What is Lipoprotein associated with carrying cholesterol from peripheral tissues to liver is - and explain in detail?
Ans. is 'a' i.e., HDL o HDL particles transport cholesterol from extrahepatic tissues to liver (i.e. reverse cholesterol transport) which is then excreted through bile.o The HDL particles are referred to as scavengers because their primary role is to remove free (unesterified) cholesterol from the extrahepatic tissues.o HDL particles transport cholesterol from extrahepatic tissues to liver (i.e. reverse cholesterol transport) which is then excreted through bile.Reverse cholesterol transporto 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 excretion. This is facilitated by HDL 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 small intestine. Nascent HDL contain phospholipids and unesterified cholesterol and Apo-A, 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 LCAT.o There are two pathway by which this cholesterol is transported to liver1. Indirect pathwayCholesteryl ester is tranfered from HDL to VLDL and chylomicrons in exchange with triglyceride by the cholesteryl ester transfer protein (CETP).This cholesteryl ester is then transported to liver (see previous explanation).2. Direct pathwayHDL cholesterol can also be taken up directly by hepatocytes via the scavenger receptors class BI (SR-BI).o This question is a direct repeat from NiBE based AJ 2013-14.