cholesterol

cholesterol , fatty lipid found in the body tissues and blood plasma of vertebrates; it is only sparingly soluble in water, but much more soluble in some organic solvents. A steroid , cholesterol can be found in large concentrations in the brain, spinal cord, and liver. The liver is the most important site of cholesterol biosynthesis, although other sites include the adrenal glands and reproductive organs. By means of several enzymatic reactions, cholesterol is synthesized from acetic acid ; it then serves as the major precursor for the synthesis of vitamin D3, of the various steroid hormones , including cortisol , cortisone , and aldosterone in the adrenal glands , and of the sex hormones progesterone, estrogen, and testosterone. Cholesterol is excreted from the liver in the form of a secretion known as bile ; it sometimes crystallizes in the gall bladder to form gallstones. The insolubility of cholesterol in water is also a factor in the development of atherosclerosis (see arteriosclerosis ), the pathological deposition of plaques of cholesterol and other lipids on the insides of major blood vessels, a condition associated with coronary artery disease . This buildup of cholesterol in the blood vessels may constrict the passages considerably and inhibit the flow of blood to and from the heart. Recent research has shown that the relative abundance of certain protein complexes, called lipoproteins, to which cholesterol becomes attached may be the real cause of cholesterol buildup in the blood vessels. High-density lipoprotein (HDL) carries cholesterol out of the bloodstream for excretion, while low-density lipoprotein (LDL) carries it back into the system for use by various body cells. Researchers believe that HDL and LDL levels in the bloodstream may be at least as important as cholesterol levels, and now measure both to determine risk for heart disease. Reducing consumption of foods containing cholesterol and saturated fat has been found to lower blood cholesterol levels. Cholesterol levels can also be reduced with drugs, most especially with HMG-CoA reductase inhibitors (commonly called "statins" ), such as lovastatin (Mevacor) and atorvastatin (Lipitor), and by regular exercise.

cholesterol White, fatty steroid, occurring in large concentrations in the brain, spinal cord and liver. It is synthesized in the liver, intestines and skin, and is an intermediate in the synthesis of vitamin D and many hormones. Gallstones are composed mainly of cholesterol. Meat-rich diets may produce Low-density lipoprotein cholesterol (LDL-cholesterol), which can become high cholesterol in blood vessels and lead to atherosclerosis (hardening of the arteries) and arteriosclerosis (degenerative disease of the arteries). High-density lipoprotein cholesterol (HDL-cholesterol) is a beneficial form that reduces LDL-cholesterol and fat by transporting them to the liver which breaks them down. Certain diets, such as those reducing saturated fat, can lower the dangers of cholesterol. Home kits are available to check cholesterol levels.

cholesterol (kŏl-est-er-ol) n. a fatlike material (a sterol) present in the blood and most tissues, especially nervous tissue. Elevated blood concentration of cholesterol (hypercholesterolaemia) is often associated with atheroma, of which cholesterol is a major component. Cholesterol is also a constituent of gallstones.