Este artículo necesita ser reescrito para mejorar su relevancia para los psicólogos.. Please help to improve this page yourself if you can.. Cholesterol Chemical name 10,13-dimethyl-17- (6-methylheptan-2-yl)- 2,3,4,7,8,9,11,12,14,15,16,17- dodecahydro-1H- cyclopenta[un]phenanthren-3-ol Chemical formula C27H46O Molecular mass 386.65 g/mol CAS number [57-88-5] Melting point 146-147 °C SMILES C[[email protected]]3C4[C@](CC[C@@H]4 [[email protected]](C)CCCC(C)C)([H])[C@]2 ([H])CC=C1C[C@@H](O)CC[C@]1 (C)[C@@]2([H])C3 Disclaimer and references Cholesterol is a lipid found in the cell membranes of all tissues, and it is transported in the blood plasma of all animals. Cholesterol is also considered a sterol (a combination steroid and alcohol). Because cholesterol is synthesized by all eukaryotes, trace amounts of cholesterol are also found in membranes of plants and fungi. 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 by François Poulletier de la Salle in 1769. Sin embargo, it is only in 1815 that chemist Michel Eugène Chevreul named the compound "cholesterine".[1] Most of the cholesterol in the body is synthesized by the body and some has dietary origin. Cholesterol is more abundant in tissues which either synthesize more or have more abundant densely-packed membranes, por ejemplo, the liver, spinal cord and brain. It plays a central role in many biochemical processes, such as the composition of cell membranes and the synthesis of steroid hormones. 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. The main types, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) carry cholesterol from and to the liver, respectively. According to the lipid hypothesis, abnormally high cholesterol levels (hypercholesterolemia) and abnormal proportions of LDL and HDL are associated with cardiovascular disease by promoting atheroma development in arteries (atherosclerosis). This disease process leads to myocardial infarction (heart attack), stroke and peripheral vascular disease. As high LDL contributes to this process, it is termed "bad cholesterol", while high levels of HDL ("good cholesterol") offer a degree of protection. The balance can be redressed with exercise, a healthy diet, and sometimes medication. Contents 1 Fisiología 1.1 Función 1.2 Synthesis and intake 1.2.1 Regulation 1.3 Excretion 1.4 In blood 2 Clinical significance 2.1 Hypercholesterolemia 2.2 Hypocholesterolemia 3 Behavioral medicine and cholesterol 4 Cholesterol and violent death 5 Food sources 6 Ver también 7 Imágenes adicionales 8 Referencias 9 External links Physiology Function Cholesterol is required to build and maintain cell membranes; it regulates membrane fluidity over a wide range of temperatures. The hydroxyl group on cholesterol interacts with the phosphate head of the membrane, while the bulky steroid and the hydrocarbon chain is embedded in the membrane. Some research indicates that cholesterol may act as an antioxidant.[2] Cholesterol also aids in the manufacture of bile (which is stored in the gallbladder and helps digest fats), and is also important for the metabolism of fat soluble vitamins, including vitamins A, D, E and K. It is the major precursor for the synthesis of vitamin D and of the various steroid hormones (which include cortisol and aldosterone in the adrenal glands, and the sex hormones progesterone, the various estrogens, testosterone, and derivatives).  Recientemente, cholesterol has also been implicated in cell signaling processes, where it has been suggested that it forms lipid rafts in the plasma membrane. It also reduces the permeability of the plasma membrane to hydrogen ions (protons) and sodium ions.[3] Cholesterol is essential for the structure and function of invaginated caveolae and clathrin-coated pits, including the caveolae-dependent endocytosis and clathrin-dependent endocytosis. The role of cholesterol in caveolae-dependent and clathrin-dependent endocytosis can be investigated by using methyl beta cyclodextrin (MβCD) to remove cholesterol from the plasma membrane. Synthesis and intake The HMG-CoA reductase pathway Cholesterol is required in the membrane of mammalian cells for normal cellular function, and is either synthesized in the endoplasmic reticulum, or derived from the diet, in which case it is delivered by the bloodstream in low-density lipoproteins. These are taken into the cell by LDL receptor-mediated endocytosis in clathrin-coated pits, and then hydrolysed in lysosomes. Cholesterol is primarily synthesized from acetyl CoA through the HMG-CoA reductase pathway in many cells and tissues. Sobre 20 – 25% of total daily production (~1 g/day) occurs in the liver; other sites of higher synthesis rates include the intestines, adrenal glands and reproductive organs. For a person of about 150 Libras (68 kg), typical total body content is about 35 gramo, typical daily internal production is about 1 g and typical daily dietary intake is 200 Para 300 mg in the United States and societies adopting its dietary patterns. Of the cholesterol input to the intestines via bile production, 92-97% is reabsorbed in the intestines and recycled via enterohepatic circulation. Konrad Bloch and Feodor Lynen shared the Nobel Prize in Physiology or Medicine in 1964 for their discoveries concerning the mechanism and regulation of the cholesterol and fatty acid metabolism. Regulation Biosynthesis of cholesterol is directly regulated by the cholesterol levels present, though the homeostatic mechanisms involved are only partly understood. A higher intake from food leads to a net decrease in endogenous production, while lower intake from food has the opposite effect. The main regulatory mechanism is the sensing of