Fat Digestion and Absorption

8/2/2019 Fat Digestion and Absorption

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VEGETABLE ORIGIN

DIETARY FATS:

ANIMAL ORIGIN Mostly : Neutral fat (TAGs)

Small amounts of phospholipids, cholesterol,

some free F.As, lecithin and cholesterol esters.Daily intake: varies from 25-160 grams.


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Lipolytic enzymes:

Lingual lipase (Mouth), Gastric lipase (Stomach)

Insignificant role. Gastric lipase: acts only on butter.

Gastric PH: 1-2.

While the optimum pH of Gastric lipase 4.5, Exceptional conditions:

Achlorhydria production of gastric HCl is low orabsent.

Regurgitation of bile.

newborns


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Mechanism of Digestion

Emulsification of fat by bile salts.

Hydrolysis of fat by pancreatic and intestinal

lipolytic enzymes. Acceleration of fat digestion by micelle

formation.


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EMULSIFICATION


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Large fat drops is broken down into smaller

droplets. Prerequisite for the action of

pancreatic lipase.

Surface area for action of lipase is increased

several folds by emulsification.

Pancreatic lipase water soluble. It acts only

on oil water interface.


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Micelle formation of enhanced by:

Bile salts: Lowers the surface tension

(detergent action)

Peristaltic movements of intestine. Lecithin (component of bile)


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Bile salts surrounds the fine droplets in such a

way that their lipophilic non-polar ends are

towards the fat and their hydrophilic polar

ends separate the fat droplets from aqueous

phase.


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2. Hydrolysis of fat by pancreatic and

intestinal lipolytic enzymes.

1. Pancreatic lipase:

Very powerful.

Digests fat rapidly after emulsification

COLIPASE: A protein present in pancreatic

juice. Displaces bile salts from fat droplet andallows the action of lipase.

Colipase is activated by Trypsin.


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Pancreatic lipase hydrolyses almost all TGs to

produce mainly 2 MAG and to some extent 1

MAG, glycerol & Fatty acids.

2.CHOLESTEROL ESTER HYDROLASE:

Most of the dietary cholesterol is in the form

of cholesterol esters.

Cholesterol esters Cholesterol + Fatty

acid


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3. Phospholipase A2:

Phospholipid + H2O Lysophospholipid +

Fatty acid.


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Intestinal lipolytic enzymes

Brush border of epithelial cells covering

intestinal villi contains small amount of lipase

& cholesterol esterase.

Mode of action is Similar to pancreatic

enzymes.

Buttheir action is minimal.


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Acceleration of fat digestion by micelle

formation

Accumulation of Monoglycerides and Free fatty

acids blocks further digestion.

This is solved by Micelle formation.

Micelles are small water soluble cylindrical disc

shaped particles.

Each Micelle is composed of a central fat globule

and surrounded by about 30 molecules of bile

salts in such a way that their hydrophilic end face

outside and hydrophobic end face inside.


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Micellar formation is essential for the

absorption of Fat soluble vitamins such as A,

D, E & K.

As Insolubility of fat globules prevents their

diffusion.


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ABSORPTION : Duodenum

Micelle diffuse through aqueous medium of

intestinal lumen to reach the brush border

membrane (Transport vehicle).

Once the Micelle comes in contact with the

cell membrane the Monoglycerides, free fatty

acids, cholesterol and fat soluble vitamins

diffuse passively at rapid speed.

The bile salts are left b

Fat Digestion and Absorption

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