TOTAL CHOLESTEROL

  Lipids are transported in the plasma a lipoproteins (96%) and free fatty acids 4%(micelle + albumin/free fatty acid). There are four major lipid classes are present in lipoproteins: Triacylglycerols (16%) Phospholipids (30%) Cholesterol (14%) Cholesteryl esters (36%).

Generalized structure of a plasma lipoprotein

Generalized structure of a plasma lipoprotein Lipoproteins consist of a nonpolar core & a single surface layer of amphipathic lipids. The nonpolar lipid core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules.These are oriented so that their polar groups face outward to the aqueous medium, as in the cell membrane. The protein moiety of a lipoprotein is known as an apolipoprotein or apoprotein, constituting nearly 70% of some HDL and as little as 1% of chylomicrons. Some apolipoproteins are integral and cannot be removed, whereas others are free to transfer to other lipoproteins.

There are four major groups of plasma lipoproteins: 1-Chylomicrons, derived from intestinal absorption of triacylglycerol and other lipids. P.219 2-Very low density lipoproteins (VLDL, or pre-β-lipoproteins), derived from the liver for the export of triacylglycerol. P.220 3-Low-density lipoproteins (LDL, or β-lipoproteins), representing a final stage in the catabolism of VLDL. 4-High-density lipoproteins (HDL, or α-lipoproteins), involved in VLDL and chylomicron metabolism and also in cholesterol transport. P.221

Serum total cholesterol is slightly higher in men than in women. P.221 Total cholesterol is a little lower in persons under 20 years but rises with age. In pregnancy there is an increase which may reach 20% above normal at the 30th week.

The lipid profile is used as an index of its possible effect in precipitating atherosclerosis. P. 61 LDL= Total cholesterol-HDL- VLDL VLDL= TG/5 Atherogenic index= Total cholesterol/HDL

Hypercholesterolaemia Raised serum cholesterol signifies hypercholesterolaemia which is considered to be a cardiovascular risk factor that may predispose to coronary thrombosis appearing as angina pectoris or myocardial infarction. Increases are found in the Nephrotic syndrome, hypothyroidism, obstructive jaundice, primary biliary cirrhosis and diabetes mellitus.

Hypocholesterolaemia Decreases are not so well defined. Conditions that may create hypocholesterolaemia include hyperthyroidism, malabsorption syndrome malnutrition and pernicious anaemia. Very low values occur in a beta lipoproteinaemia. Therapeutic reduction of serum cholesterol is seen during administration of lipid lowering drugs such as clofibrate,cholestyramine and nicotinic acid.

Measurement of Serum Cholesterol P. 63