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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 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 ...
. In humans, bile is produced continuously by the liver (liver bile) and stored and concentrated in the gallbladder. After eating, this stored bile is discharged 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 ...
. The composition of hepatic bile is (97–98)% water, 0.7% bile salts, 0.2%
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 ...
, 0.51% fats (cholesterol, fatty acids, and
lecithin Lecithin (, from the Greek ''lekithos'' "yolk") is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues which are amphiphilic – they attract both water and fatty substances (and so ar ...
), and 200 meq/L inorganic salts. The two main pigments of bile are bilirubin, which is yellow, and its oxidised form
biliverdin Biliverdin (latin for green bile) is a green tetrapyrrolic bile pigment, and is a product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. It is the pi ...
, which is green. When mixed, they are responsible for the brown color of feces. About 400 to 800 millilitres of bile is produced per day in adult human beings.


Function

Bile or gall acts to some extent as a
surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...
, helping to
emulsify An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...
the lipids in food. Bile salt anions are hydrophilic on one side and hydrophobic on the other side; consequently, they tend to aggregate around droplets of lipids ( triglycerides and
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) to form micelles, with the hydrophobic sides towards the fat and hydrophilic sides facing outwards. The hydrophilic sides are negatively charged, and this charge prevents fat droplets coated with bile from re-aggregating into larger fat particles. Ordinarily, the micelles in the duodenum have a diameter around 1–50 μm in humans. The dispersion of food fat into micelles provides a greatly increased surface area for the action of the enzyme pancreatic lipase, which digests the triglycerides, and is able to reach the fatty core through gaps between the bile salts. A triglyceride is broken down into two fatty acids and a monoglyceride, which are absorbed by the villi on the intestine walls. After being transferred across the intestinal membrane, the fatty acids reform into triglycerides (re-esterified), before being absorbed into the lymphatic system through lacteals. Without bile salts, most of the lipids in food would be excreted in feces, undigested. Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble substances, such as the vitamins A, D, E, and K. Besides its digestive function, bile serves also as the route of excretion for bilirubin, a byproduct of
red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...
recycled by the liver. Bilirubin derives from hemoglobin by glucuronidation. Bile tends to be
alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
on average. The pH of common duct bile (7.50 to 8.05) is higher than that of the corresponding gallbladder bile (6.80 to 7.65). Bile in the gallbladder becomes more
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
ic the longer a person goes without eating, though resting slows this fall in pH. As an alkali, it also has the function of neutralizing excess stomach acid before it enters 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 ...
, the first section 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 ...
. Bile salts also act as bactericides, destroying many of the microbes that may be present in the food.


Clinical significance

In the absence of bile, fats become indigestible and are instead excreted in
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
, a condition called
steatorrhea Steatorrhea (or steatorrhoea) is the presence of excess fat in feces. Stools may be bulky and difficult to flush, have a pale and oily appearance, and can be especially foul-smelling. An oily anal leakage or some level of fecal incontinence may oc ...
. Feces lack their characteristic brown color and instead are white or gray, and greasy. Steatorrhea can lead to deficiencies in essential fatty acids and fat-soluble vitamins. In addition, past 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 ...
(which is normally responsible for absorbing fat from food) the
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...
and
gut flora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...
are not adapted to processing fats, leading to problems in the large intestine. The cholesterol contained in bile will occasionally accrete into lumps in the gallbladder, forming gallstones. Cholesterol gallstones are generally treated through surgical removal of the gallbladder. However, they can sometimes be dissolved by increasing the concentration of certain naturally occurring bile acids, such as chenodeoxycholic acid and ursodeoxycholic acid. On an empty stomach – after repeated vomiting, for example – a person's vomit may be green or dark yellow, and very bitter. The bitter and greenish component may be bile or normal digestive juices originating in the stomach. Bile may be forced into the stomach secondary to a weakened valve ( pylorus), the presence of certain drugs including
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
, or powerful muscular contractions and duodenal spasms. This is known as
biliary reflux Biliary reflux, bile reflux (gastritis), duodenogastroesophageal reflux (DGER) or duodenogastric reflux is a condition that occurs when bile and/or other contents like bicarbonate, and pancreatic enzymes flow upward (refluxes) from the duodenum in ...
.


