Bile (from Latinbilis), orgall, is a yellow-green/misty green fluid produced by theliver of mostvertebrates that aids thedigestion oflipids in thesmall intestine. In humans, bile is primarily composed ofwater, is produced continuously by the liver, and is stored and concentrated in thegallbladder. After a human eats, this stored bile is discharged into the first section of thesmall intestine, known as theduodenum.[1]
In the humanliver, bile is composed of 97–98%water, 0.7%bile salts, 0.2%bilirubin, 0.51% fats (cholesterol,fatty acids, andlecithin), and 200 meq/L inorganic salts.[2][3] The two main pigments of bile arebilirubin, which is orange-yellow, and its oxidised formbiliverdin, which is green. When mixed, they are responsible for the brown color offeces.[4] About 400 to 800 milliliters (14 to 27 U.S. fluid ounces) of bile is produced per day in adult human beings.[5]
Action of bile salts in digestionRecycling of the bile
Bile or gall acts to some extent as asurfactant, helping toemulsify the lipids in food. Bile saltanions arehydrophilic on one side andhydrophobic on the other side; consequently, they tend to aggregate around droplets of lipids (triglycerides andphospholipids) to formmicelles, with the hydrophobic sides towards the fat and hydrophilic sides facing outwards.[6] 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 theduodenum have a diameter around 1–50 μm in humans.[7]
The dispersion of food fat into micelles provides a greatly increased surface area for the action of the enzymepancreatic lipase, which digests the triglycerides, and is able to reach the fatty core through gaps between the bile salts.[8] A triglyceride is broken down into two fatty acids and amonoglyceride, which are absorbed by thevilli 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 throughlacteals. Without bile salts, most of the lipids in food would be excreted in feces, undigested.[9]
Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble substances,[10] such as thevitaminsA,D,E, andK.[11]
Besides its digestive function, bile serves also as the route of excretion for bilirubin, a byproduct ofred blood cells recycled by the liver. Bilirubin derives fromhemoglobin byglucuronidation.
Bile tends to bealkaline on average. ThepH 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 moreacidic the longer a person goes without eating, though resting slows this fall in pH.[12] As an alkali, it also has the function of neutralizing excessstomach acid before it enters the duodenum, the first section of thesmall intestine.Bile salts also act asbactericides, destroying many of the microbes that may be present in the food.[13]
In the absence of bile, fats become indigestible and are instead excreted infeces, a condition calledsteatorrhea. Feces lack their characteristic brown color and instead are white or gray, and greasy.[14] Steatorrhea can lead to deficiencies inessential fatty acids andfat-soluble vitamins.[15] In addition, past the small intestine (which is normally responsible for absorbing fat from food) thegastrointestinal tract andgut flora are not adapted to processing fats, leading to problems in the large intestine.[16]
Thecholesterol contained in bile will occasionally accrete into lumps in the gallbladder, forminggallstones. 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 aschenodeoxycholic acid andursodeoxycholic acid.[17][18]
On an empty stomach – after repeatedvomiting, 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.[19] Bile may be forced into the stomach secondary due to a weakened valve (pylorus), the presence of certain drugs includingalcohol, or powerful muscular contractions and duodenal spasms. This is known asbiliary reflux.[20]
Biliary obstruction refers to a condition whenbile ducts which deliver bile from the gallbladder or liver to the duodenum become obstructed. The blockage of bile might cause a buildup ofbilirubin in thebloodstream which can result injaundice. There are several potential causes for biliary obstruction including gallstones, cancer,[21] trauma,choledochal cysts, or other benign causes of bile duct narrowing.[22] 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 orcystic duct may causecholecystitis. If the blockage is beyond the confluence of the pancreatic duct, this may cause gallstonepancreatitis. In some instances of biliary obstruction, the bile may become infected by bacteria resulting inascending cholangitis.
In medical theories prevalent in the West fromclassical antiquity to theMiddle Ages, the body's health depended on the equilibrium offour "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").[23]
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 wordscholera (from Greek χολήkholē, "bile") andmelancholia. In the former of those senses, the same theories explain the derivation of the English word bilious frombile, the meaning of gall in English as "exasperation" or "impudence", and the Latin wordcholera, derived from the Greekkholé, which was passed along into some Romance languages as words connoting anger, such ascolère (French) andcólera (Spanish).[24]
Soap can be mixed with bile from mammals, such asox gall. This mixture, called bile soap[25] 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.[26]
Pinapaitan is a dish inPhilippine cuisine that uses bile as flavoring.[27] Other areas where bile is commonly used as a cooking ingredient includeLaos and northern parts ofThailand.
In regions where bile products are a popular ingredient intraditional medicine, theuse 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.[29]
^Shanbhogue, Alampady Krishna Prasad; Tirumani, Sree Harsha; Prasad, Srinivasa R.; Fasih, Najla; McInnes, Matthew (2011-08-01). "Benign Biliary Strictures: A Current Comprehensive Clinical and Imaging Review".American Journal of Roentgenology.197 (2):W295 –W306.doi:10.2214/AJR.10.6002.ISSN0361-803X.PMID21785056.
^Johansson, Ingvar; Lynøe, Niels (2008).Medicine & Philosophy: A Twenty-First Century Introduction. Walter de Gruyter. p. 27.ISBN9783110321364. Retrieved2015-04-23.If blood is poured into a glass jar, a process of coagulation and sedimentation starts. It ends with four clearly distinct layers: a red region, a yellowish one, a black one, and a white one (Figure 4, left) ... The lowest part of the same column consists of sediment that is too dense to permit light to pass through. Therefore, this part of the column looks black and might be referred to as the 'black bile'. On the top of the column there is a white layer, which we today classify as fibrin; it might correspond to Galen's 'phlegm'. The remaining part is a rather clear but somewhat yellowish fluid that surrounds the coagulated column in the middle. It might be called 'yellow bile', but today we recognize it as blood serum.
Krejčí, Z; Hanuš L.; Podstatová H.; Reifová E (1983). "A contribution to the problems of the pathogenesis and microbial etiology of cholelithiasis".Acta Universitatis Palackianae Olomucensis Facultatis Medicae.104:279–286.PMID6222611.
Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993).Human Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall.ISBN0-13-981176-1.
