cholesterol

(kəlĕs`tərōl'), fatty lipidlipids,
a broad class of organic products found in living systems. Most are insoluble in water but soluble in nonpolar solvents. The definition excludes the mineral oils and other petroleum products obtained from fossil material.
..... Click the link for more information. 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 steroidsteroids,
class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals.
..... Click the link for more information. , 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 acidacetic acid
, CH₃CO₂H, colorless liquid that has a characteristic pungent odor, boils at 118&degC;, and is miscible with water in all proportions; it is a weak organic carboxylic acid (see carboxyl group). Glacial acetic acid is concentrated, 99.
..... Click the link for more information. ; it then serves as the major precursor for the synthesis of vitamin D3, of the various steroid hormoneshormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
..... Click the link for more information. , including cortisolcortisol
or hydrocortisone,
steroid hormone that in humans is the major circulating hormone of the cortex, or outer layer, of the adrenal gland. Like cortisone, cortisol is classed as a glucocorticoid; it stimulates liver glycogen formation while it decreases the rate
..... Click the link for more information. , cortisonecortisone
, steroid hormone whose main physiological effect is on carbohydrate metabolism. It is synthesized from cholesterol in the outer layer, or cortex, of the adrenal gland under the stimulation of adrenocorticotropic hormone (ACTH).
..... Click the link for more information. , and aldosteronealdosterone
, steroid secreted by the cortex of the adrenal gland. It is the most potent hormone regulating the body's electrolyte balance. Aldosterone acts directly on the kidney to decrease the rate of sodium-ion excretion (with accompanying retention of water), and to
..... Click the link for more information. in the adrenal glandsadrenal gland
or suprarenal gland
, endocrine gland (see endocrine system) about 2 in. (5.1 cm) long situated atop each kidney. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and
..... Click the link for more information. , and of the sex hormones progesterone, estrogen, and testosterone. Cholesterol is excreted from the liver in the form of a secretion known as bilebile,
bitter alkaline fluid of a yellow, brown, or green color, secreted, in man, by the liver. Bile, or gall, is composed of water, bile acids and their salts, bile pigments, cholesterol, fatty acids, and inorganic salts.
..... Click the link for more information. ; it sometimes crystallizes in the gall bladdergall bladder,
small pear-shaped sac that stores and concentrates bile. It is connected to the liver (which produces the bile) by the hepatic duct. When food containing fat reaches the small intestine, the hormone cholecystokinin is produced by cells in the intestinal wall and
..... Click the link for more information. to form gallstones. The insolubility of cholesterol in water is also a factor in the development of atherosclerosis (see arteriosclerosisarteriosclerosis
, general term for a condition characterized by thickening, hardening, and loss of elasticity of the walls of the blood vessels. These changes are frequently accompanied by accumulations inside the vessel walls of lipids, e.g.
..... Click the link for more information. ), the pathological deposition of plaques of cholesterol and other lipids on the insides of major blood vessels, a condition associated with coronary artery diseasecoronary artery disease,
condition that results when the coronary arteries are narrowed or occluded, most commonly by atherosclerotic deposits of fibrous and fatty tissue. Coronary artery disease is the most common underlying cause of cardiovascular disability and death.
..... Click the link for more information. . 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

A cyclic hydrocarbon alcohol commonly classified as a lipid because it is insoluble in water but soluble in a number of organic solvents. It is the major sterol in all vertebrate cells and the most common sterol of eukaryotes. In vertebrates, the highest concentration of cholesterol is in the myelin sheath that surrounds nerves and in the plasma membrane that surrounds all cells. See Lipid

Cholesterol can exist either in the free (1) (unesterified) form (see structure below) or in the esterified form, in which a fatty acid is bound to the hydroxyl group of cholesterol by an ester bond. The free form is found in membranes. Cholesteryl esters are normally found in lipid droplets either within the cells of steroidogenic tissues, where it can be converted to free cholesterol and then to steroid hormones, or in the middle of spherical lipid-protein complexes, called lipoproteins, that are found in blood. See Cell membranes

Cholesterol, together with phospholipids and proteins, is important in the maintenance of normal cellular membrane fluidity. At physiological temperatures, the cholesterol molecule interacts with the fatty acids of the membrane phospholipids and causes increased packing of the lipid molecules and hence a reduction of membrane fluidity. Thus, all vertebrate cells require cholesterol in their membranes in order for the cell to function normally. Cholesterol is also important as a precursor for a number of other essential compounds, including steroid hormones, bile acids, and vitamin D. See Lipid metabolism; Steroid

Cellular cholesterol is obtained both from the diet, following its absorption in the intestine, and from synthesis within all cells of the body. Foods that are particularly high in cholesterol include eggs, red meat, and organs such as liver and brain. About 40–50% of the dietary cholesterol is absorbed from the intestine per day. In contrast, plant sterols are very poorly absorbed. Cholesterol synthesis occurs in all vertebrate cells but is highest in the liver, intestine, and skin, and in the brain at the time of myelination.

