."
The philosophical idea of an immortal soul was a belief first appearing with either Pherecydes or the Orphics, and most importantly advocated by Plato and his followers. This, however, never became the general norm in Hellenistic thought. As may be witnessed even into the Christian era, not least by the complaints of various philosophers over popular beliefs, many or perhaps most traditional Greeks maintained the conviction that certain individuals were resurrected from the dead and made physically immortal and that others could only look forward to an existence as disembodied and dead, though everlasting, souls.
Zoroastrianism[edit]
Zoroastrians believe that on the fourth day after death, the human soul leaves the body and the body remains as an empty shell. Souls would go to either heaven or hell; these concepts of the afterlife in Zoroastrianism may have influenced Abrahamic religions. The Persian word for "immortal" is associated with the month "Amurdad", meaning "deathless" in Persian, in the Iranian calendar (near the end of July). The month of Amurdad or Ameretat is celebrated in Persian culture as ancient Persians believed the "Angel of Immortality" won over the "Angel of Death" in this month.
Norse Mythology[edit]
Delving into the intricate weave of ancient Norse religious beliefs, we find a captivating exploration of the concept of immortality that transcends the mortal realm. The Norse cosmos, with its diverse realms and deities, unfolds a tapestry of ideas that enrich our understanding of life beyond earthly existence.
In the cosmic expanse of Norse mythology, three primary realms stand as pillars of existence: Asgard, the realm of the Aesir gods; Midgard, the world of humans; and Hel, the underworld governed by the enigmatic goddess Hel. Within this cosmic framework, immortality takes on multifaceted dimensions, offering warriors and mortals diverse paths in their journey beyond life.
At the heart of Norse belief is the dynamic afterlife, a realm not confined to a singular destination but a vast and varied landscape. Valhalla, the majestic hall of Odin, awaits those warriors who meet their end in glorious battle. Here, the chosen Einherjar, the honored dead, revel in eternal feasting and prepare for the cataclysmic events of Ragnarök, the end of the world. This warrior’s paradise embodies a unique form of immortality, where valorous deeds echo through eternity.
Contrastingly, the realm of Hel unfolds a different aspect of the afterlife. Hel, presided over by the goddess Hel, serves as the final destination for those who did not meet a heroic end. This realm is a place of rest and reflection, marking a departure from the celebratory atmosphere of Valhalla. Hel’s domain reflects the Norse acknowledgment of a more subdued form of immortality, one tied to the continuation of the soul in a distinct afterlife.
Central to the cosmological interplay is Yggdrasil, the cosmic tree that binds and connects these realms. Yggdrasil symbolizes the profound interconnectedness of all existence, from the divine Aesir to the mortal realm of Midgard and down to the underworld of Hel. Its branches reach into the heavens, touching Asgard, while its roots extend into the depths of Hel, embodying the cyclical nature of life, death, and rebirth.
This comprehensive examination of Norse cosmology unveils a rich and nuanced understanding of immortality. It is not a singular concept but a dynamic interplay of destinies, where the valiant find eternal glory in Valhalla, the departed rest in the halls of Hel, and the cosmic tree Yggdrasil weaves the threads of existence into a profound tapestry that resonates throughout the ages.
Philosophical religions[edit]
Within the realm of philosophical religious paradigms, engage in a profound exploration of the concept of immortality. Simultaneously, expand the breadth and depth of this intellectual inquiry to afford a more intricate examination of the subject matter.
Taoism[edit]
See also: Chinese alchemy, Taoism and death, and Xian (Taoism)
It is repeatedly stated in the Lüshi Chunqiu that death is unavoidable. Henri Maspero noted that many scholarly works frame Taoism as a school of thought focused on the quest for immortality. Isabelle Robinet asserts that Taoism is better understood as a way of life than as a religion, and that its adherents do not approach or view Taoism the way non-Taoist historians have done. In the Tractate of Actions and their Retributions, a traditional teaching, spiritual immortality can be rewarded to people who do a certain amount of good deeds and live a simple, pure life. A list of good deeds and sins are tallied to determine whether or not a mortal is worthy. Spiritual immortality in this definition allows the soul to leave the earthly realms of afterlife and go to pure realms in the Taoist cosmology.
Philosophical arguments for the immortality of the soul[edit]
Alcmaeon of Croton[edit]
Alcmaeon of Croton argued that the soul is continuously and ceaselessly in motion. The exact form of his argument is unclear, but it appears to have influenced Plato, Aristotle, and other later writers.
Plato[edit]
Plato's Phaedo advances four arguments for the soul’s immortality:
The Cyclical Argument, or Opposites Argument explains that Forms are eternal and unchanging, and as the soul always brings life, then it must not die, and is necessarily "imperishable". As the body is mortal and is subject to physical death, the soul must be its indestructible opposite. Plato then suggests the analogy of fire and cold. If the form of cold is imperishable, and fire, its opposite, was within close proximity, it would have to withdraw intact as does the soul during death. This could be likened to the idea of the opposite charges of magnets.
The Theory of Recollection explains that we possess some non-empirical knowledge (e.g. The Form of Equality) at birth, implying the soul existed before birth to carry that knowledge. Another account of the theory is found in Plato's Meno, although in that case Socrates implies anamnesis (previous knowledge of everything) whereas he is not so bold in Phaedo.
The Affinity Argument, explains that invisible, immortal, and incorporeal things are different from visible, mortal, and corporeal things. Our soul is of the former, while our body is of the latter, so when our bodies die and decay, our soul will continue to live.
The Argument from Form of Life or The Final Argument explains that the Forms, incorporeal and static entities, are the cause of all things in the world, and all things participate in Forms. For example, beautiful things participate in the Form of Beauty; the number four participates in the Form of the Even, etc. The soul, by its very nature, participates in the Form of Life, which means the soul can never die.
Plotinus[edit]
Plotinus offers a version of the argument that Kant calls "The Achilles of Rationalist Psychology". Plotinus first argues that the soul is simple, then notes that a simple being cannot decompose. Many subsequent philosophers have argued both that the soul is simple and that it must be immortal. The tradition arguably culminates with Moses Mendelssohn's Phaedon.
Metochites[edit]
Theodore Metochites argues that part of the soul's nature is to move itself, but that a given movement will cease only if what causes the movement is separated from the thing moved – an impossibility if they are one and the same.
Avicenna[edit]
Avicenna argued for the distinctness of the soul and the body, and the incorruptibility of the former.
Aquinas[edit]
The full argument for the immortality of the soul and Thomas Aquinas' elaboration of Aristotelian theory is found in Question 75 of the First Part of the Summa Theologica.
Descartes[edit]
René Descartes endorses the claim that the soul is simple, and also that this entails that it cannot decompose. Descartes does not address the possibility that the soul might suddenly disappear.
Leibniz[edit]
In early work, Gottfried Wilhelm Leibniz endorses a version of the argument from the simplicity of the soul to its immortality, but like his predecessors, he does not address the possibility that the soul might suddenly disappear. In his monadology he advances a sophisticated novel argument for the immortality of monads.
Moses Mendelssohn[edit]
Moses Mendelssohn's Phaedon is a defense of the simplicity and immortality of the soul. It is a series of three dialogues, revisiting the Platonic dialogue Phaedo, in which Socrates argues for the immortality of the soul, in preparation for his own death. Many philosophers, including Plotinus, Descartes, and Leibniz, argue that the soul is simple, and that because simples cannot decompose they must be immortal. In the Phaedon, Mendelssohn addresses gaps in earlier versions of this argument (an argument that Kant calls the Achilles of Rationalist Psychology). The Phaedon contains an original argument for the simplicity of the soul, and also an original argument that simples cannot suddenly disappear. It contains further original arguments that the soul must retain its rational capacities as long as it exists.
Ethics[edit]
See also: Life extension § Ethics and politics
The possibility of clinical immortality raises a host of medical, philosophical, and religious issues and ethical questions. These include persistent vegetative states, the nature of personality over time, technology to mimic or copy the mind or its processes, social and economic disparities created by longevity, and survival of the heat death of the universe.
Undesirability[edit]
Physical immortality has also been imagined as a form of eternal torment, as in the myth of Tithonus, or in Mary Shelley's short story The Mortal Immortal, where the protagonist lives to witness everyone he cares about die around him. For additional examples in fiction, see Immortality in fiction.
Kagan (2012) argues that any form of human immortality would be undesirable. Kagan's argument takes the form of a dilemma. Either our characters remain essentially the same in an immortal afterlife, or they do not:
If our characters remain basically the same – that is, if we retain more or less the desires, interests, and goals that we have now – then eventually, over an infinite stretch of time, we will get bored and find eternal life unbearably tedious.
If, on the other hand, our characters are radically changed – e.g., by God periodically erasing our memories or giving us rat-like brains that never tire of certain simple pleasures – then such a person would be too different from our current self for us to care much what happens to them.
Either way, Kagan argues, immortality is unattractive. The best outcome, Kagan argues, would be for humans to live as long as they desired and then to accept death gratefully as rescuing us from the unbearable tedium of immortality.
Sociology[edit]
If human beings were to achieve immortality, there would most likely be a change in the world's social structures. Sociologists argue that human beings' awareness of their own mortality shapes their behavior. With the advancements in medical technology in extending human life, there may need to be serious considerations made about future social structures. The world is already experiencing a global demographic shift of increasingly ageing populations with lower replacement rates. The social changes that are made to accommodate this new population shift may be able to offer insight on the possibility of an immortal society.
Sociology has a growing body of literature on the sociology of immortality, which details the different attempts at reaching immortality (whether actual or symbolic) and their prominence in the 21st century. These attempts include renewed attention to the dead in the West, practices of online memorialization, and biomedical attempts to increase longevity. These attempts at reaching immortality and their effects in societal structures have led some to argue that we are becoming a "Postmortal Society". Foreseen changes to societies derived from the pursuit of immortality would encompass societal paradigms and worldviews, as well as the institutional landscape. Similarly, different forms of reaching immortality might entail a significant reconfiguration of societies, from becoming more technologically oriented to becoming more aligned with nature.
Immortality would increase population growth, bringing with it many consequences as for example the impact of population growth on the environment and planetary boundaries.
Politics[edit]
Although some scientists state that radical life extension, delaying and stopping aging are achievable, there are no international or national programs focused on stopping aging or on radical life extension. In 2012 in Russia, and then in the United States, Israel and the Netherlands, pro-immortality political parties were launched. They aimed to provide political support to anti-aging and radical life extension research and technologies and at the same time transition to the next step, radical life extension, life without aging, and finally, immortality and aim to make possible access to such technologies to most currently living people.
Some scholars critique the increasing support for immortality projects. Panagiotis Pentaris speculates that defeating ageing as the cause of death comes with a cost: "heightened stratification of humans in society and a wider gap between social classes". Others suggest that other immortality projects like transhumanist digital immortality, radical life extension and cryonics are part of the capitalist fabric of exploitation and control, which aims to extend privileged lives of the economic elite. In this sense, immortality could become a political-economic battleground for the twenty-first century between the haves and have-nots.
Symbols[edit]
The ankh
There are numerous symbols representing immortality. The ankh is an Egyptian symbol of life that holds connotations of immortality when depicted in the hands of the gods and pharaohs, who were seen as having control over the journey of life. The Möbius strip in the shape of a trefoil knot is another symbol of immortality. Most symbolic representations of infinity or the life cycle are often used to represent immortality depending on the context they are placed in. Other examples include the Ouroboros, the Chinese fungus of longevity, the ten kanji, the phoenix, the peacock in Christianity, and the colors amaranth (in Western culture) and peach (in Chinese culture).
See also[edit]
Afterlife
Akal (Sikh term)
Ambrosia
Amrita
Bioethics
Biogerontology
Brooke Greenberg
Crown of Immortality
Dyson's eternal intelligence
Elixir of life
Eternal return
Eternal youth
Ghost
Immortal DNA strand hypothesis
Immortalist Society
Immortality in fiction
Lich
List of people claimed to be immortal in myth and legend
Methuselah Mouse Prize
Molecular nanotechnology
Negligible senescence
Tipler's Omega Point
Organlegging
Neidan
Posthuman
Resurrection
Queen Mother of the West
Simulated reality
Suspended animation
Undead
Regeneration (theology)
Footnotes[edit]
^
The basic idea is to take a particular brain, scan its structure in detail, and construct a software model of it that is so faithful to the original that, when run on appropriate hardware, it will behave in essentially the same way as the original brain.
— Sandberg & Boström (2008)
^
"Even as we are conscious of the broad and very common biblical usage of the term "soul", we must be clear that scripture does not present even a rudimentarily developed theology of the soul. The creation narrative is clear that all life originates with God. Yet the Hebrew scripture offers no specific understanding of the origin of individual souls, of when and how they become attached to specific bodies, or of their potential existence, apart from the body, after death. The reason for this is that, as we noted at the beginning, the Hebrew Bible does not present a theory of the soul developed much beyond the simple concept of a force associated with respiration, hence, a life-force."
^
In the New Testament, "soul" (orig. ψυχή ) retains its basic Hebrew sense of meaning. "Soul" refers to one’s life: Herod sought Jesus' soul (Matt. 2:20); one might save a soul or take it (Mark 3:4); death occurs when God "requires your soul" (Luke 12:20).
^ For Avicenna's views, see:
Moussa, Dunya, & Zayed (1960);
Arberry (1964);
Michot (1986);
Janssen (1987);
Marmura (2005)(complete translation).
Notes[edit]
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^
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^ 2 Maccabees 7.11, 28
^ 1 Enoch. 61.2, 5.
^ 2 Baruch. 50.2, 51.5.
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^
Josephus. Antiquities of the Jews. 18.16;
Matthew 22.23; Mark 12.18; Luke 20.27; Acts 23.8
^ Acts 23.8
^
Josephus. Jewish War. 2.8.14; cf.
Josephus. Antiquities of the Jews. 8.14–15.
^ Book of Jubilees. 23.31.
^ Maharishi Mahesh Yogi on the Bhagavad-Gita, a New Translation and Commentary, Chapter 1–6. Penguin Books, 1969, pp. 94–95 (v 15)
^ "vallalar.org". vallalar.org. 7 July 2010. Retrieved 4 November 2010.
^ Adam Schroeder (6 March 2010). In the Fabled East: A Novel. D & M Publishers. p. 174. ISBN 978-1553656159.
^ Rangdrol & Matthieu 2001, p. 153.
^ Emma and Ludwig Edelstein, Asclepius: Collection and Interpretation of the Testimonies, Volume 1, Page 51
^ Sabine G. MacCormack Concise Encyclopedia of Greek and Roman Mythology p.47
^ Theony Condos, Star Myths of the Greeks and Romans, p.141
^ Endsjø, Greek Resurrection Beliefs, 54-64; cf. Finney, Resurrection, Hell and the Afterlife, 13-20.
^ N.T. Wright, The Resurrection of the Son of God (2003), p.53
^ Parallel Lives, Life of Romulus 28:4-6
^ Collins, Adela Yarbro (2009), "Ancient Notions of Transferal and Apotheosis", pp 46,51
^ Justin Martyr. First Apology. 21.
^ Hoshang, J. Bhadha, Dr. (nd). "Effect of wearing cap on Zarathustri Urvaan". Zoroastrianism. topic 33. Archived from the original on 27 July 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
^ archive.org/1/items/proseedda00snor/proseedda00snor.pdf
^ https://logoilibrary.com/wp-content/uploads/2019/07/The-Viking-Spirit-Daniel-McCoy.pdf
^ Crossley-Holland, Kevin (4 January 1980). The Norse myths. Knopf Doubleday Publishing. ISBN 978-0-394-74846-7.
^ "H.R. Ellis Davidson - Gods and Myths of Northern Europe | PDF | Religion and Belief".
^ Creel, Herrlee G. (1982). What is Taoism?: and other studies in Chinese cultural history. Chicago: University of Chicago Press. p. 17. ISBN 978-0226120478.
^ Maspero, Henri. Translated by Frank A. Kierman, Jr. Taoism and Chinese Religion (University of Massachusetts Press, 1981), p. 211.
^ Robinet, Isabelle. Taoism: Growth of a Religion (Stanford: Stanford University Press, 1997 [original French 1992]), p. 3–4.
^ Translated by Legge, James. The Texts of Taoism. 1962, Dover Press. NY.
^ "Alcmaeon". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. 2021.
^ "Plato". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. 2017.
^ Henry, D. (2008) "The Neoplatonic Achilles" in "The Achilles of Rationalist Psychology". Springer. Volume 7 of the series Studies in the History of Philosophy of Mind pp. 59–74.
^ "Byzantine Philosophy". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab. Stanford University. 2018.
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Moussa, Mohammad Youssef; Dunya, Solayman; Zayed, Sa'id, eds. (1960). Avicenna's Metaphysics: Al-Shifâ', Al-Ilâhiyyât. Vol. II. Cairo, EG: Organisme Général des Imprimeries Gouvernementales. pp. 431–432.
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Aspects of Islamic Civilization. Translated by Arberry, A.J. London, UK: George Allen & Unwin. 1964. p. 153.
^
Michot, Jean R. (1986). La destinée de l'homme selon Avicenne. Louvain: Peeters. pp. 22–56, esp. 26–27, 43.
^
Janssen, J. (1987). "Ibn Sînâ's ideas of ultimate realities, neoplatonism and the Qur'ân as problem-solving paradigms in the Avicennian system". Ultimate Reality and Meaning. 10: 259–261.
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Marmura, Michael (2005). Avicenna: The metaphysics of the healing. Provo, UT: Brigham Young University Press.
^ "Saint Thomas Aquinas". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. 2018.
^ Rozemond, M. (2010). "Descartes and the Immortality of the Soul". in Mind, Method and Morality: Essays in Honor of Anthony Kenny. Oxford University Press.
^ "Gottfried Wilhelm Leibniz". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. 2020.
^ Sassen, B. (2008). "Kant and Mendelssohn on the Implications of the 'I Think' ".in "The Achilles of Rationalist Psychology". Springer. Volume 7 of the series Studies in the History of Philosophy of Mind pp. 59–74.
^
Kagan, Shelly (2012). Death. New Haven, CT: Yale University Press. pp. 238–246.
Kagan notes that his argument is an adaptation of a similar argument given by the British philosopher B. Williams (1973).
^
Williams, B. (1973). Problems of the Self.
^ [Dossey, Larry; In: Explore: The Journal of Science & Healing; Mar/Apr2017; v.13. n.2, 81–87. 7p. (editorial) ISSN 1550-8307 PMID 28108110, Database: CINAHL Complete]
^ He, Goodkind, Kowal, Wan, Daniel, Paul (March 2016). "An Aging World: 2015". International Population Reports: U.S. Census Bureau. 1 (16): 1–30. Retrieved 1 March 2018.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Walter, Tony (2 October 2019). "The pervasive dead". Mortality. 24 (4): 389–404. doi:10.1080/13576275.2017.1415317. ISSN 1357-6275.
^ Elaine Kasket MA, Psy D (1 July 2012). "Continuing bonds in the age of social networking: Facebook as a modern-day medium". Bereavement Care. 31 (2): 62–69. doi:10.1080/02682621.2012.710493. ISSN 0268-2621. S2CID 218602211.
^ Lafontaine, Céline (September 2009). "The Postmortal Condition: From the Biomedical Deconstruction of Death to the Extension of Longevity". Science as Culture. 18 (3): 297–312. doi:10.1080/09505430903123008. ISSN 0950-5431. S2CID 145387514.
^ Postmortal society towards a sociology of immortality. Michael Hviid Jacobsen. London; New York. 2018. ISBN 978-0-367-08538-4. OCLC 1107015985.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: others (link)
^ Hurtado Hurtado, Joshua (25 January 2021). "Towards a postmortal society of virtualised ancestors? The Virtual Deceased Person and the preservation of the social bond". Mortality. 28: 90–105. doi:10.1080/13576275.2021.1878349. hdl:10138/353467. ISSN 1357-6275.
^ Hurtado Hurtado, Joshua (18 July 2022). "Envisioning postmortal futures: six archetypes on future societal approaches to seeking immortality". Mortality. 29: 18–36. doi:10.1080/13576275.2022.2100250. ISSN 1357-6275. S2CID 250650618.
^ Gavrilov, Leonid A.; Gavrilova, Natalia S. (April 2010). "Demographic Consequences of Defeating Aging". Rejuvenation Research. 13 (2–3): 329–334. doi:10.1089/rej.2009.0977. ISSN 1549-1684. PMC 3192186. PMID 20426616.
^ "Scientists' Open Letter on Aging". Retrieved 20 April 2015.
^ "A Single-Issue Political Party for Longevity Science". Fight Aging!. 27 July 2012. Retrieved 20 April 2015.
^ Pentaris, Panagiotis (2021). Dying in a transhumanist and posthuman society. Abingdon / New York: Routledge. p. 83.
^ Hurtado Hurtado, Joshua (9 October 2023). "Exploited in immortality: techno-capitalism and immortality imaginaries in the twenty-first century". Mortality: 1–18. doi:10.1080/13576275.2023.2266373. ISSN 1357-6275.
^ Huberman, Jenny (2022). "Funding Immortality: Making Futures in the Era of Techno-Philanthropy". Études sur la mort. 157 (1).
^ Wilson, Ralph F. "Peacock as an Ancient Christian Symbol of Eternal Life". Jesus Walk Bible Study Series. Retrieved 18 January 2011. | biology | 690697 | https://da.wikipedia.org/wiki/Procesteologi | Procesteologi | Procesteologi er en teologisk tænkning baseret på filosoffen og matematikeren Alfred North Whiteheads filosofi, kendt som procesmetafysik. Den er udviklet især af Charles Hartstorne og John B. Cobb.
Procesteologerne tager udgangspunkt i at verden er i stadig udvikling, og dermed er også gudsforståelsen det. Virkelighedsforståelse og gudsforståelse afspejler hinanden. Procesteologer lægger vægt på at enhver tid har sine måder at beskrive Gud på, ud fra sine erfaringer og sin virkelighedsopfattelse. Beskrivelsen af Gud er ikke givet en gang for alle, men er i stadig udvikling og ændring.
En af de første teologer der blev interesserede i Whiteheads tænkning var den kommende Ærkebiskob af Canterbury, William Temple. I Temples Gifford Lectures fra 1932-1934 (senere udgivet som "Nature, Man and God") figurerer Whitehead som en af flere filosoffer, der forfægter begrebet om emergent evolution, som Temple interesserer sig for Senere var interessen for Whitehead centreret omkring University of Chicago's Divinity School, hvor Henry Nelson Wieman startede en procesteologisk bølge, der varede omkring tredive år. Professorer som Wieman, Charles Hartshorne, Bernard Loomer, Bernard Meland, and Daniel Day Williams gjorde Whiteheads filosofi til den vigtigste indflydelse her. De uddannede flere generationer af Whiteheadeeksperter, hvoraf den mest kendte er John B. Cobb, Jr. Interessen for Whitehead døde ud i Chicago, men Cobb bragte den videre til Claremont, California, hvor han blev ansat i 1958 ved Claremont School of Theology. 1973 grundlagde han, sammen med David Ray Griffin, Center for Process Studies. På grund af Cobb er Claremont stadigt i dag stærkt præget af Whiteheads tænknng.
Procesteologer understreger typisk Guds relationelle natur. I stedet for at se Gud som urørlig eller følelsesløs, ser procesteologier Gud som "the fellow sufferer who understands", og som det væsen der er mest påvirket af begivenheder. Hartstorne understreger, at mennesker ikke ville hylde en menneskelig leder, der var upåvirket af hans følgeres glæder eller sorger, og spørger, hvorfor dette skulle være en prisværdig kvalitet for Gud. Da Gud er det væsen, der er mest påvirket af verden, er Gud samtidigt det væsen, som kan reagere mest passende i forhold til verden.
Procesteologi findes i mange forskellige versioner. C. Robert Mesle, er f.eks. fortaler for en "process naturalism", dvs. en procesteologi uden Gud. Procesteologi er vanskeligt at definere, da procesteologer er så diverse og flerdisciplinære i deres synspunkter og interesser. John B. Cobb, Jr. har også udgivet bøger om biologi og økonomi. Roland Faber og Catherine Keller forbinder Whitehead med poststrukturalisme, postkolonialisme og feministisk teori. Charles Birch var både teolog og genetiker. Franklin I. Gamwell skriver om teologi og politisk teologi. I Syntheism - Creating God in The Internet Age''' mener futorologerne Alexander Bard ogJan Söderqvist at procesteoologi vil forbinde sig med den deltagende kultur, de forventer vil dominere den digitale tidsalder.
Whiteheads gudsbegreb
Whiteheads ide om Gud adskiller sig fra traditionelle monoteistiske ideer. Hans måske mest kendte kritik af kristendommens gudsbegreb er den, at "the Church gave unto God the attributes which belonged exclusively to Caesar." Whitehead kritiserer kristendommen for at definere Gud som primært en guddommelig konge, som påtvinger verden sin vilje, og hvis mest vigtige attribut er magt. Overfor de mest udbredte former for kristendom, forfægtede Whitehead et gudsbegreb som han kaldte "den korte gallilæiske vision af ydmyghed":
"It does not emphasize the ruling Caesar, or the ruthless moralist, or the unmoved mover. It dwells upon the tender elements in the world, which slowly and in quietness operates by love; and it finds purpose in the present immediacy of a kingdom not of this world. Love neither rules, nor is it unmoved; also it is a little oblivious as to morals. It does not look to the future; for it finds its own reward in the immediate present."
For Whitehead er Gud ikke nødvendigvis forbundet med religion. I stedet for at stamme fra religiøs tro, mente Whitehead at Gud var en nødvendighed for hans metafysiske system. Hans system nødvendiggjorde, at der fandtes en orden i mulighederne, en orden, der tillod nye ting i verden, og som gav et formål til alle entiteter. Whitehead postulerede at disse ordnede potentialer findes i, hvad han kalder Guds primordial nature. Men Whitehead var også interesseret i religiøs erfaring. Det førte ham til at overveje mere intenst, hvad han så som Guds anden natur, consequent nature. Whiteheads gudsbegreb som en "dipolær" entitet har tiltrukket teologisk interesse.
Guds primordial nature beskrev han som "the unlimited conceptual realization of the absolute wealth of potentiality,", dvs, universets ubegrænsede mulighed. Denne primordial nature er evig og uforanderlig, hvilket giver entiteterne i universet muligheder, som de kan realisere. Whitehead kalder også det primordiale aspekt for "the lure for feeling, the eternal urge of desire,", der trækker entiteterne i universet imod endnu uvirkeliggjorte muligheder.
Guds consequent nature er på den anden side alt andet end uforanderlig. Den er Guds modtagelse af verdens aktivitet. Som Whitehead siger "God saves the world as it passes into the immediacy of his own life. It is the judgment of a tenderness which loses nothing that can be saved." Mao. bevarer Gud alle erfaringer for evigt, og disse erfaringer ændrer den måde, hvormed Gud interagerer med verden. Således forandres Gud virkeligt af hvad der sker i verden og i universet som sådan, hvilket giver en uendelig betydning til endelige skabningers handlinger.
Whitehead ser altså Gud og verden som gensidigt kompletterende hinanden. Han ser entiteter i verden som flydende og foranderlige ting, der længes efter en permanens, kun Gud kan tilbyde, ved at optage dem i Guds selv, hvorved de forandrer Gud, og påvirker resten af universet for evigt. På den anden side ser han Gud som permanent, men som mangelfuld i aktualitet og forandring; isoleret set er Gud ikke andet end evigt urealiserede muligheder, og har brug for en verden til at realisere dem. Gud giver skabninger permanens, mens skabningerne giver Gud aktualitet og forandring.
"In this way God is completed by the individual, fluent satisfactions of finite fact, and the temporal occasions are completed by their everlasting union with their transformed selves, purged into conformation with the eternal order which is the final absolute 'wisdom.' The final summary can only be expressed in terms of a group of antitheses, whose apparent self-contradictions depend on neglect of the diverse categories of existence. In each antithesis there is a shift of meaning which converts the opposition into a contrast.
"It is as true to say that God is permanent and the World fluent, as that the World is permanent and God is fluent.
"It is as true to say that God is one and the World many, as that the World is one and God many.
"It is as true to say that, in comparison with the World, God is actual eminently, as that, in comparison with God, the World is actual eminently.
"It is as true to say that the World is immanent in God, as that God is immanent in the World.
"It is as true to say that God transcends the World, as that the World transcends God.
"It is as true to say that God creates the World, as that the World creates God ...
"What is done in the world is transformed into a reality in heaven, and the reality in heaven passes back into the world ... In this sense, God is the great companion – the fellow-sufferer who understands."
Ovenstående var medvirkende til at inspirere procesteologi.Roland Faber, God as Poet of the World: Exploring Process Theologies (Louisville: Westminster John Knox Press, 2008), chapter 1.
Procesteologer
Bradley Shavit Artson
Thomas Berry
Charles Birch
Joseph A. Bracken
Philip Clayton
John B. Cobb
Monica Coleman
Bruce G. Epperly
Roland Faber
Paul S. Fiddes
Stephen T. Franklin
Terence E. Fretheim
Franklin I. Gamwell
David Ray Griffin
Charles Hartshorne
Nancy R. Howell
Tony Jones
William E. Kaufman
Catherine Keller
Harold Kushner
Michael Lerner
C. Robert Mesle
Jay McDaniel
Schubert M. Ogden
Thomas Jay Oord
Blake Ostler
Arthur Peacocke
Norman Pittenger
Richard Rice
Marjorie Hewitt Suchocki
Alfred North Whitehead
Daniel Day Williams
George V. Pixley
Litteratur
Bruce G. Epperly Process Theology: A Guide for the Perplexed (NY: T&T Clark, 2011, )
Marjorie Hewitt Suchocki's God Christ Church: A Practical Guide to Process Theology, new rev. ed. (New York: Crossroad, 1989, )
C. Robert Mesle's Process Theology: A Basic Introduction (St. Louis: Chalice Press, 1993, )
Schubert M. Ogden The Reality of God and Other Essays (Dallas: Southern Methodist University Press, 1992, ); John B. Cobb, Doubting Thomas: Christology in Story Form (New York: Crossroad, 1990, );
Charles Hartshorne, Omnipotence and Other Theological Mistakes (Albany: State University of New York Press, 1984, )
Richard Rice, God's Foreknowledge & Man's Free Will (Minneapolis, Minn.: Bethany House Publishers, 1985
André Gounelle, Le Dynamisme Créateur de Dieu: Essai sur la Théologie du Process, édition revue, modifiée et augmentee (Paris: Van Dieren, 2000, ).
Bryan P. Stone og Thomas Jay Oord, Thy Nature and Thy Name is Love: Wesleyan and Process Theologies in Dialogue (Nashville: Kingswood, 2001, ).
Paul S. Fiddes: The Creative Suffering of God (Oxford: Oxford University Press, 1992); see also his short overview "Process Theology," in A. E. McGrath, ed., The Blackwell Encyclopaedia of Modern Christian Thought (Oxford: Blackwell, 1993), 472–76.
Norman Pittenger: God in Process, London: SCM Press, 1967-
Norman Pittenger:'Process-Thought and Christian Faith (New York: Macmillan Company, 1968.
Norman Pittenger:Becoming and Belonging (Wilton, CT: Morehouse Publications, 1989, ).
Constance Wise: Hidden Circles in the Web: Feminist Wicca, Occult Knowledge, and Process Thought (Lanham, Md.: AltaMira Press, 2008, )
Michel Weber, « Shamanism and proto-consciousness », i René Lebrun, Julien De Vos et É. Van Quickelberghe (éds), Deus Unicus, Turnhout, Brepols, coll. Homo Religiosus série II, 14, 2015, pp. 247–260.
Eksterne links
The Center for Process Studies
Process and Faith
Noter
Teologi | danish | 0.531654 |
immortal_organisms/Biological_immortality.txt | Biological immortality (sometimes referred to as bio-indefinite mortality) is a state in which the rate of mortality from senescence is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or after living long enough. A biologically immortal living being can still die from means other than senescence, such as through injury, poison, disease, predation, lack of available resources, or changes to environment.
This definition of immortality has been challenged in the Handbook of the Biology of Aging, because the increase in rate of mortality as a function of chronological age may be negligible at extremely old ages, an idea referred to as the late-life mortality plateau. The rate of mortality may cease to increase in old age, but in most cases that rate is typically very high.
The term is also used by biologists to describe cells that are not subject to the Hayflick limit on how many times they can divide.
Cell lines[edit]
Main articles: Cell culture and Immortalised cell line
Biologists chose the word "immortal" to designate cells that are not subject to the Hayflick limit, the point at which cells can no longer divide due to DNA damage or shortened telomeres. Prior to Leonard Hayflick's theory, Alexis Carrel hypothesized that all normal somatic cells were immortal.
The term "immortalization" was first applied to cancer cells that expressed the telomere-lengthening enzyme telomerase, and thereby avoided apoptosis—i.e. cell death caused by intracellular mechanisms. Among the most commonly used cell lines are HeLa and Jurkat, both of which are immortalized cancer cell lines. These cells have been and still are widely used in biological research such as creation of the polio vaccine, sex hormone steroid research, and cell metabolism. Embryonic stem cells and germ cells have also been described as immortal.
Immortal cell lines of cancer cells can be created by induction of oncogenes or loss of tumor suppressor genes. One way to induce immortality is through viral-mediated induction of the large T-antigen, commonly introduced through simian virus 40 (SV-40).
Organisms[edit]
According to the Animal Aging and Longevity Database, the list of animals with negligible aging (along with estimated longevity in the wild) includes:
Blanding's turtle (Emydoidea blandingii) – 77 years
Olm (Proteus anguinus) – 102 years
Eastern box turtle (Terrapene carolina) – 138 years
Red sea urchin (Strongylocentrotus franciscanus) – 200 years
Rougheye rockfish (Sebastes aleutianus) – 205 years
Ocean quahog clam (Arctica islandica) – 507 years
Greenland shark (Somniosus microcephalus) - 250 to 500 years
In 2018, scientists working for Calico, a company owned by Alphabet, published a paper in the journal eLife which presents possible evidence that Heterocephalus glaber (Naked mole rat) do not face increased mortality risk due to aging.
Bacteria and some yeast[edit]
Many unicellular organisms age: as time passes, they divide more slowly and ultimately die. Asymmetrically dividing bacteria and yeast also age. However, symmetrically dividing bacteria and yeast can be biologically immortal under ideal growing conditions. In these conditions, when a cell splits symmetrically to produce two daughter cells, the process of cell division can restore the cell to a youthful state. However, if the parent asymmetrically buds off a daughter only the daughter is reset to the youthful state—the parent is not restored and will go on to age and die. In a similar manner stem cells and gametes can be regarded as "immortal".
Hydra[edit]
Hydra
Hydras are a genus of the Cnidaria phylum. All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Hydras are simple, freshwater animals possessing radial symmetry and contain post-mitotic cells (cells that will never divide again) only in the extremities. All hydra cells continually divide. It has been suggested that hydras do not undergo senescence, and, as such, are biologically immortal. In a four-year study, 3 cohorts of hydra did not show an increase in mortality with age. It is possible that these animals live much longer, considering that they reach maturity in 5 to 10 days. However, this does not explain how hydras are subsequently able to maintain telomere lengths.
Jellyfish[edit]
Turritopsis dohrnii, or Turritopsis nutricula, is a small (5 millimeters (0.20 in)) species of jellyfish that uses transdifferentiation to replenish cells after sexual reproduction. This cycle can repeat indefinitely, potentially rendering it biologically immortal. This organism originated in the Caribbean sea, but has now spread around the world. Key molecular mechanisms of its rejuvenation appear to involve DNA replication and repair, and stem cell renewal, according to a comparative genomics study.
Similar cases include hydrozoan Laodicea undulata and scyphozoan Aurelia sp.1.
Lobsters[edit]
Further information: Lobster § Longevity
Research suggests that lobsters may not slow down, weaken, or lose fertility with age, and that older lobsters may be more fertile than younger lobsters. This does not however make them immortal in the traditional sense, as they are significantly more likely to die at a shell moult the older they get (as detailed below).
Their longevity may be due to telomerase, an enzyme that repairs long repetitive sections of DNA sequences at the ends of chromosomes, referred to as telomeres. Telomerase is expressed by most vertebrates during embryonic stages but is generally absent from adult stages of life. However, unlike vertebrates, lobsters express telomerase as adults through most tissue, which has been suggested to be related to their longevity. Contrary to popular belief, lobsters are not immortal. Lobsters grow by moulting, which requires considerable energy, and the larger the shell the more energy is required. Eventually, the lobster will die from exhaustion during a moult. Older lobsters are also known to stop moulting, which means that the shell will eventually become damaged, infected, or fall apart, causing them to die. The European lobster has an average life span of 31 years for males and 54 years for females.
Planarian flatworms[edit]
Polycelis felina, a freshwater planarian
Planarian flatworms have both sexually and asexually reproducing types. Studies on genus Schmidtea mediterranea suggest these planarians appear to regenerate (i.e. heal) indefinitely, and asexual individuals have an "apparently limitless [telomere] regenerative capacity fueled by a population of highly proliferative adult stem cells". "Both asexual and sexual animals display age-related decline in telomere length; however, asexual animals are able to maintain telomere lengths somatically (i.e. during reproduction by fission or when regeneration is induced by amputation), whereas sexual animals restore telomeres by extension during sexual reproduction or during embryogenesis like other sexual species. Homeostatic telomerase activity observed in both asexual and sexual animals is not sufficient to maintain telomere length, whereas the increased activity in regenerating asexuals is sufficient to renew telomere length... "
For sexually reproducing planaria: "the lifespan of individual planarian can be as long as 3 years, likely due to the ability of neoblasts to constantly replace aging cells". Whereas for asexually reproducing planaria: "individual animals in clonal lines of some planarian species replicating by fission have been maintained for over 15 years".
See also[edit]
Aging brain
American Academy of Anti-Aging Medicine
Calico (company)
Cryptobiosis
DNA damage theory of aging
Maximum life span
Methuselah Foundation
Reliability theory of aging and longevity
Rejuvenation (aging)
Strategies for engineered negligible senescence (SENS)
Telomerase in cancer cell
Timeline of senescence research | biology | 4813461 | https://sv.wikipedia.org/wiki/Biophytum%20polyphyllum | Biophytum polyphyllum | Biophytum polyphyllum är en harsyreväxtart som beskrevs av William Munro. Biophytum polyphyllum ingår i släktet Biophytum och familjen harsyreväxter. Inga underarter finns listade i Catalogue of Life.
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Harsyreväxter
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immortal_organisms/Senescence.txt | Senescence (/sɪˈnɛsəns/) or biological aging is the gradual deterioration of functional characteristics in living organisms. The word senescence can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence involves an increase in death rates and/or a decrease in fecundity with increasing age, at least in the later part of an organism's life cycle. However, the resulting effects of senescence can be delayed. The 1934 discovery that calorie restriction can extend lifespans by 50% in rats, the existence of species having negligible senescence, and the existence of potentially immortal organisms such as members of the genus Hydra have motivated research into delaying senescence and thus age-related diseases. Rare human mutations can cause accelerated aging diseases.
Environmental factors may affect aging – for example, overexposure to ultraviolet radiation accelerates skin aging. Different parts of the body may age at different rates and distinctly, including the brain, the cardiovascular system, and muscle. Similarly, functions may distinctly decline with aging, including movement control and memory. Two organisms of the same species can also age at different rates, making biological aging and chronological aging distinct concepts.
Definition and characteristics[edit]
Organismal senescence is the aging of whole organisms. Actuarial senescence can be defined as an increase in mortality and/or a decrease in fecundity with age. The Gompertz–Makeham law of mortality says that the age-dependent component of the mortality rate increases exponentially with age.
Aging is characterized by the declining ability to respond to stress, increased homeostatic imbalance, and increased risk of aging-associated diseases including cancer and heart disease. Aging has been defined as "a progressive deterioration of physiological function, an intrinsic age-related process of loss of viability and increase in vulnerability."
In 2013, a group of scientists defined nine hallmarks of aging that are common between organisms with emphasis on mammals:
genomic instability,
telomere attrition,
epigenetic alterations,
loss of proteostasis,
deregulated nutrient sensing,
mitochondrial dysfunction,
cellular senescence,
stem cell exhaustion,
altered intercellular communication
In a decadal update, three hallmarks have been added, totaling 12 proposed hallmarks:
disabled macroautophagy
chronic inflammation
dysbiosis
The environment induces damage at various levels, e.g. damage to DNA, and damage to tissues and cells by oxygen radicals (widely known as free radicals), and some of this damage is not repaired and thus accumulates with time. Cloning from somatic cells rather than germ cells may begin life with a higher initial load of damage. Dolly the sheep died young from a contagious lung disease, but data on an entire population of cloned individuals would be necessary to measure mortality rates and quantify aging.
The evolutionary theorist George Williams wrote, "It is remarkable that after a seemingly miraculous feat of morphogenesis, a complex metazoan should be unable to perform the much simpler task of merely maintaining what is already formed."
Variation among species[edit]
Further information: Longevity § Non-human biological longevity
Different speeds with which mortality increases with age correspond to different maximum life span among species. For example, a mouse is elderly at 3 years, a human is elderly at 80 years, and ginkgo trees show little effect of age even at 667 years.
Almost all organisms senesce, including bacteria which have asymmetries between "mother" and "daughter" cells upon cell division, with the mother cell experiencing aging, while the daughter is rejuvenated. There is negligible senescence in some groups, such as the genus Hydra. Planarian flatworms have "apparently limitless telomere regenerative capacity fueled by a population of highly proliferative adult stem cells." These planarians are not biologically immortal, but rather their death rate slowly increases with age. Organisms that are thought to be biologically immortal would, in one instance, be Turritopsis dohrnii, also known as the "immortal jellyfish", due to its ability to revert to its youth when it undergoes stress during adulthood. The reproductive system is observed to remain intact, and even the gonads of Turritopsis dohrnii are existing.
Some species exhibit "negative senescence", in which reproduction capability increases or is stable, and mortality falls with age, resulting from the advantages of increased body size during aging.
Theories of aging[edit]
This section needs expansion. You can help by adding to it. (March 2023)
More than 300 different theories have been posited to explain the nature (mechanisms) and causes (reasons for natural emergence or factors) of aging. Good theories would both explain past observations and predict the results of future experiments. Some of the theories may complement each other, overlap, contradict, or may not preclude various other theories.
Theories of aging fall into two broad categories, evolutionary theories of aging and mechanistic theories of aging. Evolutionary theories of aging primarily explain why aging happens, but do not concern themselves with the molecular mechanism(s) that drive the process. All evolutionary theories of aging rest on the basic mechanisms that the force of natural selection declines with age. Mechanistic theories of aging can be divided into theories that propose aging is programmed, and damage accumulation theories, i.e. those that propose aging to be caused by specific molecular changes occurring over time.
This section is an excerpt from Stem cell theory of aging § Other theories of aging.[edit]
The aging process can be explained with different theories. These are evolutionary theories, molecular theories, system theories and cellular theories. The evolutionary theory of ageing was first proposed in the late 1940s and can be explained briefly by the accumulation of mutations (evolution of ageing), disposable soma and antagonistic pleiotropy hypothesis. The molecular theories of ageing include phenomena such as gene regulation (gene expression), codon restriction, error catastrophe, somatic mutation, accumulation of genetic material (DNA) damage (DNA damage theory of aging) and dysdifferentiation. The system theories include the immunologic approach to ageing, rate-of-living and the alterations in neuroendocrinal control mechanisms. (See homeostasis). Cellular theory of ageing can be categorized as telomere theory, free radical theory (free-radical theory of aging) and apoptosis. The stem cell theory of aging is also a sub-category of cellular theories.
Evolutionary aging theories[edit]
Main article: Evolution of ageing
Antagonistic pleiotropy[edit]
Main article: Antagonistic pleiotropy hypothesis
One theory was proposed by George C. Williams and involves antagonistic pleiotropy. A single gene may affect multiple traits. Some traits that increase fitness early in life may also have negative effects later in life. But, because many more individuals are alive at young ages than at old ages, even small positive effects early can be strongly selected for, and large negative effects later may be very weakly selected against. Williams suggested the following example: Perhaps a gene codes for calcium deposition in bones, which promotes juvenile survival and will therefore be favored by natural selection; however, this same gene promotes calcium deposition in the arteries, causing negative atherosclerotic effects in old age. Thus, harmful biological changes in old age may result from selection for pleiotropic genes that are beneficial early in life but harmful later on. In this case, selection pressure is relatively high when Fisher's reproductive value is high and relatively low when Fisher's reproductive value is low.
Cancer versus cellular senescence tradeoff theory of aging[edit]
Main article: Immunosenescence
Senescent cells within a multicellular organism can be purged by competition between cells, but this increases the risk of cancer. This leads to an inescapable dilemma between two possibilities—the accumulation of physiologically useless senescent cells, and cancer—both of which lead to increasing rates of mortality with age.
Disposable soma[edit]
Main article: Disposable soma theory of aging
The disposable soma theory of aging was proposed by Thomas Kirkwood in 1977. The theory suggests that aging occurs due to a strategy in which an individual only invests in maintenance of the soma for as long as it has a realistic chance of survival. A species that uses resources more efficiently will live longer, and therefore be able to pass on genetic information to the next generation. The demands of reproduction are high, so less effort is invested in repair and maintenance of somatic cells, compared to germline cells, in order to focus on reproduction and species survival.
Programmed aging theories[edit]
Programmed theories of aging posit that aging is adaptive, normally invoking selection for evolvability or group selection.
The reproductive-cell cycle theory suggests that aging is regulated by changes in hormonal signaling over the lifespan.
Damage accumulation theories[edit]
The free radical theory of aging[edit]
Main article: Free-radical theory of aging
One of the most prominent theories of aging was first proposed by Harman in 1956. It posits that free radicals produced by dissolved oxygen, radiation, cellular respiration and other sources cause damage to the molecular machines in the cell and gradually wear them down. This is also known as oxidative stress.
There is substantial evidence to back up this theory. Old animals have larger amounts of oxidized proteins, DNA and lipids than their younger counterparts.
Chemical damage[edit]
This section may be too long to read and navigate comfortably. Please consider splitting content into sub-articles, condensing it, or adding subheadings. Please discuss this issue on the article's talk page. (March 2023)
Elderly Klamath woman photographed by Edward S. Curtis in 1924
See also: DNA damage theory of aging
One of the earliest aging theories was the Rate of Living Hypothesis described by Raymond Pearl in 1928 (based on earlier work by Max Rubner), which states that fast basal metabolic rate corresponds to short maximum life span.
While there may be some validity to the idea that for various types of specific damage detailed below that are by-products of metabolism, all other things being equal, a fast metabolism may reduce lifespan, in general this theory does not adequately explain the differences in lifespan either within, or between, species. Calorically restricted animals process as much, or more, calories per gram of body mass, as their ad libitum fed counterparts, yet exhibit substantially longer lifespans. Similarly, metabolic rate is a poor predictor of lifespan for birds, bats and other species that, it is presumed, have reduced mortality from predation, and therefore have evolved long lifespans even in the presence of very high metabolic rates. In a 2007 analysis it was shown that, when modern statistical methods for correcting for the effects of body size and phylogeny are employed, metabolic rate does not correlate with longevity in mammals or birds.
With respect to specific types of chemical damage caused by metabolism, it is suggested that damage to long-lived biopolymers, such as structural proteins or DNA, caused by ubiquitous chemical agents in the body such as oxygen and sugars, are in part responsible for aging. The damage can include breakage of biopolymer chains, cross-linking of biopolymers, or chemical attachment of unnatural substituents (haptens) to biopolymers.
Under normal aerobic conditions, approximately 4% of the oxygen metabolized by mitochondria is converted to superoxide ion, which can subsequently be converted to hydrogen peroxide, hydroxyl radical and eventually other reactive species including other peroxides and singlet oxygen, which can, in turn, generate free radicals capable of damaging structural proteins and DNA. Certain metal ions found in the body, such as copper and iron, may participate in the process. (In Wilson's disease, a hereditary defect that causes the body to retain copper, some of the symptoms resemble accelerated senescence.) These processes termed oxidative stress are linked to the potential benefits of dietary polyphenol antioxidants, for example in coffee, and tea. However their typically positive effects on lifespans when consumption is moderate have also been explained by effects on autophagy, glucose metabolism and AMPK.
Sugars such as glucose and fructose can react with certain amino acids such as lysine and arginine and certain DNA bases such as guanine to produce sugar adducts, in a process called glycation. These adducts can further rearrange to form reactive species, which can then cross-link the structural proteins or DNA to similar biopolymers or other biomolecules such as non-structural proteins. People with diabetes, who have elevated blood sugar, develop senescence-associated disorders much earlier than the general population, but can delay such disorders by rigorous control of their blood sugar levels. There is evidence that sugar damage is linked to oxidant damage in a process termed glycoxidation.
Free radicals can damage proteins, lipids or DNA. Glycation mainly damages proteins. Damaged proteins and lipids accumulate in lysosomes as lipofuscin. Chemical damage to structural proteins can lead to loss of function; for example, damage to collagen of blood vessel walls can lead to vessel-wall stiffness and, thus, hypertension, and vessel wall thickening and reactive tissue formation (atherosclerosis); similar processes in the kidney can lead to kidney failure. Damage to enzymes reduces cellular functionality. Lipid peroxidation of the inner mitochondrial membrane reduces the electric potential and the ability to generate energy. It is probably no accident that nearly all of the so-called "accelerated aging diseases" are due to defective DNA repair enzymes.
DNA damage was proposed in a 2021 review to be the underlying cause of aging because of the mechanistic link of DNA damage to nearly every aspect of the aging phenotype. DNA damage-induced epigenetic alterations, such as DNA methylation and many histone modifications, appear to be of particular importance to the aging process. Evidence for the theory that DNA damage is the fundamental cause of aging was first reviewed in 1981.
It is believed that the impact of alcohol on aging can be partly explained by alcohol's activation of the HPA axis, which stimulates glucocorticoid secretion, long-term exposure to which produces symptoms of aging.
Mutation accumulation[edit]
Main article: Mutation accumulation theory
Natural selection can support lethal and harmful alleles, if their effects are felt after reproduction. The geneticist J. B. S. Haldane wondered why the dominant mutation that causes Huntington's disease remained in the population, and why natural selection had not eliminated it. The onset of this neurological disease is (on average) at age 45 and is invariably fatal within 10–20 years. Haldane assumed that, in human prehistory, few survived until age 45. Since few were alive at older ages and their contribution to the next generation was therefore small relative to the large cohorts of younger age groups, the force of selection against such late-acting deleterious mutations was correspondingly small. Therefore, a genetic load of late-acting deleterious mutations could be substantial at mutation–selection balance. This concept came to be known as the selection shadow.
Peter Medawar formalised this observation in his mutation accumulation theory of aging. "The force of natural selection weakens with increasing age—even in a theoretically immortal population, provided only that it is exposed to real hazards of mortality. If a genetic disaster... happens late enough in individual life, its consequences may be completely unimportant". Age-independent hazards such as predation, disease, and accidents, called 'extrinsic mortality', mean that even a population with negligible senescence will have fewer individuals alive in older age groups.
Other damage[edit]
A study concluded that retroviruses in the human genomes can become awakened from dormant states and contribute to aging which can be blocked by neutralizing antibodies, alleviating "cellular senescence and tissue degeneration and, to some extent, organismal aging".
Stem cell theories of aging[edit]
This section is an excerpt from Stem cell theory of aging.[edit]
The stem cell theory of aging postulates that the aging process is the result of the inability of various types of stem cells to continue to replenish the tissues of an organism with functional differentiated cells capable of maintaining that tissue's (or organ's) original function. Damage and error accumulation in genetic material is always a problem for systems regardless of the age. The number of stem cells in young people is very much higher than older people and thus creates a better and more efficient replacement mechanism in the young contrary to the old. In other words, aging is not a matter of the increase in damage, but a matter of failure to replace it due to a decreased number of stem cells. Stem cells decrease in number and tend to lose the ability to differentiate into progenies or lymphoid lineages and myeloid lineages.
Maintaining the dynamic balance of stem cell pools requires several conditions. Balancing proliferation and quiescence along with homing (See niche) and self-renewal of hematopoietic stem cells are favoring elements of stem cell pool maintenance while differentiation, mobilization and senescence are detrimental elements. These detrimental effects will eventually cause apoptosis.
There are also several challenges when it comes to therapeutic use of stem cells and their ability to replenish organs and tissues. First, different cells may have different lifespans even though they originate from the same stem cells (See T-cells and erythrocytes), meaning that aging can occur differently in cells that have longer lifespans as opposed to the ones with shorter lifespans. Also, continual effort to replace the somatic cells may cause exhaustion of stem cells.
Hematopoietic stem cell aging
Hematopoietic stem cells (HSCs) regenerate the blood system throughout life and maintain homeostasis. DNA strand breaks accumulate in long term HSCs during aging. This accumulation is associated with a broad attenuation of DNA repair and response pathways that depends on HSC quiescence. DNA ligase 4 (Lig4) has a highly specific role in the repair of double-strand breaks by non-homologous end joining (NHEJ). Lig4 deficiency in the mouse causes a progressive loss of HSCs during aging. These findings suggest that NHEJ is a key determinant of the ability of HSCs to maintain themselves over time.
Hematopoietic stem cell diversity aging
A study showed that the clonal diversity of stem cells that produce blood cells gets drastically reduced around age 70 to a faster-growing few, substantiating a novel theory of ageing which could enable healthy aging.
Hematopoietic mosaic loss of chromosome Y
A 2022 study showed that blood cells' loss of the Y chromosome in a subset of cells, called 'mosaic loss of chromosome Y' (mLOY) and reportedly affecting at least 40% of 70 years-old men to some degree, contributes to fibrosis, heart risks, and mortality in a causal way.
Biomarkers of aging[edit]
Main article: Biomarkers of aging
If different individuals age at different rates, then fecundity, mortality, and functional capacity might be better predicted by biomarkers than by chronological age. However, graying of hair, face aging, skin wrinkles and other common changes seen with aging are not better indicators of future functionality than chronological age. Biogerontologists have continued efforts to find and validate biomarkers of aging, but success thus far has been limited.
Levels of CD4 and CD8 memory T cells and naive T cells have been used to give good predictions of the expected lifespan of middle-aged mice.
Aging clocks[edit]
This section needs expansion. You can help by adding to it. (March 2023)
There is interest in an epigenetic clock as a biomarker of aging, based on its ability to predict human chronological age. Basic blood biochemistry and cell counts can also be used to accurately predict the chronological age. It is also possible to predict the human chronological age using the transcriptomic aging clocks.
There is research and development of further biomarkers, detection systems and software systems to measure biological age of different tissues or systems or overall. For example, a deep learning (DL) software using anatomic magnetic resonance images estimated brain age with relatively high accuracy, including detecting early signs of Alzheimer's disease and varying neuroanatomical patterns of neurological aging, and a DL tool was reported as to calculate a person's inflammatory age based on patterns of systemic age-related inflammation.
Aging clocks have been used to evaluate impacts of interventions on humans, including combination therapies.
Genetic determinants of aging[edit]
Main article: Genetics of aging
A number of genetic components of aging have been identified using model organisms, ranging from the simple budding yeast Saccharomyces cerevisiae to worms such as Caenorhabditis elegans and fruit flies (Drosophila melanogaster). Study of these organisms has revealed the presence of at least two conserved aging pathways.
Gene expression is imperfectly controlled, and it is possible that random fluctuations in the expression levels of many genes contribute to the aging process as suggested by a study of such genes in yeast. Individual cells, which are genetically identical, nonetheless can have substantially different responses to outside stimuli, and markedly different lifespans, indicating the epigenetic factors play an important role in gene expression and aging as well as genetic factors. There is research into epigenetics of aging.
The ability to repair DNA double-strand breaks declines with aging in mice and humans.
A set of rare hereditary (genetics) disorders, each called progeria, has been known for some time. Sufferers exhibit symptoms resembling accelerated aging, including wrinkled skin. The cause of Hutchinson–Gilford progeria syndrome was reported in the journal Nature in May 2003.
This report suggests that DNA damage, not oxidative stress, is the cause of this form of accelerated aging.
A study indicates that aging may shift activity toward short genes or shorter transcript length and that this can be countered by interventions.
Healthspans and aging in society[edit]
Past and projected age of the human world population through time as of 2021
Healthspan-lifespan gap (LHG)
Healthspan extension relies on the unison of social, clinical and scientific programs or domains of work.
Healthspan can broadly be defined as the period of one's life that one is healthy, such as free of significant diseases or declines of capacities (e.g. of senses, muscle, endurance and cognition).
These paragraphs are an excerpt from Global health § Multimorbidity, age-related diseases and aging.[edit]
With aging populations, there is a rise of age-related diseases which puts major burdens on healthcare systems as well as contemporary economies or contemporary economics and their appendant societal systems. Healthspan extension and anti-aging research seek to extend the span of health in the old as well as slow aging or its negative impacts such as physical and mental decline. Modern anti-senescent and regenerative technology with augmented decision making could help "responsibly bridge the healthspan-lifespan gap for a future of equitable global wellbeing". Aging is "the most prevalent risk factor for chronic disease, frailty and disability, and it is estimated that there will be over 2 billion persons age > 60 by the year 2050", making it a large global health challenge that demands substantial (and well-orchestrated or efficient) efforts, including interventions that alter and target the inborn aging process.
Biological aging or the LHG comes with a great cost burden to society, including potentially rising health care costs (also depending on types and costs of treatments). This, along with global quality of life or wellbeing, highlight the importance of extending healthspans.
Many measures that may extend lifespans may simultaneously also extend healthspans, albeit that is not necessarily the case, indicating that "lifespan can no longer be the sole parameter of interest" in related research. While recent life expectancy increases were not followed by "parallel" healthspan expansion, awareness of the concept and issues of healthspan lags as of 2017. Scientists have noted that "[c]hronic diseases of aging are increasing and are inflicting untold costs on human quality of life".
Interventions[edit]
This section is an excerpt from Life extension.[edit]
Life extension is the concept of extending the human lifespan, either modestly through improvements in medicine or dramatically by increasing the maximum lifespan beyond its generally-settled limit of 125 years. Several researchers in the area, along with "life extensionists", "immortalists", or "longevists" (those who wish to achieve longer lives themselves), postulate that future breakthroughs in tissue rejuvenation, stem cells, regenerative medicine, molecular repair, gene therapy, pharmaceuticals, and organ replacement (such as with artificial organs or xenotransplantations) will eventually enable humans to have indefinite lifespans through complete rejuvenation to a healthy youthful condition (agerasia). The ethical ramifications, if life extension becomes a possibility, are debated by bioethicists.
The sale of purported anti-aging products such as supplements and hormone replacement is a lucrative global industry. For example, the industry that promotes the use of hormones as a treatment for consumers to slow or reverse the aging process in the US market generated about $50 billion of revenue a year in 2009. The use of such hormone products has not been proven to be effective or safe.
See also[edit]
Anti-aging movement
Antimuscarinics
Dementia
DNA repair
Geriatrics
Gerontology
Heavy metals
Homeostatic capacity
Immortality
Index of topics related to life extension
Mitohormesis
Old age
Phenoptosis
Plant senescence
Programmed cell death
Strategies for engineered negligible senescence (SENS)
Sub-lethal damage
Transgenerational design
Timeline of senescence research | biology | 998 | https://da.wikipedia.org/wiki/Art | Art | Arten (species, forkortet sp., flertal: spp.) er den grundlæggende systematiske enhed inden for biologien. Arten defineres ofte som en naturlig gruppe af populationer, hvor udveksling af gener finder sted (eller kan finde sted) og som i forhold til forplantning er isoleret fra andre grupper. Det vil sige at kun individer inden for samme art kan parre sig og få forplantningsdygtigt afkom. Dette kaldes det biologiske artsbegreb. For organismer, der formerer sig ukønnet eller ved selvbestøvning, må arter afgrænses ud fra ligheder og forskelle mellem forskellige individer. Nogle dyrearter kan i fangenskab hybridisere og få fertilt afkom, men da dette ikke vil ske i naturen, selv om de mødes her, betragtes de som forskellige arter.
Eksempel
To heste kan parre sig og få et føl, der igen kan få føl med andre heste – hestene tilhører derfor samme art. En hest og et æsel kan også parre sig og deres unger kaldes enten muldyr eller mulæsel, afhængig af hvem der er moren, men muldyret eller mulæselet kan (normalt) ikke få unger, da de oftest er sterile. Af den grund regnes hest og æsel som to forskellige arter. Det samme princip gælder også for planterne. Denne naturskabte afgrænsning mellem to arter kaldes en artsbarriere. Den kan af og til gennembrydes, når ellers sterile krydsninger spontant eller kunstigt får gennemført en kromosomfordobling. Se f.eks. Vadegræs (Spartina pectinata).
Arter over for hybrider
Man kan dog godt komme ud for, at arter kan krydses og får blandet afkom, men hybriden vil kun kunne bestå på steder, hvor ingen af forældrearterne kan klare sig. Dette er et særligt udpræget problem med Rododendron (Rhododendron) og Tjørn (Crataegus), fordi disse slægter breder sig voldsomt efter skovbrand eller stormfald. Da hybriderne bliver frugtbare i en yngre alder end arterne, kan de dominere i en periode, men når skoven lukker sig, så fortrænges hybriderne og kun de specialiserede arter kan overleve i skovens dybe skygge eller ude i lyset i sumpe, på ur og i kalksten, m.m.
Flere artsbegreber
Fordi det biologiske artsbegreb kan være besværligt at anvende i praksis, er der efterhånden skabt en række andre artsbegreber:
Morfologisk artsbegreb Arterne adskiller sig fra hinanden ved deres bygning. Dette begreb er blevet meget anvendt gennem tiden.
Økologisk artsbegreb Definerer en art som en gruppe af organismer, der udfylder samme niche. Krydsninger mellem to nærtstående arter vil ikke være optimalt tilpasset til forældrearternes nicher og vil ikke klare sig i konkurrencen.
Evolutionære artsbegreb Også kaldet det kladistiske eller fylogenetiske artsbegreb. Naturen er dynamisk, ikke statisk - alle arter ændrer sig med tiden og bliver, hvis de ikke uddør som følge af konkurrence, naturkatastrofer m.v., til én eller flere nye arter. Det evolutionære artsbegreb minder om det biologiske, men inddrager tidsdimensionen, det vil sige at en art udvikler sig over tid og at nye arter opstår ved artsdannelse. Individer der fylogenetisk har samme stamfader tilhører samme art.
Pluralistisk artsbegreb En art er et samfund af populationer, der formerer sig og lever inden for en bestemt niche i naturen.
Se også
Systematik
Evolutionsteori
Kilder
Lars Skipper: Hvad er en art? Citat: "...Arten er den eneste [klassifikations-kategori] der eksisterer i virkeligheden, alle andre (slægter, familier, ordener m.v.) er indført for overskuelighedens skyld..."
Eksterne henvisninger
2003-12-31, ScienceDaily: Working On The 'Porsche Of Its Time': New Model For Species Determination Offered Citat: "...two species of dinosaur that are members of the same genera varied from each other by just 2.2 percent. Translation of the percentage into an actual number results in an average of just three skeletal differences out of the total 338 bones in the body. Amazingly, 58 percent of these differences occurred in the skull alone. "This is a lot less variation than I'd expected," said Novak..."
2003-08-08, ScienceDaily: Cross-species Mating May Be Evolutionarily Important And Lead To Rapid Change, Say Indiana University Researchers Citat: "...the sudden mixing of closely related species may occasionally provide the energy to impel rapid evolutionary change..."
2004-01-09 ScienceDaily: Mayo Researchers Observe Genetic Fusion Of Human, Animal Cells; May Help Explain Origin Of AIDS Citat: "...The researchers have discovered conditions in which pig cells and human cells can fuse together in the body to yield hybrid cells that contain genetic material from both species..."What we found was completely unexpected," says Jeffrey Platt, M.D..."
2000-09-18, ScienceDaily: Scientists Unravel Ancient Evolutionary History Of Photosynthesis Citat: "...gene-swapping was common among ancient bacteria early in evolution..."
2004-06-07, Sciencedaily: Parting Genomes: University Of Arizona Biologists Discover Seeds Of Speciation Citat: "...There's a huge amount of biodiversity out there, and we don't know where it comes from. Evolutionary biologists are excited to figure out what causes what we see out there--the relative forces of selection and drift--whether things are adapting to their environment or variation is random..."
2005-07-05, Sciencedaily: Trees, Vines And Nets -- Microbial Evolution Changes Its Face Citat: "... EBI researchers have changed our view of 4 billion years of microbial evolution...In all, more than 600,000 vertical transfers are observed, coupled with 90,000 gene loss events and approximately 40,000 horizontal gene transfers...A few species, including beneficial nitrogen-fixing soil bacteria, appear to be 'champions'of horizontal gene transfer; "it's entirely possible that apparently harmless organisms are quietly spreading antibiotic resistance under our feet," concludes Christos Ouzounis..."
2005-11-11, Sciencedaily: Lateral Thinking Produces First Map Of Gene Transmission Citat: "...Their results clearly show genetic modification of organisms by lateral transfer is a widespread natural phenomenon, and it can occur even between distantly related organisms... it was assumed that transfer of genes could only be vertical, i.e. from parents to offspring..."
Økologi
Biologi | danish | 0.791178 |
virus_used_as_antibiotics/be-antibiotics-aware.html.txt |
Centers for Disease Control and Prevention. CDC twenty four seven. Saving Lives, Protecting People Centers for Disease Control and Prevention. CDC twenty four seven. Saving Lives, Protecting People Search Submit
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Be Antibiotics Aware: Smart Use, Best Care Español (Spanish) | Print Minus Related Pages Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations. Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website . More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page Last Reviewed: November 12, 2021 Source: Centers for Disease Control and Prevention , National Center for Emerging and Zoonotic Infectious Diseases (NCEZID) , Division of Healthcare Quality Promotion (DHQP) Facebook Twitter LinkedIn Syndicate home Patient Safety Clean Hands Count for Safe Healthcare Get Ahead of Sepsis â Know the Risks. Spot the Signs. Act Fast. Be Antibiotics Aware: Smart Use, Best Care plus icon Antibiotics Arenât Always the Answer Tome Conciencia sobre los Antibióticos: Buen Uso, Mejor Tratamiento Vaccine Safety Protect Your Children: Store & Use Medicines Safely plus icon Spoons are for Soup, Milliliters are for Medicine Put Your Medicines Up and Away and Out of Sight Getting Medical Care? How to Avoid Getting an Infection What You Should Know Before Your Surgery Contact DHQP Partnerships
Be Antibiotics Aware: Smart Use, Best Care Español (Spanish) | Print Minus Related Pages Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations. Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website . More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page
Be Antibiotics Aware: Smart Use, Best Care Español (Spanish) | Print Minus Related Pages Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations. Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website . More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page
Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations. Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website . More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page
Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations.
Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance. Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations.
Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance.
Be Antibiotics Aware is the Centers for Disease Control and Prevention’s (CDC) national educational effort to help improve antibiotic prescribing and use and combat antibiotic resistance.
Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result. Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority. Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations.
Antibiotic resistance is one of the most urgent threats to the public’s health. Antibiotic resistance happens when germs, like bacteria and fungi, develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. More than 2.8 million antibiotic-resistant infections occur in the United States each year, and more than 35,000 people die as a result.
Antibiotics can save lives, but any time antibiotics are used, they can cause side effects and contribute to the development of antibiotic resistance. Each year, at least 28% of antibiotics are prescribed unnecessarily in U.S. doctors’ offices and emergency rooms (ERs), which makes improving antibiotic prescribing and use a national priority.
Helping healthcare professionals improve the way they prescribe antibiotics, and improving the way we take antibiotics, helps keep us healthy now, helps fight antibiotic resistance, and ensures that these life-saving drugs will be available for future generations.
Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website .
Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy). When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance. What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website .
Viruses or Bacteria What’s got you sick? [PDF – 1 Page] When Antibiotics Are Needed Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy).
Antibiotics are only needed for treating certain infections caused by bacteria, but even some bacterial infections get better without antibiotics. We rely on antibiotics to treat serious, life-threatening conditions such as pneumonia and sepsis , the body’s extreme response to an infection. Effective antibiotics are also needed for people who are at high risk for developing infections. Some of those at high risk for infections include patients undergoing surgery, patients with end-stage kidney disease, or patients receiving cancer therapy (chemotherapy).
When Antibiotics Aren’t Needed Antibiotics DO NOT work on viruses, such as those that cause colds, flu, or COVID-19 . Antibiotics also are not needed for many sinus infections and some ear infections. When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include: Rash Dizziness Nausea Diarrhea Yeast infections More serious side effects can include: Clostridioides difficile infection (also called difficile or C. diff ), which causes severe diarrhea that can lead to severe colon damage and death Severe and life-threatening allergic reactions, such as wheezing, hives, shortness of breath, and anaphylaxis (which also includes feeling like your throat is closing or choking, or your voice is changing) Antibiotic use can also lead to the development of antibiotic resistance.
When antibiotics aren’t needed, they won’t help you, and the side effects could still cause harm. Common side effects of antibiotics can include:
What You Can Do To Feel Better A sk your healthcare professional about the best w ay to feel better while your body fights off the virus. If you need antibiotics, take them exactly as prescribed. Talk with your healthcare professional if you have any questions about your antibiotics. Talk with your healthcare professional if you develop any side effects , especially severe diarrhea, since that could be a C. diff. infection, which needs to be treated immediately. Do your best to stay healthy and keep others healthy: Clean hands by washing with soap and water for at least 20 seconds or use a hand sanitizer that contains at least 60% alcohol Cover your mouth and nose with a tissue when you cough or sneeze Stay home when sick Get recommended vaccines, such as the flu vaccine. To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website . To learn more about antibiotic resistance, visit CDC’s Antibiotic Resistance website .
To learn more about antibiotic prescribing and use, visit CDC’s Antibiotic Prescribing and Use website .
More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page
More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program Top of Page
More Information CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program
CDC’s Be Antibiotics Aware Educational Effort U.S. Antibiotic Awareness Week Partner Toolkit Patient Education Materials Healthcare Professional Materials Antibióticos (en Español) Antibiotic Use in the United States, Current Report Antibiotic Resistance Antibiotic Resistance Threats in the United States, 2019 About Antibiotic Resistance What CDC is Doing: Antibiotic Resistance Solutions Initiative Antibiotic Resistant Germs in Hospitals: Information for Patients and their Families Medication Safety Program
Last Reviewed: November 12, 2021 Source: Centers for Disease Control and Prevention , National Center for Emerging and Zoonotic Infectious Diseases (NCEZID) , Division of Healthcare Quality Promotion (DHQP) Facebook Twitter LinkedIn Syndicate
Last Reviewed: November 12, 2021 Source: Centers for Disease Control and Prevention , National Center for Emerging and Zoonotic Infectious Diseases (NCEZID) , Division of Healthcare Quality Promotion (DHQP)
Source: Centers for Disease Control and Prevention , National Center for Emerging and Zoonotic Infectious Diseases (NCEZID) , Division of Healthcare Quality Promotion (DHQP)
home Patient Safety Clean Hands Count for Safe Healthcare Get Ahead of Sepsis â Know the Risks. Spot the Signs. Act Fast. Be Antibiotics Aware: Smart Use, Best Care plus icon Antibiotics Arenât Always the Answer Tome Conciencia sobre los Antibióticos: Buen Uso, Mejor Tratamiento Vaccine Safety Protect Your Children: Store & Use Medicines Safely plus icon Spoons are for Soup, Milliliters are for Medicine Put Your Medicines Up and Away and Out of Sight Getting Medical Care? How to Avoid Getting an Infection What You Should Know Before Your Surgery Contact DHQP Partnerships
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About CDC Contact Us 800-232-4636 Facebook Twitter Instagram LinkedIn Youtube Pinterest Snapchat CONTACT CDC Contact Us Call 800-232-4636 Email Us ABOUT CDC About CDC Jobs Funding POLICIES Accessibility External Links Privacy Policies No Fear Act FOIA OIG Nondiscrimination Vulnerability Disclosure Policy CONNECT WITH US Facebook Twitter Instagram LinkedIn Youtube Pinterest Snapchat Email LANGUAGES Español ç¹é«ä¸æ Tiếng Viá»t íêµì´ Tagalog Ð ÑÑÑкий اÙعربÙØ© Kreyòl Ayisyen Français Polski Português Italiano Deutsch æ¥æ¬èª ÙØ§Ø±Ø³Û English
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Links with this icon indicate that you are leaving the CDC website. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website. Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website. You will be subject to the destination website's privacy policy when you follow the link. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. For more information on CDC's web notification policies, see Website Disclaimers . | biology | 2563 | https://da.wikipedia.org/wiki/Antibiotikaresistens | Antibiotikaresistens | Antibiotikaresistens er modstandsdygtighed (resistens) overfor antibiotika. Bakterier og andre organismer, f.eks. svampe, kan udvikle resistens overfor antibiotika, hvilket betyder at antibiotika ikke længere påvirker dem. Ministeriet for Fødevarer, Landbrug og Fiskeri anslår at der hvert eneste år dør over 25.000 europæere som følge af infektioner med bakterier, der har udviklet resistens mod antibiotika som følge af overforbrug af antibiotika til både mennesker og dyr.
Bakterier fører til stadighed en biologisk-biokemisk "krig om overlevelse", hvor resultatet følger Darwins lov om overlevelse af den mest egnede og hvor resultatet viser sig hurtigt på grund af bakteriers meget korte generationstid. Resistente mikroorganismer viser sig ofte at producere et eller flere enzymer, der binder og nedbryder antibiotika-molekylerne og gør dem inaktive. Genet for et antibiotika-nedbrydende enzym kan, ligesom andre gener, overføres fra den ene mikroorganisme til den anden, og dermed kan resistensen spredes mellem bakterierne. Det betyder at en bakterie der er blevet resistent kan overføre sin resistens til andre bakterier. Det kan ske ved de processer der kaldes for konjugation, transduktion og transformation, for eksempel ved overførsel af plasmider. Resistens vil i sidste ende medføre uhelbredelige infektioner. Resistente mikroorganismer omtales på engelsk som “MDR”, “multidrug resistant”, "pig-MRSA", "livestock-associate MRSA", “superbug” eller “super bacterium” og sågar som "nightmare bacteria".
I Danmark er der en stigende tendens til forekomsten af resistente infektioner, om end problemet her er noget mindre end i mange andre lande. Fra 2008 til 2012 er der på danske sygehuse indlagt 15 personer med farlige resistente bakterier fra udlandet, hvoraf de 7 patienter var fra Libyen og alle havde den samme resistente tarmbakterie. Langt hyppigere på danske sygehuse er de multiresistente tarmbakterier ESBL, der har navn efter det antibiotika-nedbrydende enzym extended spectrum beta-lactamase. På trods af den potentielle risiko for spredning af uhelbredelige infektioner, er der endnu (marts 2012) ingen systematisk overvågning i Danmark af nogen af disse resistente bakterier. I en status over 2014 anfører Statens Seruminstitut, at der på de danske hospitaler er en stor stigning i antallet af patienter, som fik infektioner med multiresistente bakterier som VRE (op 30%) og CPE (op 100%).
Resistensproblemet
På grund af antibiotikaresistens er der en stadig større risiko for at der udvikles infektioner, som slår mennesker ihjel. De resistente bakterier er mere dødelige end deres ikke-resistente slægtninge, således følger døden af 40% af alle blodforgiftninger i USA med CRE.. Resistensproblemet er i begyndelsen af 2013 blevet så alvorligt, at Storbritianniens øverste medicinaldirektør, Dame Sally Davies, har advaret om at antibiotikaresistens er blevet så udbredt, at det udgør en dommedags-lignende trussel, hvor selv små infektioner i fremtiden ikke kan behandles. Derfor anbefaler hun de britiske myndigheder at udvide det nationale register over over katastrofesituationer som terrorangreb, globale epidemier og naturkatastrofer med antibiotikaresistens.
Center for Disease Control i USA anslår, at 2 millioner amerikanere hvert år smittes med resistente bakterier, og at der i USA hvert år dør 23.000 mennesker som følge af infektion med resistente bakterier; CDC advarer derfor i en rapport mod den truende situation, hvor der ikke længere findes liv-reddende antibiotika.
Danske eksperter kalder udviklingen en ond spiral og er enige ud fra betragtninger af, at også i Danmark er resistente bakterier som stafylokokker i fremmarch, og at 80-90 % af danske slagtesvin indeholder resistente bakterier. Overførsel af resistente bakterier fra kæle- og husdyr til mennesker er en potentiel risiko efter fund af resistente bakterier i kæle- og husdyr.
I begyndelsen af 2013 opererede sundhedsvæsenet med tre typer resistente tuberkulosebakterier: multiresistente, ekstremt resistente og fuldkommen resistente eller totalt resistente tuberkulosebakterier, der kræver meget lang og kostbar antibiotikabehandling med stor risiko for at fremkalde resistens, og for de totalt resistente en eksperimentel behandling, hvis udfald ikke kan forudsiges.
Det er anslået, at omkring 700.000 mennesker dør i 2016 som følge af resistente bakterier, og at dette tal inden for få årtier øges til flere millioner mennesker der dør hvert år.
Selektionspresset
Al brug af antibiotika vil medføre et selektionspres, der gør at de følsomme mikroorganismer dør og de resistente trives.
Resistens fremkaldes således over tiden ved utilstrækkelig eller overdreven behandling. Dette kan på længere sigt få betydning for behandling af infektioner som skyldes f.eks. Staphylococcus aureus. Det er af afgørende betydning at fastholde et lavt og smalspektret antibiotikaforbrug, samt opsporing og behandling af bærere af Methicillin-resistent Staphylococcus aureus bakterier og carbapenem-resistente bakterier som NDM-1 (bakterier med det antibiotika-nedbrydende enzym NDM-1, New Delhi Metallo-beta-lactamase 1).
Multiresistens opstår ved at en bakterie med et antibiotika-nedbrydende enzym får overført genet for et andet antibiotika-nedbrydende enzym, og derfor ikke kan behandles med to typer antibiotika. Denne proces kan fortsætte og slutte med bakterier, der producerer enzymer, der nedbryder alle kendte antibiotika.
I Danmark er der i landbrugets svineproduktion et meget stort forbrug af antibiotika. I 2010 brugte det danske landbrug i alt 100,3 ton antibiotika, og trods større produktion kunne der konstateres et glædeligt fald i forbruget til 81,4 ton i 2011.
Antibiotikaresistente bakterier
CA-MRSA (community-acquired MRSA) engelsk udtryk for smitsom MRSA
CC97 eller MRSA CC97 (methicillin resistant Staphylococcus aureus clonal complex 97) stammer oprindeligt fra køer.
CC398 eller MRSA CC398 (methicillin resistant Staphylococcus aureus clonal complex 398) eller * ST398 (sequence type 398) også kaldet "svine-MRSA" er resistent over for både methicillin og tetracyclin
CPE, carbapenemase-producerende enterobakterier
CRE, carbapenem-resistente enterobakterier, herunder carbapenem-resistente Klebsiella er udbredte i Grækenland, UK og USA.
ESBL (extended-spectrum beta-lactamase), bakterie der indeholder det antibiotika-nedbrydende enzym ESBL
HA-MRSA (healthcare-associated MRSA) engelsk udtryk for hospitalsinfektion.
KPC, K. pneumoniae carbapenemase-producerende Klebsiella, panresistent, findes i USA.
LA-MRSA (livestock-associated MRSA) "svine-MRSA"
MRAB (multiresistent Acinetobacter baumannii) blodinfektioner hos soldater i Irak og Afghanistan
MRSA (methicillin resistant Staphylococcus aureus) resistent over for methicillin. Smittevejene fra dyr til mennesker er i 2013 ved at blive klarlagt. Den følsomme bakterie, der kan behandles med methicillin. benævnes MSSA (methicillin-sensitiv Staphylococcus aureus)
Mycobacterium tuberculosis, multiresistente bakterier er udbredt i Østeuropa og totalt resistente bakterier i Sydafrika.
Mycoplasma genitalium med udbredt resistens
NDM-1, New Delhi-metallo-beta-lactamase 1-producerende enterobakterier (Klebsiella pneumoniae, E. coli, Vibrio colerae og Shigella boydeii) er udbredt i Indien, Pakistan, Bangladesh og på Balkan.
ORSA (oxacillin-resistant Staphylococcus aureus)
t127 eller MRSA t127 (methicillin resistant Staphylococcus aureus) konstateret hos 9 nyfødte børn på Hvidovre Hospital, 2014.
ST22-MRSA-IV (sequence type 22 methicillin resistant Staphylococcus aureus type IV) – en hospitalsinfektion i Irland
VRE, vancomycin-resistent enterokok, forekommer som hospitalsinfektion
VRSA, vancomycin-resistant Staphylococcus aureus
XDR (forkortelse eng. extensively drug-resistant) superresistente bakterier, bruges om tuberkulose-bakterie.
Medfødt resistens
Nogle organismer er naturligt udstyret med resistens over for diverse stoffer i kraft af deres DNA. Nogle organismer har ikke genet for en bestemt receptor for et givent antibiotikum. F.eks. virker amphotericin B ved at binde sig til steroler i svampes cellemembran, og da bakterier ikke har steroler i deres cellemembran, er de naturligt resistente over for amphotericin B.
Et andet eksempel på medfødt resistens er en organismes ydre barriere, der kan forhindre visse antibiotika i at nå deres mål i cellen.
Opnået resistens
Begrebet opnået resistens eller overført resistens dækker over at en mikroorganisme udvikler antibiotikaresistens. Overført resistens betyder at en mikroorganisme bliver resistent over for antibiotika ved at blive "smittet" af en anden mikroorganisme.
