Lipid digestion
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Lipids make up a large portion of diet in carnivores, where as they form only a minor portion of diets in herbivores.
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Primary dietary lipid is triglyceride; other lipids include cholesterol and cholesterol esters from animal sources, waxes from plant sources and phospholipids from both plant and animal sources.
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Lipid digestion occurs in four phases; emulsification, hydrolysis, micelle formation and absorption.
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Emulsification is a process of reducing lipid droplets to a smaller size for their suspension in water.
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In the gut, lipid globules are broken down to droplets by the mixing and agitating actions of distal stomach.
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Emulsification is completed in the small intestine by the detergent action of bile acids and phospholipids.
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Bile salts reduce the surface tension of the lipid droplets and further, reduce in size of the fat droplets.
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The bile coated or emulsified droplets are subjected to hydrolytic enzyme action.
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Triglycerides are the major dietary lipid, undergo hydrolysis by the action of gastric, pancreatic lipase and co-lipase, which are secreted as active form.
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The co-lipase “make a pathway” through the bile product coating the emulsified lipid droplet, giving access to the lipase to reach the underlying triglyceride.
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Lipase cleaves the fatty acids from the end of triglyceride molecule resulting in the formation of two free nonesterified fatty acids and a monoglyceride.
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The products of these enzymes are nonesterified fatty acids, cholesterol and lysophopholipid. The fatty acids, monoglycerides etc., combine with bile acids and phospholipids to form very small lipid droplets, micelles . The micelles are water soluble allow the lipids to diffuse through glycocalyx and into close contact with absorptive surface of the enterocytes.
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Last modified: Thursday, 9 June 2011, 5:16 AM