Figure 1.

Development of the extrahepatic biliary tract. (a) Embryological development of the extrahepatic biliary tract. In humans, the extrahepatic duct originates from the caudal part of the hepatic bud, whereas in mice, the gallbladder primordium is associated with the ventral pancreas. E, embryonic day. (b) Development of the liver, pancreas, and biliary tree. (Left) The biliary system (gallbladder and cystic duct) initially arises as a tubular structure (pars cystica) formed by the elongation of the caudal portion of the hepatic diverticulum. The dorsal and ventral pancreas fuse after the ventral bud rotates clockwise around the caudal side of the foregut. (Right) During fusion of the dorsal and ventral pancreas, the attachments of the developing common bile duct and pancreatic duct are moved to their native positions in the dorsal duodenum. The pancreas drains mainly from the ventral pancreatic duct and joins the common bile duct at the level of the greater papilla. The main pancreatic duct arises from the merging of dorsal and ventral pancreatic ducts. (c) Molecular regulation of the extrahepatic and intrahepatic biliary tract. The transcription factors PDX1 and SOX17 regulate the development of the extrahepatic biliary tract.