Chylomicrons:

Chylomicrons:

            Chylomicrons are the largest of the lipoproteins. Their primary function is to transport the dietary or exogenous triglycerides and cholesterol from the intestinal lumen to sites of metabolism or storage. In the lumen of the GI tract, dietary fat is degraded into free fatty acids and monoglycerides. These substances enter the intestinal villi, where they are reconstructed into a triglyceride particle.

            The triglycerides and cholesterol esters are then combined with Apolipoproteins-B-48, A I and A IV within the intestinal wall to form chylomicron particles.

            The nascent chylomicrons enter the systemic circulation by the way of the lymphatics. Apos E and C are then added to the particles. Normally the chylomicrons are cleared rapidly from the blood and are virtually absent in the fasting state. The cleaning of the chylomicrons is modulated by the enzyme lipoprotein lipase (LPL). The chylomicron remnants are cleared rapidly from the circulation by receptors present on the surface of liver cells. These receptors recognize the Apo and components of the remnant particle. Chylomicron remnants are thought to be atherogenic and an abnormal delay in their clearance is therefore undesirable. The delay in clearance may be secondary to a genetically inherited deficiency of LPL as its activator; Apo CII. Clearance of the remnant particles may damage the vascular endothelium and then predispose to atherosclerosis. Hyperchylomicronemia also may be secondary to other acquired hypertryglyceridemic states, such as those seen with exogenous estrogen use, uncontrolled diabetes and excessive alcohol intake. The presence of chylomicrons in the serum is necessary for the diagnosis of type-I or V hyperlipoproteinemia in the Fredrickson and Lee’s classification system.