The biliary tract, (biliary tree or biliary system) refers to the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

, gallbladder and bile ducts, and how they work together to make, store and secrete

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bi ...

. Bile consists of water,

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...

bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primar ...

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...

phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...

s and conjugated bilirubin. Some components are synthesized by

hepatocyte A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass. These cells are involved in: * Protein synthesis * Protein storage * Transformation of carbohydrates * Synthesis of cholesterol, ...

s (liver cells), the rest are extracted from the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

by the liver. Bile is secreted by the liver into small ducts that join to form the

common hepatic duct The common hepatic duct is the first part of the biliary tract. It joins the cystic duct coming from the gallbladder to form the common bile duct. Structure The common hepatic duct is the first part of the biliary tract. It is formed by the c ...

. Between meals, secreted bile is stored in the gallbladder. During a meal, the bile is secreted into the

duodenum The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...

(part of the small intestine) to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils.

Structure

The biliary tract refers to the path by which

is secreted by the

then transported to the

, the first part of the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

. A structure common to most members of the

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

family, the biliary tract is often referred to as a tree because it begins with many small branches that 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 The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approx ...

form the central axis of the

portal triad In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocy ...

. Bile flows in the direction opposite to that of the blood present in the other two channels. The system is usually referred to as the biliary tract or system, and can include the use of the term "hepatobiliary" when used to refer just to the liver and bile ducts. 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. The tract is as follows: *

Bile canaliculi Bile canaliculus (plural:bile canaliculi; also called bile capillaries) is a thin tube that collects bile secreted by hepatocytes. The bile canaliculi empty into a series of progressively larger bile ductules and ducts, which eventually become comm ...

Canals of Hering The canals of Hering, or intrahepatic bile ductules, are part of the outflow system of exocrine bile product from the liver. Liver stem cells are located in the canals of Hering. Structure They are found between the bile canaliculi and interlob ...

>> intrahepatic bile ductule (in portal tracts / triads) >> interlobular bile ducts >> left and right hepatic ducts * These merge to form the

* The

exits the liver and joins with the cystic duct from gall bladder * Together these form the common bile duct which joins the pancreatic duct * These pass through the

ampulla of Vater The ampulla of Vater, also known as the or the hepatopancreatic duct, is formed by the union of the pancreatic duct and the common bile duct. The ampulla is specifically located at the major duodenal papilla. The ampulla of Vater is an imp ...

and enter the duodenum

Function

Bile is secreted by the liver into small ducts that join to form the

. 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, causing bile to be secreted into the

to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils by solubilizing them using

bile acids Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primar ...

Clinical significance

Diagram showing the bile ducts in the pancreas CRUK 293

Gallstones can form within the gallbladder and get stuck within the biliary tract, leading to various diseases depending on the location of the stone. Gallstone disease, or

cholelithiasis A gallstone is a stone formed within the gallbladder from precipitated bile components. The term cholelithiasis may refer to the presence of gallstones or to any disease caused by gallstones, and choledocholithiasis refers to the presence of mig ...

, is very common in the United States, impacting over 20 million people. Gallstones frequently occur without causing symptoms– this is known as asymptomatic cholelithiasis. Sometimes gallstones may get stuck in the cystic duct, which serves as a bridge between the gallbladder and the common bile duct, and can lead to inflammation in the wall of the gallbladder. This inflammation of the gallbladder is known as

cholecystitis Cholecystitis is inflammation of the gallbladder. Symptoms include right upper abdominal pain, pain in the right shoulder, nausea, vomiting, and occasionally fever. Often gallbladder attacks (biliary colic) precede acute cholecystitis. The pai ...

and is a common indication for surgical removal of the gallbladder, or

cholecystectomy Cholecystectomy is the surgical removal of the gallbladder. Cholecystectomy is a common treatment of symptomatic gallstones and other gallbladder conditions. In 2011, cholecystectomy was the eighth most common operating room procedure performed i ...

. 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 as choledocholithiasis and is another indication for

. The common bile duct, commonly abbreviated CBD, is formed by the union of the cystic duct and common hepatic duct, and it later joins the pancreatic duct to terminate in the

Ampulla of Vater The ampulla of Vater, also known as the or the hepatopancreatic duct, is formed by the union of the pancreatic duct and the common bile duct. The ampulla is specifically located at the major duodenal papilla. The ampulla of Vater is an imp ...

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. 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 as acute cholangitis and is commonly associated with a triad of clinical symptoms known as

Charcot's Triad Charcot's cholangitis triad is the combination of jaundice; fever, usually with rigors; and right upper quadrant abdominal pain. It occurs as a result of ascending cholangitis (an infection of the bile duct in the liver). When the presentation al ...

, which includes fever, right upper quadrant abdominal pain, and jaundice. This constellation of symptoms has a 96% specificity for cholangitis, and can be expanded upon with the addition of hypotension and altered mental status to form Reynold's Pentad. 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. 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. An obstruction of the biliary tract can result in jaundice, a yellowing of the skin and whites of the eyes.

References

{{DEFAULTSORT:Hepatobiliary System Hepatology