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{{short description|Digestive tract waste expulsion opening}}{{Redirect|Butthole|the slang word|Asshole}}
]
{{Redirect|Pooper|the fan nickname of the fictional Pokémon species|Wooper}}{{About|the anuses of animals in general|details specific to humans|Human anus|other uses}}
]
{{pp-semi|small=yes}}
{{otheruses1|the bodily orifice}}
{{redirect|Anal}} {{pp-move-indef}}
{{Infobox anatomy
| Name = Anus
| Latin = anus
| Image = File:Dog’s anus.jpg
| Caption = Anus of a ]
| Width =
| Image2 = Protovsdeuterostomes.svg
| Caption2 = Formation of anus in proto- and deuterostomes
| Precursor = ]
| System = ]
| Artery = ]
| Vein = ]
| Nerve = ]
| Lymph = ]
}}


In ]s, ]s and most ],<ref>{{cite book|last1=Helms|first1=Doris R.|last2=Helms|first2=Carl W.|last3=Kosinski|first3=Robert J.|last4=Cummings|first4=John C.|title=Biology in the Laboratory With BioBytes 3.1 CD-ROM|url=https://books.google.com/books?id=Fw54Ce6DfPYC&pg=SA36-PA12|publisher=W. H. Freeman|page=36-12|date=1997|isbn=978-0-7167-3146-7 }}</ref><ref>{{cite book|title=A living bay: the underwater world of Monterey Bay|year=2000|publisher=University of California Press|isbn=978-0-520-22149-9|author=Langstroth, Lovell|author2=Libby Langstroth|author3=Todd Newberry|author4=Monterey Bay Aquarium|page=|url=https://archive.org/details/livingbayunderwa0000lang/page/244}}</ref> the '''anus''' ({{plural form}}: '''anuses''' or '''ani'''; from ], 'ring' or 'circle') is the external ] at the ''exit'' end of the ] (]), i.e. the opposite end from the ]. Its function is to facilitate the ] of wastes that remain after ].
In ], the '''anus''' (from ] ''ānus'' "ring, anus") is the external opening of the ]. Closure is controlled by ] ]s. ] are expelled from the body through the anus during the act of ], which is the primary function of the anus. Most animals &mdash; from simple worms to elephants and humans &mdash; have a tubular ], with a ] at one end and an anus at the other.


Bowel contents that pass through the anus include the gaseous ] and the semi-solid ], which (depending on the type of animal) include: indigestible matter such as ]s, ] ]s, ] ]s and ]s;<ref name="ChinEtal1998KingSizeCoprolite">{{cite journal |date=1998-06-18 |title=A king-sized theropod coprolite |journal=] |volume=393 |pages=680 |author=Chin, K. |author2=Erickson, G.M. |doi=10.1038/31461 |issue=6686 |bibcode=1998Natur.393..680C |s2cid=4343329 |url=https://zenodo.org/record/3943146 |display-authors=etal }} Summary at {{cite journal |author=Monastersky, R. |title=Getting the scoop from the poop of ''T. rex'' |journal=Science News |volume=153 |issue=25 |date=1998-06-20 |pages=391 |url=http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |doi=10.2307/4010364 |publisher=Society for Science &#38 |jstor=4010364 |access-date=2009-04-24 |archive-date=2013-05-11 |archive-url=https://web.archive.org/web/20130511121022/http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |url-status=dead }}</ref> residual ] material after the digestible ]s have been extracted, for example ] or ]; ingested matter which would be toxic if it remained in the digestive tract; ] ]s like ]-containing ]; and dead ]l ] or excess ] and other ]s. Passage of feces through the anus is typically controlled by ] ]s, and failure to stop unwanted passages results in ].
The anus is often considered a ] part of the body, and is known by a large number of usually ] ] terms.


