VPB 121: Veterinary Physiology - II (2+1)

LIPID DIGESTION

• Lipids make up a large portion of diet in carnivores, where as they form only a minor portion of diets in herbivores.
• 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.
• Lipid digestion occurs in four phases; emulsification, hydrolysis, micelle formation and absorption.

  
  

• Emulsification is a process of reducing lipid droplets to a smaller size  for their suspension in water.
• In the gut, lipid globules are broken down to droplets by the mixing and agitating actions of distal stomach.
• Emulsification is completed in the small intestine  by the detergent action of bile acids and phospholipids.
• Bile salts reduce the surface tension of the lipid droplets and further, reduce in size of the fat droplets.
• The bile coated or emulsified droplets are subjected to hydrolytic enzyme action.
• Triglycerides are the major dietary lipid, undergo hydrolysis by the action of gastric, pancreatic lipase and co-lipase, which are secreted as active form.
• 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.
• Lipase cleaves the fatty acids from the end of triglyceride molecule  resulting in the formation of two free nonesterified  fatty acids and a monoglyceride.
• Cholesterol esterase and phospholipase are the other lipid digesting enzymes of pancreas.  
• 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.