bile

(bīl)

1. A bitter, alkaline, brownish-yellow or greenish-yellow fluid that is secreted by the liver, stored in the gallbladder, and discharged into the duodenum and aids in the emulsification, digestion, and absorption of fats. Also called gall.
2. Bitterness of temper; ill humor; irascibility.
3. Either of two bodily humors, black bile or yellow bile, in ancient and medieval physiology.

[French, from Latin bīlis.]

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Fluid produced by the liver and stored in the gall bladder before secretion into the small intestine (duodenum) via the bile duct. It contains the bile salts, which function in the emulsification and hence digestion of fats, bile pigments (bilirubin and biliverdin, which are the result of breakdown of the haemoglobin of red blood cells), phospholipids, and cholesterol. It is alkaline, and hence neutralizes the acid from the stomach as the food reaches the small intestine. Relatively large amounts of vitamin B₁₂ and folic acid are secreted in the bile and then reabsorbed from the small intestine. Most of the cholesterol and bile salts are also reabsorbed from the small intestine. See also gastro-intestinal tract.

A greenish-yellow or brownish fluid produced in the liver and stored in the gall-bladder. Its constituents include bile pigments (breakdown products of haemoglobin), salts, and cholesterol. Bile is stored in the gall-bladder and released into the small intestine where bile salts aid the digestion and absorption of fats through their detergent-like action. See also gallstones.

Bile is a greenish-yellow fluid produced by the liver, and passing from there into the duodenum; it has a number of functions, which will be described shortly. But bile also has a remarkable history, for in early medicine bile made up two of the four humours, which were blood, phlegm, yellow bile, and black bile. For about 2000 years an excess of black bile was thought to make patients melancholic, and an excess of yellow bile to make them choleric.

But let your friends in verse suppose
What ne'er shall be allowed in prose,
Anatomists can make it clear
The liver minds its own affair;
And parts and strains the vital juices,
Still layes some useful bile aside,
To tinge the chyles insipid tide;
Else we should want both bile and satire
And all be burst with pure good nature.

Bile acids and bile salts

The function of these remarkable molecules is inextricably involved with cholesterol. The two main bile acids, cholic acid and chenodeoxycholic acid, are both made from cholesterol in the liver and pass into the bile in combination with amino acids, as bile salts. Cholesterol is virtually insoluble in water, and in the words of the 1989 Nobel prizewinners, Brown and Goldstein, ‘Cholesterol is a Janus-faced molecule. The very property that makes it useful in the cell membrane, namely its insolubility in water, also makes it lethal.’ (The authors were referring to the crucial part played by cholesterol in the pathological process of atherosclerosis.) So the body has resorted to some remarkable strategies to excrete this difficult substance, and it seems that cholesterol excreted by the liver is partly extracted from the circulation and partly made by the liver itself. The body's main strategy is to use bile salts as detergents: the molecules have a water-soluble (hydrophilic) side and a fat-soluble (hydrophobic) side. This enables bile salts to make small parcels (‘micelles’) including several different molecules, with cholesterol as contents and bile salts as the wrapping. The hydrophobic aspect of the bile salt faces inwards, and the hydrophilic aspect faces outwards into the aqueous component of bile.

The bile micelles pass into the duodenum, where the detergent action of the bile salts emulsifies fats, which are then broken down by the enzyme lipase from the pancreas. Bile salts also assist the final absorption of the products of fat digestion. Both bile and lipase are necessary for the proper absorption of fats by the small intestine. Without one or other of these two, there is deficiency of the vital fat-soluble vitamins, A, D, E and K, and malabsorption causes fat to appear in the faeces (steatorrhoea).

Bile salts pass down the entire length of the small intestine, but instead of their being degraded or excreted in faeces, a remarkable phenomenon occurs. The bile salts are absorbed as whole molecules at the far end of the small intestine (the terminal ileum) and pass up the portal vein to the liver, whence they are re-secreted into bile. This circuit, known as the entero-hepatic circulation, represents extraordinary parsimony, for at any one time only 3-5 g of bile acids are present in the body; this 3-5 g is known as the bile acid pool, and it circulates 6-10 times a day. About 0.5 g of bile acids is lost in the faeces per day, which means that an average bile acid molecule survives in the entero-hepatic circulation for about 3 days, making 18-30 cycles. During this time, it will escort many hydrophobic molecules (such as cholesterol) into the small intestine, and help with the emulsification and absorption of a significant quantity of fat. We have no idea why the body should indulge in this metabolic penny-pinching. If the terminal ileum is diseased, or has to be surgically removed, the bile acids pass into the colon, where they produce watery diarrhoea.

