Abstract

The morphologic development of the liver in the embryonic period is described in serial sections of 18 human embryos representative of Horizons 12 to 23 . In the earliest specimen of horizon 12, the liver is seen as branching cord of endodermal cells originating from the hepatic diverticulum and invading into the loose stroma of septum transversum, transforming the surrounding stromal cells into primitive blood spaces and blood cells. Thereafter, the parenchymal cells rapidly proliferated so that the size of the organ was reaching a fifth of the CR length in horizon 23. The vascular system of the liver was in a symmetric configuration in horizon 12, which is composed of umbilical and vitelline veins and hepatocardiac channels on both sides. The evolution of the vascular system includes intergration of the vitelline veins into the portal vein, obliteration of the right umbilical vein and left hepatocardiac channel, and creation of the ductus venosus. The intrahepatic biliary tract is found to be formed by the "in situ transformation" mechanism, which involves transformation of the parenchymal cells, adjacent to the fibrous tissue surrounding the portal and umbilical veins, to networks of cuboidal epithelial cells lining the ductal lumen. These intrahepatic duct systems were found to communicate with the extrahepatic system at the porta hepatis.

• Keywords: Liver;Development;Embryo;Hepatic diverticulum