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small in·tes·tine(smawl in-tes'tin) [TA]
small intestineThe longest, but narrowest part of the intestine. The part in which digestion and absorption of food is performed. The small intestine extends from the outlet of the stomach (the PYLORUS) to the CAECUM at the start of the large intestine (COLON), and consists of the DUODENUM, the JEJUNUM and the ILEUM.
small intestinea narrow tube, which in humans is over 7m long, linking the stomach to the caecum. It is divided into an anterior part, the duodenum (25 cm), a central part, the jejunum (5.6 m) and a posterior part, the ileum (125 cm). CHYME from the stomach stimulates secretion of PANCREATIC JUICE on passing into the duodenum. Bile is added from the liver and flows into the duodenum through the bile duct. The jejunum has a larger diameter than the duodenum and larger VILLI than the rest of the intestine; it is the main absorptive region.
Large amounts of MUCUS are produced by the glandular cells, and a number of enzymes including maltase, peptidases, sucrase, lactase, enterokinase and nucleotidases are also secreted. The enzymes are thought to be largely produced in the CRYPTS OF LIEBERKUHN. The secretions of the small intestine are collectively called the succus entericus. The entire intestinal lining in humans is replaced every 36 hours and is the main site of the absorption of food.