]s, ]s and ]s use a similar orifice (known as the ]) for excreting liquid and solid wastes, for ] and ]. ] mammals also have a cloaca, which is thought to be a feature inherited from the earliest ]s. ]s have a single orifice for excreting both solids and liquids and, in females, a separate ] for reproduction. Female ] mammals have completely separate orifices for ], ], and reproduction; males have one opening for defecation and ], although the channels flowing to that orifice are almost completely separate.
== Structure ==
The human anus is situated between the ]s, ] to the ]. It has two anal sphincters, one internal, the other external. These hold the anus closed until time to defecate.<!-- or time for sexual activity.--> One sphincter consists of smooth muscle and its action is involuntary; the other consists of striated muscle and its action is voluntary. In many animals, the anus is surrounded by ].


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 ]s and ]s. This accompanied or facilitated other important evolutionary developments: the ], the ], and ], in which the body was built of repeated "modules" which could later specialize, such as the heads of most ], which are composed of fused, specialized segments.
== Role in defecation ==
{{main|Defecation}}


In ], there are species with one and sometimes two permanent anuses, species like the ] grows an anus, which then disappear when it is no longer needed.<ref></ref>
When the ] is full, the increase in intrarectal pressure forces the walls of the ] apart allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincters of the anus allow the feces to be passed by muscles pulling the anus up over the exiting feces.


==Development==
To prevent diseases of the anus and to promote general hygiene, humans often clean the anus after emptying the bowels. A wash with a ] or a wiping with ] are often used to clear the anus of fecal matter.
{{main|Protostome|Deuterostome}}
In animals at least as complex as an ], the ] forms a dent on one side, the ], which deepens to become the ], the first phase in the growth of the ]. 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 ('']'' 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.<ref>{{cite journal|title=Evolution of the bilaterian larval foregut |author=Arendt, D. |author2=Technau, U. |author3=Wittbrodt, J. |name-list-style=amp |journal=] |volume=409 |pages=81–85 |date=4 January 2001 |doi=10.1038/35051075 |pmid=11343117 |issue=6816|bibcode=2001Natur.409...81A |s2cid=4406268 }}</ref>


==See also==
== Role in sexuality ==
{{Portal|Evolutionary biology}}
{{main|Anal sex}}
*{{wiktionary-inline|anus}}
<!-- Please keep entries in alphabetical order -->
* {{annotated link|Anal canal}}
* {{annotated link|Anorectal manometry}}
* {{annotated link|Imperforate anus}}
<!-- please keep entries in alphabetical order -->


==References==
The anus has a relatively high concentration of ]s and is an ]. ]'s theory of ], for example, described an ], hypothesizing that toddlers derive pleasure from retaining and expelling feces. This is the source of the term "anal" and the derived, ] vulgarism "]."
{{reflist}}

] can be pleasurable for both the insertive partner and the receptive partner. For the receptive partner, pleasure from anal intercourse is also thought to be related to the shared wall between the rectum and the ] (for females) as well as the ] or ] (for males). For the insertive partner, the tightness of the anus is often said to be a source of pleasure in penetrative anal sex.

Anal intercourse, sometimes referred to as ] or ], is a human sexual activity, but is considered ] in a number of moral systems, and it has been, and in some ] continues to be, a crime carrying severe punishment.

Anal sexual activity need not include penetration. The anus also plays an important role in ], ] and ].

] can stimulate the nerves around the anus and can be considered pleasurable. Care must be taken to maintain elasticity.

==Puberty==
During ] as testosterone triggers off growth in other places in the male body, pubic hair begins to appear around the anus around age 13-14 but only appears as thin colourless hairs. As the male's genitals mature and pubic hair gets darker and thicker, the anus hair also changes and follows the same characteristics. By the age of 18, the anus is surrounded by pubic hair.

==Health==
]
Hygiene is important for good anal health and anal sex. Washing with a mild soap and water will keep the anus clean. Harsh soaps or wiping vigorously with toilet paper can irritate the skin around the anus, making it itchy or sore. ] are sometimes the source of ].

Care should be taken not to strip the anus of natural oils that keep the skin around the opening supple and elastic.

