Cholesterol is a sterol (a combination steroid and alcohol), a lipid found in the cell membranes of all body tissues, and is transported in the blood plasma of all animals. Trace amounts of cholesterol are also found in plant membranes.
The name originates from the Greek chole- (bile) and stereos (solid), and the chemical [[suffix -ol for an alcohol, as researchers first identified cholesterol in solid form in gallstones in 1784.
Cholesterol is not necessarily dietary in origin; it is synthesized internally by the body from unburned food metabolites. Its level in blood can be raised beyond natural levels by eating raised food amounts, especially with cholesterol-containing foods. Cholesterol is more abundant in tissues which either synthesize more or have more abundant densely-packed membranes, for example, the liver, spinal cord, brain, and atheromata (arterial plaques).
Cholesterol plays a central role in many biochemical processes, but is best known for the association of cardiovascular disease with various lipoprotein cholesterol transport patterns and high levels of cholesterol in the blood. Cholesterol is insoluble in blood, but is transported in the circulatory system bound to one of the varieties of lipoprotein, spherical particles which have an exterior composed mainly of water-soluble proteins.
In recent years, the somewhat imprecise term "bad cholesterol" has been used to refer to LDL (low-density lipoprotein) which, according to the lipid hypothesis, is thought to have harmful actions, and "good cholesterol" to refer to HDL (high-density lipoprotein), thought to have beneficial actions.
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