Anus: Difference between revisions

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	{{otheruses1\|the bodily orifice}}
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	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 — from simple worms to elephants and humans — have a tubular ], with a ] at one end and an anus at the other.

	The anus plays a role in sexuality, though attitudes towards ] vary and it is even illegal in some countries. The anus is also the site of potential infections and other conditions including ]. The subject is often considered a ] part of the body, and is known by a large number of usually ] ] terms.

	== Structure ==
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	The human anus is situated between the ]s, ] to the ]. It has two anal sphincters, one ], the other ]. These hold the anus closed until the need arises to defecate. 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 ].

	== Role in defecation ==
	{{main\|Defecation}}

	Intra-rectal pressure builds as the ] fills with feces, pushing the feces against the walls of the ]. Contractions of abdominal and pelvic floor muscles can create intra-abdominal pressure which further increases intra-rectal pressure. The ] (an involuntary muscle) responds to the pressure by relaxing, thus allowing the feces to enter the canal. The rectum shortens as feces are pushed into the anal canal and ] push the feces out of the rectum. Relaxation of the internal and external anal sphincters allows the feces to exit from the anus, finally, as the ] muscles pull the anus up over the exiting feces.

	To prevent diseases of the anus{{Fact\|date=June 2007}} and to promote general hygiene, humans often clean the exterior of the anus after emptying the bowels. A rinse with water from a ] or a wipe with ] are often used for this purpose.

	== Role in sexuality ==
	{{main\|Anal sex}}
	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 "]."

	] 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 ]s continues to be, a crime carrying severe punishment.

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

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

	Lubricant is widely regarded as a necessity while performing anal sex.

	==Puberty==
	During ], as testosterone triggers ] growth on the body, pubic hair begins to appear around the anus. Although initially sparse, it fills out by the end of puberty, if not earlier.

	==Health==
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	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. ]s 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 ] 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 fecal incontinence. Similarly if the anus is torn, this can occasionally cause a fistula formation which can not only cause fecal leaking, but also can be very difficult to treat.

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

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

	] is a process where the perineum, which darkens over the years, is lightened for a more youthful appearance. This practice has been linked to anal incontinence, and other health problems.

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

	== Pathology ==
	Diseases of the anus include ], ], ]s, ], ], ]ing and ]. The anus is also a frequent site of ]s. These benefit from medical intervention.

	] of the anus include ] and ]. These benefit from surgical intervention.

	Damaged ] (] in more severe cases) — caused by careless or sometimes necessarily sacrificial surgery in the ] region or by rough/abrupt penetration in ] — can lead to ] and/or ], chronic ] and, ultimately, ].

	In ] the ]ian term ] is used.

	==Additional images==
	<gallery>
	Image:Gray406.png\|Muscles of male perineum.
	Image:Gray408.png\|Muscles of the female perineum.
	Image:Gray1077.png\|The posterior aspect of the rectum and anus exposed by removing the lower part of the sacrum and the coccyx.
	</gallery>

	==See also==
	{{wiktionarypar\|anus}}
	{{commons\|Category:Anus\|Anus}}
	* ] (Freudian psychosexual stage)
	* ]
	* ]
	* ]
	* ]
	* ]

	{{digestive system}}
	{{human anatomical features}}

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Revision as of 01:19, 28 October 2007