Intestine

The major part of the digestive tract (see digestive system), extending from the exit of the stomach to the anus. It forms a long tube divided into 2 main sections: the small and large intestines. The small intestine is about 6.5 m in length and has 3 sections: the duodenum, the jejunum and the ileum. Partially digested food from the stomach is forced along the intestine by peristalsis. The small intestine is concerned with the digestion and absorption of food. Digestive enzymes and bile are added to the partly digested food in the duodenum via the bile and pancreatic ducts (see biliary system). Glands within the walls of each section of the small intestine produce mucus and other enzymes, which help to break down the food. Blood vessels in the intestinal walls absorb nutrients and carry them to the liver for distribution to the rest of the body. The large intestine is about 1.5 m long. The main section, the colon, is divided into an ascending, a transverse, a descending, and a pelvic portion (the sigmoid colon). The appendix hangs from a pouch (the caecum) between the small intestine and the colon. The final section before the anu s is the rectum. Unabsorbed material leaves the small intestine as liquid and fibre. As this material passes through the large intestine, water, vitamins, and mineral salts are absorbed into the bloodstream, leaving faeces made up of undigested food residue, fat, various secretions, and bacteria. The faeces are compressed and pass into the rectum for evacuation.