Der kendes flere biologiske, genetiske og biokemiske mekanismer:
ved en mutation
overførsel af et gen for et antibiotika-nedbrydende enzym som f.eks. beta-laktamase
overførsel af et gen for et membran-protein, en pumpe, der pumper antibiotika ud af cellen (sammenlign f.eks. med natrium-kalium-pumpen
overførsel af et gen der ændrer celleoverfladen, så antibiotika ikke binder til cellen eller ikke kan trænge igennem celleoverfladen.
Overførslen af et eller flere gener sker ved konjugation, transduktion eller transformation. Ofte sker det ved overførsel af et plasmid, f.eks. er Shigella og E. coli i stand til at overføre plasmider mellem hinanden. Overførsel af plasmider mellem bakterie-populationer er en effektiv måde til spredning af antibiotika-resistens mellem mikroorganismer.
Kromosomal mutation
Der sker konstant mutationer med lav frekvens i forskellige organismers DNA, hvorved nogle af dem opnår en vækstfordel, eksempelvis i form af resistens over for antibiotika. F.eks. kan gram-negative bakterier, der har et muteret gen for β-laktamase opnå en overproduktion af dette enzym, hvorved de bliver resistente over for cefalosporiner, som ellers betragtes som uimodtagelige over for β-laktamase.
Vaccination
Antibiotikaresistens er en af verdens førende dødsårsager og kræver flere menneskeliv end aids eller malaria. Hvor de er tilgængelige, er vacciner nogle af de bedste værktøjer, der er til at forhindre fremtidige katastrofer.
Alternativ bekæmpelse af superbakterier
Multiresistente bakterier udvikler resistens mod mange eller evt. alle anvendte antibiotika, og derfor er der stort behov for nye antibiotika. Desværre er den farmaceutiske forskning ikke i stand til at følge med i denne biologiske krig ad de traditionelle veje med opdagelse og masseproduktion af nye antibiotika, som er en langsommelig proces.
Forsker har vendt sig mod “gamle” antibiotika, som er blevet opgivet, måske p.gr.a. deres giftighed, som f.eks. streptotricinerne.
Den farmaceutiske forskning leder efter alternative måder at bekæmpe multiresistente bakterier. Eksempler herpå er antimikrobielle peptider (se f.eks. Indledende case: Plectasin), hæmmere af beta-lactamase, kulilte-frigivende molekyler, ler og bakteriofager, også kaldet fager, jvf. bakteriofagterapi.
Se også
Tyfus
Referencer
Eksterne henvisninger
1,000-year-old onion and garlic remedy kills antibiotic-resistant bugs. Science Alert
Antibiotika og resistens. Biotech Academy
Resistente bakterier. Mennesker og medicin.dk
Svine-MRSA stammer fra mennesker, Statens Seruminstitut, februar 2012
Fakta om antibiotika-resistens fra Statens Seruminstitut
Taber vi krigen mod resistente bakterier?
Om antibiotika-resistens fra Videnskab.dk
Udsigt til mindre antibiotikaforbrug i landbruget. Københavns Universitet, marts, 2012
Historien om en bakterie der løb løbsk
CC398. emaxhealth, marts, 2012.
Carbapenem-resistente enterobakterier. EPI-nyt 2012
Forskere finder farlige bakteriers oprindelse. Videnskab.dk 2013
ESBL producerende Enterobakterier (Escherichia coli og Klebsiella pneumoniae). Statens Seruminstitut
Antistoffer kan afløse problematisk tungmetal. Information, oktober 2014
Understanding CRE, the 'nightmare' superbug... CNN Health
Se også
Antibiotikum
Β-lactamantibiotika
Gonorré
Herbicidresistens
ICD-10 Kapitel I - Infektiøse inkl. parasitære sygdomme (WHO's liste)
Mikrobiom
Staphylococcus aureus
Antibiotika
Farmakologi | danish | 0.534453 |
virus_used_as_antibiotics/Phage_therapy.txt |
Phage therapy, viral phage therapy, or phagotherapy is the therapeutic use of bacteriophages for the treatment of pathogenic bacterial infections. This therapeutic approach emerged at the beginning of the 20th century but was progressively replaced by the use of antibiotics in most parts of the world after the Second World War. Bacteriophages, known as phages, are a form of virus that attach to bacterial cells and inject their genome into the cell. The bacteria's production of the viral genome interferes with its ability to function, halting the bacterial infection. The bacterial cell causing the infection is unable to reproduce and instead produces additional phages. Phages are very selective in the strains of bacteria they are effective against.
Advantages include reduced side effects and reduced risk of the bacterium developing resistance, since bacteriophages are much more specific than antibiotics. They are typically harmless not only to the host organism but also to other beneficial bacteria, such as the gut microbiota, reducing the chances of opportunistic infections. They have a high therapeutic index; that is, phage therapy would be expected to give rise to few side effects, even at higher-than-therapeutic levels. Because phages replicate in vivo (in cells of living organism), a smaller effective dose can be used.
Disadvantages include the difficulty of finding an effective phage for a particular infection; a phage will kill a bacterium only if it matches the specific strain. However, virulent phages can be isolated much more easily than other compounds and natural products. Consequently, phage mixtures ("cocktails") are sometimes used to improve the chances of success. Alternatively, samples taken from recovering patients sometimes contain appropriate phages that can be grown to cure other patients infected with the same strain. Ongoing challenges include the need to increase phage collections from reference phage banks, the development of efficient phage screening methods for the fast identification of the therapeutic phage(s), the establishment of efficient phage therapy strategies to tackle infectious biofilms, the validation of feasible phage production protocols that assure quality and safety of phage preparations, and the guarantee of stability of phage preparations during manufacturing, storage, and transport.
Phages tend to be more successful than antibiotics where there is a biofilm covered by a polysaccharide layer, which antibiotics typically cannot penetrate. Phage therapy can disperse the biofilm generated by antibiotic-resistant bacteria. However, the interactions between phages and biofilms can be complex, with phages developing symbiotic as well as predatory relationships with biofilms.
Phages are currently being used therapeutically to treat bacterial infections that do not respond to conventional antibiotics, particularly in Russia and Georgia. There is also a phage therapy unit in Wrocław, Poland, established in 2005, which continues several-decades-long research by the Institute of Immunology and Experimental Therapy of the Polish Academy of Sciences, the only such centre in a European Union country. Phages are the subject of renewed clinical attention in Western countries, such as the United States. In 2019, the United States Food and Drug Administration approved the first US clinical trial for intravenous phage therapy.
Phage therapy has many potential applications in human medicine as well as dentistry, veterinary science, and agriculture. If the target host of a phage therapy treatment is not an animal, the term "biocontrol" (as in phage-mediated biocontrol of bacteria) is usually employed, rather than "phage therapy".
History[edit]
Frederick Twort
Félix d'Hérelle, discoverer of phage therapy
Phage in action on cultured Bacillus anthracis
The discovery of bacteriophages was reported by British bacteriologist Frederick Twort in 1915 and by French microbiologist Felix d'Hérelle in 1917. D'Hérelle said that the phages always appeared in the stools of Shigella dysentery patients shortly before they began to recover. He "quickly learned that bacteriophages are found wherever bacteria thrive: in sewers, in rivers that catch waste runoff from pipes, and in the stools of convalescent patients". Phage therapy was immediately recognized by many to be a key way forward for the eradication of pathogenic bacterial infections. A Georgian, George Eliava, was making similar discoveries. He travelled to the Pasteur Institute in Paris, where he met d'Hérelle, and in 1923, he founded the Institute of Bacteriology, which later became known as the George Eliava Institute, in Tbilisi, Georgia, devoted to the development of phage therapy. Phage therapy is used in Russia, Georgia and Poland, and was used prophylactically for a time in the Soviet army, most notably during the Second World War.
In Russia, extensive research and development soon began in this field. In the United States during the 1940s, commercialization of phage therapy was undertaken by Eli Lilly and Company.
While knowledge was being accumulated regarding the biology of phages and how to use phage cocktails correctly, early uses of phage therapy were often unreliable. Since the early 20th century, research into the development of viable therapeutic antibiotics had also been underway, and by 1942, the antibiotic penicillin G had been successfully purified and saw use during the Second World War. The drug proved to be extraordinarily effective in the treatment of injured Allied soldiers whose wounds had become infected. By 1944, large-scale production of penicillin had been made possible, and in 1945, it became publicly available in pharmacies. Due to the drug's success, it was marketed widely in the US and Europe, leading Western scientists to mostly lose interest in further use and study of phage therapy for some time.
Isolated from Western advances in antibiotic production in the 1940s, Russian scientists continued to develop already successful phage therapy to treat the wounds of soldiers in field hospitals. During World War II, the Soviet Union used bacteriophages to treat soldiers infected with various bacterial diseases, such as dysentery and gangrene. Russian researchers continued to develop and to refine their treatments and to publish their research and results. However, due to the scientific barriers of the Cold War, this knowledge was not translated and did not proliferate across the world. A summary of these publications was published in English in 2009 in "A Literature Review of the Practical Application of Bacteriophage Research".
There is an extensive library and research center at the George Eliava Institute in Tbilisi, Georgia. Phage therapy is today a widespread form of treatment in that region.
As a result of the development of antibiotic resistance since the 1950s and an advancement of scientific knowledge, there has been renewed interest worldwide in the ability of phage therapy to eradicate bacterial infections and chronic polymicrobial biofilm (including in industrial situations).
Phages have been investigated as a potential means to eliminate pathogens like Campylobacter in raw food and Listeria in fresh food or to reduce food spoilage bacteria. In agricultural practice, phages have been used to fight pathogens like Campylobacter, Escherichia, and Salmonella in farm animals, Lactococcus and Vibrio pathogens in fish aquaculture, and Erwinia, Xanthomonas, and others in plants of agricultural importance. The oldest use is, however, in human medicine. Phages have been used against diarrheal diseases caused by E. coli, Shigella, or Vibrio and against wound infections caused by facultative pathogens of the skin like staphylococci and streptococci. Recently, the phage therapy approach has been applied to systemic and even intracellular infections, and non-replicating phage and isolated phage enzymes like lysins have been added to the antimicrobial arsenal. However, actual proof for the efficacy of these phage approaches in the field or the hospital is not available.
Some of the interest in the West can be traced back to 1994, when James Soothill demonstrated (in an animal model) that the use of phages could improve the success of skin grafts by reducing the underlying Pseudomonas aeruginosa infection. Recent studies have provided additional support for these findings in the model system.
Although not "phage therapy" in the original sense, the use of phages as delivery mechanisms for traditional antibiotics constitutes another possible therapeutic use. The use of phages to deliver antitumor agents has also been described in preliminary in vitro experiments for cells in tissue culture.
In June 2015, the European Medicines Agency hosted a one-day workshop on the therapeutic use of bacteriophages, and in July 2015, the US National Institutes of Health hosted a two-day workshop titled "Bacteriophage Therapy: An Alternative Strategy to Combat Drug Resistance".
In January 2016, phages were used successfully at Yale University by Benjamin Chan to treat a chronic Pseudomonas aeruginosa infection in ophthalmologist Ali Asghar Khodadoust. This successful treatment of a life-threatening infection sparked a resurgence of interest in phage therapy in the United States.
In 2017, a pair of genetically engineered phages along with one naturally occurring (so-called "phage Muddy") each from among those catalogued by SEA-PHAGES (Science Education Alliance-Phage Hunters Advancing Genomics and Evolutionary Science) at the Howard Hughes Medical Institute by Graham Hatfull and colleagues, was used by microbiologist James Soothill at Great Ormond Street Hospital for Children in London to treat an antibiotic-resistant bacterial (Mycobacterium abscessus) infection in a young woman with cystic fibrosis.
In 2022, two mycobacteriophages were administered intravenously twice daily to a young man with treatment-refractory Mycobacterium abscessus pulmonary infection and severe cystic fibrosis lung disease. Airway cultures for M. abscessus became negative after approximately 100 days of combined phage and antibiotic treatment, and a variety of biomarkers confirmed the therapeutic response. The individual received a bilateral lung transplant after 379 days of treatment, and cultures from the explanted lung tissue confirmed eradication of the bacteria. In a second case, successful treatment of disseminated cutaneous Mycobacterium chelonae was reported with a single phage administered intravenously twice daily in conjunction with antibiotic and surgical management.
Potential benefits[edit]
Phage therapy is the use of bacteriophages to treat bacterial infections.
Bacteriophage treatment offers a possible alternative to conventional antibiotic treatments for bacterial infection. It is conceivable that, although bacteria can develop resistance to phages, the resistance might be easier to overcome than resistance to antibiotics. Viruses, just like bacteria, can evolve resistance to different treatments.
Bacteriophages are very specific, targeting only one or a few strains of bacteria. Traditional antibiotics have a more wide-ranging effect, killing both harmful and useful bacteria, such as those facilitating food digestion. The species and strain specificity of bacteriophages makes it unlikely that harmless or useful bacteria will be killed when fighting an infection.
A few research groups in the West are engineering a broader-spectrum phage and also a variety of forms of MRSA treatments, including impregnated wound dressings, preventative treatment for burn victims, and phage-impregnated sutures. Enzybiotics are a new development at Rockefeller University that create enzymes from phages. Purified recombinant phage enzymes can be used as separate antibacterial agents in their own right.
Phage therapy also has the potential to prevent or treat infectious diseases of corals. This could mitigate the global coral decline.
Applications[edit]
Collection[edit]
Phages for therapeutic use can be collected from environmental sources that likely contain high quantities of bacteria and bacteriophages, such as effluent outlets, sewage, or even soil. The samples are taken and applied to bacterial cultures that are to be targeted. If the bacteria die, the phages can be grown in liquid cultures.
Modes of treatment[edit]
Phages are "bacterium-specific", and therefore, it is necessary in many cases to take a swab from the patient and culture it prior to treatment. Occasionally, isolation of therapeutic phages can require a few months to complete, but clinics generally keep supplies of phage cocktails for the most common bacterial strains in a geographical area.
Phage cocktails are commonly sold in pharmacies in Eastern European countries, such as Russia and Georgia. The composition of bacteriophagic cocktails has been periodically modified to add phages effective against emerging pathogenic strains.
Phages in practice are applied orally, topically on infected wounds or spread onto surfaces, or during surgical procedures. Injection is rarely used, avoiding any risks of trace chemical contaminants that may be present from the bacteria amplification stage, and recognizing that the immune system naturally fights against viruses introduced into the bloodstream or lymphatic system.
Reviews of phage therapy indicate that more clinical and microbiological research is needed to meet current standards.
Clinical trials[edit]
This section needs to be updated. Please help update this article to reflect recent events or newly available information. (February 2022)
Funding for phage therapy research and clinical trials is generally insufficient and difficult to obtain, since it is a lengthy and complex process to patent bacteriophage products. Due to the specificity of phages, phage therapy would be most effective as a cocktail injection, a modality generally rejected by the US Food and Drug Administration (FDA). Therefore, researchers and observers have predicted that if phage therapy is to gain traction, the FDA must change its regulatory stance on combination drug cocktails. Public awareness and education about phage therapy are generally limited to scientific or independent research rather than mainstream media.
In 2007, phase-1 and 2 clinical trials were completed at the Royal National Throat, Nose and Ear Hospital, London, for Pseudomonas aeruginosa infections (otitis).
Phase-1 clinical trials were conducted at the Southwest Regional Wound Care Center of Lubbock, Texas, for a cocktail of phages against P. aeruginosa, Staphylococcus aureus, and Escherichia coli, developed by Intralytix. PhagoBurn, a phase-1 and 2 trial of phage therapy against P. aeruginosa wound infection in France and Belgium in 2015–17, was terminated early due to lack of effectiveness.
Locus Biosciences has created a cocktail of three CRISPR-modified phages. A 2019 study examined its effectiveness against E. coli in the urinary tract, and a phase-1 trial was completed shortly before March 2021. In February 2019, the FDA approved the first clinical trial of intravenously administered phage therapy in the United States.
In July 2020, the FDA approved the first clinical trial of nebulized phage therapy in the United States. This double-blind, placebo-controlled study at Yale University will be focused on treating P. aeruginosa infections in patients with cystic fibrosis.
In February 2020, the FDA approved a clinical trial to evaluate bacteriophage therapy in patients with urinary tract infections. The study started in December 2020 and aims to identify ideal bacteriophage treatment regimens based on improvements in disease control rates.
In February 2021, the FDA approved a clinical trial to evaluate bacteriophage therapy in patients with chronic prosthetic joint infections (PJI). The study was to begin in October 2022 and be conducted by Adaptive Phage Therapeutics, in collaboration with the Mayo Clinic.
Administration[edit]
Phages can usually be freeze-dried and turned into pills without materially reducing efficiency. Temperature stability up to 55 °C and shelf lives of 14 months have been shown for some types of phages in pill form. Application in liquid form is possible, stored preferably in refrigerated vials. Oral administration works better when an antacid is included, as this increases the number of phages surviving passage through the stomach. Topical administration often involves application to gauzes that are laid on the area to be treated.
Successful treatments[edit]
Phages were used successfully at Yale University by Benjamin Chan to treat a Pseudomonas infection in 2016. Intravenous phage drip therapy was successfully used to treat a patient with multidrug-resistant Acinetobacter baumannii in Thornton Hospital at UC San Diego in 2017. Nebulized phage therapy has been used successfully to treat numerous patients with cystic fibrosis and multidrug-resistant bacteria at Yale University as part of their compassionate use program. In 2019, a Brownsville, Minnesota resident with a longstanding bacterial infection in his knee received a phage treatment at the Mayo Clinic that eliminated the need for amputation of his lower leg. Individualised phage therapy was also successfully used by Robert T. Schooley and others to treat a case of multi-drug-resistant Acinetobacter baumannii in 2015. In 2022, an individually adjusted phage-antibiotic combination as an antimicrobial resistance treatment was demonstrated and described in detail. The scientists called for scaling up the research and for further development of this approach.
Treatment of biofilm infections[edit]
The different steps at which phages may disrupt biofilm formation. The biofilm surrounding the bacteria would inhibit the ability of antibiotics to reach bacteria, but may have less impact on the phages.
Phage therapy is being used to great effect in the treatment of biofilm infections, especially Pseudomonas aeruginosa and Staphylococcus aureus. From 78 recent cases of treatment of biofilm infections, 96% of patients saw clinical improvement using phage therapy, and 52% of patients saw complete symptom relief or a full expungement of the affecting bacteria. Biofilm infections are very challenging to treat with antibiotics. The biofilm matrix and surrounding bacterial membranes can bind to the antibiotics, preventing them from penetrating the biofilm. The matrix may contain enzymes that deactivate antibiotics. Biofilms also have low metabolic activity, which means antibiotics that target growing processes have much lower efficacy. These factors make phage therapy an enticing option for the treatment of such infections, and there are currently two ways to go about such treatment. The first is to isolate the initial bacteria and make a specific treatment phage to target it, while the second way is to use a combination of more general phages. The advantage of the second method is that it can easily be made commercially available for treatment, although there are some concerns that it may be substantially less effective.
The process of treating biofilms or more generic infections using phage therapy. Depending on the case, steps 2 and 3 may involve either specially tailored phages or more general alternatives.
Limitations[edit]
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The high bacterial strain specificity of phage therapy may make it necessary for clinics to make different cocktails for treatment of the same infection or disease, because the bacterial components of such diseases may differ from region to region or even person to person. In addition, this means that "banks" containing many different phages must be kept and regularly updated with new phages.
Further, bacteria can evolve different receptors either before or during treatment. This can prevent phages from completely eradicating them.
The need for banks of phages makes regulatory testing for safety harder and more expensive under current rules in most countries. Such a process would make the large-scale use of phage therapy difficult. Additionally, patent issues (specifically on living organisms) may complicate distribution for pharmaceutical companies wishing to have exclusive rights over their "invention", which would discourage a commercial corporation from investing capital in this.
As has been known for at least thirty years, mycobacteria such as Mycobacterium tuberculosis have specific bacteriophages. No lytic phage has yet been discovered for Clostridium difficile, which is responsible for many nosocomial diseases, but some temperate phages (integrated in the genome, also called lysogenic) are known for this species; this opens encouraging avenues but with additional risks, as discussed below.
The negative public perception of viruses may also play a role in the reluctance to embrace phage therapy.
Development of resistance[edit]
One of the major concerns usually associated with phage therapy is the emergence of phage-insensitive mutants (BIMs) that could hinder the success of this therapy. In fact, several in vitro studies have reported a fast emergence of BIMs within a short period of time after phage treatment. The emergence of BIMs has also been observed in vivo using different animal models, although this usually occurs later than in vitro (reviewed in ). This fast adaptation of bacteria to phage attack is usually caused by mutations on genes encoding phage receptors, which include lipopolysaccharides (LPS), outer membrane proteins, capsules, flagella, and pili, among others. However, some studies suggest that when phage resistance is caused by mutations in phage receptors, this might result in fitness costs to the resistance bacterium, which will ultimately become less virulent. Moreover, it has been shown that the evolution of bacterial resistance to phage attack changes the efflux pump mechanism, causing increased sensitivity to drugs from several antibiotic classes. Therefore, it is conceivable to think that phage therapy that uses phages that exert selection for multidrug-resistant bacteria to become antibiotic-sensitive could potentially reduce the incidence of antibiotic-resistant infections.
Besides the prevention of phage adsorption by loss or modification of bacterial receptors, phage insensitivity can be caused by: (i) prevention of phage DNA entry by superinfection exclusion systems; (ii) degradation of phage DNA by restriction-modification systems or by CRISPR-Cas systems; and (iii) use of abortive infection systems that block phage replication, transcription, or translation, usually in conjunction with suicide of the host cell. Altogether, these mechanisms promote a quick adaptation of bacteria to phage attack and therefore, the emergence of phage-resistant mutants is frequent and unavoidable.
It is still unclear whether the wide use of phages would cause resistance similar to what has been observed for antibiotics. In theory, this is not very likely to occur, since phages are very specific, and therefore, their selective pressure would affect a very narrow group of bacteria. However, we should also consider the fact that many phage resistance systems are mounted on mobile genetic elements, including prophages and plasmids, and thus may spread quite rapidly even without direct selection. Nevertheless, in contrast to antibiotics, phage preparations for therapeutic applications are expected to be developed in a personalized way because of the high specificity of phages. In addition, strategies have been proposed to counter the problem of phage resistance. One of the strategies is the use of phage cocktails with complementary host ranges (different host ranges, which, when combined, result in an overall broader host range) and targeting different bacterial receptors. Another strategy is the combination of phages with other antimicrobials such as antibiotics, disinfectants, or enzymes that could enhance their antibacterial activity. The genetic manipulation of phage genomes can also be a strategy to circumvent phage resistance.
Safety aspects[edit]
Bacteriophages are bacterial viruses, evolved to infect bacterial cells. To do that, phages must use characteristic structures at cell surfaces (receptors), and to propagate they need appropriate molecular tools inside the cells. Bacteria are prokaryotes, and their cells differ substantially from eukaryotes, including humans or animals. For this reason, phages meet the major safety requirement: they do not infect treated individuals. Even engineered phages and induced artificial internalization of phages into mammalian cells do not result in phage propagation. Natural transcytosis of unmodified phages, that is, uptake and internal transport to the other side of a cell, which was observed in human epithelial cells, did not result in phage propagation or cell damage. Recently, however, it was reported that filamentous temperate phages of P. aeruginosa can be endocytosed into human and murine leukocytes, resulting in transcription of the phage DNA. In turn, the product RNA triggers maladaptive innate viral pattern-recognition responses and thus inhibits the immune clearance of the bacteria. Whether this also applies to dsDNA phages like Caudovirales has not yet been established; this is an important question to be addressed as it may affect the overall safety of phage therapy.
Due to many experimental treatments in human patients conducted in past decades, and to already existing RCTs (see section: Clinical experience and randomized controlled trials), phage safety can be assessed directly. The first safety trial in healthy human volunteers for a phage was conducted by Bruttin and Brüssow in 2005. They investigated the oral administration of Escherichia coli phage T4 and found no adverse effects of the treatment. Historical record shows that phages are safe, with mild side effects, if any. The most frequent (though still rare) adverse reactions to phage preparations found in patients were symptoms from the digestive tract, local reactions at the site of administration of a phage preparation, superinfections, and a rise in body temperature. Notably, these reactions may have been (i) due to the liberation of endotoxins from bacteria lysed in vivo by the phages, since such effects also can be observed when antibiotics are used, or (ii) caused by bacterial debris that accompanied the phage in cases where unpurified lysates were used.
Bacteriophages must be produced in bacteria that are lysed (i.e., fragmented) during phage propagation. As such, phage lysates contain bacterial debris that may affect the human organism even when the phage itself is harmless. For these and other reasons, purification of bacteriophages is considered important, and phage preparations need to be assessed for their safety as a whole, particularly when phages are to be administered intravenously. This is consistent with general procedures for other drug candidates. In 2015, a group of phage therapy experts summarized the quality and safety requirements for sustainable phage therapy.
Phage effects on the human microbiome also contribute to safety issues in phage therapy. It is important to note that many phages, especially temperate ones, carry genes that can affect the pathogenicity of the host. Even lambda, a temperate phage of the E. coli K-12 laboratory strain, carries two genes that provide potential virulence benefits to the lysogenic host, one that increases intestinal adherence and the other that confers resistance to complement killing in the blood. For this reason, temperate phages are generally to be avoided as candidates for phage therapy, although in some cases, the lack of lytic phage candidates and emergency conditions may make such considerations moot. Another potential problem is generalized transduction, a term for the ability of some phages to transfer bacterial DNA from one host to another. This occurs because the systems for packaging of the phage DNA into capsids can mistakenly package host DNA instead. Indeed, with some well-characterized phages, up to 5% of the virus particles contain only bacterial DNA. Thus in a typical lysate, the entire genome of the propagating host is present in more than a million copies in every milliliter. For these reasons, it is imperative that any phage to be considered for therapeutic usage should be subjected to thorough genomic analysis and tested for the capacity for generalized transduction.
As antibacterials, phages may also affect the composition of microbiomes, by infecting and killing phage-sensitive strains of bacteria. However, a major advantage of bacteriophages over antibiotics is the high specificity of bacteriophages. This specificity limits antibacterial activity to a sub-species level; typically, a phage kills only selected bacterial strains. For this reason, phages are much less likely (than antibiotics) to disturb the composition of a natural microbiome or to induce dysbiosis. This was demonstrated in experimental studies where microbiome composition was assessed by next-generation sequencing that revealed no important changes correlated with phage treatment in human treatments.
Much of the difficulty in obtaining regulatory approval is proving to be the risks of using a self-replicating entity that has the capability to evolve.
As with antibiotic therapy and other methods of countering bacterial infections, endotoxins are released by the bacteria as they are destroyed within the patient (Jarisch–Herxheimer reaction). This can cause symptoms of fever; in extreme cases, toxic shock (a problem also seen with antibiotics) is possible. Janakiraman Ramachandran argues that this complication can be avoided in those types of infection where this reaction is likely to occur by using genetically engineered bacteriophages that have had their gene responsible for producing endolysin removed. Without this gene, the host bacterium still dies but remains intact, because the lysis is disabled. On the other hand, this modification stops the exponential growth of phages, so one administered phage means at most one dead bacterial cell. Eventually, these dead cells are consumed by the normal house-cleaning duties of the phagocytes, which utilize enzymes to break down the whole bacterium and its contents into harmless proteins, polysaccharides, and lipids.
Temperate (or lysogenic) bacteriophages are not generally used therapeutically, since this group can act as a way for bacteria to exchange DNA. This can help spread antibiotic resistance or even, theoretically, make the bacteria pathogenic, such as in cases of cholera. Carl Merril has claimed that harmless strains of corynebacterium may have been converted into C. diphtheriae that "probably killed a third of all Europeans who came to North America in the seventeenth century". Fortunately, many phages seem to be lytic only with negligible probability of becoming lysogenic.
Regulation and legislation[edit]
Approval of phage therapy for use in humans has not been given in Western countries, with a few exceptions. In the United States, Washington and Oregon law allows naturopathic physicians to use any therapy that is legal anywhere in the world on an experimental basis, and in Texas, phages are considered natural substances and can be used in addition to (but not as a replacement for) traditional therapy (they have been used routinely in a wound care clinic in Lubbock since 2006).
In 2013, "the 20th biennial Evergreen International Phage Meeting ... conference drew 170 participants from 35 countries, including leaders of companies and institutes involved with human phage therapies from France, Australia, Georgia, Poland, and the United States."
In France, phage therapy disappeared officially with the withdrawal of the Vidal dictionary (France's official drug directory), in 1978. The last phage preparation, produced by l'Institut du Bactériophage, was an ointment against skin infections. Phage therapy research ceased at about the same time across the country, with the closure of the bacteriophage department at the Pasteur Institute. Some hospital physicians continued to offer phage therapy until the 1990s, when production died out.
On their rediscovery, at the end of the 1990s, phage preparations were classified as medicines, i.e., "medicinal products" in the EU or "drugs" in the US. However, the pharmaceutical legislation that had been implemented since their disappearance from Western medicine was mainly designed to cater for industrially-made pharmaceuticals, devoid of any customization and intended for large-scale distribution, and it was not deemed necessary to provide phage-specific requirements or concessions.
Today's phage therapy products need to comply with the entire battery of medicinal product licensing requirements: manufacturing according to GMP, preclinical studies, phase I, II, and III clinical trials, and marketing authorisation. Technically, industrially produced predefined phage preparations could make it through the conventional pharmaceutical processes, minding some adaptations. However, phage specificity and resistance issues are likely to cause these defined preparations to have a relatively short useful lifespan. The pharmaceutical industry is currently not considering phage therapy products. Yet, a handful of small and medium-sized enterprises have shown interest, with the help of risk capital and/or public funding. Currently, no defined therapeutic phage product has made it to the EU or US markets.
Conventional drug development process vs. magistral preparation
According to some, therapeutic phages should be prepared individually and kept in large phage banks, ready to be used, upon testing for effectiveness against the patient's bacterial pathogen(s). Intermediary or combined (industrially made as well as precision phage preparations) approaches could be appropriate. However, it turns out to be difficult to reconcile classical phage therapy concepts, which are based on the timely adaptation of phage preparations, with current Western pharmaceutical R&D and marketing models. Repeated calls for a specific regulatory framework have not been heeded by European policymakers. A phage therapy framework based on the Biological Master File concept has been proposed as a (European) solution to regulatory issues, but European regulations do not allow for an extension of this concept to biologically active substances such as phages.
Meanwhile, representatives from the medical, academic, and regulatory communities have established some (temporary) national solutions. For instance, phage applications have been performed in Europe under the umbrella of Article 37 (Unproven Interventions in Clinical Practice) of the Helsinki Declaration. To enable the application of phage therapy after Poland had joined the EU in 2004, the Ludwik Hirszfeld Institute of Immunology and Experimental Therapy in Wrocław opened its own Phage Therapy Unit (PTU). Phage therapy performed at the PTU is considered an "experimental treatment", covered by the adapted Act of 5 December 1996 on the Medical Profession (Polish Law Gazette, 2011, No. 277 item 1634) and Article 37 of the Helsinki Declaration. Similarly, in the last few years, a number of phage therapy interventions have been performed in the US under the FDA's emergency Investigational New Drug (eIND) protocol.
Some patients have been treated with phages under the umbrella of "compassionate use", which is a treatment option that allows a physician to use a not-yet-authorized medicine in desperate cases. Under strict conditions, medicines under development can be made available for use in patients for whom no satisfactory authorized therapies are available and who cannot participate in clinical trials. In principle, this approach can only be applied to products for which earlier study results have demonstrated efficacy and safety, but have not yet been approved. Much like Article 37 of the Helsinki Declaration, the compassionate use treatment option can only be applied when the phages are expected to help in life-threatening or chronic and/or seriously debilitating diseases that are not treatable with formally approved products.
In France, ANSM, the French medicine agency, has organized a specific committee—Comité Scientifique Spécialisé Temporaire (CSST)—for phage therapy, which consists of experts in various fields. Their task is to evaluate and guide each phage therapy request that ends up at the ANSM. Phage therapy requests are discussed together with the treating physicians and consensus advice is sent to the ANSM], which then decides whether or not to grant permission. Between 2006 and 2018, fifteen patients were treated in France (eleven recovered) using this pathway.
In Belgium, in 2016 and in response to a number of parliamentary questions, Maggie De Block, the Minister of Social Affairs and Health, acknowledged that it is indeed not evident to treat phages as industrially made drugs, and therefore she proposed to investigate if the magistral preparation pathway could offer a solution. Magistral preparations (compounding pharmacies in the US) are not subjected to certain constraints such as GMP compliance and marketing authorization. As the "magistral preparation framework" was created to allow for adapted patient treatments and/or to use medicines for which there is no commercial interest, it seemed a suitable framework for precision phage therapy concepts. Magistral preparations are medicines prepared in a pharmacy in accordance with a medical prescription for an individual patient. They are made by a pharmacist (or under his/her supervision) from their constituent ingredients, according to the technical and scientific standards of pharmaceutical technology. Phage active pharmaceutical ingredients to be included in magistral preparations must meet the requirements of a monograph, which describes their production and quality control testing. They must be accompanied by a certificate of analysis, issued by a "Belgian Approved Laboratory", which has been granted an accreditation to perform batch-release testing of medicinal products. Since 2019, phages have been delivered in the form of magistral preparations to nominal patients in Belgium.
The first phage therapy case in China can be traced back to 1958, at Shanghai Jiao Tong University School of Medicine. However, many regulations were not yet established back then, and phage therapy soon lost people's interest due to the prevalence of antibiotics, which eventually led to the antimicrobial resistance crisis. This prompted researchers in China as well as the Chinese government to pay attention to phage therapy again, and following the first investigator-initiated trial (IIT) by the Shanghai Institute of Phage in 2019, phage therapy rapidly flourished. Currently, commercial phage therapy applications must go through either one of two pathways. The first is for fixed-ingredient phage products. The second pathway is for personalized phage products, which need to go through IITs. This way, the products are considered restrictive medical technologies.
Application in other species[edit]
Animals[edit]
Phage therapy has been a relevant mode of treatment in animals for decades. It has been proposed as a method of treating bacterial infections in the veterinary medical field in response to the rampant use of antibiotics. Studies have investigated the application of phage therapy in livestock species as well as companion animals. Brigham Young University has been researching the use of phage therapy to treat American foulbrood in honeybees. Phage therapy is also being investigated for potential applications in aquaculture.
Plants[edit]
Phage therapy has been studied for bacterial spot of stonefruit, caused by Xanthomonas pruni (syn. X. campestris pv. pruni, syn. X. arboricola pv. pruni) in prunus species. Some treatments have been very successful.
Cultural impact[edit]
The 1925 novel and 1926 Pulitzer Prize winner Arrowsmith by Sinclair Lewis used phage therapy as a plot point.
Greg Bear's 2002 novel Vitals features phage therapy, based on Soviet research, used to transfer genetic material.
The 2012 collection of military history essays about the changing role of women in warfare, Women in War – From Home Front to Front Line includes a chapter featuring phage therapy: "Chapter 17: Women who thawed the Cold War".
Steffanie A. Strathdee's book The Perfect Predator: An Epidemiologist's Journey to Save Her Husband from a Deadly Superbug, co-written with her husband, Thomas Patterson, was published by Hachette Book Group in 2019. It describes Strathdee's ultimately successful attempt to introduce phage therapy as a life-saving treatment for her husband, critically ill with a completely antibiotic-resistant Acinetobacter baumannii infection following severe pancreatitis.
See also[edit]
Viruses portal
Antimicrobial resistance
Paul E. Turner
Phage display
Phage monographs
Prophage | biology | 2599056 | https://sv.wikipedia.org/wiki/Metioche%20tacitus | Metioche tacitus | Metioche tacitus är en insektsart som först beskrevs av Henri Saussure 1878. Metioche tacitus ingår i släktet Metioche och familjen syrsor. Inga underarter finns listade i Catalogue of Life.
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Family Medicine, Primary Care Featured Topics Behavioral Health Cancer Children's Health (Pediatrics) Exercise and Fitness Heart Health Men's Health Neurosurgery Obstetrics and Gynecology Orthopedic Health Weight Loss and Bariatric Surgery Women's Health Speaking of Health Wednesday, May 10, 2023 Why antibiotics aren't always the answer for an illness Topics in this Post Family Medicine Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better. Bacteria or virus: What's the difference? Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses. How is it determined if a bacteria or a virus is causing an illness? Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue. For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic. Why aren't antibiotics used to help a person recover quicker? The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover. If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed. This may have you wondering why healthcare professionals don't prescribe antibiotics to help people recover quicker. The answer is trifold: 1. Antibiotics don't work for viruses. Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them. 2. Antibiotics have side effects. If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects. 3. Using antibiotics to treat viruses causes superbugs. Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly. Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy. The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses. Carrie Kern, D.O. , is a family medicine physician in Ellsworth , Wisconsin, and Red Wing , Minnesota. Topics in this Post Family Medicine Related Posts Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions? 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Posted By Carrie Kern, D.O. Family Medicine, Primary Care Featured Topics Behavioral Health Cancer Children's Health (Pediatrics) Exercise and Fitness Heart Health Men's Health Neurosurgery Obstetrics and Gynecology Orthopedic Health Weight Loss and Bariatric Surgery Women's Health Speaking of Health Wednesday, May 10, 2023 Why antibiotics aren't always the answer for an illness Topics in this Post Family Medicine Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better. Bacteria or virus: What's the difference? Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses. How is it determined if a bacteria or a virus is causing an illness? Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue. For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic. Why aren't antibiotics used to help a person recover quicker? The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover. If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed. This may have you wondering why healthcare professionals don't prescribe antibiotics to help people recover quicker. The answer is trifold: 1. Antibiotics don't work for viruses. Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them. 2. Antibiotics have side effects. If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects. 3. Using antibiotics to treat viruses causes superbugs. Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly. Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy. The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses. Carrie Kern, D.O. , is a family medicine physician in Ellsworth , Wisconsin, and Red Wing , Minnesota. Topics in this Post Family Medicine Related Posts Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions?
Posted By Carrie Kern, D.O. Family Medicine, Primary Care Featured Topics Behavioral Health Cancer Children's Health (Pediatrics) Exercise and Fitness Heart Health Men's Health Neurosurgery Obstetrics and Gynecology Orthopedic Health Weight Loss and Bariatric Surgery Women's Health Speaking of Health Wednesday, May 10, 2023 Why antibiotics aren't always the answer for an illness Topics in this Post Family Medicine Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better. Bacteria or virus: What's the difference? Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses. How is it determined if a bacteria or a virus is causing an illness? Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue. For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic. Why aren't antibiotics used to help a person recover quicker? The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover. If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed. This may have you wondering why healthcare professionals don't prescribe antibiotics to help people recover quicker. The answer is trifold: 1. Antibiotics don't work for viruses. Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them. 2. Antibiotics have side effects. If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects. 3. Using antibiotics to treat viruses causes superbugs. Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly. Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy. The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses. Carrie Kern, D.O. , is a family medicine physician in Ellsworth , Wisconsin, and Red Wing , Minnesota. Topics in this Post Family Medicine Related Posts Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions?
Posted By Carrie Kern, D.O. Family Medicine, Primary Care Featured Topics Behavioral Health Cancer Children's Health (Pediatrics) Exercise and Fitness Heart Health Men's Health Neurosurgery Obstetrics and Gynecology Orthopedic Health Weight Loss and Bariatric Surgery Women's Health
Featured Topics Behavioral Health Cancer Children's Health (Pediatrics) Exercise and Fitness Heart Health Men's Health Neurosurgery Obstetrics and Gynecology Orthopedic Health Weight Loss and Bariatric Surgery Women's Health
Speaking of Health Wednesday, May 10, 2023 Why antibiotics aren't always the answer for an illness Topics in this Post Family Medicine Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better. Bacteria or virus: What's the difference? Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses. How is it determined if a bacteria or a virus is causing an illness? Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue. For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic. Why aren't antibiotics used to help a person recover quicker? The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover. If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed. This may have you wondering why healthcare professionals don't prescribe antibiotics to help people recover quicker. The answer is trifold: 1. Antibiotics don't work for viruses. Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them. 2. Antibiotics have side effects. If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects. 3. Using antibiotics to treat viruses causes superbugs. Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly. Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy. The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses. Carrie Kern, D.O. , is a family medicine physician in Ellsworth , Wisconsin, and Red Wing , Minnesota. Topics in this Post Family Medicine Related Posts Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions?
Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better. Bacteria or virus: What's the difference? Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses. How is it determined if a bacteria or a virus is causing an illness? Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue. For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic. Why aren't antibiotics used to help a person recover quicker? The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover. If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed. This may have you wondering why healthcare professionals don't prescribe antibiotics to help people recover quicker. The answer is trifold: 1. Antibiotics don't work for viruses. Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them. 2. Antibiotics have side effects. If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects. 3. Using antibiotics to treat viruses causes superbugs. Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly. Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy. The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses. Carrie Kern, D.O. , is a family medicine physician in Ellsworth , Wisconsin, and Red Wing , Minnesota.
Have you ever left your healthcare professional's office feeling frustrated that you didn't get an antibiotic for a sinus infection, sore throat or ear infection? If you answered yes, you aren't alone. Millions of people visit their healthcare team each year looking for antibiotics to cure infections. The reality is that if you have a virus that cause illnesses like bronchitis, sinus infection and the common cold, you don't need antibiotics to get better.
Though both bacteria and viruses are germs too small to see with the naked eye and are spread in a similar way, the similarities end there. Bacteria are cells capable of surviving on their own. Viruses are not cells — they are even smaller particles that require a host, such as your healthy sinus or lung cells, to survive and multiply. This key difference is why antibiotics aren't effective against viruses.
Determining whether bacteria or a virus has caused an infection can be difficult. Your healthcare team may run blood tests, collect a urine sample or perform a throat swab to help answer this question. The type of infection often is a clue.
For example, scientists know viruses cause bronchitis, so healthcare professionals no longer use antibiotics to treat it. Likewise, over 90% of sinus infections are caused by viruses. Antibiotics typically are not used to treat a sinus infection unless it lasts longer than 10 days without improvement. Your healthcare professional will evaluate, test and review your symptoms to be confident your infection is caused by a bacteria before prescribing an antibiotic.
The body needs time to fight an infection, whether bacteria or a virus causes that infection. After the infection is gone, the body needs additional time to recover.
If an illness does not improve with an antibiotic, this is an indication that the infection causing the illness is viral. Unless an illness becomes severe, additional antibiotics are not needed.
Antibiotics work by destroying bacterial cell membranes and bacterial replication. Since viruses are not cells, they do not have cell membranes, so antibiotics are ineffective against them.
If you take antibiotics for a viral infection, you are putting yourself at risk for side effects. All antibiotics can cause diarrhea and nausea. Some antibiotics are hard on your kidneys, liver or other body parts. In certain instances, side effects can be life-threatening, such as an allergic reaction. Every antibiotic can have side effects.
Superbugs are bacteria that become resistant to antibiotics. This happens when antibiotics are inappropriately used to treat viral infections. When a person gets an infection caused by a superbug, antibiotics don't work. Thousands of people die from these infections every year. Infants, young children and older adults are at greatest risk. These deaths are preventable — but only if antibiotics are used correctly.
Viral infections are as common as they are frustrating. Your body is designed to fight these infections. You can help your body heal and strengthen your immune system by getting plenty of rest, staying hydrated and eating healthy.
The next time you see your healthcare team for an infection, you have an opportunity to be a good steward of antibiotics. If your healthcare team determines that you don't need antibiotics, you can contribute to the greater good by avoiding unnecessary use of these medications for viral illnesses.
Related Posts Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions?
Self-care tips for moms Should I use antibiotics or home remedies to treat my child's illness? Need motivation to tackle your New Year's resolutions?
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beginning of content What is the difference between bacterial and viral infections? 3-minute read Print Share share via Facebook share via Email Save Share via email There is a total of 5 error s on this form, details are below. Please enter your name Please enter your email Your email is invalid. Please check and try again Please enter recipient's email Recipient's email is invalid. Please check and try again Agree to Terms required Thank you for sharing our content. A message has been sent to your recipient's email address with a link to the content webpage. Your name: is required Error: This is required Your email: is required Error: This is required Error: Not a valid value Send to: is required Error: This is required Error: Not a valid value Error: This is required I have read and agree to the Terms of Use and Privacy Policy is required . Submit Listen Key facts Bacteria are single cells that can survive on their own, inside or outside the body. Viruses cause infections by entering and multiplying inside the host's healthy cells. It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Antibiotics won't work for viral infections. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance. Antibiotics won't cure viral infections. How are bacteria different from viruses? Bacteria and viruses are too tiny to see with the naked eye. They can cause similar symptoms and are often spread in the same way, but are different in most other ways. Bacteria are single cells that can survive on their own, inside or outside the body. Most bacteria aren't harmful. In fact, you have many harmless and helpful bacteria on your skin and inside your body, especially in the gut to help digest food. Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the body's healthy cells. How are bacterial infections different from viral infections? It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Your doctor may need a sample of your urine, stool or blood, or a swab from your nose or throat to see what sort of infection you have. If you have symptoms on an infection, it is important to know if it is caused by bacteria or viruses, because the treatments differ. Examples of bacterial infections include whooping cough , strep throat , ear infection and urinary tract infection (UTI) . Examples of viral infections include the common cold and flu , most coughs and bronchitis , chickenpox , monkeypox , COVID-19 and HIV/AIDS . What treatment will I receive for bacterial and viral infections? Treating a bacterial infection Doctors usually treat bacterial infections with antibiotics. It's important to match the antibiotic with the specific type of bacterial infection you have. The right antibiotic will kill bacteria or stop them multiplying. Antibiotic resistance is a growing problem in Australia and the world. It is caused, in part, by overuse of antibiotics in humans, animals and the environment. This is one of the reasons why your doctor will only prescribe antibiotics when they are confident that the benefits of treatment are greater than the risks. Treating a viral infection Antibiotics aren't effective against viral infections. If you have a viral infection, your doctor may recommend one or more of the following treatments: rest at home to allow your immune system to fight the virus managing symptoms, such as warm drinks or chicken soup to soothe your throat and stay hydrated paracetamol to relieve fever stopping viral reproduction using antiviral medicines, such as medicines for HIV/AIDS and cold sores preventing infection in the first place, such as vaccines for flu and hepatitis Source s : University of Queensland Institute for molecular Bioscience (What’s the difference between bacteria and viruses?) , Department of Health and Aged care (Antimicrobial resistance) , Royal Children's Hospital (Viral illnesses) Learn more here about the development and quality assurance of healthdirect content . Last reviewed: September 2022 Back To Top Related pages Bacterial infections Search our site for Antibiotics Antibiotic Resistance Hygiene Abscess Infectious diseases Neutropenia Need more information? These trusted information partners have more on this topic. General search results Results for medical professionals Top results Infections – bacterial and viral - Better Health Channel Many bacterial infections can be treated with antibiotics, but they are useless against viral infections. Read more on Better Health Channel website Antibiotic resistance: what you need to know | Children's Health Queensland Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work. Read more on Queensland Health website About antibiotics Learn when antibiotics are really needed - for infections caused by bacteria, not viruses. Read more on NPS MedicineWise website Antibiotics - MyDr.com.au Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections. Read more on myDr website Antibiotics and children - MyDr.com.au Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics. Read more on myDr website Meningitis in children - MyDr.com.au Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection. Read more on myDr website Streptococcal sore throat | SA Health Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes. Read more on SA Health website Infections - Liver Foundation People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or… Read more on Liver Foundation website Conjunctivitis | SA Health Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies. Read more on SA Health website Meningitis - Better Health Channel Meningitis can cause death and requires urgent medical attention. Read more on Better Health Channel website Show more Top results Strep Throat Symptoms and Related Conditions | Ausmed Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15. Read more on Ausmed Education website Sputum culture | Pathology Tests Explained A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact Read more on Pathology Tests Explained website Stool culture | Pathology Tests Explained The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types Read more on Pathology Tests Explained website Syphilis serology | Pathology Tests Explained The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated Read more on Pathology Tests Explained website Blood culture | Pathology Tests Explained Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv Read more on Pathology Tests Explained website Gum Disease (Gingivitis and Periodontitis) | Ausmed Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation. Read more on Ausmed Education website The Common Cold: Symptoms, Prevention & Treatment | Ausmed The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat. Read more on Ausmed Education website Rickettsial diseases testing | Pathology Tests Explained The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms Read more on Pathology Tests Explained website Epstein-Barr Virus Antibodies | Pathology Tests Explained Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h Read more on Pathology Tests Explained website Procalcitonin | Pathology Tests Explained This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I Read more on Pathology Tests Explained website Show more Disclaimer Healthdirect Australia is not responsible for the content and advertising on the external website you are now entering. OK
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Key facts Bacteria are single cells that can survive on their own, inside or outside the body. Viruses cause infections by entering and multiplying inside the host's healthy cells. It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Antibiotics won't work for viral infections. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance. Antibiotics won't cure viral infections. How are bacteria different from viruses? Bacteria and viruses are too tiny to see with the naked eye. They can cause similar symptoms and are often spread in the same way, but are different in most other ways. Bacteria are single cells that can survive on their own, inside or outside the body. Most bacteria aren't harmful. In fact, you have many harmless and helpful bacteria on your skin and inside your body, especially in the gut to help digest food. Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the body's healthy cells. How are bacterial infections different from viral infections? It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Your doctor may need a sample of your urine, stool or blood, or a swab from your nose or throat to see what sort of infection you have. If you have symptoms on an infection, it is important to know if it is caused by bacteria or viruses, because the treatments differ. Examples of bacterial infections include whooping cough , strep throat , ear infection and urinary tract infection (UTI) . Examples of viral infections include the common cold and flu , most coughs and bronchitis , chickenpox , monkeypox , COVID-19 and HIV/AIDS . What treatment will I receive for bacterial and viral infections? Treating a bacterial infection Doctors usually treat bacterial infections with antibiotics. It's important to match the antibiotic with the specific type of bacterial infection you have. The right antibiotic will kill bacteria or stop them multiplying. Antibiotic resistance is a growing problem in Australia and the world. It is caused, in part, by overuse of antibiotics in humans, animals and the environment. This is one of the reasons why your doctor will only prescribe antibiotics when they are confident that the benefits of treatment are greater than the risks. Treating a viral infection Antibiotics aren't effective against viral infections. If you have a viral infection, your doctor may recommend one or more of the following treatments: rest at home to allow your immune system to fight the virus managing symptoms, such as warm drinks or chicken soup to soothe your throat and stay hydrated paracetamol to relieve fever stopping viral reproduction using antiviral medicines, such as medicines for HIV/AIDS and cold sores preventing infection in the first place, such as vaccines for flu and hepatitis
Key facts Bacteria are single cells that can survive on their own, inside or outside the body. Viruses cause infections by entering and multiplying inside the host's healthy cells. It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Antibiotics won't work for viral infections. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance. Antibiotics won't cure viral infections.
Bacteria and viruses are too tiny to see with the naked eye. They can cause similar symptoms and are often spread in the same way, but are different in most other ways.
Bacteria are single cells that can survive on their own, inside or outside the body. Most bacteria aren't harmful. In fact, you have many harmless and helpful bacteria on your skin and inside your body, especially in the gut to help digest food.
Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the body's healthy cells.
It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Your doctor may need a sample of your urine, stool or blood, or a swab from your nose or throat to see what sort of infection you have.
If you have symptoms on an infection, it is important to know if it is caused by bacteria or viruses, because the treatments differ.
Examples of bacterial infections include whooping cough , strep throat , ear infection and urinary tract infection (UTI) .
Examples of viral infections include the common cold and flu , most coughs and bronchitis , chickenpox , monkeypox , COVID-19 and HIV/AIDS .
Doctors usually treat bacterial infections with antibiotics. It's important to match the antibiotic with the specific type of bacterial infection you have. The right antibiotic will kill bacteria or stop them multiplying.
Antibiotic resistance is a growing problem in Australia and the world. It is caused, in part, by overuse of antibiotics in humans, animals and the environment. This is one of the reasons why your doctor will only prescribe antibiotics when they are confident that the benefits of treatment are greater than the risks.
Antibiotics aren't effective against viral infections. If you have a viral infection, your doctor may recommend one or more of the following treatments:
Source s : University of Queensland Institute for molecular Bioscience (What’s the difference between bacteria and viruses?) , Department of Health and Aged care (Antimicrobial resistance) , Royal Children's Hospital (Viral illnesses)
University of Queensland Institute for molecular Bioscience (What’s the difference between bacteria and viruses?) , Department of Health and Aged care (Antimicrobial resistance) , Royal Children's Hospital (Viral illnesses)
General search results Results for medical professionals Top results Infections – bacterial and viral - Better Health Channel Many bacterial infections can be treated with antibiotics, but they are useless against viral infections. Read more on Better Health Channel website Antibiotic resistance: what you need to know | Children's Health Queensland Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work. Read more on Queensland Health website About antibiotics Learn when antibiotics are really needed - for infections caused by bacteria, not viruses. Read more on NPS MedicineWise website Antibiotics - MyDr.com.au Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections. Read more on myDr website Antibiotics and children - MyDr.com.au Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics. Read more on myDr website Meningitis in children - MyDr.com.au Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection. Read more on myDr website Streptococcal sore throat | SA Health Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes. Read more on SA Health website Infections - Liver Foundation People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or… Read more on Liver Foundation website Conjunctivitis | SA Health Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies. Read more on SA Health website Meningitis - Better Health Channel Meningitis can cause death and requires urgent medical attention. Read more on Better Health Channel website Show more Top results Strep Throat Symptoms and Related Conditions | Ausmed Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15. Read more on Ausmed Education website Sputum culture | Pathology Tests Explained A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact Read more on Pathology Tests Explained website Stool culture | Pathology Tests Explained The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types Read more on Pathology Tests Explained website Syphilis serology | Pathology Tests Explained The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated Read more on Pathology Tests Explained website Blood culture | Pathology Tests Explained Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv Read more on Pathology Tests Explained website Gum Disease (Gingivitis and Periodontitis) | Ausmed Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation. Read more on Ausmed Education website The Common Cold: Symptoms, Prevention & Treatment | Ausmed The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat. Read more on Ausmed Education website Rickettsial diseases testing | Pathology Tests Explained The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms Read more on Pathology Tests Explained website Epstein-Barr Virus Antibodies | Pathology Tests Explained Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h Read more on Pathology Tests Explained website Procalcitonin | Pathology Tests Explained This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I Read more on Pathology Tests Explained website Show more
General search results Results for medical professionals Top results Infections – bacterial and viral - Better Health Channel Many bacterial infections can be treated with antibiotics, but they are useless against viral infections. Read more on Better Health Channel website Antibiotic resistance: what you need to know | Children's Health Queensland Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work. Read more on Queensland Health website About antibiotics Learn when antibiotics are really needed - for infections caused by bacteria, not viruses. Read more on NPS MedicineWise website Antibiotics - MyDr.com.au Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections. Read more on myDr website Antibiotics and children - MyDr.com.au Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics. Read more on myDr website Meningitis in children - MyDr.com.au Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection. Read more on myDr website Streptococcal sore throat | SA Health Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes. Read more on SA Health website Infections - Liver Foundation People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or… Read more on Liver Foundation website Conjunctivitis | SA Health Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies. Read more on SA Health website Meningitis - Better Health Channel Meningitis can cause death and requires urgent medical attention. Read more on Better Health Channel website Show more Top results Strep Throat Symptoms and Related Conditions | Ausmed Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15. Read more on Ausmed Education website Sputum culture | Pathology Tests Explained A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact Read more on Pathology Tests Explained website Stool culture | Pathology Tests Explained The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types Read more on Pathology Tests Explained website Syphilis serology | Pathology Tests Explained The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated Read more on Pathology Tests Explained website Blood culture | Pathology Tests Explained Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv Read more on Pathology Tests Explained website Gum Disease (Gingivitis and Periodontitis) | Ausmed Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation. Read more on Ausmed Education website The Common Cold: Symptoms, Prevention & Treatment | Ausmed The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat. Read more on Ausmed Education website Rickettsial diseases testing | Pathology Tests Explained The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms Read more on Pathology Tests Explained website Epstein-Barr Virus Antibodies | Pathology Tests Explained Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h Read more on Pathology Tests Explained website Procalcitonin | Pathology Tests Explained This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I Read more on Pathology Tests Explained website Show more
General search results Results for medical professionals Top results Infections – bacterial and viral - Better Health Channel Many bacterial infections can be treated with antibiotics, but they are useless against viral infections. Read more on Better Health Channel website Antibiotic resistance: what you need to know | Children's Health Queensland Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work. Read more on Queensland Health website About antibiotics Learn when antibiotics are really needed - for infections caused by bacteria, not viruses. Read more on NPS MedicineWise website Antibiotics - MyDr.com.au Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections. Read more on myDr website Antibiotics and children - MyDr.com.au Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics. Read more on myDr website Meningitis in children - MyDr.com.au Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection. Read more on myDr website Streptococcal sore throat | SA Health Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes. Read more on SA Health website Infections - Liver Foundation People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or… Read more on Liver Foundation website Conjunctivitis | SA Health Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies. Read more on SA Health website Meningitis - Better Health Channel Meningitis can cause death and requires urgent medical attention. Read more on Better Health Channel website Show more Top results Strep Throat Symptoms and Related Conditions | Ausmed Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15. Read more on Ausmed Education website Sputum culture | Pathology Tests Explained A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact Read more on Pathology Tests Explained website Stool culture | Pathology Tests Explained The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types Read more on Pathology Tests Explained website Syphilis serology | Pathology Tests Explained The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated Read more on Pathology Tests Explained website Blood culture | Pathology Tests Explained Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv Read more on Pathology Tests Explained website Gum Disease (Gingivitis and Periodontitis) | Ausmed Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation. Read more on Ausmed Education website The Common Cold: Symptoms, Prevention & Treatment | Ausmed The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat. Read more on Ausmed Education website Rickettsial diseases testing | Pathology Tests Explained The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms Read more on Pathology Tests Explained website Epstein-Barr Virus Antibodies | Pathology Tests Explained Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h Read more on Pathology Tests Explained website Procalcitonin | Pathology Tests Explained This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I Read more on Pathology Tests Explained website Show more
Many bacterial infections can be treated with antibiotics, but they are useless against viral infections.
Many bacterial infections can be treated with antibiotics, but they are useless against viral infections.
Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work.
Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work.
Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections.
Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections.
Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics.
Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics.
Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection.
Meningitis means inflammation of the meninges - the lining around the brain and spinal cord. It is usually caused by a bacterial or viral infection.
Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes.
Streptococcal sore throat is a bacterial infection of the throat and tonsils caused by Streptococcus pyogenes.
People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or…
People with liver disease are much more likely than other people to get a bacterial infection (an infection caused by bacteria). The most common infections you might get are cellulitis (infection in the skin of the legs or belly) urinary tract infections, pneumonia, peritonitis (infection in ascites), dental infection or…
Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies.
Conjunctivitis is an inflammation of the lining of the eye and eyelid caused by bacteria, viruses, chemicals or allergies.
Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15.
Strep throat, otherwise known as group A strep, is a bacterial infection of the throat and tonsils. The bacteria that causes strep throat is called group A streptococcus. It is most common among school-aged children and teenagers between 5 and 15.
A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact
A sputum culture detects the presence of pathogenic bacteria in those who have bacterial pneumonia or a lower respiratory tract infections. Pathogenetic bact
The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types
The stool culture is a test that detects and identifies bacteria that cause infections of the lower digestive tract. The test distinguishes between the types
The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated
The test is looking for evidence of Treponema pallidum, the bacterium that causes syphilis. Syphilis is a sexually transmitted disease. It is easily treated
Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv
Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Some bacteria prefer oxygen (aerobes), while others thriv
Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation.
Gum disease occurs when the gum (gingiva) - the mucosal tissue surrounding and protecting the teeth - becomes infected and inflamed. Gum disease is usually caused by plaque, a sticky coating of bacteria that accumulates on the teeth along the gum line and causes irritation.
The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat.
The common cold (or upper respiratory tract infection) is a highly prevalent viral infection that can be caused by over 200 types of viruses including some strains of the coronavirus family. It affects the nose, ears and throat.
The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms
The most important diseases in Australia are Queensland tick typhus, Scrub typhus, Flinders Island spotted fever, and Murine typhus. The causative organisms
Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h
Epstein-Barr virus (EBV) antibodies are a group of tests that are ordered to help diagnose a current, recent, or past EBV infection. EBV is a member of the h
This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I
This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. I
Disclaimer Healthdirect Australia is not responsible for the content and advertising on the external website you are now entering. OK
Healthdirect Australia is not responsible for the content and advertising on the external website you are now entering.
Healthdirect Australia is not responsible for the content and advertising on the external website you are now entering.
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Overview - Antibiotics Contents Overview Uses Side effects Interactions Antibiotic resistance Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything. Many mild bacterial infections get better on their own without using antibiotics. Antibiotics do not work for viral infections such as colds and flu, and most coughs. Antibiotics are no longer routinely used to treat: chest infections ear infections in children sore throats When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future. When antibiotics are needed Antibiotics may be used to treat bacterial infections that: are unlikely to clear up without antibiotics could infect others could take too long to clear without treatment carry a risk of more serious complications People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis. Read more about when antibiotics are used and why antibiotics are not routinely used to treat infections . How to take antibiotics Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist. Antibiotics can come as: tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections Missing a dose of antibiotics If you forget to take a dose of your antibiotics, check the patient information leaflet that came with your medicine to find out what to do. If you're not sure, speak to a pharmacist or a GP. In most cases, you can take the dose you missed as soon as you remember and then continue to take your course of antibiotics as normal. But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Accidentally taking an extra dose There's an increased risk of side effects if you take 2 doses closer together than recommended. Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm. But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick. If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible. Side effects of antibiotics As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare. The common side effects include: being sick feeling sick bloating and indigestion diarrhoea Some people may have an allergic reaction to antibiotics, especially penicillin and another type of antibiotic called cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis) , which is a medical emergency. Call 999 or go to A&E now if: you get a skin rash that may include itchy, red, swollen, blistered or peeling skin you're wheezing you get tightness in the chest or throat you have trouble breathing or talking your mouth, face, lips, tongue or throat start swelling You could be having a serious allergic reaction and may need immediate treatment in hospital. Read more about the side effects of antibiotics . Considerations and interactions Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding. Tell your healthcare professional if you're pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you. Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member. Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol. Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP. Read more about how antibiotics interact with other medicines . Types of antibiotics There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups. Penicillins (such as penicillin, amoxicillin , co-amoxiclav , flucloxacillin and phenoxymethylpenicillin ) – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections Cephalosporins (such as cefalexin ) – used to treat a wide range of infections, but some are also effective for treating more serious infections, such as sepsis and meningitis Aminoglycosides (such as gentamicin and tobramycin) – tend to only be used in hospital to treat very serious illnesses such as sepsis, as they can cause serious side effects, including hearing loss and kidney damage; they're usually given by injection, but may be given as drops for some ear or eye infections Tetracyclines (such as tetracycline, doxycycline and lymecycline ) – can be used to treat a wide range of infections, but are commonly used to treat acne and a skin condition called rosacea Macrolides (such as azithromycin , erythromycin and clarithromycin ) – can be particularly useful for treating lung and chest infections, or as an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria Fluoroquinolones (such as ciprofloxacin and levofloxacin) – are broad-spectrum antibiotics that were once used to treat a wide range of infections, especially respiratory and urinary tract infections; these antibiotics are no longer used routinely because of the risk of serious side effects Other antibiotics include chloramphenicol (used for eye and ear infections), fusidic acid (used for skin and eye infections), and nitrofurantoin and trimethoprim (used for urinary tract infections). Page last reviewed: 11 November 2022 Next review due: 11 November 2025 Next : Uses
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything. Many mild bacterial infections get better on their own without using antibiotics. Antibiotics do not work for viral infections such as colds and flu, and most coughs. Antibiotics are no longer routinely used to treat: chest infections ear infections in children sore throats When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future. When antibiotics are needed Antibiotics may be used to treat bacterial infections that: are unlikely to clear up without antibiotics could infect others could take too long to clear without treatment carry a risk of more serious complications People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis. Read more about when antibiotics are used and why antibiotics are not routinely used to treat infections . How to take antibiotics Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist. Antibiotics can come as: tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections Missing a dose of antibiotics If you forget to take a dose of your antibiotics, check the patient information leaflet that came with your medicine to find out what to do. If you're not sure, speak to a pharmacist or a GP. In most cases, you can take the dose you missed as soon as you remember and then continue to take your course of antibiotics as normal. But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Accidentally taking an extra dose There's an increased risk of side effects if you take 2 doses closer together than recommended. Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm. But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick. If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible. Side effects of antibiotics As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare. The common side effects include: being sick feeling sick bloating and indigestion diarrhoea Some people may have an allergic reaction to antibiotics, especially penicillin and another type of antibiotic called cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis) , which is a medical emergency. Call 999 or go to A&E now if: you get a skin rash that may include itchy, red, swollen, blistered or peeling skin you're wheezing you get tightness in the chest or throat you have trouble breathing or talking your mouth, face, lips, tongue or throat start swelling You could be having a serious allergic reaction and may need immediate treatment in hospital. Read more about the side effects of antibiotics . Considerations and interactions Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding. Tell your healthcare professional if you're pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you. Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member. Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol. Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP. Read more about how antibiotics interact with other medicines . Types of antibiotics There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups. Penicillins (such as penicillin, amoxicillin , co-amoxiclav , flucloxacillin and phenoxymethylpenicillin ) – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections Cephalosporins (such as cefalexin ) – used to treat a wide range of infections, but some are also effective for treating more serious infections, such as sepsis and meningitis Aminoglycosides (such as gentamicin and tobramycin) – tend to only be used in hospital to treat very serious illnesses such as sepsis, as they can cause serious side effects, including hearing loss and kidney damage; they're usually given by injection, but may be given as drops for some ear or eye infections Tetracyclines (such as tetracycline, doxycycline and lymecycline ) – can be used to treat a wide range of infections, but are commonly used to treat acne and a skin condition called rosacea Macrolides (such as azithromycin , erythromycin and clarithromycin ) – can be particularly useful for treating lung and chest infections, or as an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria Fluoroquinolones (such as ciprofloxacin and levofloxacin) – are broad-spectrum antibiotics that were once used to treat a wide range of infections, especially respiratory and urinary tract infections; these antibiotics are no longer used routinely because of the risk of serious side effects Other antibiotics include chloramphenicol (used for eye and ear infections), fusidic acid (used for skin and eye infections), and nitrofurantoin and trimethoprim (used for urinary tract infections). Page last reviewed: 11 November 2022 Next review due: 11 November 2025 Next : Uses
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything. Many mild bacterial infections get better on their own without using antibiotics. Antibiotics do not work for viral infections such as colds and flu, and most coughs. Antibiotics are no longer routinely used to treat: chest infections ear infections in children sore throats When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future. When antibiotics are needed Antibiotics may be used to treat bacterial infections that: are unlikely to clear up without antibiotics could infect others could take too long to clear without treatment carry a risk of more serious complications People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis. Read more about when antibiotics are used and why antibiotics are not routinely used to treat infections . How to take antibiotics Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist. Antibiotics can come as: tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections Missing a dose of antibiotics If you forget to take a dose of your antibiotics, check the patient information leaflet that came with your medicine to find out what to do. If you're not sure, speak to a pharmacist or a GP. In most cases, you can take the dose you missed as soon as you remember and then continue to take your course of antibiotics as normal. But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Accidentally taking an extra dose There's an increased risk of side effects if you take 2 doses closer together than recommended. Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm. But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick. If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible. Side effects of antibiotics As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare. The common side effects include: being sick feeling sick bloating and indigestion diarrhoea Some people may have an allergic reaction to antibiotics, especially penicillin and another type of antibiotic called cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis) , which is a medical emergency. Call 999 or go to A&E now if: you get a skin rash that may include itchy, red, swollen, blistered or peeling skin you're wheezing you get tightness in the chest or throat you have trouble breathing or talking your mouth, face, lips, tongue or throat start swelling You could be having a serious allergic reaction and may need immediate treatment in hospital. Read more about the side effects of antibiotics . Considerations and interactions Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding. Tell your healthcare professional if you're pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you. Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member. Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol. Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP. Read more about how antibiotics interact with other medicines . Types of antibiotics There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups. Penicillins (such as penicillin, amoxicillin , co-amoxiclav , flucloxacillin and phenoxymethylpenicillin ) – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections Cephalosporins (such as cefalexin ) – used to treat a wide range of infections, but some are also effective for treating more serious infections, such as sepsis and meningitis Aminoglycosides (such as gentamicin and tobramycin) – tend to only be used in hospital to treat very serious illnesses such as sepsis, as they can cause serious side effects, including hearing loss and kidney damage; they're usually given by injection, but may be given as drops for some ear or eye infections Tetracyclines (such as tetracycline, doxycycline and lymecycline ) – can be used to treat a wide range of infections, but are commonly used to treat acne and a skin condition called rosacea Macrolides (such as azithromycin , erythromycin and clarithromycin ) – can be particularly useful for treating lung and chest infections, or as an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria Fluoroquinolones (such as ciprofloxacin and levofloxacin) – are broad-spectrum antibiotics that were once used to treat a wide range of infections, especially respiratory and urinary tract infections; these antibiotics are no longer used routinely because of the risk of serious side effects Other antibiotics include chloramphenicol (used for eye and ear infections), fusidic acid (used for skin and eye infections), and nitrofurantoin and trimethoprim (used for urinary tract infections). Page last reviewed: 11 November 2022 Next review due: 11 November 2025 Next : Uses
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything.
When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future.
People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis.
Read more about when antibiotics are used and why antibiotics are not routinely used to treat infections .
Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist.
If you forget to take a dose of your antibiotics, check the patient information leaflet that came with your medicine to find out what to do. If you're not sure, speak to a pharmacist or a GP.
In most cases, you can take the dose you missed as soon as you remember and then continue to take your course of antibiotics as normal.
But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick.
If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible.
As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare.
Some people may have an allergic reaction to antibiotics, especially penicillin and another type of antibiotic called cephalosporins.
In very rare cases, this can lead to a serious allergic reaction (anaphylaxis) , which is a medical emergency.
Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding.
Tell your healthcare professional if you're pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you.
Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP.
There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups.
Other antibiotics include chloramphenicol (used for eye and ear infections), fusidic acid (used for skin and eye infections), and nitrofurantoin and trimethoprim (used for urinary tract infections).
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Support links Home Health A to Z Live Well Mental health Care and support Pregnancy NHS services Coronavirus (COVID-19) NHS App Find my NHS number View your GP health record View your test results About the NHS Healthcare abroad Contact us Other NHS websites Profile editor login About us Accessibility statement Our policies Cookies © Crown copyright
Home Health A to Z Live Well Mental health Care and support Pregnancy NHS services Coronavirus (COVID-19) NHS App Find my NHS number View your GP health record View your test results About the NHS Healthcare abroad Contact us Other NHS websites Profile editor login About us Accessibility statement Our policies Cookies | biology | 30738 | https://no.wikipedia.org/wiki/Antibiotika | Antibiotika | Antibiotika (entall: antibiotikum, fra gresk anti - mot, bios - liv) er benevnelsen på en rekke medikamenter som hemmer formeringen av, eller dreper, mikroorganismer. For biologer betyr det stoffer produsert av levende organismer for å holde andre organismer borte. For eksempel lever både bakterier og sopp enten som parasitter eller av å bryte ned dødt materiale. Siden begge har samme matkilde, prøver de å forgifte hverandre ved å skille stoffer som de andre ikke tolererer. For eksempel produserer enkelte muggsopper penicillin for å holde bakterier unna, mens aktinobakterier produserer amfotericin for å holde sopp unna.
De antibiotika som har blitt kjent for helsepersonell og i forlengelsen for allmenheten er de som kan benyttes som legemidler. Når det snakkes om antibiotika i dagligtalen, viser man til legemidler mot bakterier i sin alminnelighet, også preparater som er syntetiske, det vil si som mangler motstykker i naturen. Slike legemidler kan enten være baktericide (bakteriedrepende) eller bakteriostatiske (veksthemmende).
Historie
Antibiotika ble opprinnelig fremstilt av mikroskopiske sopparter, men produseres i dag syntetisk. Antibiotika brukes mot bakterie- og amøbeinfeksjoner, men ikke virus siden virus ikke er levende. Penicillin er en type antibiotika de fleste har hørt om, og var også den første typen som ble oppdaget. I 1928 ble penicillin oppdaget ved en tilfeldighet av den skotske legen Alexander Fleming (1881–1955). Først i 1950-årene ble penicillin tatt ordentlig i bruk.
Typer antibiotika etter angrepspunkt
For at et antibiotikum skal kunne brukes må det være i stand til å skade eller drepe bakterieceller (prokaryote celler) uten i alt for stor grad å skade menneske- eller dyreceller (eukaryote celler). Det må derfor virke på elementer eller prosesser i bakterier som mangler, eller er svært forskjellige fra, eukaryote celler. Det er kun et fåtall som kan virke slik.
Folatsyntese eller virkning
Til forskjell fra eukaryote celler kan bakterier produsere folsyre. Trimetoprim er ett eksempel på et vanlig antibiotikum som hemmer denne produksjonen. Det benyttes også innimellom sammen med sulfonamid som også hemmer folatsyntesen.
Betalaktam-ring
De aller fleste bakterier, til forskjell fra alle dyreceller, har en cellevegg. Antibiotika som ødelegger eller hindrer oppbygging av denne tillhører de mest brukte antibakterielle legemidlene. Den største gruppen av disse kalles betalaktamantibiotika og omfatter penicilliner, cefalosporiner og karbapenemer.
Betalaktamantibiotika har en baktericid virkemåte.
Enkelte glykopeptider, for eksempel vankomycin, ødelegger også oppbyggingen av celleveggen.
Proteinsyntesen
Såvel bakterier som eukaryoter har ribosomer som produserer proteiner etter RNA-tegninger. Det finnes likevel forskjeller i oppbygningen deres, prokaryoter har en 70 S-ribosom bygget opp av en 30S- og en 50S-enhet, mens eukaryoter har en 80S-ribosom som består av en 40S- og en 60S-enhet. Antibiotika som tetracykliner, aminoglykosider, linkosamider (klindamycin), kloramfenikol, makrolider og linezolid hemmer på forskjellige måter proteinsyntesen i ribosomene.
Andre eksempler på slike antibiotika er streptograminer og Fusidinsyre.
Nukleinsyresyntese
Bakterier mangler cellekjerne, men har på samme måte som eukaryote celler DNA. Kinoloner og metronidazol ødelegger på forskjellige måter DNA-syntesen mens rifampicin hemmer RNA-syntesen.
Cellemembranfunksjon
Noen polypeptider, for eksempel Polymyxin E, fungerer som løsningsmiddel i det fettrike cellemembranet, og dette medfører at bakteriens celleinnhold lekker ut og bakterien dør.
Topoisomerase II
Fluorokinoloner
Andre
Anti-tuberkulose
Anti-lepra
Bredspektrumantibiotika
Det er mange ulike slag bakterier som forårsaker infeksjoner. De fleste antibiotika er derfor bare i stand til å påvirke en del av disse bakteriene. Antibiotika som påvirker mange ulike bakterier sies å ha et bredt spektrum., mens antibiotika som kun påvirker en mindre gruppe bakterier sies å ha et smalt spektrum.
Det er bedre at det oftest mulig velges antibiotika med smalt spektrum som ikke påvirker den normale beskyttende bakteriefloraen, man kun dreper de bakteriene som forårsaker en spesifikk sykdom.
Kinoloner og tetracykliner er eksempler på bredspektrumantibiotika.
Nye antibiotika
Den grunnleggende utfordringen i utviklingen av nye antibiotika er å identifisere og utnytte forskjeller i cellestruktur og mekanismer mellom på den ene siden vertsorganismens celler og på en andre siden bakteriecellene. Det er avgjørende for et antibiotikums verdi som legemiddel at det har en effektiv virkning mot en eller flere mikroorganismer, samtidig som det utøver så lite skade som mulig på den vertsorganismen der infeksjonssykdom skal kureres. Dette vilkåret navnga Paul Ehrlich som "selektiv toksisitet", altså forholdet at stoffet er skadelig for de sykdomsfremkallende mikroorganismene, men ikke eller i liten utstrekning skader vertsorganismens celler.
Resistens
Etterhvert som bruken av antibiotika har tiltatt, har det oppstått stadig større problemer med såkalt antibiotikaresistens eller motstandsdyktighet. Slik resistens medfører at de vanlige antibiotiske midlene ikke lenger er virksomme.
Ved dyrkning av en bakterieprøve skilles først ut forskjellige typer bakterier. Deretter kan hver bakteriestamme fra prøven gå igjennom resistensbestemmelse som viser om bakterien er følsom eller resistent mot forskjellige aktuelle antibiotika.
Det antas at den genetiske koden som gir antibiotikaresistens har sin opprinnelse i det naturlige miljø der ulike mikroorganismer benytter antibiotika i sin innbyrdes "krigføring". Resistens kan enten forekomme gjennom spontane mutasjoner i bakteriens genom eller ved at bakterien får andre bakteriers resistensgener gjennom en av tre mekanismer:
Konjugasjon -
Overføring av plasmider mellom bakterier (skjer normalt mellom kroppens egen normalflora og fremmede bakterier)
Transformasjon -
Opptak av fritt DNA fra døde bakterier i nærheten
Transduksjon -
Overføring av gener mellom bakterier gjennom en bakteriofag, dvs et bakterievirus
Den stadige økningen i antalle motstandsdyktige bakterier som følge av antibiotikabruk bør føre til at legene bare skriver ut resepter på antibiotika når det er nødvendig, og at det om mulig brukes såkalte smalspektrede antibiotika. I Norge lå antibiotikabruken stabilt fra 1993–2004, men har steget med 6 % årlig fra 2004. Norge har lenge hatt lite resistensproblematikk sammenliknet med andre europeiske land, men større reiseaktivitet har ført til økt import av resistente bakterier.
Det er risikofritt å ta antibiotika så lenge man tar hele dosen, på nøyaktig foreskrevet tid. Ved hver antibiotikabehandling som ikke tar livet av 100 prosent av bakteriene er det bakteriene som har den største motstandskraften som overlever. Dette kan skje om behandlingen avbrytes for tidlig eller om dosen er for lav. Da er det stor risiko for at man blir syk igjen (de overlevende bakteriene er resistente mot den tidligere medisinen og da må en ny medisin benyttes). Det er også en fare for at samme effekt kan oppstå ved at bakterier utsettes for små mengder antibiotika fra søl, rester av antibakterielle rengjøringsmidler eller urin og avføring fra antibiotikabehandlede. Gjennom et slikt utvalg øker bakteriestammens resistens. Viktige tiltak for å forebygge resistens er å minke den totale bruken av antibiotika og å sørge for at antibiotikabehandlinger ikke avbrytes for tidlig.
Referanser
Eksterne lenker
Legemiddelhåndboka
Felleskatalogen
Slik virker antibiotika - artikkel fra forskning.no 5.11.04
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Main Content Ask the right questions Use antibiotics smartly Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top Ask the right questions Use antibiotics smartly
Main Content Ask the right questions Use antibiotics smartly Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top Ask the right questions Use antibiotics smartly
Main Content Ask the right questions Use antibiotics smartly Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top Ask the right questions Use antibiotics smartly
Main Content Ask the right questions Use antibiotics smartly Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top Ask the right questions Use antibiotics smartly
Main Content Ask the right questions Use antibiotics smartly Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top Ask the right questions Use antibiotics smartly
Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015 Page : | 1 | Top
Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu). Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause: Germs Disease example(s) Bacteria Escherichia coli (E.coli) Urinary tract infection, diarrhoeal diseases Streptococcus pneumoniae Chest infection, middle ear infection Staphylococcus aureus Skin and soft tissue infection Viruses Rhinovirus Cold Influenza virus, e.g. H1N1, H3N2 Influenza Varicella-zoster virus Chickenpox Enterovirus Hand, foot and mouth disease 2. Why antibiotic is not effective for virus infection? Antibiotics use different methods to kill the bacteria within your body (like stop making the cell wall or stop making the genes of bacteria). As mentioned before viruses do not use these methods to reproduce themselves but use your body cells to reproduce. Therefore antibiotics are not effective for virus infections. 3. If I have fever, do I need antibiotics? Fever is a common symptom which may or may not be caused by bacteria. If you have fever, please consult your doctor first. 4. Do I need antibiotics when my nasal discharge changes to yellow or green? It is quite normal for the discharge to become thick and change colour during a cold or flu. There may or may not be an associated bacterial infection. If you have queries, please consult your doctor. Ask the right questions Use antibiotics smartly Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 Printed in April 2015
Ask the right questions Use antibiotics smartly Antibiotics are not panacea Antibiotics are effective for treating bacterial infections but they cannot treat all types of infections. They do not work for viral infections like cold and influenza (flu).
Taking antibiotics for cold and flu will NOT: • cure the infections • help you recover faster Cold and flu No antibiotics please Antibiotics can be harmful Antibiotics may cause adverse outcomes such as • side effects, which include nausea, vomiting, constipation or diarrhoea and headache • allergic reactions such as rash, itchiness, breathlessness • Antibiotic resistance: while antibiotics will kill the germs, they will also kill the normal bacteria in our bodies and increase the risk of acquiring more antibiotic resistant bacteria. Infections due to antibiotic resistant bacteria are difficult to treat. As shown by data in recent years, antibiotic resistance in bacteria has been increasing and posing a significant threat to population health. What to do for cold and flu? • Maintain good indoor ventilation, have adequate rest and drink plenty of water. If symptoms persist, consult your doctor • Follow your doctor’s advice on the use of drugs • Do not push your doctor to prescribe antibiotics • Do not self-medicate antibiotics
Use antibiotics only when they are likely to be beneficial Frequently asked questions 1. What is the difference between bacteria and viruses? o Bacteria are a class of microorganisms which cannot be seen with naked eye. They can reproduce themselves with suitable nutrients and environment. Viruses have even simpler structure than bacteria, they cannot reproduce independently. They need to enter other cells and use their help to reproduce. Bacteria and viruses have different properties and cause different illnesses and is treated with different types of drugs. Indeed, most cases of upper respiratory tract infections are caused by viruses which do not need antibiotics. The following table shows some examples of bacteria and viruses as well as the diseases they cause:
Centre for Health Protection Website www.chp.gov.hk 24-Hour Health Education Hotline of the Department of Health 2833 0111 | biology | 2526469 | https://sv.wikipedia.org/wiki/Mycterothrips%20albus | Mycterothrips albus | Mycterothrips albus är en insektsart som först beskrevs av Dudley Moulton 1911. Mycterothrips albus ingår i släktet Mycterothrips och familjen smaltripsar. Inga underarter finns listade i Catalogue of Life.
