Bile

The bile (gr. χολή cholé Latin: bilis ) is a hardy body fluid that is produced in the liver to be stored in the gallbladder and to be distributed to the meals in the duodenum (duodenum ). Your coloring changes according to the proportion of the major bile pigments bilirubin and biliverdin from yellowish to greenish. Thickened Stark assumes a brownish tone.

The bile used in fat digestion by emulsifying lipids, that is in small for lipolytic enzymes (lipases ) decomposes vulnerable droplets. Furthermore, the bile is an excretory medium for substances that are insoluble in water and placed on the liver in the form of an eliminable.

The locomotion of bile in the bile ducts, including associated movements of the gallbladder and bile ducts is known as Cholekinese.

Composition

Bile consists mostly of water ( 82%), dissolved in the inorganic electrolytes in a similar composition in blood plasma ( see table at right ). Bile is slightly alkaline. However, the most important functional constituents are the bile salts ( 12%), which play a central role in the digestion of fat. In addition, it also includes alkaline phosphatases, a group of enzymes that hydrolyze the phosphoric acid esters.

Furthermore you can find in the bile lecithin and other phospholipids ( 4%), unesterified cholesterol ( 0.7 %) and degradation products of the liver, which pass through the bile into the digestive tract and are excreted with the feces from there. The latter include bilirubin, the breakdown product of the blood pigment hemoglobin, as well as some hormones and drugs.

Their color is replaced by the bile mainly by the bile pigments: the yellow to red depending on the concentration of bilirubin and biliverdin, the greenish. Bilirubin is broken down in the intestine by the resident bacteria, among other things stercobilin, Bilifuscin and Mesobilifuscin that give the chair its characteristic color.

The transport of cholesterol in the bile will take place in micelles which are formed from lecithin, cholesterol, and bile salts. The mixing ratio of these three substances are permitted to fluctuate only within very narrow limits, so that the transport of cholesterol to function. Otherwise, the cholesterol is crystallized out, and it leads to the formation of gallstones.

Physiology

Education

The human body produces daily about 700 ml bile which interdigestiv, that is, between meals, are stored in the gallbladder.

Bile is produced in the cells of the hepatocytes of the liver. Between two adjacent hepatocytes are the bile canaliculi ( canaliculi ), in which the bile is excreted by transmembrane transport. These canaliculi unite to form larger ducts that carry bile to ultimately the digestive tract ( see below).

Substances that are secreted into the canaliculi are lecithin, conjugated bile salts, cholesterol, bilirubin conjugated with glucuronic acid, and hormones. With glutathione -conjugated drugs can also be excreted in the bile. Hepatocytes remove the conjugated bile salts from the sinusoids, microscopic blood vessels that carry blood to the hepatocytes.

The liver cells have both in its sinusoids and canaliculi adjacent cell membranes transport proteins (carrier ) especially for bile salts. From the sinusoids they are secondary actively taken using a sodium symport transport protein ( NTCP = Na - taurocholate cotransporting polypeptide ), while it primarily operates using an ATP-dependent transporter ( hBSEP: human bile salt export pump, also CBAT: canalicular bile acid transporter ) are secreted into the lumen of the canaliculi.

Transport and storage

The extrahepatic ( located outside the liver) bile ducts begin with the common hepatic duct (common hepatic duct ), of which the cystic duct ( cystic duct, connection between the gallbladder and common bile duct ) branches off to the gallbladder. The section after this junction is called the common bile duct and finally flows together with the pancreatic duct of the pancreas into the duodenum at the major duodenal papilla.

In the gallbladder, the bile is stored and concentrated to about ten percent of its volume. Get lipids with the food into the small intestine, so they encourage the production of the hormone cholecystokinin ( CCK) in the small intestinal mucosa. CCK stimulates the smooth muscles in the body wall of the gallbladder, so that these contracts and their contents are added to the chyme in the duodenum. Increased activity of the parasympathetic vagus nerve ( vagal tone ) has the same effect. However, a gallbladder is not formed in all vertebrates.

Importance

Bile plays an important role in the processing of fats from the food and helps neutralize the stomach after passage strongly acidic chyme at. It also serves as the excretion of various substances from the body such as cholesterol, bilirubin, and many drugs and their metabolites. Bile formation is essential for the cholesterol balance in the body.

