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

. 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 dis ...

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. Primary b ...

s, cholesterol,

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 Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...

. Some components are synthesized by hepatocytes (liver cells), the rest are extracted from the blood by the liver. Bile is secreted by the liver into small ducts that join to form the common hepatic duct. 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 liver then transported to the

, the first part of the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

. 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 or ...

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. Approxima ...

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 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 >>

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 interlobu ...

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

and enter the duodenum

Function

Bile is 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, 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.

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, 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 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 import ...

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 Ascending cholangitis, also known as acute cholangitis or simply cholangitis, is inflammation of the bile duct, usually caused by bacteria ascending from Ampulla of Vater, its junction with the duodenum (first part of the small intestine). It ten ...

and is commonly associated with a triad of clinical symptoms known as Charcot's Triad, 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 obstruction Bowel obstruction, also known as intestinal obstruction, is a mechanical or Ileus, functional obstruction of the Gastrointestinal tract#Lower gastrointestinal tract, intestines which prevents the normal movement of the products of digestion. Eith ...

s. 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 Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme meta ...

, a yellowing of the skin and whites of the eyes.

References

{{DEFAULTSORT:Hepatobiliary System Hepatology