Dietary cholesterol and triglycerides are hydrolysed by lipases into cholesterol and free fatty acids. Bile salts (derivatives of cholesterol) facilitate absorption of fats into enterocytes by emulsification. Cholesterol has been shown to be absorbed by a specific transport protein (NPC1L1).
Small fatty acids are directly released into the circulation. More complex fats are packaged as triglycerides and cholesterol esters and combined with apoproteins and phospholipids to form chylomicrons. These are released in the lymphatic vessels and join the venous circulation via the thoracic duct.
During transport, chylomicrons are depleted from triglycerides through LPL (lipoprotein lipase) and progressively off-loaded in the periphery. The free fatty acids are used as energy fuel in adipose and muscle tissue. The remnant chylomicron particles (low on triglycerides), are cleared by the liver via an apoE-mediated process.
The liver uses some of the cholesterol for bile acid synthesis, to be excreted into bile and made available for the next round of dietary sterol absorption. The rest of the cholesterol is used to form VLDL particles, which transport cholesterol to peripheral cells.
The intestine plays a key role in regulating serum cholesterol levels by
All of the following are true of mixed micelles formed in the intestine EXCEPT
The major function of chylomicrons is transport of