Concentration of which is inversely related to the risk of coronary heart disease -

Ans. is 'c' i.e., HDL o The level of HDL in serum is inversely related to the incidence of MI.o As it is "antiatherogenic" or "protective" in nature, HDL is known as "good cholesterol",o HDL has its beneficial effect by reverse cholesterol transporto Lecithine-Cholesterol acetyltransferase (LCAT) esterifes cholesterol in HDL during reverse cholesterol transport,o All nucleated cells in different tissues synthesize cholesterol, but the excretion of cholesterol is mainly by liver in the bile or by enterocytes in gut lumen. So, cholesterol must be transported from peripheral tissue to liver for excretion2. This is facilitated by HDLQ and is called reverse cholesterol transport because it transports the cholesterol in reverse direction to that is transported from liver to peripheral tissues through VLDL --> LDL cycle.Processo HDL is synthesized in liver and smalt intestine. Nascent HDL contain phospholipids and unesterified cholesterol and Apo-Ar, C, E. This nascent HDL is secreted into circulation where it acquires additional unesterified cholesterol from peripheral tissues. Within the HDL particle, the cholesterol is esterified by lecithin - cholesterol acetyltransferase (LCAT) to form cholesteryl ester and additional lipid are transported to HDL from VLDL and chylomicrons. Apo-A, activates LCATr.o There are twro pathway by which this cholesterol is transported to liver.Indirect pathwayo Cholesteryl ester is tranfered from HDL to VLDL and chylomicrons in exchange with triglyceride by the cholesteryl ester transfer protein (CETP).o This cholesteryl ester is then transported to liver (see previous explanation).Direct pathwayo HDL cholesterol can also be taken up directly by hepatocytes via the scavenger receptors class BI (SR - BI).