The chylomicrons are secreted into the lymph and eventually end up in the circulation, where they can distribute dietary lipids to all tissues of the body.
#Where are lipids digested free
The intestinal epithelial cells resynthesize triacylglycerol from free fatty acids and 2-monoacylglycerol and package them with a protein, apolipoprotein B-48, phospholipids, and cholesterol esters into a soluble lipoprotein particle known as a chylomicron. The lymph fluid is similar in composition to that of the blood but lacks the cells found in blood. These vessels are designed so that under normal conditions the contents of the blood cannot enter the lymphatic system. In the case of the intestinal lymph system, the lymph enters the bloodstream through the thoracic duct. Cells secrete various compounds into the lymph, and the lymph vessels transport these fluids away from the interstitial spaces in the body tissues and into the bloodstream. The lymph system is a network of vessels that surround interstitial cavities in the body. This allows the bile salts to be used multiple times in fat digestion. They remain in the intestinal lumen, travel farther down, and are then reabsorbed and sent back to the liver by the enterohepatic circulation.
The bile acids, however, do not enter the enterocyte at this time. The micelles interact with the enterocyte membrane and allow diffusion of the lipid-soluble components across the enterocyte membrane into the cell. The products of enzymatic digestion (free fatty acids, glycerol, lysophospholipids, and cholesterol) form micelles with bile acids in the intestinal lumen. Both of these enzymes are secreted from the pancreas. Phospholipids are hydrolyzed in the intestinal lumen by phospholipase A 2, and cholesterol esters are hydrolyzed by cholesterol esterase. In addition to triacylglycerols, phospholipids, cholesterol, and cholesterol esters (cholesterol esterified to fatty acids) are present in the foods we eat. When partially digested food enters the intestine, the hormone cholecystokinin is secreted by the intestine, which signals the gallbladder to contract and release bile acids, and the pancreas to release digestive enzymes. Degradation products are free fatty acids and 2-monoacylglycerol. This increases the available surface area of the lipids for pancreatic lipase and colipase to bind and to digest the triglycerides. In the intestine, however, the fats are emulsified by bile salts that are released from the gallbladder.
Limited digestion of these lipids occurs in the mouth ( lingual lipase ) and stomach ( gastric lipase ) because of the low solubility of the substrate. Triacylglycerols are the major fat in the human diet, consisting of three fatty acids esterified to a glycerol backbone. Digestion and Transport of Dietary Lipids
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