Obstruction

Biliary obstruction refers to a condition when bile ducts which deliver bile from the gallbladder or liver to 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 ...
become obstructed. The blockage of bile might cause a buildup of
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 ...
in the bloodstream which 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 ...
. There are several potential causes for biliary obstruction including gallstones, cancer, trauma,
choledochal cysts Choledochal cysts (a.k.a. bile duct cyst) are congenital conditions involving cystic dilatation of bile ducts. They are uncommon in western countries but not as rare in East Asian nations like Japan and China. Signs and symptoms Most patients ha ...
, or other benign causes of bile duct narrowing. The most common cause of bile duct obstruction is when gallstone(s) are dislodged from the gallbladder into the cystic duct or common bile duct resulting in a blockage. A blockage of the gallbladder or cystic duct may cause cholecystitis. If the blockage is beyond the confluence of the pancreatic duct, this may cause gallstone pancreatitis. In some instances of biliary obstruction, the bile may become infected by bacteria resulting in
ascending cholangitis Ascending cholangitis, also known as acute cholangitis or simply cholangitis, is inflammation of the bile duct, usually caused by bacteria ascending from its junction with the duodenum (first part of the small intestine). It tends to occur if th ...
.


Society and culture

In medical theories prevalent in the West from Classical Antiquity to the Middle Ages, the body's health depended on the equilibrium of four "humors", or vital fluids, two of which related to bile: blood, phlegm, "yellow bile" (choler), and "black bile". These "humors" are believed to have their roots in the appearance of a blood sedimentation test made in open air, which exhibits a dark clot at the bottom ("black bile"), a layer of unclotted erythrocytes ("blood"), a layer of white blood cells ("phlegm") and a layer of clear yellow serum ("yellow bile"). Excesses of black bile and yellow bile were thought to produce depression and aggression, respectively, and the Greek names for them gave rise to the English words
cholera Cholera is an infection of the small intestine by some strains of the bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and ...
(from Greek χολή ''kholē'', "bile") and melancholia. In the former of those senses, the same theories explain the derivation of the English word bilious from ''bile'', the meaning of gall in English as "exasperation" or "impudence", and the Latin word ''cholera'', derived from the Greek ''kholé'', which was passed along into some Romance languages as words connoting anger, such as '' colère'' (French) and ''cólera'' (Spanish).


Soap

Soap can be mixed with bile from mammals, such as ox gall. This mixture, called bile soap or gall soap, can be applied to textiles a few hours before washing as a traditional and effective method for removing various kinds of tough stains.


Food

"Pinapaitan" is a dish in Philippine cuisine that uses bile as flavoring. Other areas where bile is commonly used as a cooking ingredient include
Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist ...
and northern parts of Thailand.


Bears

In regions where bile products are a popular ingredient in traditional medicine, the use of bears in bile-farming has been widespread. This practice has been condemned by activists, and some pharmaceutical companies have developed synthetic (non-ursine) alternatives.


Principal acids

Image:Cholic acid.svg, Cholic acid Image:Chenodeoxycholic acid.svg, Chenodeoxycholic acid Image:Glycocholsäure.svg, Glycocholic acid Image:Taurocholic acid.svg, Taurocholic acid Image:Deoxycholic acid.svg, Deoxycholic acid Image:Lithocholic_acid_acsv.svg, Lithocholic acid


See also

* Bile acid sequestrant * Enterohepatic circulation *
Intestinal juice In histology, an intestinal gland (also crypt of Johann Nathanael Lieberkühn, Lieberkühn and intestinal crypt) is a gland found in between villi in the intestinal epithelium lining of the small intestine and large intestine (or colon). The gland ...


References

Seleem HM, Nada AS, Naguib MA, Abdelmaksoud OR, El-Gazzarah AR. Serum immunoglobulin G4 in patients with nonmalignant common bile duct stricture. Menoufia Med J erial online2021 ited 2022 Jan 2134:1275-83. Available from: http://www.mmj.eg.net/text.asp?2021/34/4/1275/333263


Bibliography

* * * {{Authority control Body fluids Digestive system Biomolecules Hepatology