It is of interest that vitamin B₁₂ is also absorbed from the terminal ileum, and passes up the portal vein; the liver metabolizes some of it and the products pass into the watery phase of the bile; reabsorption provides an entero-hepatic circulation. Vitamins B₁₂ cannot be synthesized in the body, so this is an appropriate device for conservation of a precious molecule. Damage to, or surgical removal of, the terminal ileum produces the syndrome of pernicious anaemia, a consequence of vitamin B₁₂ deficiency.

Cholesterol gallstones

The commonest disorder of bile formation is the presence of gallstones, and the commonest type of gallstone consists of cholesterol, which comes out of solution in the gall bladder. Gallstones cause symptoms by passing out of the gall bladder and obstructing the bile duct; the time-honoured treatment consists of surgically removing the gall bladder. More recently, stones have been treated medically, by increasing the bile acid/cholesterol ratio of bile. This is achieved simply by taking synthetic bile acids by mouth. Unfortunately it may take many months to dissolve existing gallstones, and even if it does have the desired effect, the patient will need to take bile acids indefinitely to prevent the recurrence of stones. Stones can also be disintegrated inside the gall bladder by the ingenious use of high frequency waves (‘lithotrypsy’).

Some races (Finns, Swedes and North American Indian women) have high cholesterol/bile acid ratios in their bile, and are very prone to gallstones. These races have a high animal fat diet, rich in cholesterol. In races whose diets contain little animal fat (Japanese and Masai for example) the bile contains little cholesterol, and gallstones are rare — but the formation of cholesterol stones is not just a question of diet. It has been found that the cholesterol concentration of bile varies with the time of day, for example, which makes the phenomenon of cholesterol crystallization much more difficult to analyse.

Bile pigments

The life of red blood cells is about 120 days, and their death is associated with the release of haemoglobin, which makes up the greater part of the red cells. Macrophages are chiefly responsible for their destruction; the globin protein is reused, while the haem is detached from the iron, which is also reused. Haem is a ring (tetrapyrrole) structure and cannot be reused. Within the macrophage the ring is broken, and the four constitutent pyrrole groups are arranged in a straight chain — biliverdin (green) — and finally bilirubin (yellow). The changes in skin seen after bruising represent this conversion, for blood produced by the bruise is taken up by the local macrophages, and the blood in the macrophage undergoes the red to green to yellow conversion.

Under normal circumstances, bilirubin is released by the macrophage into blood. Bilirubin is insoluble in water, and is transported in blood by being attached to very large molecules, plasma albumin. When this bound bilirubin reaches the liver it separates from the plasma protein, and enters the liver cell, but, because of its insolubility, some device needs to be employed by the liver to incorporate it into bile. The way that the liver achieves this is not to include it in the centre of a micelle, but to attach, or conjugate, it to glucuronic acid, which makes the bilirubin water-soluble. (The yellow-green colour of bile is derived from bilirubin.)

Conjugated bilirubin (or bilirubin glucuronide) passes down the bile duct in the bile; unlike bile salts, it has no role in digestion. It passes into the intestine, where bacterial action converts it to urobilinogen, which is very water-soluble. Some urobilinogen is absorbed across the gut wall and passes into the blood whence it may be either resecreted into bile (as an entero-hepatic circulation), or excreted by the kidneys. It is urobilinogen that gives urine its yellow colour. The urobilinogen that is not absorbed from the gut passes down the small intestine to the colon, and its final product, stercobilin, gives rise to the brown colour of faeces. Bilirubin is thus a ubiquitous colouring agent.

— John Henderson

See also alimentary system; jaundice; liver.

A greenish-yellow or brownish fluid produced in the liver. Bile contains cholesterol, inorganic salt, and bile pigments (bilirubin and biliverdin, breakdown products of red blood cells). It is stored in the gall bladder and released into the small intestine, where it aids the digestion and adsorption of fats through its alkali, emulsifying action.

A bitter fluid produced by the liver and stored in the gallbladder. Bile is discharged into the small intestine when needed to aid in the digestion of fats (see digestive system).

