Chylomicron

Chylomicrons are one of the major classes of lipoproteins, particles that transport lipids through the circulatory system. They are formed in enterocytes of the small intestine after dietary fat intake and are responsible for conveying dietary triglycerides, cholesterol esters, and fat-soluble vitamins to peripheral tissues and the liver.

Chylomicrons have a large triglyceride-rich core surrounded by a surface monolayer containing phospholipids, cholesterol esters, and apolipoproteins. The defining apolipoprotein is ApoB-48, with additional ApoC-II and ApoE acquired from HDL during circulation.

In enterocytes, fatty acids and monoglycerides are re-esterified to triglycerides and assembled with apolipoproteins in the endoplasmic reticulum and Golgi. Mature chylomicrons are secreted into the lymphatic system via intestinal lacteals and reach the bloodstream through the thoracic duct.

As they circulate, lipoprotein lipase (LPL) hydrolyzes their triglycerides, releasing fatty acids for uptake by muscle and adipose tissue. ApoC-II activates LPL; ApoE on chylomicron remnants mediates uptake by the liver via receptor pathways. After triglyceride removal, remnants are cleared from the circulation.

Elevated chylomicrons in fasting blood is seen in familial chylomicronemia syndrome (type I hyperlipoproteinemia). In typical adults, chylomicrons appear after meals and are not present in a standard fasting lipid panel. Postprandial lipemia can influence triglyceride measurements and cardiovascular risk assessment.