Chylomicron

Chylomicrons are large lipoprotein particles (having a diameter of 75 to 1,200nm) that are created by the absorptive cells of the small intestine. Chylomicrons transport exogenous lipids to adipose, cardiac and skeletal tissue where they are broken down by lipoprotein lipase. The way from the intestines to the adipose tissue is this: 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 place where the lymphatic system falls into the blood stream, at the thoracic duct's connection with the left subclavian vein.

Contents when Released

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

Changes during Circulation

While circulating in lymph and blood, chylomicron exchanges components with High Densisity Lipoprotein (HDL). The HDL donates Apolipoprotein C II (ApoC-II) and Apolipoprotein E (ApoE) to the nascent chylomicron and thus matures it into a "chylomicron." The ApoC-II protein is the cofactor for lipoprotein lipase (LPL) activity. Once triglyceride stores are distributed, the chylomicron returns the ApoC-II (but keeps ApoE) protein back to the HDL and thus becomes a chylomicron remnant. The ApoB-48 and ApoE proteins are important to identify the chylomicron remnant in the liver for endocytosis and breakdown.