Development and transformation of the ductal plate in the developing human liver

The livers of 15 embryos and fetuses measuring from 0.5 cm to 21 cm in crown-rump length were examined. The liver of the smallest embryo showed a sheet of hepatocytes without any ductal plates or intrahepatic bile ducts. Transformation of the hepatocytes of a hilar ductal plate was first observed in a 1.8-cm embryo. A 10.0-cm fetus had ductal plates virtually throughout the liver. Focal transformation of the flattened cells of the ductal plates into tubules composed of columnar or cuboidal ductal cells was observed. Mature interlobular ducts were observed predominantly in the hilum whereas scattered primitive interlobular ducts were scattered throughout the parenchyma. The transformation of hepatocytes into interlobular bile ducts thus seemed to occur in two stages: in the first, the hepatocytes of the ductal plate became flattened and developed increased cytokeratin; in the second, these flattened cells became focally cuboidal or columnar, lost their carcinoembryonic antigen, became strongly positive for epithelial membrane antigen, and formed tubules and primitive interlobular bile ducts.