Transpo of lipids from the intestine to other tissues is by -
Ans. is 'a' i.e., ChylomicronsTranspo of lipidso There are two pathways of lipid transpo in the body ?1. Transpo of dietry lipid (Exogenous pathway)o It is the transpo of 1 ipid.from intestine to liver.Chylomicrons transpo the dietry lipid from intestine to liver.o In Diet the major lipids are triglyceride and Aolesterol.o Cholesterol is absorbed as such in proximal small intestine and is esterified to cholesteryl ester (ChE). o Triglycerides are hydrolysed by lipases to glycerol and fatty acids which are absorbed in intestine. o Inside intestinal cells triglyceride is synthesized by fatty acids.Chylomicrons are synthesized in the small intestine that contain triglyceride, cholesteryl ester, cholesterol, phospholipids and apoprotein B-48 (apo B-48).o These chylomicrons are secreted in the intestinal lymph and reach the systemic circulation thoracic duct.In the circulation Apo E and Apo C are transfered to chylomicrones by HDL, so now chylomicrons contain Apo B-48, Apo E, & Apo C.o In the circulation, Triglycerides of chylomicrones are hydrolysed by lipoprotein lipase (LPL) present on endothelial cells of vessels of skeletal muscles, adipose tissue and hea.o The released fatty acids are utilized locally by these tissues.o The chilomicron paicle progressively shrinks in size by action of LPL and, cholesterol, phospholipids and apo C are transferred to HDL, creating chylomicron remnants that contains more cholesterol, less triglycerides, apo E & apo B-48.o Chylomicron remnants are removed by liver by the LDL receptors that require apo E as ligand.Note - Apo C-II, that is transfered from HDL to chylomicrons act as a cofactor for lipoprotein lipase. Apo A-V promotes LPL mediated triglyceride lipolysis in VLDL and chilomicrons.2. Transpo of Hepatic lipids (Endogenous pathway)o VLDL is synthesized in liver that contains high triglyceride, ChE, cholesterol, phospholipid and Apo B-100.(VLDL paicles resembel chylomicrones in composition except that VLDL contains Apo B-100 instead of ApoB-48).o VLDL paicles are secreted in the plasma and as with chylomicron, Apo E and Apo C are transferred from HDLto VLDL. Now VLDL contains Apo B-100, Apo E and Apo C.o In plasma, triglycerides of VLDL are hydrolysed by same lipoprotein lipase (see above) and apo C is transferredto HDL and the remmants are called IDL.o 40-60% of IDL is removed by liver LDL receptor mediated endocytosis, this process require Apo E whichacts as ligand for LDL receptors.o Remaining 1 DL is remodeled by hepatic lipase to form LDL that contains maximum cholesterol.o 70% of LDL is removed by liver LDL receptor and 30% is utilized by peripheral tissues as a source ofcholesterol.
Chylomicrons
LDL
HDL
VI DL