Dictionary:

bile

  (bīl)

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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.]

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.

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.

For more information on bile, visit Britannica.com.

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).

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.

Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. In many species, it is stored in the gallbladder between meals and upon eating is discharged into the duodenum where it excretes waste and aids the process of digestion of lipids.

Components

The components of bile:

• Cholesterol
• Lecithin (a phospholipid)
• Bile pigments (bilirubin & biliverdin)
• Bile salts (sodium glycocholate & sodium taurocholate)
• Bicarbonate ions

Production

Digestive system diagram showing the bile duct

Bile is produced by hepatocytes in the liver, draining through the many bile ducts that penetrate the liver. During this process, the epithelial cells add a watery solution that is rich in bicarbonates that dilutes and increases alkalinity of the solution. Bile then flows into the common hepatic duct, which joins with the cystic duct from the gallbladder to form the common bile duct. The common bile duct in turn joins with the pancreatic duct to empty into the duodenum. If the sphincter of Oddi is closed, bile is prevented from draining into the intestine and instead flows into the gall bladder, where it is stored and concentrated to up to five times its original potency between meals. This concentration occurs through the absorption of water and small electrolytes, while retaining all the original organic molecules. Cholesterol is also released with the bile, dissolved in the acids and fats found in the concentrated solution. When food is released by the stomach into the duodenum in the form of chyme, the gallbladder releases the concentrated bile to complete digestion.

The human liver can produce close to one litre of bile per day (depending on body size). 95% of the salts secreted in bile are reabsorbed in the terminal ileum and re-used. Blood from the ileum flows directly to the hepatic portal vein and returns to the liver where the hepatocytes resorb the salts and return them to the bile ducts to be re-used, sometimes two to three times with each meal.

Physiological functions

Bile acts to some extent as a detergent, helping to emulsify fats (increasing surface area to help enzyme action), and thus aids in their absorption in the small intestine. The most important compounds are the salts of taurocholic acid and deoxycholic acid. Bile salts combine with phospholipids to break down fat globules in the process of emulsification by associating its hydrophobic side with lipids and the hydrophilic side with water. Emulsified droplets then are organized into many micelles which increases absorption. Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble vitamins D, E, K and A. Besides its digestive function, bile serves as the route of excretion for the hemoglobin breakdown product (bilirubin) created by the spleen which gives bile its colour; it also neutralises any excess stomach acid before it enters the ileum, the final section of the small intestine. Bile salts are also bacteriocidal to the invading microbes that enter with food.

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

Abnormal conditions associated with bile

• The cholesterol contained in bile will occasionally accrete into lumps in the gall bladder, forming gallstones.
• After excessive consumption of alcohol, a person's vomit may be green. The green component is bile.
• In the absence of bile, fats become indigestible and are instead excreted in feces. In this case, the feces lacks its characteristic brown colour and instead are white or grey, and greasy. This causes significant problems in the distal parts of the intestine as normally all fats are absorbed earlier in the gastrointestinal tract. Past the small intestine the organs and gut flora are not adapted to processing fats.

Four humours

Yellow bile (sometimes called ichor) and black bile were two of the four vital fluids or humours of ancient and medieval medicine (the other two were phlegm and blood). The Latin names for the terms gave rise to the words "choler" (bile) and "melancholia" (black bile). Excessive bile was supposed to produce an aggressive temperament, known as "choleric". This is the origin of the word "bilious." Depressive and other mental illnesses (melancholia) were ascribed to a bodily surplus of black bile. This is the origin of the word "melancholy."

See also

• Intestinal juice
• Bile acid sequestrant

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. Retrieved on 2007-02-08. 

General references

• 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. 
• Bowen, R. (November 23, 2001). Secretion of Bile and the Role of Bile Acids In Digestion. Retrieved on 2007-07-17.

Digestive system, physiology: gastrointestinal physiology
Enteric nervous system	Meissner's plexus - Auerbach's plexus
Exocrine	Chief cells (Pepsinogen) - Parietal cells (Gastric acid, Intrinsic factor) - Goblet cells (Mucus)
Endocrine/paracrine	G cells (gastrin), D cells (somatostatin) - ECL cells (Histamine) - enterogastrone: I cells (CCK), K cells (GIP), S cells (secretin)
Border	Brunner's glands - Paneth cells - Enterocytes
Fluids	Saliva - Bile - Intestinal juice - Gastric juice - Pancreatic juice
Processes	Swallowing - Vomiting - Peristalsis (Interstitial cell of Cajal) - Migrating motor complex - Borborygmus - Gastrocolic reflex - Segmentation contractions - Defecation

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

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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