Digestion and

Absorption

Of

Lipids

Heterogenous group of Organic compounds,

Contains C, H, O and some times P and S

Esters of Fatty acids with alcohol

Insoluble in water

Soluble in organic solvents

SOURCES OF LIPIDS

Endogenous source: Lipids which are synthesized in body, Fatty acids, TAG, Cholesterol, Cholesterol esters, Phospho lipids

Exogenous Sources:Lipids obtained through diet,TAG – 90%, Phospholipids, CholesterolCholesterol esters, Free fatty acids,And Fat soluble vitamins – 10%

Exogenous sourcesof lipids

Animal source: Milk, Butter, Ghee, Meat, Egg yolk, Pork

Vegetable Sources:Oils from various oil seeds likeGround nut, Sunflower, Coconut, Mustered seed, Cotton seed

How much is required ?

TAG, 90

FFA, 4 PL - 5

cholesterol,

2

TAG Cholesterol Phospholipid FFA

Dietary Lipid contents

What is digestion?Complex lipid food molecules are

converted to simple and absorbable forms

• Requirements

• Place • Emulsifiers… Bile,

PL• Enzymes…….Lipases

• Difficulty• Hydrophobic

molecules in hydrophilic environment

• Solution• Emulsified,• increased surface

area, • made accessible for

STRUCTURE OF A LIPID

Digestion in Mouth

Lingual Lipase

Ebner’s glandShort chain fatty acids

From TAG of milk

Short chain fatty acids+ Glycerol

Pediatric group important

Absorbed directlyinto blood stream

Digestion in the stomach

Churning of the food Brings emulsification Tri acyl glyceride having

medium chain FA hydrolysed

Action of lingual lipase continued

TAG → MAG + FA

DAGImportant in infantsdigestion of milk fat

Less important or not at all in adult

30% digestionTAG

Digestion in small intestine

Helped by 1. Emulsification

2. Action of lipase

LIPID DIGESTION AND ABSORPTION.

ACTION OF ESTERASES

PANCREATIC ESTERASEFFA

CHOLESTEROL ESTERASES

TAG 2,3-DAG 2-MAG

1-MAG GLYCEROL FFA2-MAG

LIPASE LIPASE

ISOMERASE LIPASE

Action of pancreatic lipase on Tri acyl glycerolPlay major role

ColipaseBile acids

Olestra and orlistat powrful inhibitor of pancreatic lipase

ACTION OF PACREATIC LIPASES

End product of Triacyl glyceride digestion

Glycerol, Mono acyl glycerol,

Di acyl glycerol and

free fatty acids

Digestion of phospholipids

Enzymes --- Phospholipases

Four different types

Pancreatic ---Phopholipase A2

Product lysophospholipid

Phospholipase A1Phospholipase A2

Phospholipase C Phospholipase D

Action of Phospholipases

Action of EsterasesPancreatic origin

Cholesterol Ester

Cholesterol

Free fatty acid

Cholesterol esterase

Bile acids+

1. EMULSIFICATION

2. STABLISE THE EMULSION

3. PROVIDES ALKALINE MEDIUM

4. HELPS IN ABSORPTION

5. PRODUCE SURFACTANTS

6. POTENT CHOLERETICS

7. EXCRETES THE WASTE

8. SOLUBLISES THE CHOLESTEROL

ABSORPTION THEORIES

LIPOLYTIC THEORY BY VERZAR

PARTITION THEORY BY FRAZER

BERGSTROM THEORY

Bergstrom

ABSORPTION

MICELLE

CLINICAL ASPECTSDigestion and absorption of lipids

Steatorrhea

Cystic fibrosis

Chyluria

Chylothorax

STEATORRHEA

A clinical condition

Daily excretion of fat in feces is more than 6 gm per day.

CAUSES:

– Defective digestion of fat

– Defective absorption of fat

Defective Digestion - 1

• Bile duct obstruction

• Gall stone

• Emulsification defective

• Improper digestion

• Split fat in stool

Defective Digestion -2

• Disease of pancreas

• Pancreatitis

• Tumor- head of pancreas

• Partial or complete Pancreactomy

• Pancreatic juice block

• No lipase

• Unsplit fat in stool

• Normal

• Pancreatic lipase is found in high concentration in pancreatic secretions.

• It has high catalytic activity.

• BUT

• Cystic Fibrosis:

• Severe pancreatic lipase deficiency seen in cystic fibrosis results in malabsorption of lipids.

Bacterial infection

Causes of steatorrhea

Gastractomy

Pancreactomy

Surgical removal of Small intestine

Cholecystectomy

Normal Absorption in small intestine

Coeliac sprue Change in the intestinal mucosal cell membraneleads to improper

absorption

Prevent Fat Absorption and Obesity• Olestra:• Commercial lipid produced by esterification of

natural fatty acids with sucrose instead glycerol.

• 6 to 8 fatty acids are covalently coupled with sucrose

• They taste like lipid but not hydrolyzed to absorbable constituents and hence excreted.

• Orlistat:• Non hydrolysable analog of triacylglycerol.

• Powerful inhibitor of pancreatic lipase.

• Blocks lipid absorption and hence results in lipid excretion

• Chyluria

• Abnormal connection between lymphatics and urinary tract.

• Milky urine

• Chylothrorax

• Abnormal connection between pleural cavity and thoracic duct

• Leakage of lipid in pleural fluid

Oral fat tolerance test

Deficiency of lipoprotein lipase in the peripheral tissues