Fettabsorptions

Fettabsorptions, or fat absorption, is the process by which dietary fats are digested and absorbed in the small intestine. It begins with emulsification by bile acids released from the gallbladder in response to fat intake; this increases surface area for pancreatic enzymes. Pancreatic lipase, aided by colipase, hydrolyzes triglycerides into free fatty acids and monoglycerides. Other enzymes include cholesterol esterase and phospholipase A2.

The products form mixed micelles with bile acids and bile salts, which facilitate transport of lipids to the enterocyte brush border. Free fatty acids, monoglycerides, cholesterol, and fat-soluble vitamins diffuse into enterocytes; short- and medium-chain fatty acids can also be absorbed directly into the portal circulation, whereas long-chain fatty acids and monoglycerides are re-esterified into triglycerides within the enterocyte.

Re-esterified triglycerides, cholesterol esters, and fat-soluble vitamins are packaged with apolipoproteins (notably ApoB-48) into chylomicrons in the endoplasmic reticulum and Golgi apparatus. Chylomicrons are secreted from enterocytes by exocytosis and enter the lymphatic system via lacteals, eventually reaching the systemic circulation. This transport route delays entry into the bloodstream compared with other nutrients.

Most dietary fats are absorbed in the small intestine, with the jejunum playing a major role. Efficient fat absorption depends on adequate bile acids, pancreatic lipase activity, and an intact absorptive surface. Impairment leads to steatorrhea and deficiencies of fat-soluble vitamins A, D, E, and K. Fecal fat measurement can quantify malabsorption.