Ductus choledochus

The common bile duct, sometimes abbreviated CBD, is a duct in the gastrointestinal tract of organisms that have a gall bladder. It is formed by the union of the common hepatic duct and the cystic duct (from the gall bladder). It is later joined by the pancreatic duct to form the ampulla of Vater. There, the two ducts are surrounded by the muscular sphincter of Oddi. When the sphincter of Oddi is closed, newly synthesized bile from the liver is forced into storage in the gall bladder. When open, the stored and concentrated bile exits into the duodenum. This conduction of bile is the main function of the common bile duct. The hormone cholecystokinin, when stimulated by a fatty meal, promotes bile secretion by increased production of hepatic bile, contraction of the gall bladder, and relaxation of the Sphincter of Oddi. Several problems can arise within the common bile duct. A diameter of more than 8 mm is regarded as abnormal dilatation and is a sign of cholestasis. It normally gets slightly dilated after cholecystectomy, with upper limit (95% prediction interval) being about 10 mm after a few months. On abdominal ultrasonography, the common bile duct is generally seen most readily in the perihilar area (the border area between the common hepatic duct and the CBD, by the hilum of the liver). The absence of Doppler signal distinguishes it from the portal vein and hepatic artery. If clogged by a gallstone, a condition called choledocholithiasis can result. In this clogged state, the duct is especially vulnerable to an infection called ascending cholangitis. Very rare deformities of the common bile duct are cystic dilations (4 cm), choledochoceles (cystic dilation of the ampula of Vater (3–8 cm)), and biliary atresia. Blockage of the common bile duct and related jaundice has been documented since at least since the time of Erasistratus.