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DIGESTION & ABSORPTION OF LIPIDS
3/9/2015 7:58 AM
Dr. Vijay Marakala, MBBS, MD.
Senior Lecturer
BIOCHEMISTRY
IMS, MSU.
DIETARY LIPIDS
Dietary lipids derived from plants and animals
Essential for growth and development
They are oxidized for energy or stored as reserve fat in adipose tissue.
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DIETARY LIPIDS
TRIGLCERIDES
PHOSPHOLIPID
FFA
CHOLESTEROL ESTER
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DIGESTION OF LIPIDS
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DIGESTION OF LIPIDSIN MOUTH
Lingual lipase – secreted by dorsal surface of the tongue
But this enzyme is not significant in humans
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LITTLE OR NO DIGESTION OF LIPIDS IN MOUTH
DIGESTION OF LIPIDSIN STOMACH
Lipids delay the rate of emptying the stomach by ENTEROGASTRONE Inhibits gastric motility
Retards discharge of food from stomach
FATS HAVE SATIETY VALUE
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DIGESTION OF LIPIDSIN STOMACH
Heat of the stomach –liquidising dietary lipids
Peristaltic movements of the stomach –emulsification of lipids
Gastric lipase and lingual lipase
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DIGESTION OF LIPIDSIN STOMACH
Both enzymes are relatively acid-stable
Play a particularly important role in lipid digestion in neonates
in individuals with pancreatic
insufficiency - cystic fibrosis
Hydrolyses TAG molecules especially those with short- to medium-chain fatty acids
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GASTRIC LIPASE AND LINGUAL LIPASE - “ACID LIPASES”
DIGESTION OF LIPIDSIN SMALL INTESTINE
ACIDIC CHYME STIMULATES DUDENAL MUCOSA TO RELEASE
• SECTRETIN
• CHOLECYSTOKININ
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DIGESTION OF LIPIDSIN SMALL INTESTINE
SECRETIN
Stimulates pancreas to release
bicarbonate & pancreatic juice
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DIGESTION OF LIPIDSIN SMALL INTESTINE
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GALL BLADDER
BILE
PANCREAS
LIPASE
PANCREAS
PHOSPHOLIPASE A2
PANCREAS
CHOLESTEROL ESTERASE
CCK
DIGESTION OF LIPIDSIN SMALL INTESTINE
The major function of bile
Is to provide emulsifying agents:
Bile salts & Phosphtidylcholine
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DIGESTION OF LIPIDSIN SMALL INTESTINE
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Hydrolysis of dietary TG
Hydrolysis of dietary
PL
Hydrolysis of
Cholesterol Ester
HYDROLYSIS OF DIETARY TG
OH
OH
OH
OH
OH
OH
Triacylglycerol (TAG)
Diacylglycerol (DAG)
Monoacylglycerol(MAG)
Glycerol
HYDROLYSIS OF DIETARY PLby Phospholipase –A2
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HYDROLYSIS OF CHOLESTEROL ESTER
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PRODUCTS OF LIPID DIGESTION
2-MAG
FFA
CHOLESTEROL
LYSO PL
1-MAG
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ABSORPTION OF LIPIDS
The products of digestion are incorporated into molecular aggregates to form mixed micelle
Micellar formation is essential for the absorption of fat soluble vitamins A, D, E and K
Site of absorption is jejunal mucosa
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MIXED MICELLES
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2-MAG
FFA
CHOLESTEROL
LYSO PL
1-MAG
Vitamin A,D,E,K
ABSORPTION OF LIPIDS BY INTESTINAL MUCOSAL CELLS
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2-MAG
FA
C
LysoPL
VitaminA,D,E,K
2-MAG
FA
C
LysoPL
VitaminA,D,E,K
CoA-SH
Fatty acyl-CoA
TG
CE
PL
VitaminA,D,E,K
APOLIPOPROTEINB-48
Free CHOLASTEROL
MIXED MICELLES
ABSORPTION OF LIPIDS
CHYLOMICRONS from intestinal mucosal cells are absorbed into lymphatic system then into systemic circulation via thoracic duct
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ABSORPTION OF SHORT & MEDIUM CHAIN FATTY ACIDS
Short and medium chain fatty acids do not need re-estrification
They can directly enter into blood vessels
So they are better absorbed than long chain fatty acids
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ENTEROHEPATIC CIRCULATION OF BILE SALTS
Bile salts are reabsorbed from ileum and returned to the liver to be re-excreted
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LIPID DIGESTION & ABSORPTION
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ABNORMALITIES : LIPID MALABSORPTION
Steatorrhea
Bile salt deficiency
Pancreatic enzyme
deficiency
Congenital abetalipoproteine
mia
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