"කොලෙස්ටරෝල්" හි සංශෝධන අතර වෙනස්කම්

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| Appearance= white crystalline powder <ref name=MSDS>{{cite web |url=http://physchem.ox.ac.uk/MSDS/CH/cholesterol.html |title=Safety (MSDS) data for cholesterol |accessdate=2007-10-20 |format= |work=}}</ref>

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'''Cholesterol''' is a lipidic, waxy alcohol found in the [[cell membrane]]s and transported in the [[blood plasma]] of all [[animal]]s. It is an essential component of mammalian cell membranes where it is required to establish proper [[membrane permeability]] and [[membrane fluidity|fluidity]]. Cholesterol is the principal sterol synthesized by animals, but small quantities are synthesized in other [[eukaryote]]s, such as [[plant]]s and [[fungus|fungi]]. It is almost completely absent among [[prokaryote]]s, which include bacteria.<ref name="pmid14660793">{{cite journal | author = Pearson A, Budin M, Brocks JJ | title = Phylogenetic and biochemical evidence for sterol synthesis in the bacterium Gemmata obscuriglobus | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 100 | issue = 26 | pages = 15352–7 | year = 2003 | month = December | pmid = 14660793 | pmc = 307571 | doi = 10.1073/pnas.2536559100 | url = | issn = }}</ref> Cholesterol is classified as a [[sterol]] (a contraction of [[steroid|'''ster'''oid]] and [[alcohol|alcoh'''ol''']]).

The name cholesterol originates from the [[Greek language|Greek]] ''chole-'' ([[bile]]) and ''stereos'' (solid), and the [[chemical]] [[suffix]] ''-ol'' for an alcohol, as François Poulletier de la Salle first identified cholesterol in solid form in [[gallstone]]s, in 1769. However, it was only in 1815 that chemist [[Michel Eugène Chevreul|Eugène Chevreul]] named the compound "cholesterine".<ref>{{cite journal |author=Olson RE |title=Discovery of the lipoproteins, their role in fat transport and their significance as risk factors |journal=J. Nutr. |volume=128 |issue=2 Suppl |pages=439S–443S |year=1998 |pmid=9478044 |url=http://jn.nutrition.org/cgi/content/full/128/2/439S |month=Feb |day=01}}</ref>

 

 

Recently, cholesterol has also been implicated in cell signaling processes, assisting in the formation of [[lipid rafts]] in the [[plasma membrane]]. It also reduces the permeability of the plasma membrane to protons (positive [[hydrogen]] ions) and [[sodium ion]]s.<ref name=Haines2001>{{cite journal |author=Haines TH |title=Do sterols reduce proton and sodium leaks through lipid bilayers? |journal=Prog. Lipid Res. |volume=40 |issue=4 |pages=299–324 |year=2001 |pmid=11412894 |doi=10.1016/S0163-7827(01)00009-1}}</ref>

Cholesterol is oxidized by the liver into a variety of [[bile acids]]. These in turn are [[phase 2 reaction|conjugated]] with [[glycine]], [[taurine]], [[glucuronic acid]], or [[sulfate]]. A mixture of conjugated and non-conjugated bile acids along with cholesterol itself is excreted from the [[liver]] into the [[bile]]. Approximately 95% of the bile acids are reabsorbed from the intestines and the remainder lost in the feces.<ref name="pmid12529265">{{cite journal | author = Wolkoff AW, Cohen DE | title = Bile acid regulation of hepatic physiology: I. Hepatocyte transport of bile acids | journal = Am. J. Physiol. Gastrointest. Liver Physiol. | volume = 284 | issue = 2 | pages = G175–9 | year = 2003 | month = February | pmid = 12529265 | doi = 10.1152/ajpgi.00409.2002 | url = | issn = }}</ref> The excretion and reabsorption of bile acids forms the basis of the [[enterohepatic circulation]] which is essential for the digestion and absorption of dietary fats. Under certain circumstances, when more concentrated, as in the [[gallbladder]], cholesterol crystallises and is the major constituent of most [[gallstone]]s, although [[lecithin]] and [[bilirubin]] gallstones also occur less frequently.

 

