Merck Manual

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Rectum and Anus

By

Atenodoro R. Ruiz, Jr.

, MD, The Medical City, Pasig City, Metro-Manila, Philippines

Last full review/revision Oct 2019| Content last modified Oct 2019
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The rectum is a chamber that begins at the end of the large intestine, immediately following the sigmoid colon, and ends at the anus (see also Overview of the Anus and Rectum). Ordinarily, the rectum is empty because stool is stored higher in the descending colon. Eventually, the descending colon becomes full, and stool passes into the rectum, causing an urge to move the bowels (defecate). Adults and older children can withstand this urge until they reach a bathroom. Infants and young children lack the muscle control necessary to delay bowel movement.

The anus is the opening at the far end of the digestive tract through which stool leaves the body. The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine. The anus is lined with a continuation of the external skin. A muscular ring (anal sphincter) keeps the anus closed until the person has a bowel movement.

Locating the Rectum and Anus

Locating the Rectum and Anus
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