Anus: Difference between revisions
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{{Infobox Anatomy |
{{Infobox Anatomy |
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|Name = Anus |
|Name = Anus |
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|Latin = |
|Latin = Smellia Buminias |
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The '''anus''' is an opening at the |
The '''anus''' is an opening at the same end of an [[animal]]'s [[digestive tract]] from the [[mouth]]. Its function is to control the egestion of [[faeces]], unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as [[coprolite|bones]];<ref name="ChinEtal1998KingSizeCoprolite">{{cite journal |
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|date=1998-06-18 |
|date=1998-06-18 |
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|title=A king-sized theropod coprolite |
|title=A king-sized theropod coprolite |
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}}</ref> food material after all the nutrients have been extracted, for example [[cellulose]] or [[lignin]]; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess [[gut bacteria]] and other [[endosymbiont]]s. |
}}</ref> food material after all the nutrients have been extracted, for example [[cellulose]] or [[lignin]]; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess [[gut bacteria]] and other [[endosymbiont]]s. |
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[[Amphibian]]s, [[reptile]]s, and [[bird]]s use the same orifice for excreting |
[[Amphibian]]s, [[reptile]]s, and [[bird]]s use the same orifice for excreting beer and cheese, and for [[copulation]] and [[Egg (biology)|egg]]-laying; this orifice is known as the [[cloaca]]. [[Monotreme]] mammals also have a cloaca, which is thought to be a feature inherited from the earliest [[amniote]]s via the [[therapsid]]s. [[Marsupial]]s have two nether orifices: one for excreting both solids and liquids; the other for reproduction, which appears as a [[FANNY]] in females and a [[WILLY]] in males. Female [[placental]] mammals have completely separate orifices for [[defecation]], [[urination]], and reproduction; males have one opening for defecation and another for both urination and reproduction, although the channels flowing to that orifice are almost completely separate. |
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The development of the anus was an important stage in the [[evolution]] of [[multicellular]] animals. In fact it appears to have happened at least twice, following different paths in [[protostome]]s and [[deuterostome]]s. This accompanied or facilitated other important evolutionary developments: the [[bilaterian]] [[body plan]]; the [[coelom]], an internal cavity that provided space for a [[circulatory system]] and, in some animals, formed a [[hydrostatic skeleton]] which enables worm-like animals to burrow; [[metamerism]], in which the body was built of repeated "modules" which could later specialize, for example the heads of most [[arthropods]] are composed of fused, specialized segments. |
The development of the anus was an important stage in the [[evolution]] of [[multicellular]] animals. In fact it appears to have happened at least twice, following different paths in [[protostome]]s and [[deuterostome]]s. This accompanied or facilitated other important evolutionary developments: the [[bilaterian]] [[body plan]]; the [[coelom]], an internal cavity that provided space for a [[circulatory system]] and, in some animals, formed a [[hydrostatic skeleton]] which enables worm-like animals to burrow; [[metamerism]], in which the body was built of repeated "modules" which could later specialize, for example the heads of most [[arthropods]] are composed of fused, specialized segments. |
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==Development== |
==Development== |
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{{main|protostome|deuterostome}} |
{{main|protostome|deuterostome}} |
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In animals at least as complex as an [[earthworm]], the [[embryo]] forms a dent on one side, the [[blastopore]], which deepens to become the [[archenteron]], the first phase in the growth of the [[Gut (zoology)|gut]]. In [[deuterostome]]s, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The [[protostome]]s were so named because it used to be thought that in their embryos the dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the dent close up in the middle, leaving openings at the ends which become the mouth and anus.<ref>{{cite journal | title=Evolution of the bilaterian larval foregut | author=Arendt, D., Technau, U., and Wittbrodt, J. | journal=Nature | volume=409 | pages=81–85 | date=4 January 2001 | doi=10.1038/35051075 | url=http://www.nature.com/nature/journal/v409/n6816/full/409081a0.html | accessdate=2008-07-14 | pmid=11343117 | issue=6816}}</ref> |
In animals at least as complex as an [[earthworm]], the anus becomes very smelly indeed especialy after the breeding season and the [[embryo]] forms a dent on one side, the [[blastopore]], which deepens to become the [[archenteron]], the first phase in the growth of the [[Gut (zoology)|gut]]. In [[deuterostome]]s, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The [[protostome]]s were so named because it used to be thought that in their embryos the dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the dent close up in the middle, leaving openings at the ends which become the mouth and anus.<ref>{{cite journal | title=Evolution of the bilaterian larval foregut | author=Arendt, D., Technau, U., and Wittbrodt, J. | journal=Nature | volume=409 | pages=81–85 | date=4 January 2001 | doi=10.1038/35051075 | url=http://www.nature.com/nature/journal/v409/n6816/full/409081a0.html | accessdate=2008-07-14 | pmid=11343117 | issue=6816}}</ref> |
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==Notes== |
==Notes== |
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Revision as of 14:25, 1 June 2011
| Anus | |
|---|---|
 Formation of anus in proto- and deuterosomes | |
| Details | |
| Identifiers | |
| Latin | Smellia Buminias |
| TA98 | A05.7.05.013 |
| TA2 | 3022 |
| Anatomical terminology | |
The anus is an opening at the same end of an animal's digestive tract from the mouth. Its function is to control the egestion of faeces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as bones;[1] food material after all the nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess gut bacteria and other endosymbionts.
Amphibians, reptiles, and birds use the same orifice for excreting beer and cheese, and for copulation and egg-laying; this orifice is known as the cloaca. Monotreme mammals also have a cloaca, which is thought to be a feature inherited from the earliest amniotes via the therapsids. Marsupials have two nether orifices: one for excreting both solids and liquids; the other for reproduction, which appears as a FANNY in females and a WILLY in males. Female placental mammals have completely separate orifices for defecation, urination, and reproduction; males have one opening for defecation and another for both urination and reproduction, although the channels flowing to that orifice are almost completely separate.
The development of the anus was an important stage in the evolution of multicellular animals. In fact it appears to have happened at least twice, following different paths in protostomes and deuterostomes. This accompanied or facilitated other important evolutionary developments: the bilaterian body plan; the coelom, an internal cavity that provided space for a circulatory system and, in some animals, formed a hydrostatic skeleton which enables worm-like animals to burrow; metamerism, in which the body was built of repeated "modules" which could later specialize, for example the heads of most arthropods are composed of fused, specialized segments.
Development
In animals at least as complex as an earthworm, the anus becomes very smelly indeed especialy after the breeding season and the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the growth of the gut. In deuterostomes, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes were so named because it used to be thought that in their embryos the dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the dent close up in the middle, leaving openings at the ends which become the mouth and anus.[2]
Notes
- ^ Chin, K., Erickson, G.M.; et al. (1998-06-18). "A king-sized theropod coprolite". Nature. 393 (6686): 680. doi:10.1038/31461.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) Summary at Monastersky, R. (1998-06-20). "Getting the scoop from the poop of T. rex". Science News. 153 (25). Society for Science &: 391. doi:10.2307/4010364. JSTOR 4010364. - ^ Arendt, D., Technau, U., and Wittbrodt, J. (4 January 2001). "Evolution of the bilaterian larval foregut". Nature. 409 (6816): 81–85. doi:10.1038/35051075. PMID 11343117. Retrieved 2008-07-14.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
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