Bile
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'''Bile''' or '''gall''' is a bitter yellow or green [[alkali]]ne fluid secreted by [[hepatocyte]]s from the [[liver]] of most [[vertebrate]]s. In many species, '''bile''' is stored in the [[gallbladder]] between meals and upon eating is discharged into the [[duodenum]] where the bile aids the process of [[digestion]] of [[lipids]].
== General infomation (summary) ==
Bile has various components, some of which are produced by [[hepatocytes]] (liver cells). Its constituents include:
*Water
*Cholesterol
*Bile pigments
*Bile salts
The bile salts sodium glycocholate and sodium taurocholate are produced by the liver from cholesterol. They are secreted in bile by hepatocytes along the bile canaliculi, which then join the bile duct, and thence into the gall bladder.
Ordinarily the concentration of bile salts in bile is 0.8%, however the gall bladder removes water from the bile, concentrating it between meals. It concentrates it up to 5 times (increasing concentration to 4%), before contracting the walls and releasing it into the duodenum once chyme has entered the small intestine.
==Components- in more detail==
'''The components of bile:'''
*
* [[Cholesterol]]
* [[Phospholipids]] (mainly [[Lecithin]])
* [[Bilin (biochemistry)|Bile pigment]]s (bilirubin diglucoronoide)
* [[Bile acid|Bile salts]] ([[sodium glycocholate]] & [[sodium taurocholate]])
* [[Bicarbonate]] ions
==Production==
[[Image:Digestive system showing bile duct.png|thumb|Digestive system diagram showing the bile duct]]
Bile is produced by [[hepatocyte]]s in the liver, draining through the many [[bile duct]]s that penetrate the liver. During this process, the [[Epithelium|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 gallbladder, 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 salts are composed of a hydrophilic side, and a hydrophobic side. This means that they are more likely to aggregate to form micelles, with the hydrophobic sides towards the centre and hydrophilic towards the outside. In the centre of these micelles are triglycerides, which are separated from a larger globule of lipid, as shown in the diagram.
Pancreatic lipase is able to get to the molecules of triglyceride through gaps between the bile salts, providing a largely increased surface area for digestion.
Ordinarily, the micelles in the duodenum have a diameter of around 14-33μm. However, it is possible for these to be much smaller, as small as 160nm when using artificial means.
Should bile not be present in the duodenum, not all of the lipid is able to be digested during digestion, and a lot of it is passed out in feces. As a result the time taken for the lipid to be broken down would be greatly increased if there was no [[bile]] present in the duodenum. This is how the body is able to efficiently digest and absorb lipids for metabolism.
Bile acts to some extent as a [[detergent]], helping to [[emulsification|emulsify]] [[fat]]s (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 [[micelle]]s which increases absorption. Since bile increases the absorption of [[fat]]s, it is an important part of the absorption of the fat-soluble [[vitamin]]s [[vitamin D|D]], [[Tocopherol|E]], [[vitamin K|K]] and [[vitamin A|A]]. Besides its digestive function, bile serves as the route of excretion for the [[hemoglobin]] breakdown product ([[bilirubin]]) created by breakdown of erythrocytes, which are conjugated by glucuronidation in the liver ; 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 soaps ==
Bile from slaughtered animals can be mixed with [[soap]]. This mixture, called [[bile soap]],<ref> {{cite journal|title=The invention of certain improvements in the manufacture of soap, which will be particularly applicable to the felting of woollen cloths.|journal=The London Journal Of Arts And Sciences; And Repertory Of Patent Inventions|date=1837|first=W. |last=NEWTON|coauthors=|volume=IX|issue=|pages=289|id= |url=http://www.google.co.uk/books?vid=0MfyvmoTsdK02ZeP86W&id=GhMAAAAAMAAJ&pg=RA19-PA291&lpg=RA19-PA291&dq=bile+soap&as_brr=1|format=|accessdate=2007-02-08}}</ref> 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 gall bladder, forming [[Cholelithiasis|gallstones]].
* On an empty stomach, for example, after repeated [[vomit]]ing caused by excessive consumption of alcohol, (Note: The vomiting does not have to be caused by alcohol. If you dry heave long enough, bile will surface) a person's vomit may be green or dark yellow, and very bitter. The bitter and greenish component is bile. (The color of bile is often likened to “fresh-cut grass,” but in a vomit it may be mixed with other components in the stomach to 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 colour and instead are white or grey, and greasy.<ref>{{cite journal |author=Barabote RD, Tamang DG, Abeywardena SN, ''et al'' |title=Extra domains in secondary transport carriers and channel proteins |journal=Biochim. Biophys. Acta |volume=1758 |issue=10 |pages=1557–79 |year=2006 |pmid=16905115 |doi=10.1016/j.bbamem.2006.06.018}}</ref> Steatorrhea can lead to deficiencies in [[essential fatty acid]]s 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 [[Anatomical_terms_of_location#Proximal_and_distal|distal]] parts of the intestine.
==Four humors==
[[Four humors#Choleric|Yellow bile]] (sometimes called [[ichor]]) and [[Melancholia|black bile]] were two of the four vital fluids or [[Humorism|humors]] of ancient and medieval Greco-Roman alternative 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 "[[Four_humours#Choleric|choleric]]". This is the origin of the word "bilious." Depression and other mental illnesses ([[melancholia]]) were ascribed to a bodily surplus of black bile. This is the origin of the word "melancholy."
==See also==
*[[Bile acid sequestrant]]
*[[Bile bear]]
*[[Intestinal juice]]
==Footnotes==
{{reflist}}
==References==
* {{cite journal | last = Krejčí | first = Z | coauthors = Hanuš L., Podstatová H. & Reifová E | title = A contribution to the problems of the pathogenesis and microbial etiology of cholelithiasis | journal = Acta Universitatis Palackianae Olomucensis Facultatis Medicae
| pages = 279–286 | volume = 104 | year = 1983 | pmid = 6222611 }}
* {{cite web | url = http://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.html | title = Secretion of Bile and the Role of Bile Acids In Digestion | source = Colorado State Hypertextbook article on Bile | last = Bowen | first = R. | date = 2001-11-23 | accessdate = 2007-07-17}}
* {{cite book
| last = Maton
| first = Anthea
| authorlink =
| coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
| title = Human Biology and Health
| publisher = Prentice Hall
| date = 1993
| location = Englewood Cliffs, New Jersey, USA
| pages =
| url =
| doi =
| id =
| isbn = 0-13-981176-1}}
{{Gastrointestinal physiology}}
[[Category:Body fluids]]
[[Category:Digestive system]]
[[Category:Biomolecules]]
[[Category:Hepatology]]
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