Biliary Ducts

The biliary ducts convey bile from the liver to the duodenum. Bile is produced continuously by the liver and stored and concentrated in the gallbladder, which releases it intermittently when fat enters the duodenum. Bile emulsifi es the fat so that it can be absorbed in the distal intestine.

Normal hepatic tissue, when sectioned, is traditionally described as demonstrating a pattern of hexagonal-shaped liver lobules (Fig. 2.69A) when viewed under low magnifi - cation. Each lobule has a central vein running through its center from which sinusoids (large capillaries) and plates of hepatocytes (liver cells) radiate toward an imaginary peri meter extrapolated from surrounding interlobular portal triads (terminal branches of the hepatic portal vein and hepatic artery and initial branches of the biliary ducts). Although commonly said to be the anatomical units of the liver, hepatic “lobules” are not structural entities; instead, the lobular pattern is a physiological consequence of pressure gradients and is altered by disease. Because the bile duct is not central, the hepatic lobule does not represent a functional unit like acini of other glands. However, the hepatic lobule is a fi rmly established concept and is useful for descriptive purposes.

The hepatocytes secrete bile into the bile canaliculi formed between them. The canaliculi drain into the small interlobular biliary ducts and then into large collecting bile ducts of the intrahepatic portal triad, which merges to form the hepatic ducts (Fig. 2.69B). The right and left hepatic ducts drain the right and left (parts of the) liver, respectively. Shortly after leaving the porta hepatis, these hepatic ducts unite to form the common hepatic duct, which is joined on the right side by the cystic duct to form the bile duct (part of the extrahepatic portal triad of the lesser omentum), which conveys the bile to the duodenum.

BILE DUCT

The bile duct (formerly called the common bile duct) forms in the free edge of the lesser omentum by the union of the cystic duct and common hepatic duct (Figs. 2.65 and 2.69B). The length of the bile duct varies from 5 to 15 cm, depending on where the cystic duct joins the common hepatic duct.

The bile duct descends posterior to the superior part of the duodenum and lies in a groove on the posterior surface of the head of the pancreas. On the left side of the descending part of the duodenum, the bile duct comes into contact with the main pancreatic duct. These ducts run obliquely through the wall of this part of the duodenum, where they unite, forming a dilation, the hepatopancreatic ampulla (Fig. 2.69C). The distal end of the ampulla opens into the duodenum through the major duodenal papilla (see Fig. 2.45C). The circular muscle around the distal end of the bile duct is thickened to form the sphincter of the bile duct (L. ductus choledochus) (Fig. 2.69C). When this sphincter contracts, bile cannot enter the ampulla and the duodenum; hence, bile backs up and passes along the cystic duct to the gallbladder for concentration and storage.

The arterial supply of the bile duct is from the (Fig. 2.71):

• Cystic artery: supplying the proximal part of the duct.

• Right hepatic artery: supplying the middle part of the duct.

• Posterior superior pancreaticoduodenal artery and gastroduodenal artery: supplying the retroduodenal part of the duct.

The venous drainage from the proximal part of the bile duct and the hepatic ducts usually enter the liver directly (Fig. 2.72). The posterior superior pancreaticoduodenal vein drains the distal part of the bile duct and empties into the hepatic portal vein or one of its tributaries.

The lymphatic vessels from the bile duct pass to the cystic lymph nodes near the neck of the gallbladder, the lymph node of the omental foramen, and the hepatic lymph nodes (Figs. 2.70 and 2.71). Efferent lymphatic vessels from the bile duct pass to the celiac lymph nodes.