Penetration with a penis or sex toy can irritate or tear the inside of the anus. Lubrication is often recommended to ease penetration.
The risk of injury to the anal sphincter should be a concern, which can lead on to lack of control of defecation and faecal incontinence. Similarly if the anus is torn, this can occasionally cause a fistula formation which can not only cause faecal leaking, but also can be very difficult to treat.

]s can improve the tone of the outer sphincter muscle.

==Cosmetics==
Shaving, trimming, ], or ] can clear the perineum of hair.

] is a relatively new ] phenomenon where the perineum, which darkens over the years,{{fact}} is lightened for a more youthful appearance. In April 2000, gossip columnist ] reported that actresses including ] have had their anuses bleached.

] is among the more extreme piercings and usually interferes with the function of the anus.

== Pathology ==
], ], ], ], ], ] and ] are among the diseases of the anus that benefit from medical intervention. Birth defects of the anus include ] and ]. The anus is also a frequent site of ]s.
Damaged ] (] in more severe cases) — caused by careless surgery in the ] region or by rough/abrupt penetration in ] — can lead to ] and/or ], chronic ] and, ultimately, ].

In ] the ]ian term ] is used.

==See also==
{{wiktionarypar|anus}}
* ]
* ]
* ]
* ]
* ]
* ]


== External links == == External links ==
* {{commons category-inline|Anus}}
* Patient Queries answered by Physicians and Gastroenterologists pertaining to problems of the Anus


{{digestive system}} {{Authority control}}
{{human anatomical features}}


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Latest revision as of 22:22, 30 December 2024

Digestive tract waste expulsion opening"Butthole" redirects here. For the slang word, see Asshole. "Pooper" redirects here. For the fan nickname of the fictional Pokémon species, see Wooper.This article is about the anuses of animals in general. For details specific to humans, see Human anus. For other uses, see Anus (disambiguation).

Anus
Anus of a dog
Formation of anus in proto- and deuterostomes
Details
PrecursorProctodeum
SystemAlimentary
ArteryInferior rectal artery
VeinInferior rectal vein
NerveInferior rectal nerves
LymphSuperficial inguinal lymph nodes
Identifiers
Latinanus
TA98A05.7.05.013
TA23022
Anatomical terminology[edit on Wikidata]

In mammals, invertebrates and most fish, the anus (pl.: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the exit end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facilitate the expulsion of wastes that remain after digestion.

Bowel contents that pass through the anus include the gaseous flatus and the semi-solid feces, which (depending on the type of animal) include: indigestible matter such as bones, hair pellets, endozoochorous seeds and digestive rocks; residual food material after the digestible nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; excreted metabolites like bilirubin-containing bile; and dead mucosal epithelia or excess gut bacteria and other endosymbionts. Passage of feces through the anus is typically controlled by muscular sphincters, and failure to stop unwanted passages results in fecal incontinence.

Amphibians, reptiles and birds use a similar 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. 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 comb jellies, there are species with one and sometimes two permanent anuses, species like the warty comb jelly grows an anus, which then disappear when it is no longer needed.

Development

Main 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.

See also

References

  1. Helms, Doris R.; Helms, Carl W.; Kosinski, Robert J.; Cummings, John C. (1997). Biology in the Laboratory With BioBytes 3.1 CD-ROM. W. H. Freeman. p. 36-12. ISBN 978-0-7167-3146-7.
  2. Langstroth, Lovell; Libby Langstroth; Todd Newberry; Monterey Bay Aquarium (2000). A living bay: the underwater world of Monterey Bay. University of California Press. p. 244. ISBN 978-0-520-22149-9.
  3. 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. 153 (25). Society for Science &#38: 391. doi:10.2307/4010364. JSTOR 4010364. Archived from the original on 2013-05-11. Retrieved 2009-04-24.
  4. What is a warty comb jelly? | BBC Science Focus Magazine
  5. 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.

External links

  • Media related to Anus at Wikimedia Commons
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