bile, bitter alkaline fluid of a yellow, brown, or green color, secreted, in man, by the liver. Bile, or gall, is composed of water, bile acids and their salts, bile pigments, cholesterol, fatty acids, and inorganic salts. In man it is stored in the gall bladder and, in response to the action of the hormone cholecystokinen (whose secretion by the intestine is stimulated by the presence of food), is secreted via the cystic and common ducts into the duodenum. The bile salts aid in digestion by emulsifying fats, enabling the absorption of fats and of the fat-soluble vitamins (A, D, E, and K) through the intestinal wall. Since unabsorbed fats tend to coat other foods and prevent the action of digestive enzymes, adequate fat absorption mediated by bile salts is necessary for the complete digestion of food and the prevention of decomposition of partially digested foods by intestinal bacteria. The alkaline bile acts to neutralize the stomach acid in the small intestine, providing a more optimum environment for the pancreatic enzymes. The bile is a route of excretion for many drugs and metabolites; cholesterol is excreted almost entirely in the bile, as are breakdown products of heme, such as bilirubin, which color the bile and are known as the bile pigments. If the flow of bile is impeded by inflammation, gall stones, or other abnormality, digestive disturbances and frequently jaundice result.
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