Cholesterol and cholesteryl esters are essentially insoluble in water. In order to transport these compounds around the body in the blood, the liver and intestine produce various lipid-protein complexes, called lipoproteins, which serve to solubilize them. Lipoproteins are large, complex mixtures of cholesterol, cholesteryl esters, phospholipids, triglycerides (fats), and various proteins. The major lipoproteins include chylomicrons, very low density lipoprotein (VLDL), low-density lipoprotein, and high-density lipoprotein (HDL).

Total plasma cholesterol levels of less than 200 mg/100 ml are considered desirable. Values of 200–239 or greater than 239 mg per 100 ml are considered, respectively, borderline high or high risk values, indicating the potential for a heart attack. High levels of low-density lipoprotein in the plasma are associated with increased risk of atherosclerosis, (“hardening of the arteries”), which involves deposition of cholesterol and other lipids in the artery wall. Diets low in cholesterol and saturated fats often result in a reduction in total plasma and LDL cholesterol levels. Such changes in blood cholesterol levels are thought to be beneficial and to reduce the incidence of heart attacks.

Cholesterol

an organic compound of the steroid class; the most important sterol in animals (seeSTEROL).

Cholesterol was first isolated from a gallstone (hence the name, from the Greek chole, “bile”). It is obtained as colorless crystals, with a melting point of 149°C. It is insoluble in water but readily soluble in nonpolar organic solvents. A characteristic chemical property of cholesterol is the capacity to form molecular complexes with many salts, acids, amines, proteins, and such neutral compounds as saponins and vitamin D₃ (cholecalciferol).

Cholesterol is present in virtually all living organisms, including bacteria and blue-green algae. Its content in plants is usually low except in seed oils and pollen. In vertebrate animals, large amounts of cholesterol are found in nerve tissue lipids, where it is bound to structural elements of the myelin sheath, as well as in ova and sperm cells, the liver (the principal organ of cholesterol biosynthesis), the adrenal glands, the cutaneous sebum, and erythrocyte cell walls. It is present in blood plasma in the form of complex esters of higher fatty acids (for example, oleic acid) and serves as a carrier during their transport. These esters are formed in the intestinal walls with the participation of the enzyme cholesterol esterase. Most organisms, except some microorganisms, annelid worms, mollusks, echinoderms, and sharks, can synthesize cholesterol from squalene (seeSQUALENE).

The most important biochemical function of cholesterol in vertebrates is its conversion to the hormone progesterone in the placenta, testes, corpus luteum, and adrenal glands. This conversion initiates the chain of biosynthesis of steroid sex hormones and corticosteroids. Another result of cholesterol metabolism in vertebrates is the formation of bile acids and vitamin D₃. Cholesterol also participates in the regulation of cell permeability and protects erythrocytes from hemolytic toxins. In insects, the cholesterol present in their food is used to synthesize ecdysones, the molting hormones.

In some animals, the cholesterol level is controlled by a feedback mechanism: when excess dietary cholesterol is ingested, cholesterol biosynthesis is inhibited. Human beings lack such a mechanism, and consequently the blood level of cholesterol, which is normally 150–200 mg percent, may rise considerably, especially in individuals between 30 and 60 years of age whose diet is high in fat. This leads to the blockage of the bile ducts and encourages fatty infiltration of the liver, the formation of gallstones, and the deposition of atherosclerotic plaques on the walls of blood vessels containing cholesterol. Cholesterol is excreted mainly with feces, in the form of coprosterol, or coprostanol.

In the pharmaceutical industry, cholesterol is used as a starting material in the production of many steroid preparations. Its main source is the bone marrow of dead cattle.

