Hepatobiliary system

Digestive system diagram showing the common bile duct

The hepatobiliary system refers to the liver, gall bladder and bile ducts, and how they work together to make bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and conjugated bilirubin. Some components are synthesised by liver cells, the rest are extracted from the blood by the liver.

Structure

Bile is then secreted by the liver into small ducts that join to form the common hepatic duct. Between meals, secreted bile is stored in the gall bladder, where 80%-90% of the water and electrolytes can be absorbed, leaving the bile acids and cholesterol. During a meal, the smooth muscles in the gallbladder wall contract, leading to the bile being secreted into the duodenum.

Biliary tract

The biliary tract (or biliary tree, biliary system) is the common anatomical term for the path by which bile is secreted by the liver then transported to the first part of the small intestine, also known as the duodenum. A structure common to most members of the mammal family, it is referred to as a tree because it begins with many small branches which end in the common bile duct, sometimes referred to as the trunk of the biliary tree. The duct, the branches of the hepatic artery, and the portal vein form the central axis of the portal triad. Bile flows in the direction opposite to that of the blood present in the other two channels.

The name usually excludes the liver,^[1] but sometimes does include it.^[2]

The path is as follows:

• Bile canaliculi >> Canals of Hering >> intrahepatic bile ductule (in portal tracts / triads) >> interlobular bile ducts >> left and right hepatic ducts >>
• merge to form >> common hepatic duct >>
• exits liver and joins >> cystic duct (from gall bladder) >>
• forming >> common bile duct >> joins with >> pancreatic duct >>
• forming >> ampulla of Vater >> enters duodenum

Function

To see how this relates to the metabolism of bile, read bilirubin metabolism.

Clinical significance

Pressure inside in the biliary tree can give rise to gallstones and lead to cirrhosis of the liver.

Blockage can cause jaundice.^[3]

The biliary tract can also serve as a reservoir for intestinal tract infections. Since the biliary tract is an internal organ, it has no somatic nerve supply, and biliary colic due to infection and inflammation of the biliary tract is not a somatic pain. Rather, pain may be caused by luminal distension, which causes stretching of the wall. This is the same mechanism that causes pain in bowel obstructions.

An obstruction of the biliary tract can result in jaundice, a yellowing of the skin and whites of the eyes.

References