[[Animal fat]]s are complex mixtures of [[triglyceride]]s, with lesser amounts of [[phospholipid]]s and cholesterol. Consequently all foods containing animal fat contain cholesterol to varying extents.<ref name=Christie>{{cite book |last = Christie | first = W. W. | coauthors = | title = Lipid analysis | issue=3 | publisher = PJ Barnes and associates | year = 2003 | pages=416 | isbn=0-9531949-5-7}}</ref> Cholesterol is not present in plant based food sources unless it has been added during the food's preparation.<ref name=USDA>{{cite web | last = | first = | title = USDA National Nutrient Database for Standard Reference, Release 21 | publisher = United States Department of Agriculture | url = http://www.nal.usda.gov/fnic/foodcomp/Data/SR21/nutrlist/sr21w601.pdf | format=PDF | accessdate = 2008-10-24}}</ref> However plant products such as [[flax seed]]s and [[peanut]]s contain healthy cholesterol-like compounds called [[phytosterols]], which are suggested to help lower [[serum]] cholesterol levels.<ref name=ostlund2003>{{cite journal | author=Ostlund RE, Racette, SB, and Stenson WF | title=Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ | journal=Am J Clin Nutr | year=2003 | pages=1385–1589 | volume=77 | issue=6 |pmid=12791614}}</ref> Major dietary sources of cholesterol include [[cheese]], [[egg yolk]]s, [[beef]], [[pork]], [[poultry]], and [[shrimp]].<ref name=USDA/> Human [[breast milk]] also contains significant quantities of cholesterol.<ref name=ajcn-breastmilk>{{cite journal | author=Jensen RG, Hagerty MM, McMahon KE | title=Lipids of human milk and infant formulas: a review | journal=Am J Clin Nutr | year=1978 | pages=990–1016 | volume=31 | pmid=352132 | url=http://www.ajcn.org/cgi/reprint/31/6/990 | format=PDF | issue=6 | month=Jun | day=01}}</ref>

 

Dietary cholesterol plays a smaller role in blood cholesterol levels in comparison to fat intake. A number of measures can be taken to reduce blood cholesterol levels through changes in lifestyle, one of which is a change in diet. [[Trans fat|Trans]] and [[saturated fat]]s are significant contributors to elevated cholesterol levels in the blood stream. Avoiding animal products may decrease the cholesterol levels in the body not through dietary cholesterol reduction alone, but primarily through a reduced saturated fat intake. Those wishing to reduce their cholesterol through a change in diet should aim to consume less than 7% of their daily [[calorie]]s from saturated fat and less than 200mg of cholesterol per day.<ref>{{cite web | last = | first = | title = High blood cholesterol: what you need to know | publisher = National cholesterol education program | url =http://www.nhlbi.nih.gov/health/public/heart/chol/wyntk.htm | accessdate = 2008-10-24}}</ref>

 

{{main|hypercholesterolemia|lipid hypothesis}}

 

A small group of scientists, united in [[The International Network of Cholesterol Skeptics]], continues to question the link between cholesterol and atherosclerosis.<ref>{{cite book |author=Uffe Ravnskov |title=The Cholesterol Myths : Exposing the Fallacy that Saturated Fat and Cholesterol Cause Heart Disease |publisher=New Trends Publishing, Incorporated |location= |year= 2000|pages= |isbn=0-96708-970-0 |oclc= |doi=}}</ref> However, the vast majority of doctors and medical scientists accepts the link as fact.<ref>{{cite book |author=Daniel Steinberg |title=The Cholesterol Wars: The Cholesterol Skeptics vs the Preponderance of Evidence |publisher=Academic Press |location=Boston |year= 2007|pages= |isbn=0-12-373979-9 |oclc= |doi=}}</ref>

 

Abnormally low levels of cholesterol are termed ''[[hypocholesterolemia]]''. Research into the causes of this state is relatively limited, but some studies suggest a link with [[depression (mood)|depression]], [[cancer]] and [[cerebral hemorrhage]]. Generally, the low cholesterol levels seem to be a consequence of an underlying illness, rather than a cause.<ref name=PSC/>

 

It is recommended by the [[American Heart Association]] to test cholesterol every 5 years for people aged 20 years or older. <ref>{{cite web|author=American Heart Association| title= How To Get Your Cholesterol Tested| url= http://www.americanheart.org/presenter.jhtml?identifier=541}}</ref>

A blood sample taken after fasting is taken by a doctor or a home cholesterol monitoring device to determine a lipoprotein profile. This measures total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol and triglycerides. It is recommended to have cholesterol tested more frequently than 5 years if a person: has total cholesterol of 200 mg/dL or more, if a man over age 45 or a woman over age 50, has HDL (good) cholesterol less than 40 mg/dL, or other risk factors for heart disease and stroke.

 

Some cholesterol derivatives, (among other simple cholesteric lipids) are known to generate the [[liquid crystal]]line ''cholesteric phase''. The cholesteric phase is in fact a [[chirality (chemistry)|chiral]] [[Liquid crystal|nematic phase]], and changes colour when its temperature changes. Therefore, cholesterol derivatives are commonly used in liquid crystal [[thermometer]]s and temperature-sensitive paints.

 

* [[Triglyceride]]s

* [[Diet and heart disease]]

* [[Niemann Pick disease]] Type C

 

<gallery>

Image:Steroidogenesis.svg|[[Steroidogenesis]]

</gallery>

 

{{Reflist|2}}

 

* [http://www.nhlbi.nih.gov/guidelines/cholesterol/ Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults] US National Institutes of Health Adult Treatment Panel III

* [http://www.fao.org/docrep/V4700E/V4700E08.htm Aspects of fat digestion and metabolism – UN/WHO Report 1994]

* [http://www.americanheart.org/cholesterol/about.jsp American Heart Association] – "About Cholesterol"

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{{Sterols}}

 

 

{{Link FA|ja}}

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