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A clear yellow, orange or green fluid produced by the liver. It is concentrated and stored in the gallbladder, and is poured into the small intestine via the bile ducts when needed for digestion. Bile helps in alkalinizing the intestinal contents and plays a role in the digestion and absorption of fat; its chief constitutents are conjugated bile salts, cholesterol, phospholipid, bilirubin and electrolytes. See also bile duct, biliary.

• b. acids — steroid acids derived from cholesterol; classified as primary, those synthesized in the liver, e.g. cholic and chenodeoxycholic acid, or secondary, those produced from primary bile acids by intestinal bacteria and returned to the liver by enterohepatic circulation, e.g. deoxycholic and lithocholic acid.
• b. acid assay — are used in the diagnosis of liver disease and portacaval shunts when there are increased levels in the blood.
• b. lake — bile duct obstruction may cause distention and rupture of biliary canaliculi. Small bile lakes result causing focal hepatic necrosis.
• b. passages — bile canaliculi drain into bile ductules and interlobular ducts. These unite to form a series of hepatic ducts which carry the bile to the porta where they unite to form the common hepatic duct. This duct receives a cystic duct from the gallbladder (absent in the horse) and thence becomes the bile duct.
• b. peritonitis — leakage of bile from the common bile duct or gallbladder may occur as a result of trauma, including perforation during percutaneous needle biopsy of the liver, and (rarely) erosion from biliary calculi. A chemical peritonitis results and may be fatal unless surgical repair is accomplished.
• b. pigment — any one of the coloring matters of the bile; they are bilirubin, biliverdin, bilifuscin, biliprasin, choleprasin, bilihumin and bilicyanin. See also urobilinogen, stercobilin.
• b. pleuritis — inflammation of the pleura resulting from perforating thoracic trauma with hepatodiaphragmatic fistula or iatrogenically from percutaneous liver biopsy techniques.
• b. reflux — usually refers to movement of bile from the duodenum into the stomach where it may alter the gastric mucosal barrier causing gastritis and ulceration.
• b. salts — see taurocholate, chenodeoxycholic acid, glycocholic acid.
• white b. — 1. bile containing much mucin.
— 2. bile trapped in obstructed system for a long period and from which pigments have been resorbed.

• Endocrine System and Glands - bile: green, alkaline liquid produced by liver that forms emulsion with fat to assist enzyme action
• Physiology - bile: greenish liver secretion that is stored in gallbladder until released to emulsify fats in small intestine

Bile (yellow material) in a liver biopsy in the setting of bile stasis, i.e. cholestasis. H&E stain

Action of bile salts in digestion

Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum. Bile is a composition of the following materials: water (85%), bile salts (10%), mucus and pigments (3%), fats (1%), inorganic salts (0.7%) and cholesterol (0.3%).

In the medical theories prevalent in the West from Classical Antiquity up to the Middle Ages, the body's health depended on the equilibrium between four "humors" or vital fluids: blood, phlegm, "yellow bile" (or choler) and "black bile". Excesses of the last two humors were thought to produce aggression and depression, respectively; and the Greek names for them gave rise to the English words "cholera" and "melancholia". Those same theories explain the derivation of the English word "bilious" from "bile", and the meaning of "gall" in English as "exasperation" or "impudence".

Contents 1 Physiological functions 2 Bile soap 3 Abnormal conditions associated with bile 4 Principal bile acids 5 See also 6 References 7 External links

Physiological functions

Bile acts to some extent as a surfactant, helping to emulsify the fats in the food. Bile salt anions have a hydrophilic side and a hydrophobic side, and therefore tend to aggregate around droplets of fat (triglycerides and phospholipids) to form micelles, with the hydrophobic sides towards the fat and hydrophilic towards the outside. The hydrophilic sides are positively charged due to the lecithin and other phospholipids that compose bile, 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 of around 14-33 μm.

The dispersion of food fat into micelles thus provide a largely increased surface area for the action of the enzyme pancreatic lipase, which actually 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, fatty acids are reformed into triglycerides, then absorbed into the lymphatic system through lacteals. Without bile salts, most of the lipids in the food would be passed out 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 D, E, K and A.

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 haemoglobin by glucuronidation.

The alkaline bile also has the function of neutralizing any excess stomach acid before it enters the ileum, the final section of the small intestine. Bile salts also act as bactericides, destroying many of the microbes that may be present in the food.

