Cholesterol is the major steroid alcohol in animals. It is needed for essential functions of the body. For example, cholesterol is a content of the cell membrane. It modulates the fluidity of the cell membrane. It is the precursor of bile acids, steroid hormones, and vitamin D. Liver plays a major role in the regulation of body cholesterol levels. Newly synthesized cholesterol in extrahepatic tissues, liver, and dietary cholesterol contribute to the liver cholesterol pool. And by the liver, cholesterol is eliminated as unmodified cholesterol secreted to bile and as well as bile salts.
Cholesterol is a hydrophobic compound. It consists of four fused carbon rings, a hydroxyl group, and a branched hydrocarbon chain. Cholesterol is present in both esterified and free(non-esterified) forms.
Because of their hydrophobic nature, cholesterol and cholesteryl esters must be transported in the blood via lipoproteins. Lipoproteins are spherical complexes of lipids and proteins. Cholesterol is transported mainly via LDL (low-density lipoprotein) and HDL (high-density lipoprotein).
LDL
LDL particles contain high concentrations of cholesterol and cholesteryl esters and less amount of triglyceride. Most of the plasma cholesterol is in LDL. The main function of LDL is to distribute cholesterol to peripheral tissues. It is called bad cholesterol because high levels of LDL cause plaque formation in vessels causing atherosclerosis, eventually leading to heart disease and stroke.
HDL
HDL particles take up cholesterol from non hepatic tissues and return it to the liver as cholesteryl esters. This process is known as reverse cholesterol transport and it is very important in cholesterol homeostasis. HDL particles decrease the risk of atherosclerosis and therefore it is called good cholesterol.
High LDL levels and low HDL levels are both great risks for health. Mainly the diets containing fatty meats and meat products like sausages and fat-rich other products cause an increase in LDL. Genetic factors may also affect this condition. If you have these conditions talk to your doctor. He may recommend your medication and lifestyle changes to improve your health.
Lippincott illustrated reviews Biochemistry 7th edition
Written by: Binuri Lokuhapuarachchi