Källor
Smaltripsar
albus | swedish | 1.20131 |
eyes_smooth_transition/Smooth_pursuit.txt | In the scientific study of vision, smooth pursuit describes a type of eye movement in which the eyes remain fixated on a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit is asymmetric: most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making catch-up saccades. Most humans are also better at downward than upward pursuit. Pursuit is modified by ongoing visual feedback.
Measurement[edit]
There are two basic methods for recording smooth pursuit eye movements, and eye movement in general. The first is with a search coil. This technique is most common in primate research, and is extremely accurate. An eye movement shifts the orientation of the coil to induce an electric current, which is translated into horizontal and vertical eye position. The second technique is an eye tracker. This device, while somewhat more noisy, is non-invasive and is often used in human psychophysics and recently also in instructional psychology. It relies on the infrared illumination of the pupil to track eye position with a camera.
During oculomotor experiments, it is often important to ensure that no saccades occurred when the subject was supposed to be smoothly pursuing a target. Such eye movements are called catch-up saccades and are more common when pursuing at high speeds. Researchers are able to discard portions of eye movement recordings that contain saccades, in order to analyze the two components separately. Saccadic eye movements differ from the smooth pursuit component by their very high initial acceleration and deceleration, and peak velocity.
Neural circuitry[edit]
The neural circuitry underlying smooth pursuit is an object of debate. The first step towards the initiation of pursuit is to see a moving target. Signals from the retina ascend through the lateral geniculate nucleus and activate neurons in primary visual cortex. Primary visual cortex sends the information about the target to the middle temporal visual cortex, which responds very selectively to directions of movement. The processing of motion in this area is necessary for smooth pursuit responses. This sensory area provides the motion signal, which may or may not be smoothly pursued. A region of cortex in the frontal lobe, known as the frontal pursuit area, responds to particular vectors of pursuit, and can be electrically stimulated to induce pursuit movements. Recent evidence suggests that the superior colliculus also responds during smooth pursuit eye movement. These two areas are likely involved in providing the "go"-signal to initiate pursuit, as well as selecting which target to track. The "go"-signal from the cortex and the superior colliculus is relayed to several pontine nuclei, including the dorsolateral pontine nuclei and the nucleus reticularis tegmenti pontis. The neurons of the pons are tuned to eye velocity and are directionally selective, and can be stimulated to change the velocity of pursuit. The pontine nuclei project to the cerebellum, specifically the vermis and the paraflocculus. These neurons code for the target velocity and are responsible for the particular velocity profile of pursuit. The cerebellum, especially the vestibulo-cerebellum, is also involved in the online correction of velocity during pursuit. The cerebellum then projects to optic motoneurons, which control the eye muscles and cause the eye to move.
Stages of smooth pursuit[edit]
Pursuit eye movement can be divided into two stages: open-loop pursuit and closed-loop pursuit. Open-loop pursuit is the visual system's first response to a moving object we want to track and typically lasts ~100 ms. Therefore, this stage is ballistic: Visual signals have not yet had time to correct the ongoing pursuit velocity or direction. The second stage of pursuit, closed-loop pursuit, lasts until the pursuit movement has ceased. This stage is characterized by the online correction of pursuit velocity to compensate for retinal slip. In other words, the pursuit system tries to null retinal velocity of the object of interest. This is achieved at the end of the open-loop phase. In the closed-loop phase, the eye angular velocity and target angular velocity are nearly equal.
Smooth pursuit and spatial attention[edit]
Various lines of research suggests a tight coupling for closed loop pursuit and spatial attention. For instance, during the close loop phase selective attention is coupled to the pursuit target such that untracked targets which move in the same direction with the target are poorly processed by the visual system. Recently, a loose coupling of open loop pursuit and attention was suggested, when there is only one possible moving target. This difference between pursuit and saccades may be accounted for by the differences in latency. Pursuit eye movements are initiated within 90-150 ms, while typical latencies for voluntary saccades are in the order of 200-250 ms
Smooth pursuit in the absence of a visual target[edit]
Performing smooth pursuit without a moving visual stimulus is difficult, and typically results in a series of saccades. However, pursuit without a visible target is possible under some particular conditions, that show the importance of high-level functions in smooth pursuit maintenance.
If you know which way a target will move, or know the target trajectory (because it is periodic for instance), you can initiate pursuit before the target motion actually starts, especially if you know exactly when the motion will start.
It is also possible to maintain pursuit if a target momentarily disappears, especially if the target appears to be occluded by a larger object.
Under conditions in which there is no visual stimulation (in total darkness), we can still perform smooth pursuit eye movements with the help of a proprioceptive motion signal (e.g. your moving finger).
Following stimuli from peripheral gaze[edit]
When a bright light appears in the periphery, the fastest it can achieve a smooth pursuit is 30°/second. It first fixes the gaze to the peripheral light, and if not in excess of 30°/second, will follow the target equally with the movement. At higher velocities, the eye will not move smoothly, and requires corrective saccades. Unlike saccades, this process uses a continuous feedback system, which is based strictly on error.
Distinction between smooth pursuit, optokinetic nystagmus, and ocular following response[edit]
Although we can clearly separate smooth pursuit from the vestibulo-ocular reflex, we can not always draw a clear separation between smooth pursuit and other tracking eye movements like the slow phase of the optokinetic nystagmus and the ocular following response (OFR), discovered in 1986 by Miles, Kawano, and Optican, which is a transient ocular tracking response to full-field motion. The latter are both slow eye movements in response to extended targets, with the purpose of stabilizing the image. Therefore, some processing stages are shared with the smooth pursuit system. Those different kinds of eye movements may not be simply differentiated by the stimulus that is appropriate to generate them, as smooth pursuit eye movements can be generated to track extended targets as well. The main difference may lie in the voluntary nature of pursuit eye movements.
Smooth-pursuit deficits[edit]
Smooth pursuit requires the coordination of many brain regions that are far away from each other. This makes it particularly susceptible to impairment from a variety of disorders and conditions.
Schizophrenia[edit]
There is significant evidence that smooth pursuit is deficient in people with schizophrenia and their relatives. People with schizophrenia tend to have trouble pursuing very fast targets. This impairment is correlated with less activation in areas known to play a role in pursuit, such as the frontal eye field. However, other studies have shown that people with schizophrenia show relatively normal pursuit, compared to controls, when tracking objects that move unexpectedly. The greatest deficits are when the patients track objects of a predictable velocity which begin moving at a predictable time. This study speculates that smooth pursuit deficits in schizophrenia are a function of the patients' inability to store motion vectors.
Autism[edit]
People with autism show a plethora of visual deficits. One such deficit is to smooth pursuit. Children with autism show reduced velocity of smooth pursuit compared to controls during ongoing tracking. However, the latency of the pursuit response is similar to controls. This deficit appears to only emerge after middle adolescence.
Trauma[edit]
People with post traumatic stress disorder, with secondary psychotic symptoms, show pursuit deficits. These patients tend to have trouble maintaining pursuit velocity above 30 degree/second. A correlation has also been found between performance on tracking tasks and a childhood history of physical and emotional abuse.
Drugs and Alcohol[edit]
"Lack of Smooth Pursuit" is a scorable clue on the NHTSA's standardized field sobriety tests. The clue, in combination with others, may be used to determine if a person is impaired by alcohol and/or drugs. Drugs causing lack of smooth pursuit include depressants, some inhalants, and dissociative anesthetics (such as phencyclidine or ketamine).
Preterm Birth[edit]
Children born very preterm show smooth pursuit deficits compared to paired controls born at full term. This delay in smooth pursuit has also been linked to later neurodevelopment in toddlerhood in children born very preterm.
See also[edit]
Eye movement
Eye tracking
Frontal eye fields
Saccade
Superior colliculus
Endophenotype | biology | 696877 | https://sv.wikipedia.org/wiki/R%C3%B6relse%20%28fysik%29 | Rörelse (fysik) | Rörelse är inom fysiken en kropps lägesändring. Beskrivningen av läge som funktion av tid är kinematik, en gren av klassisk mekanik. Grundbegrepp är position, hastighet och acceleration, som i två och tre dimensioner beskrivs med vektorer.
Historia
I enlighet med erfarenhet och observation lärde Aristoteles att de jordiska tingens naturliga tillstånd var vila. Rörelse kom till ett slut, eftersom kroppar strävade efter vila. Endast himlakroppars rörelse var konstant, eftersom deras naturliga tillstånd var cirkulär rörelse.
Mekaniken utvecklades under medeltiden, och fann sitt moderna sätt att betrakta rörelse hos Galilei och Newton. Här är det inte något speciellt med vila, eftersom rörelse och vila är relativa begrepp. En kropp i rörelse utan yttre påverkan fortsätter sin rörelse med samma hastighet, dvs med samma fart och i samma riktning.
Rätlinjig rörelse
Rörelse längs en rak linje kan mätas med en Mikola-tub med en rörlig bubbla i ett rakt rör. Bubblans hastighet uppskattas vid 20° och 40° vinkel. De samlade data ger två grafer i ett diagram med samma hastighet mot tid.
Den rätlinjiga rörelsen kan ritas som en matematisk funktion av avstånd eller position som funktion av tid. Man kan också rita kroppens hastighet eller dess acceleration som funktion av tid. Dessa funktioner har en matematisk relation till varandra: hastighet är positionens derivata med avseende på tid. Acceleration är hastighetens tidsderivata, eller positionens andraderivata:
Figuren till höger visar ett exempel. Den gröna linjen anger läge som funktion av tid. Först är kroppen i vila, sedan börjar den röra på sig. Den blå kurvan visar att hastigheten är konstant under en tid tills kroppen stannar en stund, börjar röra sig åt motsatt håll och stannar nära utgångsläget. Accelerationen är skild från noll endast, när hastigheten ändrar sig. Enligt Newtons rörelselagar är det endast då, som det verkar en kraft på kroppen.
Några specialfall av rätlinjig rörelse är likformig rörelse (när hastigheten är konstant) och likformigt föränderlig rörelse (när accelerationen är konstant). Ett annat specialfall är harmonisk rörelse, när kroppens läge oscillerar fram och tillbaka enligt en sinusfunktion.
Kroklinjiga rörelser
Kroklinjiga rörelser kräver beskrivning med två eller tre rymdkoordinater. Såväl läge som hastighet och acceleration är vektorer, med båda storlek och riktning. Hastighet är ändring i position och dess riktning är parallell med kroppens bana. Så är inte nödvändigtvis fallet med acceleration. När hastigheten ändrar riktning, är accelerationen inte parallell med rörelseriktningen. Även här finns specialfall. Enklast är uniform cirkulär rörelse och kastparabeln.
Uniform cirkulär rörelse
Vid uniform cirkulär rörelse färdas en partikel med konstant fart i en cirkelbana. Rörelsen kan beskrivas med banans radie R och partikelns vinkelhastighet ω, som är tidsderivatan av vinkelpositionen β. Vinkelhastigheten har SI-enheten radianer per sekund. Partikelns fart är
Figuren till höger visar att den infinitesimala hastighetsändringen dv är riktad mot cirkelns centrum och att dess storlek är proportionell mot hastigheten och mot dβ. Accelerationens belopp ges av
Om vektorn ω är vinkelrät mot cirkelns plan och dess belopp är rotationshastigheten i radianer per sekund, kan hastigheten för en kropp i cirkulär bana beskrivas med kryssprodukten
och accelerationen som
vilket är en vektor vinkelrät mot både ω och v.
Externa länkar | swedish | 0.666916 |
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## Contents
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* 1 Physical visual illusions
* 2 Physiological visual illusions
* 3 Cognitive illusions
* 4 Explanation of cognitive illusions Toggle Explanation of cognitive illusions subsection
* 4.1 Perceptual organization
* 4.2 Depth and motion perception
* 4.3 Color and brightness constancies
* 4.4 Object
* 4.5 Future perception
* 5 Pathological visual illusions (distortions)
* 6 Connections to psychological disorders Toggle Connections to psychological disorders subsection
* 6.1 The rubber hand illusion (RHI)
* 6.2 Illusions and schizophrenia
* 7 In art
* 8 Cognitive processes hypothesis
* 9 Gallery
* 10 See also
* 11 Notes
* 12 References
* 13 Further reading
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# Optical illusion
58 languages
* [ العربية ](https://ar.wikipedia.org/wiki/%D8%AE%D8%AF%D8%A7%D8%B9_%D8%A8%D8%B5%D8%B1%D9%8A "خداع بصري – Arabic")
* [ Asturianu ](https://ast.wikipedia.org/wiki/Ilusi%C3%B3n_%C3%B3ptica "Ilusión óptica – Asturian")
* [ বাংলা ](https://bn.wikipedia.org/wiki/%E0%A6%A6%E0%A7%83%E0%A6%B7%E0%A7%8D%E0%A6%9F%E0%A6%BF%E0%A6%AD%E0%A7%8D%E0%A6%B0%E0%A6%AE "দৃষ্টিভ্রম – Bangla")
* [ Български ](https://bg.wikipedia.org/wiki/%D0%9E%D0%BF%D1%82%D0%B8%D1%87%D0%BD%D0%B0_%D0%B8%D0%BB%D1%8E%D0%B7%D0%B8%D1%8F "Оптична илюзия – Bulgarian")
* [ Català ](https://ca.wikipedia.org/wiki/Il%C2%B7lusi%C3%B3_%C3%B2ptica "Il·lusió òptica – Catalan")
* [ Čeština ](https://cs.wikipedia.org/wiki/Optick%C3%BD_klam "Optický klam – Czech")
* [ Dansk ](https://da.wikipedia.org/wiki/Synsbedrag "Synsbedrag – Danish")
* [ Deutsch ](https://de.wikipedia.org/wiki/Optische_T%C3%A4uschung "Optische Täuschung – German")
* [ Español ](https://es.wikipedia.org/wiki/Ilusi%C3%B3n_%C3%B3ptica "Ilusión óptica – Spanish")
* [ Esperanto ](https://eo.wikipedia.org/wiki/Optika_iluzio "Optika iluzio – Esperanto")
* [ Euskara ](https://eu.wikipedia.org/wiki/Ilusio_optiko "Ilusio optiko – Basque")
* [ فارسی ](https://fa.wikipedia.org/wiki/%D8%AE%D8%B7%D8%A7%DB%8C_%D8%AF%DB%8C%D8%AF "خطای دید – Persian")
* [ Français ](https://fr.wikipedia.org/wiki/Illusion_d%27optique "Illusion d'optique – French")
* [ Galego ](https://gl.wikipedia.org/wiki/Ilusi%C3%B3n_%C3%B3ptica "Ilusión óptica – Galician")
* [ 한국어 ](https://ko.wikipedia.org/wiki/%EC%B0%A9%EC%8B%9C "착시 – Korean")
* [ Հայերեն ](https://hy.wikipedia.org/wiki/%D5%8F%D5%A5%D5%BD%D5%B8%D5%B2%D5%A1%D5%AF%D5%A1%D5%B6_%D5%BA%D5%A1%D5%BF%D6%80%D5%A1%D5%B6%D6%84 "Տեսողական պատրանք – Armenian")
* [ हिन्दी ](https://hi.wikipedia.org/wiki/%E0%A4%A6%E0%A5%83%E0%A4%B7%E0%A5%8D%E0%A4%9F%E0%A4%BF%E0%A4%AD%E0%A5%8D%E0%A4%B0%E0%A4%AE "दृष्टिभ्रम – Hindi")
* [ Hrvatski ](https://hr.wikipedia.org/wiki/Percepcijske_varke "Percepcijske varke – Croatian")
* [ Bahasa Indonesia ](https://id.wikipedia.org/wiki/Ilusi_optis "Ilusi optis – Indonesian")
* [ Interlingua ](https://ia.wikipedia.org/wiki/Illusion_optic "Illusion optic – Interlingua")
* [ Íslenska ](https://is.wikipedia.org/wiki/Sj%C3%B3nvilla "Sjónvilla – Icelandic")
* [ Italiano ](https://it.wikipedia.org/wiki/Illusione_ottica "Illusione ottica – Italian")
* [ עברית ](https://he.wikipedia.org/wiki/%D7%90%D7%A9%D7%9C%D7%99%D7%94_%D7%90%D7%95%D7%A4%D7%98%D7%99%D7%AA "אשליה אופטית – Hebrew")
* [ ქართული ](https://ka.wikipedia.org/wiki/%E1%83%9D%E1%83%9E%E1%83%A2%E1%83%98%E1%83%99%E1%83%A3%E1%83%A0%E1%83%98_%E1%83%98%E1%83%9A%E1%83%A3%E1%83%96%E1%83%98%E1%83%90 "ოპტიკური ილუზია – Georgian")
* [ Lëtzebuergesch ](https://lb.wikipedia.org/wiki/Optesch_T%C3%A4uschung "Optesch Täuschung – Luxembourgish")
* [ Lietuvių ](https://lt.wikipedia.org/wiki/Optin%C4%97_apgaul%C4%97 "Optinė apgaulė – Lithuanian")
* [ Magyar ](https://hu.wikipedia.org/wiki/Optikai_csal%C3%B3d%C3%A1s "Optikai csalódás – Hungarian")
* [ Македонски ](https://mk.wikipedia.org/wiki/%D0%9E%D0%BF%D1%82%D0%B8%D1%87%D0%BA%D0%B0_%D0%BC%D0%B0%D0%BC%D0%BA%D0%B0 "Оптичка мамка – Macedonian")
* [ მარგალური ](https://xmf.wikipedia.org/wiki/%E1%83%9D%E1%83%9E%E1%83%A2%E1%83%98%E1%83%99%E1%83%A3%E1%83%A0%E1%83%98_%E1%83%98%E1%83%9A%E1%83%A3%E1%83%96%E1%83%98%E1%83%90 "ოპტიკური ილუზია – Mingrelian")
* [ Bahasa Melayu ](https://ms.wikipedia.org/wiki/Ilusi_optik "Ilusi optik – Malay")
* [ မြန်မာဘာသာ ](https://my.wikipedia.org/wiki/%E1%80%A1%E1%80%99%E1%80%BC%E1%80%84%E1%80%BA%E1%80%95%E1%80%AD%E1%80%AF%E1%80%84%E1%80%BA%E1%80%B8%E1%80%86%E1%80%AD%E1%80%AF%E1%80%84%E1%80%BA%E1%80%9B%E1%80%AC_%E1%80%9C%E1%80%BE%E1%80%8A%E1%80%B7%E1%80%BA%E1%80%85%E1%80%AC%E1%80%B8%E1%80%99%E1%80%BE%E1%80%AF "အမြင်ပိုင်းဆိုင်ရာ လှည့်စားမှု – Burmese")
* [ Nederlands ](https://nl.wikipedia.org/wiki/Gezichtsbedrog "Gezichtsbedrog – Dutch")
* [ 日本語 ](https://ja.wikipedia.org/wiki/%E9%8C%AF%E8%A6%96 "錯視 – Japanese")
* [ Norsk bokmål ](https://no.wikipedia.org/wiki/Optisk_illusjon "Optisk illusjon – Norwegian Bokmål")
* [ Norsk nynorsk ](https://nn.wikipedia.org/wiki/Optisk_illusjon "Optisk illusjon – Norwegian Nynorsk")
* [ Occitan ](https://oc.wikipedia.org/wiki/Illusion_d%27optica "Illusion d'optica – Occitan")
* [ Oʻzbekcha / ўзбекча ](https://uz.wikipedia.org/wiki/Optik_illyuziya "Optik illyuziya – Uzbek")
* [ Polski ](https://pl.wikipedia.org/wiki/Z%C5%82udzenie_optyczne "Złudzenie optyczne – Polish")
* [ Português ](https://pt.wikipedia.org/wiki/Ilus%C3%A3o_de_%C3%B3ptica "Ilusão de óptica – Portuguese")
* [ Română ](https://ro.wikipedia.org/wiki/Iluzie_optic%C4%83 "Iluzie optică – Romanian")
* [ Русский ](https://ru.wikipedia.org/wiki/%D0%9E%D0%BF%D1%82%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B0%D1%8F_%D0%B8%D0%BB%D0%BB%D1%8E%D0%B7%D0%B8%D1%8F "Оптическая иллюзия – Russian")
* [ Shqip ](https://sq.wikipedia.org/wiki/Iluzioni_optik "Iluzioni optik – Albanian")
* [ Simple English ](https://simple.wikipedia.org/wiki/Optical_illusion "Optical illusion – Simple English")
* [ Slovenčina ](https://sk.wikipedia.org/wiki/Optick%C3%BD_klam "Optický klam – Slovak")
* [ Slovenščina ](https://sl.wikipedia.org/wiki/Opti%C4%8Dna_iluzija "Optična iluzija – Slovenian")
* [ Српски / srpski ](https://sr.wikipedia.org/wiki/%D0%9E%D0%BF%D1%82%D0%B8%D1%87%D0%BA%D0%B0_%D0%B2%D0%B0%D1%80%D0%BA%D0%B0 "Оптичка варка – Serbian")
* [ Srpskohrvatski / српскохрватски ](https://sh.wikipedia.org/wiki/Opti%C4%8Dke_iluzije "Optičke iluzije – Serbo-Croatian")
* [ Suomi ](https://fi.wikipedia.org/wiki/Optinen_harha "Optinen harha – Finnish")
* [ Svenska ](https://sv.wikipedia.org/wiki/Optisk_illusion "Optisk illusion – Swedish")
* [ தமிழ் ](https://ta.wikipedia.org/wiki/%E0%AE%92%E0%AE%B3%E0%AE%BF%E0%AE%AF%E0%AE%BF%E0%AE%AF%E0%AE%B1%E0%AF%8D_%E0%AE%95%E0%AE%A3%E0%AF%8D%E0%AE%AE%E0%AE%BE%E0%AE%AF%E0%AE%AE%E0%AF%8D "ஒளியியற் கண்மாயம் – Tamil")
* [ ไทย ](https://th.wikipedia.org/wiki/%E0%B8%A0%E0%B8%B2%E0%B8%9E%E0%B8%A5%E0%B8%A7%E0%B8%87%E0%B8%95%E0%B8%B2 "ภาพลวงตา – Thai")
* [ Türkçe ](https://tr.wikipedia.org/wiki/Optik_ill%C3%BCzyon "Optik illüzyon – Turkish")
* [ Українська ](https://uk.wikipedia.org/wiki/%D0%9E%D0%BF%D1%82%D0%B8%D1%87%D0%BD%D0%B0_%D1%96%D0%BB%D1%8E%D0%B7%D1%96%D1%8F "Оптична ілюзія – Ukrainian")
* [ اردو ](https://ur.wikipedia.org/wiki/%D9%81%D8%B1%DB%8C%D8%A8_%D9%86%D8%B8%D8%B1 "فریب نظر – Urdu")
* [ Tiếng Việt ](https://vi.wikipedia.org/wiki/%E1%BA%A2o_%E1%BA%A3nh_\(quang_h%E1%BB%8Dc\) "Ảo ảnh \(quang học\) – Vietnamese")
* [ 吴语 ](https://wuu.wikipedia.org/wiki/%E8%A7%86%E9%94%99%E8%A7%89 "视错觉 – Wu")
* [ 粵語 ](https://zh-yue.wikipedia.org/wiki/%E9%8C%AF%E8%A6%8B "錯見 – Cantonese")
* [ 中文 ](https://zh.wikipedia.org/wiki/%E8%A6%96%E9%8C%AF%E8%A6%BA "視錯覺 – Chinese")
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From Wikipedia, the free encyclopedia
Visually perceived images that differ from objective reality
This article is about visual perception. For the album, see [ Optical Illusion
(album) ](/wiki/Optical_Illusion_\(album\) "Optical Illusion \(album\)") . For
the film, see [ Optical Illusions (film) ](/wiki/Optical_Illusions_\(film\)
"Optical Illusions \(film\)") .
[
 ](/wiki/File:Checker_shadow_illusion.svg)
The checker shadow illusion. Although square A appears a darker shade of gray
than square B, in the image the two have exactly the same luminance.
[
](/wiki/File:Grey_square_optical_illusion_proof2.svg)
Drawing a connecting bar between the two squares breaks the illusion and shows
that they are the same shade.
[
](/wiki/File:Gregory_categorization_of_illusions_1991.png) Gregory's
categorization of illusions [1] [
](/wiki/File:Mach_bands_-_animation.gif) In this animation, [ Mach bands
](/wiki/Mach_bands "Mach bands") exaggerate the [ contrast
](/wiki/Contrast_\(vision\) "Contrast \(vision\)") between edges of the
slightly differing shades of gray as soon as they come in contact with one
another.
In [ visual perception ](/wiki/Visual_perception "Visual perception") , an
**optical illusion** (also called a **visual illusion** [2] ) is an [
illusion ](/wiki/Illusion "Illusion") caused by the [ visual system
](/wiki/Visual_system "Visual system") and characterized by a visual [ percept
](/wiki/Perception "Perception") that arguably appears to differ from [
reality ](/wiki/Reality "Reality") . Illusions come in a wide variety; their
categorization is difficult because the underlying cause is often not clear
[3] but a classification [1] [4] proposed by [ Richard Gregory
](/wiki/Richard_Gregory "Richard Gregory") is useful as an orientation.
According to that, there are three main classes: physical, physiological, and
cognitive illusions, and in each class there are four kinds: Ambiguities,
distortions, paradoxes, and fictions. [4] A classical example for a physical
distortion would be the apparent bending of a stick half immerged in water; an
example for a physiological paradox is the [ motion aftereffect
](/wiki/Motion_aftereffect "Motion aftereffect") (where, despite movement,
position remains unchanged). [4] An example for a physiological fiction is
an [ afterimage ](/wiki/Afterimage "Afterimage") . [4] Three typical
cognitive distortions are the [ Ponzo ](/wiki/Ponzo_illusion "Ponzo illusion")
, [ Poggendorff ](/wiki/Poggendorff_illusion "Poggendorff illusion") , and [
Müller-Lyer ](/wiki/M%C3%BCller-Lyer_illusion "Müller-Lyer illusion")
illusion. [4] Physical illusions are caused by the physical environment,
e.g. by the optical properties of water. [4] Physiological illusions arise
in the eye or the visual pathway, e.g. from the effects of excessive
stimulation of a specific receptor type. [4] [ Cognitive ](/wiki/Cognitive
"Cognitive") visual illusions are the result of [ unconscious inferences
](/wiki/Unconscious_inference "Unconscious inference") and are perhaps those
most widely known. [4]
Pathological visual illusions arise from pathological changes in the
physiological [ visual perception ](/wiki/Visual_perception "Visual
perception") mechanisms causing the aforementioned types of illusions; they
are discussed e.g. under [ visual hallucinations ](/wiki/Hallucination#Visual
"Hallucination") .
Optical illusions, as well as multi-sensory illusions involving visual
perception, can also be used in the monitoring and rehabilitation of some [
psychological ](/wiki/Psychological_disorder "Psychological disorder")
disorders, including [ phantom limb syndrome ](/wiki/Phantom_limb "Phantom
limb") [5] and [ schizophrenia ](/wiki/Schizophrenia "Schizophrenia") . [6]
## Physical visual illusions [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=1 "Edit section:
Physical visual illusions") ]
A familiar phenomenon and example for a physical visual illusion is when
mountains appear to be much nearer in clear weather with low humidity ( [
Foehn ](/wiki/Foehn_wind "Foehn wind") ) than they are. This is because haze
is a cue for [ depth perception ](/wiki/Depth_perception "Depth perception") ,
[7] signalling the distance of far-away objects ( [ Aerial perspective
](/wiki/Depth_perception#Aerial_perspective "Depth perception") ).
The classical example of a physical illusion is when a stick that is half
immersed in water appears bent. This phenomenon was discussed by [ Ptolemy
](/wiki/Ptolemy "Ptolemy") ( c. 150 ) [8] and was often a prototypical
example for an illusion.
## Physiological visual illusions [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=2 "Edit section:
Physiological visual illusions") ]
Physiological illusions, such as the [ afterimages ](/wiki/Afterimage
"Afterimage") [9] following bright lights, or adapting stimuli of excessively
longer alternating patterns ( [ contingent perceptual aftereffect
](/wiki/Contingent_aftereffect "Contingent aftereffect") ), are presumed to be
the effects on the eyes or brain of excessive stimulation or interaction with
contextual or competing stimuli of a specific type—brightness, color,
position, tile, size, movement, etc. The theory is that a stimulus follows its
individual dedicated neural path in the early stages of visual processing and
that intense or repetitive activity in that or interaction with active
adjoining channels causes a [ physiological ](/wiki/Physiological
"Physiological") [ imbalance ](https://en.wiktionary.org/wiki/imbalance
"wikt:imbalance") that alters perception.
The Hermann [ grid illusion ](/wiki/Grid_illusion "Grid illusion") and [ Mach
bands ](/wiki/Mach_bands "Mach bands") are two [ illusions ](/wiki/Illusion
"Illusion") that are often explained using a biological approach. [ Lateral
inhibition ](/wiki/Lateral_inhibition "Lateral inhibition") , where in [
receptive fields ](/wiki/Receptive_field "Receptive field") of the retina
receptor signals from light and dark areas compete with one another, has been
used to explain why we see bands of increased brightness at the edge of a
color difference when viewing Mach bands. Once a receptor is active, it
inhibits adjacent receptors. This inhibition creates contrast, highlighting
edges. In the Hermann grid illusion, the gray spots that appear at the
intersections at peripheral locations are often explained to occur because of
[ lateral inhibition ](/wiki/Lateral_inhibition "Lateral inhibition") by the
surround in larger receptive fields. [10] However, [ lateral inhibition
](/wiki/Lateral_inhibition "Lateral inhibition") as an explanation of the
Hermann [ grid illusion ](/wiki/Grid_illusion "Grid illusion") [ has been
disproved ](/wiki/Grid_illusion#Theories "Grid illusion") . [11] [12] [13]
[14] [15] More recent empirical approaches to optical illusions have had
some success in explaining optical phenomena with which theories based on
lateral inhibition have struggled. [16]
## Cognitive illusions [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=3 "Edit section:
Cognitive illusions") ]
[
 ](/wiki/File:NeptunesGrottoOrganPlayer.jpg)
"The Organ Player" – [ Pareidolia ](/wiki/Pareidolia "Pareidolia") phenomenon
in [ Neptune's Grotto ](/wiki/Neptune%27s_Grotto "Neptune's Grotto") [
stalactite ](/wiki/Stalactite "Stalactite") cave ( [ Alghero ](/wiki/Alghero
"Alghero") , [ Sardinia ](/wiki/Sardinia "Sardinia") )
Cognitive illusions are assumed to arise by interaction with assumptions about
the world, leading to "unconscious inferences", an idea first suggested in the
19th century by the [ German ](/wiki/Germany "Germany") physicist and
physician [ Hermann Helmholtz ](/wiki/Hermann_von_Helmholtz "Hermann von
Helmholtz") . [17] Cognitive illusions are commonly divided into [ ambiguous
illusions ](/wiki/Ambiguous_image "Ambiguous image") , distorting illusions,
paradox illusions, or fiction illusions.
* _Ambiguous illusions_ are pictures or objects that elicit a perceptual "switch" between the alternative interpretations. The [ Necker cube ](/wiki/Necker_cube "Necker cube") is a well-known example; other instances are the [ Rubin vase ](/wiki/Rubin_vase "Rubin vase") and the "squircle", based on [ Kokichi Sugihara ](/wiki/Kokichi_Sugihara "Kokichi Sugihara") 's ambiguous cylinder illusion. [18]
* _Distorting_ or _[ geometrical-optical illusions ](/wiki/Geometrical-optical_illusions "Geometrical-optical illusions") _ are characterized by distortions of size, length, position or curvature. A striking example is the [ Café wall illusion ](/wiki/Caf%C3%A9_wall_illusion "Café wall illusion") . Other examples are the famous [ Müller-Lyer illusion ](/wiki/M%C3%BCller-Lyer_illusion "Müller-Lyer illusion") and [ Ponzo illusion ](/wiki/Ponzo_illusion "Ponzo illusion") .
* _Paradox illusions_ (or _[ impossible object ](/wiki/Impossible_object "Impossible object") illusions _ ) are generated by objects that are paradoxical or impossible, such as the [ Penrose triangle ](/wiki/Penrose_triangle "Penrose triangle") or [ impossible staircase ](/wiki/Penrose_staircase "Penrose staircase") seen, for example, in [ M. C. Escher ](/wiki/M._C._Escher "M. C. Escher") 's _[ Ascending and Descending ](/wiki/Ascending_and_Descending "Ascending and Descending") _ and _[ Waterfall ](/wiki/Waterfall_\(M._C._Escher\) "Waterfall \(M. C. Escher\)") _ . The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.
* _Fictions_ are when a figure is perceived even though it is not in the stimulus, like with the [ Kanizsa ](/wiki/Gaetano_Kanizsa "Gaetano Kanizsa") triangle, using [ illusory contours ](/wiki/Illusory_contours "Illusory contours") . [19] [20]
## Explanation of cognitive illusions [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=4 "Edit section:
Explanation of cognitive illusions") ]
### Perceptual organization [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=5 "Edit section:
Perceptual organization") ]
[
](/wiki/File:Two_silhouette_profile_or_a_white_vase.svg) Reversible figures
and vase, or the [ figure-ground ](/wiki/Figure-ground_\(perception\) "Figure-
ground \(perception\)") illusion [
 ](/wiki/File:Duck-
Rabbit_illusion.jpg) [ Rabbit–duck illusion
](/wiki/Rabbit%E2%80%93duck_illusion "Rabbit–duck illusion")
To make sense of the world it is necessary to organize incoming sensations
into information which is meaningful. [ Gestalt psychologists
](/wiki/Gestalt_psychology "Gestalt psychology") believe one way this is done
is by perceiving individual sensory stimuli as a meaningful whole. [21]
Gestalt organization can be used to explain many illusions including the [
rabbit–duck illusion ](/wiki/Rabbit%E2%80%93duck_illusion "Rabbit–duck
illusion") where the image as a whole switches back and forth from being a
duck then being a rabbit and why in the [ figure–ground ](/wiki/Figure-
ground_\(perception\) "Figure-ground \(perception\)") illusion the figure and
ground are reversible.
[  ](/wiki/File:Kanizsa_triangle.svg) [ Kanizsa's
triangle ](/wiki/Kanizsa%27s_Triangle "Kanizsa's Triangle")
In addition, gestalt theory can be used to explain the [ illusory contours
](/wiki/Illusory_Contours "Illusory Contours") in the [ Kanizsa's triangle
](/wiki/Kanizsa%27s_Triangle "Kanizsa's Triangle") . A floating white
triangle, which does not exist, is seen. The brain has a need to see familiar
simple objects and has a tendency to create a "whole" image from individual
elements. [21] _Gestalt_ means "form" or "shape" in German. However, another
explanation of the Kanizsa's triangle is based in [ evolutionary psychology
](/wiki/Evolutionary_psychology "Evolutionary psychology") and the fact that
in order to survive it was important to see form and edges. The use of
perceptual organization to create meaning out of stimuli is the principle
behind other well-known illusions including [ impossible objects
](/wiki/Impossible_objects "Impossible objects") . The brain makes sense of
shapes and symbols putting them together like a jigsaw puzzle, formulating
that which is not there to that which is believable.
The [ gestalt principles
](/wiki/Gestalt_psychology#Theoretical_framework_and_methodology "Gestalt
psychology") of perception govern the way different objects are grouped. Good
form is where the perceptual system tries to fill in the blanks in order to
see simple objects rather than complex objects. Continuity is where the
perceptual system tries to disambiguate which segments fit together into
continuous lines. Proximity is where objects that are close together are
associated. Similarity is where objects that are similar are seen as
associated. Some of these elements have been successfully incorporated into
quantitative models involving optimal estimation or Bayesian inference. [22]
[23]
The double-anchoring theory, a popular but recent theory of lightness
illusions, states that any region belongs to one or more frameworks, created
by gestalt grouping principles, and within each frame is independently
anchored to both the highest luminance and the surround luminance. A spot's
lightness is determined by the average of the values computed in each
framework. [24]
### Depth and motion perception [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=6 "Edit section:
Depth and motion perception") ]
[
](/wiki/File:Vertical%E2%80%93horizontal_illusion.png) The [
vertical–horizontal illusion ](/wiki/Vertical%E2%80%93horizontal_illusion
"Vertical–horizontal illusion") where the vertical line is thought to be
longer than the horizontal [  ](/wiki/File:Ponzo_illusion.gif) [ Ponzo illusion
](/wiki/Ponzo_illusion "Ponzo illusion")
Illusions can be based on an individual's ability to see in three dimensions
even though the image hitting the retina is only two dimensional. The [ Ponzo
illusion ](/wiki/Ponzo_illusion "Ponzo illusion") is an example of an illusion
which uses monocular cues of depth perception to fool the eye. But even with
two-dimensional images, the brain exaggerates vertical distances when compared
with horizontal distances, as in the [ vertical–horizontal illusion
](/wiki/Vertical%E2%80%93horizontal_illusion "Vertical–horizontal illusion")
where the two lines are exactly the same length.
In the Ponzo illusion the converging [ parallel lines
](/wiki/Parallel_\(geometry\) "Parallel \(geometry\)") tell the brain that the
image higher in the [ visual field ](/wiki/Visual_field "Visual field") is
farther away, therefore, the brain perceives the image to be larger, although
the two images hitting the [ retina ](/wiki/Retina "Retina") are the same
size. The optical illusion seen in a [ diorama ](/wiki/Diorama "Diorama") / [
false perspective ](/wiki/False_perspective "False perspective") also exploits
assumptions based on monocular cues of [ depth perception
](/wiki/Depth_perception "Depth perception") . The [ M.C. Escher
](/wiki/M.C._Escher "M.C. Escher") painting _[ Waterfall
](/wiki/Waterfall_\(M._C._Escher\) "Waterfall \(M. C. Escher\)") _ exploits
rules of depth and proximity and our understanding of the physical world to
create an illusion. Like [ depth perception ](/wiki/Depth_perception "Depth
perception") , [ motion perception ](/wiki/Motion_perception "Motion
perception") is responsible for a number of sensory illusions. Film [
animation ](/wiki/Animation "Animation") is based on the illusion that the
brain perceives a series of slightly varied images produced in rapid
succession as a moving picture. Likewise, when we are moving, as we would be
while riding in a vehicle, stable surrounding objects may appear to move. We
may also perceive a large object, like an airplane, to move more slowly than
smaller objects, like a car, although the larger object is actually moving
faster. The [ phi phenomenon ](/wiki/Phi_phenomenon "Phi phenomenon") is yet
another example of how the brain perceives motion, which is most often created
by blinking lights in close succession.
The ambiguity of direction of motion due to lack of visual references for
depth is shown in [ the spinning dancer illusion ](/wiki/The_Spinning_Dancer
"The Spinning Dancer") . The spinning dancer appears to be moving clockwise or
counterclockwise depending on spontaneous activity in the brain where
perception is subjective. Recent studies show on the fMRI that there are
spontaneous fluctuations in cortical activity while watching this illusion,
particularly the parietal lobe because it is involved in perceiving movement.
[25]
### Color and brightness constancies [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=7 "Edit section:
Color and brightness constancies") ]
[  ](/wiki/File:Gradient-
optical-illusion.svg) Simultaneous contrast illusion. The background is a [
color gradient ](/wiki/Color_gradient "Color gradient") and progresses from
dark gray to light gray. The horizontal bar appears to progress from light
grey to dark grey, but is in fact just one color.
Perceptual constancies are sources of illusions. [ Color constancy
](/wiki/Color_constancy "Color constancy") and brightness constancy are
responsible for the fact that a familiar object will appear the same color
regardless of the amount of light or color of light reflecting from it. An
illusion of color difference or luminosity difference can be created when the
luminosity or color of the area surrounding an unfamiliar object is changed.
The luminosity of the object will appear brighter against a black field (that
reflects less light) than against a white field, even though the object itself
did not change in luminosity. Similarly, the eye will compensate for color
contrast depending on the color cast of the surrounding area.
In addition to the gestalt principles of perception, water-color illusions
contribute to the formation of optical illusions. Water-color illusions
consist of object-hole effects and coloration. Object-hole effects occur when
boundaries are prominent where there is a figure and background with a hole
that is 3D volumetric in appearance. Coloration consists of an assimilation of
color radiating from a thin-colored edge lining a darker chromatic contour.
The water-color illusion describes how the human mind perceives the wholeness
of an object such as top-down processing. Thus, contextual factors play into
perceiving the brightness of an object. [26]
### Object [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=8 "Edit section:
Object") ]
[
 ](/wiki/File:Shepard_tables.jpg) "Shepard tables"
deconstructed. The two tabletops appear to be different, but they are the same
size and shape.
Just as it perceives color and brightness constancies, the brain has the
ability to understand familiar objects as having a consistent shape or size.
For example, a door is perceived as a rectangle regardless of how the image
may change on the retina as the door is opened and closed. Unfamiliar objects,
however, do not always follow the rules of shape constancy and may change when
the perspective is changed. The [ Shepard tables ](/wiki/Shepard_tables
"Shepard tables") illusion [27] is an example of an illusion based on
distortions in shape constancy.
### Future perception [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=9 "Edit section:
Future perception") ]
[ _[ dubious ](/wiki/Wikipedia:Accuracy_dispute#Disputed_statement
"Wikipedia:Accuracy dispute") – [ discuss
](/wiki/Talk:Optical_illusion#Section_"Future_perception"_questionable
"Talk:Optical illusion") _ ]
Researcher [ Mark Changizi ](/wiki/Mark_Changizi "Mark Changizi") of [
Rensselaer Polytechnic Institute ](/wiki/Rensselaer_Polytechnic_Institute
"Rensselaer Polytechnic Institute") in New York has a more imaginative take on
optical illusions, saying that they are due to a neural lag which most humans
experience while awake. When light hits the retina, about one-tenth of a
second goes by before the brain translates the signal into a visual perception
of the world. Scientists have known of the lag, yet they have debated how
humans compensate, with some proposing that our motor system somehow modifies
our movements to offset the delay. [28]
Changizi asserts that the human visual system has evolved to compensate for
neural delays by generating images of what will occur one-tenth of a second
into the future. This foresight enables humans to react to events in the
present, enabling humans to perform reflexive acts like catching a fly ball
and to maneuver smoothly through a crowd. [29] In an interview with ABC
Changizi said, "Illusions occur when our brains attempt to perceive the
future, and those perceptions don't match reality." [30] For example, an
illusion called the [ Hering illusion ](/wiki/Hering_illusion "Hering
illusion") looks like bicycle spokes around a central point, with vertical
lines on either side of this central, so-called vanishing point. [31] The
illusion tricks us into thinking we are looking at a perspective picture, and
thus according to Changizi, switches on our future-seeing abilities. Since we
are not actually moving and the figure is static, we misperceive the straight
lines as curved ones. Changizi said:
> Evolution has seen to it that geometric drawings like this elicit in us
> premonitions of the near future. The converging lines toward a vanishing
> point (the spokes) are cues that trick our brains into thinking we are
> moving forward—as we would in the real world, where the door frame (a pair
> of vertical lines) seems to bow out as we move through it—and we try to
> perceive what that world will look like in the next instant. [29]
## Pathological visual illusions (distortions) [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=10 "Edit section:
Pathological visual illusions \(distortions\)") ]
A [ pathological ](/wiki/Pathology "Pathology") visual illusion is a
distortion of a real external stimulus [32] and is often diffuse and
persistent. Pathological visual illusions usually occur throughout the visual
field, suggesting global excitability or sensitivity alterations. [33]
Alternatively visual hallucination is the perception of an external visual
stimulus where none exists. [32] Visual hallucinations are often from focal
dysfunction and are usually transient.
Types of visual illusions include [ oscillopsia ](/wiki/Oscillopsia
"Oscillopsia") , [ halos around objects ](/wiki/Halo_\(optical_phenomenon\)
"Halo \(optical phenomenon\)") , [ illusory palinopsia
](/wiki/Illusory_palinopsia "Illusory palinopsia") ( [ visual trailing
](/wiki/Illusory_palinopsia#Visual_trailing "Illusory palinopsia") , [ light
streaking ](/wiki/Illusory_palinopsia#Light_streaking "Illusory palinopsia") ,
[ prolonged indistinct afterimages
](/wiki/Illusory_palinopsia#Prolonged_indistinct_afterimage "Illusory
palinopsia") ), [ akinetopsia ](/wiki/Akinetopsia "Akinetopsia") , [ visual
snow ](/wiki/Visual_snow "Visual snow") , [ micropsia ](/wiki/Micropsia
"Micropsia") , [ macropsia ](/wiki/Macropsia "Macropsia") , [ teleopsia
](/wiki/Teleopsia "Teleopsia") , [ pelopsia ](/wiki/Pelopsia "Pelopsia") , [
metamorphopsia ](/wiki/Metamorphopsia "Metamorphopsia") , [ dyschromatopsia
](/wiki/Dyschromatopsia "Dyschromatopsia") , intense [ glare
](/wiki/Glare_\(vision\) "Glare \(vision\)") , [ blue field entoptic
phenomenon ](/wiki/Blue_field_entoptic_phenomenon "Blue field entoptic
phenomenon") , and [ purkinje trees ](/wiki/Entoptic_phenomena "Entoptic
phenomena") .
These symptoms may indicate an underlying disease state and necessitate seeing
a medical practitioner. Etiologies associated with pathological visual
illusions include multiple types of [ ocular disease ](/wiki/Eye_disease "Eye
disease") , [ migraines ](/wiki/Migraine "Migraine") , [ hallucinogen
persisting perception disorder
](/wiki/Hallucinogen_persisting_perception_disorder "Hallucinogen persisting
perception disorder") , [ head trauma ](/wiki/Closed_head_injury "Closed head
injury") , and [ prescription drugs ](/wiki/Prescription_drug "Prescription
drug") . If a medical work-up does not reveal a cause of the pathological
visual illusions, the idiopathic visual disturbances could be analogous to the
altered excitability state seen in visual aura with no migraine headache. If
the visual illusions are diffuse and persistent, they often affect the
patient's quality of life. These symptoms are often refractory to treatment
and may be caused by any of the aforementioned etiologies, but are often
idiopathic. There is no standard treatment for these visual disturbances.
## Connections to psychological disorders [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=11 "Edit section:
Connections to psychological disorders") ]
### The rubber hand illusion (RHI) [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=12 "Edit section:
The rubber hand illusion \(RHI\)") ]
[  ](/wiki/File:Phantom-limb-
illusion.jpg) A visual representation of what an amputee with [ phantom limb
syndrome ](/wiki/Phantom_limb "Phantom limb") senses
The [ rubber hand illusion ](/wiki/Rubber_hand_illusion "Rubber hand
illusion") (RHI), a [ multi-sensory ](/wiki/Multisensory_integration
"Multisensory integration") illusion involving both [ visual perception
](/wiki/Visual_perception "Visual perception") and [ touch ](/wiki/Touch
"Touch") , has been used to study how [ phantom limb syndrome
](/wiki/Phantom_limb "Phantom limb") affects amputees over time. [5] [
Amputees ](/wiki/Amputation "Amputation") with the syndrome actually responded
to RHI more strongly than controls, an effect that was often consistent for
both the sides of the intact and the amputated arm. [5] However, in some
studies, amputees actually had stronger responses to RHI on their intact arm,
and more recent amputees responded to the illusion better than amputees who
had been missing an arm for years or more. [5] Researchers believe this is a
sign that the [ body schema ](/wiki/Body_schema "Body schema") , or an
individual's sense of their own body and its parts, progressively adapts to
the post-amputation state. [5] Essentially, the amputees were learning to no
longer respond to sensations near what had once been their arm. [5] As a
result, many have suggested the use of RHI as a tool for monitoring an
amputee's progress in reducing their phantom limb sensations and adjusting to
the new state of their body. [5]
Other research used RHI in the rehabilitation of amputees with [ prosthetic
](/wiki/Prosthesis "Prosthesis") limbs. [34] After prolonged exposure to
RHI, the amputees gradually stopped feeling a dissociation between the
prosthetic (which resembled the rubber hand) and the rest of their body. [34]
This was thought to be because they adjusted to responding to and moving a
limb that did not feel as connected to the rest of their body or senses. [34]
RHI may also be used to diagnose certain disorders related to impaired [
proprioception ](/wiki/Proprioception "Proprioception") or impaired sense of [
touch ](/wiki/Touch "Touch") in non-amputees. [34]
### Illusions and schizophrenia [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=13 "Edit section:
Illusions and schizophrenia") ]
[  ](/wiki/File:Perception-
Action_Cycle.png) Top-down processing involves using action plans to make
perceptual interpretations and vice versa. (This is impaired in
schizophrenia.)
[ Schizophrenia ](/wiki/Schizophrenia "Schizophrenia") , a mental disorder
often marked by [ hallucinations ](/wiki/Hallucination "Hallucination") , also
decreases a person's ability to perceive high-order optical illusions. [6]
This is because schizophrenia impairs one's capacity to perform [ top-down
](/wiki/Top-down_and_bottom-up_design "Top-down and bottom-up design")
processing and a higher-level integration of visual information beyond the
primary visual cortex, [ V1 ](/wiki/Primary_visual_cortex "Primary visual
cortex") . [6] Understanding how this specifically occurs in the brain may
help in understanding how visual [ distortions ](/wiki/Distortion
"Distortion") , beyond imaginary [ hallucinations ](/wiki/Hallucination
"Hallucination") , affect schizophrenic patients. [6] Additionally,
evaluating the differences between how schizophrenic patients and unaffected
individuals see illusions may enable researchers to better identify where
specific illusions are processed in the [ visual ](/wiki/Visual_system "Visual
system") streams. [6]
[
](https://upload.wikimedia.org/wikipedia/commons/5/5e/Dualing_Illusions.svg
"https://upload.wikimedia.org/wikipedia/commons/5/5e/Dualing_Illusions.svg")
An example of the [ peripheral drift illusion
](/wiki/Peripheral_drift_illusion "Peripheral drift illusion") : alternating
lines appear to be moving horizontally left or right. [
 ](/wiki/File:Bjorn_Borg_Hollow_Face.jpg) An
example of the [ hollow face illusion ](/wiki/Hollow-Face_illusion "Hollow-
Face illusion") which makes concave masks appear to be jutting out (or convex)
[
 ](/wiki/File:MotionBlindness.gif) An example of [ motion
induced blindness ](/wiki/Motion-induced_blindness "Motion-induced blindness")
: while fixating on the flashing dot, the stationary dots may disappear due to
the brain prioritizing motion information.
One study on schizophrenic patients found that they were extremely unlikely to
be fooled by a three dimensional optical illusion, the [ hollow face illusion
](/wiki/Hollow-Face_illusion "Hollow-Face illusion") , unlike [ neurotypical
](/wiki/Neurotypical "Neurotypical") volunteers. [35] Based on [ fMRI
](/wiki/Functional_magnetic_resonance_imaging "Functional magnetic resonance
imaging") data, researchers concluded that this resulted from a disconnection
between their systems for [ bottom-up ](/wiki/Top-down_and_bottom-up_design
"Top-down and bottom-up design") processing of visual cues and top-down
interpretations of those cues in the [ parietal cortex ](/wiki/Parietal_lobe
"Parietal lobe") . [35] In another study on the [ motion-induced blindness
](/wiki/Motion-induced_blindness "Motion-induced blindness") (MIB) illusion
(pictured right), schizophrenic patients continued to perceive stationary
visual targets even when observing distracting motion stimuli, unlike [
neurotypical ](/wiki/Neurotypical "Neurotypical") [ controls
](/wiki/Controlling_for_a_variable "Controlling for a variable") , who
experienced motion induced blindness. [36] The schizophrenic test subjects
demonstrated impaired cognitive organization, meaning they were less able to
coordinate their processing of [ motion cues ](/wiki/Motion_perception "Motion
perception") and stationary image cues. [36]
## In art [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=14 "Edit section: In
art") ]
[
](/wiki/File:Ambigram_Escher_and_tessellation_background_-
_photomontage_with_reversible_hands.jpg) [ Ambigram ](/wiki/Ambigram
"Ambigram") [ tessellation ](/wiki/Tessellation "Tessellation") " [ Escher
](/wiki/M._C._Escher "M. C. Escher") " using [ negative space
](/wiki/Negative_space "Negative space") to reveal letters upside down
Artists who have worked with optical illusions include [ M. C. Escher
](/wiki/M._C._Escher "M. C. Escher") , [37] [ Bridget Riley
](/wiki/Bridget_Riley "Bridget Riley") , [ Salvador Dalí
](/wiki/Salvador_Dal%C3%AD "Salvador Dalí") , [ Giuseppe Arcimboldo
](/wiki/Giuseppe_Arcimboldo "Giuseppe Arcimboldo") , [ Patrick Bokanowski
](/wiki/Patrick_Bokanowski "Patrick Bokanowski") , [ Marcel Duchamp
](/wiki/Marcel_Duchamp "Marcel Duchamp") , [ Jasper Johns ](/wiki/Jasper_Johns
"Jasper Johns") , [ Oscar Reutersvärd ](/wiki/Oscar_Reutersv%C3%A4rd "Oscar
Reutersvärd") , [ Victor Vasarely ](/wiki/Victor_Vasarely "Victor Vasarely")
and [ Charles Allan Gilbert ](/wiki/Charles_Allan_Gilbert "Charles Allan
Gilbert") . Contemporary artists who have experimented with illusions include
[ Jonty Hurwitz ](/wiki/Jonty_Hurwitz "Jonty Hurwitz") , [ Sandro del Prete
](/wiki/Sandro_del_Prete "Sandro del Prete") , [ Octavio Ocampo
](/wiki/Octavio_Ocampo "Octavio Ocampo") , [ Dick Termes ](/wiki/Dick_Termes
"Dick Termes") , [ Shigeo Fukuda ](/wiki/Shigeo_Fukuda "Shigeo Fukuda") , [
Patrick Hughes ](/wiki/Patrick_Hughes_\(artist\) "Patrick Hughes \(artist\)")
, [ István Orosz ](/wiki/Istv%C3%A1n_Orosz "István Orosz") , [ Rob Gonsalves
](/wiki/Rob_Gonsalves "Rob Gonsalves") , [ Gianni A. Sarcone
](/wiki/Gianni_A._Sarcone "Gianni A. Sarcone") , [ Ben Heine ](/wiki/Ben_Heine
"Ben Heine") and [ Akiyoshi Kitaoka ](/wiki/Akiyoshi_Kitaoka "Akiyoshi
Kitaoka") . Optical illusion is also used in film by the technique of [ forced
perspective ](/wiki/Forced_perspective "Forced perspective") .
[ Op art ](/wiki/Op_art "Op art") is a style of art that uses optical
illusions to create an impression of movement, or hidden images and patterns.
_[ Trompe-l'œil ](/wiki/Trompe-l%27%C5%93il "Trompe-l'œil") _ uses realistic
imagery to create the optical illusion that depicted objects exist in three
dimensions.
Tourists attractions employing large-scale illusory art allowing visitors to
photograph themselves in fantastic scenes have opened in several Asian
countries, such as the [ Trickeye Museum ](/wiki/Trickeye_Museum "Trickeye
Museum") and [ Hong Kong 3D Museum ](/wiki/Hong_Kong_3D_Museum "Hong Kong 3D
Museum") . [38] [39]
## Cognitive processes hypothesis [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=15 "Edit section:
Cognitive processes hypothesis") ]
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The hypothesis claims that visual illusions occur because the neural circuitry
in our visual system evolves, by neural learning, to a system that makes very
efficient interpretations of usual 3D scenes based in the emergence of
simplified models in our brain that speed up the interpretation process but
give rise to optical illusions in unusual situations. In this sense, the
cognitive processes hypothesis can be considered a framework for an
understanding of optical illusions as the signature of the empirical
statistical way vision has evolved to solve the inverse problem. [40]
Research indicates that 3D vision capabilities emerge and are learned jointly
with the planning of movements. [41] That is, as depth cues are better
perceived, individuals can develop more efficient patterns of movement and
interaction within the 3D environment around them. [41] After a long process
of learning, an internal representation of the world emerges that is well-
adjusted to the perceived data coming from closer objects. The representation
of distant objects near the horizon is less "adequate". [ _[ further
explanation needed ](/wiki/Wikipedia:Please_clarify "Wikipedia:Please
clarify") _ ] In fact, it is not only the [ Moon that seems larger
](/wiki/Moon_illusion "Moon illusion") when we perceive it near the horizon.
In a photo of a distant scene, all distant objects are perceived as smaller
than when we observe them directly using our vision.
## Gallery [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=16 "Edit section:
Gallery") ]
Some images need to be viewed in full resolution to see their effect.
* [ Motion aftereffect ](/wiki/Motion_aftereffect "Motion aftereffect") : this video produces a distortion illusion when the viewer looks away after watching it.
* [  ](/wiki/File:Mond-vergleich.svg "Ebbinghaus illusion: the orange circle on the left appears smaller than that on the right, but they are in fact the same size.")
[ Ebbinghaus illusion ](/wiki/Ebbinghaus_illusion "Ebbinghaus illusion") : the
orange circle on the left appears smaller than that on the right, but they are
in fact the same size.
* [  ](/wiki/File:Caf%C3%A9_wall.svg "Café wall illusion: the parallel horizontal lines in this image appear sloped.")
[ Café wall illusion ](/wiki/Caf%C3%A9_wall_illusion "Café wall illusion") :
the parallel horizontal lines in this image appear sloped.
* [  ](/wiki/File:Optical-illusion-checkerboard-twisted-cord.svg "Checker version: the diagonal checker squares at the larger grid points make the grid appear distorted.")
Checker version: the diagonal checker squares at the larger grid points make
the grid appear distorted.
* [  ](/wiki/File:Optical-illusion-checkerboard-twisted-cord2.svg "Checker version with horizontal and vertical central symmetry")
Checker version with horizontal and vertical central symmetry
* [  ](/wiki/File:Lilac-Chaser.gif "Lilac chaser: if the viewer focuses on the black cross in the center, the location of the disappearing dot appears green.")
[ Lilac chaser ](/wiki/Lilac_chaser "Lilac chaser") : if the viewer focuses on
the black cross in the center, the location of the disappearing dot appears
green.
* [  ](/wiki/File:Motion_illusion_in_star_arrangement.png "Motion illusion: contrasting colors create the illusion of motion.")
[ Motion illusion ](/wiki/Motion_illusion "Motion illusion") : contrasting
colors create the illusion of motion.
* [ ![Watercolor illusion: this shape's yellow and blue border create the illusion of the object being pale yellow rather than white\[42\]](//upload.wikimedia.org/wikipedia/commons/thumb/2/20/Subjectively_constructed_water-color.svg/120px-Subjectively_constructed_water-color.svg.png) ](/wiki/File:Subjectively_constructed_water-color.svg "Watercolor illusion: this shape's yellow and blue border create the illusion of the object being pale yellow rather than white\[42\]")
[ Watercolor illusion ](/wiki/Watercolor_illusion "Watercolor illusion") :
this shape's yellow and blue border create the illusion of the object being
pale yellow rather than white [42]
* [ ![Subjective cyan filter, left: subjectively constructed cyan square filter above blue circles, right: small cyan circles inhibit filter construction\[43\]\[44\]](//upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Optical_illusion_-_subjectively_constructed_cyan_sqare_filter_above_blue_cirles.gif/120px-Optical_illusion_-_subjectively_constructed_cyan_sqare_filter_above_blue_cirles.gif) ](/wiki/File:Optical_illusion_-_subjectively_constructed_cyan_sqare_filter_above_blue_cirles.gif "Subjective cyan filter, left: subjectively constructed cyan square filter above blue circles, right: small cyan circles inhibit filter construction\[43\]\[44\]")
Subjective cyan filter, left: subjectively constructed cyan square filter
above blue circles, right: small cyan circles inhibit filter construction
[43] [44]
* [ ![Pinna's illusory intertwining effect\[45\] and Pinna illusion \(scholarpedia\).\[46\] The picture shows squares spiralling in, although they are arranged in concentric circles.](//upload.wikimedia.org/wikipedia/commons/thumb/4/45/Pinna%27s_illusory_intertwining_effect.gif/120px-Pinna%27s_illusory_intertwining_effect.gif) ](/wiki/File:Pinna%27s_illusory_intertwining_effect.gif "Pinna's illusory intertwining effect\[45\] and Pinna illusion \(scholarpedia\).\[46\] The picture shows squares spiralling in, although they are arranged in concentric circles.")
Pinna's illusory intertwining effect [45] and Pinna illusion (scholarpedia).
[46] The picture shows squares spiralling in, although they are arranged in
concentric circles.
* [  ](/wiki/File:Politeness_simulation_\(LOC_cph.3g08085\).gif "Phenakistoscope which is spun displaying the illusion of motion of a man bowing and a woman curtsying to each other in a circle at the outer edge of the disc, 1833")
[ Phenakistoscope ](/wiki/Phenakistoscope "Phenakistoscope") which is spun
displaying the illusion of motion of a man bowing and a woman curtsying to
each other in a circle at the outer edge of the disc, 1833
* [  ](/wiki/File:Hybrid_image_decomposition.jpg "A hybrid image constructed from low-frequency components of a photograph of Marilyn Monroe \(left inset\) and high-frequency components of a photograph of Albert Einstein \(right inset\). The Einstein image is clearer in the full image.")
A [ hybrid image ](/wiki/Hybrid_image "Hybrid image") constructed from low-
frequency components of a photograph of [ Marilyn Monroe
](/wiki/Marilyn_Monroe "Marilyn Monroe") (left inset) and high-frequency
components of a photograph of [ Albert Einstein ](/wiki/Albert_Einstein
"Albert Einstein") (right inset). The Einstein image is clearer in [ the full
image ](/wiki/File:Hybrid_image_decomposition.jpg "File:Hybrid image
decomposition.jpg") .
* [  ](/wiki/File:Roman_geometric_mosaic.jpg "An ancient Roman geometric mosaic. The cubic texture induces a Necker-cube-like optical illusion.")
An ancient Roman geometric mosaic. The cubic texture induces a [ Necker-cube
](/wiki/Necker_cube "Necker cube") -like optical illusion.
* A set of colorful spinning disks that create illusion. The disks appear to move backwards and forwards in different regions.
* [ ![Pinna-Brelstaff illusion: the two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.\[47\]](//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Revolving_circles.svg/120px-Revolving_circles.svg.png) ](/wiki/File:Revolving_circles.svg "Pinna-Brelstaff illusion: the two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.\[47\]")
[ Pinna-Brelstaff illusion ](/w/index.php?title=Pinna-
Brelstaff_illusion&action=edit&redlink=1 "Pinna-Brelstaff illusion \(page does
not exist\)") : the two circles seem to move when the viewer's head is moving
forwards and backwards while looking at the black dot. [47]
* [  ](/wiki/File:Spinning_Dancer.gif "The Spinning Dancer appears to move both clockwise and counter-clockwise.")
The [ Spinning Dancer ](/wiki/Spinning_Dancer "Spinning Dancer") appears to
move both clockwise and counter-clockwise.
* [  ](/wiki/File:Europe_2007_Disk_1_340.jpg "Forced perspective: the man is made to appear to be supporting the Leaning Tower of Pisa in the background.")
[ Forced perspective ](/wiki/Forced_perspective "Forced perspective") : the
man is made to appear to be supporting the [ Leaning Tower of Pisa
](/wiki/Leaning_Tower_of_Pisa "Leaning Tower of Pisa") in the background.
* [  ](/wiki/File:Grid_illusion.svg "Scintillating grid illusion: Dark dots seem to appear and disappear rapidly at random intersections, hence the label "scintillating".")
[ Scintillating grid illusion ](/wiki/Grid_illusion "Grid illusion") : Dark
dots seem to appear and disappear rapidly at random intersections, hence the
label "scintillating".
* [  ](/wiki/File:Illusion_Museum_Antwerp_-_3.jpg "Building rooms where the furniture is attached to the ceiling makes it appear the two men are upside down.")
Building rooms where the furniture is attached to the ceiling makes it appear
the two men are upside down.
## See also [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=17 "Edit section:
See also") ]
Wikimedia Commons has media related to [ Optical illusion
](https://commons.wikimedia.org/wiki/Category:Optical_illusions
"commons:Category:Optical illusions") .
**Optical illusion** at Wikipedia's [ sister projects
](/wiki/Wikipedia:Wikimedia_sister_projects "Wikipedia:Wikimedia sister
projects")
*  [ Definitions ](https://en.wiktionary.org/wiki/optical_illusion "wikt:optical illusion") from Wiktionary
*  [ Quotations ](https://en.wikiquote.org/wiki/Illusion "q:Illusion") from Wikiquote
*  [ Data ](https://www.wikidata.org/wiki/Q174923 "d:Q174923") from Wikidata
* [ Auditory illusion ](/wiki/Auditory_illusion "Auditory illusion")
* [ Barberpole illusion ](/wiki/Barberpole_illusion "Barberpole illusion") (Barber's pole)
* [ Camouflage ](/wiki/Camouflage "Camouflage")
* [ Chronostasis ](/wiki/Chronostasis "Chronostasis") (stopped-clock illusion)
* [ Closed-eye hallucination ](/wiki/Closed-eye_hallucination "Closed-eye hallucination") /visualization
* [ Contour rivalry ](/wiki/Contour_rivalry "Contour rivalry")
* [ Ebbinghaus illusion ](/wiki/Ebbinghaus_illusion "Ebbinghaus illusion")
* [ Emmert's law ](/wiki/Emmert%27s_law "Emmert's law")
* [ Flashed face distortion effect ](/wiki/Flashed_face_distortion_effect "Flashed face distortion effect")
* [ Fraser spiral illusion ](/wiki/Fraser_spiral_illusion "Fraser spiral illusion")
* [ Gravity hill ](/wiki/Gravity_hill "Gravity hill")
* [ Human reactions to infrasound ](/wiki/Infrasound#Suggested_relationship_to_ghost_sightings "Infrasound")
* [ Hidden faces ](/wiki/Hidden_faces "Hidden faces")
* [ Infinity edge pool ](/wiki/Infinity_edge_pool "Infinity edge pool")
* [ Kinetic depth effect ](/wiki/Kinetic_depth_effect "Kinetic depth effect")
* [ List of optical illusions ](/wiki/List_of_optical_illusions "List of optical illusions")
* [ Mirage ](/wiki/Mirage "Mirage")
* [ Multistable perception ](/wiki/Multistable_perception "Multistable perception")
* [ Rabbit–duck illusion ](/wiki/Rabbit%E2%80%93duck_illusion "Rabbit–duck illusion")
* [ Silencing ](/wiki/Silencing "Silencing")
* [ The dress ](/wiki/The_dress_\(viral_phenomenon\) "The dress \(viral phenomenon\)")
* [ Troxler's fading ](/wiki/Troxler%27s_fading "Troxler's fading")
* [ Visual space ](/wiki/Visual_space "Visual space")
* [ Watercolour illusion ](/wiki/Watercolour_illusion "Watercolour illusion")
## Notes [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=18 "Edit section:
Notes") ]
1. ^ _**a** _ _**b** _ Gregory, Richard (1991). "Putting illusions in their place". _Perception_ . **20** (1): 1–4. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p200001 ](https://doi.org/10.1068%2Fp200001) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 1945728 ](https://pubmed.ncbi.nlm.nih.gov/1945728) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 5521054 ](https://api.semanticscholar.org/CorpusID:5521054) .
2. ** ^ ** In the scientific literature the term "visual illusion" is preferred because the older term gives rise to the assumption that the optics of the eye were the general cause for illusions (which is only the case for so-called _physical illusions_ ). "Optical" in the term derives from the Greek _optein_ = "seeing", so the term refers to an "illusion of seeing", not to [ optics ](/wiki/Optics "Optics") as a branch of modern physics. A regular scientific source for illusions are the journals [ _Perception_ ](https://uk.sagepub.com/en-gb/eur/perception/journal202440) and [ _i-Perception_ ](http://journals.sagepub.com/home/ipe)
3. ** ^ ** Bach, Michael; Poloschek, C. M. (2006). [ "Optical Illusions" ](https://web.archive.org/web/20210120054520/http://www.dfisica.ubi.pt/~hgil/p.v.2/Ilusoes-Visuais/Visual-Illusions.2.pdf) (PDF) . _Adv. Clin. Neurosci. Rehabil_ . **6** (2): 20–21. Archived from [ the original ](http://www.dfisica.ubi.pt/~hgil/p.v.2/Ilusoes-Visuais/Visual-Illusions.2.pdf) (PDF) on 2021-01-20 . Retrieved 2017-12-29 .
4. ^ _**a** _ _**b** _ _**c** _ _**d** _ _**e** _ _**f** _ _**g** _ _**h** _ Gregory, Richard L. (1997). [ "Visual illusions classified" ](http://invibe.net/biblio_database_dyva/woda/data/att/c9cf.file.pdf) (PDF) . _Trends in Cognitive Sciences_ . **1** (5): 190–194. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1016/s1364-6613(97)01060-7 ](https://doi.org/10.1016%2Fs1364-6613%2897%2901060-7) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 21223901 ](https://pubmed.ncbi.nlm.nih.gov/21223901) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 42228451 ](https://api.semanticscholar.org/CorpusID:42228451) .
5. ^ _**a** _ _**b** _ _**c** _ _**d** _ _**e** _ _**f** _ _**g** _ DeCastro, Thiago Gomes; Gomes, William Barbosa (2017-05-25). "Rubber Hand Illusion: Evidence for a multisensory integration of proprioception". Avances en Psicología Latinoamericana. 35 (2): 219. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") :10.12804/revistas.urosario.edu.co/apl/a.3430. [ ISSN ](/wiki/ISSN_\(identifier\) "ISSN \(identifier\)") 2145-4515.
6. ^ _**a** _ _**b** _ _**c** _ _**d** _ _**e** _ King, Daniel J.; Hodgekins, Joanne; Chouinard, Philippe A.; Chouinard, Virginie-Anne; Sperandio, Irene (2017-06-01). "A review of abnormalities in the perception of visual illusions in schizophrenia". Psychonomic Bulletin & Review. 24 (3): 734–751. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") :10.3758/s13423-016-1168-5. [ ISSN ](/wiki/ISSN_\(identifier\) "ISSN \(identifier\)") 1531-5320.
7. ** ^ ** Goldstein, E. Bruce (2002). _Sensation and Perception_ . Pacific Grove, CA: Wadsworth. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 0-534-53964-5 ](/wiki/Special:BookSources/0-534-53964-5 "Special:BookSources/0-534-53964-5") . , Chpt. 7
8. ** ^ ** Wade, Nicholas J. (1998). _A natural history of vision_ . Cambridge, MA: MIT Press.
9. ** ^ ** [ "After Images" ](http://www.worqx.com/color/after_image.htm) . _worqx.com_ . [ Archived ](https://web.archive.org/web/20150422033200/http://www.worqx.com/color/after_image.htm) from the original on 2015-04-22.
10. ** ^ ** Pinel, J. (2005) Biopsychology (6th ed.). Boston: Allyn & Bacon. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 0-205-42651-4 ](/wiki/Special:BookSources/0-205-42651-4 "Special:BookSources/0-205-42651-4")
11. ** ^ ** Lingelbach B, Block B, Hatzky B, Reisinger E (1985). "The Hermann grid illusion -- retinal or cortical?". _Perception_ . **14** (1): A7.
12. ** ^ ** Geier J, Bernáth L (2004). "Stopping the Hermann grid illusion by simple sine distortion". _Perception_ . Malden Ma: Blackwell. pp. 33–53. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 978-0631224211 ](/wiki/Special:BookSources/978-0631224211 "Special:BookSources/978-0631224211") .
13. ** ^ ** Schiller, Peter H.; Carvey, Christina E. (2005). [ "The Hermann grid illusion revisited" ](https://web.archive.org/web/20111212013609/http://perceptionweb.com/abstract.cgi?id=p5447) . _Perception_ . **34** (11): 1375–1397. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p5447 ](https://doi.org/10.1068%2Fp5447) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 16355743 ](https://pubmed.ncbi.nlm.nih.gov/16355743) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 15740144 ](https://api.semanticscholar.org/CorpusID:15740144) . Archived from [ the original ](http://www.perceptionweb.com/abstract.cgi?id=p5447) on 2011-12-12 . Retrieved 2011-10-03 .
14. ** ^ ** Geier J, Bernáth L, Hudák M, Séra L (2008). "Straightness as the main factor of the Hermann grid illusion". _Perception_ . **37** (5): 651–665. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p5622 ](https://doi.org/10.1068%2Fp5622) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 18605141 ](https://pubmed.ncbi.nlm.nih.gov/18605141) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 21028439 ](https://api.semanticscholar.org/CorpusID:21028439) .
15. ** ^ ** Bach, Michael (2008). "Die Hermann-Gitter-Täuschung: Lehrbucherklärung widerlegt (The Hermann grid illusion: the classic textbook interpretation is obsolete)". _Ophthalmologe_ . **106** (10): 913–917. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1007/s00347-008-1845-5 ](https://doi.org/10.1007%2Fs00347-008-1845-5) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 18830602 ](https://pubmed.ncbi.nlm.nih.gov/18830602) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 1573891 ](https://api.semanticscholar.org/CorpusID:1573891) .
16. ** ^ ** Howe, Catherine Q.; Yang, Zhiyong; Purves, Dale (2005). [ "The Poggendorff illusion explained by natural scene geometry" ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1093311) . _PNAS_ . **102** (21): 7707–7712. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 2005PNAS..102.7707H ](https://ui.adsabs.harvard.edu/abs/2005PNAS..102.7707H) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1073/pnas.0502893102 ](https://doi.org/10.1073%2Fpnas.0502893102) . [ PMC ](/wiki/PMC_\(identifier\) "PMC \(identifier\)") [ 1093311 ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1093311) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 15888555 ](https://pubmed.ncbi.nlm.nih.gov/15888555) .
17. ** ^ ** David Eagleman (April 2012). [ _Incogito: The Secret Lives of the Brain_ ](https://books.google.com/books?id=nkPj3dNFYwoC&q=Helmholtz&pg=PT30) . Vintage Books. pp. 33–. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 978-0-307-38992-3 ](/wiki/Special:BookSources/978-0-307-38992-3 "Special:BookSources/978-0-307-38992-3") . [ Archived ](https://web.archive.org/web/20131012233416/http://books.google.com/books?id=nkPj3dNFYwoC&lpg=PP1&pg=PT30&q=Helmholtz) from the original on 12 October 2013 . Retrieved 14 August 2013 .
18. ** ^ ** Gili Malinsky (22 July 2019). [ "An optical illusion that seems to be both a circle and a square is baffling the internet — here's how it works" ](https://www.msn.com/en-us/lifestyle/lifestyle-buzz/an-optical-illusion-that-seems-to-be-both-a-circle-and-a-square-is-baffling-the-internet-—-heres-how-it-works/ar-AAEHiPa?ocid=spartanntp) . _Insider_ .
19. ** ^ ** Petry, Susan; Meyer, Glenn E. (2012-12-06). [ _The Perception of Illusory Contours_ ](https://books.google.com/books?id=RPIxBwAAQBAJ) . Springer; 1987th edition. p. 696. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 9781461247609 ](/wiki/Special:BookSources/9781461247609 "Special:BookSources/9781461247609") .
20. ** ^ ** Gregory, R. L. (1972). [ "Cognitive Contours" ](https://doi.org/10.1038/238051a0) . _[ Nature ](/wiki/Nature_\(journal\) "Nature \(journal\)") _ . **238** (5358): 51–52. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 1972Natur.238...51G ](https://ui.adsabs.harvard.edu/abs/1972Natur.238...51G) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1038/238051a0 ](https://doi.org/10.1038%2F238051a0) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 12635278 ](https://pubmed.ncbi.nlm.nih.gov/12635278) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 4285883 ](https://api.semanticscholar.org/CorpusID:4285883) . Retrieved 2021-09-04 .
21. ^ _**a** _ _**b** _ Myers, D. (2003). Psychology in Modules, (7th ed.) New York: Worth. [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 0-7167-5850-4 ](/wiki/Special:BookSources/0-7167-5850-4 "Special:BookSources/0-7167-5850-4")
22. ** ^ ** Yoon Mo Jung and Jackie (Jianhong) Shen (2008), J. Visual Comm. Image Representation, **19** (1):42–55, [ _First-order modeling and stability analysis of illusory contours_ ](http://portal.acm.org/citation.cfm?id=1326364.1326487&coll=&dl=&CFID=11849883&CFTOKEN=72040242) .
23. ** ^ ** Yoon Mo Jung and Jackie (Jianhong) Shen (2014), arXiv:1406.1265, [ _Illusory shapes via phase transition_ ](https://arxiv.org/abs/1406.1265) [ Archived ](https://web.archive.org/web/20171124185300/https://arxiv.org/abs/1406.1265) 2017-11-24 at the [ Wayback Machine ](/wiki/Wayback_Machine "Wayback Machine") .
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40. ** ^ ** Gregory, Richard L. (1997). [ "Knowledge in perception and illusion" ](http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf) (PDF) . _Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences_ . **352** (1358): 1121–7. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 1997RSPTB.352.1121G ](https://ui.adsabs.harvard.edu/abs/1997RSPTB.352.1121G) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1098/rstb.1997.0095 ](https://doi.org/10.1098%2Frstb.1997.0095) . [ PMC ](/wiki/PMC_\(identifier\) "PMC \(identifier\)") [ 1692018 ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692018) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 9304679 ](https://pubmed.ncbi.nlm.nih.gov/9304679) . [ Archived ](https://web.archive.org/web/20050404073125/http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf) (PDF) from the original on 2005-04-04.
41. ^ _**a** _ _**b** _ Sweet, Barbara; Kaiser, Mary (August 2011). [ "Depth Perception, Cueing, and Control" ](https://human-factors.arc.nasa.gov/publications/AIAA.2011.DepthPerceptionCueCntrl.pdf) (PDF) . _AIAA Modeling and Simulation Technologies Conference_ . NASA Ames Research Center. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.2514/6.2011-6424 ](https://doi.org/10.2514%2F6.2011-6424) . [ hdl ](/wiki/Hdl_\(identifier\) "Hdl \(identifier\)") : [ 2060/20180007277 ](https://hdl.handle.net/2060%2F20180007277) . [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 978-1-62410-154-0 ](/wiki/Special:BookSources/978-1-62410-154-0 "Special:BookSources/978-1-62410-154-0") . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 16425060 ](https://api.semanticscholar.org/CorpusID:16425060) – via American Institute of Aeronautics and Astronautics.
42. ** ^ ** Bangio Pinna; Gavin Brelstaff; Lothar Spillman (2001). "Surface color from boundaries: a new watercolor illusion". _Vision Research_ . **41** (20): 2669–2676. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1016/s0042-6989(01)00105-5 ](https://doi.org/10.1016%2Fs0042-6989%2801%2900105-5) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 11520512 ](https://pubmed.ncbi.nlm.nih.gov/11520512) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 16534759 ](https://api.semanticscholar.org/CorpusID:16534759) .
43. ** ^ ** Hoffmann, Donald D. (1998). _Visual Intelligence. How we create what we see_ . Norton. , p.174
44. ** ^ ** Stephen Grossberg; Baingio Pinna (2012). [ "Neural Dynamics of Gestalt Principles of Perceptual Organization: From Grouping to Shape and Meaning" ](https://web.archive.org/web/20131004222301/http://gth.krammerbuch.at/sites/default/files/articles/AHAH%20callback/Grossberg_Neural_Dynamics.pdf) (PDF) . _Gestalt Theory_ . **34** (3+4): 399–482. Archived from [ the original ](http://gth.krammerbuch.at/sites/default/files/articles/AHAH%20callback/Grossberg_Neural_Dynamics.pdf) (PDF) on 2013-10-04 . Retrieved 2013-07-14 .
45. ** ^ ** Pinna, B.; Gregory, R.L.; Spillmann, L. (2002). "Shifts of Edges and Deformations of Patterns". _Perception_ . **31** (12): 1503–1508. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p3112pp ](https://doi.org/10.1068%2Fp3112pp) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 12916675 ](https://pubmed.ncbi.nlm.nih.gov/12916675) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 220053062 ](https://api.semanticscholar.org/CorpusID:220053062) .
46. ** ^ ** Pinna, Baingio (2009). [ "Pinna illusion" ](https://doi.org/10.4249%2Fscholarpedia.6656) . _Scholarpedia_ . **4** (2): 6656. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 2009SchpJ...4.6656P ](https://ui.adsabs.harvard.edu/abs/2009SchpJ...4.6656P) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.4249/scholarpedia.6656 ](https://doi.org/10.4249%2Fscholarpedia.6656) .
47. ** ^ ** Baingio Pinna; Gavin J. Brelstaff (2000). [ "A new visual illusion of relative motion" ](http://psy.mq.edu.au/vision/~peterw/corella/315/pinna.pdf) (PDF) . _Vision Research_ . **40** (16): 2091–2096. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1016/S0042-6989(00)00072-9 ](https://doi.org/10.1016%2FS0042-6989%2800%2900072-9) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 10878270 ](https://pubmed.ncbi.nlm.nih.gov/10878270) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 11034983 ](https://api.semanticscholar.org/CorpusID:11034983) . [ Archived ](https://web.archive.org/web/20131005010254/http://psy.mq.edu.au/vision/~peterw/corella/315/pinna.pdf) (PDF) from the original on 2013-10-05.