REFERENCES

Biosintez lipidov: Simpozium VII. Moscow, 1962. (Tr. V Mezhdunarodnogo biokhimicheskogo kongressa, vol. 7.)
Miasnikov, A. L. Gipertonicheskaia bolezn’ i ateroskleroz. Moscow, 1965.
Heftmann, E. Biokhimiia steroidov. Moscow, 1972. (Translated from English.)
Schwartzman, A. Cholesterol and the Heart. New York, 1965.

E. P. SEREBRIAKOV

cholesterol

[kə′les·tə‚rȯl] (biochemistry) C₂₇H₄₆O A sterol produced by all vertebrate cells, particularly in the liver, skin, and intestine, and found most abundantly in nerve tissue.

cholesterol

a sterol found in all animal tissues, blood, bile, and animal fats: a precursor of other body steroids. A high level of cholesterol in the blood is implicated in some cases of atherosclerosis, leading to heart disease. Formula: C₂₇H₄₅OH

cholesterol

[ko-les´ter-ol] a steroid alcohol found in animal fats and oils, bile, blood, brain tissue, milk, egg yolk, myelin sheaths of nerve fibers, liver, kidneys, and adrenal glands. It is a precursor of bile acids and steroid hormones, and it occurs in the most common type of gallstone, in atheroma of the arteries, in various cysts, and in carcinomatous tissue. Most of the body's cholesterol is synthesized by the liver, but some is obtained in the diet from animal-derived foods. Plant-derived foods are cholesterol-free. Cholesterol is not transported free in the blood but is bound to certain proteins to form lipoproteins. Two important fractions of the serum lipoproteins are high-density lipoproteins (HDL) and low-density lipoproteins (LDL).
High levels of total serum cholesterol have been shown to be associated with a high risk for coronary artery disease and myocardial infarction. Research has drawn a distinction between HDL-C, the cholesterol carried on high-density lipoproteins and LDL-C, the cholesterol carried on low-density lipoproteins. The balance between HDL-C and LDL-C is more significant than the total concentration of cholesterol in the blood. The risk of coronary heart disease increases as LDL-C increases and HDL-C decreases.
Because HDL-C promotes the removal of excess cholesterol from the cells and its excretion from the body, it is thought to be beneficial rather than harmful. In contrast, LDL-C picks up cholesterol from ingested fats and from cells that synthesize it in the body and delivers it to blood vessels and muscles where it is deposited in the cells. The concentration of cholesterol in cells within the linings of the arteries contributes to the build-up of atherosclerotic plaques. (See also atherosclerosis.)
A third type of lipoprotein is known as very-low-density lipoprotein (VLDL). There is a preponderance of triglyceride and very little cholesterol in VLDL. Triglyceride is the basic type of lipid used for the storage of energy. The role of serum triglyceride in the formation of atherosclerotic plaques is not known. Those persons who are at high risk for heart disease, already have a heart condition, or are obese should limit the amount of fats and cholesterol in the foods they eat. LDL-C levels can be reduced by limiting dietary intake of saturated fat and cholesterol. Organ meats and egg yolks are high in cholesterol. HDL-C levels can be raised by exercise, stopping cigarette smoking, and losing excess body fat.

Structure and metabolism of cholesterol. From Dorland's, 2000.Blood Cholesterol. Laboratory testing of cholesterol in the blood is often used as a preliminary test for a disorder of blood lipids. Although the normal values for total blood cholesterol vary according to age, diet, and nationality, levels above 200 mg/dl indicate a need for further testing and efforts to reduce the cholesterol level. In general, as the total cholesterol level rises above 150 mg/dl, the risk for coronary artery disease gradually increases. Persons with cholesterol levels above 260 mg/dl may require medication to lower their LDL-C levels and reduce the risk of heart disease.
Increased levels of cholesterol in the blood are found in cardiovascular disease and atherosclerosis, obstructive jaundice, hypothyroidism, nephrosis, and uncontrolled diabetes mellitus. Cholesterol exists in both a free and esterified form; the ratio of free to esterified cholesterol is significant in the diagnosis of certain diseases. For example, there is a markedly abnormal ratio of these two forms of cholesterol in hepatic biliary disease, infectious diseases, and extreme cholesterolemia.
Decreased levels of cholesterol in the blood are noted when there is malabsorption of cholesterol from the intestinal tract as in pernicious anemia, hemolytic jaundice, hyperthyroidism, and terminal cancer.

