The remodeling of the primitive human biliary system.

From 12 weeks of gestation on, a progressive remodeling of the human primitive biliary structure or ductal plate occurs. A few parts of the primitive biliary structure (peripheral tubular or ductular structures) dilate, migrate toward the center of the portal tract, and transform into mature bile ducts, while most of them gradually disappear. To the best of our knowledge, quantitative studies have been performed only to evaluate the ratio between the number of remodeled bile ducts and portal tracts during human fetal development. We studied the remodeling of the intrahepatic fetal biliary structures as well as the bile duct to portal tract ratio in the developing human liver by immunohistochemistry with monoclonal antibodies anti-bile duct type cytokeratins and using a computer-based image-analysis system. We found that the surface and the perimeter of the portal tracts, the longest axis of the migrating peripheral tubular structures, and the maturation of bile ducts follow a process continuous and active up to term, but they slow between the 20th and the 32nd week of gestation, when intraportal granulopoiesis of the liver is active.