## References [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=19 "Edit section:
References") ]
* Bach, Michael; Poloschek, C. M. (2006). [ "Optical Illusions" ](https://web.archive.org/web/20210120054520/http://www.dfisica.ubi.pt/~hgil/p.v.2/Ilusoes-Visuais/Visual-Illusions.2.pdf) (PDF) . _Adv. Clin. Neurosci. Rehabil_ . **6** (2): 20–21. Archived from [ the original ](http://www.dfisica.ubi.pt/~hgil/p.v.2/Ilusoes-Visuais/Visual-Illusions.2.pdf) (PDF) on 2021-01-20 . Retrieved 2017-12-29 .
* Changizi, Mark A.; Hsieh, Andrew; Nijhawan, Romi; Kanai, Ryota; Shimojo, Shinsuke (2008). [ "Perceiving the Present and a Systematization of Illusions" ](http://csjarchive.cogsci.rpi.edu/2008v32/3/HCOG_A_303687_O.pdf) (PDF) . _Cognitive Science_ . **32** (3): 459–503. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1080/03640210802035191 ](https://doi.org/10.1080%2F03640210802035191) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 21635343 ](https://pubmed.ncbi.nlm.nih.gov/21635343) .
* [ Eagleman, D. M. ](/wiki/David_Eagleman "David Eagleman") (2001). [ "Visual Illusions and Neurobiology" ](http://physiology.elte.hu/gyakorlat/cikkek/Visual%20illusions%20and%20neurobiology.pdf) (PDF) . _Nature Reviews Neuroscience_ . **2** (12): 920–6. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1038/35104092 ](https://doi.org/10.1038%2F35104092) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 11733799 ](https://pubmed.ncbi.nlm.nih.gov/11733799) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 205023280 ](https://api.semanticscholar.org/CorpusID:205023280) .
* Gregory, Richard (1991). "Putting illusions in their place". _Perception_ . **20** (1): 1–4. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p200001 ](https://doi.org/10.1068%2Fp200001) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 1945728 ](https://pubmed.ncbi.nlm.nih.gov/1945728) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 5521054 ](https://api.semanticscholar.org/CorpusID:5521054) .
* Gregory, Richard (1997). [ "Knowledge in perception and illusion" ](http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf) (PDF) . _Phil. Trans. R. Soc. Lond. B_ . **352** (1358): 1121–1128. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 1997RSPTB.352.1121G ](https://ui.adsabs.harvard.edu/abs/1997RSPTB.352.1121G) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1098/rstb.1997.0095 ](https://doi.org/10.1098%2Frstb.1997.0095) . [ PMC ](/wiki/PMC_\(identifier\) "PMC \(identifier\)") [ 1692018 ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692018) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 9304679 ](https://pubmed.ncbi.nlm.nih.gov/9304679) .
* Purves, D.; Lotto, R.B.; Nundy, S. (2002). "Why We See What We Do". _American Scientist_ . **90** (3): 236–242. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1511/2002.9.784 ](https://doi.org/10.1511%2F2002.9.784) .
* Purves, D.; Williams, M. S.; Nundy, S.; Lotto, R. B. (2004). "Perceiving the intensity of light". _Psychological Review_ . **111** (1): 142–158. [ CiteSeerX ](/wiki/CiteSeerX_\(identifier\) "CiteSeerX \(identifier\)") [ 10.1.1.1008.6441 ](https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1008.6441) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1037/0033-295x.111.1.142 ](https://doi.org/10.1037%2F0033-295x.111.1.142) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 14756591 ](https://pubmed.ncbi.nlm.nih.gov/14756591) .
* Renier, L.; Laloyaux, C.; Collignon, O.; Tranduy, D.; Vanlierde, A.; Bruyer, R.; De Volder, A. G. (2005). "The Ponzo illusion using auditory substitution of vision in sighted and early blind subjects". _Perception_ . **34** (7): 857–867. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1068/p5219 ](https://doi.org/10.1068%2Fp5219) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 16124271 ](https://pubmed.ncbi.nlm.nih.gov/16124271) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 17265107 ](https://api.semanticscholar.org/CorpusID:17265107) .
* Renier, L.; Bruyer, R.; De Volder, A. G. (2006). [ "Vertical-horizontal illusion present for sighted but not early blind humans using auditory substitution of vision" ](https://doi.org/10.3758%2Fbf03208756) . _Perception & Psychophysics _ . **68** (4): 535–542. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.3758/bf03208756 ](https://doi.org/10.3758%2Fbf03208756) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 16933419 ](https://pubmed.ncbi.nlm.nih.gov/16933419) .
* Yang, Z.; Purves, D. (2003). "A statistical explanation of visual space". _Nature Neuroscience_ . **6** (6): 632–640. [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1038/nn1059 ](https://doi.org/10.1038%2Fnn1059) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 12754512 ](https://pubmed.ncbi.nlm.nih.gov/12754512) . [ S2CID ](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [ 610068 ](https://api.semanticscholar.org/CorpusID:610068) .
* Dixon, E.; Shapiro, A.; Lu, Z. (2014). [ "Scale-Invariance in brightness illusions implicates object-level visual processing" ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3905277) . _Scientific Reports_ . **4** : 3900. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 2014NatSR...4E3900D ](https://ui.adsabs.harvard.edu/abs/2014NatSR...4E3900D) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.1038/srep03900 ](https://doi.org/10.1038%2Fsrep03900) . [ PMC ](/wiki/PMC_\(identifier\) "PMC \(identifier\)") [ 3905277 ](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3905277) . [ PMID ](/wiki/PMID_\(identifier\) "PMID \(identifier\)") [ 24473496 ](https://pubmed.ncbi.nlm.nih.gov/24473496) .
## Further reading [ [ edit
](/w/index.php?title=Optical_illusion&action=edit§ion=20 "Edit section:
Further reading") ]
* Purves, Dale; et al. (2008). [ "Visual illusions:An Empirical Explanation" ](https://doi.org/10.4249%2Fscholarpedia.3706) . _[ Scholarpedia ](/wiki/Scholarpedia "Scholarpedia") _ . **3** (6): 3706. [ Bibcode ](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)") : [ 2008SchpJ...3.3706P ](https://ui.adsabs.harvard.edu/abs/2008SchpJ...3.3706P) . [ doi ](/wiki/Doi_\(identifier\) "Doi \(identifier\)") : [ 10.4249/scholarpedia.3706 ](https://doi.org/10.4249%2Fscholarpedia.3706) .
* David Cycleback. 2018. _[ Understanding Human Minds and Their Limits ](https://bookboon.com/en/understanding-human-minds-and-their-limits-ebook) _ . Publisher Bookboon.com [ ISBN ](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [ 978-87-403-2286-6 ](/wiki/Special:BookSources/978-87-403-2286-6 "Special:BookSources/978-87-403-2286-6")
* [ v ](/wiki/Template:Optical_illusions "Template:Optical illusions")
* [ t ](/wiki/Template_talk:Optical_illusions "Template talk:Optical illusions")
* [ e ](/wiki/Special:EditPage/Template:Optical_illusions "Special:EditPage/Template:Optical illusions")
Optical illusions ( [ list ](/wiki/List_of_optical_illusions "List of optical
illusions") )
---
Illusions |
* [ Afterimage ](/wiki/Afterimage "Afterimage")
* [ Ambigram ](/wiki/Ambigram "Ambigram")
* [ Ambiguous image ](/wiki/Ambiguous_image "Ambiguous image")
* [ Ames room ](/wiki/Ames_room "Ames room")
* [ Autostereogram ](/wiki/Autostereogram "Autostereogram")
* [ Barberpole ](/wiki/Barberpole_illusion "Barberpole illusion")
* [ Bezold ](/wiki/Bezold_effect "Bezold effect")
* [ Café wall ](/wiki/Caf%C3%A9_wall_illusion "Café wall illusion")
* [ Checker shadow ](/wiki/Checker_shadow_illusion "Checker shadow illusion")
* [ Chubb ](/wiki/Chubb_illusion "Chubb illusion")
* [ Cornsweet ](/wiki/Cornsweet_illusion "Cornsweet illusion")
* [ Delboeuf ](/wiki/Delboeuf_illusion "Delboeuf illusion")
* [ Ebbinghaus ](/wiki/Ebbinghaus_illusion "Ebbinghaus illusion")
* [ Ehrenstein ](/wiki/Ehrenstein_illusion "Ehrenstein illusion")
* [ Flash lag ](/wiki/Flash_lag_illusion "Flash lag illusion")
* [ Fraser spiral ](/wiki/Fraser_spiral_illusion "Fraser spiral illusion")
* [ Gravity hill ](/wiki/Gravity_hill "Gravity hill")
* [ Grid ](/wiki/Grid_illusion "Grid illusion")
* [ Hering ](/wiki/Hering_illusion "Hering illusion")
* [ Impossible trident ](/wiki/Impossible_trident "Impossible trident")
* [ Irradiation ](/wiki/Irradiation_illusion "Irradiation illusion")
* [ Jastrow ](/wiki/Jastrow_illusion "Jastrow illusion")
* [ Lilac chaser ](/wiki/Lilac_chaser "Lilac chaser")
* [ Mach bands ](/wiki/Mach_bands "Mach bands")
* [ McCollough ](/wiki/McCollough_effect "McCollough effect")
* [ Müller-Lyer ](/wiki/M%C3%BCller-Lyer_illusion "Müller-Lyer illusion")
* [ Necker cube ](/wiki/Necker_cube "Necker cube")
* [ Oppel-Kundt ](/wiki/Oppel-Kundt_illusion "Oppel-Kundt illusion")
* [ Orbison ](/wiki/Orbison_illusion "Orbison illusion")
* [ Penrose stairs ](/wiki/Penrose_stairs "Penrose stairs")
* [ Penrose triangle ](/wiki/Penrose_triangle "Penrose triangle")
* [ Peripheral drift ](/wiki/Peripheral_drift_illusion "Peripheral drift illusion")
* [ Poggendorff ](/wiki/Poggendorff_illusion "Poggendorff illusion")
* [ Ponzo ](/wiki/Ponzo_illusion "Ponzo illusion")
* [ Rubin vase ](/wiki/Rubin_vase "Rubin vase")
* [ Sander ](/wiki/Sander_illusion "Sander illusion")
* [ Schroeder stairs ](/wiki/Schroeder_stairs "Schroeder stairs")
* [ Shepard tables ](/wiki/Shepard_tables "Shepard tables")
* [ Spinning dancer ](/wiki/Spinning_dancer "Spinning dancer")
* [ Ternus ](/wiki/Ternus_illusion "Ternus illusion")
* [ Vertical–horizontal ](/wiki/Vertical%E2%80%93horizontal_illusion "Vertical–horizontal illusion")
* [ White's ](/wiki/White%27s_illusion "White's illusion")
* [ Wundt ](/wiki/Wundt_illusion "Wundt illusion")
* [ Zöllner ](/wiki/Z%C3%B6llner_illusion "Zöllner illusion")
|
[ 
](/wiki/File:Optical_Illustion-Ambiguous_Patterns.svg)
Popular culture |
* [ Op art ](/wiki/Op_art "Op art")
* _[ Trompe-l'œil ](/wiki/Trompe-l%27%C5%93il "Trompe-l'œil") _
* _[ Spectropia ](/wiki/Spectropia "Spectropia") _ (1864 book)
* _[ Ascending and Descending ](/wiki/Ascending_and_Descending "Ascending and Descending") _ (1960 drawing)
* _[ Waterfall ](/wiki/Waterfall_\(M._C._Escher\) "Waterfall \(M. C. Escher\)") _ (1961 drawing)
* _[ The dress ](/wiki/The_dress "The dress") _ (2015 photograph)
Related |
* [ Accidental viewpoint ](/wiki/Accidental_viewpoint "Accidental viewpoint")
* [ Auditory illusions ](/wiki/Auditory_illusion "Auditory illusion")
* [ Illusions ](/wiki/Illusion "Illusion")
* [ Tactile illusions ](/wiki/Tactile_illusion "Tactile illusion")
* [ Temporal illusion ](/wiki/Time_perception "Time perception")
* [ v ](/wiki/Template:Op_art "Template:Op art")
* [ t ](/wiki/Template_talk:Op_art "Template talk:Op art")
* [ e ](/wiki/Special:EditPage/Template:Op_art "Special:EditPage/Template:Op art")
[ Op art ](/wiki/Op_art "Op art")
---
Artists |
* [ Yaacov Agam ](/wiki/Yaacov_Agam "Yaacov Agam")
* [ Josef Albers ](/wiki/Josef_Albers "Josef Albers")
* [ Getulio Alviani ](/wiki/Getulio_Alviani "Getulio Alviani")
* [ Edna Andrade ](/wiki/Edna_Andrade "Edna Andrade")
* [ Richard Anuszkiewicz ](/wiki/Richard_Anuszkiewicz "Richard Anuszkiewicz")
* [ Carlos Cruz-Diez ](/wiki/Carlos_Cruz-Diez "Carlos Cruz-Diez")
* [ Wojciech Fangor ](/wiki/Wojciech_Fangor "Wojciech Fangor")
* [ Gerhard von Graevenitz ](/wiki/Gerhard_von_Graevenitz "Gerhard von Graevenitz")
* [ Edwin Mieczkowski ](/wiki/Edwin_Mieczkowski "Edwin Mieczkowski")
* [ Andrzej Nowacki ](/wiki/Andrzej_Nowacki "Andrzej Nowacki")
* [ Julio Le Parc ](/wiki/Julio_Le_Parc "Julio Le Parc")
* [ Bridget Riley ](/wiki/Bridget_Riley "Bridget Riley")
* [ Arnold Alfred Schmidt ](/wiki/Arnold_Alfred_Schmidt "Arnold Alfred Schmidt")
* [ Francisco Sobrino ](/wiki/Francisco_Sobrino "Francisco Sobrino")
* [ Jesús Rafael Soto ](/wiki/Jes%C3%BAs_Rafael_Soto "Jesús Rafael Soto")
* [ Julian Stanczak ](/wiki/Julian_Stanczak "Julian Stanczak")
* [ Gregorio Vardanega ](/wiki/Gregorio_Vardanega "Gregorio Vardanega")
* [ Grazia Varisco ](/wiki/Grazia_Varisco "Grazia Varisco")
* [ Victor Vasarely ](/wiki/Victor_Vasarely "Victor Vasarely")
* [ Jean-Pierre Yvaral ](/wiki/Jean-Pierre_Yvaral "Jean-Pierre Yvaral")
|
[  ](/wiki/File:Hungary_pecs_-
_vasarely0.jpg)
* [ Color theory ](/wiki/Color_theory "Color theory")
* [ Figure–ground ](/wiki/Figure%E2%80%93ground_\(perception\) "Figure–ground \(perception\)")
* [ François Morellet ](/wiki/Fran%C3%A7ois_Morellet "François Morellet")
* [ Hard-edge painting ](/wiki/Hard-edge_painting "Hard-edge painting")
* [ M. C. Escher ](/wiki/M._C._Escher "M. C. Escher")
* Optical illusion
[ Authority control databases ](/wiki/Help:Authority_control "Help:Authority
control") : National [ 
](https://www.wikidata.org/wiki/Q174923#identifiers "Edit this at Wikidata") |
* [ France ](https://catalogue.bnf.fr/ark:/12148/cb11938445g)
* [ BnF data ](https://data.bnf.fr/ark:/12148/cb11938445g)
* [ Israel ](http://olduli.nli.org.il/F/?func=find-b&local_base=NLX10&find_code=UID&request=987007548413005171)
* [ United States ](https://id.loc.gov/authorities/sh85095148)
* [ Japan ](https://id.ndl.go.jp/auth/ndlna/01105716)
* [ Czech Republic ](https://aleph.nkp.cz/F/?func=find-c&local_base=aut&ccl_term=ica=ph211778&CON_LNG=ENG)
---|---
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* [ Optical illusions ](/wiki/Category:Optical_illusions "Category:Optical illusions")
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* [ Articles containing video clips ](/wiki/Category:Articles_containing_video_clips "Category:Articles containing video clips")
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* How To Create Seamless Transitions: Mastering The Art Of Dynamic Video Editing
# How To Create Seamless Transitions: Mastering The Art Of Dynamic Video
Editing
Table of contents
The Principle Of Seamlessness
Shot Planning For Seamless Transitions
Top Transitions To Use In Dynamic Video Editing
* The Zoom Transition
* The Fade Through Glow Transition (Lens Leak)
* The Speed-Match Transition: Whip
* Speed-Match+Stability: Throw
* Stability + Motion Match: Rotation
* Masking - Foreground Object Blocking (Speed Match Relevance)
* The Blur Transition
* Motion Blur + Speedup
Stacking Transitions: Which Transitions Can Be Compounded?
Best Software for Seamless Transitions
* Adobe After Effects
* DaVinci Resolve
* Final Cut Pro
Transition Mistakes To Avoid
Final Thoughts
Where choppy transitions can have a jarring effect, **seamless transitions can
have a hypnotic one** . That's why dynamic video editing can improve your
audience engagement. Smooth transitions are **easy to follow** but can be
incredibly difficult to create.
To create seamless transitions, you must **match the speed and direction of
the movement in both shots** , **add motion blur** , and switch shots
**quicker than the eye can follow** . There are Adobe After Effects presets
and DaVinci Resolve templates that you can use for **smooth transitions** .
This article is your crash course on smooth transitions. You will learn
specific transitions as well as the principles of seamlessness in shot-
shifting. Multiple videos are throughout this resource **for specific
instructions** as well. Bookmark this post for future reference.
## The Principle Of Seamlessness
We, here at ContentFries, **are always researching engagement** . As the
biggest facilitators of content repurposing in our region, **we have to stay
on the cutting edge of things** . Having analyzed over 1000 most viewed
videos, we have concluded that the next best thing for user engagement, after
short-form captioning, **is smooth editing** .
We have learned that seamless transitions occur when the eye is **fixated on a
constant while the shot shifts faster than the eye can detect** . That's why
you **might not notice** the cuts in your favorite Youtuber's commentary
videos.
To create seamless transitions, **you have to keep the eye occupied and shift
the shot** . The specific tactics and transitions you can use for this are
covered later in this post. But to make any one of those work, **you have to
be able to understand the role of shot planning** .
## Shot Planning For Seamless Transitions
The number one way to make your video transitions smooth is to plan your shots
around transitions. You can do a lot of magic in post, but what elevates a
well-timed transition is the **contrast between shot A and shot B** . If the
camera is in motion, **then its speed and direction should be the same** .
And if the subject is moving, **his pace should be uniform across multiple
shots** . The harsher the contrast, **the harder you have to work to make the
transition** .
* **Always shoot motion-following shots** \- These shots can save a shot shift that would otherwise be too distracting.
* **Shoot more than you need** \- B-Roll can come in handy when you're running out of material.
* **Keep one aspect similar between shots** \- It always helps to have similar color schemes, environments, and other aspects to smooth out a transition.
* **Drop/Throw objects in and out of the frame** \- As a precautionary measure, film your subjects throwing a specific object in and out of the frame in different shots. So, whenever your main transition material doesn't work, you can use a drop transition.
## Top Transitions To Use In Dynamic Video Editing
Simply understanding what makes a transition smooth **won't help you make a
great video** . You need to know different applications of the transition
smoothness principles to **keep your video editing from becoming monotonous
and predictable** .
In this section, you will discover several transitions that build on top of
each other. The first one is the easiest, and the last one is the most
complicated. If you master these transitions in the order that they are
listed, though, **you'll become a transition expert in no time** .
### The Zoom Transition
The zoom transition is a very quick transition that doesn't give the viewer
enough time to spot the differences between the two shots. Because it happens
almost as quickly as a cut, **it can sometimes be a little jarring** . You
need to match the shots, at least in theme, if not in color and subject, **to
make this transition work** .
Zoom transition works because it keeps the eyes engaged while shifting shots.
**There are only two ways to keep the eyes engaged** . The first is motion,
and the second is color.
### The Fade Through Glow Transition (Lens Leak)
The fade-through-glow transition works by keeping the viewer engaged with
light instead of motion. The basic version of this transition is the classic
fade-through-white transition. Fading to black **can instill a sense of
completion** , while fading through **can distract the viewer from the actual
shot** .
Letting a light leak or glow fill up enough of the screen to change shots can
work. But for that, **the leak must work on both shots** . The leak has to
appear, expand, contract, and vanish. It is overlayed on the timeline as it
shifts from one shot to the other. The expansion stage of the light leak
**must occupy the entire screen** when the first shot cuts to the second one.
### The Speed-Match Transition: Whip
Speed is a lot easier to use than light for unplanned transitions. But if you
plan your shots properly, **you can make a whip transition which has an
incredibly smooth effect** . To create a whip transition that works, you have
to follow the subject in two shots at the same speed and in the same
direction.
Then at the peak of one shot's camera movement, **you can switch to the next
shot** . As long as the speed of both shots matches, the transition occurs
**before the viewer is aware of the shot change** .
### Speed-Match+Stability: Throw
If you want to level up the impact of speed-matching, you can add a stable
object to create a "throw" transition. By fixing the camera to a single
object, like a ball, **you can take two different shots in different
environments** . Follow the object at the same speed and shift shots in
between to create a transition that's **quicker than the eye can catch** .
### Stability + Motion Match: Rotation
Stability and motion-matching work not just for object-throwing transitions.
It can also work with subjects. **Rotating transitions can be incredibly
smooth** if there's a subject in the mix.
Follow the main character in a shot as they're walking. Keep everything but
the environment the **same in the next shot** . That includes the pace of your
character's walk and the speed at which the camera follows them. In both
shots, **you must rotate the camera 360 degrees** .
**This requires a gimbal with a rotation feature** . You have to cut the shots
when the camera is at the same angle to create a powerful yet smooth shift. It
is good to wait for at least a **quarter of a rotation before making the
shift** .
**Only when the viewer is subconsciously expecting an entire rotation** does
this transition work. You can also add speed to the rotation (in post) and
**match the speed in both shots** . So the rotation can start slow, speed up,
switch shots at the same speed, and then slow down.
### Masking - Foreground Object Blocking (Speed Match Relevance)
Masking is a high-quality transition tool that even modern movies use. If it
is good enough for cinema, **it's good enough for digital video** . Speed-
matching is the relevant principle for the masking transition.
You have to create a mask that **conceals the environment behind the subject**
. For this to work as a transition, **the subject** (or object) **must cover
the entire screen in a sweep** .
It could be a tree in a forest scene or a football in a picnic highlights
video. When the tree or the football passes across the screen, **it erases the
first shot** (because of the masking effect) and **reveals the shot on which
it is overlaid** .
To make this transition subtle, you must ensure that the **shot revealed is
thematically similar** . It works best when the two shots are in the same
environment but reveal a different perspective.
### The Blur Transition
Another transition that works for the same environment shot shifts is the blur
transition. It uses the same screen-filling principle that is used by fading
through white or lens leak transitions. **You can use it whenever the same
object shifts environments** .
By blurring it in one shot and then reducing the blur to complete clarity in
another, **you can produce a smoother shift** . Ideally, the subject or object
should be in the same position in the frame in both shots. Blurring has an
inherent smoothness that **fading through white and direct cuts don't** .
### Motion Blur + Speedup
Finally, you can add motion blur to any speed used in your transitions to
**create an additional layer of smoothness** . Whether you use speed when
rotating the camera in one shot or speed-match in a whip transition, **you can
add motion blur** to a part of the effect to create a super-smooth transition.
Adding motion blur to motion is only one instance of transition stacking. You
can stack complementing transitions to **enhance shot shifts and make them
seamless** .
## Stacking Transitions: Which Transitions Can Be Compounded?
Transitions are tricky because even a single bad choice **can make the entire
video look like amateur hour** . Stacking the wrong transitions can make the
video look worse, but compounding the right transitions can make you look like
a master of video wizardry. The following are a **few transitions that
complement each other** :
* **Zoom In + Zoom Out** \- Zooming in on one shot and zooming out on the next can create a seamless transition if the shots are thematically aligned.
* **Rotation + Speed Up** \- Adding speed to a rotating shot allows you to cut to another rotating shot at the same speed.
* **Light leak + Blur** \- If there is no object to blur between shots, you can add a light leak and then blur to diffuse it. This creates a smooth shift.
* **Motion Blur + Speed** \- Speedmatching shots can be enhanced with motion blur.
* **Motion + Motion Blur + Speed + Zoom Out** \- A masterful yet complicated transition requires movement of the camera, motion blur, and speed on one shot and motion blur alongside a zoom-out at the same speed on the next one.
* **Zoom In + Speed + Motion Blur + Zoom Out** \- This is a zoom-in and out transition stack with speed and motion blue added to it.
As you can see, speed and blur are two of the most versatile transition-
creating tools. In fact, **over 95% of the After Effects transition presets**
use speed, blur, or both. By now, you know the effects you need for seamless
transitions. Now, **let's look at how you can implement them** .
## Best Software for Seamless Transitions
If your video transitions are choppy, **your video editor might be to blame**
. Not all editors have the same transition-creating capabilities. In this
section, **you'll find the best video editors for seamless shot shifts** .
### Adobe After Effects
No conversation around transitions would be complete without After Effects. It
is Adobe's motion graphics tool that complements Adobe Premiere, Adobe's
**flagship video editing tool** . There are **hundreds of transition
templates** for Adobe After Effects that make seamless transitions pretty
easy.
### DaVinci Resolve
DaVinci Resolve has great light management tools that make **incredible
transitions possible** . There are dozens of very specific tutorials that
cover creating transitions from scratch in this control-expansive editing
tool. It is like Adobe Premiere and Adobe After Effects rolled into a single
program. However, **it is pretty difficult to master** .
### Final Cut Pro
If you're an Apple user, you might already have Final Cut Pro. It is the
equivalent of Premiere and DaVinci Resolve for iOS. Multiple movies and TV
shows have been made on this program, **so there's no doubt regarding its
output quality** . Final Cut also has **transition packs and multiple plug-
and-play options for creating transitions** .
## Transition Mistakes To Avoid
Now that you know what to do to make your video transitions seamless, **let's
go over what you shouldn't do if you want to avoid rough shot shifts** .
* **Using a transition effect without a planned shot** \- Random drag-and-drop transitions rarely work.
* **Using distracting transition effects** \- One shot bouncing off the frame while the other bursts into a heart frame is a transition. But it is not a smooth one.
* **Using dissolve** \- Dissolve transitions have to be the most distracting ones in standard editors.
* **Making the transition too slow or too quick** \- If a transition makes you go to sleep or causes whiplash, it isn't a good transition.
## Final Thoughts
Transitions that are too choppy, jarring, or contrast-carrying **can be
distracting** . When shifting shots, you must use motion, blur, speed, and
direction alignment, **alongside well-planned shots to create seamless
transitions** . Moreover, you can use other engagement-enhancing tools like
short-form subtitles and context-specific video layouts to keep people
watching till the end. [ **ContentFries** ](https://www.contentfries.com/) is
a content-multiplying engine that can help **with the latter** , while After
Effects, DaVinci Resolve, and Final Cut Pro are the editors that **can help
you create seamless transitions** .
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| biology | 366501 | https://da.wikipedia.org/wiki/Motion%20blur | Motion blur | Motion blur er i computergrafikkens verden en metode til at lave en replika af hurtigt bevægende objekter.
Filmkameraer bruger dette trick til at få film til at virke mere flydende, ved at det ligner at en masse billeder er på det samme billede. Denne effekt er først kommet til brug i meget nye computerspil, men uden motion blur kan computerspil virke hakkende og langsomme selv med en billedehastighed på 30-40 frames per second.
Computergrafik | danish | 0.664185 |
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4. article
Smooth tracking of visual targets distinguishes lucid REM sleep dreaming and
waking perception from imagination
[ Download PDF ](/articles/s41467-018-05547-0.pdf)
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* Article
* [ Open access ](https://www.springernature.com/gp/open-research/about/the-fundamentals-of-open-access-and-open-research)
* Published: 17 August 2018
# Smooth tracking of visual targets distinguishes lucid REM sleep dreaming
and waking perception from imagination
* Stephen LaBerge 1 na1 nAff3 ,
* Benjamin Baird 2 na1 &
* Philip G. Zimbardo 1
[ _Nature Communications_ ](/ncomms) ** volume 9 ** , Article number: 3298
( 2018 ) Cite this article
* 13k Accesses
* 36 Citations
* 181 Altmetric
* [ Metrics details ](/articles/s41467-018-05547-0/metrics)
### Subjects
* [ Consciousness ](/subjects/consciousness)
* [ Motor control ](/subjects/motor-control)
* [ Perception ](/subjects/perception)
* [ REM sleep ](/subjects/rem-sleep)
## Abstract
Humans are typically unable to engage in sustained smooth pursuit for imagined
objects. However, it is unknown to what extent smooth tracking occurs for
visual imagery during REM sleep dreaming. Here we examine smooth pursuit eye
movements during tracking of a slow-moving visual target during lucid dreams
in REM sleep. Highly similar smooth pursuit tracking was observed during both
waking perception and lucid REM sleep dreaming, in contrast to the
characteristically saccadic tracking observed during visuomotor imagination.
Our findings suggest that, in this respect, the visual imagery that occurs
during REM sleep is more similar to perception than imagination. The data also
show that the neural circuitry of smooth pursuit can be driven by a visual
percept in the absence of retinal stimulation and that specific voluntary
shifts in the direction of experienced gaze within REM sleep dreams are
accompanied by corresponding rotations of the physical eyes.
### Similar content being viewed by others
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Article Open access 02 February 2022
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Article 20 July 2020
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Article 17 November 2022
## Introduction
Is the visual imagery of dreams more like perception or imagination? This
question has been asked at least since Aristotle but until now has lacked
empirical data [ 1 ](/articles/s41467-018-05547-0#ref-CR1 "Nir, Y. & Tononi,
G. Dreaming and the brain: from phenomenology to neurophysiology. Trends Cogn.
Sci. 14, 88–100 \(2010\).") . Here we perform an objective test of this
question by determining the extent to which smooth pursuit eye movements
(SPEMs) are observed when an individual tracks a slow-moving visual target
during lucid rapid eye movement (REM) sleep dreaming. Humans are typically
unable to smoothly track slowly an imagined object in a sustained fashion,
exhibiting instead saccadic eye movements [ 2
](/articles/s41467-018-05547-0#ref-CR2 "Spering, M. & Montagnini, A. Do we
track what we see? Common versus independent processing for motion perception
and smooth pursuit eye movements: a review. Vision Res. 51, 836–852
\(2011\).") . Since SPEMs elicited during visual tracking are known to depend
on visual motion signals, they may be used as an objective assessment of
visual imagery during REM sleep.
Since the discovery of REM sleep in the 1950s, dreams have been believed to be
vivid enough to suppose that the REMs that give the state its name are caused
by the dreamer scanning the dream scene. Substantial evidence has shown that
the strong version of the scanning hypothesis, which suggests that all REMs
are due to tracking dream imagery, is untenable. For example, REMs are
observed in fetuses, neonates, pontine cats and congenitally blind subjects
despite their lack of sight [ 3 ](/articles/s41467-018-05547-0#ref-CR3
"Leclair-Visonneau, L., Oudiette, D., Gaymard, B., Leu-Semenescu, S. & Arnulf,
I. Do the eyes scan dream images during rapid eye movement sleep? Evidence
from the rapid eye movement sleep behaviour disorder model. Brain 133,
1737–1746 \(2010\).") . However, equally substantial evidence indicates that,
in other circumstances, there is a close link between the direction of
subjective gaze during dreaming and objective eye movements [ 4
](/articles/s41467-018-05547-0#ref-CR4 "Dement, W. & Kleitman, N. The relation
of eye movements during sleep to dream activity: an objective method for the
study of dreaming. J. Exp. Psychol. 53, 339–346 \(1957\).") , [ 5
](/articles/s41467-018-05547-0#ref-CR5 "Herman, J. H. et al. Evidence for a
directional correspondence between eye movements and dream imagery in REM
sleep. Sleep 7, 52–63 \(1984\).") . For instance, the pattern of REMs has been
found to be related to the visual imagery and reported gaze direction of REM
sleep dreams [ 6 ](/articles/s41467-018-05547-0#ref-CR6 "Dement, W. &
Wolpert, E. A. The relation of eye movements, body motility, and external
stimuli to dream content. J. Exp. Psychol. 55, 543–552 \(1958\).") .
Furthermore, REMs precisely track saccadic eye movement signals in lucid
dreams [ 7 ](/articles/s41467-018-05547-0#ref-CR7 "LaBerge, S. P., Nagel, L.
E., Dement, W. C. & Zarcone, V. P. Lucid dreaming verified by volitional
communication during REM sleep. Percept. Mot. Skills 52, 727–732 \(1981\).")
and goal-directed actions in dreams of patients with REM sleep behavior
disorder [ 3 ](/articles/s41467-018-05547-0#ref-CR3 "Leclair-Visonneau, L.,
Oudiette, D., Gaymard, B., Leu-Semenescu, S. & Arnulf, I. Do the eyes scan
dream images during rapid eye movement sleep? Evidence from the rapid eye
movement sleep behaviour disorder model. Brain 133, 1737–1746 \(2010\).") .
Furthermore, as during waking perception, REMs are associated with transient
modulation of spiking activity in the medial temporal lobe associated with
visual-mnemonic processes [ 8 ](/articles/s41467-018-05547-0#ref-CR8
"Andrillon, T., Nir, Y., Cirelli, C., Tononi, G. & Fried, I. Single-neuron
activity and eye movements during human REM sleep and awake vision. Nat.
Commun. 6, 7884 \(2015\).") . Together, this evidence suggests that there are
multiple sources of eye movements in REM sleep, a subset of which include
correspondence between dreamed gaze direction and eye movements.
In order to directly compare visual eye movement tracking in REM sleep
dreaming, waking perception and visuomotor imagination, we designed tracking
tasks that could be carried out analogously in all three states. Participants
were selected for excellent dream recall and high reported frequency of lucid
dreams with demonstrated ability to have lucid dreams in the sleep laboratory.
Precise psychophysiological correlations were made possible by participants
marking the exact moments of initiation of lucidity and the initiation and
completion of the tracking tasks with volitional left–right–left–right (LRLR)
eye movement signals [ 7 ](/articles/s41467-018-05547-0#ref-CR7 "LaBerge, S.
P., Nagel, L. E., Dement, W. C. & Zarcone, V. P. Lucid dreaming verified by
volitional communication during REM sleep. Percept. Mot. Skills 52, 727–732
\(1981\).") . Using this eye movement signaling methodology, individuals who
are able to reliably attain awareness that they are dreaming while they are
dreaming can remember pre-sleep instructions to carry out experiments and mark
the exact time of particular dream events with eye movement signals [ 7
](/articles/s41467-018-05547-0#ref-CR7 "LaBerge, S. P., Nagel, L. E., Dement,
W. C. & Zarcone, V. P. Lucid dreaming verified by volitional communication
during REM sleep. Percept. Mot. Skills 52, 727–732 \(1981\).") , 9 , 10 ,
[ 11 ](/articles/s41467-018-05547-0#ref-CR11 "LaBerge S. in Varieties of
Anomalous Experience: Examining the Scientific Evidence 2nd edn \(eds Cardeña
E., Lynn S. J., Krippner S.\) 145–173 \(American Psychological Association,
Washington, 2014\).") . As illustrated by LaBerge [ 12
](/articles/s41467-018-05547-0#ref-CR12 "LaBerge S. in Sleep and Cognition
\(eds Bootzin R. R., Kihlstrom J. F., Schacter D. L.\) 109–126 \(American
Psychological Association, Washington, 1990\).") these LRLR eye signals are
clearly discernable in the electrooculogram (EOG), enabling precise time-
stamping of tasks and events during REM sleep (for replications and extensions
see, e.g., refs. [ 9 ](/articles/s41467-018-05547-0#ref-CR9 "LaBerge, S.,
Nagel, L., Taylor, W., Dement, W. & Zarcone, V. Jr Psychophysiological
correlates of the initiation of lucid dreaming. Sleep Res. 10, 149 \(1981\).")
, [ 13 ](/articles/s41467-018-05547-0#ref-CR13 "LaBerge, S. & Dement, W. C.
Voluntary control of respiration during REM sleep. Sleep Res. 11, 107
\(1982\).") , [ 14 ](/articles/s41467-018-05547-0#ref-CR14 "Erlacher, D.,
Schredl, M. & LaBerge, S. Motor area activation during dreamed hand clenching:
a pilot study on EEG alpha band. Sleep Hypn. 5, 182–187 \(2003\).") ; for
recent implementations see, e.g., refs. [ 10
](/articles/s41467-018-05547-0#ref-CR10 "Dresler, M. et al. Neural correlates
of dream lucidity obtained from contrasting lucid versus non-lucid REM sleep:
a combined EEG/fMRI case study. Sleep 35, 1017–1020 \(2012\).") , [ 15
](/articles/s41467-018-05547-0#ref-CR15 "Oudiette, D. et al. REM sleep
respiratory behaviors match mental content in narcoleptic lucid dreamers. Sci.
Rep. 8, 2636 \(2018\).") ).
After making the LRLR signal, participants attempted to carry out one of two
tracking tasks: (i) circle tracking and (ii) one-dimensional (1D) movement
tracking on the horizontal meridian (see Methods). One participant performed a
variant of the circle task by tracking a lemniscate (infinity sign). The
tracking protocols were carried out in three conditions: (i) lucid REM sleep
dreaming (“dreaming”), (ii) awake with eyes open (“perception”) and (iii)
tracking the imagined movement while awake with eyes closed (“imagination”).
Additionally, one participant completed a fourth condition in which she
imagined tracking the movement during a lucid REM sleep dream (“imagination in
dreaming”) after completion of the standard tracking task. Immediately upon
awakening, participants were interviewed as to whether they performed the
task. If participants reported completing the tracking task during a lucid
dream, they filled out a dream report form in which they reported their entire
dream (see “Dream report methods and analysis“ in “Methods”; see Supplementary
Note [ 1 ](/articles/s41467-018-05547-0#MOESM1) for examples of participants'
reports). Our data provide evidence that intentional slow tracking of visual
motion during REM sleep dreams results in SPEMs that are highly similar to
waking perception, suggesting that, in this respect, the visual quality of
imagery during REM sleep dreaming is more similar to waking perception than
imagination.
## Results
### Lucid REM sleep dream tracking and phenomenological reports
Out of the 7 participants, 6 completed at least one tracking task in their
lucid REM sleep dreams: 5 participants completed the tracking task a total of
21 times for the circular tracking task (range 1–7) and 3 participants
completed the tracking task a total of 5 times for the 1D horizontal meridian
tracking task (range 1–3). The total number of trials and results for each
condition and participant is provided in Supplementary Table [ 2
](/articles/s41467-018-05547-0#MOESM1) and Supplementary Table [ 3
](/articles/s41467-018-05547-0#MOESM1) . Participants reported completing the
tracking task as instructed by tracking the thumb of their dominant hand as
perceived in the dream in 27 out of the 27 lucid dream tracking trials.
Furthermore, 27 out of the 27 lucid dream tracking trials were accompanied by
a dream report which described a subjective experience of performing the task
by tracking their visual imagery during dreaming, as judged by two independent
raters (inter-rater reliability: 100%) (see “Dream report methods and
analysis“ in “Methods”). Examples of participants’ dream reports of the
tracking task during their lucid REM sleep dreams are provided in
Supplementary Note [ 1 ](/articles/s41467-018-05547-0#MOESM1) .
All 27 lucid dream tracking trials occurred during unambiguous REM sleep (see
Fig. [ 1 ](/articles/s41467-018-05547-0#Fig1) for a representative example).
Suppression of electromyogram (EMG) and H-reflex amplitude along with
suppressed alpha in occipital electroencephalography (EEG) confirmed that both
LRLR signals and completion of the slow tracking task occurred in
uninterrupted REM sleep (Fig. [ 1b ](/articles/s41467-018-05547-0#Fig1) ). All
27 signal-verified lucid dreams met the conventional criteria for REM sleep,
including activated EEG, episodic REMs and atonic sub-mental EMG. During the
experiment, one participant reported a non-lucid dream in which he practiced
the circular smooth tracking task (the participant reported dreaming that he
was in the laboratory practicing the tracking task but he did not realize he
was dreaming until after he woke up). This unique record afforded us an
opportunity to compare smooth tracking behavior across lucid and non-lucid REM
sleep dreaming (see “Circle tracking”).
**Fig. 1**
[ 
](/articles/s41467-018-05547-0/figures/1)
Line tracking during lucid REM sleep dreaming in a single participant. **a**
Enlarged section showing LRLR eye movement signals and smooth tracking task as
recorded in the horizontal EOG (HEOG). Upon awakening, the subject reported
becoming lucid in the dream, making a LRLR signal (1), fully extending his
right thumb, and tracking his thumb nail as he slowly swung his arm
horizontally from center to approximately 30° left, back through center to 30°
right, and finally leftward back to center. While tracking to the right, he
noticed moving his head slightly in the direction of tracking both rightward
and leftward as he reversed motion back to the center (2). He marked the end
of the smooth tracking task (estimated 10 s) with a second LRLR signal (3).
Having completed the task, he spent the remainder of his lucid dream exploring
the dream environment, waking approximately 60 s later. See Supplementary Note
[ 1 ](/articles/s41467-018-05547-0#MOESM1) “Report of line tracking task” for
the report associated with this figure. **b** Six channels of physiological
data (HEOG, vertical EOG (VEOG), skin potential response (SPR)), occipital EEG
bandpass filtered for alpha (OZ (8–12 Hz)), H-reflex amplitude (a measure of
spinal reflex excitability) (upward black triangles mark H-reflex STIM), and
electromyogram (EMG)) are shown during an initial period of wakefulness, REM
period onset (REMP onset), transition to lucid REM sleep and awakening.
Suppression of EMG and H-reflex amplitude along with reduced alpha in EEG
confirm that the participant remained in uninterrupted REM sleep during lucid
dreaming, including LRLR signals and during completion of the slow tracking
task. Lucid dream onset is localized by the autonomic nervous system surprise
response (scalp skin potential response (SPR; black asterisk)) before the LRLR
signal
[ Full size image ](/articles/s41467-018-05547-0/figures/1)
### Circle tracking
We observed a main effect of STATE for number of saccades per second (NSPS)
(likelihood ratio: 59.03, _P_ = 0.00001, two-tailed bootstrap likelihood ratio
test). Imagination had a higher saccade rate compared to both perception ( _β_
= −1.84, _P_ _ < _ 0.00001, 95% confidence interval (CI) (−2.25, −1.48), two-
tailed bootstrap test) and dreaming ( _β_ = −1.36, _P_ < 0.00003, 95% CI
(−1.81, −0.92), two-tailed bootstrap test) (Supplementary Table [ 1
](/articles/s41467-018-05547-0#MOESM1) ; Supplementary Figure [ 1
](/articles/s41467-018-05547-0#MOESM1) and [ 2
](/articles/s41467-018-05547-0#MOESM1) ). No significant difference was
observed between perception and dreaming ( _β_ = 0.48, _P_ = 0.14, 95% CI
(0.03, 0.94), two-tailed bootstrap test). The smooth pursuit ratio (the amount
of time in smooth pursuit divided by the total time spent tracking the
movement (SP%)) also revealed a main effect of STATE (likelihood ratio: 66.41,
_P_ = 0.00001, two-tailed bootstrap likelihood ratio test). Both perception (
_β_ = 25.26, _P_ < 0.00001, 95% CI (20.81, 30.34), two-tailed bootstrap test)
and dreaming ( _β_ = 22.18, _P_ < 0.00001, 95% CI (16.28, 27.82), two-tailed
bootstrap test) had increased smooth pursuit compared to imagination. No
significant difference was observed between perception and dreaming ( _β_ =
−3.10, _P_ = 0.50, 95% CI (−9.08, 2.40), two-tailed bootstrap test). SP% was
higher for all 5 participants, while NSPS was lower for 4/5 participants
during dreaming compared to imagination (Supplementary Table [ 2
](/articles/s41467-018-05547-0#MOESM1) ).
SP% and NSPS were highly anti-correlated ( _r_ s = −0.80, _P_ < 10 −15 ,
two-tailed Spearman’s rank-order correlation), indicating that both variables
converged in their measurement of pursuit. No significant difference was
observed between clockwise and counterclockwise tracking for either NSPS ( _β_
= −0.11, _P_ = 0.68, 95% CI (−0.46, 0.21), two-tailed bootstrap test) or SP% (
_β_ = 1.15, _P_ = 0.75, 95% CI (−3.22, 5.72), two-tailed bootstrap test). As
noted above, one participant reported performing one trial of the circle
tracking task (LRLR–counterclockwise circle tracking–LRLR) during a non-lucid
dream. Both measures of pursuit during this trial (SP%: 90.58; NSPS: 0) were
within the 90% prediction interval for the dreaming condition (SP% (68.14,
98.15), NSPS (0, 1.93)), and were outside the 90% prediction interval for the
imagination condition (SP% (32.19, 86.51), NSPS (0.30, 4.28)).
### Horizontal vs. vertical eye movements in circle tracking
Both horizontal EOG (HEOG) and vertical EOG (VEOG) distinguished perception
and dreaming from imagination for both NSPS and SP% (all _P_ < 0.0005, two-
tailed bootstrap test). Quantification of the area under the ROC curve (AUC)
revealed that HEOG had numerically higher classification accuracy compared to
VEOG for both perception (0.93 vs. 0.87 respectively) and dreaming (0.91 vs.
0.83 respectively) contrasted with imagination, though this difference was not
statistically significant (all _P_ _≥_ 0.24, two-tailed bootstrap test, see
below). Across all states, HEOG had increased SP% compared to VEOG (all _P_ <
0.00001, two-tailed bootstrap test). The fact that HEOG had increased SP%
specifically during waking perception suggests that HEOG was more sensitive to
SPEMs. This is consistent with other studies that have shown that HEOG is more
accurate and less prone to artifact than VEOG [ 16
](/articles/s41467-018-05547-0#ref-CR16 "Ke, S. R., Lam, J., Pai, D. K. &
Spering, M. Directional asymmetries in human smooth pursuit eye movements.
Invest. Ophthalmol. Vis. Sci. 54, 4409–4421 \(2013\).") . Our second task, 1D
horizontal meridian tracking, was therefore designed to isolate the horizontal
component in evaluating differences in SPEMs between states.
### 1D horizontal meridian tracking
We observed a main effect of STATE for NSPS (likelihood ratio: 16.85, _P_ =
0.017, two-tailed bootstrap likelihood ratio test). Imagination had a higher
saccade rate compared to both perception ( _β_ = −0.93, _P_ = 0.0044, 95% CI
(−1.26, −0.59), two-tailed bootstrap test) and dreaming ( _β_ = −0.91, _P_ =
0.0029, 95% CI (−1.23, −0.57), two-tailed bootstrap test) (Fig. [ 2
](/articles/s41467-018-05547-0#Fig2) ; Supplementary Table [ 1
](/articles/s41467-018-05547-0#MOESM1) ). No significant difference was
observed between perception and dreaming ( _β_ = 0.01, _P_ = 0.868, 95% CI
(−0.32, 0.33), two-tailed bootstrap test). SP% also revealed a main effect of
STATE (likelihood ratio: 18.32, _P_ = 0.01, two-tailed bootstrap likelihood
ratio test) (Fig. [ 3a ](/articles/s41467-018-05547-0#Fig3) ). Both perception
( _β_ = 12.63, _P_ = 0.003, 95% CI (8.75, 16.57), two-tailed bootstrap test)
and dreaming ( _β_ = 11.35, _P_ = 0.0093, 95% CI (7.60, 15.10), two-tailed
bootstrap test) had increased smooth pursuit compared to imagination (Fig. [ 2
](/articles/s41467-018-05547-0#Fig2) ; Supplementary Table [ 1
](/articles/s41467-018-05547-0#MOESM1) ). No significant difference was
observed between perception and dreaming ( _β_ = −1.29, _P_ = 0.794, 95% CI
(−5.11, 2.68), two-tailed bootstrap test).
**Fig. 2**
[ 
](/articles/s41467-018-05547-0/figures/2)
Classification of 1D horizontal meridian tracking for a single participant.
Eye-tracking is shown during **a** waking perception, **b** lucid REM sleep
dreaming and **c** visuomotor imagination conditions. Slow tracking during
imagination showed intrusions of saccadic eye movements during the tracking
movement, while waking perception and REM sleep dreaming showed predominately
smooth pursuit eye movements. Bottom panels show velocity (degrees/s) as the
derivative of the best-fit sine function plus saccades
[ Full size image ](/articles/s41467-018-05547-0/figures/2)
**Fig. 3**
[ 
](/articles/s41467-018-05547-0/figures/3)
Pursuit ratio scores for perception, dreaming and imagination tracking. **a**
Median values of normalized pursuit ratio scores in horizontal line tracking
(Line tracking), horizontal (H comp circle), vertical (V Comp Circle) and
joint (Circle tracking) components of circle tracking during imagination (I,
red line and symbols), perception (P, blue line and symbols) and dreaming (D,
green line and symbols). Symbols designate medians for individual subjects.
Green stars to the right of D indicate pursuit ratio _z_ -score values for the
non-lucid REM sleep dream tracking trial. Given that the data were not
normally distributed and contained varied numbers of repeated observations
within subjects, data were analyzed using a linear mixed model and
nonparametric bootstrapping (two-sided, paired test) was used to compare P
(circle tracking: _N_ = 5, trials = 28; line tracking: _N_ = 2, trials = 3), D
(circle tracking: _N_ = 5, trials = 21; line tracking: _N_ = 3, trials = 5)
and I (circle tracking: _N_ = 5, trials = 28; line tracking: _N_ = 2, trials =
3) conditions (replications = 1), _*_ _P_ < 0.001, _*P_ < 0.0001, _***_ _P_ <
0.00001. Error bars show s.e.m. **b** Boxplot showing pursuit ratio _z_
-scores during horizontal line tracking task for imagination (I), imagination
in the dream (I in D), perception (P) and dreaming (D) conditions. The bottoms
and tops of the boxes show the 25th and 75th percentiles (the lower and upper
quartiles), respectively; the inner band shows the median; and the whiskers
show the upper and lower quartiles ± 1.5 × the interquartile range (IQR).
**c** Area under the ROC curve (AUC) for perception versus imagination (PvI) H
(horizontal EOG) (thin blue solid line) and V (vertical EOG) (thin blue dotted
line) and dreaming versus imagination (DvI) H (thick green solid line) and V
(thick green dotted line) components of eye movements
[ Full size image ](/articles/s41467-018-05547-0/figures/3)
NSPS was significantly lower for both perception ( _β_ = −1.27, _P_ = 0.006,
two-tailed bootstrap test) and dreaming ( _β_ = −1.25, _P_ = 0.009, two-tailed
bootstrap test) compared to imagination within the dream, and SP% was
significantly higher for both perception ( _β_ = 31.17, _P_ = 0.002, two-
tailed bootstrap test) and dreaming ( _β_ = 28.75, _P_ = 0.009, two-tailed
bootstrap test) compared to imagination during dreaming (Fig. [ 3b
](/articles/s41467-018-05547-0#Fig3) ). For both dreaming and perception, SP%
was higher and NSPS was lower for all participants (Supplementary Table [ 3
](/articles/s41467-018-05547-0#MOESM1) ).
### Bayesian classification of states
SP% as a single indicator yielded 94.7% classification accuracy for perception
and 90.0% classification accuracy for dreaming for circle tracking. Bayesian
combination of SP% and NSPS increased classification accuracy to 99.6% for
perception trials and 98.9% for dream trials (Supplementary Table [ 4
](/articles/s41467-018-05547-0#MOESM1) ). In the 1D horizontal meridian
tracking task, 100% classification accuracy (Bayesian posterior probability
(BPP) = 1.00) was achieved for both perception and dreaming (Supplementary
Table [ 5 ](/articles/s41467-018-05547-0#MOESM1) ), with an associated
sensitivity and specificity of 1.0.
## Discussion
Our data show that intentional slow tracking of visual motion during REM sleep
dreams results in SPEMs. Pursuit eye movements in REM sleep did not differ
from pursuit during waking perception, and both were characterized by high
pursuit ratios and low saccade rates. In contrast, tracking in imagination was
characterized by low pursuit with frequent saccadic intrusions. A Bayesian
classification model that included pursuit ratio and saccade rate
discriminated both REM sleep dreaming and perception from imagination with
greater than 98% accuracy. Together, these findings suggest that, at least in
this respect, the visual quality of REM sleep dream imagery is more similar to
waking perception than imagination.
Evidence suggests that both imagining and dreaming involve activation of the
same brain areas as perception in the corresponding sensory modality (see,
e.g., refs. 17 , 18 , 19 , [ 20 ](/articles/s41467-018-05547-0#ref-CR20
"Farah, M. J. Is visual imagery really visual? Overlooked evidence from
neuropsychology. Psychol. Rev. 95, 307–317 \(1988\).") ). For example,
imagining a face or a house activates the same specific brain areas (fusiform
face area and parahippocampal place area) involved with perceiving these
stimuli [ 19 ](/articles/s41467-018-05547-0#ref-CR19 "O’Craven, K. M. &
Kanwisher, N. Mental imagery of faces and places activates corresponding
stimulus-specific brain regions. J. Cogn. Neurosci. 12, 1013–1023 \(2000\).")
. Likewise, dreaming of specific perceptual content, such as faces or speech,
recruits overlapping cortical regions as waking perception of these contents
[ 17 ](/articles/s41467-018-05547-0#ref-CR17 "Siclari, F. et al. The neural
correlates of dreaming. Nat. Neurosci. 20, 872–878 \(2017\).") . Given these
findings, what could explain the reason why perceived and dreamed visual
motion are able to drive sustained pursuit while imagined visual motion is
not? We hypothesize that it could be attributable to the degree of activation
in extrastriate visual areas, particularly the middle temporal visual area
(MT) and regions of the superior temporal sulcus that process visual motion.
Specifically, evidence suggests that vividness is related to the intensity of
neural activation [ 21 ](/articles/s41467-018-05547-0#ref-CR21 "Amedi, A.,
Malach, R. & Pascual-Leone, A. Negative BOLD differentiates visual imagery and
perception. Neuron 48, 859–872 \(2005\).") , [ 22
](/articles/s41467-018-05547-0#ref-CR22 "Cui, X., Jeter, C. B., Yang, D.,
Montague, P. R. & Eagleman, D. M. Vividness of mental imagery: individual
variability can be measured objectively. Vision Res. 47, 474–478 \(2007\).")
and images, which are typically less vivid, also involve a lesser degree of
neural activation than the corresponding perceptions [ 19
](/articles/s41467-018-05547-0#ref-CR19 "O’Craven, K. M. & Kanwisher, N.
Mental imagery of faces and places activates corresponding stimulus-specific
brain regions. J. Cogn. Neurosci. 12, 1013–1023 \(2000\).") . Furthermore,
imagination interferes with perception in the same modality (see, e.g., ref.
[ 23 ](/articles/s41467-018-05547-0#ref-CR23 "Segal, S. J. & Fusella, V.
Influence of imaged pictures and sounds on detection of visual and auditory
signals. J. Exp. Psychol. 83, 458–464 \(1970\).") ), and we may infer the
reverse is true as well. In contrast, during REM sleep, sensory input is
actively suppressed, preventing competition from externally driven perceptual
processes. One interpretation of our results is therefore that under
conditions of low levels of competing sensory input and high levels of
activation in extrastriate visual cortices (conditions associated with REM
sleep), the intensity of neural activation underlying the imagery of visual
motion (and therefore its vividness) is able to reach levels typically only
associated with waking perception. Sufficient activation of regions such as MT
and medial superior temporal areas that are part of the primary pursuit
pathway may be needed to drive the pursuit-related motor regions of the
cerebellum, such as the flocculus and ventral paraflocculus, which in turn
control the output motor nuclei for the eye muscles to engage in sustained
pursuit behavior [ 24 ](/articles/s41467-018-05547-0#ref-CR24 "Krauzlis, R.
J. Recasting the smooth pursuit eye movement system. J. Neurophysiol. 91,
591–603 \(2004\).") .
Our results help to address a central research question on the topic of smooth
pursuit eye movements in humans and non-human primates, which is whether
retinal image motion is necessary to drive the neural circuitry of pursuit [
2 ](/articles/s41467-018-05547-0#ref-CR2 "Spering, M. & Montagnini, A. Do we
track what we see? Common versus independent processing for motion perception
and smooth pursuit eye movements: a review. Vision Res. 51, 836–852
\(2011\).") . While it was initially thought that pursuit required retinal
image motion from an external physical motion stimulus, evidence now indicates
that smooth pursuit can occur during apparent motion [ 25
](/articles/s41467-018-05547-0#ref-CR25 "Steinbach, M. J. Pursuing the
perceptual rather than the retinal stimulus. Vision Res. 16, 1371–1376
\(1976\).") , including motion aftereffects [ 26
](/articles/s41467-018-05547-0#ref-CR26 "Braun, D. I., Pracejus, L. &
Gegenfurtner, K. R. Motion aftereffect elicits smooth pursuit eye movements.
J. Vision 6, 671–684 \(2006\).") , isoluminant motion [ 27
](/articles/s41467-018-05547-0#ref-CR27 "Braun, D. I. et al. Smooth pursuit
eye movements to isoluminant targets. J. Neurophysiol. 100, 1287–1300
\(2008\).") and illusory moving contours [ 28
](/articles/s41467-018-05547-0#ref-CR28 "Madelain, L. & Krauzlis, R. J.
Pursuit of the ineffable: perceptual and motor reversals during the tracking
of apparent motion. J. Vision 3, 642–653 \(2003\).") , suggesting that SPEMs
are linked to the visual percept rather than retinal stimulation [ 2
](/articles/s41467-018-05547-0#ref-CR2 "Spering, M. & Montagnini, A. Do we
track what we see? Common versus independent processing for motion perception
and smooth pursuit eye movements: a review. Vision Res. 51, 836–852
\(2011\).") . The current results demonstrate that a perceived image with no
retinal counterpart (as in the case of the visual imagery during REM sleep) is
sufficient to drive sustained smooth pursuit in humans. By demonstrating that
smooth pursuit can occur even when there is a complete absence of visual
afferent input to the cortex, our findings provide strong evidence that
neither a physical motion stimulus nor readout of retinal image motion are
necessary for SPEMs.
The current results also provide support for the following form of the
scanning hypothesis: intentional shifts in the direction of gaze within a
dream are accompanied by corresponding movements of the sleeper’s eyes. Our
results show for the first time that tracing circles, lines and infinity signs
by tracking visual imagery with one’s eyes in a dream (i.e., the dreamed
bodily image of one’s thumb) results in electrooculogram recordings of these
shapes. These data provide novel evidence that shifts in the perceived gaze
direction in dreams give rise to the appropriate corresponding eye movements.
Together, these data are consistent with evidence reviewed above, which
suggest that a subset of eye movements during REM sleep are linked to the
direction of subjective gaze during dreams.
One limitation of the current study is the small sample size. Only six
participants were able to successfully attain lucidity during REM sleep and
perform the eye movement tracking task at least once during the study. The
limitation in sample size is due to the fact that we worked with an
exceptional sample of frequent lucid dream recallers who would be able to
reliably attain lucidity and carry out a high-level experimental task in their
REM sleep dreams in a sleep laboratory setting. However, despite the
relatively small sample, we were able to obtain a substantial number of
tracking trials (27) during REM sleep. Furthermore, the fact that our analyses
were conducted using mixed models allowed us to analyze data from trials
rather than single-subject averages, which allowed us to obtain estimates of
effects based on a large number of data points. Nevertheless, studies using
larger samples examining these questions would be a desirable goal for future
research.
The fact that our study sample was comprised of a highly selected group of
frequent lucid dreamers may, on the one hand, be seen as a methodological
strength, in line with a long tradition in neuropsychology of gleaning
insights about the brain and behavior from the study of special populations.
Indeed, without studying this specialized group it is difficult to imagine how
this experiment could have been conducted. On the other hand, it might be
asked whether, or to what extent, the current results extend generally to
(non-lucid) REM sleep dreaming. In the course of data collection, we
fortuitously obtained data that directly address this issue. Specifically,
during the experiment one participant reported a non-lucid dream in which he
practiced the circular smooth tracking task. That is, the participant had a
dream in which he was in the laboratory practicing the tracking task, and he
did not realize he was only dreaming that he was doing the task until after he
woke up. Analysis of this record indicated that it had 0 saccades during the
tracking motion, and that both metrics of smooth pursuit during non-lucid
circle tracking were within the 90% prediction interval of lucid REM sleep
dreaming trials and were outside the 90% prediction interval for imagination
trials. These data suggest that one need not be aware of the fact that one is
dreaming (lucid) in order for the imagery of REM sleep dreaming to guide
smooth pursuit behavior. This is consistent with other research, which has
observed that repeated voluntary saccadic left–right eye movement signals show
no observable differences in shape or amplitude in lucid and non-lucid REM
sleep dreams [ 11 ](/articles/s41467-018-05547-0#ref-CR11 "LaBerge S. in
Varieties of Anomalous Experience: Examining the Scientific Evidence 2nd edn
\(eds Cardeña E., Lynn S. J., Krippner S.\) 145–173 \(American Psychological
Association, Washington, 2014\).") . Together, these data suggest that the
explicit consciousness of the fact that one is dreaming is not likely to be
the determining factor for the oculomotor behavior of either saccadic or
pursuit eye movements during REM sleep dreaming and support the interpretation
that lucid and non-lucid dreaming are largely continuous with respect to these
processes.
Altogether, the present study illustrates the potential of lucid dreaming as a
paradigm for the study of consciousness in general and REM sleep dreaming in
particular. Experienced lucid dreamers are capable of exercising volitional
control over their actions while dreaming and are therefore able to conduct
experiments from within EEG-verified REM sleep dreams. This methodology helps
to overcome the shot-in-the-dark approach of traditional psychophysiological
studies of REM sleep dreams [ 29 ](/articles/s41467-018-05547-0#ref-CR29
"Foulkes, D. in Sleep \(ed. Koella W. P.\) 246–257 \(Karger, Basel, 1980\).")
, which relies on collecting large numbers of recordings and extracting small
subsets of data in which the content of interest appears by chance. In
conclusion, lucid dreaming presents a methodological paradigm that has the
potential to open new ways of studying the relationship between consciousness
and neurophysiological processes using the dreaming brain as a model system.
## Methods
### Participants
Seven participants (4 men, 3 women) participated in the study (age range = 20
**–** 48 years). Participants were selected for excellent dream recall
(recalling at least one dream a minimum of 5–6 nights per week) and high
reported frequency of lucid dreams (3–4 lucid dreams per week minimum, or
approximately one lucid dream every other night), with a demonstrated ability
to successfully have lucid dreams in a sleep laboratory setting. As there was
no pre-specified effect size for these data, we obtained as many trials from
as many participants as possible given experimental constraints (see below).
All participants had no history of neurological disorder and had normal or
corrected-to-normal vision. The study complied with all relevant ethical
regulations for research with human subjects and the study protocol was
conducted in accordance with the Declaration of Helsinki. Signed informed
consent was obtained from all participants before the experiment, and ethical
approval for the study was obtained from the Stanford University Institutional
Review Board.
### Procedures
Participants spent between 1 and 8 nights in the laboratory during the course
of the study. We scheduled multiple nights (depending on participant
availability and availability of sleep laboratory facilities) in order to
allow for more chances to successfully complete the tracking task during lucid
dreams recorded in the sleep laboratory and in order to obtain as many
tracking trials from each participant as possible. On each night, EEG (29
channels), sub-mental EMG and vertical and horizontal EOG were continuously
recorded. EEG and EOG recordings were made with a Neuroscan 32-channel SynAMP
system with a DC amplifier and sampled at 250–1000 Hz. Eye movement analysis
and quantification was performed on DC recordings of the EOG. Sleep staging
was performed offline using standard criteria of the AASM (American Academy of
Sleep Medicine).
### Lucid dream eye signaling and detection
Participants were instructed to mark the moment of initiation of lucidity as
well as the initiation and completion of the tracking tasks with volitional
LRLR eye movement signals [ 7 ](/articles/s41467-018-05547-0#ref-CR7
"LaBerge, S. P., Nagel, L. E., Dement, W. C. & Zarcone, V. P. Lucid dreaming
verified by volitional communication during REM sleep. Percept. Mot. Skills
52, 727–732 \(1981\).") (referred to as “LRLR”), in which they rapidly moved
their eyes all the way to the left then all the way to the right two times
consecutively. As demonstrated by LaBerge [ 12
](/articles/s41467-018-05547-0#ref-CR12 "LaBerge S. in Sleep and Cognition
\(eds Bootzin R. R., Kihlstrom J. F., Schacter D. L.\) 109–126 \(American
Psychological Association, Washington, 1990\).") these LRLR eye signals are
clearly discernable in the electrooculogram (EOG), and can be used to provide
objective evidence of lucidity as well as precise time-stamping of tasks and
events during lucid REM sleep (for replications and extensions see, e.g.,
refs. [ 9 ](/articles/s41467-018-05547-0#ref-CR9 "LaBerge, S., Nagel, L.,
Taylor, W., Dement, W. & Zarcone, V. Jr Psychophysiological correlates of the
initiation of lucid dreaming. Sleep Res. 10, 149 \(1981\).") , [ 13
](/articles/s41467-018-05547-0#ref-CR13 "LaBerge, S. & Dement, W. C. Voluntary
control of respiration during REM sleep. Sleep Res. 11, 107 \(1982\).") ; for
recent implementations see, e.g., refs. [ 10
](/articles/s41467-018-05547-0#ref-CR10 "Dresler, M. et al. Neural correlates
of dream lucidity obtained from contrasting lucid versus non-lucid REM sleep:
a combined EEG/fMRI case study. Sleep 35, 1017–1020 \(2012\).") , [ 15
](/articles/s41467-018-05547-0#ref-CR15 "Oudiette, D. et al. REM sleep
respiratory behaviors match mental content in narcoleptic lucid dreamers. Sci.
Rep. 8, 2636 \(2018\).") ). The instructions provided to participants were as
follows: “When making an eye movement signal, we would like you to look all
the way to the left then all the way to the right two times consecutively, as
if you are looking at each of your ears. Specifically, we would like you to
look at your left ear, then your right ear, then your left ear, then your
right ear, and then finally back to center. Make the eye movements by only
moving your eyes (without moving your head), and make the full left-right-
left-right motion as one rapid continuous movement without pausing.” The
instruction to look at each ear is critical, as it encourages full-scale eye
movements without corresponding head movements. Detection of lucid dream eye
movement signals was performed with a custom algorithm that used template
matching and detection of successive L–R–L–R patterned saccades. 100% of the
detected signals were subsequently validated by two expert judges (S.L. and
B.B.), with an inter-rater reliability of 100%.
### Tracking tasks
Participants performed either circle tracking or 1D horizontal meridian line
tracking in each of three conditions: (i) lucid REM sleep dreaming
(“dreaming”), (ii) awake with eyes open (“perception”) and (iii) tracking the
imagined movement while awake with eyes closed (“imagination”). Additionally,
one participant completed a fourth condition in which she imagined tracking
the movement in a lucid dream (“imagination in dreaming”). Participants
completed the perception and imagination tracking tasks before the overnight
sleep recording during the same study visit. Participants were instructed to
track the movement using only their eyes (not to move their head), to refrain
from blinking until the completion of the tracking motion, and to make the
movement slowly. They were instructed to spend approximately 1 s tracking each
quarter of the movement. Participants time-stamped the beginning and end of
each tracking trial with LRLR eye movement signals. The instruction for the
circle tracking task was as follows: “Signal with LRLR; extend your dominant
hand at arm’s length with your thumb up, follow the movement of the thumb nail
as it moves clockwise in a circle centered in the visual field; signal with
LRLR; track a circle counterclockwise; and signal with LRLR.” The instruction
for the line task was identical to the circle tracking, with the exception
that the task was to “follow the tip of your thumb as you move your hand to
the far left, then to the far right passing center, and then back to center.”
The tracking instructions were identical for all three conditions (dreaming,
perception and imagination) with the exception that for the imagination
condition the instruction was to “imagine extending your dominant hand” and to
“follow the movement of your imagined thumb”.
### Dream report methods and analysis
Upon awakening, participants were interviewed by the experimenter as to (i)
whether they had a lucid dream (YES/NO) and (ii) whether they completed the
tracking task of visually tracking the thumb of their hand in the dream
(YES/NO). For dreams in which participants reported that they completed the
task, they filled out a dream report form in which they wrote a full report of
the dream. Participants were instructed to describe in detail the narrative of
the dream, including the sequence of events and detailing any thoughts,
feelings or sensations that they experienced, as well as how they knew they
were dreaming (e.g., if it was triggered by a particular event in the dream).
Following standard procedures (i.e., ref. [ 7
](/articles/s41467-018-05547-0#ref-CR7 "LaBerge, S. P., Nagel, L. E., Dement,
W. C. & Zarcone, V. P. Lucid dreaming verified by volitional communication
during REM sleep. Percept. Mot. Skills 52, 727–732 \(1981\).") ), lucid dreams
were validated through the convergence between phenomenological reports of
lucidity and objective eye movement signals in the EOG with concurrent
EEG/polysomnography evidence of REM sleep (see “Procedures and Lucid dream eye
signaling and detection” above for details on the eye signaling methodology).
Reports were also judged for evidence that participants performed the smooth
tracking task in the instructed manner (by tracking visual imagery in their
dream) by two independent judges. In order to meet this criterion, reports had
to include a description of a subjective experience of performing the tracking
task during the dream (i.e., “I traced a circle by following my thumb”; “I put
out my thumb and followed it down to the right counterclockwise”) (example
excerpts of dream reports are provided in Supplementary Note [ 1
](/articles/s41467-018-05547-0#MOESM1) ).
### Eye movement analysis
Raw EOG signals were converted to angular degrees according to pre- and post-
sleep calibrations, baseline corrected and denoised using a 25-pt (100 ms)
median filter, which provides optimal noise reduction of the EOG signal [ 30
](/articles/s41467-018-05547-0#ref-CR30 "Bulling, A., Ward, J. A., Gellersen,
H. & Troster, G. Eye movement analysis for activity recognition using
electrooculography. IEEE Trans. Pattern Anal. Mach. Intell. 33, 741–753
\(2011\).") . Onsets and offsets of tracking trials were manually marked by a
researcher blinded to condition by plotting the HEOG and HEOG vs. VEOG signals
between the offset of the initiation LRLR signal and the onset of the
completion LRLR signal and removing any data points preceding or following the
tracking movement tasks. Automated classification of the EOG during tracking
tasks was performed using Velocity and Movement Pattern Identification (I-VMP)
implemented in Eye Movement Classification for Matlab, a validated algorithm
that classifies saccades, fixations and smooth pursuit eye movements 31 ,
32 , [ 33 ](/articles/s41467-018-05547-0#ref-CR33 "San Agustin J. Off-the-
shelf gaze interaction. PhD dissertation, IT-Universitetet i København
\(2010\).") . The classifier first identifies saccades using a velocity
threshold; signals exceeded this threshold (i.e., 70°/s) that also meet
minimum amplitude and duration criteria are classified as saccades.
Subsequently, movement patterns in the remainder of the EOG signal are
analyzed to classify smooth pursuit movements and fixations. Movement patterns
are analyzed in a temporal window ( _T_ w ) by computing a set of angles of
the eye positional samples in the window. Specifically, lines of best fit to
the data points in the window are computed for each set of eye position points
in the window in increasing order ( _p_ 1 \+ _p_ 2 ; _p_ 1 \+ _p_ 2 \+ _p_
3 ; _p_ 1 \+ _p_ 2 \+ _p_ 3 \+ … _p_ _i_ ) and the angles of dispersion
between each fitted line are calculated. During pursuit eye movements the
dispersion angles tend to follow a linear trend [ 33
](/articles/s41467-018-05547-0#ref-CR33 "San Agustin J. Off-the-shelf gaze
interaction. PhD dissertation, IT-Universitetet i København \(2010\).") . The
magnitude of the movement is then calculated by the sum of angles pointing in
a specific direction. In the implementation used here [ 32
](/articles/s41467-018-05547-0#ref-CR32 "Komogortsev, O. V. & Karpov, A.
Automated classification and scoring of smooth pursuit eye movements in the
presence of fixations and saccades. Behav. Res. Methods 45, 203–215
\(2013\).") , the magnitude of movement is normalized between 0 and 1 and
values are separated with a range threshold _T_ m . Values exceeding _T_ m
are classified as pursuit and values below _T_ m are classified as fixations.
From the segmented EOG, we then computed two scale-free metrics of smooth
tracking behavior: (i) number of saccades per second (NSPS), and (ii) the
pursuit ratio (SP%), which quantified the amount of time in smooth pursuit
divided by the total time spent tracking the movement (SP% = ( _T_ pursuit /
_T_ total ) × 100). Parameter values for the classification algorithm were
selected based on recommended thresholds [ 32
](/articles/s41467-018-05547-0#ref-CR32 "Komogortsev, O. V. & Karpov, A.
Automated classification and scoring of smooth pursuit eye movements in the
presence of fixations and saccades. Behav. Res. Methods 45, 203–215
\(2013\).") . Saccades met three criteria: amplitude ≥4°, velocity ≥70°/s and
duration ≥20 ms. I-VMP classification used a range threshold value of 0.2 and
temporal window size of _T_ w = 0.12 s. Additionally, total circle tracking
time had to exceed a threshold of _T_ t = 2.0 s. Trials with a total duration
less than 2 s (waking: _N_ = 0, dreaming: _N_ = 1, imagination: _N_ = 3) were
discarded prior to analysis based on pre-established criteria to exclude the
possibility that subjects engaged in eye movements other than slow tracking,
as tracking time less than 2 s exceeds the 30°/s velocity threshold for smooth
pursuit eye movements with a circle diameter of approximately 30° used here [
2 ](/articles/s41467-018-05547-0#ref-CR2 "Spering, M. & Montagnini, A. Do we
track what we see? Common versus independent processing for motion perception
and smooth pursuit eye movements: a review. Vision Res. 51, 836–852
\(2011\).") .
### Statistical analysis
Linear mixed models were used in analysis to account for repeated measures
with varied numbers of repeated observations within subjects. The model used
restricted maximum likelihood estimation, and included participant (SUB) as a
random effect, and SESSION, STATE (perception, dreaming, imagination), and
(for the circle tracking task) tracking direction (DIR) (clockwise,
counterclockwise) as fixed effects. Shapiro–Wilk tests indicated that both
NSPS and SP% significantly deviated from a normal distribution (NSPS:
Shapiro–Wilk’s _W_ = 0.77, _P_ _ < _ 10 −10 ; SP%: Shapiro–Wilk’s _W_ =
0.85, _P_ _ < _ 10 −7 ). We therefore used nonparametric bootstrapping for
significance tests. Hypothesis testing of regression coefficients (pairwise
tests) from the mixed models was obtained by the following steps: (i)
constructing a model based on the null hypothesis of no differences between
STATE ( _H_ 0 ); (ii) resampling with replacement the distribution of the
response residuals, reconstructing a bootstrap _y_ response vector by adding
the resampled residuals to _y_ , and refitting the _H_ 1 model to the
bootstrap response vectors to generate 100,000 bootstrap estimates of the
regression coefficients ( _β_ ) under _H_ 0 ; and (iii) comparing the
observed value of the test statistic against the bootstrap distribution under
_H_ 0 (two-tailed frequentist _P_ value). The 95% CIs on regression
coefficients were obtained by computing 1000 bootstrap estimates of the
parameter through resampling the residuals under the _H_ 1 model and
computing the 2.5% and 97.5% values (frequestist CI). Mixed model construction
and mixed model bootstrapping were performed with the lme4 package [ 34
](/articles/s41467-018-05547-0#ref-CR34 "Bates, D, Mächler, M., Bolker, B. &
Walker, S. Fitting linear mixed-effects models using lme4. J. Stat. Softw. 67,
1–48 \(2015\).") in the R environment (R Development Core Team, 2006). Mixed
model fixed effects were assessed by means of a bootstrap likelihood ratio
test on mixed effects models (PBmodcomp in R) specified with maximum
likelihood estimation. ROC analysis was performed using the pROC package in R
[ 35 ](/articles/s41467-018-05547-0#ref-CR35 "Robin, X. et al. pROC: an open-
source package for R and S+ to analyze and compare ROC curves. BMC Bioinforma.
12, 77 \(2011\).") . Differences in AUC were assessed using a two-tailed
bootstrap significance test with 100,000 bootstrap replicates.
### Bayesian classification
Classification of STATE (perception, dreaming, imagination) used a Bayesian
classification procedure developed and validated by Allen et al. [ 36
](/articles/s41467-018-05547-0#ref-CR36 "Allen, J. J., Iacono, W. G. &
Danielson, K. D. The identification of concealed memories using the
event‐related potential and implicit behavioral measures: a methodology for
prediction in the face of individual differences. Psychophysiology 29, 504–522
\(1992\).") . The primary advantages of this classification procedure are that
it captures within-participant variation and that it allows combination of
multiple response indicators to improve classification accuracy. We performed
a two-step split-half classification. We first randomly partitioned the
dataset into two halves. In the first half, we computed the within-participant
_z_ -scores for each indicator (predictor variable), and determined the _z_
-score cut-point across the dataset that maximized sensitivity and specificity
for each indicator. In the second half of the dataset, we then combined the
multiple indicators in a Bayesian fashion to calculate the BPP (i.e., the
probability that a tracking trial was either from perception or REM sleep
dreaming (considered separately) as opposed to imagination given an observed
combination of indicators (i.e., high SP% and low NSPS)). Conceptually, the
probability ratio is equal to the proportion of tracking trials elicited by
perception or dreaming, respectively, that show the combination of indicators
divided by the proportion of all trials showing the combination of indicators
(1.000 = perfect classification).
### Data availability
The data that support the findings of this study are available from the
corresponding author on reasonable request.
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## Acknowledgements
We thank Michael Franklin, Daniel Erlacher and others for assistance in
conducting the research, and especially the lucid dreamers: B.D., E.H., K.G.,
N.L., J.S., D.E., S.W. and others. Financial assistance was from Kenny Felder,
Lucidity Institute, The Fetzer Foundation, The Institute of Noetic Sciences,
The Bial Foundation and the University of Arizona Center for Consciousness
Studies. Thanks also to Dr. Steve Sands, founder of NeuroScan, Inc., for the
donation of the SynAmp 32-channel DC EEG amplifier.
## Author information
Author notes
1. Stephen LaBerge
Present address: Lucidity Institute,
2. These authors contributed equally: Stephen LaBerge, Benjamin Baird.
### Authors and Affiliations
1. Department of Psychology, Stanford University, Stanford, CA, 94305-2130, USA
Stephen LaBerge & Philip G. Zimbardo
2. Wisconsin Institute for Sleep and Consciousness, Department of Psychiatry, University of Wisconsin–Madison, Madison, WI, 53719, USA
Benjamin Baird
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### Contributions
S.L. designed research; B.B. and S.L. analyzed data; B.B. and S.L. wrote the
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### Cite this article
LaBerge, S., Baird, B. & Zimbardo, P.G. Smooth tracking of visual targets
distinguishes lucid REM sleep dreaming and waking perception from imagination.
_Nat Commun_ **9** , 3298 (2018). https://doi.org/10.1038/s41467-018-05547-0
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* Received : 26 January 2017
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* DOI : https://doi.org/10.1038/s41467-018-05547-0
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| biology | 34062 | https://sv.wikipedia.org/wiki/Maple | Maple | Maple är ett datoralgebrasystem, det vill säga ett datorprogram för symbolisk lösning av matematiska problem och tekniska beräkningar, från företaget Maplesoft. Maple utvecklades 1981 vid Symbolic Computation Group - University of Waterloo i Ontario, Kanada. Maple täcker aspekter av teknisk databehandling, inklusive visualisering, dataanalys, matrisberäkning och anslutning. En verktygslåda, MapleSim, lägger till funktionalitet för multidomain fysisk modellering och kodgenerering.
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end proc;
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myfac := n -> product( i, i=1..n );
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int(cos(x/a), x);
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M:= Matrix([[1,2,3], [a,b,c], [x,y,z]]);
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M := Matrix([[400,400,200], [100,100,-400], [1,1,1]], datatype=float[8]):
plot3d(1, x=0..2*Pi, y=0..Pi, axes=none, coords=spherical, viewpoint=[path=M]);
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f := (1+A*t+B*t^2)*exp(c*t);
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eyes_smooth_transition/PMC9602694.txt | Skip to main content
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Int J Environ Res Public Health. 2022 Oct; 19(20): 13101.
Published online 2022 Oct 12. doi: 10.3390/ijerph192013101
PMCID: PMC9602694
PMID: 36293678
Rapid Eye Movement Sleep during Early Life: A Comprehensive Narrative Review
Hai-Lin Chen,1,† Jin-Xian Gao,1,2,† Yu-Nong Chen,1 Jun-Fan Xie,1 Yu-Ping Xie,2 Karen Spruyt,3 Jian-Sheng Lin,4 Yu-Feng Shao,1,4,5,* and Yi-Ping Hou1,5,*
Paul B. Tchounwou, Academic Editor and Marco Fabbri, Academic Editor
Author information Article notes Copyright and License information PMC Disclaimer
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Abstract
The ontogenetic sleep hypothesis suggested that rapid eye movement (REM) sleep is ontogenetically primitive. Namely, REM sleep plays an imperative role in the maturation of the central nervous system. In coincidence with a rapidly developing brain during the early period of life, a remarkably large amount of REM sleep has been identified in numerous behavioral and polysomnographic studies across species. The abundant REM sleep appears to serve to optimize a cerebral state suitable for homeostasis and inherent neuronal activities favorable to brain maturation, ranging from neuronal differentiation, migration, and myelination to synaptic formation and elimination. Progressively more studies in Mammalia have provided the underlying mechanisms involved in some REM sleep-related disorders (e.g., narcolepsy, autism, attention deficit hyperactivity disorder (ADHD)). We summarize the remarkable alterations of polysomnographic, behavioral, and physiological characteristics in humans and Mammalia. Through a comprehensive review, we offer a hybrid of animal and human findings, demonstrating that early-life REM sleep disturbances constitute a common feature of many neurodevelopmental disorders. Our review may assist and promote investigations of the underlying mechanisms, functions, and neurodevelopmental diseases involved in REM sleep during early life.
