DIGESTION ABSORPTION OF LIPIDS LIPID METABOLISM Dietary lipids

DIGESTION & ABSORPTION OF LIPIDS

LIPID METABOLISM • Dietary lipids are ingested in form of *triglycerides (90%) *cholesterol, *phospholipids and *free fatty acids. • Solubilization (emulsification) of lipids in the aqueous intestinal environment needs: - bile salts - mechanical agitation in the gut - colipase and - phospholipids.

Emulsification of lipids

DIGESTION OF LIPIDS - The emulsified fats are degraded by pancreatic lipases (lipase and phospholipase A 2). pancreatic lipase - Triacylglycerols mono-acylglycerol - Phospholipids phospholipase A 2 lysophospholipid 2 fatty acids + fatty acid + Cholesterol ester hydrolase (esterase) - Cholesterol ester Cholesterol FA

ABSORPTION OF LIPIDS - 72% of 2 -monoacylglycerol to the intestinal cells. absorbed as such isomerized - The remaining (28%) 1 -monoacylglycerol - 6 % of 1 -monoacylglycerol is absorbed to the intestinal cells as such. - 22% of 1 -monoacylglycerol is hydrolyzed by pancreatic lipase glycerol + free fatty acids.

The absorption of the digestive products of Lipids occurs by forming mixed micelles with bile salts

Inside the intestinal cell • • Following absorption of the products of pancreatic lipases by the intestinal mucosal cells resynthesis of triacylglycerols. The triacylglycerols are then solubilized in lipoprotein complexes (chylomicron). A chylomicron contains lipid droplets surrounded by the more polar lipids and finally a layer of proteins

Chylomicron structure 48 48 48

CHYLOMICRON STRUCTURE

Chylomicrons in the circulation cause turbidity of serum that is cleared by the effect of lipoprotein lipase (LPL) = clearing factor. LPL TG 2 FFA+ MAG Glycerol +FFA

• • glycerol passes mainly to the liver or other tissues having active glycerol kinase enzyme. Free fatty acids *enter the adipose tissue stored *pass to other tissues to be oxidized and give energy