New clues for the developing human biliary system at the porta hepatis

The human biliary system is formed from the hepatic diverticulum, a structure which develops from the embryonic foregut in the fourth week of gestation. The cephalic portion of the hepatic diverticulum lies within the septum transversum, and gives rise to entodermal cells which become the primitive hepatocytes. The caudal part of the hepatic diverticulum is molded by mesenchyme to form the gallbladder, cystic duct, and extrahepatic bile duct. The gallbladder is initially tubular in shape, and undergoes morphological changes to become saccular during the 11th week of gestation. The extrahepatic bile duct elongates and widens as gestation progresses, and intramural mucus glands develop. There is no solid stage during the development of the extrahepatic bile duct. The extrahepatic bile duct is a well-defined tubular structure by the 6th week of gestation, whereas the intrahepatic biliary system during this period of gestation is represented by the primitive ductal plate. The ductal plate undergoes structural changes from the 11th week of gestation, beginning at the porta hepatis and progressing through gestation to the periphery of the liver. This remodeling process shapes the ductal plate from a flat sheath of biliary epithelium surrounding the portal vein branches into a network of interconnecting tubular structures. Mesenchyme plays an important role in ductal plate remodeling. The intrahepatic biliary system is in luminal continuity with the extrahepatic bile duct throughout gestation at the porta hepatis. The major bile ducts at the porta hepatis are fully formed by the 16th week of gestation. Received: September 30, 2000 / Accepted: January 10, 2001