Digestion and absorption of lipids

Lipids are mostly consumed in the form of natural fats, which are also known as triglycerides

The triglycerides are made up of a glycerol molecules and free fatty acids

Triglycerides are more in animal food and less in food of plant origin

Diet also contains small amount of cholesterol and cholesterol esters

Dietary fats are classified into two types

Saturated  fatty acids

Contains triglycerides

Maximum amount of hydrogen ions

Without any double bonds between carbon atoms

Unsaturated fatty acids

Dehydrogenation of saturated fatty acids

Digestion of lipids

Stomach

In the stomach, mixing breaks lipids into droplets to droplets to increase the surface area for digestion by pancreatic enzymes

Lingual lipases digest some of the ingested triglycerides to monoglycerides and fatty acids

The most of the ingested lipids are digested in the intestine by pancreatic lipases

Small intestine

Bile acids emulsify  lipids in the small intestine, increasing the surface area for digestion

Pancreatic lipases hydrolyze lipids to fatty acids, monoglycerides, cholesterols and lysolecithin

The enzymes are pancreatic lipase, cholesterol ester hydrolase’s and phospholipase A

The hydrophobic produces of lipid digestion are solubilized in micelles by bile acids

 

Absorption of lipids

Monoglycerides, cholesterol and fatty acids from the micelles enter the cells of intestinal mucosa by simple diffusion

In the mucosal cells,  most of the monoglycerides are converted into triglycerides.

The triglycerides and some of the cholesterol is esterified

The triglycerides and cholesterol esters are coated with a layer of protein, cholesterol and phospholipids to form the particles called chylomicrons

Chylomicrons cannot pass through the membrane of the blood  capillaries because of the larger size

So these lipid particles enter the lymph vessels and then are transferred into blood from lymph

Fatty acids containing less than 10-12 carbon atoms enter the portal blood from mucosal cells and are transported as free fatty acids or unesterified fatty acids

Most of the fats are absorbed in upper part of small intestine

The presence of bile is essential for fat absorption

 

DIGESTION OF FATS

 

AREA	JUICE	ENZYME	SUBSTRATE	END POINT
MOUTH	SALIVA	LINGUAL LIPASE	TRIGLYCERIDES	FATTY ACIDS  & GLYCEROL
STOMACH	GASTRIC JUICE	GASRIC LIPASE (WEAK LIPASE)	TRYGLICERIDES	FATTY ACIDS  & GLYCEROL
SMALL INTESTINE	PANCREATIC JUICE SUCCUS ENTERICUS	PANCREATIC LYPASE CHOLESTEROL ESTER HYDROLASE PHOSPHOLIPASE A & PHOSPHOLIPASE B INTESTINAL LIPASE	TRIGLYCERIDES CHOLESTEROL ESTER PHOSPHOLIPIDES LYSO PHOSPHOLIPIDES TRIGLYCERIDES	MONOGLYCERIDES FATTY ACIDS FREE CHLOESTEROL  &   FATTY ACIDS LYSO PHOSPHOLIPIDES PHOSPHORYL CHOLINE FREE FATTY ACIDS FATTY ACIDS  & GLYCEROL

 

FATS METABOLISM