Plasma Lipoprotein Metabolism

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Plasma Lipoproteins Metabolism Lipoproteins are complexes of lipids and specialized proteins known as apolipoproteins. Lipoprotein metabolism is divided into two ways, exogenous and endogenous, depending on whether the lipoproteins are made up, mainly of dietary (exogenous) lipids or if they originate from the liver(endogenous). Abnormalities in the metabolism or synthesis of lipoproteins can lead to accelerated atherosclerosis and hyperglycemia. (David A. Chappell et al 21). In the exogenous path the Epithelial, cell lining also known as the small intestines, readily takes in lipids from the food. These lipids including phospholipids, cholesterol and triglycerides, merge with apolipoprotein B-48. In their circulation via the lymphatic vessels, the nascent chylomicrons pass the liver circulation and draining through the thoracic duct and into the bloodstream follows. In the bloodstream, High Density Lipid particles donate apolipoprotein E and apolipoprotein C-II to the nascent chylomicron that is now mature. Through apolipoprotein C-II, the mature chylomicrons activate lipoprotein lipase (LPL). Lipoprotein lipase is an enzyme found on the endothelial cells that line the blood vessels, which catalyzes the hydrolysis of triacyglycerol (glycerol covalently bonded to three fatty acids). Triacyglycerol releases glycerol along with fatty acids found in the chylomicrons. Fatty acids and glycerol can be absorbed in muscle, peripheral tissues, and adipose, for energy as well as storage. The hydrolyzed chylomicrons become chylomicron remnants. These remnants continue to circulate until they interact through apolipoprotein E together with the chylomicron remnants receptors, originated mainly in the liver. This contact normally causes the endocytosis of these chylomicron remnants, which hydrolyze within the lissome. The lysosomal hydrolysis leads to the release of fatty

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