The hepatobiliary structures develop from a diverticulum that originates on the ventral aspect of the distal foregut, extends into the septum transversum, and divides. The larger, more cranially located pars hepatica gives rise to the liver and intrahepatic ducts, whereas the caudal pars cystica develops into the gallbladder and cystic duct. The pedicle of the hepatic diverticulum narrows and recanalizes to form the extrahepatic bile duct. The common bile duct is carried 90° clockwise (as viewed from below) along with the duodenum. It rotates an additional 180° to ultimately lie adjacent to the pancreatic duct of Wirsung (from the ventral anlage) in the concavity of the duodenal sweep. The reticuloen-dothelial elements of the liver arise from the mesoderm of the septum transversum. As it enlarges, most of the liver becomes peritonealized, but the posterior aspect retains contiguity with the diaphragm in the region known as the bare area.34 During this complex process, islands of liver cords may lose their connection to the liver proper, resulting in ectopic foci of liver tissue35 (Fig. 2-25). These are usually found in the gallbladder, pancreas, and lesser omentum, which share a relatively common embryologic origin, but they may also occur in other structures such as the adrenal gland.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.