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The anlage of the biliary ducts and liver is a diverticulum appearing on the ventral foregut in 3 mm embryos. The cranial portion becomes the liver; a caudal bud, the ventral pancreas; and an intermediate bud, the gallbladder. The hepatic diverticulum becomes a solid mass of cells that later recanalizes to form ducts. The smallest, the bile canaliculi, first appear as a basal network between the primitive hepatocytes (Figure 27–1). In most cases, the common hepatic duct is formed by the union of a single right and left duct. In 25% of individuals, the anterior and posterior divisions of the right duct join the left duct separately. The origin of the common hepatic duct is close to the liver but always outside its substance. It runs 4 cm before joining the cystic duct to form the common bile duct. The common duct begins in the hepatoduodenal ligament, passes behind the first portion of the duodenum, and runs in a groove on the posterior surface of the pancreas before entering the duodenum. Its terminal 1 cm is intimately adherent to the duodenal wall. The total length of the common duct is about 9 cm.
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In 80%-90% of individuals, the main pancreatic duct joins the common duct to form a common channel about 1 cm long. The intraduodenal segment of the duct is called the hepatopancreatic ampulla, or ampulla of Vater.
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The gallbladder is a pear-shaped organ adherent to the undersurface of liver segments 4b and 5 by a veil of peritoneum known as the, cystic plate. The fundus projects 1-2 cm below the hepatic edge. The gallbladder rarely has a complete peritoneal covering. The lumen of the cystic duct contains a thin mucosal septum, the spiral valve of Heister, that offers mild resistance to bile flow. The neck of the gallbladder tapers into the narrow cystic duct, which in 75% of people connects with the common duct. However, biliary anatomy is highly variable. The cystic duct can be short or long and can insert directly into the right hepatic duct, runs parallel to the hepatic duct, or winds around it before joining the common duct. An accessory right hepatic duct is also common (Figure 27–2).
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In the hepatoduodenal ligament, the hepatic artery is to the left of the common ...