Overview
The biliary tree (also known as the biliary tract or biliary system) describes the route bile takes after being produced in the liver. Bile is made of water, bile acids, cholesterol, and conjugated bilirubin and its function involves aiding fat absorption.
Anatomy of the Biliary Tree
Overview
Hepatocytes secrete bile into small tubes known as bile canaliculi. These empty into progressively larger ducts (such as the canals of Hering, interlobular bile ducts, and intrahepatic bile ducts), and eventually into the left and right hepatic ducts.
The right and left hepatic ducts merge and form the common hepatic duct which leaves the liver and joins the cystic duct from the gallbladder to form the common bile duct.
The common bile duct joins the pancreatic duct to form the ampulla of Vater which opens into the duodenum. A ring of muscle known as the sphincter of Oddi surrounds the ampulla of Vater which controls the flow of bile and pancreatic secretions into the duodenum.
Physiology of the Biliary Tree
Overview
Bile is produced by the liver and secreted into the biliary tree and stored in the gallbladder when fasting. While in the gallbladder, water is absorbed and the bile salts and cholesterol in bile become more concentrated.
When eating a meal, a peptide hormone called cholecystokinin (CCK) is released from the duodenum when food is present in its lumen. This stimulates the contraction of the gallbladder, releasing bile down the rest of the biliary tree into the duodenum.
Bile acids emulsify large lipid molecules into smaller particles to increase the surface area for hydrolysis by lipase. Bile is also the primary route for the elimination of cholesterol.
Clinical Significance
Overview
Gallstones can form within the gallbladder and obstruct the biliary tree, resulting in different clinical manifestations depending on where in the biliary tree the obstruction is.
Gallstones that obstruct the cystic duct can impair the flow of bile from the gallbladder, which can cause inflammation and acute cholecystitis.
Common bile duct stones
Gallstones that obstruct the common bile duct obstruct the flow of bile from both the liver and gallbladder to the duodenum. This can lead to infection of these bile ducts, known as acute cholangitis.
Common bile duct obstruction can also cause obstructive jaundice, as bile pigments accumulate in the blood due to impaired movement to the duodenum. This can present with yellow discolouration of the skin, dark urine, and pale stools.
They can also obstruct the flow of pancreatic secretions which can precipitate acute pancreatitis.
Prophylactic surgery is more commonly performed if common bile duct stones are present due to the increased risk of these complications, which can be severe.
Autoimmune and inflammatory disorders
Primary biliary cholangitis and primary sclerosing cholangitis are characterised by inflammation of the ducts in the biliary tree. Over time, this can cause hardening and narrowing of these ducts, which can cause obstructive jaundice.
Terms used in Gallbladder Diseases
Cholestasis describes the blockage of bile flow from the liver to the duodenum. Some causes may be mechanical (e.g. gallstones, tumours), inflammatory (e.g. primary biliary cholangitis), or metabolic (e.g. some drugs and genetic disorders).
Cholelithiasis describes the presence of gallstones.
Choledocholithiasis describes the presence of gallstones in the common bile duct.
Cholecystitis describes inflammation of the gallbladder.
Cholangitis describes inflammation of the bile ducts.
Biliary colic describes episodes of colicky right upper quadrant pain due to gallstones.
Cholecystectomy describes the surgical removal of the gallbladder.
Cholecystostomy describes inserting a drain into the gallbladder.
Gallstone disease is a general term describing the presence of one or more stones in the gallbladder or other parts of the biliary tree and the symptoms and complications they may cause.
