Anus

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Female Human Anatomy

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Male Human Anatomy

For other uses, see the bodily orifice.

"Anal" redirects here. For other uses, see Anal (disambiguation).

In anatomy, the anus (from Latin ānus "ring, anus") is the external opening of the rectum. Closure is controlled by sphincter muscles. Feces are expelled from the body through the anus during the act of defecation, which is the primary function of the anus. Most animals — from simple worms to elephants and humans — have a tubular gut, with a mouth at one end and an anus at the other.

The anus is often considered a taboo part of the body, and is known by a large number of usually vulgar slang terms.

Structure

The human anus is situated between the buttocks, posterior to the perineum. It has two anal sphincters, one internal, the other external. These hold the anus closed until time 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 anal sacs.

Role in defecation

Main article: Defecation

When the rectum is full, the increase in intrarectal pressure forces the walls of the anal canal 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.

To prevent diseases of the anus and to promote general hygiene, humans often clean the anus after emptying the bowels. A wash with a bidet or a wiping with toilet paper are often used to clear the anus of fecal matter.

Role in sexuality

The anus has a relatively high concentration of nerve endings and is an erogenous zone. Sigmund Freud's theory of psychosexual development, for example, described an anal stage, hypothesizing that toddlers derive pleasure from retaining and expelling feces. This is the source of the derogatory term anal-retentive.

Anal intercourse 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 vagina (for females) as well as the G-spot or Prostate (for males). For the insertive partner, the tightness of the anus is often said to be a source of pleasure in penetrative anal sex, while the presence of the prostate gland near the rectal wall is generally seen as a source of pleasure during receptive anal intercourse. Other animals have also been observed practicing anal intercourse.

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

Puberty

During puberty 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

Pinworms are sometimes the source of anal itching.

Penetration with a penis or sex toy can irritate or tear the inside of the anus. 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.

Cosmetics

Shaving, trimming, depilatory, or Brazilian waxing can clear the perineum of hair.

Anal bleaching is a relatively new West coast phenomenon where the perineum, which darkens over the years, is lightened for a more youthful appearance. In April 2000, gossip columnist Ted Casablanca reported that actresses including Lara Flynn Boyle have had their anuses bleached. [1]

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

Pathology

Anal cancer, abscess, warts, fistula, anal fissure, itching and hemorrhoids are among the diseases of the anus that benefit from medical intervention. Birth defects of the anus include stenosis and imperforation. The anus is also a frequent site of sexually transmitted infections. Damaged anal sphincter (patulous anus in more severe cases) — caused by careless surgery in the perineal region or by rough/abrupt penetration — can lead to flatus and/or fecal incontinence, chronic constipation and, ultimately, megacolon.

See also

• Arse
• Digestive system
• Flatulence
• Sodomy

External links

• Patient Queries - Anus Patient Queries answered by Physicians and Gastroenterologists pertaining to problems of the Anus