The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, depending on the type of animal, includes: matter which the animal cannot digest, such as bones;[1] food material after 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 (known as the cloaca) for excreting liquid and solid wastes, for copulation and egg-laying. Monotreme mammals also have a cloaca, which is thought to be a feature inherited from the earliest amniotes via the therapsids. Marsupials have a single orifice for excreting both solids and liquids and, in females, a separate vagina for reproduction. 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. 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, and metamerism, in which the body was built of repeated "modules" which could later specialize, such as the heads of most arthropods, which are composed of fused, specialized segments.
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. 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 was thought that in their embryos the dent formed the mouth first (proto– meaning "first") and the anus was formed later at the opening made by the other end of the gut. Research from 2001 shows the edges of the dent close up in the middles of protosomes, leaving openings at the ends which become the mouths and anuses.[2]
^Chin, K.; Erickson, G.M.; et al. (1998-06-18). "A king-sized theropod coprolite". Nature. 393 (6686): 680. Bibcode:1998Natur.393..680C. doi:10.1038/31461. S2CID 4343329. Summary at Monastersky, R. (1998-06-20). . Science News. Society for Science &. 153 (25): 391. doi:10.2307/4010364. JSTOR 4010364. Archived from the original on 2013-05-11. Retrieved 2009-04-24.
^Arendt, D.; Technau, U. & Wittbrodt, J. (4 January 2001). "Evolution of the bilaterian larval foregut". Nature. 409 (6816): 81–85. Bibcode:2001Natur.409...81A. doi:10.1038/35051075. PMID 11343117. S2CID 4406268.
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January 31, 2023
anus, details, specific, humans, human, anus, other, uses, disambiguation, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, so. For details specific to humans see Human anus For other uses see Anus disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Anus news newspapers books scholar JSTOR September 2021 Learn how and when to remove this template message The anus Latin ring or circle is an opening at the opposite end of an animal s digestive tract from the mouth Its function is to control the expulsion of feces the residual semi solid waste that remains after food digestion which depending on the type of animal includes matter which the animal cannot digest such as bones 1 food material after 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 AnusFormation of anus in proto and deuterostomesDetailsPrecursorProctodeumSystemAlimentary sometimes reproductiveArteryInferior rectal arteryVeinInferior rectal veinNerveInferior rectal nervesLymphSuperficial inguinal lymph nodesIdentifiersLatinAnusTA98A05 7 05 013TA23022Anatomical terminology edit on Wikidata Amphibians reptiles and birds use the same orifice known as the cloaca for excreting liquid and solid wastes for copulation and egg laying Monotreme mammals also have a cloaca which is thought to be a feature inherited from the earliest amniotes via the therapsids Marsupials have a single orifice for excreting both solids and liquids and in females a separate vagina for reproduction 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 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 and metamerism in which the body was built of repeated modules which could later specialize such as the heads of most arthropods which are composed of fused specialized segments Contents 1 Development 2 See also 3 References 4 External linksDevelopmentMain articles Protostome and Deuterostome 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 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 was thought that in their embryos the dent formed the mouth first proto meaning first and the anus was formed later at the opening made by the other end of the gut Research from 2001 shows the edges of the dent close up in the middles of protosomes leaving openings at the ends which become the mouths and anuses 2 See also Evolutionary biology portal The dictionary definition of anus at Wiktionary Anal canal Functional segment of the large intestine Anorectal manometry Medical functional test of the anus and rectum Cloaca Posterior opening in zoology Imperforate anus Birth defect of malformed rectumReferences Chin K Erickson G M et al 1998 06 18 A king sized theropod coprolite Nature 393 6686 680 Bibcode 1998Natur 393 680C doi 10 1038 31461 S2CID 4343329 Summary at Monastersky R 1998 06 20 Getting the scoop from the poop of T rex Science News Society for Science amp 38 153 25 391 doi 10 2307 4010364 JSTOR 4010364 Archived from the original on 2013 05 11 Retrieved 2009 04 24 Arendt D Technau U amp Wittbrodt J 4 January 2001 Evolution of the bilaterian larval foregut Nature 409 6816 81 85 Bibcode 2001Natur 409 81A doi 10 1038 35051075 PMID 11343117 S2CID 4406268 External links Media related to Anus at Wikimedia Commons Retrieved from https en wikipedia org w index php title Anus amp oldid 1122907214, wikipedia, wiki, book, books, library,