Keywords: rapid eye movement (REM) sleep, sleep ontogeny, neurodevelopmental disorders, infant, childhood
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1. Introduction
Rapid eye movements (REM) during sleep were first reported in adult humans in 1953 [1]. This sleep state associated with REM was then termed REM sleep by William Dement [2,3,4]. Human REM sleep was subsequently found to be associated with vivid dreaming [4,5], cortical EEG desynchronization, loss of muscle tone [4,6], penile erections, and fluctuation of autonomic systems [6,7,8].
Next, an assessment of the proportions of REM sleep in various age periods demonstrated remarkably similar findings in humans [9,10,11,12,13] and animals [14,15,16,17,18,19,20,21,22,23,24], i.e., a higher percentage of REM sleep in neonates than in adults. In other words, across species, REM sleep during the early development of life (in this paper, we defined early life in humans, rats, and cats as 38 gestational weeks (GW) to 2 years, postnatal day 0 (P0) to P30, and P0 to P45, respectively) is remarkably abundant. More recently, it is thought that REM sleep provides a frequently activated brain state during this critical maturational period. It allows adequate and inherent neuronal activities favorable to brain maturation, ranging from neuronal differentiation, migration, and myelination to synapse formation and elimination [25,26]. It equally plays a critical role in the plasticity of the developing brain [26,27,28]. Blumberg et al. concluded that more myoclonic twitches of skeletal muscles occurring during early life REM sleep trigger sensory feedback and therefore contribute to the establishment of the sensorimotor system [27,29,30]. The ontogenetic sleep hypothesis pointed out that the dramatic decline in REM sleep amounts across development manifests that REM sleep ontogenesis is a remarkably conserved feature of mammalian sleep [28], which suggested that REM sleep is ontogenetically primitive.
This review focuses on the characteristics of REM sleep in early life, some REM sleep-related disorders in humans, and their underlying mechanisms as examined in animals. We aim to bring REM sleep back into the spotlight, and particularly to foster the potential of translational research through our cross-species approach.
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2. REM Sleep in Early Development of Humans
2.1. REM Sleep Amount across Early Development
Between 28 and 30 weeks of gestation, most a fetus’s time is spent in REM sleep, with little signs of an NREM sleep state [13,31,32]. Thus, along with the gestational age, REM sleep is progressively reduced from 80% at 30 weeks to 67% between 33 and 35 weeks, and further to 58% between 36 and 38 weeks.
REM sleep and NREM sleep in newborn infants are also known respectively as active sleep (AS) and quiet sleep (QS) [11,33,34,35,36,37,38]. Indeterminate sleep, namely when the exact sleep state cannot be distinguished, is also observed during the early phase of life [11,33,34].
Full-term newborns spend one-third of their day and one-half of their sleep in REM sleep [9,10,11,12,38]. Preterm infants have less sleep but more frequent REM episodes. Later, the percentage in REM sleep over total sleep time (TST) progressively declines with age and reaches a roughly stable proportion of 20% in REM sleep and 80% in NREM sleep at about the age of three years to remain approximately constant throughout childhood, adolescence, and early adulthood [9,11,12,39,40], whereas in late adulthood, it does decline slightly [41].
2.2. Polysomnographic, Behavioral and Physiological Characteristics of REM Sleep in Early Development
2.2.1. Polysomnographic Features
In humans, sleep and electroencephalographic (EEG) patterns of REM and NREM sleep can be difficult to decipher before 30 weeks of gestation. They become constant by 36 to 38 weeks of gestation [13,31,34,37,42]. Yet their classification remains complex, and their EEG remains atypical during this period of two weeks given the precocious developmental stage [13,34,35].
The sleep states in full-term newborns are discerned by EEG, electro-oculograms (EOG), and electromyograms (EMG). EEG during periods of REM sleep is a low-voltage, relatively fast activity, sometimes appearing a little slower than the waking EEG. Meanwhile, EOG invariably appears as single or clustered high-amplitude bursting waves of rapid eye movements. On EMG, notably, phasic muscular contractions in the background of the absence of resting muscle activity during REM sleep are numerously traced. EEG during NREM sleep, in contrast, is characterized by high-voltage slow waves without eye movement tracings and phasic muscular contractions [12,35,43,44].
Another characteristic EEG pattern observed in newborn infants is that unlike the normal adult pattern in which NREM sleep precedes always REM sleep, REM sleep directly succeeds waking episodes at sleep onset [12,45,46], similar to the occurrence of sleep-onset REM sleep (SOREMS) in narcoleptic patients [47,48]. With increasing age, the EEG patterns during REM sleep show a progressive increase in frequency and amplitude. The average duration of these patterns decreases from around 25 and 30 min at 2 and 4 weeks of age to about 16 min at 16–24 weeks [49].
The mature stage 2 of NREM sleep with EEG spindles emerges between 6 and 9 weeks, and slow delta waves mixed with theta frequencies appear at approximately 12 weeks of age [11,50,51]. K-complex begins to have a drastic increase in the percentage of stage 2 of NREM sleep over TST by the end of 6 months.
Stage 3 of NREM sleep tends to occur during the nocturnal hours and peaks in the early period of the night at 4–6 months of age [50]. The percentage of sleep periods beginning with REM sleep declines with age, and REM/NREM cycles lengthen. Infants at 3 weeks of age have 60% REM sleep onset, however, those whose sleep at 6 months begins with REM sleep are reduced to 20% [46].
2.2.2. Behavioral and Physiological Features
Other conspicuous behavioral features in early human life associated with the EEG pattern of REM sleep are eye movements, local muscle contractions, facial appearances, and body movements [12,13,34,35,38,52,53], which is why this state is also called active sleep [35,38,53].
Eye movements are very rare before the 28th gestational week, and their number remains lower in preterm than in full-term newborns [35,54]. However, rapid eye movements in the form of clusters start to increase after birth, reaching a plateau at about 4 months [55].
Fetuses between 38 and 40 weeks of gestational age show a large number of spontaneous body movements during REM sleep, though fewer than those among newborns [53]. REM sleep atonia becomes obvious after the 40th gestational week [56]. During REM sleep, term newborns frequently display, in addition to rapid eye movement bursts; grimaces; small weak cries; smiles; twitches of the face and extremities; and brief athetoid writhing of the torso, limbs, and digits. Some facial mimicries may resemble the appearance of sophisticated expressions of emotion or thought such as perplexity, disdain, skepticism, and mild amusement are observed, but fascinatingly, such nuance of expression is not seen when the same newborns are awake [12,13]. Smiles during REM sleep in newborns are highly frequent [9,57,58,59,60] and are considered to be endogenous and therefore not related to social experience [60]. They are therefore termed spontaneous smiles. Spontaneous smiles, as signs of immaturity, generally diminish and disappear at 2–3 months to be replaced by social smiles [61,62,63,64]. In some rare cases, however, spontaneous smiles can be observed even in 1-year-olds [65]. Nevertheless, smiling configuration during REM sleep often results in smiles with a closed mouth, whereas the smiles during wakefulness can be associated with an open mouth [52], indicating an inevitable social interactive impact.
Irregular breathing is always recorded in premature infants, while regular respiration, which characterizes NREM sleep in full-term newborns, is less recorded. Apnea is frequently observed during sleep in preterm and term infants [13,66]. Periodic breathing is abundant until 38 weeks of gestational age and then disappears in full-term infants. Contrary to the chest fluctuations during REM sleep, respiration during NREM sleep is regular. Respiratory patterns between REM and NREM sleep in full-term newborns are different. Remarkably, very irregular breathing constantly displays variation and is usually but not exclusively associated with rapid eye movements. During REM sleep, the respiratory rate is 18% greater than that during NREM sleep.
In full-term newborns, the mean frequency of the regular heart rate is 115–120 beats/min [67]. The heart rate is very rapid in prematures. The heart rate between REM and NREM sleep is as different as the disparity in respiratory rates; mean heart rate is 3.4% higher during REM sleep [12].
A cohort study of respiratory and heart rates during REM and NREM sleep across the first year of life shows that in infants from 1 month to >9 months of age, the mean respiratory rate during REM sleep decreases from 35.8 to 22.3 breath/min, whereas during NREM sleep, it reduces from 37.9 to 22.6 breath/min. The mean heart rate during REM sleep decreases from 134.7 to 110.8 beats/min, whereas during NREM sleep, it reduces from 132.1 to 107.8 beats/min [68].
2.3. REM Sleep Timing in Developmental Sleep-Wake Cycle
The emergent timing of sleep-wake cyclicity remains controversial until now. Different results are obtained according to different methodological approaches used [35,37]. By measuring rapid eye movements and EEG discontinuity, the sleep state cycle with a mean duration of 68 min is observed in a majority of neonates who are about 30 weeks of postconceptional age (PCA) [69]. The sleep cycle assessed by a motility monitoring system is found at 36 weeks of PCA, and the cycle length is approximately 60 min [34,70]. These data suggest that the ultradian biologic rhythm begins to be established in the early perinatal stage of brain development.
When the sleep–wake profile in full-term newborns is recorded using polysomnography for 4 h, Roffwarg et al. found that REM sleep appears soon after sleep begins, and the 1st sleep cycle has a shorter average duration than later cycles. The initial period of REM sleep is proportionately briefer than ensuing REM sleep periods, even though the lengths of sleep cycles are considered. The amount of REM sleep in the 1st cycle is approximately 1/2 of that in subsequent individual cycles. The mean duration of REM sleep prolongs almost threefold in the second cycle and tends to diminish slightly in the third cycle. Generally, the second and third cycles are split almost evenly between the REM and NREM sleep phases. The REM sleep percentage is fairly constant from the second cycle on. Thus, the mean duration of sleep cycles and mean length of REM sleep in newborns are respectively 52.9 and 25.4 min [12].
During the neonatal period, sleep onsets mostly begin with REM sleep, and the REM sleep episodes and those of NREM sleep alternate with a period of 50 to 60 min [12,71,72,73]. Within the first few weeks of life, though wakefulness involves a smaller proportion of time, and REM sleep involves a larger amount than in any other period of life, the total amount and percentage of REM sleep are diminished with increasing protracted intervals of wakefulness, particularly when locomotive capacity is attained [12,34].
The predictable appearance in the evening (around 20:00 h) of a long period of sleep, highly organized into REM-NREM sleep stages, occurs first in infants of 3 months of age [46]. Meanwhile, the appearance of NREM sleep at sleep onset and cyclic alternating patterns are sometimes observed [11,51]. Furthermore, NREM sleep is largely increased at night [50,73,74,75]. The circadian swing to the day–night cycle thus results from the consolidation of sleep-wake states and their finer coordination.
Between 4 1/2 and 6 months of age, REM sleep at sleep onset is brief and frequently interrupted by other stages or wakefulness. The amount of REM sleep decreases with age: as an infant matures, she shows less daytime REM sleep and sleep-onset REM sleep [46]. Additionally, the length of sleep cycles across the first year of age increases with age because of the proportional increase of NREM sleep [76]. Spindles and K complexes are fully formed by the ages of 3 and 6 months, respectively [39].
The initial REM period in children appears much later and is shorter than that in children who nap. Meanwhile, deep slow wave sleep extends and occupies the first hours. When children progressively approximate the diurnal pattern of uninterrupted daytime wakefulness, the 1st REM sleep period of the night usually appears 50 to 70 min after falling asleep, and REM sleep periods become longer towards the morning hours [12]. By 5 years old, daytime napping ceases and overnight sleep duration gradually declines throughout childhood, due to a shift to later bedtimes, with wake times remaining stable during the routine week [77]. After the age of 10, the sleep cycle lasts about 90–110 min as in an adult [39].
Collectively, the ontogenetic development of REM sleep in humans is summarized in Table 1, showing the developmental changes in amount, polysomnographic, behavioral, and physiological characteristics, and timing in the sleep-wake cycle of REM sleep from immature to mature.
Table 1
Developmental changes of amount, polysomnographic, behavioral, and physiological characteristics, and timing in the sleep-wake cycle of REM sleep across early development of humans.
Parameters REM Sleep References
Amount Preterm 80% of TST at 30 GW, 67% between 33 and 35 GW, 58% between 36 and 38 GW. [13,31,32]
Full-term 50% of TST in full-term newborns. [9,10,11,12,38]
Postnatal Progressive reduction with age, reaching 20% of TST at about three years of age and remaining constant throughout childhood, adolescence, and adulthood. [9,11,12,39,40]
EEG Preterm Inconstant EEG of REM sleep is surveyed <30 GW, a constant pattern is observed during 36–38 GW. EEG remains atypical. [13,31,34,37,42]
Full-term Easy identification with low-voltage, relatively fast activities, frequent occurrence of REM sleep directly succeeds waking episodes at sleep onset. [12,35,43,44]
Postnatal EEG patterns progressively increase in frequency and amplitude. The occurrence of sleep beginning with REM sleep declines with age, from 60% at 3 weeks to 20% at 6 months. [49]
Rapid eye movements (REMS) Preterm Eye movements are very rare <28 GW. number of REMS remains lower. [35,54]
Full-term More REMS, EOG invariably appears as single or clustered high-amplitude bursting waves. [43,44]
Postnatal REMS starts to increase after birth, reaching a plateau at about 4 months. [55]
Spontaneous body movements Preterm A large number between 38 and 40 GW, but the amount is lesser than that in full-term newborns. [53]
Full-term Atonia becomes obvious. Grimaces, small weak cries, smiles, and twitches of the face and extremities are frequently observed.
EMG shows phasic muscular contractions in the background of the absence of resting muscle activity. [12,13]
Postnatal Spontaneous smiles generally diminish and disappear at 2–3 months and are replaced by social smiles.
Spontaneous body movements decline with age. [62,64]
Breathing Preterm Irregular, frequent apnea, periodic breathing <38 GW. [13,66]
Full-term The respiratory rate during REM sleep is 18% greater than that during NREM sleep. Frequent apnea. [12]
Postnatal For infants from 1 month to >9 months of age, the mean respiratory rate during REM sleep decreases from 35.8 to 22.3 breath/min [68]
Heart rate Preterm Irregular, 130 beats/min at 37 GW. [13,35]
Full-term 115–120 beats/min, the mean heart rate is 3.4% higher during REM sleep than during NREM sleep. [12,67]
Postnatal For infants from 1 month to >9 months of age, REM sleep decreases from 134.7 to 110.8 beats/min [68]
Sleep-wake cycle Preterm Approximately 60 min. [34,69]
Full-term The mean duration of sleep cycles and mean length of REM sleep in newborns are respectively 52.9 and 25.4 min.
The amount of REM sleep in the 1st cycle is approximately 1/2 of that in subsequent individual cycles.
The mean duration of REM sleep prolongs almost threefold in the 2nd cycle and tends to diminish slightly in the 3rd cycle. [12]
Postnatal Length of sleep cycles across the first year of age is progressively increasing with age.
REM sleep periods become longer towards the morning hours. After the age of 10, the sleep cycle lasts about 90–110 min as in an adult. [12,39,76]
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3. Neurodevelopmental Disorders Associated with REM Sleep Disturbances during Early Development of Humans
3.1. Sudden Unexpected Infant Death (SUID), Sudden Infant Death Syndrome (SIDS)
Every year in the USA, approximately 3500 infants die suddenly and unexpectedly [78]. The sudden death of a baby less than 1 year old that is unexpected, unexplained, and with undetermined causes is labeled SUID [78]. The terminology reflecting the unexplained sudden death of an infant has been under discussion [78]. Namely, SIDS was first defined in 1969, and as a consequence, the majority of papers apply this terminology. SIDS victims are thought to succumb during sleep, commonly exhibit symptoms of asphyxia, and show signs of having been subjected to chronic hypoxia [79]. The majority of SUIDs, particularly in the SIDS literature, suggests that sudden death occurs mainly during a narrow developmental window of postnatal 1–6 months. This is a period when significant changes occur in sleep organization and in the maturation of the brainstem and cortical centers involved in cardiovascular, respiratory, and arousal state control [80,81,82]. In normal infants, irregular breathing and periods of apnea commonly appear during REM sleep [12]. Regular breathing occurs during periodic appearances of REM and NREM sleep episodes, intermixed with waking, following each other in succession throughout the sleep period.
Newborns at risk for SIDS have longer intervals between REM sleep epochs during the sleep cycle and a decreased tendency for short waking periods at 2 and 3 months of age [36]. It is known that the number of arousals during sleep in normal infants at 2–3 months old is greater than that in children at a mean age of 4.6 years. Spontaneous arousals occurred every 3–6 min in infants compared with 6–10 min in children [82,83]. These data indicate that the periodicity of sleep states in SIDS victims is disturbed and then results in a failure to arouse from sleep during a critical transient event, such as apnea, that might subsequently lead to death. Moreover, infants at risk for SIDS have an increased nighttime REM sleep that coincides with an early morning time period when most SIDS deaths occur, suggesting a link between disordered REM sleep and SIDS [84]. Therefore, the link between the peak occurrence of SIDS and the period of major sleep developmental changes suggests that SIDS might be state-related and could involve abnormal interactions between the state-modulated arousal threshold and central regulatory mechanisms of cardiovascular and respiratory control. Indeed, several hypothetical models exist, such as the triple risk [85], the quadruple risk, and the allostatic load model [86,87], with each highlighting a critical period. More recently, butyrylcholinesterase [88], an enzyme of the cholinergic system potentially providing a measure of autonomic (dys)function, has been suggested as a SIDS biomarker.
3.2. Narcolepsy
Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness, cataplexy (sudden loss of muscle tone during waking), and loss of boundaries between sleep and wake, with frequent state transitions and intrusions of REM sleep into the other ongoing states [47,48,89,90]. It is estimated that the prevalence of narcolepsy ranges from 0.2 to 600 per 100,000 people in various countries [91]. Narcolepsy is due to a deficiency of hypothalamic hypocretin/orexin [92,93] likely following an autoimmune etiology [94]. More than 50% of the disease onsets occur in childhood before puberty [95], and the disease is often misdiagnosed with other neurological or psychiatric disorders such as epilepsy and attention deficit hyperactivity disorder (ADHD) [39]. Thus, the diagnosis is often delayed to a few years after the symptom onset [95]. In the International Classification of Sleep Disorders (ICSD) 3rd Edition, narcolepsy with and without cataplexy are divided into narcolepsy type 1 and narcolepsy type 2, respectively.
Cataplexy is often triggered by positive emotions, especially laughing. In addition, a recent cohort study found that during REM sleep, children with narcolepsy type 1 have more severe motor instability that emerges also from wakefulness (status cataplecticus). This motor instability occurring during REM sleep significantly affects subjective complaints of impaired nocturnal sleep and excessive daytime sleepiness [47]. Fortunately, although impaired by their sleep disorder, most children with narcolepsy develop quite normally, most likely by escaping the most critical period of brain development, i.e., before 2 years old. Indeed, narcolepsy occurs extremely rarely before age of 5 years.
3.3. Developmental Disabilities
The evolution of sleep architecture and sleep-wake organization in infants coupled with the development of systems critical to language, attention, and executive functions suggest that deficient REM sleep and disorders of sleep continuity could have a significant impact on infants and children by potentially altering the developmental trajectory of the brain [96]. Infants who suffer sleep fragmentation during the first year of life perform worse on executive functional tasks, have much more risk of poor language learning, and display less efficient attention processing in their later lives [97,98,99]. This suggests that early sleep fragmentation results in long-term consequences and that sleep potentially serves as a critical window for developmental disabilities.
A paucity of studies correlates REM sleep in developmental disabilities with degree of mental retardation. For example, the presence of autistic spectrum disorders (ASD) or Down syndrome is associated with fewer and briefer episodes of REM sleep [100]. Children with ASD show lower EEG beta activity during REM sleep over cortical visual areas compared with healthy controls [101]. This suggests that many of the cognitive profiles encountered in developmental disabilities could be a function of REM sleep deficits related to genetic anomalies or involvement of the ontogenetical brain regions susceptible to pathophysiological processes alike ASD.
Premature infants are at a higher risk for the development of cognitive delays and disabilities [102]. REM sleep with rapid eye movements is considered to reflect a more organized and mature CNS functioning as compared to REM sleep without them [103,104]. Premature neonates with more rapid eye movements during REM sleep have a better cognitive outcome at 6 months than those with less rapid eye movements [54].
Among infants with developmental disabilities of unknown etiology, higher REM sleep proportions of the TST are related to better motor, exploratory, social, eating, and intellectual outcomes [105], whereas less REM sleep has been found in mentally retarded subjects compared with typically developing controls [106]. More REM sleep without rapid eye movements characterizes infants with developmental delays and is found, for instance, among infants with intrauterine growth retardation [107]. Thus, REM sleep amount and the number of rapid eye movements during this sleep state might serve as a predictor of cognitive development above and beyond birth status and medical risk.
ADHD is a common neurodevelopmental disorder, affecting around 63 million children worldwide [108]. Sleep problems have been found in around 55% of children diagnosed with ADHD [109] and are associated with poorer cognitive and behavioral outcomes [110]. The core symptoms of ADHD are inattention, impulsivity, and general hyperactivity [111], which is associated with neurocognitive deficits [112]. Although numerous hypothetical models of ADHD exist, initially and based on behavioral observations, it is considered a disorder due to delayed structural brain maturation [113]. Compared with controls, one out of seven studies demonstrated lower REM sleep duration [114], whereas six observed a higher proportion [115,116,117,118]. Studies on sleep architecture and efficiency found that children with ADHD display shorter REM sleep latency in polysomnographic recording than typically developing children and have more subjectively reported sleep problems and daytime sleepiness levels [119]. When ADHD coexists with a tic disorder, the children with this comorbidity show not only shorter REM sleep latency but also an increased duration of REM sleep compared with healthy controls. Moreover, microarousals in light and REM sleep and short motor-related arousal occur during the sleep period in children with ADHD and comorbid children with ADHD and tic disorder [120]. Collectively, this may suggest that the pathophysiological mechanisms of ADHD could be closely related to REM sleep.
3.4. REM Sleep Behavior Disorder (RBD)
RBD is characterized by the resurgence of fetal and early postnatal motor activity patterns that closely resemble the early REM sleep of life. Several lines of evidence from basic research and documented clinical and video-polysomnographic findings in humans indicate that dysregulation of the developing sleep neuromotor system can be expected to have adverse long-term effects. For instance, behavioral and dream disturbances emerge during sleep as RBD later in the life of humans, dogs, and cats [121,122,123]. Neuromotor system dysfunction during REM sleep in the early development of life may thus have played an instrumental role in generating the long RBD prodrome leading up to the eventual emergence of clinical RBD [124].
Clinical characteristics of RBD are abnormal behaviors (i.e., sleep-related vocalizations or complex motor behaviors such as dream enactment, without the typical REM atonia) and EMG abnormalities during REM sleep are noted yet the literature on childhood is scant [125]. This parasomnia warrants in childhood a differential diagnosis with narcolepsy type 1 [126] and amongst other brainstem tumors. Approximately 0.5 to 1.25 percent in the general population may suffer from RBD [127].
Taken together, the key features of disordered REM sleep during early development presented in the neurodevelopmental disorders mentioned above are summarized and emphasized in Table 2.
Table 2
Disordered REM sleep features during early development related to neurodevelopmental disorders in humans.
Diseases Onset Period Disordered REM Sleep References
SUID/SIDS Infant (1–6 months) Longer intervals between REM sleep epochs during the sleep cycle and a decreased tendency for short waking periods.
Failure to arouse from sleep during a critical transient event, such as apnea.
An increased nighttime REM sleep coincides with an early morning time period. [36,84]
Narcolepsy Childhood Intrusions of REM sleep into the other ongoing states.
Narcolepsy Type 1 has more severe motor instability during REM sleep. [47,48,90]
ASD Childhood Fewer and briefer episodes of REM sleep.
Lower EEG beta activity during REM sleep over cortical visual areas. [100,101]
Prematurity Infant REM sleep with less or without REMS.
Less REM sleep. [54,106]
ADHD Childhood Shorter REM sleep latency and more daytime sleepiness.
ADHD coexists with tic disorder showing not only shorter REM sleep latency but also an increased duration of REM sleep.
Microarousals and short motor-related arousal during REM sleep. [119,120]
RBD Adulthood Neuromotor system dysfunction during REM sleep in early development. [124]
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4. REM Sleep in Early Development of Mammalia
The early sleep pattern of most animal models follows a similar evolution to that of humans in that they also have abundant REM sleep in early life, although postnatal differences can be noticed. The ontogenetic development of polysomnographic, behavioral, and physiological characteristics of REM sleep in many mammals displays similar features to those in humans [128,129]. Furthermore, the maturational stage of sleep patterns in neonatal animals appears to be well correlated with their central nervous system (CNS) maturity [28,130]. On the one hand, animals born with an immature CNS, such as the cat, rat, mouse, and rabbit, undergo considerable postnatal development of their sleep–wake patterns before an adulthood pattern is established. On the other hand, animals born with more advanced CNS maturation, such as the chimpanzee, monkey, and sheep, show sleep–wake patterns qualitatively and quantitatively similar to those of their adulthood. In animals born immature and during their early developmental phase, some authors suggested that sleep starts actually in a disorganized manner because of the indistinct cortical EEG activities [131,132]. Based on the muscle activity and behavioral criteria, AS and QS, i.e., early forms of REM and NREM sleep are also documented in altricial animals [80,130,133,134].
Table 3 summarizes the changes in the amount of REM sleep during early development in animal models. The data in Mammalia born immature clearly show a negative correlation between REM sleep amount along with the levels of postnatal development. Compared with mammals born immature, mammals born mature clearly show a lesser amount of REM sleep indicating that early brain development requires a greater amount of REM sleep. The function of REM sleep during early life would be to promote brain development which is in consistence with the ontogenesis hypothesis of REM sleep.
Table 3
Changes in amount of REM sleep during early development in animals.
Animals REM Sleep References
Animals born with advanced maturation Chimpanzee 22.4% of TST < 1 year, 16.0% between 1 and 2 years, and 13.1% above 2 years old. [135]
Rhesus monkey 31% of TST at birth, a brief increase to 43% at day 7, then, gradually decreases to 35% at day 30, to 27% between 9 and 13 months, and 19% (15% to 23%) at 2 years old. [136,137,138,139,140]
Sheep 60% of TST at 120 days of gestation, 45% at birth, 18% at day 7, and 14.71% at day 15. [23,141]
Animals born with immaturity Kitten In its first days, 50% in REM sleep (100% of TST) and 50% in wakefulness.
50% of total recording time (TRT) on day 7, and 20% on day 35. [18,142,143,144,145,146,147]
Rat 72% of TRT in the first week, 58% at day 11, 8% at day 30. [16,18]
Mouse 40% of TRT in the first week, 6% at day 19. [148]
Rabbit 75% of TST at birth, 33% on day 14, and 10% on day 23. [149]
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Regulatory Mechanisms of Early REM Sleep Development
In humans, mice, rats and cats, REM sleep has generally been regarded as the most archaic state and is mediated by neural networks mainly located in the brainstem [73,80,150,151,152]. That is, the first cerebral structure to mature and the primary one to ensure basic cerebral and behavioral function from early life [153]. More recently, the REM sleep regulatory concept has been evaluated and several hypothalamic and forebrain networks including newly identified neuropeptides such as orexin and melanin-concentrating hormone (MCH) have been involved, both in the control and final expression of this behavioral state [6,27,154,155,156,157,158,159,160]. One of the most obvious correlations has been that when the human or animal brain at birth is less mature, the greater time spent in REM sleep in early postnatal life, such as REM sleep directly succeeding waking at sleep onset, is often observed in newborn humans [12,46,73] and mammals [16,18,20,22,23,138,152,161,162,163].
Concerning the brainstem mechanisms, several studies on rats suggest that cholinergic neurons of the laterodorsal (LDT) and pedunculopontine tegmentum (PPT) send projections to and activate glutamatergic neurons, with the pontine reticular formation to initiate and maintain REM sleep. However, serotonergic (5-HT) neurons within the dorsal raphe nuclei and noradrenergic neurons within the locus coeruleus project to the LDT and PPT to inhibit REM sleep [157]. Furthermore, several pontine and medullary areas that mediate muscle atonia and twitches during REM sleep in adults are also involved in the generation of these REM sleep components in the early development of life [30,164,165,166,167]. Brain neural structures responsible for REM sleep are therefore functional as early as pre- and postnatal stages and the appearance of adult-like NREM sleep requires cortical maturation.
The cerebral cortex of a newborn cat has a higher level of maturity than the newborn rat’s [168], which may explain why polysomnographic recording in the kitten immediately after birth shows an EEG activity that is not present in the newborn rat such as NREM sleep signs [18,169]. Rat cortical neurons between the birthday (P0) and P10 show explosive growth, cortical oscillations are only weakly modulated by behavioral states, and EEG activity is discontinuous. At around P11-P12, a pivotal cortical maturity transition occurs [130,170,171], coinciding at which NREM sleep appears [130].
Moreover, the effects of the numerous transmitter systems on the membrane potential of the neurons in the pedunculopontine nucleus in rats during the developmental decrease in REM sleep change, including increased 5-HT1 inhibition [172], decreased NMDA excitation [173], increased kainic acid activation [173], decreased noradrenergic inhibition [174], and increased cholinergic [175] and GABAergic inhibition [176]. These data suggest a reorganization of REM sleep-controlling neurons within the mesopontine tegmentum, such that the neuromodulation of REM sleep undergoes drastic changes from birth to the end of human puberty [177], i.e., from an early to mature modality.
During REM sleep, brainstem circuits actively suppress motor neurons in the spinal cord to keep skeletal muscle atonia [6,154,155,157,178]. Conversely, a marked amount of twitching and gross body movement is observed during REM sleep but not during NREM sleep during the early development of humans [12,13,34,35,38,52,53] and Mammalia [16,18,20,29,30,163,179,180]. This distinguished pattern of REM sleep in early life suggests that the inhibiting mechanisms of spinal cord motor neurons wired with the brainstem circuits are immature. On the other hand, strong motor excitation has to conquer tonic and phasic motor activity suppression, leading to muscle twitches during REM sleep in early life [11,181]. The origin of the excitatory drives to generate twitches during REM sleep is located in the brainstem of mice, rats, and cats [182,183,184], whereas the supraspinal drives that mediate motor suppression during REM sleep have their origin in the brainstem inhibitory centers of mice and rats [6,154,155,157]. Thus, excitatory and inhibitory brainstem outputs determine the occurrence of muscle twitches and gross body movements during REM sleep.
Collectively, the brainstem REM sleep circuits mature while increasingly interacting mutually/bidirectionally with those in the hypothalamic and forebrain across early development to coalesce REM sleep components, and consolidate REM sleep episodes, express sleep-wake ultradian and circadian rhythmicity.
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5. Underlying Mechanisms Involved in Neurodevelopmental Disorders Associated with Early REM Sleep Disturbances in Mammalian Models
5.1. CNS Development
The primary function of REM sleep is proposed to be inducing the CNS development in the fetus as well as the neonates of humans, rats, cats, and guinea pigs [12,18,152] and constituting the major CNS stimulator in a period when waking life is limited in time and scope with the little occasion for stimulation in cats [142,185,186]. The functional stimulation commences in fetal life and may result not only from actual sensory stimulation but perhaps also from the REM sleep process, which starts to operate at some points in fetal development. The ascending impulses originating in the brainstem during REM sleep may be required in promoting neuronal differentiation, maturation, and myelination in higher brain centers as well as the maturation of the cardiorespiratory regulating center within the brainstem. Thus, the abundance of REM sleep in early life and its ensuing decline to lower levels in adulthood strongly suggest that REM sleep is an integral part of the activity-dependent processes that enable normal physiological and structural brain development in humans, rats, and cats [28,30,130,177,187]. Conversely, the early developmental deficiency of REM sleep and the neurons or neurotransmitters involved in brainstem circuits will cause neurodevelopmental disorders.
Increasing numbers of studies in animal models have provided the underlying mechanisms involved in some REM sleep-related disorders (Table 4). For example, REM sleep in postnatal rats is dramatically reduced throughout 2 weeks, and REM sleep-deprived rats in adulthood have reduced brain size, hyperactivity, anxiety, attention, and learning difficulties [28,82]. The ADHD-like behaviors and symptoms induced by REM sleep deprivation may be linked to decreased alpha2A-adrenoceptor signaling, particularly in the hippocampus [188]. When REM sleep deprivation in infant rats is carried out from P16 to P19 for 4 h per day, it reduces the stability of hippocampal neuronal circuits, possibly by hindering the expression of mature glutamatergic synaptic components that are involved in several neural processes such as brain maturation and memory consolidation [189], whereas an increase in REM sleep amounts induced by exposure to an enriched environment in the juvenile rat results in a significant increase in the adult brain weight, particularly the cerebral cortex and hypothalamus [190]. Similarly, REM sleep enhancement has also been reported in infant animals following learning tasks [191], suggesting that during the developmental period, the increased amount of REM sleep after a learning experience promotes brain growth.
5.2. Social Behaviors
REM sleep abnormalities in early life are prevalent in ASD. REM sleep reduction in early life causes long-lasting compensatory changes in GABAergic parvalbumin in the primary somatosensory cortex, impairments of pair bond formation, and alteration in object preference in adult prairie voles [192], suggesting that early life REM sleep is crucial for tuning inhibitory neural circuits and development of species-typical affiliative social behaviors. While sleep in male mice was deprived for 3 h per day from P5 to P52, these sleep-deprived mice displayed autistic-like behaviors including long-lasting hypoactivity and impaired social behavior in adolescence. These behavior changes were accompanied by an increase in the downstream signaling products of the mammalian target of the rapamycin pathway [193]. These shreds of evidence indicate that sleep deprivation can play a causative role in the development of behavioral abnormalities.
In addition, REM sleep deprivation in neonatal rats also induces depression-like behaviors in their adulthood, such as reduction of male sexual behaviors, pleasure-seeking, shock-induced aggression, REM sleep latency, and the enhancement of defensive responses, motor restlessness associated with the fear or stress, amount of REM sleep, voluntary alcohol consumption and despair behavior [194,195,196,197,198,199]. Thus, REM sleep appears to be closely related to emotional and mental development in early life.
5.3. SUID/SIDS
Several recent studies of animal models for underlying mechanisms involved in SUID/SIDS have found that neonatal Lmx1bf/f/p mice selectively lacked 5-HT neurons, displayed frequent and severe apnea, and had high mortality during early development. Excess mortality at the time of breathing abnormalities was the most severe [200]. While rat pups were deficient in central 5-HT, they were profoundly more apneic in REM sleep but not NREM sleep, and their arousal in hypoxia was delayed in REM sleep compared with NREM sleep [201]. Furthermore, in perinatal nicotine-exposed 5-HT-deficient rat pups, impaired autoresuscitation along with significantly delayed post-anoxic recovery of normal breathing and heart rate was observed at P10 [202]. These shreds of evidence indicate that the CNS 5-HT plays an important role in REM sleep and cardiorespiratory control, that infants who are deficient in central 5-HT may be at increased risk for SIDS in REM sleep because of increased apnea and delayed arousal, and that cigarette smoking during pregnancy increases the risk of SIDS also.
5.4. Narcolepsy
Narcolepsy, a neurodevelopmental disorder characterized primarily by REM sleep dysregulation, the animal model of prepro-orexin gene knockout mice exhibited a phenotype strikingly similar to human narcolepsy patients including hypersomnolence during their active dark phase, fragmented waking periods, SOREMS, [203] and cataplexy episodes [204]. In addition, orexin/ataxin-3 mice [205] and rats [206] were born with orexins but loose orexin-containing neurons later in life. Accordingly, the onset of narcoleptic attacks in orexin/ataxin-3 mice was later than in prepro-orexin knockout mice, which showed behavioral arrests, premature entry into REM sleep, poorly consolidated sleep patterns, and late-onset obesity [205]. The orexin/ataxin-3 rats exhibited postnatal loss of orexinergic neurons that resulted in the expression of a phenotype with fragmented vigilance states, a decreased latency to REM sleep, and increased REM sleep time during the dark active phase. SOREMS, a defining characteristic of narcolepsy, and cataplexy occurred frequently in these orexin/ataxin-3 transgenic rats [206]. These results provide evidence that orexin-containing neurons play important roles in regulating vigilance states and energy homeostasis.
Table 4
Animal models for underlying mechanisms involved in the neurodevelopmental disorders associated with REM sleep disturbances.
Animal Models Phenotypes Underlying Mechanisms Ref.
SIDS c Frequent and severe apnea, high mortality during development. Selectively lack of 5-HT neurons induces abnormality of cardiorespiratory control. [200]
TPH2-/- rat pups Increased apnea only in REM sleep. Arousal responses in hypoxia condition were selectively delayed in REM sleep. Deficient in central 5-HT leads to a loss of inhibitory effect on LDT/PPT activation, and a failure in breathing. [201]
Perinatal nicotine-exposed 5-HT deficient rat pups Autoresuscitation failure in response to hypoxia. 5-HT deficiency and perinatal nicotine exposure increase the vulnerability to environmental stressors and exacerbate defects in cardiorespiratory protective reflexes to repetitive anoxia during the development period. [202]
Narcolepsy Prepro-orexin gene KO mice Hypersomnolence during the active phase, fragmented wakefulness, SOREMS, cataplexy. Orexin deficiency fails to regulate the physiologic sleep-wake cycle. [203,204]
Orexin/ataxin-3 mice Behavioral arrests, premature entry into REM sleep, poorly consolidated sleep patterns and obesity. Postnatal loss of orexin fails to regulate vigilance states and energy homeostasis. [205]
Orexin/ataxin-3 rats Fragmented vigilance states, decreased latency to REM sleep, and increased REM sleep time during the active phase, SOREMS and cataplexy. The presence of orexin impacts vigilance state control through acting as a circadian arousal signal and inhibiting the SOREMS. [206]
ASD RSD in infant prairie voles Impair pair bond formation and alter object preference in adulthood. Early REM sleep is crucial for tuning inhibitory neural circuits and developing species-typical affiliative social behaviors. [192]
SD in infant mice from P5-P52 Long-lasting hypoactivity and impaired social behavior in adolescent. Early sleep deprivation increases downstream signaling products of the mammalian target of rapamycin pathway. [193]
ADHD RSD in infant rats for 2 weeks Reduced brain size, hyperactivity, anxiety, attention and learning difficulties. Early REM deprivation damages brain maturation and cause ADHD-like behaviors. [28,82]
RED in infant rats Memory deficit. Reduction of stability of hippocampal neuronal circuits. [189]
Depression RSD in neonatal rats Reduction of male sexual behaviors, pleasure-seeking, shock-induced aggression, REM sleep latency. REM sleep promotes early emotional and mental development. [197,198,199]
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Abbreviation: Ref., references; RSD, REM sleep deprivation; SD, sleep deprivation; SOREMS, sleep-onset REM sleep.
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6. Conclusions
The investigation of the ontogenetic development of REM sleep from humans to animals demonstrates that the appearance of recognizable REM sleep by EEG and its subsequently mechanistic maturation appears to follow a similar developmental program: REM sleep is remarkably abundant during the early period and declines progressively across development, and REM sleep ontogenesis presents a remarkably conserved feature of mammalian sleep. A core set of findings after multiple studies across species demonstrates that REM sleep in early life plays a critical role in the maturation and plasticity of the developing brain, physiology, and behaviors. Conversely, if REM sleep is deficient, significant changes occur in sleep organization and the maturation of the brainstem and cortical centers; cardiovascular and respiratory control may be jeopardized and neurodevelopment disorders may occur such as SUID/SIDS, narcolepsy, developmental disabilities, and various forms of mental retardation are increased. Based on these findings, the neurological mechanisms and functions of REM sleep involved in the drastic change from immature to mature modality and neurodevelopmental disorders require future in-depth studies. Further assessment of the relationship between early life REM sleep and the developing brain is necessary for preventing and treating these disorders. Similarly, the progress of research technology and the continuous improvement of EEG data collection during early human life are also important directions for improved understanding of REM sleep and its role in mammalian development.
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Funding Statement
This work was funded by the National Natural Science Foundation of China (Nos. 81771426, 81471347, 31872770, 82001396, 82160267), the China Scholarship Council (No. 201906185012), the Talent-Introducing Project of State Administration of Foreign Experts Affairs of China (Nos. G2022175003L, X2017008), the program of Gansu Provincial Science and Technology Department (No. 20JR5RA228), and the Fundamental Research Funds for the Central University (Nos. lzujbky-2019-cd03, lzujbky-2021-39).
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Author Contributions
Conceptualization, investigation, methodology, writing—review and editing, supervision, H.-L.C., J.-X.G., Y.-N.C., J.-F.X. and Y.-P.H.; funding acquisition, review and editing, Y.-P.X., K.S., J.-S.L., Y.-F.S. and Y.-P.H. All authors have read and agreed to the published version of the manuscript.
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Institutional Review Board Statement
Not applicable.
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Informed Consent Statement
Not applicable.
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Data Availability Statement
Not applicable.
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Conflicts of Interest
The authors declare no conflict of interest.
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Footnotes
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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| biology | 115845 | https://sv.wikipedia.org/wiki/Dykreflex | Dykreflex | Dykreflexen är egentligen flera reflexer som aktiveras när en människa kommer under vattnet.
Strupreflexen (LCR, den Laryngeala ChemoReflexen) är en skyddsreflex som gör så att struphuvudet stängs när vatten eller andra vätskor åker ner i svalget. Andningen upphör då tillfälligt. Den lilla mängd vatten (cirka 3–4 mm) som ev. finns i luftröret kommer då att sväljas ned. Dessutom slår hjärtat långsammare (ibland hälften så fort), blodtrycket höjs och blodet omfördelas från lemmarna till de inre organen. På detta sätt sparas syre. I reflexen ingår också rörelser med armar och ben för att hjälpa även små barn upp till ytan igen. Reflexen är medfödd och mattas av med ökad ålder och trycks i vuxen ålder oftast undan av den mer dominanta hjärnbarken.
Trigeminusreflexen aktiveras när området runt näsan och pannan kommer i kontakt med vatten och ger ett likartat svar som strupreflexen förutom att det inte ingår några sväljningsrörelser i denna.
Facialisreflexen aktiveras när ansiktet kommer i kontakt med vatten och även den hjälper till att skydda luftvägarna från vatten.
De båda sistnämnda reflexerna finns aktiva även i vuxen ålder, medan strupreflexen inte aktiveras normalt men kan göra det i vissa fall.
Förr trodde man att "dykreflexen" var nödvändig för att ett barn skulle kunna gå på babysim. Nu vet man att det viktigaste är att man lär barnet att viljemässigt hålla andan för att kunna klara sig om barnet skulle hamna i vattnet ofrivilligt. Reflexerna har alltså ingen praktisk betydelse för barn som går på babysim.
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Reflexer
Pediatrik
Simning
Dykning
Fridykning | swedish | 0.565069 |
twins_with_different_fathers/Sibling.txt | A sibling is a relative that shares at least one parent with the other person. A male sibling is a brother, and a female sibling is a sister. Somebody with no siblings is an only child.
While some circumstances can cause siblings to be raised separately (such as foster care), most societies have siblings grow up together. This causes the development of strong emotional bonds, with siblinghood considered a unique type of relationship. The emotional bond between siblings is often complicated and is influenced by factors such as parental treatment, birth order, personality, and personal experiences outside the family.
Medically, a full-sibling is a first-degree relative and a half-sibling is a second-degree relative as they are related by 50% and 25%, respectively.
Definitions[edit]
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Two brothers from Haiti.
The word sibling was reintroduced in 1903 in an article in Biometrika, as a translation for the German Geschwister, having not been used since 1425.
Siblings or full-siblings ([full] sisters or brothers) share the same biological parents. Full-siblings are also the most common type of siblings. Twins are siblings that are born from the same pregnancy. Often, twins with a close relationship will develop a twin language from infanthood, a language only shared and understood between the two. Studies corroborate that identical twins appear to display more twin talk than fraternal twins. At about 3, twin talk usually ends. Twins generally share a greater bond due to growing up together and being the same age.
Half-siblings (half-sisters or half-brothers) are people who share one parent. They may share the same mother but different fathers (in which case they are known as uterine siblings or maternal half-siblings), or they may have the same father but different mothers (in which case, they are known as agnate siblings or paternal half-siblings. In law, the term consanguine is used in place of agnate). In law (and especially inheritance law), half-siblings have often been accorded treatment unequal to that of full-siblings. Old English common law at one time incorporated inequalities into the laws of intestate succession, with half-siblings taking only half as much property of their intestate siblings' estates as siblings of full-blood. Unequal treatment of this type has been wholly abolished in England, but still exists in Florida.
Three-quarter siblings share one parent, while the unshared parents are siblings to each other, for example, if a man has children with two women who are sisters, or a woman has children with a man and his son. In the first case, the children are half-siblings as well as first cousins; in the second, the children are half-siblings as well as an avuncular pair. They’re genetically closer than half-siblings but less genetically close than full-siblings, a degree of genetic relationship that is rare in humans and little-studied.
Diblings, a portmanteau of donor sibling, or donor-conceived sibling, or donor-sperm sibling, are biologically connected through donated eggs or sperm. Diblings are biologically siblings though not legally for the purposes of family rights and inheritance. The anonymity of donation is seen to add complication to the process of courtship.
Non-blood relations[edit]
Related through affinity:
Stepsiblings (stepbrothers or stepsisters) are the children of one's stepparent from a previous relationship.
Adoptive siblings are raised by a person who is the adoptive parent of one and the adoptive or biological parent of the other.
Siblings-in-law are the siblings of one's spouse, the spouse of one's sibling, or the spouse of one's spouse's sibling. The spouse of one's spouse's sibling may also be called a co-sibling.
Not related:
Foster siblings are children who are raised in the same foster home: foster children of one's parent(s), or the children or foster children of one's foster parent.
God siblings are the children of the godfather or godmother or the godchildren of the father or mother.
Milk siblings are children who have been nursed by the same woman. This relationship exists in cultures with milk kinship and in Islamic law.
Cross-siblings are individuals who share one or more half-siblings; if one person has at least one maternal half-sibling and at least one paternal half-sibling, the maternal and paternal half-siblings are cross-siblings to each other.
Siblings and half-siblings
AdamAgathaAnthony
BryanBettyCyrus
Bryan and Betty are full siblings while Cyrus is their half brother; their relation percentage of consanguinity is 50%.
Siblings, half-siblings, and three-quarter siblings
AliceAnthony
BertCorinaBobbyEdwina
DonnaDavidEmilyFrank
Donna and David are full siblings.Emily is their three-quarter sibling and Frank's half sister.
Siblings, half siblings, three-quarter siblings, and cross siblings
EgresAbigaAbalBelina
ErikaEframVeniaAbramAsernaZakAgniaBeinMagnolea
JrakeJadenJuliaJanineJakob
Erika and Efram are full siblings; to them, Abram, Aserna, and Agnia are their half-siblings, and Bein is their cross sibling.Julia and Janine were born to one father and two full-sibling mothers, and are thus three-quarter siblings. Jaden is their cousin, while Jrake and Jakob are their half-cousins.Jrake and Jaden were born to one mother and two half-sibling fathers, and are thus three-quarter siblings, however, their actual percentage of genetic relation is 31.25% instead of 37.5%. Jrake and Jakob are cross-cousins.
Consanguinity and genetics[edit]
Consanguinity is the measure of how closely people are related. Genetic relatedness measures how many genes a person shares. As all humans share over 99% of the same genes, consanguinity only matters for the small fraction of genes which vary between different people. Inheritance of genes has a random element to it, and these two concepts are different. Consanguinity decreases by half for every generation of reproductive separation through their most recent common ancestor. Siblings are 50% related by consanguinity as they are separated from each other by two generation (sibling to parent to sibling), and they share two parents as common ancestors (
(
1
2
)
2
+
(
1
2
)
2
{\displaystyle \left({\tfrac {1}{2}}\right)^{2}+\left({\tfrac {1}{2}}\right)^{2}}
).
A fraternal twin is a sibling and, therefore, is related by 50% consanguinity. Fraternal twins are no more genetically similar than regular siblings. As identical twins come from the same zygote, their most recent common ancestor is each other. They’re genetically identical and 100% consanguineous as they’re separated by zero generations (
(
1
2
)
0
{\displaystyle \left({\tfrac {1}{2}}\right)^{0}}
). Twin studies have been conducted by scientists to examine the roles that genetics and environment play in the development of various traits. Such studies examine how often identical twins possess the same behavioral trait and compare it to how often fraternal twins possess the same trait. In other studies twins are raised in separate families, and studies compare the passing on of a behavioral trait by the family environment and the possession of a common trait between identical twins. This kind of study has revealed that for personality traits which are known to be heritable, genetics play a substantial role throughout life and an even larger role during early years.
Half-siblings are 25% related by consanguinity as they share one parent and separated from each other by two generations (
(
1
2
)
2
{\displaystyle \left({\tfrac {1}{2}}\right)^{2}}
).
A person may share more than the standard consanguinity with their sibling if their parents are related (the coefficient of inbreeding is greater than zero). Interestingly, half-siblings can be related by as "three-quarters siblings" (related by 3/8) if their unshared parents have a consanguinity of 50%. This means the unshared parents are either siblings, making the half-siblings cousins, or parent and child, making them half- aunt-uncle and niece-nephew.
Percentage distribution[edit]
In practice, full siblings do not share exactly 50% of their DNA, as chromosomal crossover only occurs a limited number of times and, therefore, large chunks of a chromosome are shared or not shared at one time. In fact, the mean DNA fraction shared is 50.28% with a standard deviation of 3.68%, meaning approximately 1/4 of sibling pairs share more than 52.76% of their DNA, while 1/4 share less than 47.8%.
There is a very small chance that two half-siblings might not share any genes if they didn't inherit any of the same chromosomes from their shared parent. This is possible for full-siblings as well, though even more unlikely. But because of how homologous chromosomes swap genes (due to chromosomal crossover during meiosis) during the development of an egg or sperm cell, however, the odds of this ever actually occurring are practically non-existent.
Birth order[edit]
Main article: Birth order
The Benzon Daughters by Peder Severin Krøyer
Emperor Pedro II of Brazil with his sisters Princesses Francisca and Januária, 1839
Birth order is a person's rank by age among his or her siblings. Typically, researchers classify siblings as "eldest", "middle child", and "youngest" or simply distinguish between "first-born" and "later-born" children.
Birth order is commonly believed in pop psychology and popular culture to have a profound and lasting effect on psychological development and personality. For example, firstborns are seen as conservative and high-achieving, middle children as natural mediators, and youngest children as charming and outgoing. Despite its lasting presence in the public domain, studies have failed to consistently produce clear, valid, compelling findings; therefore, it has earned the title of a pseudo-psychology amongst the scientific psychological community.
History[edit]
The theorizing and study of birth order can be traced back to Francis Galton's (1822–1911) theory of birth order and eminence and Alfred Adler's (1870–1937) theory of birth order and personality characteristics.
Galton[edit]
In his book English Men of Science: Their Nature and Nurture (1874), Galton noted that prominent composers and scientists are over-represented as first-borns. He theorized three main reasons as to why first-borns are generally more eminent:
Primogeniture laws: first-borns have access to their parents' financial resources to continue their education.
First-borns are given more responsibility than their younger siblings and are treated more as companions by their parents.
First-borns are given more attention and nourishment in families with limited financial resources.
Adler[edit]
First Borns: Fulfilling family roles of leadership and authority, obedient of protocol and hierarchy. Seek out and prefer order, structure and adherence to norms and rules. They partake in goal-striving behaviour as their lives are centred around achievement and accomplishment themes. They fear the loss of their position in the top of the hierarchy.
Middle Children: Feel like outcasts of families as they lack primacy of the first child and the "attention garnering recency" of the youngest. These children often go to great lengths to de-identify themselves with their siblings, in an attempt to make a different and individualized identity for themselves as they feel like they were "squeezed out" of their families.
Youngest Children: Feel disadvantaged compared to older siblings, are often perceived as less capable or experienced and are therefore indulged and spoiled. Because of this, they are skilled in coaxing/charming others to do things for them or provide. This contributes to the image of them being popular and outgoing, as they engage in attention-seeking behaviour to meet their needs.
Contemporary findings[edit]
Today, the flaws and inconsistencies in birth order research eliminate its validity. It is very difficult to control solely for factors related to birth order, and therefore most studies produce ambiguous results. Embedded into theories of birth order is a debate of nature versus nurture. It has been disproved that there is something innate in the position one is born into, and therefore creating a preset role. Birth order has no genetic basis.
The social interaction that occurs as a result of birth order however is the most notable. Older siblings often become role models of behaviour, and younger siblings become learners and supervisees. Older siblings are at a developmental advantage both cognitively and socially. The role of birth order also depends greatly and varies greatly on family context. Family size, sibling identification, age gap, modeling, parenting techniques, gender, class, race, and temperament are all confounding variables that can influence behaviour and therefore perceived behaviour of specific birth categories. The research on birth order does have stronger correlations, however, in areas such as intelligence and physical features, but are likely caused by other factors other than the actual position of birth. Some research has found that firstborn children have slightly higher IQs on average than later born children. However, other research finds no such effect. It has been found that first-borns score three points higher compared to second borns and that children born earlier in a family are on average, taller and weigh more than those born later. However, it is impossible to generalize birth order characteristics and apply them universally to all individuals in that subgroup.
Contemporary explanations for IQ findings[edit]
Resource dilution model[edit]
(Blake, 1981) provide three potential reasons for the higher scoring of older siblings on IQ tests:
Parental resources are finite, first-born children get full and primary access to these resources.
As the number of a children in a family goes up, the more resources must be shared.
These parental resources have an important impact on a child's educational success.
Confluence model[edit]
Robert Zajonc proposed that the intellectual environment within a family is ever-changing due to three factors, and therefore more permissive of first-born children's intellectual advancement:
Firstborns do not need to share parental attention and have their parents' complete absorption. More siblings in the family limit the attention devoted to each of them.
Firstborns are exposed to more adult language. Later-borns are exposed to the less-mature speech of their older siblings.
Firstborns and older siblings must answer questions and explain things to younger siblings, acting as tutors. This advances their cognitive processing of information and language skills.
In 1996, interest in the science behind birth order was re-sparked when Frank Sulloway’s book Born To Rebel was published. In this book, Sulloway argues that firstborns are more conscientious, more socially dominant, less agreeable, and less open to new ideas compared to later-borns. While being seemingly empirical and academic, as many studies are cited throughout the book, it is still often criticized as a biased and incomplete account of the whole picture of siblings and birth order. Because it is a novel, the research and theories proposed throughout were not criticized and peer-reviewed by other academics before its release.
Literature reviews that have examined many studies and attempted to control for confounding variables tend to find minimal effects for birth order on personality.
In her review of the scientific literature, Judith Rich Harris suggests that birth order effects may exist within the context of the family of origin, but that they are not enduring aspects of personality.
In practice, systematic birth order research is a challenge because it is difficult to control for all of the variables that are statistically related to birth order. For example, large families are generally lower in socioeconomic status than small families, so third-born children are more likely than first-born children to come from poorer families. Spacing of children, parenting style, and gender are additional variables to consider.
Regressive behavior at birth[edit]
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A newborn and his brothers
Four Sisters (Frank Eugene, about 1900)
Regressive behaviors are the child's way of demanding the parents' love and attention.
The arrival of a new baby is especially stressful for firstborns and for siblings between 3 and 5 years old. In such situations, regressive behavior may be accompanied by aggressive behavior, such as handling the baby roughly. All of these symptoms are considered to be typical and developmentally appropriate for children between the ages of 3 and 5. While some can be prevented, the remainder can be improved within a few months. Regressive behavior may include demand for a bottle, thumb sucking, requests to wear diapers (even if toilet-trained), or requests to carry a security blanket.
The American Academy of Pediatrics suggests that instead of protesting or telling children to act their age, parents should simply grant their requests without becoming upset. The affected children will soon return to their normal routine when they realize that they now have just as important a place in the family as the new sibling. Most of the behaviors can be improved within a few months.
The University of Michigan Health System advises that most occurrences of regressive behavior are mild and to be expected; however, it recommends parents to contact a pediatrician or child psychologist if the older child tries to hurt the baby, if regressive behavior does not improve within 2 or 3 months, or if the parents have other questions or concerns.
Rivalry[edit]
Main article: Sibling rivalry
Portrait of Lady Cockburn and her Three Eldest Sons (1773–1775) by Joshua Reynolds
"Sibling rivalry" is a type of competition or animosity among brothers and sisters. It appears to be particularly intense when children are very close in age or of the same gender. Sibling rivalry can involve aggression; however, it is not the same as sibling abuse where one child victimizes another.
Sibling rivalry usually starts right after, or before, the arrival of the second child. While siblings will still love each other, it is not uncommon for them to bicker and be malicious to each other. Children are sensitive from the age of 1 year to differences in parental treatment and by 3 years they have a sophisticated grasp of family rules and can evaluate themselves in relation to their siblings. Sibling rivalry often continues throughout childhood and can be very frustrating and stressful to parents. One study found that the age group 10–15 reported the highest level of competition between siblings. Sibling rivalry can continue into adulthood and sibling relationships can change dramatically over the years. Approximately one-third of adults describe their relationship with siblings as rivalrous or distant. However, rivalry often lessens over time and at least 80% of siblings over age 60 enjoy close ties.
Each child in a family competes to define who they are as persons and want to show that they are separate from their siblings. Sibling rivalry increases when children feel they are getting unequal amounts of their parents' attention, where there is stress in the parents' and children's lives, and where fighting is accepted by the family as a way to resolve conflicts. Sigmund Freud saw the sibling relationship as an extension of the Oedipus complex, where brothers were in competition for their mother's attention and sisters for their father's. Evolutionary psychologists explain sibling rivalry in terms of parental investment and kin selection: a parent is inclined to spread resources equally among all children in the family, but a child wants most of the resources for him or herself.
Relationships[edit]
Further information: Sibling relationship
Jealousy[edit]
See also: Attachment theory § Attachment patterns
Jealousy is not a single emotion. The basic emotions expressed in jealous interactions are fear, anger, relief, sadness, and anxiety. Jealousy occurs in a social triangle of relationships which do not require a third person. The social triangle involves the relationships between the jealous individual and the parent, the relationship between the parent and the rival, and the relationship between jealous individual and the rival.
Newborn[edit]
First-borns' attachment to their parents is directly related to their jealous behaviour. In a study by Volling, four classes of children were identified based on their different responses of jealousy to new infant siblings and parent interactions.
Regulated Exploration Children: 60% of children fall into this category. These children closely watch their parents interact with their newborn sibling, approach them positively and sometimes join the interaction. They show fewer behaviour problems in the months following the new birth and do not display problematic behaviours during the parent-infant interaction. These children are considered secure as they act how a child would be expected to act in a familiar home setting with their parents present as secure bases to explore the environment.
Approach-Avoidant Children: 30% of children fall into this category. These children observe parent-infant interaction closely and are less likely to approach the infant and the parent. They are anxious to explore the new environment as they tend to seek little comfort from their parents.
Anxious-Clingy Children: 6% of children fell into this category. These children have an intense interest in parent-infant interaction and a strong desire to seek proximity and contact with the parent, and sometimes intrude on parent-child interaction.
Disruptive Children: 2.7% of children fall into this category. These children are emotionally reactive and aggressive. They have difficulty regulating their negative emotions and may be likely to externalize it as negative behaviour around the newborn.
Parental effect[edit]
Children are more jealous of the interactions between newborns and their mothers than they are with newborns and their fathers. This is logical as up until the birth of the infant, the first-born child had the mother as their primary care-giver all to themselves. Some research has suggested that children display less jealous reactions over father-newborn interactions because fathers tend to punish negative emotion and are less tolerant than mothers of clinginess and visible distress, although this is hard to generalize.
Children that have parents with a better marital relationship are better at regulating their jealous emotions. Children are more likely to express jealousy when their parents are directing their attention to the sibling as opposed to when the parents are solely interacting with them. Parents who are involved in good marital communication help their children cope adaptively with jealousy. They do this by modelling problem-solving and conflict resolution for their children. Children are also less likely to have jealous feelings when they live in a home in which everyone in the family shares and expresses love and happiness.
Implicit theories[edit]
Implicit theories about relationships are associated with the ways children think of strategies to deal with a new situation.
Children can fall into two categories of implicit theorizing. They may be malleable theorists and believe that they can affect change on situations and people. Alternatively, they may be fixed theorists, believing situations and people are not changeable. These implicit beliefs determine both the intensity of their jealous feelings, and how long those jealous feelings last.
Malleable Theorists display engaging behaviours, like interacting with the parent or sibling in an attempt to improve the situation. They tend to have more intense and longer-lasting feelings of jealousy because they spend more time ruminating on the situation and constructing ways to make it better.
Fixed Theorists display non-engaging behaviours, for example retreating to their room because they believe none of their actions will affect or improve the situation. They tend to have less intense and shorter lasting feelings of jealousy than malleable theorists.
Different ages[edit]
Older children tend to be less jealous than their younger sibling. This is due to their ability to mentally process the social situation in a way that gives them more positive, empathetic feelings toward their younger sibling. Older children are better able to cope with their jealous feelings toward their younger sibling due to their understanding of the necessary relationship between the parent and younger sibling. Older children are also better at self-regulating their emotions and are less dependent on their caregivers for external regulation as opposed to their younger siblings.
Younger siblings' feelings of jealousy are overpowered by feelings of anger. The quality of the relationship between the younger child and the older child is also a factor in jealousy, as the better the relationship the less jealous feelings occurred and vice versa.
Conflict[edit]
Sibling conflict is pervasive and often shrugged off as an accepted part of sibling dynamics. In spite of the broad variety of conflict that siblings are often involved in, sibling conflicts can be grouped into two broader categories. The first category is conflict about equality or fairness. It is not uncommon to see siblings who think that their sibling is favored by their teachers, peers, or especially their parents. In fact it is not uncommon to see siblings who both think that their parents favor the other sibling. Perceived inequalities in the division of resources such as who got a larger dessert also fall into this category of conflict. This form of conflict seems to be more prevalent in the younger sibling.
The second category of conflict involves an invasion of a child's perceived personal domain by their sibling. An example of this type of conflict is when a child enters their sibling's room when they are not welcome, or when a child crosses over into their sibling's side of the car in a long road trip. These types of fights seem to be more important to older siblings due to their larger desire for independence.
Warmth[edit]
Sibling warmth is a term for the degree of affection and companionship shared by siblings. Sibling warmth seems to have an effect on siblings. Higher sibling warmth is related to better social skill and higher perceived social competence. Even in cases where there is a high level of sibling conflict if there is also a high level of sibling warmth then social skills and competence remain unaffected.
Negative effects of conflict[edit]
Sibling physical conflict
The saying that people "fight like siblings" shows just how charged sibling conflict can be and how well recognized sibling squabbles are. In spite of how widely acknowledged these squabbles can be, sibling conflict can have several impacts on the sibling pair. It has been shown that increased levels of sibling conflict are related to higher levels of anxiety and depression in siblings, along with lower levels of self-worth and lower levels of academic competence. In addition, sibling warmth is not a protective factor for the negative effects of anxiety, depression, lack of self-worth and lower levels of academic competence. This means that sibling warmth does not counteract these negative effects. Sibling conflict is also linked to an increase in more risky behavior including: smoking cigarettes, skipping days of school, contact with the police, and other behaviors in Caucasian sibling pairs with the exception of firstborns with younger brothers. Except for the elder brother in this pair sibling conflict is positively correlated with risky behavior, thus sibling conflict may be a risk factor for behavioral problems.
A study on what the topic of the fight was (invasion of personal domain or inequality) also shows that the topic of the fight may have a result on the effects of the conflict. This study showed that sibling conflict over personal domain were related to lower levels of self-esteem, and sibling conflict over perceived inequalities seem to be more related to depressive symptoms. However, the study also showed that greater depressive and anxious symptoms were also related to more frequent sibling conflict and more intense sibling conflict.
Parental management techniques of conflict[edit]
Techniques used by parents to manage their children's conflicts include parental non-intervention, child-centered parental intervention strategies, and more rarely the encouragement of physical conflict between siblings. Parental non-intervention included techniques in which the parent ignores the siblings' conflict and lets them work it out between themselves without outside guidance. In some cases, this technique is chosen to avoid situations in which the parent decides which sibling is in the right and may favor one sibling over the other, however, by following this technique the parent may sacrifice the opportunity to instruct their children on how to deal with conflict. Child-centered parental interventions include techniques in which the parent mediates the argument between the two children and helps them come to an agreement. Using this technique, parents may help model how the children can deal with conflicts in the future; however, parents should avoid dictating the outcome to the children, and make sure that they are mediating the argument making suggestions, allowing the children to decide the outcome. This may be especially important when some of the children have autism. Techniques in which parents encourage physical aggression between siblings may be chosen by the parents to help children deal with aggression in the future, however, this technique does not appear to be effective as it is linked to greater conflict levels between children. Parental non-intervention is also linked to higher levels of sibling conflict, and lower levels of sibling warmth. It appears that child-centered parental interventions have the best effect on sibling's relationship with a link to greater levels of sibling warmth and lower levels of sibling conflict.
Long-term effects of presence[edit]
Studies on social skill and personality differences between only children and children with siblings suggest that overall the presence of a sibling does not have any effect on the child as an adult.
Gender roles among children and parents[edit]
There have always been some differences between siblings, especially different sex siblings. Often, different sex sibling may consider things to be unfair because their brother or sister is allowed to do certain things because of their gender, while they get to do something less fun or just different. McHale and her colleague conducted a longitudinal study using middle-childhood aged children and observed the way in which the parents contributed to stereotypical attitudes in their kids. In their study the experimenters analysed two different types of families, one with the same sex siblings, and the other with different sex siblings, as well as the children's birth order. The experiment was conducted using phone interviews, in which the experimenters would ask the children about the activities they performed throughout their day outside of school. The experimenters found that in the homes where there were mixed gender kids, and the father held traditional values, the kids also held traditional values and therefore also played gender based roles in the home. In contrast, in homes where the father did not hold traditional values, the house chores were divided more equally among his kids. However, if fathers had two male children, the younger male tended to help more with household chores, but as he reached his teenage years the younger child stopped being as helpful around the house. However, education may be a confounder affecting both the father's attitude and the siblings' behavior, and the mother's attitudes did not have a noticeable impact.
Westermarck effect[edit]
Anthropologist Edvard Westermarck found that children who are brought up together as siblings are desensitized to sexual attraction to one another later in life. This is known as the Westermarck Effect. It can be seen in biological and adoptive families, but also in other situations where children are brought up in close contact, such as the Israeli kibbutz system and the Chinese shim-pua marriage.
See also[edit]
Immediate family
List of sibling groups
Sibling relationship
Sibling estrangement
Siblings Day
Sladdbarn
Step-sibling
Multiple birth
List of twins
Triplet
Twin
Other symmetric relations
Cousin
Friend
Sibling-in-law
Significant other (SO; boyfriend or girlfriend)
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twins_with_different_fathers/Superfecundation.txt | Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two separate biological fathers. The term superfecundation is derived from fecund, meaning able to produce offspring. Homopaternal superfecundation is fertilization of two separate ova from the same father, leading to fraternal twins, while heteropaternal superfecundation is a form of atypical twinning where, genetically, the twins are half siblings – sharing the same mother, but with different fathers.
Conception[edit]
Sperm cells can live inside a female's body for up to five days, and once ovulation occurs, the egg remains viable for 12–48 hours before it begins to disintegrate. Superfecundation most commonly happens within hours or days of the first instance of fertilization with ova released during the same cycle.
Ovulation is normally suspended during pregnancy to prevent further ova becoming fertilized and to help increase the chances of a full-term pregnancy. However, if an ovum is atypically released after the female was already impregnated when previously ovulating, a chance of a second pregnancy occurs, albeit at a different stage of development. This is known as superfetation.
Heteropaternal superfecundation[edit]
Heteropaternal superfecundation is common in animals such as cats and dogs. Stray dogs can produce litters in which every puppy has a different sire. Though rare in humans, cases have been documented. In one study on humans, the frequency was 2.4% among dizygotic twins whose parents had been involved in paternity suits.
Cases in Greek mythology[edit]
Greek mythology holds many cases of superfecundation:
Leda lies with both her husband Tyndareus and with the god Zeus, the latter in the guise of a swan. Nine months later, she bears two daughters: Clytemnestra by Tyndareus and Helen by Zeus. This happens again; this time Leda bears two sons: Castor by Tyndareus and Pollux by Zeus.
Alcmene lies with Zeus, who is disguised as her husband Amphitryon; Alcmene later lies with the real Amphitryon and gives birth to two sons: Iphicles by Amphitryon and Heracles by Zeus.
Chione lies with both Apollo and Hermes on the same night, and falls pregnant. She bears two sons; Autolycus for Hermes and Philammon for Apollo.
Selected cases involving superfecundation[edit]
In 1982, twins who were born with two different skin colors were discovered to be conceived as a result of heteropaternal superfecundation.
In 1995, a young woman gave birth to diamniotic monochorionic twins, who were originally assumed to be monozygotic twins until a paternity suit led to a DNA test. This led to the discovery that the twins had different fathers.
In 2001, a case of spontaneous monopaternal superfecundation was reported after a woman undergoing IVF treatments gave birth to quintuplets after only two embryos were implanted. Genetic testing supported that the twinning was not a result of the embryos splitting, and that all five boys shared the same father.
In 2008, on the Maury Show a paternity test on live television established a heteropaternal superfecundation.
In 2015, a judge in New Jersey ruled that a man should only pay child support for one of two twins, as he was only the biological father to one of the children.
In 2016, an IVF-implanted surrogate mother gave birth to two children: one genetically unrelated child from an implanted embryo, and a biological child from her own egg and her husband's sperm.
In 2019, a Chinese woman was reported to have two babies from different fathers, one of whom was her husband and the other was a man having a secret affair with her during the same time.
In 2022, a 19-year-old Brazilian from Mineiros gave birth to twins from two different fathers with whom she had sex on the same day.
See also[edit]
Chimera (genetics)
Mixed twins
Polyandry in nature
Polyspermy
Twins | biology | 8633049 | https://sv.wikipedia.org/wiki/Superfekundation | Superfekundation | Superfekundation även kallat överbefruktning är när två eller fler ägg under en menstruationscykel befruktas vid olika samlagstillfällen. Vid superfekundation är det möjligt att spermierna som befruktar äggen kommer från olika fäder vilket innebär att barnen blir halvsyskon trots att de är tvillingar eller trillingar. Tvillingarna är alltid tvåäggstvillingar.
Ordet ska inte förväxlas med superfetation vilket innebär att en kvinna är gravid med ägg från olika menstruationscykler och fostren är i olika utvecklingsstadier. Med andra ord, ett ägg som befruktas fastän kvinnan redan är gravid.
Förekomst
Superfekundation som resulterar i att avkomman har olika biologiska fäder är vanligt bland hundar, katter och nötkreatur.
Hur ofta superfekundation förekommer bland människor är förhållandevis okänt med uppskattningar mellan 1 på 400 och 1 på 13 000 av alla tvåäggstvillingar. Vid en studie av vårdnadstvister där faderskapstest efterfrågades hade 2,4% av tvåäggstvillingar olika biologiska pappor.
Referenser
Fortplantning
Graviditet | swedish | 0.658518 |
twins_with_different_fathers/Twin.txt | Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('non-identical' or 'fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell. Since identical twins develop from one zygote, they will share the same sex, while fraternal twins may or may not. In very rare cases twins can have the same mother and different fathers (heteropaternal superfecundation).
In contrast, a fetus that develops alone in the womb (the much more common case in humans) is called a singleton, and the general term for one offspring of a multiple birth is a multiple. Unrelated look-alikes whose resemblance parallels that of twins are referred to as doppelgängers.
The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side. In Central Africa, there are 18–30 twin sets (or 36–60 twins) per 1,000 live births. In South America, South Asia (India, Pakistan, Bangladesh, Nepal), and Southeast Asia, the lowest rates are found; only 6 to 9 twin sets per 1,000 live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1,000 live births.
Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term. Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper-ovulate. There is no known genetic link for identical twinning. Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births. Some women intentionally turn to fertility drugs in order to conceive twins.
The vast majority of twins are either dizygotic (fraternal) or monozygotic (identical). Less common variants are discussed further down the article.
Fraternal twins can be any of the following:
Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is 1.05 males/female, while it is 1.07 males/female in Italy. However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins.
Zygosity is the degree of identity in the genome of twins.
Dizygotic (DZ) or fraternal twins (also referred to as "non-identical twins", "dissimilar twins", "biovular twins", and, informally in the case of females, "sororal twins") usually occur when two fertilized eggs are implanted in the uterus wall at the same time. When two eggs are independently fertilized by two different sperm cells, fraternal twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular. Fraternal twins are, essentially, two ordinary siblings who happen to develop in the womb together and who are born at the same time, since they arise from two separate eggs fertilized by two separate sperm, just like ordinary siblings. This is the most common type of twin.
Dizygotic twins, like any other siblings, will practically always have different sequences on each chromosome, due to chromosomal crossover during meiosis. Dizygotic twins share on average 50 percent of each other's genes, which resemble amongst siblings that are conceived and born at different times. Like any other siblings, dizygotic twins may look similar, particularly as they are the same age. However, dizygotic twins may also look very different from each other (for example, be of opposite sexes).
Studies show that there is a genetic proclivity for dizygotic twinning. However, it is only the mother who has any effect on the chances of having such twins; there is no known mechanism for a father to cause the release of more than one ovum. Dizygotic twinning ranges from six per thousand births in Japan (similar to the rate of monozygotic twins) to 14 and more per thousand in some African countries.
Dizygotic twins are also more common for older mothers, with twinning rates doubling in mothers over the age of 35. With the advent of technologies and techniques to assist women in getting pregnant, the rate of fraternals has increased markedly.
Monozygotic (MZ) or identical twins occur when a single egg is fertilized to form one zygote (hence, "monozygotic") which then divides into two separate embryos. The chances of having identical twins is relatively rare — around 3 or 4 in every 1,000 births.
Regarding spontaneous or natural monozygotic twinning, a 2007 theory related to in vitro fertilization (IVF) proposes that monozygotic twins may be formed when a blastocyst contains two inner cell masses (ICM), each of which will lead to a separate fetus, rather than by the embryo splitting while hatching from the zona pellucida (the gelatinous protective coating around the blastocyst).
Monozygotic twins may also be created artificially by embryo splitting. It can be used as an expansion of in vitro fertilization (IVF) to increase the number of available embryos for embryo transfer.
Monozygotic twinning occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide.
The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. This is in marked contrast to dizygotic twinning, which ranges from about six per thousand births in Japan (almost similar to the rate of identical twins, which is around 4–5) to 15 and more per thousand in some parts of India and up to over 20 in some Central African countries. The exact cause for the splitting of a zygote or embryo is unknown.
IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 21 pairs of twins for every 1,000.
Monozygotic twins are genetically nearly identical and they are the same chromosomal sex unless there has been a mutation during development. The children of monozygotic twins test genetically as half-siblings (or full siblings, if a pair of monozygotic twins reproduces with another pair or with the same person), rather than first cousins. Identical twins do not have the same fingerprints however, because even within the confines of the womb, the fetuses touch different parts of their environment, giving rise to small variations in their corresponding prints and thus making them unique.
Monozygotic twins always have the same genotype. Normally due to an environmental factor or the deactivation of different X chromosomes in female monozygotic twins, and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally from an XXY Klinefelter syndrome zygote splitting unevenly.
Monozygotic twins, although genetically very similar, are not genetically exactly the same. The DNA in white blood cells of 66 pairs of monozygotic twins was analyzed for 506,786 single-nucleotide polymorphisms known to occur in human populations. Polymorphisms appeared in 2 of the 33 million comparisons, leading the researchers to extrapolate that the blood cells of monozygotic twins may have on the order of one DNA-sequence difference for every 12 million nucleotides, which would imply hundreds of differences across the entire genome. The mutations producing the differences detected in this study would have occurred during embryonic cell-division (after the point of fertilization). If they occur early in fetal development, they will be present in a very large proportion of body cells.
Another cause of difference between monozygotic twins is epigenetic modification, caused by differing environmental influences throughout their lives. Epigenetics refers to the level of activity of any particular gene. A gene may become switched on, switched off, or could become partially switched on or off in an individual. This epigenetic modification is triggered by environmental events. Monozygotic twins can have markedly different epigenetic profiles. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. However, certain characteristics become more alike as twins age, such as IQ and personality.
In January 2021, new research from a team of researchers in Iceland was published in the journal Nature Genetics suggesting that identical twins may not be quite as identical as previously thought. The four-year study of monozygotic (identical) twins and their extended families revealed that these twins have genetic differences that begin in the early stages of embryonic development.
A 1981 study of a deceased triploid XXX twin fetus without a heart showed that although its fetal development suggested that it was an identical twin, as it shared a placenta with its healthy twin, tests revealed that it was probably a polar body twin. The authors were unable to predict whether a healthy fetus could result from a polar body twinning. However, a study in 2012 found that it is possible for a polar body to result in a healthy fetus.
In 2003, a study argued that many cases of triploidy arise from sesquizygotic (semi-identical) twinning.
The degree of separation of the twins in utero depends on if and when they split into two zygotes. Dizygotic twins were always two zygotes. Monozygotic twins split into two zygotes at some time very early in the pregnancy. The timing of this separation determines the chorionicity (the number of placentae) and amniocity (the number of sacs) of the pregnancy. Dichorionic twins either never divided (i.e.: were dizygotic) or they divided within the first 4 days. Monoamnionic twins divide after the first week.
In very rare cases, twins become conjoined twins. Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined. Furthermore, there can be various degrees of shared environment of twins in the womb, potentially leading to pregnancy complications.
It is a common misconception that two placentas automatically implies dizygotic twins, but if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is in fact indistinguishable from that of dizygotic twins.
A 2006 study has found that insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning. Specifically, the study found that vegan mothers (who exclude dairy from their diets) are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation."
From 1980 to 1997, the number of twin births in the United States rose 52%. This rise can at least partly be attributed to the increasing popularity of fertility drugs and procedures such as IVF, which result in multiple births more frequently than unassisted fertilizations do. It may also be linked to the increase of growth hormones in food.
About 1 in 90 human births (1.1%) results from a twin pregnancy. The rate of dizygotic twinning varies greatly among ethnic groups, ranging as high as about 45 per 1000 births (4.5%) for the Yoruba to 10% for Linha São Pedro, a tiny Brazilian settlement which belongs to the city of Cândido Godói. In Cândido Godói, one in five pregnancies has resulted in twins. The Argentine historian Jorge Camarasa has put forward the theory that experiments of the Nazi doctor Josef Mengele could be responsible for the high ratio of twins in the area. His theory was rejected by Brazilian scientists who had studied twins living in Linha São Pedro; they suggested genetic factors within that community as a more likely explanation. A high twinning rate has also been observed in other places of the world, including:
The widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs by the mother) has caused what some call an "epidemic of multiple births". In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births. Nevertheless, the rate of monozygotic twins remains at about 1 in 333 across the globe.
In a study on the maternity records of 5750 Hausa women living in the Savannah zone of Nigeria, there were 40 twins and 2 triplets per 1000 births. Twenty-six percent of twins were monozygotic. The incidence of multiple births, which was about five times higher than that observed in any western population, was significantly lower than that of other ethnic groups, who live in the hot and humid climate of the southern part of the country. The incidence of multiple births was related to maternal age but did not bear any association to the climate or prevalence of malaria.
Twins are more common in people of African descent.
The predisposing factors of monozygotic twinning are unknown.
Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:
Women undergoing certain fertility treatments may have a greater chance of dizygotic multiple births. In the United States it has been estimated that by 2011 36% of twin births resulted from conception by assisted reproductive technology.
The risk of twin birth can vary depending on what types of fertility treatments are used. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Ovarian hyperstimulation without IVF has a very high risk of multiple birth. Reversal of anovulation with clomifene (trade names including Clomid) has a relatively less but yet significant risk of multiple pregnancy.
A 15-year German study of 8,220 vaginally delivered twins (that is, 4,110 pregnancies) in Hesse yielded a mean delivery time interval of 13.5 minutes. The delivery interval between the twins was measured as follows:
The study stated that the occurrence of complications "was found to be more likely with increasing twin-to-twin delivery time interval" and suggested that the interval be kept short, though it noted that the study did not examine causes of complications and did not control for factors such as the level of experience of the obstetrician, the wish of the women giving birth, or the "management strategies" of the procedure of delivering the second twin.
There have also been cases in which twins are born a number of days apart. Possibly the worldwide record for the duration of the time gap between the first and the second delivery was the birth of twins 97 days apart in Cologne, Germany, the first of which was born on November 17, 2018.
Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other fetus has died very early in the pregnancy and has not been detected or recorded. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes in the uterus. There are several reasons for the "vanishing" fetus, including it being embodied or absorbed by the other fetus, placenta or the mother. This is known as vanishing twin syndrome. Also, in an unknown proportion of cases, two zygotes may fuse soon after fertilization, resulting in a single chimeric embryo, and, later, fetus.
Conjoined twins (or the once-commonly used term "siamese") are monozygotic twins whose bodies are joined during pregnancy. This occurs when the zygote starts to split after day 12 following fertilization and fails to separate completely. This condition occurs in about 1 in 50,000 human pregnancies.
Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as the brain, heart, liver or lungs.
