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