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Cholangiocytes are the
epithelial cell Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
s of the
bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. ...
. They are
cuboidal epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
in the small interlobular bile ducts, but become columnar and HCO3:-secreting in larger bile ducts approaching the porta hepatis and the extrahepatic ducts. They contribute to
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, ...
survival by transporting
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 ...
s.


Function

In the healthy liver, cholangiocytes contribute to
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 ...
secretion via release of
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemi ...
and water. Several hormones and locally acting mediators are known to contribute to cholangiocyte fluid/electrolyte secretion. These include
secretin Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. It is a peptide hormone produced in the S cells of the du ...
,
acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...
, ATP, and bombesin. Cholangiocytes act through bile-acid independent bile flow, which is driven by the active transport of electrolytes. In contrast,
hepatocytes 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, ...
secrete bile through bile-acid dependent bile flow, which is coupled to canalicular secretion of bile acids via ATP-driven transporters. This results in passive transcellular and paracellular secretion of fluid and electrolytes through an osmotic effect.


Clinical significance

Disordered functioning of cholangiocytes is at the center of a variety of pathological conditions known as "cholangiopathies." These diseases include
primary biliary cirrhosis Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is an autoimmune disease of the liver. It results from a slow, progressive destruction of the small bile ducts of the liver, causing bile and other toxins to build ...
, primary sclerosing cholangitis, AIDS cholangiopathy, disappearing bile duct syndromes,
Alagille's syndrome Alagille syndrome is a genetic disorder that affects primarily the liver and the heart. Problems associated with the disorder generally become evident in infancy or early childhood. The disorder is inherited in an autosomal dominant pattern, and ...
,
cystic fibrosis Cystic fibrosis (CF) is a rare genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections. Ot ...
, and
biliary atresia Biliary atresia, also known as extrahepatic ductopenia and progressive obliterative cholangiopathy, is a childhood disease of the liver in which one or more bile ducts are abnormally narrow, blocked, or absent. It can be congenital or acquired. I ...
. Often either the best or the only curative treatment option for cholangiopathies is
liver transplantation Liver transplantation or hepatic transplantation is the replacement of a Liver disease, diseased liver with the healthy liver from another person (allograft). Liver transplantation is a treatment option for Cirrhosis, end-stage liver disease and ...
, and as a group, cholangiopathies account for a substantial percentage of both adult and pediatric liver transplants.


Research

Active scientific investigation of cholangiocytes focuses on such diverse processes as mechanisms of fluid/electrolyte secretion, regulation of cholangiocyte proliferation, roles of cholangiocytes in the pathogenesis of liver fibrosis and cirrhosis, and cholangiocyte apoptosis. Specific investigation of individual cholangiopathies is also pursued actively.


References

{{Authority control Epithelial cells Digestive system Human cells