A chimera is an ordinary person or animal except that some of their parts actually came from their twin or from the mother. A chimera may arise either from monozygotic twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin coloration in human chimeras. A chimera may be intersex, composed of cells from a male twin and a female twin. In one case DNA tests determined that a woman, Lydia Fairchild, mystifyingly, was not the mother of two of her three children; she was found to be a chimera, and the two children were conceived from eggs derived from cells of their mother's twin.
Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other.
Sometimes the parasitic twin becomes an almost indistinguishable part of the other, and sometimes this needs to be treated medically.
A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or "molar". This means that the molar zygote's cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has either triploidy or complete paternal uniparental disomy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.
Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later, as the twin is not reabsorbed.
It is very common for twins to be born at a low birth weight. More than half of twins are born weighing less than 5.5 pounds (2.5 kg), while the average birth weight of a healthy baby should be around 6–8 pounds (3–4 kg). This is largely due to the fact that twins are typically born premature. Premature birth and low birth weights, especially when under 3.5 pounds (1.6 kg), can increase the risk of several health-related issues, such as vision and hearing loss, mental disabilities, and cerebral palsy. There is an increased possibility of potential complications as the birth weight of the baby decreases.
Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the 'donor' twin, is small and anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition.
Stillbirths occurs when a fetus dies after 20 weeks of gestation. There are two types of stillbirth, including intrauterine death and intrapartum death. Intrauterine death occurs when a baby dies during late pregnancy. Intrapartum death, which is more common, occurs when a baby dies while the mother is giving birth. The cause of stillbirth is often unknown, but the rate of babies who are stillborn is higher in twins and multiple births. Caesareans or inductions are advised after 38 weeks of pregnancy for twins, because the risk of stillbirth increases after this time.
Heterotopic pregnancy is an exceedingly rare type of dizygotic twinning in which one twin implants in the uterus as normal and the other remains in the fallopian tube as an ectopic pregnancy. Ectopic pregnancies must be resolved because they can be life-threatening to the mother. However, in most cases, the intrauterine pregnancy can be salvaged.
For otherwise healthy twin pregnancies where both twins are head down a trial of vaginal delivery is recommended at between 37 and 38 weeks. Vaginal delivery in this case does not worsen the outcome for the infant as compared with Caesarean section. There is controversy on the best method of delivery where the first twin is head first and the second is not. When the first twin is not head down a caesarean section is often recommended. It is estimated that 75% of twin pregnancies in the United States were delivered by caesarean section in 2008. In comparison, the rate of caesarean section for all pregnancies in the general population varies between 14% and 40%. In twins that share the same placenta, delivery may be considered at 36 weeks. For twins who are born early, there is insufficient evidence for or against placing preterm stable twins in the same cot or incubator (co-bedding).
Twin studies are utilized in an attempt to determine how much of a particular trait is attributable to either genetics or environmental influence. These studies compare monozygotic and dizygotic twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from epigenetic and environmental influence. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been used widely in the exploration of human nature. Classical twin studies are now being supplemented with molecular genetic studies which identify individual genes.
This phenomenon is known as heteropaternal superfecundation. One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins, whose parents were involved in paternity suits, was approximately 2.4%.
Dizygotic twins from biracial couples can sometimes be mixed twins, which exhibit differing ethnic and racial features. One such pairing was born in London in 1993 to a white mother and Caribbean father.
Among monozygotic twins, in extremely rare cases, twins have been born with different sexes (one male, one female). When monozygotic twins are born with different sexes it is because of chromosomal defects. The probability of this is so small that multiples having different sexes is universally accepted as a sound basis for in utero clinical determination that the multiples are not monozygotic.
Another abnormality that can result in monozygotic twins of different sexes is if the egg is fertilized by a male sperm but during cell division only the X chromosome is duplicated. This results in one normal male (XY) and one female with Turner syndrome (45,X). In these cases, although the twins did form from the same fertilized egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.
Monozygotic twins can develop differently, due to their genes being differently activated. More unusual are "semi-identical twins", also known as "sesquizygotic". As of 2019, only two cases have been reported. These "half-identical twins" are hypothesized to occur when an ovum is fertilized by two sperm. The cell assorts the chromosomes by heterogonesis and the cell divides into two, with each daughter cell now containing the correct number of chromosomes. The cells continue to develop into a morula. If the morula then undergoes a twinning event, two embryos will be formed, with different paternal genes but identical maternal genes.
In 2007, a study reported a case of a pair of living twins, which shared an identical set of maternal chromosomes, while each having a distinct set of paternal chromosomes, albeit from the same man, and thus they most likely share half of their father's genetic makeup. The twins were both found to be chimeras. One was an intersex XX, and one a XY male. The exact mechanism of fertilization could not be determined but the study stated that it was unlikely to be a case of polar body twinning.
The likely genetic basis of semi-identical twins was reported in 2019 by Michael Gabbett and Nicholas Fisk. In their seminal publication, Gabbett, Fisk and colleagues documented a second case of sesquizygosis and presented molecular evidence of the phenomenon. The reported twins shared 100% of their maternal chromosomes and 78% of their paternal genomic information. The authors presented evidence that two sperm from the same man fertilized an ovum simultaneously. The chromosomes assorted themselves through heterogonesis to form three cell lines. The purely paternal cell line died out due to genomic imprinting lethality, while the other two cell lines, each consisting of the same maternal DNA but only 50% identical paternal DNA, formed a morula which subsequently split into twins.
Mirror image twins result when a fertilized egg splits later in the embryonic stage than normal timing, around day 9–12. This type of twinning could exhibit characteristics with reversed asymmetry, such as opposite dominant handedness, dental structure, or even organs (situs inversus). If the split occurs later than this time period, the twins risk being conjoined. There is no DNA-based zygosity test that can determine if twins are indeed mirror image. The term "mirror image" is used because the twins, when facing each other, appear as matching reflections.
There have been many studies highlighting the development of language in twins compared to single-born children. These studies have converged on the notion that there is a greater rate of delay in language development in twins compared to their single-born counterparts. The reasons for this phenomenon are still in question; however, cryptophasia was thought to be the major cause. Idioglossia is defined as a private language that is usually invented by young children, specifically twins. Another term to describe what some people call "twin talk" is cryptophasia where a language is developed by twins that only they can understand. The increased focused communication between two twins may isolate them from the social environment surrounding them. Idioglossia has been found to be a rare occurrence and the attention of scientists has shifted away from this idea. However, there are researchers and scientists that say cryptophasia or idioglossia is not a rare phenomenon. Current research is looking into the impacts of a richer social environment for these twins to stimulate their development of language.
Non-human dizygotic twinning is a common phenomenon in multiple animal species, including cats, dogs, cattle, bats, chimpanzees, and deer. This should not be confused with an animal's ability to produce a litter, because while litters are caused by the release of multiple eggs during an ovulation cycle, identical to the ovulation of dizygotic twins, they produce more than two offspring. Species such as sheep, goats, and deer have a higher propensity for dizygotic twinning, meaning that they carry a higher frequency of the allele responsible for the likelihood of twins, rather than the likelihood of litters (Whitcomb, 2021).
Cases of monozygotic twinning in the animal kingdom are rare but have been recorded on a number of occasions. In 2016, a C-section of an Irish Wolfhound revealed identical twin puppies sharing a singular placenta. South African scientists, who were called in to study the identical twins wrote that... "To the best of our knowledge, this is the first report of monozygotic twinning in the dog confirmed using DNA profiling" (Horton, 2016). Additionally, armadillos have also been known to produce monozygotic twins, sometimes birthing two sets of identical twins during one reproductive cycle. Monozygotic twinning in armadillos functions as an evolutionary adaptation preventing inbreeding. Once an armadillo offspring enters its reproductive stage, the organism is forced to leave the nest in search of its mate, rather than mating with its siblings. Not only does monozygotic twinning dissuade from armadillo siblings inbreeding, but by forcing migration from the nest, this adaptation ensures the increased genetic variation and geographical population diffusion of armadillo species.
Due to the increased parental investment provided for their offspring, larger mammals with longer life spans have slower reproductive cycles and tend to birth only one offspring at a time. This commonly repeated behavior in larger mammals evolved as a fixed, naturally-selected adaptation, resulting in a decreased twinning propensity in species such as giraffes, elephants, and hippopotami. Despite this adaptation, a case of rare monozygotic twinning has been documented in two elephant calves at the Bandipur Tiger Reserve in Karnataka, India. Chief Veterinarian of the Wildlife Trust of India, NVK Ashraf, in response to the twinning event, wrote that "in species that invest longer time in producing a baby, taking care of two twin calves will be difficult. Therefore, the incidence of twinning will be comparatively less."Ashraf's insight not only illuminates the rarity of twinning among large mammals in the natural world, but directs our attention to the increased twinning propensity of animals under human care. This increased twinning propensity is thought to be either caused by random mutation facilitated by genetic drift, or the positive selection of the "twinning" trait in human-controlled conditions. Due to the removal of natural predators and unpredictable environmental conditions with the increase of human-provided food and medical care, species residing in nature reserves, zoos, etc., carry an increased likelihood of reversing their naturally-selected traits that have been passed on for generations. When considering this phenomenon in relation to twinning, larger mammals not commonly associated with high twinning propensities can perhaps produce twins as an adaptive response to their human-controlled environment. Additionally, the high twinning propensity in species is thought to be positively correlated with the infant mortality rate of the reproducing organism's environment (Rickard, 2022, p.2). Thus if a species lives in a controlled environment with a low infant mortality rate, the frequency of the "twinning trait" could increase, leading to a higher likelihood of producing twin offspring. In the case of the monozygotic twin calves in India, their existence could be connected to a new, positively selected adaptation of twinning attributed to species living under human care (Ward, 2014, p.7-11).
Species with small physicalities and quick reproductive cycles carry high twinning propensities as a result of increased predation and high mortality rates. As scientists continue to study the origin of dizygotic twinning in the animal kingdom, many have turned to species that demonstrated an increased output of twins during periods of evolutionary distress and natural selection. Through their studies on Vespertilionidae and Cebidae species, scientists Guilherme Siniciato Terra Garbino (2021) and Marco Varella (2018) have proven that smaller species experiencing infertility in old age and/or unstable habits as a result of increased predation or human interference can experience have undergone natural selection in gaining even higher twinning propensities. In his study on the evolution of litter size in bats, Garbino discovered that the vespertilionidae genus has higher twinning propensities as a result of their high roosting habitats. When tracked phylogenetically, scientists determined that the common ancestor of bats carried a higher twinning propensity which was then lost, and picked up again, eighteen times in evolutionary history. While other bat genuses such as myotinae and murinae inevitably lost the twinning trait, the vespertilionidae genus retained a high trait frequency due to mutation and environmental conditions that triggered natural selection. The height and exposed nature of vespertilionidae's roosting locations resulted in a sharp increase in species mortality rate. Natural selection offsets these dangers by positively selecting high twinning propensity, resulting in not only vespertilionidae's increased ability to produce twins but the increased likelihood of the genus's reproductive survival. This means that despite the genus's high exposure to factors that would seemingly increase mortality rates, vespertilionidae counteracts their environmental conditions through the evolutionary adaptation of dizygotic twins.
The prevalence of dizygotic twinning in monkeys is thought to be an "insurance adaptation" for mothers reproducing at the end of their fertile years. While dizygotic twinning has been observed in species such as gorillas and chimpanzees, monkeys in the cebidae genus are found to be more likely to produce twins because of their small size and insect-based diet (Varella, 2018). This is because their small size indicates shorter gestation periods and the rapid maturation of offspring, resulting in a shorter lifespan where organisms are rapidly replaced by newer generations. The smaller size of the cebidae genus also makes these species more susceptible to predators, thus triggering the heightened pace of birth, maturation, reproduction, and death. Meanwhile, cebidae's insectivorous existence can be correlated with this genus's heightened ability to reproduce, as more resources become available, more organisms can take advantage of these resources. Thus, monkeys that are smaller and have more access to food, such as the cebidae genus, have the ability to produce more offspring at a quicker pace. In terms of dizygotic twinning, it has been observed that older mothers within the cebidae genus have a higher chance of producing twins than those at the beginning stages of their fertility. Despite their access to resources, the cebidae genus has a high mortality rate attributed to their size, meaning that in order to "keep up" their quickened lifecycle, they must produce an excess of offspring in ensuring generational survival. The positively-selected adaptation of twinning counteracts the genus's high mortality rate by giving older mothers the chance to produce more than one offspring. This not only increases the likelihood that one or more of these offspring will reach reproductive maturity, but gives the mother a chance to birth at least one viable offspring despite their age. Due to their short life cycles, the cebidae genus is more inclined to produce dizygotic twins in their older reproductive years, thus signaling that the trait of high twinning propensity is one that is passed down in service of this genus's survival.
Statistics[edit]
The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side. In Central Africa, there are 18–30 twin sets (or 36–60 twins) per 1,000 live births. In South America, South Asia (India, Pakistan, Bangladesh, Nepal), and Southeast Asia, the lowest rates are found; only 6 to 9 twin sets per 1,000 live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1,000 live births.
Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term. Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper-ovulate. There is no known genetic link for identical twinning. Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births. Some women intentionally turn to fertility drugs in order to conceive twins.
Types and zygosity[edit]
The vast majority of twins are either dizygotic (fraternal) or monozygotic (identical). Less common variants are discussed further down the article.
Fraternal twins can be any of the following:
Female–female twins: Sometimes called sororal twins (25%).
Male–male twins: Sometimes called fraternal (unrelated to zygosity) twins (25%).
Female-male twins: This is the most common pairing (50%), encompassing both "female-male" (25%) and "male-female" (25%) twins.
Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is 1.05 males/female, while it is 1.07 males/female in Italy. However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins.
Zygosity is the degree of identity in the genome of twins.
Common name
Scientific name
Zygosity
Development
Occurrence
Identification
Health
Other
Identical
Monozygotic
x
x
x
x
x
x
Fraternal
Dizygotic
x
x
x
x
x
x
Half-identical
Sesquizygotic
x
x
x
x
x
x
Mirror image
x
x
x
x
x
x
x
Mixed chromosome
x
x
x
x
x
x
x
Superfecundation
x
x
Eggs are fertilized during different acts of intercourse
x
x
x
Usage is practically equivalent with heteropaternal superfecundation, which occurs when two different males father fraternal twins, because though superfecundation by the same father is thought to be a common occurrence, it can only be proven to have occurred with multiple fathers.
Superfetation
x
x
A female gets pregnant again while already pregnant, resulting in multiple fetuses at differing developmental stages
x
x
x
x
Parasitic twin
x
x
x
x
x
By definition only healthy fully formed fetus
x
Vanishing twin
Twin resorption, twin embolisation syndrome
x
x
Up to 1 of every 8 multifetus pregnancies
x
By definition only healthy fully formed fetus
Chimerism, mosaicism
Polar body
x
x
x
x
x
x
x
Conjoined twin
x
x
x
x
x
Ranges from normal to compromised
x
Dizygotic (fraternal) twins[edit]
Adult fraternal twins
Fraternal twin brothers as young babies.
Dizygotic (DZ) or fraternal twins (also referred to as "non-identical twins", "dissimilar twins", "biovular twins", and, informally in the case of females, "sororal twins") usually occur when two fertilized eggs are implanted in the uterus wall at the same time. When two eggs are independently fertilized by two different sperm cells, fraternal twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular. Fraternal twins are, essentially, two ordinary siblings who happen to develop in the womb together and who are born at the same time, since they arise from two separate eggs fertilized by two separate sperm, just like ordinary siblings. This is the most common type of twin.
Dizygotic twins, like any other siblings, will practically always have different sequences on each chromosome, due to chromosomal crossover during meiosis. Dizygotic twins share on average 50 percent of each other's genes, which resemble amongst siblings that are conceived and born at different times. Like any other siblings, dizygotic twins may look similar, particularly as they are the same age. However, dizygotic twins may also look very different from each other (for example, be of opposite sexes).
Studies show that there is a genetic proclivity for dizygotic twinning. However, it is only the mother who has any effect on the chances of having such twins; there is no known mechanism for a father to cause the release of more than one ovum. Dizygotic twinning ranges from six per thousand births in Japan (similar to the rate of monozygotic twins) to 14 and more per thousand in some African countries.
Dizygotic twins are also more common for older mothers, with twinning rates doubling in mothers over the age of 35. With the advent of technologies and techniques to assist women in getting pregnant, the rate of fraternals has increased markedly.
Monozygotic (identical) twins[edit]
Monozygotic (MZ) or identical twins occur when a single egg is fertilized to form one zygote (hence, "monozygotic") which then divides into two separate embryos. The chances of having identical twins is relatively rare — around 3 or 4 in every 1,000 births.
Mechanism[edit]
Regarding spontaneous or natural monozygotic twinning, a 2007 theory related to in vitro fertilization (IVF) proposes that monozygotic twins may be formed when a blastocyst contains two inner cell masses (ICM), each of which will lead to a separate fetus, rather than by the embryo splitting while hatching from the zona pellucida (the gelatinous protective coating around the blastocyst).
Monozygotic twins may also be created artificially by embryo splitting. It can be used as an expansion of in vitro fertilization (IVF) to increase the number of available embryos for embryo transfer.
Incidence[edit]
Monozygotic twinning occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide.
The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. This is in marked contrast to dizygotic twinning, which ranges from about six per thousand births in Japan (almost similar to the rate of identical twins, which is around 4–5) to 15 and more per thousand in some parts of India and up to over 20 in some Central African countries. The exact cause for the splitting of a zygote or embryo is unknown.
IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 21 pairs of twins for every 1,000.
Genetic and epigenetic similarity[edit]
Comparison of zygote development in monozygotic and dizygotic twins. In the uterus, a majority of monozygotic twins (60–70%) share the same placenta but have separate amniotic sacs. In 18–30% of monozygotic twins each fetus has a separate placenta and a separate amniotic sac. A small number (1–2%) of monozygotic twins share the same placenta and amniotic sac. Fraternal twins each have their own placenta and own amniotic sac.
Monozygotic twins are genetically nearly identical and they are the same chromosomal sex unless there has been a mutation during development. The children of monozygotic twins test genetically as half-siblings (or full siblings, if a pair of monozygotic twins reproduces with another pair or with the same person), rather than first cousins. Identical twins do not have the same fingerprints however, because even within the confines of the womb, the fetuses touch different parts of their environment, giving rise to small variations in their corresponding prints and thus making them unique.
Monozygotic twins always have the same genotype. Normally due to an environmental factor or the deactivation of different X chromosomes in female monozygotic twins, and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally from an XXY Klinefelter syndrome zygote splitting unevenly.
Monozygotic twins, although genetically very similar, are not genetically exactly the same. The DNA in white blood cells of 66 pairs of monozygotic twins was analyzed for 506,786 single-nucleotide polymorphisms known to occur in human populations. Polymorphisms appeared in 2 of the 33 million comparisons, leading the researchers to extrapolate that the blood cells of monozygotic twins may have on the order of one DNA-sequence difference for every 12 million nucleotides, which would imply hundreds of differences across the entire genome. The mutations producing the differences detected in this study would have occurred during embryonic cell-division (after the point of fertilization). If they occur early in fetal development, they will be present in a very large proportion of body cells.
Another cause of difference between monozygotic twins is epigenetic modification, caused by differing environmental influences throughout their lives. Epigenetics refers to the level of activity of any particular gene. A gene may become switched on, switched off, or could become partially switched on or off in an individual. This epigenetic modification is triggered by environmental events. Monozygotic twins can have markedly different epigenetic profiles. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. However, certain characteristics become more alike as twins age, such as IQ and personality.
In January 2021, new research from a team of researchers in Iceland was published in the journal Nature Genetics suggesting that identical twins may not be quite as identical as previously thought. The four-year study of monozygotic (identical) twins and their extended families revealed that these twins have genetic differences that begin in the early stages of embryonic development.
Polar body and semi-identical twins[edit]
A 1981 study of a deceased triploid XXX twin fetus without a heart showed that although its fetal development suggested that it was an identical twin, as it shared a placenta with its healthy twin, tests revealed that it was probably a polar body twin. The authors were unable to predict whether a healthy fetus could result from a polar body twinning. However, a study in 2012 found that it is possible for a polar body to result in a healthy fetus.
In 2003, a study argued that many cases of triploidy arise from sesquizygotic (semi-identical) twinning.
Degree of separation[edit]
Various types of chorionicity and amniosity (how the baby's sac looks) in monozygotic (one egg/identical) twins as a result of when the fertilized egg divides
The degree of separation of the twins in utero depends on if and when they split into two zygotes. Dizygotic twins were always two zygotes. Monozygotic twins split into two zygotes at some time very early in the pregnancy. The timing of this separation determines the chorionicity (the number of placentae) and amniocity (the number of sacs) of the pregnancy. Dichorionic twins either never divided (i.e.: were dizygotic) or they divided within the first 4 days. Monoamnionic twins divide after the first week.
In very rare cases, twins become conjoined twins. Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined. Furthermore, there can be various degrees of shared environment of twins in the womb, potentially leading to pregnancy complications.
It is a common misconception that two placentas automatically implies dizygotic twins, but if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is in fact indistinguishable from that of dizygotic twins.
Type
Description
Day
Dichorionic-Diamniotic
Normally, twins have two separate (di- being a numerical prefix for two) chorions and amniotic sacs, termed Dichorionic-Diamniotic or "DiDi". It occurs in almost all cases of dizygotic twins (except in very rare cases of fusion between their blastocysts) and in 18–36% (or around 25%) of monozygotic (identical) twins.
DiDi twins have the lowest mortality risk at about 9 percent, although that is still significantly higher than that of singletons.
Dichorionic-Diamniotic twins form when splitting takes place by the third day after fertilization.
Monochorionic-Diamniotic
Monochorionic twins share the same placenta.
Monochorionic twins generally have two amniotic sacs (called Monochorionic-Diamniotic "MoDi"), which occurs in 60–70% of the pregnancies with monozygotic twins, and in 0.3% of all pregnancies. Monochorionic-Diamniotic twins are almost always monozygotic, with a few exceptions where the blastocysts have fused.
Monochorionic twins share the same placenta, and thus have a risk of twin-to-twin transfusion syndrome.
Days 4-8
Monochorionic-Monoamniotic
Monochorionic twins share the same amnion in 1–2% of monozygotic twin pregnancies.
Monoamniotic twins are always monozygotic.
The survival rate for monoamniotic twins is somewhere between 50% and 60%.
Monoamniotic twins, as with diamniotic monochorionic twins, have a risk of twin-to-twin transfusion syndrome. Also, the two umbilical cords have an increased chance of being tangled around the babies. Because of this, there is an increased chance that the newborns may be miscarried or suffer from cerebral palsy due to lack of oxygen.
Monoamniotic twins occur when the split takes place after the ninth day after fertilization.
Conjoined twins
When the division of the developing zygote into 2 embryos occurs, 99% of the time it is within 8 days of fertilization.
Mortality is highest for conjoined twins due to the many complications resulting from shared organs.
If the division of the zygote occurs later than the 12 days then conjoined twins are usually the result.
Dichorionic-diamniotic twins at 8 weeks and 5 days since co-incubation as part of IVF. The twin at left in the image is shown in the sagittal plane with the head pointing towards upper left. The twin at right in the image is shown in the coronal plane with the head pointing rightwards.
Abdominal ultrasonography of monoamniotic twins at a gestational age of 15 weeks. There is no sign of any membrane between the fetuses. A coronal plane is shown of the twin at left, and a sagittal plane of parts of the upper thorax and head is shown of the twin at right.
Demographics[edit]
A 2006 study has found that insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning. Specifically, the study found that vegan mothers (who exclude dairy from their diets) are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation."
From 1980 to 1997, the number of twin births in the United States rose 52%. This rise can at least partly be attributed to the increasing popularity of fertility drugs and procedures such as IVF, which result in multiple births more frequently than unassisted fertilizations do. It may also be linked to the increase of growth hormones in food.
Ethnicity[edit]
Main article: Populated places with highest incidence of multiple birth
A pair of female ere ibeji twin figures (early 20th-century) in the permanent collection of The Children's Museum of Indianapolis. The Yoruba people have the highest dizygotic twinning rate in the world.
About 1 in 90 human births (1.1%) results from a twin pregnancy. The rate of dizygotic twinning varies greatly among ethnic groups, ranging as high as about 45 per 1000 births (4.5%) for the Yoruba to 10% for Linha São Pedro, a tiny Brazilian settlement which belongs to the city of Cândido Godói. In Cândido Godói, one in five pregnancies has resulted in twins. The Argentine historian Jorge Camarasa has put forward the theory that experiments of the Nazi doctor Josef Mengele could be responsible for the high ratio of twins in the area. His theory was rejected by Brazilian scientists who had studied twins living in Linha São Pedro; they suggested genetic factors within that community as a more likely explanation. A high twinning rate has also been observed in other places of the world, including:
Igbo-Ora in Nigeria
Kodinhi, located in Kerala, India
Mohammadpur Umri, located in Uttar Pradesh, India
The widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs by the mother) has caused what some call an "epidemic of multiple births". In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births. Nevertheless, the rate of monozygotic twins remains at about 1 in 333 across the globe.
In a study on the maternity records of 5750 Hausa women living in the Savannah zone of Nigeria, there were 40 twins and 2 triplets per 1000 births. Twenty-six percent of twins were monozygotic. The incidence of multiple births, which was about five times higher than that observed in any western population, was significantly lower than that of other ethnic groups, who live in the hot and humid climate of the southern part of the country. The incidence of multiple births was related to maternal age but did not bear any association to the climate or prevalence of malaria.
Twins are more common in people of African descent.
Predisposing factors[edit]
The predisposing factors of monozygotic twinning are unknown.
Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:
She is of West African descent (especially Yoruba)
She is between the age of 30 and 40 years
She is greater than average height and weight
She has had several previous pregnancies.
Women undergoing certain fertility treatments may have a greater chance of dizygotic multiple births. In the United States it has been estimated that by 2011 36% of twin births resulted from conception by assisted reproductive technology.
The risk of twin birth can vary depending on what types of fertility treatments are used. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Ovarian hyperstimulation without IVF has a very high risk of multiple birth. Reversal of anovulation with clomifene (trade names including Clomid) has a relatively less but yet significant risk of multiple pregnancy.
Delivery interval[edit]
A 15-year German study of 8,220 vaginally delivered twins (that is, 4,110 pregnancies) in Hesse yielded a mean delivery time interval of 13.5 minutes. The delivery interval between the twins was measured as follows:
Within 15 minutes: 75.8%
16–30 minutes: 16.4%
31–45 minutes: 4.3%
46–60 minutes: 1.7%
Over 60 minutes: 1.8%
The study stated that the occurrence of complications "was found to be more likely with increasing twin-to-twin delivery time interval" and suggested that the interval be kept short, though it noted that the study did not examine causes of complications and did not control for factors such as the level of experience of the obstetrician, the wish of the women giving birth, or the "management strategies" of the procedure of delivering the second twin.
There have also been cases in which twins are born a number of days apart. Possibly the worldwide record for the duration of the time gap between the first and the second delivery was the birth of twins 97 days apart in Cologne, Germany, the first of which was born on November 17, 2018.
Complications during pregnancy[edit]
Vanishing twins[edit]
Main article: Vanishing twin
Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other fetus has died very early in the pregnancy and has not been detected or recorded. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes in the uterus. There are several reasons for the "vanishing" fetus, including it being embodied or absorbed by the other fetus, placenta or the mother. This is known as vanishing twin syndrome. Also, in an unknown proportion of cases, two zygotes may fuse soon after fertilization, resulting in a single chimeric embryo, and, later, fetus.
Conjoined twins[edit]
Main article: Conjoined twins
Chang and Eng Bunker, born in Siam (now Thailand) in 1811, were the origin of the term "Siamese twins".
Conjoined twins (or the once-commonly used term "siamese") are monozygotic twins whose bodies are joined during pregnancy. This occurs when the zygote starts to split after day 12 following fertilization and fails to separate completely. This condition occurs in about 1 in 50,000 human pregnancies.
Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as the brain, heart, liver or lungs.
Chimerism[edit]
Main article: Chimera (genetics)
A chimera is an ordinary person or animal except that some of their parts actually came from their twin or from the mother. A chimera may arise either from monozygotic twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin coloration in human chimeras. A chimera may be intersex, composed of cells from a male twin and a female twin. In one case DNA tests determined that a woman, Lydia Fairchild, mystifyingly, was not the mother of two of her three children; she was found to be a chimera, and the two children were conceived from eggs derived from cells of their mother's twin.
Parasitic twins[edit]
Main article: Parasitic twin
Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other.
Sometimes the parasitic twin becomes an almost indistinguishable part of the other, and sometimes this needs to be treated medically.
Partial molar twins[edit]
A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or "molar". This means that the molar zygote's cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has either triploidy or complete paternal uniparental disomy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.
Miscarried twin[edit]
Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later, as the twin is not reabsorbed.
Low birth weight[edit]
It is very common for twins to be born at a low birth weight. More than half of twins are born weighing less than 5.5 pounds (2.5 kg), while the average birth weight of a healthy baby should be around 6–8 pounds (3–4 kg). This is largely due to the fact that twins are typically born premature. Premature birth and low birth weights, especially when under 3.5 pounds (1.6 kg), can increase the risk of several health-related issues, such as vision and hearing loss, mental disabilities, and cerebral palsy. There is an increased possibility of potential complications as the birth weight of the baby decreases.
Twin-to-twin transfusion syndrome[edit]
Main article: Twin-to-twin transfusion syndrome
Twin-to-twin transfusion syndrome (TTTS) illustration of twins showing one fetus with exposure to more amniotic fluid while the other is "stuck" with the membrane tightly around itself.
Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the 'donor' twin, is small and anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition.
Stillbirths[edit]
Stillbirths occurs when a fetus dies after 20 weeks of gestation. There are two types of stillbirth, including intrauterine death and intrapartum death. Intrauterine death occurs when a baby dies during late pregnancy. Intrapartum death, which is more common, occurs when a baby dies while the mother is giving birth. The cause of stillbirth is often unknown, but the rate of babies who are stillborn is higher in twins and multiple births. Caesareans or inductions are advised after 38 weeks of pregnancy for twins, because the risk of stillbirth increases after this time.
Heterotopic pregnancy[edit]
Heterotopic pregnancy is an exceedingly rare type of dizygotic twinning in which one twin implants in the uterus as normal and the other remains in the fallopian tube as an ectopic pregnancy. Ectopic pregnancies must be resolved because they can be life-threatening to the mother. However, in most cases, the intrauterine pregnancy can be salvaged.
Management of birth[edit]
For otherwise healthy twin pregnancies where both twins are head down a trial of vaginal delivery is recommended at between 37 and 38 weeks. Vaginal delivery in this case does not worsen the outcome for the infant as compared with Caesarean section. There is controversy on the best method of delivery where the first twin is head first and the second is not. When the first twin is not head down a caesarean section is often recommended. It is estimated that 75% of twin pregnancies in the United States were delivered by caesarean section in 2008. In comparison, the rate of caesarean section for all pregnancies in the general population varies between 14% and 40%. In twins that share the same placenta, delivery may be considered at 36 weeks. For twins who are born early, there is insufficient evidence for or against placing preterm stable twins in the same cot or incubator (co-bedding).
Human twin studies[edit]
Main article: Twin study
Twin studies are utilized in an attempt to determine how much of a particular trait is attributable to either genetics or environmental influence. These studies compare monozygotic and dizygotic twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from epigenetic and environmental influence. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been used widely in the exploration of human nature. Classical twin studies are now being supplemented with molecular genetic studies which identify individual genes.
Unusual twinnings[edit]
Bi-paternal twins[edit]
This phenomenon is known as heteropaternal superfecundation. One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins, whose parents were involved in paternity suits, was approximately 2.4%.
Mixed twins[edit]
Main article: Mixed twins
Dizygotic twins from biracial couples can sometimes be mixed twins, which exhibit differing ethnic and racial features. One such pairing was born in London in 1993 to a white mother and Caribbean father.
Monozygotic twins of different sexes[edit]
Among monozygotic twins, in extremely rare cases, twins have been born with different sexes (one male, one female). When monozygotic twins are born with different sexes it is because of chromosomal defects. The probability of this is so small that multiples having different sexes is universally accepted as a sound basis for in utero clinical determination that the multiples are not monozygotic.
Another abnormality that can result in monozygotic twins of different sexes is if the egg is fertilized by a male sperm but during cell division only the X chromosome is duplicated. This results in one normal male (XY) and one female with Turner syndrome (45,X). In these cases, although the twins did form from the same fertilized egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.
Semi-identical (sesquizygotic) twins[edit]
Monozygotic twins can develop differently, due to their genes being differently activated. More unusual are "semi-identical twins", also known as "sesquizygotic". As of 2019, only two cases have been reported. These "half-identical twins" are hypothesized to occur when an ovum is fertilized by two sperm. The cell assorts the chromosomes by heterogonesis and the cell divides into two, with each daughter cell now containing the correct number of chromosomes. The cells continue to develop into a morula. If the morula then undergoes a twinning event, two embryos will be formed, with different paternal genes but identical maternal genes.
Twin calves of the Hereford breed in Miles City, Montana
In 2007, a study reported a case of a pair of living twins, which shared an identical set of maternal chromosomes, while each having a distinct set of paternal chromosomes, albeit from the same man, and thus they most likely share half of their father's genetic makeup. The twins were both found to be chimeras. One was an intersex XX, and one a XY male. The exact mechanism of fertilization could not be determined but the study stated that it was unlikely to be a case of polar body twinning.
The likely genetic basis of semi-identical twins was reported in 2019 by Michael Gabbett and Nicholas Fisk. In their seminal publication, Gabbett, Fisk and colleagues documented a second case of sesquizygosis and presented molecular evidence of the phenomenon. The reported twins shared 100% of their maternal chromosomes and 78% of their paternal genomic information. The authors presented evidence that two sperm from the same man fertilized an ovum simultaneously. The chromosomes assorted themselves through heterogonesis to form three cell lines. The purely paternal cell line died out due to genomic imprinting lethality, while the other two cell lines, each consisting of the same maternal DNA but only 50% identical paternal DNA, formed a morula which subsequently split into twins.
Mirror image twins[edit]
Mirror image twins result when a fertilized egg splits later in the embryonic stage than normal timing, around day 9–12. This type of twinning could exhibit characteristics with reversed asymmetry, such as opposite dominant handedness, dental structure, or even organs (situs inversus). If the split occurs later than this time period, the twins risk being conjoined. There is no DNA-based zygosity test that can determine if twins are indeed mirror image. The term "mirror image" is used because the twins, when facing each other, appear as matching reflections.
Language development[edit]
There have been many studies highlighting the development of language in twins compared to single-born children. These studies have converged on the notion that there is a greater rate of delay in language development in twins compared to their single-born counterparts. The reasons for this phenomenon are still in question; however, cryptophasia was thought to be the major cause. Idioglossia is defined as a private language that is usually invented by young children, specifically twins. Another term to describe what some people call "twin talk" is cryptophasia where a language is developed by twins that only they can understand. The increased focused communication between two twins may isolate them from the social environment surrounding them. Idioglossia has been found to be a rare occurrence and the attention of scientists has shifted away from this idea. However, there are researchers and scientists that say cryptophasia or idioglossia is not a rare phenomenon. Current research is looking into the impacts of a richer social environment for these twins to stimulate their development of language.
Animals[edit]
Non-human dizygotic twinning is a common phenomenon in multiple animal species, including cats, dogs, cattle, bats, chimpanzees, and deer. This should not be confused with an animal's ability to produce a litter, because while litters are caused by the release of multiple eggs during an ovulation cycle, identical to the ovulation of dizygotic twins, they produce more than two offspring. Species such as sheep, goats, and deer have a higher propensity for dizygotic twinning, meaning that they carry a higher frequency of the allele responsible for the likelihood of twins, rather than the likelihood of litters (Whitcomb, 2021).
Cases of monozygotic twinning in the animal kingdom are rare but have been recorded on a number of occasions. In 2016, a C-section of an Irish Wolfhound revealed identical twin puppies sharing a singular placenta. South African scientists, who were called in to study the identical twins wrote that... "To the best of our knowledge, this is the first report of monozygotic twinning in the dog confirmed using DNA profiling" (Horton, 2016). Additionally, armadillos have also been known to produce monozygotic twins, sometimes birthing two sets of identical twins during one reproductive cycle. Monozygotic twinning in armadillos functions as an evolutionary adaptation preventing inbreeding. Once an armadillo offspring enters its reproductive stage, the organism is forced to leave the nest in search of its mate, rather than mating with its siblings. Not only does monozygotic twinning dissuade from armadillo siblings inbreeding, but by forcing migration from the nest, this adaptation ensures the increased genetic variation and geographical population diffusion of armadillo species.
Due to the increased parental investment provided for their offspring, larger mammals with longer life spans have slower reproductive cycles and tend to birth only one offspring at a time. This commonly repeated behavior in larger mammals evolved as a fixed, naturally-selected adaptation, resulting in a decreased twinning propensity in species such as giraffes, elephants, and hippopotami. Despite this adaptation, a case of rare monozygotic twinning has been documented in two elephant calves at the Bandipur Tiger Reserve in Karnataka, India. Chief Veterinarian of the Wildlife Trust of India, NVK Ashraf, in response to the twinning event, wrote that "in species that invest longer time in producing a baby, taking care of two twin calves will be difficult. Therefore, the incidence of twinning will be comparatively less."Ashraf's insight not only illuminates the rarity of twinning among large mammals in the natural world, but directs our attention to the increased twinning propensity of animals under human care. This increased twinning propensity is thought to be either caused by random mutation facilitated by genetic drift, or the positive selection of the "twinning" trait in human-controlled conditions. Due to the removal of natural predators and unpredictable environmental conditions with the increase of human-provided food and medical care, species residing in nature reserves, zoos, etc., carry an increased likelihood of reversing their naturally-selected traits that have been passed on for generations. When considering this phenomenon in relation to twinning, larger mammals not commonly associated with high twinning propensities can perhaps produce twins as an adaptive response to their human-controlled environment. Additionally, the high twinning propensity in species is thought to be positively correlated with the infant mortality rate of the reproducing organism's environment (Rickard, 2022, p.2). Thus if a species lives in a controlled environment with a low infant mortality rate, the frequency of the "twinning trait" could increase, leading to a higher likelihood of producing twin offspring. In the case of the monozygotic twin calves in India, their existence could be connected to a new, positively selected adaptation of twinning attributed to species living under human care (Ward, 2014, p.7-11).
Species with small physicalities and quick reproductive cycles carry high twinning propensities as a result of increased predation and high mortality rates. As scientists continue to study the origin of dizygotic twinning in the animal kingdom, many have turned to species that demonstrated an increased output of twins during periods of evolutionary distress and natural selection. Through their studies on Vespertilionidae and Cebidae species, scientists Guilherme Siniciato Terra Garbino (2021) and Marco Varella (2018) have proven that smaller species experiencing infertility in old age and/or unstable habits as a result of increased predation or human interference can experience have undergone natural selection in gaining even higher twinning propensities. In his study on the evolution of litter size in bats, Garbino discovered that the vespertilionidae genus has higher twinning propensities as a result of their high roosting habitats. When tracked phylogenetically, scientists determined that the common ancestor of bats carried a higher twinning propensity which was then lost, and picked up again, eighteen times in evolutionary history. While other bat genuses such as myotinae and murinae inevitably lost the twinning trait, the vespertilionidae genus retained a high trait frequency due to mutation and environmental conditions that triggered natural selection. The height and exposed nature of vespertilionidae's roosting locations resulted in a sharp increase in species mortality rate. Natural selection offsets these dangers by positively selecting high twinning propensity, resulting in not only vespertilionidae's increased ability to produce twins but the increased likelihood of the genus's reproductive survival. This means that despite the genus's high exposure to factors that would seemingly increase mortality rates, vespertilionidae counteracts their environmental conditions through the evolutionary adaptation of dizygotic twins.
The prevalence of dizygotic twinning in monkeys is thought to be an "insurance adaptation" for mothers reproducing at the end of their fertile years. While dizygotic twinning has been observed in species such as gorillas and chimpanzees, monkeys in the cebidae genus are found to be more likely to produce twins because of their small size and insect-based diet (Varella, 2018). This is because their small size indicates shorter gestation periods and the rapid maturation of offspring, resulting in a shorter lifespan where organisms are rapidly replaced by newer generations. The smaller size of the cebidae genus also makes these species more susceptible to predators, thus triggering the heightened pace of birth, maturation, reproduction, and death. Meanwhile, cebidae's insectivorous existence can be correlated with this genus's heightened ability to reproduce, as more resources become available, more organisms can take advantage of these resources. Thus, monkeys that are smaller and have more access to food, such as the cebidae genus, have the ability to produce more offspring at a quicker pace. In terms of dizygotic twinning, it has been observed that older mothers within the cebidae genus have a higher chance of producing twins than those at the beginning stages of their fertility. Despite their access to resources, the cebidae genus has a high mortality rate attributed to their size, meaning that in order to "keep up" their quickened lifecycle, they must produce an excess of offspring in ensuring generational survival. The positively-selected adaptation of twinning counteracts the genus's high mortality rate by giving older mothers the chance to produce more than one offspring. This not only increases the likelihood that one or more of these offspring will reach reproductive maturity, but gives the mother a chance to birth at least one viable offspring despite their age. Due to their short life cycles, the cebidae genus is more inclined to produce dizygotic twins in their older reproductive years, thus signaling that the trait of high twinning propensity is one that is passed down in service of this genus's survival.
See also[edit]
Cloning
Doppelgänger
Evil twin
Gemini (astrology)
List of multiple births
List of notable twins
Litter (animal)
Look-alike
Mixed twins
Multiple birth
Multiverse
Superfecundation
Twin study
Twin towns and sister cities
Twins in mythology
Virtual twin | biology | 998 | https://da.wikipedia.org/wiki/Art | Art | Arten (species, forkortet sp., flertal: spp.) er den grundlæggende systematiske enhed inden for biologien. Arten defineres ofte som en naturlig gruppe af populationer, hvor udveksling af gener finder sted (eller kan finde sted) og som i forhold til forplantning er isoleret fra andre grupper. Det vil sige at kun individer inden for samme art kan parre sig og få forplantningsdygtigt afkom. Dette kaldes det biologiske artsbegreb. For organismer, der formerer sig ukønnet eller ved selvbestøvning, må arter afgrænses ud fra ligheder og forskelle mellem forskellige individer. Nogle dyrearter kan i fangenskab hybridisere og få fertilt afkom, men da dette ikke vil ske i naturen, selv om de mødes her, betragtes de som forskellige arter.
Eksempel
To heste kan parre sig og få et føl, der igen kan få føl med andre heste – hestene tilhører derfor samme art. En hest og et æsel kan også parre sig og deres unger kaldes enten muldyr eller mulæsel, afhængig af hvem der er moren, men muldyret eller mulæselet kan (normalt) ikke få unger, da de oftest er sterile. Af den grund regnes hest og æsel som to forskellige arter. Det samme princip gælder også for planterne. Denne naturskabte afgrænsning mellem to arter kaldes en artsbarriere. Den kan af og til gennembrydes, når ellers sterile krydsninger spontant eller kunstigt får gennemført en kromosomfordobling. Se f.eks. Vadegræs (Spartina pectinata).
Arter over for hybrider
Man kan dog godt komme ud for, at arter kan krydses og får blandet afkom, men hybriden vil kun kunne bestå på steder, hvor ingen af forældrearterne kan klare sig. Dette er et særligt udpræget problem med Rododendron (Rhododendron) og Tjørn (Crataegus), fordi disse slægter breder sig voldsomt efter skovbrand eller stormfald. Da hybriderne bliver frugtbare i en yngre alder end arterne, kan de dominere i en periode, men når skoven lukker sig, så fortrænges hybriderne og kun de specialiserede arter kan overleve i skovens dybe skygge eller ude i lyset i sumpe, på ur og i kalksten, m.m.
Flere artsbegreber
Fordi det biologiske artsbegreb kan være besværligt at anvende i praksis, er der efterhånden skabt en række andre artsbegreber:
Morfologisk artsbegreb Arterne adskiller sig fra hinanden ved deres bygning. Dette begreb er blevet meget anvendt gennem tiden.
Økologisk artsbegreb Definerer en art som en gruppe af organismer, der udfylder samme niche. Krydsninger mellem to nærtstående arter vil ikke være optimalt tilpasset til forældrearternes nicher og vil ikke klare sig i konkurrencen.
Evolutionære artsbegreb Også kaldet det kladistiske eller fylogenetiske artsbegreb. Naturen er dynamisk, ikke statisk - alle arter ændrer sig med tiden og bliver, hvis de ikke uddør som følge af konkurrence, naturkatastrofer m.v., til én eller flere nye arter. Det evolutionære artsbegreb minder om det biologiske, men inddrager tidsdimensionen, det vil sige at en art udvikler sig over tid og at nye arter opstår ved artsdannelse. Individer der fylogenetisk har samme stamfader tilhører samme art.
Pluralistisk artsbegreb En art er et samfund af populationer, der formerer sig og lever inden for en bestemt niche i naturen.
Se også
Systematik
Evolutionsteori
Kilder
Lars Skipper: Hvad er en art? Citat: "...Arten er den eneste [klassifikations-kategori] der eksisterer i virkeligheden, alle andre (slægter, familier, ordener m.v.) er indført for overskuelighedens skyld..."
Eksterne henvisninger
2003-12-31, ScienceDaily: Working On The 'Porsche Of Its Time': New Model For Species Determination Offered Citat: "...two species of dinosaur that are members of the same genera varied from each other by just 2.2 percent. Translation of the percentage into an actual number results in an average of just three skeletal differences out of the total 338 bones in the body. Amazingly, 58 percent of these differences occurred in the skull alone. "This is a lot less variation than I'd expected," said Novak..."
2003-08-08, ScienceDaily: Cross-species Mating May Be Evolutionarily Important And Lead To Rapid Change, Say Indiana University Researchers Citat: "...the sudden mixing of closely related species may occasionally provide the energy to impel rapid evolutionary change..."
2004-01-09 ScienceDaily: Mayo Researchers Observe Genetic Fusion Of Human, Animal Cells; May Help Explain Origin Of AIDS Citat: "...The researchers have discovered conditions in which pig cells and human cells can fuse together in the body to yield hybrid cells that contain genetic material from both species..."What we found was completely unexpected," says Jeffrey Platt, M.D..."
2000-09-18, ScienceDaily: Scientists Unravel Ancient Evolutionary History Of Photosynthesis Citat: "...gene-swapping was common among ancient bacteria early in evolution..."
2004-06-07, Sciencedaily: Parting Genomes: University Of Arizona Biologists Discover Seeds Of Speciation Citat: "...There's a huge amount of biodiversity out there, and we don't know where it comes from. Evolutionary biologists are excited to figure out what causes what we see out there--the relative forces of selection and drift--whether things are adapting to their environment or variation is random..."
2005-07-05, Sciencedaily: Trees, Vines And Nets -- Microbial Evolution Changes Its Face Citat: "... EBI researchers have changed our view of 4 billion years of microbial evolution...In all, more than 600,000 vertical transfers are observed, coupled with 90,000 gene loss events and approximately 40,000 horizontal gene transfers...A few species, including beneficial nitrogen-fixing soil bacteria, appear to be 'champions'of horizontal gene transfer; "it's entirely possible that apparently harmless organisms are quietly spreading antibiotic resistance under our feet," concludes Christos Ouzounis..."
2005-11-11, Sciencedaily: Lateral Thinking Produces First Map Of Gene Transmission Citat: "...Their results clearly show genetic modification of organisms by lateral transfer is a widespread natural phenomenon, and it can occur even between distantly related organisms... it was assumed that transfer of genes could only be vertical, i.e. from parents to offspring..."
Økologi
Biologi | danish | 0.791178 |
twins_with_different_fathers/Birth.txt | Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.
In some species, the offspring is precocial and can move around almost immediately after birth but in others, it is altricial and completely dependent on parenting.
In marsupials, the fetus is born at a very immature stage after a short gestation and develops further in its mother's womb pouch.
It is not only mammals that give birth. Some reptiles, amphibians, fish and invertebrates carry their developing young inside them. Some of these are ovoviviparous, with the eggs being hatched inside the mother's body, and others are viviparous, with the embryo developing inside their body, as in the case of mammals.
Human childbirth[edit]
Main article: Childbirth
Further information: Adaptation to extrauterine life
An illustration of normal head-first presentation by the obstetrician William Smellie from about 1792. The membranes have ruptured and the cervix is fully dilated.
Humans usually produce a single offspring at a time. The mother's body is prepared for birth by hormones produced by the pituitary gland, the ovary and the placenta. The total gestation period from fertilization to birth is normally about 38 weeks (birth usually occurring 40 weeks after the last menstrual period). The normal process of childbirth takes several hours and has three stages. The first stage starts with a series of involuntary contractions of the muscular walls of the uterus and gradual dilation of the cervix. The active phase of the first stage starts when the cervix is dilated more than about 4 cm in diameter and is when the contractions become stronger and regular. The head (or the buttocks in a breech birth) of the baby is pushed against the cervix, which gradually dilates until it is fully dilated at 10 cm diameter. At some time, the amniotic sac bursts and the amniotic fluid escapes (also known as rupture of membranes or breaking the water). In stage two, starting when the cervix is fully dilated, strong contractions of the uterus and active pushing by the mother expels the baby out through the vagina, which during this stage of labour is called a birth canal as this passage contains a baby, and the baby is born with umbilical cord attached. In stage three, which begins after the birth of the baby, further contractions expel the placenta, amniotic sac, and the remaining portion of the umbilical cord usually within a few minutes.
Enormous changes take place in the newborn's circulation to enable breathing in air. In the uterus, the fetus is dependent on circulation of blood through the placenta for sustenance including gaseous exchange and the unborn baby's blood bypasses the lungs by flowing through the foramen ovale, which is a hole in the septum dividing the right atrium and left atrium. After birth the umbilical cord is clamped and cut, the baby starts to breathe air, and blood from the right ventricle starts to flow to the lungs for gaseous exchange and oxygenated blood returns to the left atrium, which is pumped into the left ventricle, and then pumped into the main arterial system. As a result of these changes, the blood pressure in the left atrium exceeds the pressure in the right atrium, and this pressure difference forces the foramen ovale to close separating the left and right sides of the heart. The umbilical vein, umbilical arteries, ductus venosus and ductus arteriosus are not needed for life in air and in time these vessels become ligaments (embryonic remnants).
Mammals[edit]
Large mammals, such as primates, cattle, horses, some antelopes, giraffes, hippopotamuses, rhinoceroses, elephants, seals, whales, dolphins, and porpoises, generally are pregnant with one offspring at a time, although they may have twin or multiple births on occasion.
In these large animals, the birth process is similar to that of a human, though in most the offspring is precocial. This means that it is born in a more advanced state than a human baby and is able to stand, walk and run (or swim in the case of an aquatic mammal) shortly after birth.
In the case of whales, dolphins and porpoises, the single calf is normally born tail first which minimizes the risk of drowning. The mother encourages the newborn calf to rise to the surface of the water to breathe.
Most smaller mammals have multiple births, producing litters of young which may number twelve or more. In these animals, each fetus is surrounded by its own amniotic sac and has a separate placenta. This separates from the wall of the uterus during labor and the fetus works its way towards the birth canal.
Large mammals which give birth to twins is much more rare, but it does occur occasionally even for mammals as large as elephants. In April 2018, approximately 8-month old elephant twins were sighted joining their mother's herd in the Tarangire National Park of Tanzania, estimated to have been born in August 2017.
Cattle[edit]
A cow giving birth
Birthing in cattle is typical of a larger mammal. A cow goes through three stages of labor during normal delivery of a calf. During stage one, the animal seeks a quiet place away from the rest of the herd. Hormone changes cause soft tissues of the birth canal to relax as the mother's body prepares for birth. The contractions of the uterus are not obvious externally, but the cow may be restless. She may appear agitated, alternating between standing and lying down, with her tail slightly raised and her back arched. The fetus is pushed toward the birth canal by each contraction and the cow's cervix gradually begins to dilate. Stage one may last several hours, and ends when the cervix is fully dilated. Stage two can be seen to be underway when there is external protrusion of the amniotic sac through the vulva, closely followed by the appearance of the calf's front hooves and head in a front presentation (or occasionally the calf's tail and rear end in a posterior presentation). During the second stage, the cow will usually lie down on her side to push and the calf progresses through the birth canal. The complete delivery of the calf (or calves in a multiple birth) signifies the end of stage two. The cow scrambles to her feet (if lying down at this stage), turns round and starts vigorously licking the calf. The calf takes its first few breaths and within minutes is struggling to rise to its feet. The third and final stage of labor is the delivery of the placenta, which is usually expelled within a few hours and is often eaten by the normally herbivorous cow.
Dogs[edit]
Further information: Canine reproduction § Gestation and litters
Birth is termed whelping in dogs. Among dogs, as whelping approaches, contractions become more frequent. Labour in the bitch can be divided into 3 stages. The first stage is when the cervix dilates, causing discomfort and restlessness in the dog. Common signs of this stage are panting, fasting, and/or vomiting. This may last up to 12 hours. Stage two is the passage of the offspring. The amniotic sac looking like a glistening grey balloon, with a puppy inside, is propelled through the vulva. After further contractions, the sac is expelled and the bitch breaks the membranes, releasing clear fluid and exposing the puppy. The mother chews at the umbilical cord and licks the puppy vigorously, which stimulates it to breathe. If the puppy has not taken its first breath within about six minutes, it is likely to die. Further puppies follow in a similar way one by one usually with less straining than the first usually at 15-60-minute intervals. If a pup has not been passed in 2 hours a veterinarian should be contacted. Stage three is the passing of the placentas. This often occurs in conjunction with stage two with the passing of each offspring. The mother will then usually eat the afterbirth. This is an adaption to keep the den clean and prevent its detection by predators.
Marsupials[edit]
See also: Marsupial § Reproductive system, and Marsupial § Early development
A kangaroo joey firmly attached to a nipple inside the pouch
An infant marsupial is born in a very immature state. The gestation period is usually shorter than the intervals between oestrus periods. The first sign that a birth is imminent is the mother cleaning out her pouch. When it is born, the infant is pink, blind, furless and a few centimetres long. It has nostrils in order to breathe and forelegs to cling onto its mother's hairs but its hind legs are undeveloped. It crawls through its mother's fur and makes its way into the pouch. Here it fixes onto a teat which swells inside its mouth. It stays attached to the teat for several months until it is sufficiently developed to emerge. Joeys are born with "oral shields"; in species without pouches or with rudimentary pouches these are more developed than in forms with well-developed pouches, implying a role in maintaining the young attached to the mother's nipple.
Other animals[edit]
A Cladocera giving birth (100x magnification)
Many reptiles and the vast majority of invertebrates, most fish, amphibians and all birds are oviparous, that is, they lay eggs with little or no embryonic development taking place within the mother. In aquatic organisms, fertilization is nearly always external with sperm and eggs being liberated into the water (an exception is sharks and rays, which have internal fertilization). Millions of eggs may be produced with no further parental involvement, in the expectation that a small number may survive to become mature individuals. Terrestrial invertebrates may also produce large numbers of eggs, a few of which may avoid predation and carry on the species. Some fish, reptiles, and amphibians have adopted a different strategy and invest their effort in producing a small number of young at a more advanced stage which are more likely to survive to adulthood. Birds care for their young in the nest and provide for their needs after hatching and it is perhaps unsurprising that internal development does not occur in birds, given their need to fly.
Ovoviviparity is a mode of reproduction in which embryos develop inside eggs that remain in the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in that there is internal fertilization and the young are born in an advanced state, but differ in that there is no placental connection and the unborn young are nourished by egg yolk. The mother's body provides gas exchange (respiration), but that is largely necessary for oviparous animals as well. In many sharks the eggs hatch in the oviduct within the mother's body and the embryos are nourished by the egg's yolk and fluids secreted by glands in the walls of the oviduct. The Lamniforme sharks practice oophagy, where the first embryos to hatch consume the remaining eggs and sand tiger shark pups cannibalistically consume neighbouring embryos. The requiem sharks maintain a placental link to the developing young, this practice is known as viviparity. This is more analogous to mammalian gestation than to that of other fishes. In all these cases, the young are born alive and fully functional. The majority of caecilians are ovoviviparous and give birth to already developed offspring. When the young have finished their yolk sacs they feed on nutrients secreted by cells lining the oviduct and even the cells themselves which they eat with specialist scraping teeth. The Alpine salamander (Salamandra atra) and several species of Tanzanian toad in the genus Nectophrynoides are ovoviviparous, developing through the larval stage inside the mother's oviduct and eventually emerging as fully formed juveniles.
A more developed form of viviparity called placental viviparity is adopted by some species of scorpions and cockroaches, certain genera of sharks, snakes and velvet worms. In these, the developing embryo is nourished by some form of placental structure. The earliest known placenta was found recently in a group of extinct fishes called placoderms. A fossil from Australia's Gogo Formation, laid down in the Devonian period, 380 million years ago, was found with an embryo inside it connected by an umbilical cord to a yolk sac. The find confirmed the hypothesis that a sub-group of placoderms, called ptyctodontids, fertilized their eggs internally. Some fishes that fertilize their eggs internally also give birth to live young, as seen here. This discovery moved our knowledge of live birth back 200 million years. The fossil of another genus was found with three embryos in the same position. Placoderms are a sister group of the ancestor of all living jawed fishes (Gnathostomata), including both chondrichthyans, the sharks & rays, and Osteichthyes, the bony fishes.
Among lizards, the viviparous lizard Zootoca vivipara, the Jackson's chameleon, slow worms and many species of skink are viviparous, giving birth to live young. Some are ovoviviparous but others such as members of the genera Tiliqua and Corucia, give birth to live young that develop internally, deriving their nourishment from a mammal-like placenta attached to the inside of the mother's uterus. In a recently described example, an African species, Trachylepis ivensi, has developed a purely reptilian placenta directly comparable in structure and function to a mammalian placenta. Vivipary is rare in snakes, but boas and vipers are viviparous, giving birth to live young.
Female aphid giving birth
The majority of insects lay eggs but a very few give birth to offspring that are miniature versions of the adult. The aphid has a complex life cycle and during the summer months is able to multiply with great rapidity. Its reproduction is typically parthenogenetic and viviparous and females produce unfertilized eggs which they retain within their bodies. The embryos develop within their mothers' ovarioles and the offspring are clones of their mothers. Female nymphs are born which grow rapidly and soon produce more female offspring themselves. In some instances, the newborn nymphs already have developing embryos inside them.
See also[edit]
Wikiquote has quotations related to Birth.
Animal sexual behaviour
Breeding season
Caesarean section
Dystocia
Episiotomy
Foaling (horses)
Forceps delivery
Kegel exercises
Mating system
Odon device
Perineal massage
Reproduction
Reproductive system
Ventouse
Birth spacing | biology | 448889 | https://sv.wikipedia.org/wiki/Utvecklingsbiologi | Utvecklingsbiologi | Utvecklingsbiologi är den vetenskapsgren inom biologin och biovetenskaperna som studerar hur organismerna befruktas, växer, föds och utvecklas. Modern utvecklingsbiologi studerar hur organismens genotyp utmynnar i dess fenotyp, det vill säga hur instruktionerna i arvsmassan tillsammans med miljöfaktorer styr bildningen och utformningen av organismens fysiska skepnad. Generna styr utvecklingen genom att kontrollera celldelning, celldifferentiering, mönsterbildning, morfogenes och tillväxt. Traditionellt har utvecklingsbiologi ofta kallats för embryologi, som dock avser den inriktning inom utvecklingsbiologin som specifikt studerar organismerna från encellsstadiet till det embryonala stadiets slut, medan utvecklingsbiologi inbegriper även den postembryonala delen av livscykeln. Därtill syftar utvecklingsbiologi ofta på zoologisk utvecklingsbiologi, det vill säga läran om djurens utvecklingsbiologi. Embryologi var fram till 1900-talet en nästan helt beskrivande (deskriptiv) vetenskap med tyngdpunkt på embryonal morfologi, men moderna molekylärbiologiska metoder har hjälpt att kartlägga de molekylära och cellulära mekanismerna under utvecklingen.
Det besläktade fältet evolutionär utvecklingsbiologi, populärt ofta kallat evo-devo (efter den engelska termen evolutionary developmental biology) kom till på 1990-talet, och är en syntes av fynd från molekylär utvecklingsbiologi och evolutionsbiologi. Evo-devo studerar mångfalden av organismer och skillnaderna mellan dem i evolutionär kontext.
Utvecklingsbiologiska upptäckter kan ge en bas för förståelse av olika typer av fel i utvecklingsprocessen, exempelvis kromosomrubbningar såsom Downs syndrom. Kunskap om hur celler specialiserar sig under skapandet av ett embryo (embryogenesen) kan ge information om hur stamceller kan differentieras till specifika vävnader, vilket kan användas medicinskt. En viktig biologisk process som inträffar bland annat under organismens utveckling är apoptos, programmerad celldöd. Av detta skäl används många olika modeller för organismens utveckling för att kasta ljus över apoptosens fysiologi och de molekylära mekanismerna bakom den.
Utvecklingshändelser
Celldifferentiering
Celldifferentiering Celldifferentiering är den process som gör att celler blir olika, trots att de har samma genetiska utgångsmaterial och tillhör samma organism. När äggcellen befruktas sker celldelning och celldifferentiering som leder till olika celltyper. I många flercelliga organismer finns det olika sorters celler, som kan skilja sig väldigt mycket i utseende och funktion. Jämför till exempel en nervcell med en hudcell. Det är ännu inte fullt kartlagt hur celldifferentieringen regleras.
Celldelning
Celldelning är den process som ligger till grund för alla levande organismers förökning. Vid celldelningen omvandlas en cell till två celler. Man brukar skilja på tre huvudtyper av celldelning:
Celldelning hos prokaryoter (binär fission).
Mitos (vanlig celldelning) hos eukaryoter.
Meios (celldelning som producerar könsceller) hos eukaryoter.
Embryonalutvecklingen
Människan
Tidig utveckling
Befruktning sker när äggcell och spermiehuvud förenas, detta sker normalt högst upp i moderns äggledare. Den befruktade cellen kallas en zygot, som efter cirka 24-30 timmar celldelas för första gången genom mitos. Samtidigt som celldelningar sker så transporteras det ner mot livmodern med hjälp av flimmerhår och muskler.
Efter ett antal celldelningar bildas en cellklump kallad morula, detta sker dag 3-4 efter befruktningen. Ungefär samtidigt kommer den fram till livmodern.
Under dag 4-5 utvecklas en hålighet i cellmassan som gör att morulan övergår till att bli en blastocyst. Blastocysten är ungefär 0,2 mm stor. Blastocysten består av två typer av celler. De yttersta cellerna kallas trofoblaster och kommer att ge upphov till moderkaka och fosterhinnor. De inre cellerna kallas embryoblaster och kommer att bilda embryot. Kring blastocysten finns också ett skal gjort av glykoproteiner. Detta skal måste kläckas innan det befruktade ägget kan fastna i livmoderslemhinnan. Kläckningen sker på ungefär den 6:e dagen efter befruktningen genom att ägget ändrar form så att skalet går sönder, dessutom finns det enzymer i livmodern som hjälper att bryta ner skalet.
Blastocysten börjar växa in i livmoderväggen i en process som kallas implantation. Implantationen börjar dag 6 och slutar mellan dag 10 och 12 efter befruktningen. Trofoblasterna blir fler och bildar som små rötter som förankrar blastocysten.
När blastocysten blivit till en rund skiva med två lager bildar en grupp celler ett tillväxtcentrum mellan lagren. Från detta centrum skickas en cellsträng ut rätt över skivan. Embryot får en ryggsträng eller blivande ryggrad. Huden ovanför hårdnar och veckar sig till ett dike, nervdiket.
Det andra lagret börjar dela upp sig i kroppssegment. Arm- och benknoppar börjar komma fram längs sidorna. När sedan vävnaden inuti kroppen sväller ut får den huden att förtjockas till en list. Denna list kommer senare enligt en bestämd ordning att påverka innervävnader att göra fingrar, tår, underarm, med mera. Om listen blir avbruten kommer den del som den då var i färd med att tillverka saknas eller bli dåligt gjord. Formgivningen av listen tros komma från en viss mall som finns i en geléartad massa, en grundsubstans, som fyller alla mellanrum. Molekylerna i grundsubstansen styr sammanfogningarna av exempelvis näsa och panna.
I tolv strömmar utefter bålens sidor rör sig de celler som ska bli revben. De möts mitt på bröstet där de bildar ett bröstben. Celler som ska bli muskler färdas mellan revbenen och i kroppsväggen nedanför. Embryots yttersta lager celler börjar göra överhud, där det så småningom ska bli hårrötter, talgkörtlar och svettkörtlar.
Embryot gör de första rörelserna omkring graviditetsvecka 7 (det vill säga 5 veckor efter befruktningen) .
Embryoperioden hos människor räknas från andra till åttonde veckan, då fosterstadiet inleds.
Fosterperioden
Fosterperioden kallas även fetalperioden och startar hos människan i graviditetsvecka 9 (det vill säga 7 veckor efter befruktningen) och pågår fram till födseln.
Vid graviditetsvecka 10 väger fostret ungefär 5 gram. Nästan 50 procent av barnets storlek utgörs nu av huvudet. De flesta organ finns men de behöver utvecklas mer. Fostrets ögon som tidigare suttit långt ut på huvudets sidor har nu hamnat på nästan rätt plats.
I graviditetsvecka 11 har lungorna utvecklats lite och är fulla av fostervatten.
I graviditetsvecka 14 väger fostret ungefär 50 gram och dess matsmältning har kommit igång, fostret sväljer fostervatten. Den genomskinliga huden täcks av små hårstrån.
I graviditetsvecka 17 börjar fostret bilda fosterfett som skyddar dess hud från att blötas upp av fostervattnet.
Från vecka 18 till 20 börjar den gravida kvinnan kunna känna rörelser från fostret.
Efter graviditetsvecka 20 är storleken på fostret mer beroende av arvsanlag än tidigare och skillnaden i storlek hos olika foster ökar efter denna vecka.
Vissa barn som föds i graviditetsvecka 24 överlever men trots stora vårdinsatser så finns det stora risker för skador. Längden från hjässa till häl är då ungefär 30 cm och vikten omkring 600-700 gram.
Näsborrarna börjar öppna sig i graviditetsvecka 25.
I graviditetsvecka 26 kan fostret öppna och stänga ögonen. I denna vecka tränar också fostret sin andning genom att dra in och ut fostervatten i lungorna.
Om barnet skulle födas i graviditetsvecka 28 är chanserna att överleva stora. Vikten är då omkring 1,1 kg och längden cirka 36 cm.
I graviditetsvecka 32 pågår en tillväxtperiod då barnet ökar cirka 200 gram i veckan.
I graviditetsvecka 36 brukar fostret lägga sig med huvudet neråt och sjunka ner, man säger att huvudet fixeras i bäckeningången.
Det är vanligast att barn föds någon gång under graviditetsveckorna 37-42.
Fosterdeformationer
Det finns många orsaker till fosterdeformationer. De kan komma såväl av ärftliga faktorer, som av moderns kost och ålder, faderns spermiekvalitet (även den beroende av kost och ålder) och yttre miljöfaktorer så som kraftiga föroreningar av luft, vatten och livsmedel.
Kända faktorer från modern
Ålder. Mödrar över 35 får oftare barn med Downs syndrom.
Kost. Mödrar med brist på vitamin B12 löper ökad risk att föda barn med nervskador, neuralrörsdefekter, ryggmärgsskador som spina bifida, problem med tillverkningen av röda blodkroppar, skalldeformationer och hjärnskador som senare i livet kan leda till inlärningssvårigheter och depressioner.
Droger. Mödrar som äter livsmedel eller naturläkemedel med valproinsyra riskerar att ge sina barn Fetalt valproatsyndrom. Mödrar som dricker alkohol under graviditeten riskerar att ge sina barn Fetalt alkoholsyndrom.
Kända faktorer från fadern (före graviditeten)
Ålder. Äldre fäder har ökad risk att ge avkommor med autism och schizofreni.
Kost. Fäder behöver en god balans mellan folsyra och vitamin b12 för att kunna producera friska spermier.
Droger. Kokain kan passera genom faderns kropp, påverka spermierna som går in i ägget och därigenom orsaka missbildningar skada fostret.
Kända miljöfaktorer
Ftalater i plastgolv kan öka risken för att generera hormonrubbningar, något som i sin tur kan ge fosterpåverkan under graviditeten.
Källor
En version av motsvarande artikel på engelskspråkiga Wikipedia
Noter
Embryologi | swedish | 0.621835 |
twins_with_different_fathers/Father.txt |
A father is the male parent of a child. Besides the paternal bonds of a father to his children, the father may have a parental, legal, and social relationship with the child that carries with it certain rights and obligations. A biological father is the male genetic contributor to the creation of the infant, through sexual intercourse or sperm donation. A biological father may have legal obligations to a child not raised by him, such as an obligation of monetary support. An adoptive father is a man who has become the child's parent through the legal process of adoption. A putative father is a man whose biological relationship to a child is alleged but has not been established. A stepfather is a non-biological male parent married to a child's preexisting parent, and may form a family unit but generally does not have the legal rights and responsibilities of a parent in relation to the child.
The adjective "paternal" refers to a father and comparatively to "maternal" for a mother. The verb "to father" means to procreate or to sire a child from which also derives the noun "fathering". Biological fathers determine the sex of their child through a sperm cell which either contains an X chromosome (female), or Y chromosome (male). Related terms of endearment are dad (dada, daddy), baba, papa, pappa, papasita, (pa, pap) and pop. A male role model that children can look up to is sometimes referred to as a father-figure.
Paternal rights
Stockholm pedestrian sign father and daughter
The paternity rights of a father with regard to his children differ widely from country to country often reflecting the level of involvement and roles expected by that society.
Unlike motherhood, fatherhood is not mentioned in Universal Declaration of Human Rights.
Paternity leave
Parental leave is when a father takes time off to support his newly born or adopted baby. Paid paternity leave first began in Sweden in 1976, and is paid in more than half of European Union countries. In the case of male same-sex couples the law often makes no provision for either one or both fathers to take paternity leave.
Child custody
Fathers' rights movements such as Fathers 4 Justice argue that family courts are biased against fathers.
Child support
Child support is an ongoing periodic payment made by one parent to the other; it is normally paid by the parent who does not have custody.
Paternity fraud
An estimated 2% of British fathers experiences paternity fraud during a non-paternity event, bringing up a child they wrongly believe to be their biological offspring.
Role of the father
Father and child, Dhaka, Bangladesh
In almost all cultures fathers are regarded as secondary caregivers. This perception is slowly changing with more and more fathers becoming primary caregivers, while mothers go to work, or in single parenting situations and male same-sex parenting couples.
Fatherhood in the Western World
A father and his children in Florida
In the West, the image of the married father as the primary wage-earner is changing. The social context of fatherhood plays an important part in the well-being of men and their children. In the United States 16% of single parents were men as of 2013.
Importance of father or father-figure
Involved fathers offer developmentally specific provisions to their children and are impacted themselves by doing so. Active father figures may play a role in reducing behavior and psychological problems in young adults. An increased amount of father–child involvement may help increase a child's social stability, educational achievement, and their potential to have a solid marriage as an adult. Their children may also be more curious about the world around them and develop greater problem solving skills. Children who were raised with fathers perceive themselves to be more cognitively and physically competent than their peers without a father. Mothers raising children together with a father reported less severe disputes with their child.
The father-figure is not always a child's biological father and some children will have a biological father as well as a step- or nurturing father. When a child is conceived through sperm donation, the donor will be the "biological father" of the child.
Fatherhood as legitimate identity can be dependent on domestic factors and behaviors. For example, a study of the relationship between fathers, their sons, and home computers found that the construction of fatherhood and masculinity required that fathers display computer expertise.
Determination of parenthood
Paternal love (1803) by Nanette Rosenzweig, National Museum in Warsaw
Roman law defined fatherhood as "Mater semper certa; pater est quem nuptiae demonstrant" ("The [identity of the] mother is always certain; the father is whom the marriage vows indicate"). The recent emergence of accurate scientific testing, particularly DNA testing, has resulted in the family law relating to fatherhood experiencing rapid changes.
History of fatherhood
Painter Carl Larsson playing with his laughing daughter Brita
Many male animals do not participate in the rearing of their young. The development of human men as creatures which are involved in their offspring's upbringing took place during the stone age.
In medieval and most of modern European history, caring for children was predominantly the domain of mothers, whereas fathers in many societies provide for the family as a whole. Since the 1950s, social scientists and feminists have increasingly challenged gender roles in Western countries, including that of the male breadwinner. Policies are increasingly targeting fatherhood as a tool of changing gender relations. Research from various societies suggest that since the middle of the 20th century fathers have become increasingly involved in the care of their children.
Patricide
In early human history there have been notable instances of patricide. For example:
Tukulti-Ninurta I (r. 1243–1207 B.C.E.), Assyrian king, was killed by his own son after sacking Babylon.
Sennacherib (r. 704–681 B.C.E.), Assyrian king, was killed by two of his sons for his desecration of Babylon.
King Kassapa I (473 to 495 CE) creator of the Sigiriya citadel of ancient Sri Lanka killed his father king Dhatusena for the throne.
Emperor Yang of Sui in Chinese history allegedly killed his father, Emperor Wen of Sui.
Beatrice Cenci, Italian noblewoman who, according to legend, killed her father after he imprisoned and raped her. She was condemned and beheaded for the crime along with her brother and her stepmother in 1599.
Lizzie Borden (1860–1927) allegedly killed her father and her stepmother with an axe in Fall River, Massachusetts, in 1892. She was acquitted, but her innocence is still disputed.
Iyasus I of Ethiopia (1654–1706), one of the great warrior emperors of Ethiopia, was deposed by his son Tekle Haymanot in 1706 and subsequently assassinated.
In more contemporary history there have also been instances of father–offspring conflicts, such as:
Chiyo Aizawa (born 1939) murdered her own father who had been raping her for fifteen years, on October 5, 1968, in Japan. The incident changed the Criminal Code of Japan regarding patricide.
Kip Kinkel (born 1982), an Oregon boy who was convicted of killing his parents at home and two fellow students at school on May 20, 1998.
Sarah Marie Johnson (born 1987), an Idaho girl who was convicted of killing both parents on the morning of September 2, 2003.
Dipendra of Nepal (1971–2001) reportedly massacred much of his family at a royal dinner on June 1, 2001, including his father King Birendra, mother, brother, and sister.
Christopher Porco (born 1983), was convicted on August 10, 2006, of the murder of his father and attempted murder of his mother with an axe.
Terminology
Biological fathers
Paternal bonding between a father and his newborn daughter
Father and son
Emperor Pedro II of Brazil with his daughter Isabel, Princess Imperial, c. 1870. She acted as regent of the Empire of Brazil for three times during her father's absences abroad.
Baby Daddy – A biological father who bears financial responsibility for a child, but with whom the mother has little or no contact.
Birth father – the biological father of a child who, due to adoption or parental separation, does not raise the child or cannot take care of one.
Biological father – or sometimes simply referred to as "Father" is the genetic father of a child.
Posthumous father – father died before children were born (or even conceived in the case of artificial insemination).
Putative father – unwed man whose legal relationship to a child has not been established but who is alleged to be or claims that he may be the biological father of a child.
Sperm donor – an anonymous or known biological father who provides his sperm to be used in artificial insemination or in vitro fertilisation in order to father a child for a third party female. Also used as a slang term meaning "baby daddy".
Surprise father – where the men did not know that there was a child until possibly years afterward
Teenage father/youthful father – Father who is still a teenager.
Non-biological (social and legal relationship)
Adoptive father – the father who has adopted a child
Cuckolded father – where the child is the product of the mother's adulterous relationship
DI Dad – social/legal father of children produced via Donor Insemination (where a donor's sperm were used to impregnate the DI Dad's spouse)
Father-in-law – the father of one's spouse
Foster father – child is raised by a man who is not the biological or adoptive father usually as part of a couple.
Mother's partner – assumption that current partner fills father role
Mother's husband – under some jurisdictions (e.g. in Quebec civil law), if the mother is married to another man, the latter will be defined as the father
Presumed father – Where a presumption of paternity has determined that a man is a child's father regardless of if he actually is or is not the biological father
Social father – where a man takes de facto responsibility for a child, such as caring for one who has been abandoned or orphaned (the child is known as a "child of the family" in English law)
Stepfather – a married non-biological father where the child is from a previous relationship
Fatherhood defined by contact level
Absent father – father who cannot or will not spend time with his child(ren)
Second father – a non-parent whose contact and support is robust enough that near parental bond occurs (often used for older male siblings who significantly aid in raising a child, sometimes for older men who took care of younger friends (only males) who have no families)
Stay-at-home dad – the male equivalent of a housewife with child, where his spouse is breadwinner
Weekend/holiday father – where child(ren) only stay(s) with father on weekends, holidays, etc.
Non-human fatherhood
For some animals, it is the fathers who take care of the young.
Darwin's frog (Rhinoderma darwini) fathers carry eggs in the vocal pouch.
Most male waterfowl are very protective in raising their offspring, sharing scout duties with the female. Examples are the geese, swans, gulls, loons, and a few species of ducks. When the families of most of these waterfowl travel, they usually travel in a line and the fathers are usually the ones guarding the offspring at the end of the line while the mothers lead the way.
The female seahorse (Hippocampus) deposits eggs into the pouch on the male's abdomen. The male releases sperm into the pouch, fertilizing the eggs. The embryos develop within the male's pouch, nourished by their individual yolk sacs.
Male catfish keep their eggs in their mouth, foregoing eating until they hatch.
Male emperor penguins alone incubate their eggs; females do no incubation. Rather than building a nest, each male protects his egg by balancing it on the tops of his feet, enclosed in a special brood pouch. Once the eggs are hatched however, the females will rejoin the family.
Male beavers secure their offspring along with the females during their first few hours of their lives. As the young beavers mature, their fathers will teach them how to search for materials to build and repair their own dams, before they disperse to find their own mates.
Wolf fathers help feed, protect, and play with their pups. In some cases, several generations of wolves live in the pack, giving pups the care of grandparents, aunts/uncles, and siblings, in addition to parents. The father wolf is also the one who does most of the hunting when the females are securing their newborn pups.
Coyotes are monogamous and male coyotes hunt and bring food to their young.
Dolphin fathers help in the care of the young. Newborns are held on the surface of the water by both parents until they are ready to swim on their own.
A number of bird species have active, caring fathers who assist the mothers, such as the waterfowls mentioned above.
Apart from humans, fathers in few primate species care for their young. Those that do are tamarins and marmosets. Particularly strong care is also shown by siamangs where fathers carry infants after their second year. In titi and owl monkeys fathers carry their infants 90% of the time with "titi monkey infants developing a preference for their fathers over their mothers". Silverback gorillas have less role in the families but most of them serve as an extra protecting the families from harm and sometimes approaching enemies to distract them so that his family can escape unnoticed.
Many species, though, display little or no paternal role in caring for offspring. The male leaves the female soon after mating and long before any offspring are born. It is the females who must do all the work of caring for the young.
A male bear leaves the female shortly after mating and will kill and sometimes eat any bear cub he comes across, even if the cub is his. Bear mothers spend much of their cubs' early life protecting them from males. (Many artistic works, such as advertisements and cartoons, depict kindly "papa bears" when this is the exact opposite of reality.)
Domesticated dog fathers show little interest in their offspring, and unlike wolves, are not monogamous with their mates and are thus likely to leave them after mating.
Male lions will tolerate cubs, but only allow them to eat meat from dead prey after they have had their fill. A few are quite cruel towards their young and may hurt or kill them with little provocation. A male who kills another male to take control of his pride will also usually kill any cubs belonging to that competing male. However, it is also the males who are responsible for guarding the pride while the females hunt. However the male lions are the only felines that actually have a role in fatherhood.
Male rabbits generally tolerate kits but unlike the females, they often show little interest in the kits and are known to play rough with their offspring when they are mature, especially towards their sons. This behaviour may also be part of an instinct to drive the young males away to prevent incest matings between the siblings. The females will eventually disperse from the warren as soon as they mature but the father does not drive them off like he normally does to the males.
Horse stallions and pig boars have little to no role in parenting, nor are they monogamous with their mates. They will tolerate young to a certain extent, but due to their aggressive male nature, they are generally annoyed by the energetic exuberance of the young, and may hurt or even kill the young. Thus, stud stallions and boars are not kept in the same pen as their young or other females.
Finally, in some species neither the father nor the mother provides any care.
This is true for most insects, reptiles, and fish.
See also
Father complex
Fathers' rights movement
Paternal age effect
Paternal bond
Putative father
Putative father registry
Responsible fatherhood
Shared Earning/Shared Parenting Marriage
Sociology of fatherhood
"Father" can also refer metaphorically to a person who is considered the founder of a body of knowledge or of an institution. In such context the meaning of "father" is similar to that of "founder". See List of persons considered father or mother of a field.
Further reading
Elizabeth Preston (27 Jun 2021). "The riddle of how humans evolved to have fathers". Knowable Magazine / BBC.com. | biology | 1474615 | https://sv.wikipedia.org/wiki/P%C3%A4rlor%20till%20pappa | Pärlor till pappa | Pärlor till pappa är en bilderbok skriven av Maud Mangold, illustrationer av Sassa Buregren.
Handling
Boken handlar om teddybjörnen Sonja som har en pappa som sitter i fängelse. Boken tar upp de funderingar som ett litet barn kan ha om en förälder som sitter frihetsberövad. Maud Mangold är utbildad psykolog och skriver insiktsfullt om det lilla barnets frågor.
Boken tilldelades Nils Holgersson-plaketten 2009.
