Chylomicron physiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Chylomicrons are large lipoprotein particles (having a diameter of 75 to 1,200nm) that are created by the absorptive cells of the small intestine.The chylomicrons are released by exocytosis from enterocytes into lacteals, lymphatic vessels originating in the villi of the small intestine, and are then secreted into the bloodstream at the thoracic duct's connection with the left subclavian vein. Chylomicrons transport exogenous lipids to liver, adipose, cardiac and skeletal muscle tissue where they are broken down by lipoprotein lipase into very low density lipoproteins (VLDLs).

Contents when released

Nascent chylomicrons are primarily composed of triglycerides (85%) and contain some cholesterol and cholesteryl esters. The main apolipoprotein component is apolipoprotein B-48 (APOB48).

Changes during circulation

While circulating in lymph and blood, chylomicron exchanges components with High Density Lipoproteins (HDL). The HDL donates apolipoprotein C-II (APOC2) and apolipoprotein E (APOE) to the nascent chylomicron and thus matures it into a "chylomicron." APOC2 is the cofactor for lipoprotein lipase (LPL) activity. Once triglyceride stores are distributed, the chylomicron returns APOC2 (but keeps APOE) back to the HDL and thus becomes a chylomicron remnant. APOB48 and APOE are important to identify the chylomicron remnant in the liver for endocytosis and breakdown.