Editing Bile (section)

==Function==
[[File:Lipid and bile salts.svg|thumb|Action of bile salts in digestion]]
[[File:Bile recycling.png|thumb|Recycling of the bile]]

Bile or gall acts to some extent as a [[surfactant]], helping to [[emulsify]] the lipids in food. Bile salt [[anion]]s are [[hydrophilic]] on one side and [[hydrophobic]] on the other side; consequently, they tend to aggregate around droplets of lipids ([[triglyceride]]s and [[phospholipid]]s) to form [[micelle]]s, with the hydrophobic sides towards the fat and hydrophilic sides facing outwards.<ref>{{cite book |last= A. Potter|first= Patrica|date= 2013|title=Fundamentals of Nursing, 8th edition |publisher= Elsevier, Inc.|page= 1000|isbn=978-0-323-07933-4}}</ref> 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&nbsp;[[μm]] in humans.<ref>{{Cite book |url=https://books.google.com/books?id=7nAoDwAAQBAJ&pg=PA22 |title=Food Colloids: Self-Assembly and Material Science |last1=Dickinson |first1=Eric |last2=Leser |first2=Martin E.|date=2007-10-31|publisher=Royal Society of Chemistry|isbn=978-1-84755-769-8 |pages=22 |language=en}}</ref>

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.<ref>{{Cite journal|last=Lowe|first=Mark E.|date=2002-12-01|title=The triglyceride lipases of the pancreas|journal=Journal of Lipid Research|language=en|volume=43|issue=12|pages=2007–2016|doi=10.1194/jlr.R200012-JLR200 |doi-access=free |issn=0022-2275|pmid=12454260}}</ref> A triglyceride is broken down into two fatty acids and a [[monoglyceride]], which are absorbed by the [[Intestinal villus|villi]] on the intestine walls. After being transferred across the intestinal membrane, the fatty acids reform into triglycerides ({{nowrap|re-esterified}}), before being absorbed into the lymphatic system through [[lacteal]]s. Without bile salts, most of the lipids in food would be excreted in feces, undigested.<ref>{{Cite book|url=https://books.google.com/books?id=IsOcq_1PnlMC&pg=PT650|title=Biology: Concepts and Applications|last=Starr|first=Cecie|date=2007-09-20|publisher=Cengage Learning|isbn=978-0-495-11981-4|pages=650|language=en}}</ref>

Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble substances,<ref>{{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|website=www.vivo.colostate.edu|access-date=2016-06-05}}</ref> such as the [[vitamin]]s [[vitamin A|A]], [[vitamin D|D]], [[vitamin E|E]], and [[vitamin K|K]].<ref>{{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|website=www.vivo.colostate.edu|language=en|access-date=2018-04-09}}</ref>

Besides its digestive function, bile serves also as the route of excretion for bilirubin, a byproduct of [[red blood cell]]s 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 [[acid]]ic the longer a person goes without eating, though resting slows this fall in pH.<ref>{{cite journal | last1 = Sutor | first1 = D. June | year = 1976 | title = Diurnal Variations in the pH of Pathological Gallbladder Bile | journal = Gut | volume = 17 | issue = 12 | pages = 971–974 | doi = 10.1136/gut.17.12.971 | pmc = 1411240 | pmid=14056}}</ref> As an alkali, it also has the function of neutralizing excess [[stomach acid]] before it enters the duodenum, the first section of the [[small intestine]]. [[Bile salts]] also act as [[bactericide]]s, destroying many of the microbes that may be present in the food.<ref>{{Cite journal|last1=Merritt|first1=M. E.|last2=Donaldson|first2=J. R.|date=2009-09-17|title=Effect of bile salts on the DNA and membrane integrity of enteric bacteria|journal=Journal of Medical Microbiology|volume=58|issue=12|pages=1533–1541|doi=10.1099/jmm.0.014092-0|pmid=19762477|issn=0022-2615|doi-access=free}}</ref>