The bile salts used in fat digestion, by forming micelles with the water-insoluble components of food ( triacylglycerides, free fatty acids, vitamins and cholesterol ), and thus enable their transport in the blood. Drugs and their metabolites are conjugated with glutathione and thus made water soluble to be excreted with the bile through the digestive tract and ultimately the feces. This also relates to metabolites such as bilirubin, which is produced from the breakdown of hemoglobin in the liver cells. Other objects are the elimination of heavy metals, the neutralization of the duodenum by gastric emptying and activation of pancreatic enzymes. Bile acids have a bactericidal effect as well, so kill bacteria.

Circulation of bile salts

Bile salts are divided into primary and secondary bile salts. The primary bile salts, chenodeoxycholate, and cholate are synthesized in the liver from cholesterol. These are converted by bacteria in the digestive tract partly in secondary bile salts deoxycholate and Lithocholat. The deconjugated bile salts in the digestive tract will then be absorbed by the mucous membrane and in the portal vein ( vena portae ) bound to albumin, again transported to the liver. There they are taken, again conjugated with taurine and glycine and secreted again into the bile. This cycle is referred to as Enterohepatic bile salt cycle and ensure that the bile salt component of the body from only two to four grams can meet the requirements of the fat absorption of 20-30 g. In this case, it is circulated daily five to ten times. Only about 0.3-0.6 g of bile salts are lost and must be re- synthesized in the liver. Bile salts, which are not conjugated with taurine or glycine, are absorbed immediately, while those that are conjugated to participate only in the ileum ( the ileum ) by the digestion of fat.

Discomfort

The symptoms that occur during a disturbance of bile formation or biliary secretion in humans can be explained by their functions in fat digestion and the excretion of end products of metabolism. Blockage of the bile ducts with retention of bile is called in medical parlance cholestasis. This occurs on a fat intolerance, as this can be absorbed only to a small extent from the intestine. Higher fat intake in the diet leads to greasy stool ( steatorrhoea ). Furthermore, the so-called posthepatic jaundice occurs (jaundice), as the hemoglobin breakdown product bilirubin, a yellow dye, can not be properly excreted and causes a yellowing of the skin and mucous membranes. By the absence of bile pigments, the chair assumes a clay-like color, which is referred to as acholic. These blockages can have various causes such as tumors of the pancreas, gallbladder, bile ducts or the duodenum. Another cause may be gallstones in the common hepatic duct or common bile duct. Linings of the cystic duct and rarely end in blockage of the bile output ( Mirizzi syndrome).

Gallstones are crystallization products formed when the mixing ratio of lecithin, cholesterol and bile salts out of balance. Symptoms occur only in about a quarter of all cases. These include colic, pressure pain ( pain on pressure ) in the right upper abdomen and the above-mentioned jaundice. In rare cases it may lead to back pain.

Use

Bile Agar is obtained from bovine bile and is a term used in microbiology culture medium. Depending on the included beside the bile substrate numerous germs such as streptococci, Salmonella and Shigella, as well as mushrooms can be grown. If Salmonella is enriched from the blood of a patient, then a bile broth, consisting of three parts bile and one part blood mixed. In it, the Salmonella can multiply.

Also ox bile is used for the production of an enzyme prewash.

Cultural History

The word bile ( bile MHG, OHG galla ) is derived from the Indo-European root * ghel, " yellow, green " from; the bile is thus named for their color. From this root has in Greek χολή ( cholé ) " bile " developed; cholera ( χολέρα, cholera; " bile diarrhea " ) got its name from the mistaken belief they would be caused by a bile disorder.

In the humoral pathology of Hippocrates, which was developed around 400 BC and the medical teaching for over a thousand years certain until they lost with Paracelsus important that bile plays a central role. It was distinguished between yellow bile and black bile. These two are, in addition to blood and mucus, to the four so-called cardinal juices (→ four humors ). They are in equilibrium ( eucrasia ), a person is healthy. When an imbalance ( dyscrasia ) it came to disease. Yellow bile produced in the liver and is associated with Cholerikern. Black Bile produced by the humoral theory will in the testis and spleen and with melancholies (of Melaina cholé, black bile ) associated. Proverbial expressions like " me comes the bile high" or " spitting venom ", both metaphors for anger, grounded in this doctrine.