Referenser
Noter
Källor
Svenska barnböcker | swedish | 0.841391 |
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Issue Cover
Volume 40Issue 9
September 2017
Article Contents
Abstract
INTRODUCTION
METHODS
RESULTS
DISCUSSION
SUPPLEMENTARY MATERIAL
THIS STUDY WAS UNDERTAKEN AT
DISCLOSURE STATEMENT
ACKNOWLEDGMENTS
REFERENCES
Author notes
Supplementary data
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JOURNAL ARTICLE
Sleep Stage Transition Dynamics Reveal Specific Stage 2 Vulnerability in Insomnia
Yishul Wei, MSc, Michele A Colombo, MSc, Jennifer R Ramautar, PhD, Tessa F Blanken, MSc, Ysbrand D van der Werf, PhD, Kai Spiegelhalder, MD, PhD, Bernd Feige, PhD, Dieter Riemann, PhD, Eus J W Van Someren, PhD Author Notes
Sleep, Volume 40, Issue 9, September 2017, zsx117, https://doi.org/10.1093/sleep/zsx117
Published: 05 July 2017
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Abstract
Study Objectives
Objective sleep impairments in insomnia disorder (ID) are insufficiently understood. The present study evaluated whether whole-night sleep stage dynamics derived from polysomnography (PSG) differ between people with ID and matched controls and whether sleep stage dynamic features discriminate them better than conventional sleep parameters.
Methods
Eighty-eight participants aged 21–70 years, including 46 with ID and 42 age- and sex-matched controls without sleep complaints, were recruited through www.sleepregistry.nl and completed two nights of laboratory PSG. Data of 100 people with ID and 100 age- and sex-matched controls from a previously reported study were used to validate the generalizability of findings. The second night was used to obtain, in addition to conventional sleep parameters, probabilities of transitions between stages and bout duration distributions of each stage. Group differences were evaluated with nonparametric tests.
Results
People with ID showed higher empirical probabilities to transition from stage N2 to the lighter sleep stage N1 or wakefulness and a faster decaying stage N2 bout survival function. The increased transition probability from stage N2 to stage N1 discriminated people with ID better than any of their deviations in conventional sleep parameters, including less total sleep time, less sleep efficiency, more stage N1, and more wake after sleep onset. Moreover, adding this transition probability significantly improved the discriminating power of a multiple logistic regression model based on conventional sleep parameters.
Conclusions
Quantification of sleep stage dynamics revealed a particular vulnerability of stage N2 in insomnia. The feature characterizes insomnia better than—and independently of—any conventional sleep parameter.
insomnia disorder, sleep stage, sleep architecture, polysomnography, sleep fragmentation, non-REM sleep, hypnogram, Markov chain, feature selection, binary classification
Topic: sleep stageswakefulnesssleepinsomniaemotional vulnerability
Issue Section: Insomnia and Psychiatric Disorders
INTRODUCTION
Insomnia disorder (ID) is defined as a persistent complaint of difficulty initiating sleep, difficulty maintaining sleep, or early morning awakening, which subjectively impacts daytime functioning, occurs at least three times a week for a minimum of 3 months, and cannot be attributed directly to other coexisting medical conditions or to environmental or time constraints on sleep.1 Current clinical or research diagnostic criteria for ID are based solely on subjective reports.2–4 Although different dysregulated patterns of objective, polysomnographically assessed sleep have been hypothesized over the past decades to underlie the self-reported impairments,5–8 most polysomnography (PSG) studies could find only modest differences between people with ID and controls.9,10 According to a recent meta-analysis,10 the most consistently observed PSG alterations in ID across studies are: shorter total sleep time (TST), longer sleep onset latency (SOL) and wake after sleep onset (WASO), lower sleep efficiency (SE), an increased number of awakenings (NWake), and a reduced amount of slow wave sleep (SWS). The duration of rapid eye movement (REM) sleep did not differ significantly between people with ID and controls, when the meta-analysis was performed on studies that used only self-reported criteria for participant selection.10 These sleep parameters, however, do not fully utilize the information present in the polysomnogram and leave many important questions open. For example: Is the reduced time spent in SWS due to difficulties entering deep sleep or rather because SWS in ID is unstable and rapidly switches to lighter sleep or wakefulness? Several novel methodologies have recently been proposed to extract information about sleep dynamics.11 Among those methods, analyses of the transition probabilities between sleep stages, and of the duration distributions of sleep and wake bouts, can be readily applied to scored PSG without much additional processing. Thus, findings from such analyses may be followed up relatively easily using data that are collected routinely in clinical practice and are available in existing databases. Furthermore, as several independent studies have demonstrated,12–17 indices of clinical relevance can be derived from these analyses in other sleep-related conditions such as sleep-disordered breathing, providing more sensitive measures of pathological sleep patterns and of responses to interventions than the conventional sleep parameters.
Whereas to the best of our knowledge, sleep stage dynamics have not previously been investigated in ID, two studies have reported on the overall dynamics between sleep and wakefulness. One study18 showed that people with ID, in addition to having more frequent and longer nocturnal awakenings, wake from light sleep stages (non-REM sleep stages 1 and 2) significantly more often than healthy controls do. A recent study19 with a larger sample size again showed prolonged awakenings and also reported significantly shorter uninterrupted sleep bouts in people with ID than in healthy controls. Whereas the focus of these studies was on overall sleep (dis)continuity, we considered that the bout durations of individual sleep stages, as well as the transition probabilities between the stages, could aid to determine the key features of disturbed sleep in ID. In the present study, we therefore systematically investigated the transition probabilities and bout durations across all stages and evaluated how well these features discriminate people with ID from matched controls (CTRL) without sleep complaints, relative to the conventional PSG summary measures.
METHODS
Participants
The study was approved by the ethics committee of the VU University Medical Center, Amsterdam, The Netherlands. Participants were recruited through advertisement and the Sleep Registry20 and were screened by telephone followed by a face-to-face structured interview with a sleep specialist (MSc in psychology and certified clinical psychologist, specialized in Cognitive Behavioral Therapy for Insomnia). Screening also included the Insomnia Severity Index (ISI).21 All participants provided written informed consent. The inclusion criteria for the ID group (n = 46, age range 23–69 years) conformed to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition,2 International Classification of Sleep Disorders, Third Edition,3 and Research Diagnostic Criteria4 for Insomnia Disorder. The control group included age- and sex-matched volunteers (n = 42, age range 22–70 years) that reported to have no sleep difficulties during telephone screening and the face-to-face interview and were further confirmed by an ISI score less than 8. Exclusion criteria for all participants were: (1) diagnosed sleep apnea, restless legs syndrome, narcolepsy, or other somatic, neurological, or psychiatric disorders; (2) use of sleep medications within the last 2 months up to and including the recording days; (3) overt shifted or irregular sleep–wake rhythms, assessed using 1 week of actigraphy (Actiwatch AW4, Cambridge Neurotechnology Ltd., Cambridge, United Kingdom or GENEActiv Sleep, Activinsights Ltd., Kimbolton, United Kingdom) supplemented by sleep diaries. Additionally, data from participants showing signs of sleep apnea or restless legs during laboratory PSG assessments were excluded from analyses. Table 1 summarizes the demographic characteristics of the included participants and their self-reported sleep as assessed by the ISI and the 7-day sleep diary.
Table 1Demographics and Self-Reported Sleep (Mean ± Standard Deviation of the Amsterdam Sample).
Characteristic Control (n = 42) Insomnia disorder (n = 46) p
Age, years 46.9 ± 14.6 50.3 ± 13.6 .32
Sex, female/male 32/10 38/8 .60
ISI 1.93 ± 1.91 16.32 ± 4.26 <.0001
Sleep diary
Time in Bed, min 509.3 ± 50.2 522.1 ± 66.5 .36
TST, min 436.5 ± 34.5 339.1 ± 65.5 <.0001
SOL, min 13.3 ± 6.9 39.8 ± 42.8 <.0001
SE, % 90.3 ± 4.5 68.8 ± 14.7 <.0001
NWake 1.7 ± 0.9 2.6 ± 1.6 .003
WASO, min 33.1 ± 19.5 113.6 ± 69.8 <.0001
Sleep quality 3.9 ± 0.4 2.8 ± 0.6 <.0001
Restedness 3.8 ± 0.5 2.3 ± 0.7 <.0001
ISI = Insomnia Severity Index; NWake = number of awakenings; SOL = sleep onset latency; SE = sleep efficiency; TST = total sleep time; WASO = wake after sleep onset.
Sleep diary was kept for 7 days prior to laboratory visit. In addition to self-reported sleep timing estimates, the diary includes five-point Likert items for sleep quality (1: very poor to 5: very good) and restedness (1: not at all rested to 5: very well rested). p-values are determined by Fisher exact test for sex and by Wilcoxon rank-sum tests for the other variables.
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Protocol
People with ID and matched controls completed two consecutive nights of PSG in a laboratory setting. On the recording days, participants were asked to refrain from alcohol and drugs, as well as to limit consumption of caffeinated beverages to a maximum of two cups, which were allowed only before noon. PSG was performed using a 256-channel LTM HydroCel Geodesic Sensor Net and a Polygraphic Input Box (Electrical Geodesic Inc., Eugene, Oregon, United States), connected to a Net Amps 300 amplifier (input impedance: 200 MΩ, A/D converter: 24 bits). The lights-out time for each participant was adaptively chosen according to individual habitual bedtime and did not significantly differ between the two groups (mean ± standard deviation: ID = 23:27 ± 0:37, CTRL = 23:28 ± 0:45 hours, p = .69).
Scoring of Sleep Recordings
All sleep recordings were visually scored offline by an experienced scorer (JRR) blind to the participants’ group classification. Interscorer agreement in our lab generally lies between 0.67 and 0.80 (mean = 0.72 and 0.76 for ID and CTRL, respectively) in terms of Cohen’s kappa, that is, within the range of those reported in the literature.22 Scoring of sleep stages was based on signals obtained from six electroencephalogram leads (electrode # 36, 224, 72, 173, 116, 150 of the HydroCel Geodesic Sensor Net, approximately equivalent to F3, F4, C3, C4, O1, O2, respectively, in the 10–20 system) and two electrooculogram leads (1 cm below the left and above the right outer canthi) referenced to linked mastoids and one bipolar chin electromyogram channel. Each 30-second epoch was scored as one of stages W, N1, N2, N3, or R, according to the American Academy of Sleep Medicine (AASM) manual.23 The first night served as an adaption night, and data from the second night were used for analyses.
Conventional PSG Sleep Parameters
Analyses of sleep parameters and sleep stage dynamics were done using custom scripts written in MATLAB 8.3 (The Mathworks Inc., Natick, Massachusetts, United States). TST, SOL, SE, NWake, and time and percentage of each sleep stage including WASO were calculated for comparison with previously published results.10 The operational definitions of these parameters adhered to standard clinical guidelines.23,24 In particular, sleep onset was defined as the first epoch of any sleep stage, including stage N1. Additionally, the stage shift index (SSI), defined as the number of transitions between distinct stages per hour, was quantified as an index of overall sleep fragmentation.24,25
Sleep Stage Transition Probabilities
To quantify sleep stage dynamics, we assessed the empirical probabilities of transitions between the stages including wakefulness, as well as the group-level bout duration distributions for each stage. Sleep stage dynamics were analyzed for the period between sleep onset and the final awakening.
The (Markovian) transition probability,
is defined for each pair of stages—including the “transition” from one stage to the same stage—as the conditional probability of an epoch being in one stage
given the stage
of the immediately preceding epoch. Empirically,
can be estimated by the observed proportion of epochs of stage
that were immediately followed by an epoch of stage
(where
and
can be the same stage); that is, the number of epochs which were scored as stage
and immediately followed an epoch of stage
divided by the total number of epochs scored as stage
The empirical transition probabilities between all pairs of stages were calculated for each participant separately.
Sleep Stage Bout Duration Distributions
Group-level bout duration distributions, first for sleep and wakefulness and subsequently for each separate sleep stage, were assessed with survival-analytical techniques, similar to those carried out in previous studies on sleep–wake transition patterns.26–29 To first investigate overall sleep versus wake bouts as previously reported, we defined sleep bouts as consecutive epochs scored as stages N1, N2, N3, or R and wake bouts as consecutive epochs scored as stage W. Next, at a more fine-grained level, we extracted bouts of individual sleep stages, that is, consecutive epochs scored as the same sleep stage. For all bout categories (sleep, wake, individual sleep stages), nonparametric recurrent event survival analysis30 was used to estimate the bout duration distribution of each group. This yielded the survival function which gives, for each observed duration, the probability that a bout spans longer than that duration, while taking into account the fact that multiple bouts were observed from each participant.
Statistical Analyses of Group Differences
Group differences in the conventional sleep parameters were evaluated with Wilcoxon rank-sum tests. The rank-sum statistic W (also known as the Mann–Whitney U statistic), is mathematically equal to the product of group sizes
times the area under the receiver operating characteristic curve.31 Thus, the absolute deviation of W from
provides a direct measure of the discriminating power of each parameter.
For empirical transition probabilities, no formal statistical tests were performed for rare stage transitions which occurred in fewer than half of the participants in each group (ie, in fewer than 23 people with insomnia and fewer than 21 controls). The remaining values in the transition probability matrices were compared between the two groups by means of element-wise Wilcoxon rank-sum tests. To account for multiple comparisons, we applied Benjamini–Hochberg false discovery rate (FDR) correction and report group differences at a significance level of corrected p < .05 and at a trend level of corrected p < .10.
For bout duration distributions, the within-group confidence intervals of the survival functions were estimated through a bootstrap approach.32 Group differences in the survival probabilities were determined by means of permutation Mann–Whitney tests.33 For both bootstrap and permutation, resampling was done over 10,000 randomization iterations at the participant level, so that the within-participants bout recurrence information was preserved in every iteration.
Evaluation of Discriminating Power of Conventional and Novel Features With Logistic Regression
Separate logistic regression analyses were used to estimate the odds ratio (OR) of having ID per unit change in each parameter that showed a significant group difference in the above between-group comparison, adjusted for age and sex. Regression coefficients ± two standard errors were exponentiated to obtain ORs and their 95% confidence intervals. The relative importance of each sleep parameter in ID–CTRL discrimination was further investigated using forward stepwise logistic regression. The procedure started with a model including only age and sex covariates and in a stepwise fashion added the independent variable that increased the model fit the most, until no feature could further increase the model fit significantly as assessed by chi-squared likelihood ratio tests.
To evaluate whether the novel sleep stage dynamic features added ID–CTRL discriminating power to the information available in all possible combinations of the conventional sleep parameters, we moreover performed a chi-squared likelihood ratio test comparing two nested multiple logistic regression models: One included as independent variables age, sex, and the conventional sleep parameters showing significant group differences, and the other in addition included the single best discriminating bout duration or transition probability feature. All logistic regression analyses were performed in R.34
Validation of Generalizability
Validation of generalizability was pursued using sleep stage data of 100 people with ID and 100 healthy controls from a published investigation35 undertaken at the Freiburg University Medical Center, Freiburg, Germany. Both ID and CTRL groups consisted of 46 males and 54 females and the ages (mean ± standard deviation) were 42.6 ± 12.5 years for ID and 41.1 ± 14.0 years for CTRL. Thus, the mean age of the Freiburg sample was lower than that of the Amsterdam sample (Student t-tests: p = .002 and .03 for ID and CTRL, respectively), and the sex distribution was more balanced (Fisher exact tests: p = .001 and .01 for ID and CTRL, respectively). Details about the participants’ conventional PSG sleep parameters were given in the previous publication.35 For both samples, sleep stage data were obtained from the second night of a two-night protocol, and PSG scoring was both done in 30-second epochs. However, one major difference regarding sleep scoring was that the Freiburg data were scored based on the Rechtschaffen–Kales criteria,36 while the Amsterdam data were scored according to the AASM manual.23
Sleep stage data from the Freiburg validation sample were first automatically preprocessed by (1) merging stages 3 and 4 according to the Rechtschaffen–Kales criteria into a single stage to approximate stage N3 according to the AASM criteria; and (2) converting epochs scored as movement time according to the Rechtschaffen–Kales criteria either to stage W if the preceding epoch was scored as stage W or to the same stage as that of the following epoch otherwise, in accordance with the “major body movement” rules in the AASM manual. Thereafter, the conventional sleep parameters, empirical transition probabilities, and sleep stage bout durations were extracted using the same procedure as described above. Between-group comparisons of transition probabilities and logistic regression analyses as described above were repeated on the Freiburg data.
RESULTS
Table 2 summarizes the means and standard deviations of all conventional PSG sleep parameters for cases and controls in the Amsterdam sample, as well as the Wilcoxon rank-sum statistics and corresponding significance of group differences. As compared to CTRL, people with ID had significantly less TST, lower SE, a higher NWake and SSI, more WASO and stage N1 (expressed in either minutes or percentages), and less stage N3 (expressed in minutes).
Table 2Conventional Polysomnographic Sleep Parameters (Mean ± Standard Deviation of the Amsterdam Sample).
Sleep parameter Control
(n = 42) Insomnia disorder
(n = 46) Wilcoxon rank-sum statistic W Z p
TRT, minutes 481.4 ± 49.1 479.9 ± 57.3 879 –0.72 .47
TST, minutes 431.0 ± 51.2 408.0 ± 54.5 693 –2.28 .02
SOL, minutes 20.9 ± 21.7 17.3 ± 17.0 905 –0.51 .61
SE, % 89.7 ± 7.2 85.5 ± 9.2 671 –2.46 .01
NWake 18.5 ± 10.0 23.7 ± 11.8 1254.5 2.41 .02
SSI, 1/hour 10.2 ± 2.8 11.9 ± 3.3 1248 2.35 .02
WASO, minutes 29.0 ± 21.1 52.6 ± 42.8 1308 2.85 .004
Stage N1, minutes 20.4 ± 12.1 35.8 ± 23.3 1342 3.14 .002
Stage N2, minutes 186.8 ± 49.2 175.0 ± 53.8 812 –1.28 .20
Stage N3, minutes 113.9 ± 42.1 95.1 ± 52.7 697 –2.24 .02
Stage R, minutes 109.8 ± 37.1 102.1 ± 57.7 819.5 –1.22 .22
WASO, % 6.4 ± 4.7 11.1 ± 8.4 1312 2.89 .004
Stage N1, % 4.8 ± 2.9 8.9 ± 6.0 1388 3.52 .0004
Stage N2, % 43.4 ± 10.6 43.1 ± 12.6 933 –0.27 .79
Stage N3, % 26.5 ± 9.7 23.4 ± 12.2 809.5 –1.30 .19
Stage R, % 25.2 ± 7.0 24.5 ± 12.6 874 –0.76 .44
NWake = number of awakenings; SE = sleep efficiency; SOL = sleep onset latency; SSI = stage shift index; TRT = total recording time; TST = total sleep time; WASO = wake after sleep onset.
WASO percentage is relative to TRT–SOL. Sleep stage percentages are relative to TST. Bold font highlights significant group differences.
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Table 3 presents the means and standard deviations of the empirical transition probabilities for cases and controls in the Amsterdam sample. Wilcoxon rank-sum tests on the transition probabilities revealed that, as compared to CTRL, people suffering from ID had a significantly higher probability to transition from stage N2 to stage N1 (Wilcoxon W = 1408, Z = 3.70, p = .004, FDR corrected), and a trend-level higher probability to transition from stage N2 to stage W (Wilcoxon W = 1276.5, Z = 2.59, p = .096, FDR corrected). Figure 1 illustrates these differences on a Markovian state diagram.
Table 3Empirical Transition Probabilities Between Sleep Stages, Expressed as Percentage (Mean ± Standard Deviation of the Amsterdam Sample) of Epochs of the Stage Indicated at the Left Side of Each Row That Transition to Epochs of the Stage Indicated at the Top of Each Column.
a. Control (n = 42).
Transition probability Pij, expressed in % to stage …
W N1 N2 N3 R
Transition from stage … W 53.12 ± 24.06 24.68 ± 16.08 16.08 ± 16.66 0.43 ± 1.38 5.69 ± 8.86
N1 8.52 ± 6.30 54.40 ± 17.54 28.01 ± 14.83 0 9.06 ± 9.13
N2 1.75 ± 1.31 0.64 ± 0.65 93.22 ± 2.11 2.06 ± 1.18 2.33 ± 1.13
N3 1.16 ± 0.88 0.15 ± 0.28 1.65 ± 1.20 96.76 ± 1.11 0.28 ± 0.37
R 2.99 ± 2.29 1.29 ± 1.09 2.41 ± 1.57 0.01 ± 0.08 93.29 ± 3.01
b. Insomnia disorder (n = 46).
Transition probability Pij, expressed in % to stage …
W N1 N2 N3 R
Transition from stage … W 58.35 ± 24.69 24.97 ± 16.06 10.26 ± 10.25 0.31 ± 1.82 6.11 ± 9.78
N1 10.45 ± 7.72 59.89 ± 16.32 24.57 ± 14.17 0 5.09 ± 6.27
N2 2.34 ± 1.24 1.46 ± 1.19 92.05 ± 3.20 2.00 ± 1.89 2.16 ± 1.63
N3 1.35 ± 1.34 0.17 ± 0.32 1.89 ± 1.76 96.36 ± 2.61 0.23 ± 0.57
R 3.77 ± 7.15 2.75 ± 7.56 2.56 ± 2.05 0.01 ± 0.05 90.91 ± 14.28
Bold font highlights significant and trend-level group differences after false discovery rate correction (see text for test statistics).
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Figure 1
Markovian state diagram for sleep stage transitions. Red arrows indicate transitions with higher probabilities in people with insomnia disorder than in controls: from stage N2 to stage N1 (Wilcoxon W = 1408, Z = 3.70, p = .004) and from stage N2 to stage W (Wilcoxon W = 1276.5, Z = 2.59, p = .096). Gray arrows indicate transitions with no significant differences in transition probabilities between the groups (.11 < p < .98). The following transitions did not occur in at least half of the participants in each group and are not visualized: from stage W to stage N3, from stage N1 to stage N3, from stage R to stage N3, from stage N3 to stage N1, and from stage N3 to stage R. (All p-values are false discovery rate corrected.).
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Markovian state diagram for sleep stage transitions. Red arrows indicate transitions with higher probabilities in people with insomnia disorder than in controls: from stage N2 to stage N1 (Wilcoxon W = 1408, Z = 3.70, p = .004) and from stage N2 to stage W (Wilcoxon W = 1276.5, Z = 2.59, p = .096). Gray arrows indicate transitions with no significant differences in transition probabilities between the groups (.11 < p < .98). The following transitions did not occur in at least half of the participants in each group and are not visualized: from stage W to stage N3, from stage N1 to stage N3, from stage R to stage N3, from stage N3 to stage N1, and from stage N3 to stage R. (All p-values are false discovery rate corrected.).
Figure 2 shows the estimated bout survival functions for sleep, wakefulness, and individual sleep stages in ID and CTRL along with their 90% bootstrap confidence intervals. Previously reported scaling behaviors of sleep and wake bouts26,37 could be replicated in both groups: sleep bout survival curves appear almost linear on the semilogarithmic scale, whereas wake bout survival curves take convex shapes. However, the precise parametric form of the bout survival functions has been a subject of debate in the literature.12,15,16,26 Thus, in the current study, we avoided explicitly modeling the bout survival functions with parametric methods and instead tested the between-group differences in bout duration distributions without assumptions using nonparametric procedures. Permutation Mann–Whitney tests33 revealed that, as compared to CTRL, people with ID exhibited a significantly faster decaying sleep bout survival function (p = .009) and a nonsignificantly slower decaying wake bout survival function (p = .07). When bouts of each sleep stage were examined, the between-group difference was significant with respect to the stage N2 bout survival function (p = .02) but not for the other stages (p = .24, p = .16, and p = .28 for stage N1, stage N3, and stage R, respectively).
Figure 2
Estimated bout survival functions of various bout types in people with insomnia disorder (ID) and controls (CTRL). Data are shown on the semilogarithmic scale. The shaded areas indicate 90% within-group bootstrap confidence intervals. The distributions of sleep bout and stage N2 bout durations significantly differ between ID and CTRL (p = .009 and p = .02, respectively, permutation Mann–Whitney tests).
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Estimated bout survival functions of various bout types in people with insomnia disorder (ID) and controls (CTRL). Data are shown on the semilogarithmic scale. The shaded areas indicate 90% within-group bootstrap confidence intervals. The distributions of sleep bout and stage N2 bout durations significantly differ between ID and CTRL (p = .009 and p = .02, respectively, permutation Mann–Whitney tests).
The rank-sum statistics in the above between-group analyses suggest that the transition probability from stage N2 to stage N1 had the largest discriminating power among all examined features, although that of the best discriminative conventional sleep parameter, stage N1 percentage, was only slightly lower. It is worth noting that the two features were only moderately correlated: A Spearman correlation coefficient of 0.58 indicates that about two-thirds of their variance was independent. The second and third columns of Table 4 list the age- and sex-adjusted ORs of having ID and the associated 95% confidence intervals obtained via logistic regression, along with the corresponding p values. A forward stepwise search with sequential chi-squared likelihood ratio tests, starting with age and sex covariates, selected the transition probability from stage N2 to stage N1 in the first step ( χ2(1) = 17.78, p = 2 × 10–5), WASO in the second step (χ2(1) = 10.58, p = .001), and found no other sleep parameters which further increased the model fit significantly, thus affirming the relative importance of the transition probability from stage N2 to stage N1 over the other sleep parameters in ID–CTRL discrimination.
Table 4Age- and Sex-Adjusted Odds Ratio for a Diagnosis of Insomnia Disorder Per Unit Increase in Each Sleep Parameter.
Sleep parameter Amsterdam sample (N = 88) Validation (Freiburg) sample (N = 200)
Adjusted OR; 95% CI p Adjusted OR; 95% CI p
TST, minutes 0.990; [0.981, 0.999] .03 0.986; [0.979, 0.994] .0006
SE, % 0.935; [0.879, 0.994] .03 0.933; [0.896, 0.971] .0007
NWake 1.046; [1.002, 1.092] .04 1.036; [1.007, 1.066] .02
SSI, 1/hour 1.215; [1.043, 1.416] .01 1.047; [0.985, 1.112] .14
WASO, minutes 1.027; [1.008, 1.045] .004 1.015; [1.006, 1.025] .0008
Stage N1, minutes 1.052; [1.020, 1.085] .001 1.009; [0.991, 1.027] .32
Stage N3, minutes 0.990; [0.981, 1.000] .06 0.992; [0.981, 1.003] .16
Stage R, minutes 0.997; [0.988, 1.006] .49 0.975; [0.962, 0.988] .0002
WASO, % 1.136; [1.043, 1.238] .003 1.077; [1.033, 1.124] .0005
Stage N1, % 1.263; [1.102, 1.448] .0008 1.078; [1.004, 1.157] .04
Stage R, % 0.995; [0.954, 1.037] .80 0.913; [0.856, 0.973] .005
Transition probability from stage N2 to stage N1, % 3.522; [1.704, 7.281] .0007 1.243; [1.069, 1.444] .005
Transition probability from stage N2 to stage W, % 1.471; [1.023, 2.115] .04 1.334; [1.038, 1.715] .02
Transition probability from stage R to stage W, % 1.030; [0.930, 1.142] .57 1.258; [1.083, 1.462] .003
Transition probability from stage W to stage W, % 1.008; [0.990, 1.027] .39 1.034; [1.018, 1.051] <.0001
Transition probability from stage W to stage N1, % 0.999; [0.972, 1.026] .92 0.962; [0.941, 0.983] .0004
Mean sleep bout duration, minutes 0.955; [0.921, 0.989] .01 0.964; [0.944, 0.985] .0007
Mean wake bout duration, minutes 1.304; [0.912, 1.865] .15 1.276; [1.048, 1.555] .02
Mean stage N2 bout duration, minutes 0.793; [0.650, 0.968] .02 0.874; [0.766, 0.999] .05
CI = confidence interval; NWake = number of awakenings; OR = odds ratio; SE = sleep efficiency; SSI = stage shift index; TST = total sleep time; WASO = wake after sleep onset.
WASO percentage is relative to TRT–SOL. Stage N1/R percentages are relative to TST. Bold font highlights significant adjusted odds ratios.
The table shows only features that reached significance in between-group comparisons in at least one of the samples from Amsterdam and Freiburg.
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To formally evaluate the added value of quantifying whole-night sleep stage dynamics in addition to conventional sleep parameters for discriminating cases from controls, two nested multiple logistic regression models were compared using a chi-squared likelihood ratio test. The first model included as independent variables age, sex, and the conventional sleep parameters showing significant group differences; the second also included the transition probability from stage N2 to stage N1 as an additional independent variable. The second model fitted the data significantly better (χ2(1) = 5.48, p = .02), confirming that the transition probability from stage N2 to stage N1 indeed added discriminating power on top of the information available in all possible combinations of the conventional PSG sleep parameters.
The empirical transition probabilities and their comparisons between cases and controls in the Freiburg validation sample are detailed in the Supplementary Material. The two rightmost columns of Table 4 show the age- and sex-adjusted ORs of having ID in the Freiburg validation sample and the corresponding p values. Of note, all features show the same directions of increased/decreased odds across the Amsterdam and Freiburg samples. Differences between the samples are however observed regarding the magnitudes of the effects (and statistical significance). Considering conventional sleep parameters, reduction of stage R in people with ID was more pronounced in the Freiburg validation sample. Stage N1 duration and the SSI did not significantly discriminate between cases and controls in the Freiburg validation sample, whereas they did in the Amsterdam sample.
With respect to features describing sleep stage dynamics, the transition probabilities from stages W, R, and N2 to stage W significantly increased, and the transition probability from stage W to stage N1 significantly decreased, in cases as compared to controls in the Freiburg validation sample, signifying a tendency to wake from sleep and difficulty reinitiating sleep in people with ID. On the other hand, an increased transition probability from stage N2 to stage N1 and a shortened mean stage N2 bout duration also significantly discriminated cases from controls, thus confirming stage N2 vulnerability in ID which we found in the Amsterdam sample. Forward stepwise logistic regression carried out on the Freiburg validation data selected the transition probability from stage W to stage W in the first step ( χ2(1) = 19.01, p = 1 × 10–5), the transition probability from stage R to stage W in the second step ( χ2(1) = 9.17, p = .002), the transition probability from stage N2 to stage N1 in the third step ( χ2(1) = 6.86, p = .008), and found no other sleep parameters which further increased the model fit significantly. Therefore, the transition probability from stage N2 to stage N1 was consistently among the most important features in ID–CTRL discrimination across samples.
Finally, we also evaluated in the Freiburg validation sample whether the novel sleep stage dynamic features added discriminating power to the information available in all possible combinations of the conventional sleep parameters. We found that three transition probabilities significantly improved the model fit on top of age, sex, and the conventional sleep parameters showing significant group differences: from stage W to stage W (χ2(1) = 7.37, p = .007), from stage N2 to stage N1 (χ2(1) = 5.23, p = .02), and from stage W to stage N1 (χ2(1) = 4.51, p = .03). Intriguingly, the transition probability from stage R to stage W did not increase the model fit significantly on top of the conventional PSG sleep parameters (χ2(1) = 2.07, p = .15). In other words, despite the relative importance of the transition probability from stage R to stage W over any single conventional sleep parameter in discriminating cases from controls in the Freiburg sample as indicated by forward stepwise regression, its discriminating power could be compensated by combination of multiple conventional sleep parameters.
DISCUSSION
The current study is, to our knowledge, the first to analyze and compare the whole-night sleep stage dynamics of people with ID and healthy controls. We found that people with ID have a higher probability for stage N2 bouts to terminate early and to transition from stage N2 to stage N1 or wakefulness. Notably, even though people with ID show less SWS, they do not show significantly altered survival probabilities of stage N3 bouts nor altered transition probabilities from stage N3. These findings indicate that people with ID have a relatively normal tendency to remain in stage N3, once they reach this stage. Finally, logistic regression analyses showed not only that people with ID are best distinguishable from healthy controls in terms of the transition probability from stage N2 to stage N1 but also that including this transition probability can significantly improve the goodness of fit of a discriminative model on top of the conventional PSG sleep parameters.
The main findings of the current study could be replicated in an independent validation sample, confirming their generalizability. There are however a few differences regarding sleep architecture between the samples. In particular, reduced REM sleep and an increased transition probability from stage R to stage W in ID were significant in the Freiburg validation sample but not in the Amsterdam sample. Moreover, the higher transition probability from stage N2 to stage N1 in ID stood out more prominently in the Amsterdam sample than in the Freiburg validation sample. The differences may involve the different PSG scoring criteria used for the two samples. In a study comparing the Rechtschaffen–Kales and AASM scoring criteria,38 it was found that the most pronounced differences result from Rule 5.C1.b of the AASM manual, which states that stage N2 terminates upon arousals. This rule led to decreases in stage N2, increases in stage N1, and increases in the number of stage shifts, when the same sleep recordings were scored according to the AASM criteria as compared to the Rechtschaffen–Kales criteria.38,39 It is thus likely that the large effect size of the transition probability from stage N2 to stage N1 observed in the Amsterdam sample involves an elevated number of arousals in people with ID.35,40 Different scoring criteria have also been shown to affect the scoring of REM sleep in young people but not in old people.38,39 The effect of this difference on transition probabilities is uncertain, although we expect it would affect controls more than people with ID given the speculated similarity between ID and aging discussed below. The transition probability from stage R to stage W was indeed significantly smaller in the Freiburg validation sample than in the Amsterdam sample only for CTRL (Wilcoxon W = 1358.5, Z = –3.31, p = .0009) and not for ID (Wilcoxon W = 2260, Z = –0.16, p = .87). REM sleep duration and percentage however did not differ significantly between the samples either for ID or for CTRL (all p > .11).
The current findings about whole-night sleep stage dynamics in ID differ from those found in other sleep disorders such as sleep-disordered breathing.12–17 Studies on sleep-disordered breathing have reported instability of stage N2, REM sleep, and WASO—inferred from faster decaying bout survival functions for these stages14,16,17—while we have here observed a more specific vulnerability of stage N2 in ID.
On the other hand, it is worth noting that the overall sleep patterns of people with ID reported here are comparable to previous findings about the aged population. A series of studies have shown that among normal sleepers without sleep complaints, aging is associated with more stage N1 and less SWS,41,42 shorter sleep bouts,29,43 as well as relatively unstable non-REM sleep29,42 especially during stage N2,42 paralleling the current results about sleep patterns in ID. Aging, however, seems to involve a relative increase in the number of short over long wake periods43—resulting in a steeper decay of the wake bout survival function29—while we have here observed the opposite pattern in ID, albeit only at a trend level. Consistently, prolonged awakenings in people with ID have been reported in other studies.6,18,19 It should nonetheless be noted that the faster decaying wake bout survival function in aged people was only observed when data from a forced desynchrony protocol were pooled; when only data from sleep episodes taking place at the habitual circadian phase were examined, the wake bout survival probabilities of older and younger people did not differ significantly.29 Since the current protocol does not allow to discriminate possibly different contributions of circadian and homeostatic factors, future studies with more elaborate experimental protocols are needed to disentangle their influences on sleep stage dynamics in ID. The similarity between the sleep patterns in ID and those in aging has been noticed in an early study which reported similar cumulative duration of each sleep stage over the night in aged people and in people with ID and concluded that ID might represent “precocious senescence of sleep.”5 This similarity points to a possible overlap between the neural mechanisms underlying the deterioration of sleep quality associated with ID and aging, as confirmed by recent neuroimaging studies. In particular, deficits of the orbitofrontal cortex have been suggested to be involved in self-reported insomnia symptoms44,45 and in sleep fragmentation quantified by actigraphy in aged people.46 The neural mechanisms of age-related changes in sleep patterns from the cellular level up to the systems level have been studied extensively47 and may serve as “roadmaps” for future research on the neurophysiological underpinnings of ID.
Our findings with respect to the conventional sleep parameters are largely congruent with a recent meta-analysis of PSG studies on ID.10 Both the meta-analysis and the current study found reduced TST, reduced SE, increased WASO, an increased NWake, and less SWS in people with ID as compared to controls. The meta-analysis also reported longer SOL in ID. We did not find such a difference; instead, we found significantly more stage N1 in people with ID. The original publication on the Freiburg validation sample35 adopted a different definition of sleep onset (first epoch of stage N2) than that used in the current study and also reported no group difference in SOL. Further analyses confirmed that SOL did not differ between groups in either sample, regardless of the definition of sleep onset (results not shown). Finally, the meta-analysis suggested that REM sleep did not differ between controls and people with ID, when studies that selected participants with self-reported criteria only were considered. Consistently, in the current study, all of our inclusion criteria were based on self reports, and we did not find between-group differences in the amount or percentage of REM sleep (for the Amsterdam sample). REM sleep deficits were significant when the meta-analysis included also studies which selected participants with both self-reported and PSG criteria.10 These studies were nevertheless likely to select patient groups representing only a specific phenotype of ID.48
The current findings suggest that zooming in on the microstructure and phasic components of stage N2 (ie, spindles and K-complexes) may be particularly helpful in elucidating the brain mechanisms of ID. Although previous investigations into these transient components in ID have shown mixed results,49–52 these studies have limitations in that spindles or K-complexes were only scored in one electrode. Possible differences between people with ID and normal sleepers may lie in the topographical distributions of these microstructural events or in the cortical or subcortical responses to them.53,54 Alternatively, the mixed results in the literature may also involve heterogeneous subtypes within ID.55 Interestingly, studies that report alterations in characteristics of spindles or K-complexes in ID during stage N2 usually report no impairments with respect to the conventional PSG sleep parameters,51,52 and vice versa.49,50 This suggests that macrostructural and microstructural parameters might provide complementary insights into ID subtypes. Subtyping ID and characterizing the sleep patterns associated with each subtype is a continuous endeavor of sleep medicine research and may be the key to the future development of effective, targeted treatments for the disorder.55
In conclusion, whole-night sleep stage dynamics reveal a particular stage N2 vulnerability in ID. Quantification of this vulnerability can easily be done using regularly scored PSG recordings. Further investigations of the neurophysiological dynamics during stage N2 may potentially lead to sensitive biomarkers of insomnia susceptibility, severity, or treatment outcome.
SUPPLEMENTARY MATERIAL
Supplementary material is available at SLEEP online.
THIS STUDY WAS UNDERTAKEN AT
Department of Sleep and Cognition, Netherlands Institute for Neuroscience (NIN), Meibergdreef 47, Amsterdam 1105 BA, The Netherlands.
DISCLOSURE STATEMENT
This was not an industry supported study. Research leading to these results has received funding from the Bial Foundation grant 252/12, the Netherlands Organization of Scientific Research (NWO) grant VICI-453.07.001, and the European Research Council Advanced Grant 671084 INSOMNIA. This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. The authors report no biomedical financial interests or potential conflicts of interest.
ACKNOWLEDGMENTS
We thank Yvon Sweere for assisting in recruiting and interviewing the participants and the collective efforts of many people who helped with data acquisition and assessment: Frank van Schalkwijk, Rick Wassing, Wisse van der Meijden, Bart te Lindert, Floor van Oosterhout, Jessica Bruyel, Marije Vermeulen, Kim Dekker, Arjan Miedema, Katerina Nikolakopoulou, Katerina Georgopoulou, Michelle de Haan, Bahar Adibi, Lina Vandermeulen, Josien Visser, Verena Sommer, Oti Kamal, Inger van Steenoven, Brit Giesbertz, Vincent Huson.
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Author notes
Authors Yishul Wei and Michele A. Colombo contributed equally
© Sleep Research Society 2017. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail [email protected].
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| biology | 45731 | https://da.wikipedia.org/wiki/Radiohead | Radiohead | Radiohead er en britisk rockgruppe fra Oxford. Gruppens navn er taget fra sangen "Radio Head" af Talking Heads. Gruppen består af Thom Yorke (sang, guitar og keyboard), Ed O'Brien (guitar og korsang), Jonny Greenwood (guitar og elektronik), Jonny Greenwoods bror, Colin Greenwood (basguitar) og Phil Selway (trommer).
Gruppens musik er inspireret af blandt andre The Smiths, Elvis Costello, Nirvana, Queen, the Pixies, Pink Floyd, Siouxsie and the Banshees, R.E.M., U2, The Beatles og The Rolling Stones.
Gruppens historie og udvikling
Gruppens udtryk er nyere rockmusik ofte præget af langsomme og melodiske numre med elektroniske indfald. Desuden båret af forsanger Thom Yorkes karakteristiske vokal.
Selvom Radiohead normalt ikke bliver kaldt for en popgruppe, blev de i midten af halvfemserne anset for at være en del af britpop-bølgen efter udgivelsen af deres første album Pablo Honey (1993), der således bærer præg af at være guitarbaseret rockmusik i stil med grupper som Oasis, Suede og Blur fra samme tidsperiode.
Efterfølgende har Radiohead dog ændret lydmæssig stil, og deres tredje fulde studiealbum, OK Computer (1997), regnes for gruppens hovedværk. Pladen bærer præg af et mere modent udtryk end de tidligere plader, og skildrer bagsider af det moderne storbyliv som eksempelvis ensomhed, paranoia og konformitet. Lyden udvikledes på denne plade ligeledes i retning af i højere grad at være båret af elektroniske hjælpemidler, loops, samples og lignende på bekostning af den guitarprægede lyd fra de tidligere plader, der træder en smule i baggrunden.
Gruppens næste albums Kid A (2000), og Amnesiac (2001), blev begge indspillet i København i 1999-2000. Man valgte således at dele indspillingerne fra optagelserne i København over to albums. Lyden på disse albums er i endnu højere grad end tidligere præget af elektroniske eksperimenter. Teksterne er desuden i højere grad fragmenterede, usammenhængende og decideret politiske. Gruppen begyndte i denne periode ligeledes i højere grad eksplicit at udtrykke antipati overfor fascisme og politisk ensretning.
Hail To The Thief (2003), er gruppens sjette studiealbum. Mange mener at titlen er en direkte reference til det omdiskuterede amerikanske præsidentvalg i 2000 (gruppen nægter dog dette), selvom den ofte fejlagtig bliver udlagt som gruppens hyldest til internetpirater. Albummet er i højere grad en tilbagevenden til en mere guitarbaseret rocklyd, selvom de elektroniske elementer stadig er en væsentlig faktor i gruppens musikalske udtryk.
Gruppens syvende album udkom den 10. oktober 2007 og har titlen In Rainbows. Albummet blev i første omgang kun udgivet på nettet som download, hvorefter det udkom d. 3. december på fysisk medie. Hvad der er særligt specielt ved denne udgivelse er, at albummet bliver udgivet udenom noget pladeselskab, og derfor bliver solgt til en pris man selv bestemmer. Dette gælder dog naturligvis kun det album som man henter digitalt. Det beløb som man vælger at betale bliver i stedet givet ubeskåret til bandet selv. In Rainbows er blevet omtalt som et ligeså stort mesterværk som gruppens album OK Computer fra 1997.
Radioheads album The King of Limbs udkom i februar 2011 på bandets hjemmeside.
September 2014–2016 var gruppen i studiet for at optage et nyt album, A Moon Shaped Pool.
Sceneulykke
Den 16. juni 2012 til en udsolgt koncert med 40.000 tilskuere til en open-air koncert med Radiohead på Torontos Downsview Park taget på den midlertidige udendørs scene kollapsede, en time inden portene åbnedes for publikum. Radioheads trommetekniker døde og tre andre blev såret. Koncerten blev aflyst som følge af ulykken. Ulykken ødelagde også bandet unikke lysanlæg hvilket tvang dem til at udskyde deres planlagte koncerter de kommende to uger i Europa.
Diskografi
Pablo Honey (1993)
The Bends (1995)
OK Computer (1997)
Kid A (2000)
Amnesiac (2001)
Hail to the Thief (2003)
In Rainbows (2007)
The King of Limbs (2011)
A Moon Shaped Pool (2016)
Koncerter i Danmark
Huset, Århus, 2. juni 1993
Barbue (Nedlagt klub), København, 3. juni 1993
Grøn scene, Roskilde Festival, 2. juli 1994
Roskilde Festival, 13. august 1995 (Opvarmning for Pearl Jam og Neil Young)
Orange Scene, Roskilde Festival, 26. juli 1997
KB Hallen, København, 9. november 1997
Ved Valby Hallen, København, 7. september 2000 (Opvarmning: Sigur Rós)
Ved Valby Hallen, København, 8. september 2000 (Opvarmning: Sigur Rós)
KB Hallen, København, 6. maj 2006 (Opvarmning: Willy Mason)
KB Hallen, København, 7. maj 2006 (Opvarmning: Willy Mason)
Orange Scene, Roskilde Festival, 3. juli 2008
Blue Stage, Northside Festival, 11. juni 2017
Referencer
Eksterne henvisninger
Har spillet på Roskilde Festival
Musikgrupper fra 1985 | danish | 1.078477 |
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Alessandro Silvani
Alessandro Silvani
Department of Biomedical and Neuromotor Sciences, University of Bologna, Italy
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Luigi De Gennaro
Sapienza University of Rome, Italy
Raffaele Manni
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Department of Neurology and Neurorehabilitation, Neurological Institute Foundation Casimiro Mondino (IRCCS), Italy
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Discrepancies in the Time Course of Sleep Stage Dynamics, Electroencephalographic Activity and Heart Rate Variability Over Sleep Cycles in the Adaptation Night in Healthy Young Adults
\r\nAi ShirotaAi Shirota1Mayo KamimuraMayo Kamimura1Akifumi KishiAkifumi Kishi2Hiroyoshi Adachi,Hiroyoshi Adachi3,4Masako Taniike,Masako Taniike3,5Takafumi Kato,,*Takafumi Kato1,3,5*
1Department of Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan
2Graduate School of Education, The University of Tokyo, Bunkyo-ku, Japan
3Osaka University Hospital, Sleep Medicine Center, Suita, Japan
4Osaka University Health and Counseling Center, Toyonaka, Japan
5Department of Child Development, Osaka University United Graduate School of Child Development, Suita, Japan
Objective: The aim of the present study was to characterize the cyclic sleep processes of sleep-stage dynamics, cortical activity, and heart rate variability during sleep in the adaptation night in healthy young adults.
Methods: Seventy-four healthy adults participated in polysomnographic recordings on two consecutive nights. Conventional sleep variables were assessed according to standard criteria. Sleep-stage continuity and dynamics were evaluated by sleep runs and transitions, respectively. These variables were compared between the two nights. Electroencephalographic and cardiac activities were subjected to frequency domain analyses. Cycle-by-cycle analysis was performed for the above variables in 34 subjects with four sleep cycles and compared between the two nights.
Results: Conventional sleep variables reflected lower sleep quality in the adaptation night than in the experimental night. Bouts of stage N1 and stage N2 were shorter, and bouts of stage Wake were longer in the adaptation night than in the experimental night, but there was no difference in stage N3 or stage REM. The normalized transition probability from stage N2 to stage N1 was higher and that from stage N2 to N3 was lower in the adaptation night, whereas that from stage N3 to other stages did not differ between the nights. Cycle-by-cycle analysis revealed that sleep-stage distribution and cortical beta EEG power differed between the two nights in the first sleep cycle. However, the HF amplitude of the heart rate variability was lower over the four sleep cycles in the adaptation night than in the experimental night.
Conclusion: The results suggest the distinct vulnerability of the autonomic adaptation processes within the central nervous system in young healthy subjects while sleeping in a sleep laboratory for the first time.
Introduction
The sleep architecture throughout the night is continuous, but heterogeneous, and characterized by cyclic fluctuations. Alternating non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep constitute a series of sleep cycles, with the latter being related to the sleep cycle configuration (Vyazovskiy and Delogu, 2014). Sleep cycles last for approximately 90 min (Hartmann, 1968) and are repeated 3–5 times in one night (Hartmann, 1968; Hirshkowitz et al., 1992; Rosipal et al., 2013). Mutual interactions between the genesis of NREM and REM sleep underlie the stability of sleep cycles overnight (Kishi et al., 2011; Hayashi et al., 2015). Sleep processes and continuity within one sleep cycle are characterized by dynamic phenomena such as transitions among sleep stages (Lo et al., 2004; Kishi et al., 2008, 2011). Sleep stages are associated with cortical electroencephalography (EEG) and autonomic nervous system activities (Žemaitytė et al., 1984; Toscani et al., 1996; Brandenberger et al., 2001); slow-wave sleep is characterized by high cortical delta power, whereas light NREM sleep and REM sleep are characterized by low delta power (Brandenberger et al., 2001). Reciprocal changes in sympathetic and parasympathetic modulation tone are correlated with the cortical delta power within a sleep cycle (Brandenberger et al., 2001). The ratio of sleep stages and activity levels of cortical and autonomic systems in a sleep cycle gradually change from the initial to late periods of sleep cycles (Dement and Wolpert, 1958; Feinberg, 1974; Brandenberger et al., 2001; Versace et al., 2003). Therefore, the time-course changes in sleep variables over sleep cycles represent the progression of sleep processes in the integration of cortical and autonomic homeostatic sleep regulation overnight (Hayashi et al., 2015).
Previous studies demonstrated that the progression and stability of sleep can be altered when one sleeps in an unfamiliar environment. A typical example is the first-night effect, a phenomenon that is commonly observed in the first night of polysomnographic recordings for the purpose of adaptation to sleep laboratory settings (Agnew et al., 1966). Sleep in the adaptation night is characterized by poorer sleep quality than in subsequent nights due to increased sleep latency, less REM sleep, and frequent arousal (Hirshkowitz et al., 1992; Sforza et al., 2008; Rosipal et al., 2013). A difference in the sleep architecture overnight between the adaptation and experimental nights was generally detected during the initial period of sleep or in the first sleep cycle such as a delay in the onset of NREM sleep stages and REM sleep latency (Agnew et al., 1966; Tamaki et al., 2005a). We therefore hypothesized that the sleep architecture in the first sleep cycle is most influenced by the laboratory environment in the adaptation night and the influences on sleep decrease in the subsequent sleep cycles in healthy subjects.
The characteristics of sleep in the adaptation night were previously investigated by conventional analyses of sleep architecture such as the amount of each sleep stage. Recent studies analyzed sleep continuity and characterized the patterns of sleep-stage transitions in order to elucidate the dynamic nature of sleep regulation (Kishi et al., 2017, 2020). The analyses in these studies revealed the novel properties of sleep regulation that were not detected by the conventional sleep-stage variables (Norman et al., 2006; Kishi et al., 2011). Therefore, the quantification of sleep continuity and sleep-stage transitions will enable the further characterization of sleep in the adaptation night. In addition, sleep variables assessed by sleep-stage scoring may not be concordant with those by the quantitative analyses of EEG and heart rate variability (HRV) activities in the adaptation night (Toussaint et al., 1997; Le Bon et al., 2001; Curcio et al., 2004; Israel et al., 2012; Virtanen et al., 2018). As such, analysis of sleep-stage dynamics and the quantification of cortical/cardiac activities may provide physiological insights into sleep processes over sleep cycles in the adaptation night. Therefore, the aim of the present study was to investigate the time-course changes in sleep-stage transitions, cortical EEG power, and heart rate variability in the progress of sleep cycles in the adaptation night in comparison with the experimental night in healthy subjects.
Materials and Methods
Participants
One hundred participants aged between 20 and 33 years (47 women and 53 men, mean age 24.3 ± 2.9 years) were enrolled in the PSG study at Osaka University between November 25th, 2013, and September 25th, 2019. The participants were recruited via flyers posted and word of mouth. They were compensated for participation (5,000 JPY). The sample size was determined by a prior power analysis in order to detect a medium effect size (dz = 0.5) with a power of 0.90 by a two-tailed paired t-test. All participants completed a written informed consent form approved by the Research Ethics Committee of Osaka University Graduate School of Dentistry and Osaka University Dental Hospital. This study was approved by the ethics committee of the Osaka University Dental Hospital and the Graduate School of Dentistry (H25-E9-5, H29-E48-3).
Polysomnography and Sleep Stages
Polysomnographic recordings were performed on two consecutive nights in a sleep laboratory at Osaka University Graduate School of Dentistry. All subjects completed the Pittsburgh Sleep Quality Index (PSQI) for Japanese (Doi et al., 2000) and Self-rating Depression Scale: SDS (Zung, 1965): the Japanese version of the SDS (Fukuda and Kobayashi, 1973). The PSQI is a subjective questionnaire to assess sleep quality and disturbances over a 1 month period, and the SDS is a self-administered survey to quantify the depressed status of a patient. Subjects were instructed to lead a regular life prior to participating in the recording evaluation. They were not allowed to nap, perform excessive exercise, or drink alcohol before coming to the sleep lab on the two nights. On the day of the PSG recording, participants arrived at our sleep lab at approximately 8:30 pm. The light was off between 10:30 and 11:00 p.m. and on in the next morning between 6:30 and 7:30 a.m. or when they woke up. The times for lights-on and -off were the same between the two nights. After waking up, participants answered the questionnaire on the quality of sleep; they were asked about sleep latency, number of periods of wakefulness after sleep onset, total sleep time and, sleep quality score (from 1 point: “bad” to 5 points: “good”).
PSG recordings were performed using surface electroencephalography (EEGs: C3-A2, C4-A1, O1-A2, O2-A1, F3-A2, F4-A1, Fp1-A2, and Fp2-A1), bilateral electrooculography (EOG), lead II electrocardiography (ECG), and chin electromyography (EMG). Signals were amplified, filtered (EEG, EOG, and ECG: 0.3–70 Hz; EMG: > 10 Hz, with a 60 Hz hum filter), and recorded with a sampling frequency of 200 Hz using a software package (Embla N7000, REMbrandtTM PSG software, Natus Medical, Pleasanton, CA). The stage was scored by one technician (registered polysomnographic technologist) blinded to the study aims (Nonoue et al., 2017). Oronasal thermal airflow, nasal pressure, chest, and abdominal movements, arterial oxygen saturation, and body position were also recorded. Audio and video recordings were performed simultaneously. Sleep stages and respiratory events were scored according to the American Academy of Sleep Medicine criteria version 2.1 (Berry et al., 2014). The apnea–hypopnea index (AHI) was calculated as the sum of all apneas and hypopneas with 3% O2 desaturation and/or EEG arousal divided by the total sleep time. The AHI exclusion criteria followed the AASM criteria (Berry et al., 2014). Subjects with AHI ≥5 times/h were excluded from the analyses of this study; they may exhibit a lower quality of sleep than the others even though they did not exhibit signs or symptoms of sleep apnea (Okura et al., 2020).
Sleep Cycles
The sleep cycle was assessed with reference to the method proposed by Feinberg (1974). A sleep cycle was defined as the time from the end of REM sleep to the end of the next REM sleep. The first sleep cycle was defined as the time from sleep onset to the end of the first REM sleep. REM sleep was considered to be two separate REM sleep periods if it discontinued for more than 20 min and one REM sleep period if the gap was less than 20 min. Furthermore, participants were considered to have been in a REM sleep period if they woke up less than 10 min from the last REM sleep even if the sleep stage immediately before the end of the PSG recording was not REM sleep. Sleep cycles were considered to have been completed only if another sleep stage was continued more than 10 min from the last REM sleep and the number of complete cycles was measured accordingly. The number of REM sleep periods included those in which the last stage of the sleep cycle before waking up was REM sleep. In order to compare the variables (i.e., sleep stage, cortical activity, and heart rate variability) for sleep cycles between the adaptation night and the experimental night within a subject, the same number of sleep cycles was analyzed because the number of sleep cycles differed between the two nights in some subjects.
Sleep-Stage Transition
The number of sleep-stage transitions per night was measured for each participant, and the rate of stage transitions (%) was calculated by dividing the number of sleep transitions per night by the total number of epochs. The same method was used to calculate the percentage of sleep stages for each sleep cycle. Normalized transition probabilities between five sleep stages were calculated by dividing the number of transitions from the specific stage to one of the other stages by the total number of transitions from the specific stage to another stage (Kishi et al., 2008, 2011).
The continuity of sleep (regardless of sleep stage) and each sleep stage (N1, N2, N3, REM, and wake) were analyzed with the rules in the previous study (Kishi et al., 2017). A sleep run began with a transition from Wake to any stage of sleep and continued until Wake occurred. Separate from the sleep run, a run of each sleep stage (N1, N2, N3, REM, and Wake) was defined as consecutive epochs scored as the stage, terminated by one or more epochs scored as another stage.
Cortical and Cardiac Activities
During the night, continuous EEG (C4 referenced to the left ear) was digitized at 200 Hz and stored for off-line analysis. Prior to the analysis, epochs with artifacts were visually identified and removed. Spectral power was calculated using the fast Fourier transform (FFT) algorithm (Bio Trend Professional, NoruPro Light Systems). FFT windows of 2,048 points were used, and truncating error was reduced by applying a Hanning window. The frequency resolution was 0.25 Hz. The analysis window was 10.24 s with a 0.24 s overlap every 10 s, and the data for three units were averaged to obtain a value every 30 s. The limits for band frequencies were as follows: delta, 0.5–4 Hz; theta, 4–8 Hz; alpha, 8–12 Hz; sigma, 12–15 Hz; low beta, 15–23 Hz; high beta, 23–32 Hz.
Heart rate analysis was performed using complex demodulation (CD) (Shin et al., 1989). The oscillations can be characterized based on the heart rate accelerating or slowing, the wavelength, and/or the amplitude (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). The correlations of frequency components of HRV, however, diminish as the wavelength of the oscillations and the recording duration increase. The CD method uses the techniques of interpolation and detrending (Shin et al., 1989; Hayano et al., 1993) and provides the time resolution necessary to detect short-term heart rate changes and to describe the amplitude and phase of particular frequency components as functions of time (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). The mean value of the instantaneous amplitude (in ms) was calculated in 30 s windows using a computer program with a time scale of 0.1 s and a frequency resolution of 0.002 Hz (HRV LOG-Pro-DSA Analysis, NoruPro Light Systems). Following the removal of epochs with artifacts, frequency spectra in RR interval data were estimated for the range between zero and 0.40 Hz and were divided into three components depending on their central frequencies, i.e., the spectral domain with a central frequency of less than 0.04 Hz, between 0.04 and 0.15 Hz, and greater than 0.15 Hz but less than 0.40 Hz. These domains were labeled as bands with a very low frequency (VLF), low frequency (LF), and high frequency (HF), respectively (Malliani et al., 1991). HRV reflects autonomic modulation, whereas the average RR interval reflects autonomic tone. In the present study, HF amplitude was used as an index of alteration of parasympathetic nervous system activity.
Statistical Analysis
Paired t-tests were used to compare the adaptation and experimental nights, in addition to the mean duration of runs for sleep and each sleep stage. The effect size was presented in Cohen’s d, which was the mean preference index divided by the standard deviation. To individually assess variables that were significantly affected by the first-night effect, a three-way analysis of variance (ANOVA) for repeated measures [(night: two levels), (sleep stage: five levels), and (cycle: four levels)] was used. Moreover, a two-way analysis of variance (ANOVA) for repeated measures [(night: two levels) and (cycle: four levels)] was used to assess EEG and HRV parameters. The Greenhouse–Geisser ε correction was performed to evaluate F-ratios for repeated measures involving more than one degree of freedom and when the sphericity assumption was not met. The effect size was presented in partial η2, which was the sum of squares for the effect of interest divided by the total sum of squares for all data variance. Post hoc comparisons between pairs of nights were conducted using the paired t-test. Results were considered to be significant when p-values were less than 0.05.
Results
Participants
Data from 26 participants were excluded from the analysis for the following reasons: sleep apnea syndrome (AHI ≥ 5 for both nights) (n = 19) and TST/TIB < 70% or sleep latency > 60 min (N = 7). As a result, 74 participants were included (40 women and 34 men, 20–33 years old, mean age 23.8 ± 2.2 years, BMI 20.5 ± 1.6 kg/m2). The sleep quality assessed by the PSQI in all participants was 4.6 ± 1.96 (range: 0–21, cutoff score: 5.5≥). The average score on the SDS was within the standard range (range: 20–80, cutoff score: 40>, average score in all participants: 39.2 ± 5.49).
Sleep Variables for the Entire Night
Sleep variables measured during the adaptation and experimental nights are shown in Table 1. Although the time in bed did not significantly differ between the two nights, the total sleep time was shorter (p < 0.01) and sleep efficiency was lower (p < 0.001) in the adaptation night than in the experimental night. The latencies of stage N1 (i.e., sleep latency), stage N3, and stage REM were significantly longer in the adaptation night than in the experimental night (all p < 0.05). In terms of sleep stages, the adaptation night was characterized by a longer time in WASO (wakefulness after sleep onset) and stage N1 (both p < 0.01), and a shorter time in stage REM (p < 0.001) than in the experimental night. The number of REM sleep periods increased from the adaptation night to the experimental night (p < 0.05).
Table 1
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Table 1. Sleep variables in adaptation and experimental nights.
The percentage of transitions per night (%) was significantly higher in the adaptation night than in the experimental night (p < 0.001, Table 1). The arousal index was significantly higher in the adaptation night than in the experimental night (p < 0.001), but the number of awakenings did not significantly differ between the two nights. No significant difference was observed in AHI between the two nights. The subjective sleep parameters were better in the experimental night than in the adaptation night (No. of WASO, total sleep time, and sleep quality) (all p < 0.05, Table 1).
Sleep-Stage Continuity and Sleep-Stage Transitions for the Entire Night
The mean continuity time for sleep and each sleep stage is shown in Table 2. The mean duration of sleep runs was significantly shorter in the adaptation night than in the experimental night (p < 0.01). Runs of stage N1 and stage N2 were shorter in the adaptation night than in the experimental night (both p < 0.01), but no significant difference was observed in stage N3 or stage REM. On the other hand, the runs of stage Wake were significantly longer in the adaptation night than in the experimental night (p < 0.01).
Table 2
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Table 2. Mean continuity time for sleep and each sleep stage.
Normalized transition probabilities among the five vigilance states (Wake, N1, N2, N3, and REM) for the two nights are shown in Table 3. The transition from Wake to N1 (Wake → N1) in the adaptation night was significantly higher, whereas that from Wake to N2 (Wake → N2) was significantly lower in the adaptation night than in the experimental night (p < 0.01). Normalized transition probabilities from N1 to REM (N1 → REM) significantly decreased in the adaptation night than in the (p < 0.01). Normalized transition probabilities from N2 to N1 (N2 → N1) were significantly higher in the adaptation night than in the experimental night (p < 0.01), whereas those from N2 to N3 (N2 → N3) were lower in the adaptation night than in the experimental night (p < 0.01). No inter-night differences were found in transitions from stage N3 to other stages. The frequency of transition from REM to N1 (REM → N1) was significantly lower in the adaptation night than in the experimental night (p < 0.05), whereas that from REM to N2 (REM → N2) was higher in the adaptation night than in the experimental night (p < 0.01).
Table 3
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Table 3. Normalized transition probabilities between five behavioral states within the sleep period time in the adaptation and experimental nights.
Sleep Variables for Each Sleep Cycle
The percentage of each sleep stage in each sleep cycle is shown in Figure 1. In order to compare the variables for sleep cycles between the adaptation night and the experimental night within a subject, the same number of sleep cycles was analyzed (cycle 1 and cycle 2: n = 74, cycle 3: n = 63, cycle 4: n = 34). The three-way repeated-measures ANOVA (nights: two levels × sleep stage: five levels × sleep cycle: four levels) demonstrated a significant interaction [F(12,396) = 2.82, p = 0.022, ε = 0.38, partial η2 = 0.085]. Post hoc comparisons between the two nights in the first sleep cycle revealed that the percentages of stage Wake and N1 were significantly higher (p < 0.01), and that of stage N3 was significantly lower (p < 0.01) in the adaptation night than in the experimental night. Post hoc comparisons between the two nights in the second sleep cycle revealed that the percentage of stage REM was significantly lower (p < 0.05) in the adaptation night than in the experimental night. There were no significant differences between the two nights in the third and fourth sleep cycles.
Figure 1
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Figure 1. Percentage of each sleep stage in each sleep cycle. The percentage of each sleep stage is present as mean and standard deviation (red box: adaptation night, blue box: experimental night). Values that significantly differed between nights are indicated by one (p < 0.05) or two stars (p < 0.01; two-tailed paired t-test). The numbers of subjects were 74 for cycles 1 and 2, 63 for cycle 3 and 34 for cycle 4.
Quantitative EEG and HRV Analyses
The mean spectral parameters of the first four sleep cycles calculated on the adaptation night and experimental night are shown in Figure 2. The two-way repeated-measures ANOVA (nights: two levels × sleep cycle: four levels) demonstrated a significant interaction [F(3,99) = 3.49, p = 0.019, partial η2 = 0.096] only in the high Beta band in the NREM sleep period. Post hoc comparisons between the two nights revealed that the high Beta band in NREM of the first sleep cycle was significantly higher (p < 0.01) in the adaptation night than in the experimental night. There were no significant differences between the two nights in all other bands in NREM and REM sleep periods.
Figure 2
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Figure 2. EEG spectral power for each sleep cycle. EEG power was expressed as log-transformed values. The data is present as mean and standard deviation (red line: adaptation night, blue line: experimental night). Values that significantly differed between nights are indicated by one star (p < 0.05; two-tailed paired t-test). The frequency ranges were as follows: delta, 0.5–4 Hz; theta, 4–8 Hz; alpha, 8–12 Hz; sigma, 12–15 Hz; low beta, 15–23 Hz; high beta, 23–32 Hz. The numbers of subjects analyzed were the same as in Figure 1.
The mean HF band and RR intervals of the first four sleep cycles calculated on the adaptation night and experimental night are shown in Figure 3. In the NREM sleep period, the two-way repeated-measures ANOVA (nights: two levels × sleep cycle: four levels) revealed a significant interaction between nights and sleep cycles for the RR intervals and HF amplitude [RR intervals: F(3, 99) = 2.88, p = 0.040, partial η2 = 0.080; HF amplitude: F(3, 99) = 3.08, p = 0.031, partial η2 = 0.085]. Post hoc comparisons between the two nights revealed that RR intervals and HF amplitude were significantly lower over the four sleep cycles in the adaptation night than in the experimental night (both p < 0.05). There were no significant differences between the two nights in RR intervals or HF amplitude in the REM sleep periods.
Figure 3
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Figure 3. RR intervals and HF amplitude for each sleep cycle. RR intervals and HF amplitude for each sleep cycle are present as mean and standard deviation (red line: adaptation night, blue line: experimental night). Values that significantly differed between nights are indicated by one (p < 0.05) or two stars (p < 0.01; two-tailed paired t-test). The numbers of subjects analyzed were the same as in Figure 1.
Discussion
The present study investigated the process to adaptation to sleeping in a sleep laboratory in healthy young adults. The objective and subjective sleep quality was lower in the adaptation night than in the experimental night and was characterized by low sleep continuity and high sleep-stage transitions in association with the changes in cortical EEG power and heart rate variability. Cycle-by-cycle analyses revealed differences in sleep-stage distribution and cortical beta EEG power in the first sleep cycle. However, heart rate variability differed in the four sleep cycles between the two nights. This suggested that the physiological systems representing sleep-stage dynamics, cortical activity, and heart rate variability were differentially altered during the progression of sleep cycles between the adaptation and experimental nights in healthy subjects.
Sleep-Stage Dynamics in the Entire Night and Sleep Cycles
The present study revealed that the sleep macrostructure on the adaptation night was characterized by reduced sleep efficiency, less REM sleep, more stage N1, more wakefulness, and more frequent arousal than in the experimental night (Table 1). This study supports previous findings on the so-called first-night effect (Agnew et al., 1966; Browman and Cartwright, 1980; Toussaint et al., 1995; Rotenberg et al., 1997; Le Bon et al., 2001; Curcio et al., 2004; Moser et al., 2010), although sleep architecture was of good quality for the two nights in this study population (e.g., sleep efficiency > 90%). In the adaptation night, the decreased stability of sleep stages can influence the sleep process. However, cycle-by-cycle analysis revealed that the first sleep cycle was most affected with higher percentage of time in stage N1 and stage Wake and lower percentage of stage N3 (Figure 1). Moreover, reduced sleep stability can disturb the progression of sleep stages in the first sleep cycle such as a delay in the onset of stage N3 and stage REM. However, in this study, the changes in sleep-stage dynamics in the adaptation night had no major impact on sleep architecture in the following sleep cycles. This suggests that the sleep in the first sleep cycle is susceptible to environmental changes in the adaptation night. However, environmental influences on sleep processes are not carried over to later sleep cycles because mutual interactions between homeostatic sleep regulation and ultradian rhythms may have functioned in young healthy participants in this study (Lorenzo and Barbanoj, 2002; Hayashi et al., 2015; Kishi et al., 2011, 2018).
Quantitative EEG and HRV Variables
Cortical EEG power, such as delta bands, autonomic nervous system function, and sleep-stage distribution fluctuate within a sleep cycle (Brandenberger et al., 2001; Borbély et al., 2016; de Zambotti et al., 2018). Previous studies reported the difference in the sleep architecture between the adaptation (first) and experimental (second) nights in healthy subjects, but the difference in sleep architecture was not clearly correlated with that in EEG power spectra (Toussaint et al., 1997; Curcio et al., 2004) or HRV (Israel et al., 2012; Virtanen et al., 2018) throughout the entire night. Based on the cycle-by-cycle analyses of both nights, the cortical EEG power for each frequency band and HRV of NREM sleep and REM sleep exhibited typical alterations across sleep cycles such as the decrease in delta EEG power and increase in RR intervals (Achermann and Borbély, 2017; Lanfranchi et al., 2017; de Zambotti et al., 2018). However, the time-course changes in sleep architecture, EEG activity, and HRV can differ among the sleep cycles since cyclic fluctuation within a sleep cycle is modulated by the homeostatic and circadian influences over the night (Åkerstedt et al., 1998). As addressed above, in the first sleep cycle, sleep architecture differed between the adaptation and experimental nights. Delta EEG power did not differ between the two nights, as reported previously (Toussaint et al., 1997), whereas the beta EEG power was higher and RR intervals and HF amplitude were lower in the first sleep cycle in the adaptation night than in the experimental night. In the following sleep cycles, however, the difference in sleep architecture and EEG power between the two nights disappeared, whereas the RR intervals and HF amplitude, as demonstrated previously (Virtanen et al., 2018), remained lower in the adaptation night than in the experimental night (Figure 2). Previous studies showed that the correlation between cortical and autonomic activities was found to be attenuated in the latter half of the night in healthy subjects (Thomas et al., 2014; Rothenberger et al., 2015). Therefore, the distinct time course of cortical and autonomic activity suggests that the homeostatic and circadian influences can differently modulate the reactivity of cortical and autonomic activity in the adaptation night. The results also suggest the possibilities that the autonomic nervous system has lower adaptability than cortical system.
Physiological Significance of Sleep-Stage Dynamics and Cortical/Cardiac Activity
Previous studies proposed that changes in sleep in the adaptation night are related to alertness in order to ensure safety when sleeping in a new and potentially dangerous environment (Curcio et al., 2004; Tamaki et al., 2016; Tamaki and Sasaki, 2019). Therefore, alertness may enhance wake-promoting influences at the beginning of sleep and increase the latency of sleep onset and NREM sleep stages in the adaptation night (Tamaki et al., 2005a,b). High beta EEG power and low RR intervals and HF amplitude may be associated with hyperarousal and/or autonomic hyperactivation related to alertness, with an increase in phasic cortical events related to autonomic activation (i.e., arousal and EEG desynchronization) in the adaptation night (Trinder et al., 2003; Kato et al., 2004; de Zambotti et al., 2011; Silvani et al., 2015). These conditions were reported in patients with sleep disorders such as chronic pain (Lavigne et al., 2011) and insomnia (Bonnet and Arand, 1997; Jurysta et al., 2009). However, in the healthy subjects of the present study, high beta EEG power and low RR intervals and HF amplitude may have a role for sleep maintenance, rather than sleep disturbance. As sensory alertness remains functional during sleep (Oswald et al., 1960; Kato et al., 2004; Lavigne et al., 2004), sensory experience in a novel sleep environment may be processed, especially during the first sleep cycle, to ensure the safety of the sleep laboratory environment in healthy participants: autonomic activity remains functional in order to respond to the environment in subsequent cycles.
Study Limitations
The major factors causing altered sleep in a sleep laboratory have changed over time due to improvements in the sleep laboratory environment. However, disturbances cannot be completely eliminated by improving the comfort of the surrounding settings (Lorenzo and Barbanoj, 2002; Moser et al., 2010). In addition, sleep irregularity in the previous week negatively correlates with sleep efficiency during the adaptation night (Lee et al., 2016). In the present study, the possibility that sleep conditions prior to PSG recordings affected sleep in the laboratory recordings cannot be excluded because sleep–wake patterns on previous days were not fully controlled or monitored. Another limitation is that not all subjects had four sleep cycles in the adaptation and experimental nights. The results of cycle-by-cycle analysis performed on a limited number of subjects with four sleep cycles may be interpreted as the responses to the environmental influences in subjects whose sleep is more stable and regular than in those with fewer sleep cycles. Furthermore, psychological predisposition may play a role in the lower ability to adapt to a sleep laboratory environment. As the participants in the present study did not have self-rated depression, psychological effects on adaptability to the sleep laboratory environment were considered minimal.
Conclusion
The present study revealed that the time course of sleep-stage dynamics, electroencephalographic activity, and heart rate variability over sleep cycles are discrepant in the adaptation night in healthy young adults. The results suggest the distinct vulnerability of the adaptation processes within the central nervous system while sleeping in a sleep laboratory for the first time.
Data Availability Statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.
Ethics Statement
The studies involving human participants were reviewed and approved by the Research Ethics Committee of Osaka University Graduate School of Dentistry and Osaka University Dental Hospital (H25-E9-5, H29-E48-3). The patients/participants provided their written informed consent to participate in this study.
Author Contributions
AS and TK designed the study and wrote the main manuscript. AS and MK prepared the data sets and analyzed the data. MK and TK contributed to the data collection. AK, HA, and MT revised and commented on the manuscript. All authors reviewed the manuscript and agreed with its content.
Funding
This study was funded by Grants-in-Aid for Scientific Research (B) (#25293393, #18H02965) and (A) (#25253102) from the Japan Society for the Promotion of Science (JSPS), by funds from the Intractable Oral Disease at Osaka University Graduate School of Dentistry and the Center of Innovation Science and Technology Based Radical Innovation and Entrepreneurship Program (COISTREAM), and partially by a Grant-in-Aid for Challenging Research (exploratory, #17K19753) from JSPS.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments
We would like to thank the sleep laboratory members (Teruaki Nochino, Shingo Haraki, and Akiko Tsujisaka) for their helpful advice on this manuscript and technicians (Kataoka N, Takahashi C, Nakamura M, Teshima Y, Maekawa T, Yamamoto A, Koda S, Hirai N, Iwaki A, Nishida M, and Nakamura U) for their technical assistance. We also thank Mr. Nonoue S, RPSGT for his technical assistance on sleep scoring.
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Keywords: first-night effect, adaptation, sleep-stage transition, sleep-stage continuity, sleep cycle, EEG power, heart rate variability, sleep process
Citation: Shirota A, Kamimura M, Kishi A, Adachi H, Taniike M and Kato T (2021) Discrepancies in the Time Course of Sleep Stage Dynamics, Electroencephalographic Activity and Heart Rate Variability Over Sleep Cycles in the Adaptation Night in Healthy Young Adults. Front. Physiol. 12:623401. doi: 10.3389/fphys.2021.623401
Received: 30 October 2020; Accepted: 12 February 2021;
Published: 24 March 2021.
Edited by:
Alessandro Silvani, University of Bologna, Italy
Reviewed by:
Luigi De Gennaro, Sapienza University of Rome, Italy
Raffaele Manni, Fondazione Casimiro Mondino National Neurological Institute (IRCCS), Italy
Copyright © 2021 Shirota, Kamimura, Kishi, Adachi, Taniike and Kato. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Takafumi Kato, [email protected]
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
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| biology | 508989 | https://no.wikipedia.org/wiki/Kristoffer%20Rygg | Kristoffer Rygg | Kristoffer Rygg, også kjent som «Garm», «Trickster G.» og «God Head», (født ), er en norsk vokalist, musiker og produsent, kjent i heavy metal-undergrunnsmiljøer for sin utstrakte vokalbruk i black metal, ambient, elektronisk musikk, og så videre. Sammen med Tore Ylwizaker og Jørn H.Sværen utgjør han kjernen i gruppen Ulver.
Biografi
Han ble født i Oslo og vokste opp i Portugal. Som 16-åring startet han Ulver som et black-metal band sammen med Carl-Michael Eide.. Rygg var også vokalist i bandene Borknagar (1995–1997) og Arcturus (1993–2003). I 1997 møtte han musiker og produsent Tore Ylwizaker og sammen skapte duoen en ny musikalsk retning for Ulver, inspirert av Coil og eksperimentell, elektronisk musikk. Deres første utgivelse, The Marriage of Heaven and Hell fra 1998, var et dobbel-utgivelse der de satte musikk til William Blakes epos fra 1790-1793. Forfatter og forlegger Jørn H. Sværen, som Rygg beviselig møtte for første gang under Morbid Angels første Oslo-konsert i 1991, ble formelt med i Ulver rundt årtusenskiftet.
Diskografi
Ulver
Flowers of Evil (Studioalbum, 2020)
Drone Activity (Livealbum, 2019)
Sic Transit Gloria Mundi (EP, 2017)
The Assassination of Julius Cæsar (Studioalbum, 2017)
ATGCLVLSSCAP ("The Zodiac album") (Studio- og livealbum, 2016)
Riverhead (Filmmusikk, 2016)
MESSE I.X-VI.X, live fra Teatro Regio di Parma (Livealbum, 2015)
Trolsk Sortmetall 1993-1997 (2014)
Messe I.X-VI.X (Bestillingsverk. Studio- og livealbum, 2013)
Terrestrials. Ulver og SUN-O))) (Live- og studioalbum, 2013)
Childhoods end - Lost & found from the age of Aquarius. (Studioalbum, 2012)
Wars of the Roses (Studioalbum, 2011)
The Norwegian National Opera (DVD, 2011)
Shadows of the Sun (Studioalbum, 2007)
Blood Inside (Studioalbum, 2005)
UNO (2005) (OST, Jester Records har ikke enda utgitt deres egen versjon, men filmen corp er allerede utgitt)
Salto, salmiakk og kaffe (Filmmusikk til film av Mona Hoel, 2004).
Svidd Neger (Filmmusikk, 2003)
1993-2003: 1st Decade in the Machines (2003)
A Quick Fix of Melancholy (EP, 2003)
Lyckantropen Themes (Filmmusikk, 2002)
Silencing the Singing (EP, 2001)
Silence Teaches You How to Sing (EP, 2001)
Perdition City (Studioalbum, 2000)
Metamorphosis (EP, 1999)
Themes From William Blake's The Marriage of Heaven and Hell (Studioalbum, 1998)
The Trilogie - Three Journeyes through the Norwegian Netherworlde (1997)
Nattens Madrigal - Aatte Hymne til Ulven i Manden (1997)
Kveldssanger (1996)
Bergtatt - Et Eeventyr i 5 Capitler (1995)
Mysticum / Ulver (1994)
Vargnatt (1993)
Arcturus
The Sham Mirrors (2002)
Aspera Hiems Symfonia/Constellation/My Angel (2002)
True Kings of Norway (spilt album) 2000
Disguised Masters (1999)
La Masquerade Infernale (1997)
Aspera Hiems Symfonia (1995)
Constellation (1994)
Borknagar
The Olden Domain (1997)
Borknagar (1996)
Head Control System
Murder Nature (4. april 2006)
Æthenor
Betimes Black Cloudmasses (2008)
Som gjesteartist
Carpenter Brut – Leather Teeth (2018)
Dimmu Borgir – Abrahadabra (2010)
V:28 – VioLution (2007)
Solefald – Black for Death: An Icelandic Odyssey Part II (2006)
Ihsahn – The Adversary (2006)
Gehenna – Seen Through The Veils Of Darkness (1995)
Referanser
Eksterne lenker
Norske komponister
Norske plateprodusenter
Ulver-medlemmer
Norske black metal-musikere | norwegian_bokmål | 1.043387 |
fast_asleep/Cellstatetransitions.txt | Skip to Main Content
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Volume 148, Issue 20
October 2021
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ABSTRACT
Introduction
Defining and identifying cell states
Discrete versus continuous cell states
Environmental context: are cell states autonomous or non-autonomous?
Does the road cells take matter?
Transitions between states
From data to models
Perspectives
Acknowledgements
References
SPOTLIGHT| 19 OCTOBER 2021
Cell state transitions: definitions and challenges
Carla Mulas
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, Agathe Chaigne
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, Austin Smith
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, Kevin J. Chalut
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Development (2021) 148 (20): dev199950.
https://doi.org/10.1242/dev.199950
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ABSTRACT
A fundamental challenge when studying biological systems is the description of cell state dynamics. During transitions between cell states, a multitude of parameters may change – from the promoters that are active, to the RNAs and proteins that are expressed and modified. Cells can also adopt different shapes, alter their motility and change their reliance on cell-cell junctions or adhesion. These parameters are integral to how a cell behaves and collectively define the state a cell is in. Yet, technical challenges prevent us from measuring all of these parameters simultaneously and dynamically. How, then, can we comprehend cell state transitions using finite descriptions? The recent virtual workshop organised by The Company of Biologists entitled ‘Cell State Transitions: Approaches, Experimental Systems and Models’ attempted to address this question. Here, we summarise some of the main points that emerged during the workshop's themed discussions. We also present examples of cell state transitions and describe models and systems that are pushing forward our understanding of how cells rewire their state.
Keywords:Cell state transitions, Definition of cell states, Heterogeneity, Modelling
Introduction
The term ‘cell state transition’ refers to the process by which cells change states over time. Such transitions are an intrinsic part of embryonic development as cells progressively differentiate. They are also crucial during homeostasis and tissue repair, as damaged and worn cells are replaced to maintain tissue function. Moreover, many pathologies, from developmental disorders to cancers, involve aberrant transitions in cell states. Thus, understanding these transitions is of crucial importance.
