Intestine, in animals, alimentary canal extending from the pylorus of the stomach to the anus. The human intestine is approximately 24 ft (7 m) long and is divided into the small intestine and large intestine, or colon. The small intestine has a total length of approximately 10 ft (3 m). It begins with the duodenum, which receives the food mass from the stomach through the pylorus, bile from the liver and gall bladder, and pancreatic juice from the pancreas. It connects with the jejunum, which in turn joins the ileum, which is attached to the large intestine by the ileocecal, or colic, valve, controlling passage of food into the large intestine. The inner surface of the small intestine is folded to give a greater amount of surface—estimated to be 957 sq yd (800 sq m)—and it is entirely lined by minute fingerlike villi, through which the products of digestion are absorbed. There are 10–40 villi to each square mm of intestinal mucous membrane. The large intestine extends from the ileum to the anus, and consists of the cecum, colon, and rectum. The first portion of the colon, the ascending colon, extends from the cecum to the undersurface of the liver, where it becomes the transverse colon, which, in turn, at the splenic flexure, becomes the descending colon. This continues downward on the left side of the abdomen until it reaches the pelvic brim and curves like the letter S in front of the sacrum until it becomes the rectum. This S-shaped section is known as the sigmoid colon. The rectum passes downward to terminate in the lower opening of the tract, the anus, or anal opening.
See also: Digestive system.