intracellular cholesterol in the endoplasmic reticulum by the protein SREBP (Sterol Regulatory Element Binding Protein 1 y 2). In the presence of cholesterol, SREBP is bound to two other proteins: SCAP (SREBP-cleavage activating protein) and Insig1. When cholesterol levels fall, Insig-1 dissociates from the SREBP-SCAP complex, allowing the complex to migrate to the Golgi apparatus, where SREBP is cleaved by S1P and S2P (site 1/2 protease), two enzymes that are activated by SCAP when cholesterol levels are low. The cleaved SREBP then migrates to the nucleus and acts as a transcription factor to bind to the SRE (sterol regulatory element) of a number of genes to stimulate their transcription. Among the genes transcribed are the LDL receptor and HMG-CoA reductase. The former scavenges circulating LDL from the bloodstream, whereas HMG-CoA reductase leads to an increase of endogenous production of cholesterol.[4] A large part of this mechanism was clarified by Dr Michael S. Brown and Dr Joseph L. Goldstein in the 1970s. They received the Nobel Prize in Physiology or Medicine for their work in 1985.[4] Excretion Cholesterol is excreted from the liver in bile and reabsorbed from the intestines. Under certain circumstances, when more concentrated, as in the gallbladder, it crystallises and is the major constituent of most gallstones, although lecithin and bilirubin gallstones also occur less frequently. In blood See also: Blood cholesterol Cholesterol is minimally soluble in water; it cannot dissolve and travel in the water-based bloodstream. En lugar de, it is transported in the bloodstream by lipoproteins - protein "molecular-suitcases" that are water-soluble and carry cholesterol and triglycerides internally. The apolipoproteins forming the surface of the given lipoprotein particle determine from what cells cholesterol will be removed and to where it will be supplied. Cholesterol is transported towards peripheral tissues by the lipoproteins chylomicrons, very low density lipoproteins (VLDL) and low-density lipoproteins (LDL). Large numbers of small dense LDL (sdLDL) particles are strongly associated with the presence of atheromatous disease within the arteries. Por esta razón, LDL is referred to as "bad cholesterol".  Por otro lado, high-density lipoprotein (HDL) particles transport cholesterol back to the liver for excretion. Having large numbers of large HDL particles correlates with better health outcomes, and hence it is commonly called "good cholesterol". En contraste, having small amounts of large HDL particles is independently associated with atheromatous disease progression within the arteries. Clinical significance Hypercholesterolemia Main article: hypercholesterolemia Conditions with elevated concentrations of oxidized LDL particles, especialmente "small dense LDL" (sdLDL) particles, are associated with atheroma formation in the walls of arteries, a condition known as atherosclerosis, which is the principal cause of coronary heart disease and other forms of cardiovascular disease. En contraste, HDL particles (especially large HDL) have been identified as a mechanism by which cholesterol and inflammatory mediators can be removed from atheroma. Increased concentrations of HDL correlate with lower rates of atheroma progressions and even regression. The relation of cholesterol to CHD, termed the "lipid hypothesis," is still hotly debated. Elevated levels of the lipoprotein fractions, LDL, IDL and VLDL are regarded as atherogenic (prone to cause atherosclerosis).[Cómo hacer referencia y vincular a un resumen o texto] Levels of these fractions, rather than the total cholesterol level, correlate with the extent and progress of atherosclerosis. En cambio, the total cholesterol can be within normal limits, yet be made up primarily of small LDL and small HDL particles, under which conditions atheroma growth rates would still be high. En contraste, sin embargo, if LDL particle number is low (mostly large particles) and a large percentage of the HDL particles are large, then atheroma growth rates are usually low, even negative, for any given total cholesterol concentration.[Cómo hacer referencia y vincular a un resumen o texto] Multiple human trials utilizing HMG-CoA reductase inhibitors, known as statins, have repeatedly confirmed that changing lipoprotein transport patterns from unhealthy to healthier patterns significantly lowers cardiovascular disease event rates, even for people with cholesterol values currently considered low for adults. Como resultado, people with a history of cardiovascular disease may derive benefit from statins irrespective of their cholesterol levels,[5] and in men without cardiovascular disease there is benefit from lowering abnormally high cholesterol levels ("primary prevention").[6] Primary prevention in women is practiced only by extension of the findings in studies on men,[7] since in women, none of the large statin trials has shown a reduction in overall mortality or in cardiovascular end points.[8] los 1987 report of National Cholesterol Education Program, Adult Treatment Panels suggest the total blood cholesterol level should be: 240 mg/dl high cholesterol.[9]. The American Heart Association provides a similar set of guidelines for total (fasting) blood cholesterol levels and risk for heart disease:[10] Level mg/dL Level mmol/L Interpretation 240 >6.2 High risk However, as today's testing methods determine LDL ("bad") and HDL ("bueno") cholesterol separately, this simplistic view has become somewhat outdated. The desirable LDL level is considered to be less than 100 mg/dL (2.6 mmol/L)[10], although a newer target of

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