The Company of Biologists virtual workshop on ‘Cell State Transitions: Approaches, Experimental Systems and Models’ brought together experimentalists and theorists from different backgrounds who are studying cell state transitions across various systems. In themed discussions, we tackled three topics: the definition of cell states and the role of heterogeneity; the role of autonomous and non-autonomous regulation in informing cell states and transitions; and the technical challenges and opportunities facing the field. In this brief Spotlight article, we summarise some of the main messages that emerged from the discussions.
Defining and identifying cell states
A starting point of discussion was how the definitions of cell states have evolved over time. With limited tools, cell states were initially assigned based on observable and phenotypic features, such as location, morphology and inferred function. Indeed, the phrase ‘cell states’ (Zellenstaat), akin to cell ‘societies’, was a metaphor that emerged in the late nineteenth century to describe the grouping of cells based on their functions, where each ‘state’ fulfilled an essential role and contributed to the ‘economy of the organism’ (Reynolds, 2007). Over time, the definition of cell state became increasingly reliant on the description of molecular features. As technology progressed, non-specific dyes that could broadly mark populations of cells or organelles were replaced by antibodies that could recognise specific epitopes (Coons et al., 1941), and then by hybridisation-based techniques that could detect an ever-expanding repertoire of markers that underpin cell state. Global profiling using high throughput technologies, such as next generation sequencing, has further expanded the number of descriptive parameters available. Today, we generally identify cell states using complementary approaches: by molecular characterisation, i.e. the description of different molecules (whether transcripts, distribution of chromatin marks or proteins), and by functional characterisation i.e. the description of what a specific cell can do.
Molecular characterisation of cell states
The most common descriptor of cell state relies on the annotation of specific molecules that compose a particular cell. Traditionally, cell states were defined using a small number of parameters or key markers that either showed strong correlation with a functional cell state or were functionally required (Mojtahedi et al., 2016; Wheat et al., 2020). For example, in the context of mouse development, pluripotency is generally characterised by expression of the transcription factor Oct4. Increasing the number of markers allows pluripotency to be further subdivided into distinct states. For example, naïve pluripotency, which is restricted to the pre-implantation epiblast, is characterised by the co-expression of Oct4, Nanog, Sox2 and Klf2/4, whereas formative pluripotency, associated with early post-implantation development, is associated with Oct4, Sox2 and Otx2 expression (Kinoshita and Smith, 2018; Nichols and Smith, 2009).
Global profiling has enabled the identification of a much larger set of defining molecular characteristics. A series of technical advances, in particular in single cell approaches, has allowed us to characterise an ever-greater number of single cells and parameters, tackling systems of increasing complexity and size. This increased capacity has been incredibly useful for identifying and characterising rare populations (e.g. hematopoietic stem cells or primordial germ cells) and very heterogeneous or complex systems (e.g. the brain).
Molecular characterisation of cell states does not, in principle, require previous knowledge of the system. However, annotation of such datasets often relies on knowledge of marker expression. With single cell assays, we can obtain many parameters describing very complex multicellular systems. However, there is a significant limitation: as we cannot characterise all types of molecules at the same time (e.g. genes, proteins, etc.), we are often forced to pick one type of measurement, most commonly gene expression. Therefore, we assume that cell states are accurately characterised or identified by that measurement. Although multi-omics approaches are now allowing us to analyse multiple features in parallel (e.g. gene expression and chromatin accessibility), they largely remain confined to exploring regulation at the DNA level. However, a cell state is more than the sum of its parts, meaning that multiple regulatory levels are often fundamental for determining and maintaining cells in a given state. Finally, in the context of molecular characterisation of cell states, it can be challenging to identify which molecules, amongst all those present, contribute to regulating that particular state.
Functional characterisation of cell states
Functional assays are a powerful tool for identifying and defining cell states based on what cells can do. For example, the functional characterisation of cells as mature pancreatic β-cells requires cells to respond to high glucose concentrations by depolarising, increasing calcium influx and secreting physiological levels of insulin (Pagliuca et al., 2014). Immature or wrongly-specified cells fail one or more of these functional tests. In the case of stem and progenitor cells, clonal lineage tracing in vivo is a powerful method to reveal both self-renewal and tissue contributions of single cells over time (Blanpain and Simons, 2013). For example, transplantation of single haematopoietic stem cells (HSCs) proved their ability to reconstitute all lineages long-term in mice (Osawa et al., 1996) and subsequent single cell transplants uncovered functional heterogeneity within the stem cell pool (Dykstra et al., 2007). Similarly, the ability of cells to integrate into a host pre-implantation embryo and contribute to normal development in chimera assays is a defining functional property of mouse embryonic stem cells (Bradley et al., 1984; Masaki et al., 2016).
In vitro functional assays can also be very powerful. For example, cell culture assays have demonstrated the ability of single Lgr5+ cells to generate intestinal organoids (Sato et al., 2009). Culture systems similarly validated a distinct functional cell state during early embryonic development in which cells transiently acquire the competence to form primordial germ cells (Ohinata et al., 2009; Hayashi et al., 2011; Kinoshita and Smith, 2018; Mulas et al., 2017).
Functional characterisation requires appreciation of the biology of the system and can be challenging at the single cell level. Moreover, in complex and dynamic contexts, it can be difficult to link the functional response to a molecular phenotype. Often, linking function to molecular profiling relies on dividing the cell pool into subpopulations based on a limited set of markers. However, as functional assays probe cell behaviour, we can identify cell states and transitions that might arise from a complex interaction of gene expression, chromatin and protein changes; these states and transitions might not be apparent when looking at each regulatory level in isolation. A further benefit of functional assays is that theyprovide powerful readouts for phenotypic screens and thus can be used to identify potential regulators of cell states and transitions.
Multiscale descriptions
Although molecular descriptions and functional assays are powerful tools to describe cell states, the workshop emphasised that the next technical challenge is to combine different techniques to attain a multiscale description of cell states. The development of multi-omics approaches is now allowing us to characterise cells, cell states and transitions between cell states across multiple levels of regulation (Lee et al., 2020). In parallel, spatial transcriptomic methods are becoming increasingly useful in characterising cellular gene expression in systems in which function correlates with spatial location (Waylen et al., 2020). However, integrating data across regulatory levels remains challenging. For example, it would be very beneficial to merge functional and molecular descriptions of cell state. However, most molecular/high throughput sequencing techniques destroy cells. Thus, it is generally not possible to simultaneously measure the transcriptional state of a cell as well as its functional potential. New approaches are emerging to meet this challenge, either by labelling cells with markers and reporters, or by sampling labelled populations over time and integrating clonal lineage tracing with single cell transcriptomics (Wagner and Klein, 2020). Moreover, live-cell RNA-sequencing represents a major technological advance that could allow for the combination of functional and molecular assays in single cells (Chen et al., 2021 preprint).
Discrete versus continuous cell states
Defining the state of a cell based on its constituents is already a challenge in terminally differentiated tissues or tissues with limited turnover (e.g. the cerebral cortex). In such systems, cells typically maintain stable patterns of gene expression, chromatin modifications, etc., yet show staggering diversity. The challenge of defining cell states is further compounded in dynamic systems, such as during embryonic development or homeostatic tissue turnover. In such systems, it is not straightforward to determine, for example, when a cell becomes differentiated and is no longer a stem or progenitor cell. Moreover, thousands of genes and loci, and hundreds of proteins, can change over a short period of time. During the themed discussions, we debated whether cell states were discrete or continuous, and how much the categorisation of cells into states was dependent on the assay used.
Classical studies of embryonic development and haematopoiesis have supported the notion of discrete states, with cells passing through ‘commitment points’ – points in which cells have irreversibly committed to a fate and lose the ability to revert back and respond to signals in a different way (with the earliest evidence summarised in the 1980s; Heasman et al., 1985). However, technical challenges (e.g. the viability of single transplanted cells) have hindered the mapping of functional transitions at the single cell level with high temporal resolution. As such, it is currently difficult to determine whether abrupt boundaries exist, or whether properties may change gradually with intermediate phenotypes.
Conversely, more recent analysis of transitions by single cell RNA-sequencing have suggested continuous transcriptional trajectories. These observations have led many scientists to rethink one of the oldest models of stem cell differentiation: the haematopoietic hierarchy (Laurenti and Göttgens, 2018). The observations of continuous trajectories is not unexpected: even if cells abruptly switch states, mRNA and protein decay timescales are likely to result in intermediate expression values. Moreover, single cell RNA-sequencing is particularly sensitive to technical noise and batch effects. A major challenge is that computational methods, such as dimensionality reduction and pseudo-temporal ordering, while powerful visualisation tools, can also bias how we perceive the data.
Finally, intrinsic cell dynamics, such as cell cycle or circadian rhythms, and dynamic interactions between the cell and its environment, can further complicate the distinction between discrete and continuous cell states. Reliable information on the dynamics of cell state transitions is fundamental for identifying the appropriate mathematical tools that can be applied to model transitions, and it also impacts how we interpret and understand the underlying molecular logic that controls cell states. In turn, appropriate mathematical and computational tools can lead to a better understanding of these dynamics. This is an exciting area in which experimental evidence combined with new analytical approaches might help resolve how molecular and functional dynamics overlap.
Environmental context: are cell states autonomous or non-autonomous?
Whether the transitions in cell state are temporally continuous or discrete, they are also influenced by the context in which the cell is found. Indeed, the key parameters defining cell state can be cell-autonomous, but they can also be extrinsic, modulated by the environment the cell is in. In a themed discussion, we debated the extent to which cell states are dependent on their niche.
In 1924, Spemann and Mangold performed a classic experiment that is now discussed in every developmental biology manual: they grafted a part of the dorsal blastopore of a Xenopus embryo, which they suspected induced the formation of the dorso-ventral axis, onto other part of the embryo, creating an ectopic dorso-ventral axis (Spemann and Mangold, 1924). These transplantation experiments highlighted a key observation about cell states: some cells can maintain their state and, in particular, their signalling potency, irrespective of their cellular context, i.e. their state is autonomous. On the contrary, other cells can become induced towards a different fate when put in contact with a different set of neighbours, showing non-autonomous control of their fate.
A key question that arose during the workshop related to the identification of autonomous or non-autonomous cell states. This is a complex question that might have as many answers as developmental contexts and cell types. A typical example of this complexity is found in developing vertebrate somites, in which the so-called segmentation clock produces waves of transcription (Hubaud et al., 2017; Oates, 2020). The waves travel from the developing tail towards the anterior part of the embryo and stop with the formation of each somite. Single cells from this tissue (the presomitic mesoderm) can oscillate autonomously but are poorly coordinated, and coordination is only achieved at the population level (Hubaud et al., 2017; Oates, 2020). Several mechanisms have been proposed to allow coordination, including quorum sensing of signalling molecules, adhesion and mechanics-mediated signalling. Here, the cell state is both autonomous and non-autonomous, as it operates in each cell, but can only be maintained in a coordinated manner by cells in a population. Thus, to comprehend the cell state, it is important to consider the cell context, for example its neighbours and the mechanics of the surrounding environment. This calls for the development of in toto models that fully recapitulate the context the cell is in. In contrast, a complementary approach is to dissect the singular constituents of the ‘niche’ and then reconstitute the niche using a bottom-up approach.
Does the road cells take matter?
By using such bottom-up approaches, we have realised that different cell types occasionally converge towards the same state, despite the fact that they have different origins and might have taken different trajectories. In such cases, distinguishing between cell types and cell states is not always straightforward. For example, in the mouse embryo, definitive endoderm is specified when cells from the epiblast intercalate with the underlying visceral endoderm (VE) during gastrulation. Despite epiblast and VE fates segregating early during mouse embryonic development, their transcriptional profiles converge to some extent as the definitive endoderm is specified (Nowotschin et al., 2019; Pijuan-Sala et al., 2019). Schwann cells present another curious example. These cells typically arise from the neural crest and are responsible for myelinating axons in the peripheral nervous system (PNS). However, it has been shown that Schwann cells can also originate from oligodendrocyte precursor cells (OPCs), which reside exclusively in the central nervous system (CNS) and are derived from the neuroepithelium during gastrulation. Despite their different origins, both CNS- and PNS-resident Schwann cells share many defining characteristics (Chen et al., 2021 preprint). The comparison between microglia (brain-resident macrophages) and tissue-resident macrophages was also discussed. Despite sharing many molecular characteristics, it is still debated whether these two cells are the same cell type. They have different developmental origins; in the mouse microglia are specified from the embryonic yolk sac at ∼7.5 days post-fertilisation, whereas macrophages arise from multipotent progenitors 3 days later. Moreover, transplanted bone marrow-derived macrophages fail to completely converge to a microglia phenotype when they graft in the brain and instead retain many molecular characteristics of their cell of origin (Shemer et al., 2018). It therefore appears that, in some cases, the road that cells took towards their current state can be important for defining that state and potential, highlighting the value of analytical approaches that integrate lineage tracing.
Transitions between states
Reversible transitions, irreversible transitions and plasticity
Throughout the talks and discussions, the issue of ‘spontaneous’ cell state reversibility, as opposed to experimentally induced reprogramming, was also highlighted. Most biological transitions have an intrinsic directionality under homeostatic conditions. For example, a progenitor cell is more likely to give rise to a differentiated cell than a differentiated cell is to give rise to a progenitor or stem cell. Similarly, development progresses until cells become more specialised, and they generally do not spontaneously revert. Remarkable exceptions exist, however, as observed in Dictyostelium, in which dedifferentiation occurs rapidly in response to damage, following a trajectory that is remarkably similar to differentiation in reverse (Nichols et al., 2020). In mammalian systems, the most common examples of dedifferentiation occur in response to damage and activation of a regeneration response, and can result in disease if unconstrained (Yao and Wang, 2020). Are such cells that revert states in response to specific stimuli (e.g. damage), without experimentally-induced genetic or epigenetic resetting, separate cell states or are they part of a single ‘meta-state’? In the context of stem cells, Greulich and colleagues have argued for a hierarchy in which different molecularly-defined cells should all be considered stem cells if they are interconvertible and can adopt a state with the same lineage potential (Greulich et al., 2021). Clearly, how cell states are defined and modelled must account for instances of reversion.
Coordination of transitions
Most often, cell state transitions occur in a multicellular context. Coordinated transitions ensure that the right number of cells are specified at the correct time and in the correct place. During the workshop, we also discussed the strategies typically employed to achieve such coordination both in time and space.
CLONAL HISTORY
Coordination of cell state transitions can be achieved through cell-intrinsic temporal patterns, such as the cell cycle. Across a number of systems, sister cells have been shown to be highly correlated, undergoing transitions and subsequently dividing at very similar times, as seen in the context of mouse embryonic stem cell differentiation (Chaigne et al., 2020; Strawbridge et al., 2020 preprint). As it has also been proposed that the G1 phase is permissive of cell fate transitions in early mammalian development (Chaigne et al., 2020; Gonzales et al., 2015; Pauklin and Vallier, 2013; Singh et al., 2015; Waisman et al., 2017; Wang et al., 2017), coordinated cell cycles can potentially lead to coordinated signalling responses. To add a layer of complexity, key drivers of cell state transitions, such as the bHLH transcription factor Neurogenin 2, have been shown to regulate (Ali et al., 2011) and be regulated by (Lacomme et al., 2012) the cell cycle machinery during neurogenesis. Thus, clonal history and cell states are tightly intertwined.
THE ROLE OF THE MICROENVIRONMENT IN COORDINATING TRANSITIONS
Tissue mechanics can also be an effective way to coordinate cell state transitions. For example, in several cell types, mechanical stretch can induce DNA methylation, which in turn influences cell state (Maki et al., 2021; Nava et al., 2020). Tissue stretch has also been shown to induce a coordinated switch between proliferation and differentiation between post-natal and adult homeostasis in the mouse oesophagus (McGinn et al., 2021), and tissue mechanics have been shown to have an influence on the ability of CNS progenitor cells to proliferate and differentiate (Segel et al., 2019). The mechanical properties of cells can regulate cell signalling, for example by influencing ERK signalling, and in turn modify cell states (Boocock et al., 2021; De Belly et al., 2021). Similarly, we saw examples of how morphogenesis and patterning of villus and crypt regions in intestinal organoids are coordinated via osmotic changes (Yang et al., 2021). New tools are being developed to allow modulation of tissue mechanics using optogenetics, proving even greater experimental control (Martínez-Ara et al., 2021 preprint).
Beyond mechanical regulation, we also saw examples in which access to the niche or fate determinants can direct and coordinate cell fate decisions (Corominas-Murtra et al., 2020; Kitadate et al., 2019). Similarly, we discussed cases in which the in vivo environment achieves a level of coordination that is not recapitulated in vitro. During mouse embryonic development, for example, neural markers appear simultaneously as a consequence of switching from E-Cadherin- to N-Cadherin-based cell-cell adhesions, but this process is heterogeneous in vitro (Punovuori et al., 2019). Although it is possible to increase the synchrony of differentiating cells by directly modifying the activity of signalling pathways (for example by modulating negative feedback loops; Nett et al., 2018), it is not clear what factors determine the difference in synchronicity between the embryo and in vitro culture conditions.
THE ROLE OF HETEROGENEITY/ASYNCHRONY
Although transitions have to be coordinated to ensure the right cells are generated at the right time and in the correct location, asynchrony, heterogeneity and noise might play a fundamental role in cell state changes. One of the key points debated in the themed discussion was the challenge of measuring true biological noise, and the need for better methods to distinguish between technical and biological sources of variability. We also saw how heterogeneity can be used by a group of cells to increase the efficiency of information flow. For example, during the workshop we discussed how collective information processing in the context of calcium flux in cell monolayers is rendered more efficient by heterogeneity in the ability of cells to sense and receive signals (Zamir et al., 2020 preprint).
From data to models
Mathematical models allow us to obtain insights and make predictions about the inner workings of a system that might not be intuitive. As many parameters key to cell state transitions, such as heterogeneity, noise and information processing, are fundamentally mathematical concepts, it is unsurprising that mathematical models are being used increasingly to study transitions between states and are becoming integral to understanding basic biology.
Throughout the workshop, it was clear that the definitions of cell states that are employed determine the way we approach and model transitions. Defining cell states transcriptionally leads to largely descriptive analyses of cell state transitions. These analyses often leverage dimensionality reduction techniques to identify trajectories or paths that cells follow, for example during embryonic development or when stem cells become reactivated after injury. These methods also rely on the assumption that transcriptionally similar cells are likely to represent sampled timepoints within a trajectory (Saelens et al., 2019). Combining lineage tracing with sequencing shows that computationally inferred trajectories can accurately identify the paths cells follow. However, branching or commitment points (i.e. when cells choose/change fate) cannot be accurately inferred from transcriptional data alone (Weinreb et al., 2020).
Other definitions of cell states and transitions rely on stronger assumptions. We saw how cell states could be modelled as ‘attractors’, or valleys, that become destabilised as gene regulatory networks change or as noise increases, allowing cells to hop over ‘hills’ to the next valley, parameterising a model first proposed by Weddington (Camacho-Aguilar et al., 2021). Such an approach, which combines marker-based identification of cell states and experimental perturbations, has been used to construct a ‘landscape’ of cell fate decisions during pluripotent stem cell differentiation with high predictive power (Sáez et al., 2021).
Conversely, defining cell states as discrete entities leads to stepwise transitions through more or less defined macro- and micro-states (Stumpf et al., 2017). The power of discrete definitions of cell states, combined with accurate measurements of population dynamics, can be used to identify a stochastic tissue renewal program based on competition for fate determinants, such as niche access (Krieger and Simons, 2015) or growth factors (Kitadate et al., 2019). The workshop also clearly highlighted how gene-based models can be powerful tools for explaining fate transitions, and the importance of accounting for dynamics and changes in dynamics to address changes in cell states (Negrete et al., 2021).
As each model has important implications for the underlying biology, it is necessary to test the extent to which the underlying assumptions are valid. For example, describing a biological process as a phase transition implies cells must go through a critical point, characterised by the appearance of power-law patterns (i.e. when one variable changes as a power of another, independent of the initial conditions) and sharp increases in variance/disorder, as shown recently in tissue remodelling (Petridou et al., 2021). Similarly, describing a transition as a Markov-chain process (Wheat et al., 2020) implies the future state (e.g. of a differentiated cell) depends exclusively on the previous state (e.g. of the progenitor), without any previous memory of the states that preceded it.
Finally, the type of data used to describe the system ultimately constrains the models we can use. For example, a Markov process assumes we know and can measure all the variables that influence cell states and transitions. However, this is generally not possible. Moreover, even if the key parameters are known, most biological data is sparse and subject to sampling. Such datasets instead call for computational methods built upon on non-Markovian dynamics (Wang and Klein, 2021 preprint). The challenge is for theorists and experimentalists to work together to go beyond determining whether the data fit a model, and to test experimentally the assumptions behind and predictions from the models.
Perspectives
Much of the discussion around the concept of cell state was essentially philosophical. How do you define cell state? There are probably as many definitions as there are biological, biochemical and biophysical parameters that can be used to describe a cell. Furthermore, the parameters used to describe cell state are not necessarily those that are important, or sufficient, to control it. However, fully understanding transitions between states calls for dynamic, multiscale measurements combined with formal mathematical and computational modelling. Ultimately, this virtual workshop served to demonstrate the necessity and incredible power of bridging scales and disciplines to tackle the fundamental issue of how cells establish and rewire their states.
Acknowledgements
We thank everyone that participated in the discussions and The Company of Biologists for making this workshop possible.
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Cookie settings | biology | 35359 | https://sv.wikipedia.org/wiki/Cellbiologi | Cellbiologi | Cellbiologi eller cytologi är den del av biologin som beskriver hur organismen fungerar på cellnivå och behandlar cellens beståndsdelar (organeller), cellens struktur (cytoskelett) och dess enzymatiska processer, exempelvis metabolismen.
Kroppen består av ett hundratal olika celltyper, alla med en speciell uppgift. När en organism utvecklas, så sker det genom att ett fåtal celler delar på sig och specialiserar sig till mer specifika funktioner beroende på vilken vävnad cellen hör till. Cellens utseende och belägenhet bestäms av vad den ska ha för funktion. Till exempel är bukspottkörtelns (pankreas) insulinproducerande betaceller helt skilda från hjärnans neuroner, vad gäller utseende, produktion (insulin- respektive neurotransmittorer), placering i kroppen, etc.
Det som styr en cells utseende och funktion är dess genuttryck, det vill säga summan av de gener som är aktiva i en cell för tillfället. Generna kodar för olika proteiner, som kan ha olika funktioner i kroppen:
Strukturella proteiner bygger upp cellens cytoskelett och organeller.
Enzymer är en grupp proteiner som kan påverka omsättningen eller nedbrytningen av andra ämnen i cellen.
Vissa proteiner fungerar som transkriptionsfaktorer, som styr vilka gener som skall uttryckas av cellen.
Vissa proteiner fungerar som ligand eller signalsubstans för olika receptorer.
I cellbiologisk forskning försöker man ta reda på hur en viss celltyp fungerar, till exempel vilka mekanismer ligger bakom insulinfrisättningen från betacellerna i pankreas.
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Alberts, Bray, Johnson, Lewis, Raff, Roberts & Walker; Essential Cell Biology, Garland Publishing, New York (1998). | swedish | 0.670282 |
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Section
Abstract
1. Introduction
2. Data
3. One-step transitions
4. Two-step transitions
5. Markov order tests
6. Conclusion
Funding statement
Appendix A
Footnotes
Research article
Changes of sleep-stage transitions due to ageing and sleep disorder
A. Schlemmer, U. Parlitz, S. Luther, N. Wessel and T. Penzel
Published:13 February 2015https://doi.org/10.1098/rsta.2014.0093
Abstract
Transition patterns between different sleep stages are analysed in terms of probability distributions of symbolic sequences for young and old subjects with and without sleep disorder. Changes of these patterns due to ageing are compared with variations of transition probabilities due to sleep disorder.
1. Introduction
Humans spend a third of their life asleep. Sleep is a time of non-consciousness with its own structure and microstructure consisting of sleep stages, which may be identified by analysing brain waves. For this purpose, brain waves are recorded in a standardized way according to the manual of the American Academy of Sleep Medicine [1]. The recordings include an electroencephalogram (EEG) from at least three leads with well-defined positions on the cortex, an electrooculogram (EOG) from two leads near the eyes and an electromyogram (EMG) with two leads from a submental or mental muscle. Sleep stages are associated with distinct wave patterns, which may be classified according to the Rechtschaffen and Kales scheme [2] as summarized in table 1.
Table 1.
Rechtschaffen and Kales classification scheme of sleep stages [2], which is used in this publication. In 2007, stages N3 and N4 were merged into a single class [1,3].
View inlineView popup
Classification of sleep stages (sleep staging) based on EEG signals is obtained by visual inspection by trained technicians. In order to reduce the effort related to visual scoring, sleep stages are scored in 30 s epochs, effectively limiting the temporal resolution of visual classification. Another limitation of visual scoring is the uncertainty introduced during the classification process [4]. Especially sleep stages that had been scored by different sleep laboratories often show some differences. This ambiguity can be reduced by systematic training of sleep staging personnel, which indeed improves the visual classification [5]. Furthermore, efforts are made to improve sleep classification through new internet-based sleep scoring [6].
Sleep stages occur in a systematic manner during night sleep. First, a short period of wakefulness (W) is observed with eyes closed before the subject falls asleep. This may last for 5–20 min in healthy subjects. Then follows a short period of N1 as a transitional state and then stage N2, which may be longer. Stage N2 is typically followed by N3 (and N4), deep-sleep stages that are needed for physical recreation. After that a short period of REM sleep is observed and then often a very short awakening. This sequence is called a sleep cycle with a duration of roughly 90 min and it is repeated five to six times during the night. Sleep is often interrupted by very brief awakenings. Usually, they are so short that they are not remembered and good sleep is experienced. The longer the awakenings are the more likely they are realized and memorized which leads to a feeling of disturbed sleep.
Current evaluations of sleep consider mainly the following periods of time:
— sleep onset latency=duration of wakefulness before first occurrence of sleep stages,
— REM sleep latency=time until first occurrence of REM sleep,
— time in bed=time between intention to sleep/lights off and wake up/lights on,
— total sleep time=all sleep stages together except wake times, and
— the percentages spent in the different sleep stages.
In general, we know that healthy middle-aged people spend approximately 5–10% of the night awake, 10% in N1, 50% in N2, 15–20% in N3/N4 and 15–20% in REM sleep. Other quantities which are sometimes considered in publications take the number of awakenings or the number of transitions between sleep stages into account. The current focus in sleep science, however, is on durations and latencies of sleep stages that may change due to ageing and sleep disorder. This is reflected in clinical reports of sleep recordings which only present percentages of sleep stages and sleep latencies.
Many sleep disorders, however, also result in changes of sleep transitions. These sleep transitions and the time spent in a specific sleep stage have been analysed previously [7], not only in humans but also in animals and some universal laws have been found and described [8]. It is also known that sleep changes with age. A meta-analysis of sleep studies presented the changes in parameters that are commonly reported [9]. From this analysis, we know that the duration of slow wave sleep (N3 and N4) and the percentage of dream sleep (REM) decreases with age. We know that the amount of light sleep (N1 and N2) as well as time spent awake (W) increases with age. This seems to be a normal ageing process. But how does the frequency and the pattern of transitions between sleep stages change during ageing or with sleep disorder?
Single-step transitions between sleep stages have been previously studied by Kemp et al. [10], who investigated transition probabilities between stages. A different approach, with a more global perspective, is the overall analysis of spectral entropy measures for sleep-stage transitions provided by Kirsch et al. [11]. In their study, they relate the Walsh spectral entropy (WSE) and the Haar spectral entropy (HSE) to traditional sleep quality parameters such as arousal index and sleep efficacy. They also compare the new parameters to daytime sleepiness and correlate them with traditional sleep quality measures. Lo et al. [8] investigated transitions between wakefulness and sleep during the sleep period in order to derive models for the process of sleep stages (where Lo et al. reduced the transitions to wake–sleep transitions, only, by lumping all sleep stages into one class). To gain further insight into transition patterns including multistep transitions between sleep stages we analyse in the following sleep data employing symbolic dynamics.
Symbolic dynamics enables flexible data-driven strategies for signal analysis and classification, thus providing a solid basis for the quantification of the complexity of dynamical processes [12,13] with many applications in different scientific fields [14,15]. In those cases where the raw data are given by time series of real-valued samples (e.g. blood pressure, beat-to-beat intervals, EEG channels) some method of coarse graining is required to transform the data into a sequence of symbols aiming at enhancing certain signal features while discarding unessential details. By contrast, the sleep stages considered here already provide a natural symbolic representation (table 1) determined by human sleep staging based on the original EEG, EOG and EMG recordings.
This symbolic representation of the sleep process is the starting point of the sleep analysis presented in the following. In §2, the dataset is introduced and an overview of the periods of time spent in different sleep stages is presented. Then in §3a, we focus on an analysis of one-step transition probabilities between sleep stages using transition matrices and joint entropies. In §3b, we present results obtained employing spectral entropy measures. In §3c, changes of transition patterns due to ageing and sleep disorders are discussed using network representations. Section 4 expands the concept of transition probabilities to two-step transitions and visualizes differences between groups. Finally, in §5, the general question of the appropriate number of steps needed in this type of symbolic analysis of sleep stages is addressed by performing a Markov order test. In §6, all results are summarized and discussed.
2. Data
In order to investigate statistics for sleep stages and sleep transitions, it is important to have high-quality data. This means signals have to be recorded without artefacts and then human sleep scoring using these signals has to be correct and reliable. The latter is done by trained sleep technicians as a typical medical classification task with all kinds of limitations inherent to visual medical classification. From previous studies, it is known that there is a considerable human error in the classification of sleep stages [16]. Therefore, the Siesta project [17,18] funded by the European Community was initiated to record high-quality sleep in humans and provide an accurate and robust sleep classification. In order to compare the sleep of healthy subjects to clinical findings, the Siesta project recorded the sleep of patients with sleep disorders as well. Patients with sleep disorders accounted for half the number of healthy subjects, however. The sleep classification was performed independently by two sleep technicians and thereafter checked by a third sleep scorer. The third scorer made a final decision only at those epochs where the two initial scorers disagreed.
The sleep recordings for this analysis were recorded from 196 healthy subjects, who were more or less equally distributed over four age classes. An effort was made to include a similar number of male and female subjects. All subjects were recorded in a sleep center for two subsequent nights using cardiorespiratory polysomnography with EEG, EOG, EMG for at least 6 h and usually 8 h, if possible [18]. In addition to this, 98 subjects with different sleep disorders were recorded using the same protocol including subjects with sleep apnoea, insomnia, restless legs syndrome, periodic leg movements, depression and anxiety disorders.
Figure 1 shows relative durations of sleep stages for four age quartiles, distinguishing subjects with normal sleep from those with sleep disorder. For all age quartiles the fraction of N1 sleep is larger for patients suffering from sleep disorder compared with normal subjects. The fractions of sleep stages reflect well what has been described previously. With increasing age the percentage of R sleep decreases steadily. This observation has already been described by Ohayon et al. in their meta-analysis [9]. In addition, in all age classes the percentage of REM sleep is lower in patients with sleep disorders compared with healthy subjects. The percentage of wakefulness (W) during the sleep period steadily increases with age. However, the percentages of wakefulness in healthy subjects and patients with sleep disorders differ only slightly. Only for the oldest subjects were marked differences observed between normal subjects and patients with sleep disorders. This is a clear indication that among elderly subjects more patients with insomnia were observed whereas among the younger subjects more patients with sleep disordered breathing and other sleep disorders are seen.
Figure 1.
Figure 1. Fractions of duration of sleep stages awake (W), non-REM1 (N1), non-REM2 (N2), non-REM3 (N3), non-REM4 (N4) and REM (R) in four different age classes (20–37, 38–51, 52–64, 65–95). The left bar in each group gives the average result for the corresponding age quartile, while the bars in the middle (frame in blue) and the bars on the right (frame in red) represent results for normal subjects and subjects with sleep disorder, respectively. (Online version in colour.)
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3. One-step transitions
(a) Transition probabilities and transition entropies
In this section, we analyse the one-step transition probabilities between sleep stages. These probabilities are computed as the number of transitions between one source and one destination stage divided by the total number of transitions in the symbolic sequence of sleep stages (of a given dataset). Note that in §3a,c only transitions observed in the time series are counted, which results in the loss of information about the duration of sleep stages. By contrast, the spectral entropies presented in §3b explicitly cover information about durations. It is also important to point out that the analysis has been performed on a per-dataset basis, where transition matrices are computed for each night of each individual. From these transition matrices of different datasets mean transition matrices are computed by averaging the probabilities of all transitions over all datasets in the group of interest.
Figure 2 shows transition matrices obtained by averaging the transition probabilities between different sleep stages in each of the four classes: Young/Normal, Young/Sleep Disorder, Old/Normal, and Old/Sleep Disorder. One can see that the cells next to the diagonal have highest probability which shows that usually transitions occur into the neighbouring stage, except for stage R. Another apparent feature is the asymmetry between the upper and the lower diagonals which reflect the general tendency to pass the sleep stages from wakefulness to deep sleep in the order of adjacent stages. In the opposite direction, transitions to REM sleep, wakefulness or lighter sleep stages which are non-adjacent are more likely. Young healthy subjects have the highest probabilities for transitions in and out of N3 and N4. This corresponds to figure 1, which shows that these subjects have the highest percentage of N3 and N4 in the night and therefore it is likely that they also have the highest transition rates.
Figure 2.
Figure 2. Average transition probabilities (colour coded) between sleep stages awake (W), non-REM 1 (N1), non-REM 2 (N2), non-REM 3 (N3), non-REM 4 (N4) and REM (R) for four groups of subjects: Young/Normal, Old/Normal, Young/Sleep Disorder, Old/Sleep Disorder. The numbers in the cells give the transition probabilities in per mille rounded to integer values. Cells without a number correspond to transitions that never occurred in the dataset. (Online version in colour.)
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To characterize the transition patterns shown in figure 2, we compute the normalized joint entropies of the corresponding probability distributions {pij}
Display Formula
3.1
where N=6 is the number of sleep stages W, N1, N2, N3, N4 and REM. The normalization by the entropy Inline Formula of a uniform two-dimensional distribution renders H to lie in the range [0,1]. The normalized joint entropy H is computed for each subject and low values of H indicate less complex transition patterns.
Figure 3a shows the distributions of H-values for the four classes of subjects whose average transition patterns are shown in figure 2. In table 2, p-values of a Wilcoxon rank-sum test (also known as Wilcoxon–Mann–Whitney test) performed for all pairs of distributions are given, indicating significant differences. These p-values have to be interpreted carefully, because of the relatively high number of individual tests that have been carried out which lead to accumulation of type-1 errors. Nevertheless, the differences between cases with and without sleep disorders in the young and old age groups as well as the difference between the Young and Normal versus Old and Sleep Disorder groups can be detected at a high significance level.
Figure 3.
Figure 3. Distributions of joint entropies H of one-step transitions (equation (3.1)) for (a) four groups of subjects (compare transition matrices in figure 2), (b) subjects with and without sleep disorder and (c) old and young subjects. (Online version in colour.)
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Table 2.
p-Values of a Wilcoxon rank-sum test performed for all pairs of distributions shown in figure 3a.
View inlineView popup
Figure 3b and c shows comparisons of the distributions Normal versus Sleep Disorder and Young versus Old, respectively. The lower entropy values for subjects with sleep disorder (figure 3b) indicate lower complexity due to missing sleep transitions involving deep sleep.
(b) Spectral entropy measures
Kirsch et al. [11] proposed two spectral entropy measures specially suited for application to categorical time series: the WSE and the HSE. These spectral entropy measures can be interpreted as a quantification of the joint frequency distributions of all symbols contained in the original dataset. The names of the entropies are derived from the underlying Walsh- and Haar transformations, respectively. These quantities are computed as follows (the procedure is explained more in detail in [11]).
The original time series consisting of symbols st∈S,t∈[1,n],S={c1,…,cm} is in the first step transformed into m binary time series Inline Formula
Display Formula
3.2
In the second step, either the Walsh transform or the Haar transform is applied to moving temporal windows Inline Formula, t∈[w,w+l−1] of the binary time series. Both transforms make use of a corresponding matrix Inline Formula: the Hadamard matrix in the case of the Walsh transform or the Haar matrix in the case of the Haar transform, each of size l×l, l=2N (see appendix for definitions of the matrices)
Display Formula
3.3
The elements Inline Formula of the l×m matrix Inline Formula are called Walsh/Haar transform coefficients and they are used to compute the corresponding l×m periodogram matrix of the temporal window [w,w+l−1]
Display Formula
3.4
This matrix Pw is then used to define a two-dimensional (normalized) entropy
Display Formula
3.5
with Inline Formula being a normalized version of Pw
Display Formula
3.6
In [11], these entropies are called 2D-WSE and 2D-HSE depending on the applied transform. In the following, we will refer to these quantities simply as WSE and HSE, as only the two-dimensional versions are employed here.
Both quantities are calculated for matrices of size l×l, l=26 for every successive overlapping window [w,w+l−1] of each dataset. This leads to an entropy distribution for each dataset. In order to be able to compare the entropies between groups, we use the mean value of the distribution of each dataset. These mean values lead to the entropy distributions shown in figures 4 and 5. Each pair of distributions in figures 4a and 5a is compared using Wilcoxon rank-sum tests. These results are given in tables 3 and 4.
Table 3.
p-Values of a Wilcoxon rank-sum test performed for all pairs of WSE distributions shown in figure 4a.
View inlineView popup
Table 4.
p-Values of a Wilcoxon rank-sum test performed for all pairs of HSE distributions shown in figure 5a.
View inlineView popup
Figure 4.
Figure 4. Distributions of WSE for (a) four groups of subjects (compare transition matrices in figure 2), (b) subjects with and without sleep disorder and (c) old and young subjects. (Online version in colour.)
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Figure 5.
Figure 5. Distributions of HSE for (a) four groups of subjects (compare transition matrices in figure 2), (b) subjects with and without sleep disorder and (c) old and young subjects. (Online version in colour.)
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The results for the WSE and the HSE are very similar, the distributions show a nearly identical shape. Tables 3 and 4 confirm what already can be seen in figures 4 and 5. The age effect on the spectral entropies can be differentiated at a high significance level. However, a differentiation does not seem possible for the sleep disorder effect, as the p-values clearly exceed the significance threshold for the comparisons Young and Normal versus Young and Sleep Disorder and Old and Normal versus Old and Sleep Disorder.
(c) Transition graphs
In this section, the difference of transition probability matrices of different groups of subjects is used to analyse the impact of age and sleep disorder on one-step transition probabilities. These differences are visualized using pruned graphical representations where links between the sleep stages are plotted only if the distributions underlying the mean values of the particular transition in both groups are significantly different (p<0.01). Links can also be missing if the probabilities involved are too small. Note that the interpretability of p-values in this context must not be overestimated, as they are used here solely to choose relevant links for pruning the graph.
First, we consider changes of transition probabilities due to ageing. Figure 6 shows a comparison of transition patterns of normal old and young subjects. The matrices show the transition probabilities for each group (given as numbers in per mille, compare with figure 2). The graph shows all significant differences of both transition patterns. The links are annotated with the difference values of the corresponding transition probabilities from both matrices. Here, a transition is considered to be significantly different if the p-value obtained when comparing the distributions of the transition probability values from both groups is smaller than 0.01. With ageing we see an increase of transitions between light sleep stages N1 and N2 and between N1 and W. On the other hand, for elderly subjects fewer transitions occur between deep-sleep stages N3 and N4, and between N2 and R. There is no significant difference of transitions N2–N3 between young and old subjects. Elderly subjects wake up more often and exhibit fewer transitions to deep-sleep stage N4 and to REM sleep stage R.
Figure 6.
Figure 6. Difference of sleep-stage transition probabilities of normal old and young subjects displayed as a transition graph obtained from both transition matrices. The numbers at the links in the transition graph equal the difference of the transition probabilities (in per mille). Only significant links (p<0.01) are plotted in the graph. (Online version in colour.)
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To investigate the impact of sleep disorders on the transition probabilities, figure 7 shows a comparison of young subjects with and without sleep disorders. Similar to elderly subjects (figure 6), patients suffering from sleep disorders exhibit a higher probability of transitions within light sleep N1–N2, less transitions within slow wave sleep N3–N4 and no significant change in N2–N3 transitions. Also transitions from N2 to REM sleep are reduced. This can be an expression of reduced slow wave sleep and reduced REM sleep as well in elderly subjects. As a difference we see no significant increase in transitions N1–W. This reflects that young subjects with sleep disorders do not wake up more often compared with normal subjects without any sleep disorder.
Figure 7.
Figure 7. Same type of diagrams as in figure 6, but for Young/Sleep Disorder versus Young/Normal subjects. (Online version in colour.)
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4. Two-step transitions
To learn more about sleep-stage transition patterns, we consider now multistep transitions consisting of K steps starting with K=2. Figure 8 shows ranked probabilities of two-step transitions (the largest 25 values, only). The grey vertical bars give the 25 largest transition probabilities of two-step transitions averaged over all subjects under study. Most probable are transitions N2 Inline Formula N1 Inline Formula N2 and N2 Inline Formula N1 Inline Formula N2 corresponding to light sleep. These transitions occur more often in patients suffering from sleep disorder as can be seen from the dashed lines indicating transition probabilities of both groups Young/Sleep Disorder and Old/Sleep Disorder, respectively. The transition probabilities of Old/Normal subjects equal the total mean, while Young/Normal exhibit a relatively low probability of such light sleep transitions.
Figure 8.
Figure 8. Probabilities of the 25 most probable two-step transitions. Vertical grey bars give averages over all subjects, and (coloured) lines results for different groups of subjects. Dashed boxes indicate transition patterns exhibiting differences between the four groups of subjects. (Online version in colour.)
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The situation is slightly different for two-step transitions including the wake state W. Here transitions N1 Inline Formula W Inline Formula N1 and W Inline Formula N1 Inline Formula W are most probable for old subjects with sleep disorder, followed by the Old/Normal and the Young/Sleep Disorder group. The lowest probability of this transition scenario occurs with young healthy subjects. Transition patterns N4 Inline Formula N3 Inline Formula N4 of deep-sleep transitions or N1 Inline Formula N2 Inline Formula R including REM sleep occur with relatively high probability with young normal subjects and with reduced probability in the groups Old/Sleep Disorder.
5. Markov order tests
Figure 8 clearly indicates that an investigation of multiple transitions instead of single transitions can reveal subtle information about the sleep process. This raises the question which number of transition can be considered as appropriate for further analysis of symbolic dynamics. We are going to investigate this question in the framework of Markov chains.
A Markov chain is a model assuming probabilistic transitions between states with a dependency on a specific number of temporarily previous states. A Markov chain of order k is defined as a probabilistic process where the current transition probability depends on the past k states. A symbolic chain involving n states can therefore be interpreted as a Markov chain of order k=n−1.
Pethel & Hahs [19] developed an exact significance test for determining the order of such a Markov process. This test makes use of the observed data in order to generate surrogates that match the properties of the data under the assumption of a Markov chain with a specific order k. This surrogate generation procedure is done using Whittle's formula [20]. Using an exact hypothesis test a p-value is calculated, which leads in the case of a small p-value to the rejection of the respective null hypothesis. The null hypothesis states that our process is indeed a Markov process of order k. To determine the order of the Markov chain the authors propose to run the test for ascending k starting with k=0 and choose the first k for which the p-value is larger than a significance threshold pth [21].
We applied this Markov order test to each dataset individually using the algorithm published in [22]. We chose Inline Formula as the maximum Markov order and used 1000 surrogates for each test. The method was applied to time series containing only the sleep-stage transitions, the durations were taken out. Figure 9 shows the resulting p-value distributions for four different group comparisons. As mean values of p-values can be misleading we show the fraction of all cases with a p-value larger than the significance threshold pth=0.05.
Figure 9.
Figure 9. Results of the Markov order tests run on each individual dataset (each night is included in the analysis separately). The ordinate displays the fraction of non-significant cases (pth=0.05). Four different group comparisons have been performed. (a) Splitting into four groups according to age (median-split) and sleep disorder (healthy or sleep disorder). (b) Comparison of the two nights of the experiment. (c) Display of the four age-quartiles which had already been analysed in figure 1. (d) Detailed comparison of the different sleep disorders as well as the healthy group. N is the respective number of datasets in the corresponding group. (Online version in colour.)
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The distributions show a very similar pattern for all group comparisons exhibiting a very strong increase in the fraction of non-significant cases for Markov order k=2. On the other hand, the null hypothesis assuming a first-order Markov process has to be rejected in more than 80% of the cases. No clear difference between all groups is visible in the group comparisons. Especially, the comparison of individual nights shows an almost identical shape of the curve.
These results indicate very clearly that the time series of transitions of sleep stages seems to follow a second-order Markov process.
6. Conclusion
Typical patterns of sleep-stage transitions of 196 healthy subjects and 98 patients suffering from different sleep disorders have been identified and quantified in terms of transition probabilities. We compared four groups: Young/Normal, Young/Sleep Disorder, Old/Normal and Old/Sleep Disorder. For each subject, the structure of one-step sleep-stage transitions is characterized by the resulting transition matrices representing the corresponding transition probabilities. To characterize these transition matrices, we computed their (normalized) joint entropy. Entropy distributions of the four classes of subjects studied here showed slightly different patterns (figure 3), which might allow for a distinction of healthy subjects and subjects with sleep disorder. By contrast, the spectral entropy distributions (WSE and HSE) which have been presented in figures 4 and 5 indicate a relatively clear distinction between young and old subjects. Furthermore, one-step transitions are visualized and analysed using (pruned) transition graphs (figures 6 and 7). This new presentation provided evidence that changes in transitions are slightly different with the ageing process and with the presence of sleep disorders. In particular, with ageing more transitions to and from the wake stage (W) occur. We conjecture that more specific details and differences between ageing and sleep disorder may be found when studying multistep transitions. Investigations of two-step transition patterns (figure 8) clearly indicate valuable information contained in the corresponding symbolic sequence of multistep sleep transitions. Markov order tests have been carried out (figure 9) and reveal that a Markov order of 2 is suitable for sleep-stage transition analysis. This result is stable across all group comparisons performed in this publication.
In this study, we also analysed transitions between N3 and N4 because we used scorings from a large study which used Rechtschaffen & Kales [2] scorings. We observe a considerable number of transitions between stages N3 and N4 and in this, we also observe differences between normal subjects and patients with sleep disorders. However, these differences between normal subjects and patients with sleep disorders may be just fluctuations within slow wave sleep and have no further clinical impact. All sleep staging had been performed by three scorers and, therefore, we expect that the fluctuations are not the effect of scoring variability but due to physiology with more and less high amplitude delta waves.
With the low number of patients with sleep disorders (n=98) and with the high number of diverse sleep disorders in this set of studies the presented results are to be considered as preliminary providing only weak evidence for differences. Clinically, well-defined datasets with specific sleep disorders should be used with this analysis in order to show whether the proposed and applied methods allow to distinguish the specific characteristics for pathological sleep-stage transitions for sleep apnoea, periodic limb movement disorders, narcolepsy and also physiological normal ageing.
Funding statement
The authors thank the European Union DG XII for funding the Siesta Project (Biomed-2 BMH4-CT97-2040-SIESTA) through which the database was provided. This work received support through Deutsche Forschungsgemeinschaft (SFB 1002) and the German Center for Cardiovascular Research (DZHK).
Appendix A
(a) Hadamard matrix
The Hadamard matrix Inline Formula is used to compute the Walsh transform. Inline Formula is an n×n matrix containing only the elements −1 and +1. Furthermore, all rows and columns, respectively, are pairwise orthogonal to each other.
We use the so-called Sylvester construction to build an Hadamard matrix of order n
Display Formula
A 1
and
Display Formula
A 2
(b) Haar matrix
The Haar matrix Inline Formula is a matrix representation of discretized Haar wavelets and is used to compute the Haar transform. Its rows and columns, respectively, are pairwise orthogonal to each other. The Haar matrix of order n can be constructed as follows:
Display Formula
A 3
and
Display Formula
A 4
with Inline Formula being the identity matrix of order n and ⊗ being the Kronecker product defined for n p×q matrix A and a matrix B as follows:
Display Formula
A 5
The Haar matrix has to be normalized if it is used for the Haar transform.
Footnotes
One contribution of 12 to a theme issue ‘Enhancing dynamical signatures of complex systems through symbolic computation’.
© 2014 The Author(s) Published by the Royal Society. All rights reserved.
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13 February 2015
Volume 373Issue 2034
Theme issue ‘Enhancing dynamical signatures of complex systems through symbolic computation’ compiled and edited by Alberto Porta, Mathias Baumert, Dirk Cysarz and Niels Wessel
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DOI:https://doi.org/10.1098/rsta.2014.0093
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Help | biology | 85278 | https://da.wikipedia.org/wiki/Taksonomi%20for%20indl%C3%A6ringsm%C3%A5l | Taksonomi for indlæringsmål | En taksonomi for indlæringsmål er en klassifikation af indlæringsmål/læringsmål. Den mest kendte taksonomi blev oprindeligt foreslået af Benjamin Bloom, som arbejdede med affektive, psykomotoriske og kognitive områder.
Andre skelner mellem faglige, generiske og holdningsmæssige læringsmål.
Affektiv
Det affektive område handler om, hvorledes folk reagerer følelsesmæssigt – om evnen til at føle andres smerte eller glæde, men også om motivation, holdninger og værdier.
Psykomotorisk
Det psykomotoriske område handler om evnen til at agere fysisk – eksempelvis at bruge en hammer eller gennemføre gymnastiske øvelser.
Han inddeler i 5 niveauer, hvor 1 er det laveste
Imitation (copy)
Manipulation (follow instructions)
Develop Precision
Articulation (combine, integrate related skills)
Naturalization (automate, become expert)
Kognitiv
Det kognitive område handler om evnen til at "tænke et område igennem". Det kognitive kredser om viden og forståelse for et emne.
Blooms taksonomi arbejder med seks klasser, hvor de højere niveauer inkorporerer de lavere.
Lorin Anderson (en tidligere student hos Bloom) opdaterede Blooms taksonomi.
Læg mærke til skiftet fra navne- til udsagnsord. (OG dermed fra produkter til processer)
Remembering: can the student recall or remember the information? – define, duplicate, list, memorize, recall, repeat, reproduce state
Understanding: can the student explain ideas or concepts? – classify, describe, discuss, explain, identify, locate, recognize, report, select, translate, paraphrase
Applying: can the student use the information in a new way? – choose, demonstrate, dramatize, employ, illustrate, interpret, operate, schedule, sketch, solve, use, write.
Analysing: can the student distinguish between the different parts? – appraise, compare, contrast, criticize, differentiate, discriminate, distinguish, examine, experiment, question, test.
Evaluating: can the student justify a stand or decision? – appraise, argue, defend, judge, select, support, value, evaluate
Creating: can the student create new product or point of view? – assemble, construct, create, design, develop, formulate, write.
Læg mærke til at de to nederste niveauer (evaluating og creating) er byttet om i forhold til den gamle version.
Henvisninger
Generelle
Taxonomy of Educational Objectives: The Classification of Educational Goals, B. S. Bloom (Ed.) David McKay Company, Inc. 1956.
Ledelse og uddannelse – Grundbog, Forsvarskommandoen 1998.
Pædagogik | danish | 0.819379 |
fast_asleep/Ventrolateral_preoptic_nucleus.txt | The ventrolateral preoptic nucleus (VLPO), also known as the intermediate nucleus of the preoptic area (IPA), is a small cluster of neurons situated in the anterior hypothalamus, sitting just above and to the side of the optic chiasm in the brain of humans and other animals. The brain's sleep-promoting nuclei (e.g., the VLPO, parafacial zone, nucleus accumbens core, and lateral hypothalamic MCH neurons), together with the ascending arousal system which includes components in the brainstem, hypothalamus and basal forebrain, are the interconnected neural systems which control states of arousal, sleep, and transitions between these two states. The VLPO is active during sleep, particularly during non-rapid eye movement sleep (NREM sleep), and releases inhibitory neurotransmitters, mainly GABA and galanin, which inhibit neurons of the ascending arousal system that are involved in wakefulness and arousal. The VLPO is in turn innervated by neurons from several components of the ascending arousal system. The VLPO is activated by the endogenous sleep-promoting substances adenosine and prostaglandin D2. The VLPO is inhibited during wakefulness by the arousal-inducing neurotransmitters norepinephrine and acetylcholine. The role of the VLPO in sleep and wakefulness, and its association with sleep disorders – particularly insomnia and narcolepsy – is a growing area of neuroscience research.
Structure[edit]
At least 80% of neurons in the VLPO that project to the ascending arousal system are GABAergic (neurons that produce GABA).
In vitro studies in rats have shown that many neurons in the VLPO that are inhibited by norepinephrine or acetylcholine are multipolar triangular shaped cells with low threshold spikes. These triangular multipolar neurons exist in two sub-populations in the VLPO:
Type 1 – inhibited by serotonin.
Type 2 – excited by serotonin and adenosine.
As adenosine accumulates during wakefulness it is likely that type 2 cells play a role in sleep induction.
The remaining third of neurons in the VLPO are excited by norepinephrine. Their role is unclear.
Function[edit]
Sleep/wakefulness[edit]
Schematic representation of the Flip-Flop Switch Hypothesis
In the early 20th century, Constantin von Economo noted that humans who had encephalitis with lesions in the anterior hypothalamus had insomnia, and proposed a sleep-promoting influence from that area. Animal studies in the mid-20th century in rats and cats confirmed that very large lesions in the preoptic area and basal forebrain resulted in insomnia but did not identify the cell group that was responsible. In 1996, Sherin and colleagues reported the presence of a cell group in the VLPO that expresses cFos (a protein often found in neurons that have recently been active) during sleep, and that these neurons contain the inhibitory neurotransmitters GABA and galanin. These same neurons were found to innervate components of the ascending arousal system, including the tuberomammillary nucleus (TMN) and other components of the lateral hypothalamus; the raphe nuclei; the locus coeruleus (LC); the pedunculopontine (PPT) and laterodorsal tegmental nuclei (LDT); and the parabrachial nucleus (PB). More recent studies using opto- or chemogenetic activation of VLPO neurons have confirmed that they promote sleep.
The sleep-promoting effects of the VLPO neurons is thought to be due to release of GABA and possibly galanin that suppresses firing of arousal system neurons. As the VLPO is also inhibited by neurotransmitters released by components of the arousal systems, such as acetylcholine and norepinephrine, a current theory has proposed that the VLPO and the arousal system form a "flip-flop" circuit. This term from electrical engineering denotes a circuit in which mutual inhibition means that each component of the circuit, as it turns on, turns the other off, resulting in rapid transitions from one state (wake or sleep) to the other, with minimal time in transition states. This theory has been used to create mathematical models that explain much of the wake-sleep behavior in animals, including in pathological states and responses to drugs. Orexin neurons in the posterior lateral hypothalamus potentiate neurons in the ascending arousal system and help stabilize the brain in the waking state (and consolidated wakefulness, which builds up homeostatic sleep drive, helps stabilize the brain during later sleep). The loss of orexin neurons in the disorder narcolepsy destabilizes the wake-sleep switch, resulting in overwhelming sleep episodes during the waking day, as well as more frequent awakenings from sleep at night.
Circadian rhythm[edit]
There is a strong circadian rhythm of sleep in mammals. The “master clock” for circadian rhythms in mammals is the suprachiasmatic nucleus (SCN). The SCN has little if any projection directly to the VLPO neurons. Instead, they project strongly to the adjacent subparaventricular zone, which in turn contains inhibitory GABAergic neurons that innervate the dorsomedial nucleus of the hypothalamus. Lesions of the dorsomedial nucleus almost completely eliminate the circadian rhythm of sleep. GABAergic neurons in the dorsomedial nucleus innervate the VLPO, and glutamatergic neurons innervate the lateral hypothalamus, suggesting that the dorsomedial nucleus mainly promotes wakefulness during the active period (daytime for humans).
Clinical significance[edit]
Insomnia[edit]
Elderly human patients with more galanin neurons in their intermediate nucleus (the human equivalent of the VLPO galanin neurons in rodents) have better, more continuous sleep. A reduced number of VLPO neurons is associated with more fragmented sleep (more awakenings throughout the night).
Lesions in the VLPO in rats results in 50-60% decrease in NREM sleep time and prolonged insomnia. More recent research suggests that stress-induced insomnia could be due to an imbalance of input to arousal system and VLPO neurons.
Sedative/hypnotic drugs[edit]
Many sedative/hypnotic drugs act by binding to and potentiating GABA-A receptors. These include older drugs such as ethanol, chloral hydrate and barbiturates, as well as newer benzodiazepines and "non-benzodiazepine" drugs (such as zolpidem, which bind to the same receptor but have a different chemical configuration), and even anesthetics such as propofol and isoflurane. As the VLPO inputs to the arousal system use this same receptor, these drugs at low doses essentially act by potentiating the VLPO, producing a sleepy state. Animal studies show that VLPO neurons show cFos activation after sedative doses of these drugs, and that VLPO lesions produce resistance to their sedative effects. However, at high doses that produce a surgical plane of anesthesia, these drugs have much more widespread inhibitory effects, that do not depend upon the VLPO. Studies have shown that multiple sedative/hypnotic drugs that act by potentiating GABA-A receptors, including ethanol, chloral hydrate, propofol and gas anesthetics such as isoflurane, at sedative doses increase the activity of the VLPO neurons in mice. This finding suggests that at relatively low sedative doses, these medications may have a common mechanism of action, which includes potentiating the firing of VLPO neurons. High doses used in surgical anesthesia, however, reduce activity of neurons throughout the nervous system. | biology | 322049 | https://da.wikipedia.org/wiki/Neuron | Neuron | Et neuron (fra græsk: sene, nerve), også kaldet en nervecelle, er en celletype i nervesystemet.
De adskiller sig fra andre celler ved deres mange udløbere, kaldet dendritter og aksoner, og ved at være specialiseret i transmittering af signaler, dels elektrisk intraneuronalt og dels ved hjælp af transmitterstoffer interneuronalt, der virker på andre neuroners eller effektorvævenes receptorer (se for eksempel G-protein-koblede receptorer, GPCR og den motoriske endeplade). Af neurotransmittere kan nævnes serotonin, acetylkolin, dopamin, adrenalin og noradrenalin.
Formålet med hjernens netværk af neuroner er kommunikation og informationsbehandling.
Opbygning
Neuroner er de centrale komponenter i hjernen og rygmarven i centralnervesystemet (CNS) samt ganglier i det perifere nervesystem (PNS). En typisk neuron består af et cellelegeme (soma), dendritter og et axon. Dendritter er tynde strukturer, der udspringer fra cellekroppen og ofte strækker sig flere hundrede mikrometer og forgrener sig flere gange. En Axon, også kaldet en nervefiber når de er myelinerede, udspringer fra cellen ved et sted kaldet axon højen og rejser op til en en meter i mennesker og endnu længere i andre arter. En neurons cellekroppe har ofte flere dendritter, men aldrig til mere end ét Axon. Neuronets lange aksoner kan være omgivet af en isolerende fedtskede kaldet myelinskeden, som har til funktion at øge signaleringshastigheden.
Myelinskeden produceres og vedligeholdes i centralnervesystemet af oligodendrocytter og af Schwannske celler i det perifere nervesystem.
I de fleste tilfælde er neuroner genereret af særlige typer af stamceller. Det menes generelt, at neuroner ikke undergår celledeling, men nyere forskning hos hunde viser, at det i nogle tilfælde sker i nethinden. Astrocytter er stjerneformede gliaceller, der er også blevet observeret at blive til neuroner. Hos mennesker ophører neurogenese stort set i voksenalderen, men i to områder i hjernen, hippocampus og den olfaktoriske pære, er der beviser for generering af nye neuroner.
Kommunikation mellem neuroner
En neuron behandler og sender oplysninger gennem elektriske og kemiske signaler. Nervecellernes signaler bygger på en spændingsforskel mellem nervecellens indre og ydre, kaldet membranpotentialet. Er neuronet i hvile, kaldes spændingsforskellen for hvilemembranpotentialet. Er ændringen i membranpotentialet tilstrækkelig stor, genereres en (alt-eller-intet) elektrokemisk puls kaldet et aktionspotentiale, som bevæger sig hurtigt langs cellens axon og aktiverer synaptiske forbindelser til andre celler.
Neurontyper
Neuroner kan overordnet inddeles i projektionsneuroner Golgi type 1 med et enkelt langt akson, der kan kommunikere med andre regioner af nervesystemet, og interneuroner Golgi type 2 som kun befinder sig i en hjerneregion. Der er dog ikke skarp adskillelse mellem disse to typer.
Specialiserede neuroner omfatter: 1) sensoriske neuroner, der reagerer på berøring, lyd, lys og alle andre stimuli, der påvirker cellerne via vores sanser, som derefter sender signaler til rygmarven og hjernen; 2) motoriske neuroner, der modtager signaler fra hjernen og rygmarven, som bevirker muskelsammentrækninger og påvirker glandulare udgange; 3) interneuroner, der forbinder neuroner i den samme region i hjernen eller rygmarven.
Se også
Dendrit, akson, soma, gliacelle
Kranienerver
Neuropeptid
Eksterne henvisninger | danish | 0.434241 |
fiber_eating_birds/VM067.txt | 
[  ](http://sfyl.ifas.ufl.edu/)
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# [  ](/)
# Understanding Pet Bird Nutrition
Gary D. Butcher and Richard D. Miles
The decision to own and care for exotic birds is a decision which cannot be
taken lightly. A lot of responsibility has to be accepted because a pet bird
is not a low-maintenance pet. All pet birds require at least some specialized
care. Very few "beginners" know the answers to the questions that arise
concerning the management, breeding, rearing, disease prevention, and proper
nutrition of birds. The "survivors" in aviculture have successful aviaries
because their teacher has been experience, coupled with trial-and-error.
Sometimes this teacher is expensive and can result in thousands of dollars of
investment being lost. "Beginners" can increase their general knowledge in
aviculture and come up with answers to their questions by reading articles,
traveling to pet bird shows, attending lectures and talking with people who
have experience with pet birds.
Many of the problems such as poor health, poor fertility and hatchability, and
decreased life span can be related to poor nutrition. Improper nutrition can
leave the bird susceptible to many diseases and result in overall poor
performance and lack of vitality. The term "improper nutrition" does not
always mean undernutrition. It can also refer to overnutrition. Allowing any
pet to consume more than they actually require can be just as bad and cause
just as many problems for the owner as the deficiencies that develop from
undernutrition. Today, believe it or not, many pet bird owners are killing
their birds with kindness. Providing too much food (often referred to as
treats) too often and providing too much of a good thing (i.e., too little
variety) is often the cause of the problem.
There are more than 8000 species of birds alive today. There will probably
never be an ideal diet for all bird species. However, for the average pet bird
owner a general knowledge about basic nutritional concepts and feeding can be
of benefit when decisions have to be made. The following material provides
information as a starting point for beginning pet bird owners who want to try
and make the correct choices regarding the feeding of their birds.
## What provides the backbone of proper nutrition?
To properly nourish a pet bird, balanced amounts of nutrients must be
ingested, digested and absorbed into the body. The food that your pet bird
eats is composed of a variety of ingredients and the ingredients are composed
of nutrients. There are six major categories of nutrients: (1) water; (2)
proteins; (3) carbohydrates; (4) lipids; (5) minerals; and (6) vitamins.
Because of the complex nature of these nutrients in the natural ingredients
which make up your bird's diet, they have to be digested in order to release
the building blocks from which they are made. Once these building blocks are
released during the digestive process they can be absorbed into the body and
nourish the trillions of individual cells in the bird. Therefore, any food
that is eaten is really not yet inside the animal body until it is digested
and the prepared nutrients are absorbed. Remember, the digestive tract is only
a hollow muscular tube which stores and prepares the nutrients for absorption.
If the feedstuff is not able to be digested, then the animall does not usually
benefit from these nutrients the feedstuff contains. A healthy digestive tract
is essential if an animal is expected to benefit from the nutrients in
feedstuffs.
## The Six Classes of Nutrients
### Water
Water is the most important nutrient. Your pet bird can lose almost all of its
body fat and stored carbohydrate, as well as over half of its protein, and
still survive. However, a 10% loss of body water can cause serious illness.
Without replacement of the water which is lost, death will result. Water
provides a medium for digestion, absorption, transport, metabolism (actual
utilization of the nutrients by the cells), and the removal of cellular waste
products out of cells and eventually out of the bird in the urine and feces.
There are two basic sources of water, ingested and metabolic. Ingested water
is that consumed by drinking and that which is contained in food. Metabolic
water is the water produced when the food is utilized and can arise from
carbohydrate, protein and lipid metabolism inside the cells. Some feedstuffs
contain more water than other types of feedstuffs. For instance, fresh fruits
and vegetables compared to dry seeds. When the amount of water consumed in
food increases, the amount the animal drinks will usually decrease. Water
consumption increases with increased salt intake, increased environmental
temperature, increased activity and the consumption of dry feedstuffs.
Attempts should be made to have clean, fresh water available to any animal at
all times.
### Protein
Proteins are very large, complex molecules which are made up of amino acids
hooked together as links of a long chain. These linkages between amino acids
are referred to as peptide bonds. Proteins in the body are constantly being
made and broken down. When energy is in short supply the animal has to use
amino acids for energy. Amino acids have much more important jobs to do in
animals than to be used for energy. Therefore, it is always necessary to have
adequate carbohydrate and fat calories available for use as energy.
There are 22 different amino acids required by animals, and all animals
require them at the cellular level. While about 12 of these amino acids can be
made inside animal cells, the other 10 have to be consumed in the animal's
diet. Without a sufficient dietary supply of these ten "essential" amino
acids, the necessary proteins cannot be made by pet birds. The term "protein
quality" is used to describe the amount and proportion of the essential amino
acids in relation to an animal's requirement for each of these amino acids.
Animal protein is of better quality than plant protein. This means that the
plant proteins do not have an amino acid profile that resembles the amino acid
make-up of the proteins in your pet bird. Therefore, it is necessary to give
your pet bird a variety of feedstuffs so that the amino acid(s) that are
somewhat deficient in one feedstuff can be obtained from another feedstuff
that has more of that particular amino acid. Usually, plant proteins are
deficient in the amino acids methionine and lysine with regards to your pet
bird's amino acid requirement. It is best to keep the protein intake of your
pet bird adequate but not in excess. Too much protein is often fed to pet
birds and this leads to problems in the liver and kidney.
### Carbohydrates and Fiber
A carbohydrate molecule is composed of repeating units of the simple sugar
called glucose. Starch is the most common useable form of carbohydrate in the
diet and is considered a soluble carbohydrate by nutritionists. Many glucose
molecules are linked together just as the amino acids in a protein are linked
together to form a long chain. The carbohydrate, starch, is stored by the
plant in seeds for the immediate utilization by the young plant after the seed
germinates. However, the seeds also furnish an excellent source of
carbohydrate for pet birds to use as energy.
In the plant kingdom there is also another type of carbohydrate that is made
up of repeating glucose units. This is a structural carbohydrate refereed to
as cellulose or "crude fiber". Unlike starch, cellulose cannot furnish energy
to pet birds and is considered insoluble. Bacteria in the digestive tract can
utilize cellulose. The reason the bird is not able to utilize the cellulose is
because the linkage (bonding) between the glucose molecules in the long
cellulose chain is not able to be broken during digestion. Animals do not
produce the enzyme called cellulase which can free the glucose for absorption.
The reason some animals such as cattle and sheep (ruminants) can do well on
grass is because their stomachs have the bacterial population that produces
cellulase, and this structural carbohydrate can be utilized by the bacteria.
The bacterial cells are then used by the cow or sheep as food. It is important
to understand that even though crude fiber cannot be broken down for an
immediate energy source, a proper amount of cellulose is necessary in the diet
to promote normal movement of food through the bird's digestive tract. It also
helps to provide the bulk which is necessary for normal droppings. As the
crude fiber in the diet increases, the amount of water consumed by the bird
also will increase.
### Lipids
This nutrient group is composed of the fats and oils which are found in
plants, especially in the seeds. These stored fats and oils in the seed
furnish the energy necessary for the young plant to start its life processes
as germination begins. Once the young plant starts to produce leaves, then
photosynthesis occurs and the plant can manufacture and store more nutrients.
These fats and oils are made up of fatty acids. These fatty acids do not link
together to form long chains as happens with glucose to form starch and
cellulose or with amino acids to form proteins. However, because of their
chemical structure the fats and oils when used by animals for energy are known
to furnish 2.25 times more calories of energy per unit weight than the
carbohydrates and proteins. In other words, if a pet bird eats one gram of fat
it gets 2.25 times more calories from the gram of fat than from 1 gram of
protein or carbohydrate when they are used for energy. Therefore, it is
possible for pet birds to become obese if they are fed seeds high in oil. An
example is sunflower seeds.
The lipid in the diet is not only an excellent energy source but there are
essential fatty acids that are needed by birds. Without the essential fatty
acids in the diet there will be a reduction in egg size and hatchability.
Also, poor skin covering and feather growth will occur. Overall growth is
impaired, and the liver will have a tendency to accumulate fat. Without lipid
in the diet the bird cannot absorb the fat soluble vitamins A, D, E, and K.
Even though taste plays a somewhat minor role in a pet bird's eating habits,
fats are added to animal diets to enhance palatability.
### Minerals
Minerals usually make up less than 1 percent of the body weight of an animal.
The majority of the minerals in the animal belong to a group referred to as
the macro-minerals such as calcium, phosphorus, sodium, potassium, chloride,
magnesium and sulphur. The requirement for these minerals in the diet is
usually expressed as a percent of the diet because they are the most abundant
in the diet. The word "macro" is a Greek word that means big or large.
Therefore, the reason why some minerals are needed in large amounts in the
diet is because these same minerals are found in animals in large amounts.
The minerals such as iron, zinc, copper, manganese, iodine and selenium are
not found in the diet in large amounts and are called the micro- minerals.
Sometimes these minerals are called trace minerals. These minerals are just as
important to the well-being of the bird as those required in larger amounts.
The word "micro" also is a Greek word and means small. When the nutritionist
adds these minerals to the diet, they are added in very small amounts, usually
in parts per million.
The functions of the macro and micro minerals in pet birds and all other
animals is the same at the cellular level. Any nutrition text, whether basic
or advanced will give the functions of the minerals in the body. The signs of
deficiency also are given.
### Vitamins
Vitamins are divided into two groups based on their solubility rather than
their function in the animal. These groups are: fat soluble and water soluble.
The fat soluble vitamins are going to be associated in plants and animals
where fats and oils are located and stored. Whenever feedstuffs are processed
and the lipid is removed, the fat soluble vitamins also are going to be
removed. An example of this is when soybeans or corn are processed and the oil
is removed. The meal remains and has a low lipid and fat soluble vitamin
content.
The fat soluble vitamins are known as vitamins A, D, E, and K. Because in the
bird they are stored in association with fat, it usually takes an extended
period of time to develop a deficiency when the diet has a very low fat
soluble vitamin content. However, deficiencies can and do exist in pet birds,
especially when the owners are not providing the bird with enough variety of
feedstuffs in the diet. The ability of fat soluble vitamins to be stored has
its advantages, but this ability also has its disadvantages. The possibility
of hypervitaminosis exists. In other words, the fat soluble vitamins can be
toxic if consumed in large amounts. This can happen when oversupplementation
or over-fortification occurs, especially with the fat soluble vitamins capable
of being administered through the drinking water. Overfortification with
vitamins A and D should be of major concern. Normally, if pet birds are
provided with a variety of fresh, wholesome feedstuffs, supplementation of the
vitamins is unnecessary and is an additional expense that can be avoided. The
age, health, present diet and breeding status may help determine if dietary
supplementation is necessary.
The water soluble vitamins are the B complex as well as Vitamin C. These
vitamins such as thiamin, riboflavin, niacin, pyridoxine, etc., can not be
stored in the animal because they are soluble in water. They must be in the
diet on a continuous basis. The B-complex vitamins are involved in the
regulation of energy metabolism in the cells and participate in so many
biochemical reactions that it is difficult to separate out their individual
deficiency signs. These vitamins are sometimes referred to as the "sparkplugs"
in the cell that help the enzymes utilize the energy provided by the fuel
nutrients (i.e., carbohydrates, lipids, and protein).
Life in animals and plants arises from the millions of organized biochemical
reactions occurring simultaneously each second in trillions of cells. These
cellular reactions are dependent on enzymes, and most of the enzymes require
assistance to carry out these reactions. These helpers are the B-complex
vitamins. Therefore, where there is life there are enzymes and B-vitamins. It
should be obvious then that the richest source of B-vitamins in plants and
animals should be located where there are the most life processes (biochemical
reactions) occurring. In other words, the highest concentrations of B-vitamins
in plants and animals are usually found in the tissues doing the most living.
In animals these tissues would be the liver, kidney, muscle, brain, etc. Rich
sources of B-vitamins in plants are the leaves, the germ of the seed, and
young sprouts. Therefore, keeping this in mind will help the beginning pet
bird owner select proper food combinations.
The numerous cellular functions of both the fat and water soluble vitamins,
along with the signs common in their deficiencies, are discussed in detail in
basic nutrition books. As with the minerals, the functions of the vitamins at
the cellular level in animals are similar. To say that one mineral or vitamin
is the most important in birds is misleading. Each of the individual minerals
and vitamins is important. No mineral or vitamin is more or less important
than any other.
## What is the best diet to feed my pet bird?
A balanced diet, sometimes referred to as a complete diet, is the best type of
diet to feed to any companion animal. A balanced pet bird diet contains a
combination of the nutrients to meet the nutritional requirements of the bird.
Of course, the diet being fed should furnish the nutrients required by the
animal as related to age, health, breeding status, etc. For instance, a diet
designed for a growing bird or one designed to maintain an older bird is not
sufficient for breeding purposes because the nutritional requirements change.
The knowledge that now exists regarding the proper nutritional requirements of
pet birds lags behind other animal industries. There will probably never be
one perfect diet available for all the pet birds available today. The nutrient
needs and eating habits of the various birds are different. Many commercial
companies manufacture and sell properly formulated bird diets (pellets,
crumbles, etc.). In the long run, these are the best—but may not be as much
"fun" to feed or watch the pet bird eat.
## If I can't feed a balanced diet to my pet bird, then what should I do?
The nutrients that animals need are found in natural feedstuffs. These
feedstuffs can be divided into the four common food groups. These are: (1)
grains; (2) fruits and vegetables; (3) protein sources; and (4) dairy
products.
A wide variety of feedstuffs (seeds) are available in grains (group 1). The
seeds will be used mostly by the bird as an energy source. The majority of
energy will be from the starch. The seed hull is mostly complex insoluble
carbohydrate and is of very little nutritional value. In fruits and vegetables
(group 2), a greater concentration of vitamins is present than is found in
grains. This is especially true for vitamins A, E, K, and the B-complex. Even
though vitamin A is not present in plants, a plant pigment known as carotene
is present and is converted into vitamin A. Usually, most green leafy
vegetables and colorful vegetables contain carotene.
Protein sources (group 3) include beef, fish, chicken, pork, eggs, beans,
peas, etc. Animal tissue and animal products, such as milk and eggs, contain
vitamin B12. Only microorganisms can make B12 and yes, the B12 that is in your
body and other animals was produced by these microorganisms. Remember, nothing
that grows out of the earth or flies, swims or walks can synthesize vitamin
B12. This group of feedstuffs supplies the protein and essential amino acids
required by pet birds. Meat also contains other nutrients such as vitamins and
trace minerals. In dairy products (group 4), protein, essential amino acids,
vitamins and minerals (especially calcium) are furnished in the diet. If it is
not possible for a pet bird owner to provide a complete-pelleted-balanced diet
each day, then the bird should be furnished with the feedstuffs found in these
four major food groups along with fresh water. The nutritional requirements
will be met if the bird eats some feedstuffs from each group. Normally, this
type of feeding practice results in excessive nutrient consumption (above the
requirement) and wastage.
## Can I feed my pet bird only seed?
The answer is no. Do not feed pet birds only seeds. Seeds do not contain
sufficient nutrients to sustain a healthy bird or provide adequate nutrients
for reproduction. Seeds are very low in calcium. The requirement of calcium
for growing birds is probably close to 1 percent of the diet or 10,000 parts
per million in the diet. Seeds contain only 200 to 500 parts per million (0.02
to 0.05 percent) calcium. Therefore, your pet bird will be very deficient in
calcium. Bird seeds are also deficient in protein, and the quality of the
protein is poor. Sodium, zinc and manganese are deficient. Carotene (vitamin
A) and vitamin D are deficient. A lack of vitamin D is known to make the
calcium deficiency worse. Seeds are higher in phosphorus than in calcium. This
imbalance of calcium to phosphorus will cause severe problems in the bird if
all the bird eats is seed. Sunflower seeds are well-liked by parrots, and
there are 8 parts phosphorus to every part calcium in this seed. Many seeds
are rich in fat, and this can lead to obesity in the bird because they will
overconsume on energy. Birds usually eat to satisfy an energy requirement;
however, because the seeds are consumed and swallowed whole, the bird
overconsumes before the desire to stop eating occurs. Many seeds are deficient
in the essential fatty acids. All seeds are also low in iodine and goiter can
develop. If seeds are going to be fed, then a variety of other feedstuffs also
should be furnished. It is important to realize that pet birds can be fed all
seed diets for many years before they begin to look unhealthy. Usually, by the
time a pet bird really looks sick it is not long before the bird will probably
die. This is true for nutritional, bacterial and viral-related diseases.
## What about "'fortified" seed mixtures?
When a feedstuff is fortified it means that something has been added to it to
hopefully increase the nutritional value. Many manufacturers supplement seed-
based diets in a variety of manners. One of the least efficient methods is
coating the seed with nutrients (usually sprayed on the outside of the hull).
Waste occurs and very little of this nutrient is consumed in this manner. Many
vitamins and trace minerals are added to seed mixtures in this way. A pellet
which contains adequate nutrient levels is sometimes added to the seed
mixture. The pellet usually supplements the seed by providing the bird with
what is lacking in the seed. However, the pet bird owner does not really know
if the bird is being selective and eating more of the seed than the pellet.
## What are the common problems that pet bird veterinarians see today that
are caused by feeding?
Today, obesity is a big problem in the pet bird. The owner of the pet bird
wants to shower the bird with affection and one way to show affection is to
shower the bird with love and care. Many times the love is accompanied with
too many "treats". Energy intake is increased and the bird becomes obese. Fat
deposits inside the body occur around the vital organs, and the reproductive
tract is infiltrated with fat. This can cause problems with reproduction.
Also, a fat bird is subject to liver and pancreas problems.
Another problem that is commonly seen is caused by not allowing the bird
access to a variety of foods in the four basic food groups. An example is
providing only seeds. This can lead to severe nutritional deficiencies.
Variety is sometimes said to be the spice of life. However, the nutritionist
knows very well that in animal nutrition variety is essential for life.
Too much protein consumption is another problem that occurs often in pet
birds. Any excess protein above the bird's requirement for amino acids will be
converted to energy and used or stored. The nitrogen in the amino acids has to
be handled in a very special way by the liver and then this nitrogen has to be
excreted. The liver and kidney can be damaged from excess protein, especially
if it is continually fed to the bird in large amounts.
Pet birds enjoy eating as much as any companion animal. Hopefully, having read
this information, you now will enjoy feeding a variety of feedstuffs to your
pet bird. By providing a variety of feedstuffs, you are allowing your bird
access to the nutrients necessary for good health.
DOWNLOAD
### Publication # CIR1082
Release Date: June 4, 2018
Reviewed At: January 6, 2022
#### Related Experts
#### [ Miles, Richard D. ](/experts/rdmiles "Miles, Richard D.")
University of Florida
#### [ Butcher, Gary D ](/experts/butcher "Butcher, Gary D")
Specialist/SSA/RSA
University of Florida
#### Related Units
#### [ Veterinary Medicine-Large Animal Clinical Sciences
](/units/veterinary_medicine "Veterinary Medicine-Large Animal Clinical
Sciences")
#### Related Topics
#### [ Alternative Livestock ](/topics/alternative-livestock "Alternative
Livestock")
#### [ Pet Birds ](/topics/birds?association=Pet%20Birds#PET_BIRDS)
* Critical Issue: 1\. Agricultural and Horticultural Enterprises
### About this Publication
This document is CIR1082, one of a series of the Veterinary Medicine-Large
Animal Clinical Sciences Department, UF/IFAS Extension. Original publication
date February 1993. Visit the EDIS website at [ https://edis.ifas.ufl.edu
](https://edis.ifas.ufl.edu) for the currently supported version of this
publication.
### About the Authors
Gary D. Butcher, avian veterinarian, associate professor, College of
Veterinary Medicine-Large Animal Clinical Sciences; and Richard D. Miles,
professor, Animal Sciences Department; UF/IFAS Extension, Gainesville, FL
32611.
### Contacts
* Gary Butcher
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Last Modified: 8/19/2021
| biology | 4362752 | https://sv.wikipedia.org/wiki/Uebelmannia%20buiningii | Uebelmannia buiningii | Uebelmannia buiningii är en kaktusväxtart som beskrevs av Donald. Uebelmannia buiningii ingår i släktet Uebelmannia och familjen kaktusväxter. Inga underarter finns listade i Catalogue of Life.
Denna kaktus förekommer endemisk i delstaten Minas Gerais i östra Brasilien. Exemplar hittades vid 1200 meter över havet. Det kända utbredningsområdet är endast 40 km² stort. Uebelmannia buiningii växer i klippiga områden tillsammans med andra låga växter.
Flera exemplar samlas illegalt och sälj som prydnadsväxt. Även betande djur och bränder skadar populationen. IUCN listar arten som akut hotad (CR).
Källor
Externa länkar
Kaktusväxter
buiningii | swedish | 1.237426 |
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