RT Book, Section A1 Bass, Lee M. A1 Fishman, Douglas S. A2 Kline, Mark W. SR Print(0) ID 1182909445 T1 The Biliary Tract T2 Rudolph's Pediatrics, 23e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259588594 LK accesspediatrics.mhmedical.com/content.aspx?aid=1182909445 RD 2024/03/28 AB In the human embryo the first anlage of the bile ducts and liver is the hepatic diverticulum from the proximal gastrointestinal tract, as described in Chapter 413. The caudal part of this bud, known as the pars cystica, grows in length and forms the gallbladder, cystic duct, and common bile duct. At about the eighth week of gestation, the hepatic precursor cells that lie adjacent to the hilar portal vein vessels form a sleeve-like double layer of cells that extends toward the periphery along the smaller intrahepatic portal vein branches. These hepatoblasts strongly express biliary-specific cytokeratins and can be considered biliary precursor cells, which then form a continuous single-layered ring around the portal mesenchyme, known as the ductal plate. Beginning at 12 weeks of gestation and extending into the postnatal period, the ductal plate undergoes progressive remodeling. As new ductules form, they are incorporated into the periportal mesenchyme that surrounds the portal vein branches. Thus, during successive periods of fetal life, ductal plate remodeling leads to the formation of the intrahepatic biliary tree. The largest ducts are formed first, followed by segmental, interlobular, and, finally, the smallest bile ductules. Arrest or derangement in remodeling leads to the persistence of primitive bile duct configurations termed ductal plate malformations.