cho·les·ter·ol

(kō-les'ter-ol), 5-cholesten-3β-ol (cholestane with a 5,6 double bond and a 3β-hydroxyl group); the most abundant steroid in animal tissues, especially in bile and gallstones, and present in food, especially food rich in animal fats; circulates in the plasma complexed to proteins of various densities and plays an important role in the pathogenesis of atheroma formation in arteries; a precursor of steroid hormones.
See also: lipoprotein.

cholesterol

(kə-lĕs′tə-rôl′, -rōl′)n. A white crystalline substance, C₂₇H₄₅OH, that is found in animal tissues and various foods and is important as a constituent of cell membranes and a precursor to steroid hormones. Cholesterol is normally synthesized by the liver and is transported through the bloodstream by different types of lipoproteins, two of which (HDL and LDL) are routinely measured in blood tests.

cholesterol

A 27-carbon precursor of steroid hormones and bile acids which is an integral component of cell membranes and plasma lipoproteins; it is a precursor of bile acids and important in the synthesis of steroid hormones. It is the main component of the most common type of gallstones and is a major constituent of arterial atheromas; increased cholesterol is associated with ASHD, CAD, increased risk of death due to acute MIs and strokes.

Sources
Animal fat, bile, blood, brain, milk, egg yolk, myelin sheaths, liver, kidneys, adrenal gland.
Metabolism
Cholesterol is absorbed from ingested foods—diets high in saturated (animal) fats increase cholesterol levels—and synthesised in the liver. HDL-C is metabolised efficiently, and thus is “good” cholesterol; “bad cholesterol”, LDL-C, is inefficently metabolised; when the total cholesterol (TC) is increased (usually = 200 mg/dL), it is common practice to measure the levels of HDL-cholesterol and LDL-cholesterol.

Lab
TC is measured in routine chemistry panels; cholesterol is transported in the circulation by carrier proteins, which are classified according to their density (HDL, LDL, VLDL) based on density-gradient ultracentrifugation.

High risk for ASHD
• TC > 6.21 mmol/L—US: > 240 mg/dL;
• LDL-C > 160 mg/dl;
• HDL-C < 35 mg/dl.
Borderline risk
• TC = 5.17–6.18 mmol/L—US: 200–239 mg/dL;
Low risk
• TC < 5.17 mmol/L—US: 200 mg/dL;
• LDL-Cl < 130 mg/dL;
• HDL-C > 55 mg/dL.

Increased in
Hypercholesterolemia, nephrotic syndrome, hypothyroidism, biliary cirrhosis, high saturated fats in diet.

Decreased in
Malnutrition, hyperthyroidism, colorectal CA.

Management, hypercholesterolemia
Diet (decreased saturated fats), weight loss, regular exercise, medications.

cholesterol

Biochemistry A precursor of steroid hormones and bile acids; it is an integral component of cell membranes and plasma lipoproteins, and found in animal fats, bile, blood, brain, milk, egg yolk, myelin sheaths, liver, kidneys, and adrenal glands; it is absorbed from the diet and synthesized in the liver; diets high in saturated–animal fats ↑ cholesterol levels; it is the main component of the most common type of gallstones, and integral to arterial atheromas, in cysts and in malignancy; it is a precursor of bile acids and important in the synthesis of steroid hormones; diets low in saturated fats ↓ cholesterol levels, as does exercise; ↑ cholesterol is associated with ASHD, CAD, ↑ risk of death due to acute MIs and strokes; total cholesterol–TC is measured in routine chemistry panels; cholesterol is transported in the circulation by carrier proteins, which are classified according to their density–high-density lipoprotein—HDL, LDL, VLDL, based on density gradient ultracentrifugation; HDL-C is metabolized efficiently, and thus is 'good' cholesterol; 'bad cholesterol,' LDL-C, is inefficently metabolized High risk for ASHD TC > 6.21 mmol/L–US > 240 mg/dL; LDL-C > 160 mg/dl, HDL-C
< 35 mg/dl Borderline risk 5.17-6.18 mmol/L–US: 200-239 mg/dL Low risk < 5.17 mmol/L–US 200 mg/dL, LDL-Cl < 130 mg/dL, HDL-C > 55 mg/dL ↑ in Hypercholesterolemia, nephrotic syndrome, hypothyroidism, biliary cirrhosis ↓ in Malnutrition, hyperthyroidism, colorectal CA Management, ↑ cholesterol Diet–↓ saturated fats, weight loss, regular exercise, medications. See Bad cholesterol, Fish, Good cholesterol, HDL, Hypercholesterolemia, LDL, RLP, VLDL.

