Human liver development begins at around 3 weeks, when part of the hepatic diverticulum composed of endodermal cells buds from the primordial duodenum and merges with the mesenchymal cells of the septum transversum to form the primordial liver. The rest of the hepatic diverticulum gives rise to the extrahepatic biliary tree, from which the ventral pancreas also originates. The intrahepatic biliary tree later derives from the hepatoblasts through the formation of the ductal plate and its remodelling after the development of the hepatic arteries, in a centripetal fashion, beginning at the hilum and spreading to the periphery. The developing liver serves as the haematopoietic organ of the foetus. Until birth, the umbilical vein blood is shunted to the inferior vena cava through the ductus venosus. Bile starts flowing through the biliary tree at birth.