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How the Body Works : The Small Intestine
August 4, 2007
The, Small, Intestine
The Small Intestine
The small intestine, a twenty-one-foot tube, lies in coils in the abdomen. The first ten to twelve inches are called the duodenum, which is the U-shaped section of the small intestine that joins the stomach and the jejunum. The next eight feet, the jejunum and the remaining twelve feet the ileum, join the duodenum with the large intestine. The muscle layers of the small intestine are arranged longitudinally on the outside and circularly on the inside. Between the muscle layers are a series of nerve fibers which control the muscular movements that mix and move food along. The common bile duct is the opening through which bile and pancreatic juices enter the small intestine. As food reaches the duodenum from the stomach, it is mixed with these juices and further digested. At the base of the duct is a ring of smooth muscle, the sphincter, which regulates the outflow of fluid. Digested food is absorbed into the cells through the fingerlike projections lining the small intestine called the villi. The Crypts of Lieberkuhn, numerous tubular glands which open into the intestine from between the villi, secrete an alkaline fluid rich in digestive enzymes and mucus. The mucus protects the tissues of the small intestine from being digested by it's own enzymes. Brunner's glands pour out an alkaline juice to neutralize the acid chyme reaching the small intestine and to create the necessary conditions for further digestion. Tributaries of the portal vein carry digested materials away from the small intestine to the liver. The major function of the small intestine is to complete the digestion of food passing into it from the stomach and to absorb the final products of digestion.