cho·les·ter·ol

(kŏ-les'tĕr-ol) The most abundant steroid in animal tissues; circulates in the plasma complexed to proteins of various densities; plays an important role in the pathogenesis of atheroma formation in arteries.

cholesterol

An essential body ingredient found in all human cells, mainly as part of the structure of the cell membranes. It is needed to form the essential steroid hormones, CORTISOL, corticosterone and ALDOSTERONE, the male and female sex hormones and the bile acids. It is synthesized in the liver and a large quantity of cholesterol passes down the bile duct into the intestine every day. Most of it is reabsorbed. A diet high in saturated fats encourages high blood cholesterol levels. Soluble dietary fibre and various drugs can bind intestinal cholesterol and prevent its reabsorption. Cholesterol is carried to the tissues in tiny cholesterol carriers called low density lipoproteins (LDLs). Oxidation of these allows cholesterol to be deposited in the walls of arteries causing dangerous narrowing (ATHEROSCLEROSIS).

cholesterol

a steroid that occurs in the cell membranes of animal cells, but not in plants. Cholesterol is produced in the liver and when in excess is excreted in the bile but is partly reabsorbed by the ileum. It may precipitate gallstones in the gallbladder or bile duct. Alternatively, if there is excess cholesterol in the blood, it may be deposited on the walls of the blood vessels, obstructing them and often leading to an intravascular clot which if it occurs in the region of the heart gives rise to a ‘heart attack’ or coronary thrombosis. Cholesterol is the precursor of animal steroid hormones and bile acids.

Cholesterol

A fat-like substance that is made by the human body and eaten in animal products. Cholesterol is used to form cell membranes and process hormones and vitamin D. High cholesterol levels contribute to the development of atherosclerosis.Mentioned in: Atherosclerosis, Cholesterol-Reducing Drugs, Hypolipoproteinemia, Lipoproteins Test, Rickets, Vitamin D Deficiency

cho·les·ter·ol

Patient discussion about cholesterol

Q. How to lower high cholesterol? The Doctor told my husband that his cholesterol levels are very high and that he has to lower them immediately. What foods are low in cholesterol and what foods should I be cooking for him to eat?A. Any treatment of high cholesterol first begins with some lifestyle changes. This involves three simple, yet often difficult to execute, steps: improved diet, increased physical activity, and weight management.
Make sure your Husband is eating unsaturated fats instead of saturated and trans fats, avoiding cholesterol, increasing dietary fiber, and consuming more plant sterols/stanols. Increase his vegetables and whole grains intake, but decrease the fat, salt and sugar intakes.
Also, it will be easier for him to stick to his diet if the whole family changes their eating habits and eats healthier too. Start cooking healthy meals for the whole family and not just for him.

Q. I have high cholesterol. What I need to do in order to reduce him?A. How to Eat to Lower Your Cholesterol
Things You’ll Need:
Flaxseed
Fruits
Garlic
Kidney Beans
Oatmeal
Soy Foods Like Tofu
Vegetables
White Beans
Step1Eat more garlic. Add it to pasta, soups and vegetables.
Step2Increase your intake of soy foods. Enjoy more tofu, green soybeans (edamame), tempeh and TVP (texturized vegetable protein).
3Add beans to your diet three to five times a week. Try lentil soup, black beans and rice, and hummus, and toss kidney beans into green salads.
Step4Include a serving of fiber-rich fruit or vegetables at every meal and snack.
For full article: http://www.ehow.com/how_12776_eat-lower-cholesterol.html?ref=fuel&utm_source=yahoo&utm_medium=ssp&utm_campaign=yssp_art Hope this helps.

Q. Which cholesterol is the bad cholesterol and what level is considered high cholesterol? I keep on hearing about cholesterol and how it is bad for you though I understand that there are two kinds of cholesterol and that only one of them is bad, which is it? Also, what level is considered high cholesterol?A. Cholesterol can’t dissolve in the blood. It has to be transported to and from the cells by carriers called lipoproteins. Low-density lipoprotein, or LDL, is known as “bad” cholesterol. High-density lipoprotein, or HDL, is known as “good” cholesterol. These two types of lipids, along with triglycerides and Lp(a) cholesterol, make up your total cholesterol count, which can be determined through a blood test. If your total cholesterol is 200 mg/dL or greater, or if your HDL is less than 40 mg/dL, then you will probably need treatment.

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Synonyms for cholesterol

noun an animal sterol that is normally synthesized by the liver

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