The anus is the opening at the end of the digestive tract where stool leaves the body. The rectum is the section of the digestive tract above the anus where stool is held before it passes out of the body through the anus. The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine. The rectal lining consists of glistening red tissue containing mucus glands—much like the rest of the intestinal lining. The lining of the rectum is relatively insensitive to pain, but the nerves from the anus and nearby external skin are very sensitive to pain. The veins from the rectum and anus drain mostly into the portal vein, which leads to the liver, and then into the general circulation. Some of these veins drain directly into the pelvic veins and then into the general circulation.

Rectal prolapse occurs when the rectum the last section of the large intestine falls from its normal position within the pelvic area and sticks out through the anus. The word "prolapse" means a falling down or slipping of a body part from its usual position. Rectal prolapse is common in older adults who have a long-term history of constipation or a weakness in the pelvic floor muscles. It is more common in women than in men, and even more common in women over the age of 50 postmenopausal women , but occurs in younger people too. Rectal prolapse can also occur in infants — which could be a sign of cystic fibrosis — and in older children.

The rectum is the last several inches of the large intestine. Rectal cancer starts in the lining of the rectum rectal mucosa. Rectal cancer is cancer that begins in the rectum. It starts at the end of the final segment of your colon and ends when it reaches the short, narrow passage leading to the anus.