Bile (from Latin bilis), also known as gall, is a yellow-green fluid produced by the liver of most that aids the digestion of in the small intestine. In humans, bile is primarily composed of water, is produced continuously by the liver, and is stored and concentrated in the gallbladder. After a human eats, this stored bile is discharged into the first section of the small intestine, known as the duodenum.
Composition
In the human
liver, bile is composed of 97–98%
water, 0.7%
bile salts, 0.2%
bilirubin, 0.51% fats (
cholesterol,
, and
lecithin), and 200 meq/L inorganic salts.
The two main pigments of bile are
bilirubin, which is orange-yellow, and its oxidised form
biliverdin, which is green.
About of bile is produced per day in adult human beings.
Function
Bile or gall acts to some extent as a
surfactant, helping to
emulsify the lipids in food. Bile salt
are
hydrophilic on one side and
hydrophobic on the other side; consequently, they tend to aggregate around droplets of lipids (
and
) to form
, 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.
Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble substances,
Besides its digestive function, bile serves also as the route of excretion for bilirubin, a byproduct of red blood cells recycled by the liver. Bilirubin derives from hemoglobin by glucuronidation.
Bile tends to be alkaline 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 the longer a person goes without eating, though resting slows this fall in pH.
Clinical significance
In the absence of bile, fats become indigestible and are instead excreted in
feces, a condition called
steatorrhea. 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 (which is normally responsible for absorbing fat from food) the gastrointestinal tract and
gut flora 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 . 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.
Obstruction
Biliary obstruction refers to a condition when
which deliver bile from the gallbladder or liver to the duodenum become obstructed. The blockage of bile might cause a buildup of
bilirubin in the
bloodstream which can result in
jaundice. There are several potential causes for biliary obstruction including gallstones, cancer,
trauma, choledochal cysts, 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.
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
humorism, 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 (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 (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
Lao cuisine and northern parts of
Thai cuisine.
During the Boshin War, Satsuma Domain soldiers of the early Imperial Japanese Army reportedly ate human livers boiled in bile.
Bears
In regions where bile products are a popular ingredient in traditional medicine, the
Bile bear 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
File:Cholic acid.svg|Cholic acid
File:Chenodeoxycholic acid.svg|Chenodeoxycholic acid
File:Glycocholsäure.svg|Glycocholic acid
File:Taurocholic acid.svg|Taurocholic acid
File:Deoxycholic acid.svg|Deoxycholic acid
File:Lithocholic acid acsv.svg|Lithocholic acid
See also
Further reading
