| Biliary tract | |
|---|---|
 Ducts of the biliary tract | |
| Details | |
| Function | Facilitate movement ofbile, which aids in fat absorption |
| Identifiers | |
| MeSH | D001659 |
| FMA | 79646 |
| Anatomical terminology | |
Thebiliary tract (alsobiliary tree orbiliary system) refers to theliver,gallbladder andbile ducts, and how they work together to make, store and secretebile.[1] Bile consists of water,electrolytes,bile acids,cholesterol,phospholipids andconjugated bilirubin.[2] Some components are synthesized byhepatocytes (liver cells); the rest are extracted from the blood by the liver.[3]
Bile is secreted by the liver into small ducts that join to form thecommon hepatic duct.[4] Between meals, secreted bile is stored in the gallbladder.[5] During a meal, the bile is secreted into theduodenum (part of the small intestine) to rid the body of waste stored in the bile as well as aid in theabsorption of dietary fats and oils.[5]
The biliary tract refers to the path by which bile is secreted by the liver then transported to theduodenum, the first part of thesmall intestine. A structure common to most members of themammal family, the biliary tract is often referred to as a tree because it begins with many small branches that end in thecommon bile duct, sometimes referred to as the trunk of the biliary tree. The duct, the branches of thehepatic artery, and theportal vein form the central axis of theportal triad.[7] Bile flows in the direction opposite to that of the blood present in the other two channels.[8]
The system is usually referred to as the biliary tract or system,[9] and can include the use of the term "hepatobiliary" when used to refer just to the liver and bile ducts.[1] The name biliary tract is used to refer to all of the ducts, structures and organs involved in the production, storage and secretion of bile.[10]
The tract is as follows:
Bile is secreted by the liver into small ducts that join to form thecommon hepatic duct.[2] 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.[5] During a meal, the smooth muscles in the gallbladder wall contract, causing bile to be secreted into theduodenum to rid the body of waste stored in the bile as well as aid in theabsorption of dietary fats and oils by solubilizing them usingbile acids.[5]
Gallstones can form within the gallbladder and get stuck within the biliary tract, leading to various diseases depending on the location of the stone.[11]Gallstone disease, orcholelithiasis, is very common in the United States, impacting over 20 million people.[11]
Gallstones frequently occur without causing symptoms– this is known asasymptomatic cholelithiasis.[11] Sometimes gallstones may get stuck in thecystic duct, which serves as a bridge between the gallbladder and thecommon bile duct, and can lead to inflammation in the wall of the gallbladder.[11] This inflammation of the gallbladder is known ascholecystitis and is a common indication for surgical removal of the gallbladder, orcholecystectomy.[12]
Occasionally gallstones may become lodged in the common bile duct and obstruct the flow of bile from the gallbladder to the small intestine– this condition is known ascholedocholithiasis[11] and is another indication forcholecystectomy.[12] The common bile duct, commonly abbreviated CBD, is formed by the union of the cystic duct and common hepatic duct, and it later joins thepancreatic duct to terminate in theAmpulla of Vater at the small intestine. The function of the common bile duct is to allow bile to travel from the gallbladder to the small intestine, mixing with pancreatic digestive enzymes along the way.[4] One possible complication of choledocholithiasis is an infection of the bile ducts between the liver and the gallstone lodged in the common bile duct. This condition is known asacute cholangitis and is commonly associated with a triad of clinical symptoms known asCharcot's Triad, which includes fever, right upper quadrant abdominal pain, and jaundice.[11] This constellation of symptoms has a 96% specificity for cholangitis,[11] and can be expanded upon with the addition of hypotension and altered mental status to formReynold's Pentad.[11]
The biliary tract can also serve as a reservoir for intestinal tract infections. Since the biliary tract is an internal organ, it has nosomatic nerve supply, andbiliary 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 inbowel obstructions.[13]
Chronic inflammatory conditions of the biliary tract, including Primary Sclerosing Cholangitis (PSC) and Primary Biliary Cirrhosis (PBC), can lead to hardening of the ducts in the biliary tree.[14]
An obstruction of the biliary tract can result injaundice, a yellowing of the skin and whites of the eyes.[15]
