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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 also known by a large number of slang terms, which are generally considered vulgar and not used in polite speech.

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

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 follow the action of the sphincter with a cleansing activity 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.

Maintenance

Hygiene is important for good anal health. 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. Pinworms are sometimes the source of anal itching.

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.

Kegel exercises can improve the tone of the outer sphincter muscle.

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.

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

Pathology

Anal cancer, abscess, warts, fistula, 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 in anal sex – can lead to flatus and/or fecal incontinence, chronic constipation and, ultimately, megacolon.

See also

• Arse
• Digestive system
• Anal masturbation
• Cloaca
• Flatulence
• Sodomy

• Digestive system