Common Bile Duct
The common bile duct (ductus choledochus) is a tube-like anatomic structure in the human gastrointestinal tract. It is formed by the union of the common hepatic duct and the cystic duct (from the gallbladder). 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 gallbladder. 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. 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.