Bile soap

Bile from slaughtered animals can be mixed with soap. This mixture, called bile soap,^[1] can be applied to textiles a few hours before washing and is a traditional and rather effective method for removing various kinds of tough stains.

Abnormal conditions associated with bile

• 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 is commonly mistaken as bile.^{[citation needed]} The color of bile is often likened to "fresh-cut grass"^{[citation needed]}, unlike components in the stomach that look greenish yellow or dark yellow.

• 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.^[2] 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.

Principal bile acids

• 

  Cholic acid

• 

  Chenodeoxycholic acid

• 

  Glycocholic acid

• 

  Taurocholic acid

• 

  Deoxycholic acid

• 

  Lithocholic acid

See also

• Bile acid sequestrant
• Bile bear
• Intestinal juice
• Ox gall

References

Notes

1. ^ Newton, W. (1837). "The invention of certain improvements in the manufacture of soap, which will be particularly applicable to the felting of woollen cloths.". The London Journal Of Arts And Sciences; And Repertory Of Patent Inventions IX: 289. http://www.google.co.uk/books?vid=0MfyvmoTsdK02ZeP86W&id=GhMAAAAAMAAJ&pg=RA19-PA291&lpg=RA19-PA291&dq=bile+soap&as_brr=1. Retrieved 2007-02-08. 
2. ^ Barabote RD, Tamang DG, Abeywardena SN, et al. (2006). "Extra domains in secondary transport carriers and channel proteins". Biochim. Biophys. Acta 1758 (10): 1557–79. doi:10.1016/j.bbamem.2006.06.018. PMID 16905115. 

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2011)

Bibliography

• Bowen, R. (2001-11-23). "Secretion of Bile and the Role of Bile Acids In Digestion". Colorado State Hypertextbook article on Bile. http://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.html. Retrieved 2007-07-17. 
• 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. PMID 6222611. 
• 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, USA: Prentice Hall. ISBN 0-13-981176-1. 

External links

• Photo of bear bile sample in an animal welfare blog by Paul Kraaijer.

v t e Digestive system, physiology: gastrointestinal physiology GI tract Upper GI Exocrine Chief cells (Pepsinogen) · Parietal cells (Gastric acid, Intrinsic factor) · Goblet cells (Mucus) Processes Swallowing · Vomiting Fluids Saliva · Gastric juice Lower GI Enteric nervous system Meissner's plexus · Auerbach's plexus Endocrine/paracrine G cells (gastrin) · D cells (somatostatin) · ECL cells (Histamine) enterogastrone: I cells (CCK) · K cells (GIP) · S cells (secretin) Enteroendocrine cells · Enterochromaffin cell · APUD cell Fluids Intestinal juice Processes Segmentation contractions · Migrating motor complex · Borborygmus · Defecation Either/both Processes Peristalsis (Interstitial cell of Cajal · Basal electrical rhythm) · Gastrocolic reflex · Digestion Accessory Fluids Bile · Pancreatic juice Processes Enterohepatic circulation Abdominopelvic Peritoneal fluid M: DIG anat(t, g, p)/phys/devp/enzy noco/cong/tumr, sysi/epon proc, drug(A2A/2B/3/4/5/6/7/14/16), blte

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Dansk (Danish)
n. - galde

Nederlands (Dutch)
gal, galstoornis, bitterheid

Français (French)
n. - (Anat) bile, mauvaise humeur, (Hist) bile

Deutsch (German)
n. - Galle

Ελληνική (Greek)
n. - χολή, πίκρα, οργή

Italiano (Italian)
bile

Português (Portuguese)
n. - bílis (Fisiol.), mau humor (m) (fig.)

Русский (Russian)
желчь

Español (Spanish)
n. - bilis, hiel

Svenska (Swedish)
n. - galla, ilska

中文（简体）(Chinese (Simplified))
胆汁, 愤怒, 坏脾气

中文（繁體）(Chinese (Traditional))
n. - 膽汁, 憤怒, 壞脾氣

한국어 (Korean)
n. - 담즙, 화, 짜증

日本語 (Japanese)
n. - 胆汁, かんしゃく

العربيه (Arabic)
‏(الاسم) الصفراء, العصارة المرة التي يفرزها الكبد, سرعه الغضب‏

עברית (Hebrew)
n. - ‮מרה, מרירות, רגזנות‬

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