NORMAL BILIARY PHYSIOLOGY
Bile, a complex fluid secreted by hepatocytes, passes via the intrahepatic bile ducts into the common bile duct. Tonic contraction of the sphincter of Oddi during fasting diverts about half of hepatic bile into the gallbladder where it is stored and concentrated. Cholecystokinin, released after food ingestion, causes contraction of the gallbladder and relaxation of the sphincter of Oddi, allowing delivery of a nicely timed bolus of bile, rich in bile acids, into the intestine. Bile acids, detergent molecules possessing both fatsoluble and water-soluble moieties, convey phospholipids and cholesterol from the liver to the intestine, where the latter undergoes fecal excretion. In the intestinal lumen, bile acids solubilize dietary fat and promote its digestion and absorption. Bile acids are, for the most part, efficiently reabsorbed by the small intestinal mucosa, particularly in the terminal ileum, and are recycled to the liver for re-excretion, a process termed the en-terohepatic circulation.