The digestion of lipids begins in the oral cavity through exposure to lingual lipases, which are secreted by glands in the tongue to begin the process of digesting triglycerides.

1. DIGESTION AND ABSORPTION
OF LIPIDS
By.
Mr. Abhijit Bhoyar

2. Specific Learning Objectives
At the end of the lecture students will be able to
• Identify the dietary fat composition.
• List out the dietary sources of Lipids.
• Explain the digestion of Lipids.
• Describe the absorption of Lipids.
• Explain the abnormalities in lipid digestion & absorption.

3. INTRODUCTION
• Lipids are heterogeneous group of water insoluble organic molecules that can
be extracted from tissues by non polar solvents.
• Major source of energy for the body.
• Fat soluble vitamins have regulatory or coenzyme role in the body.
• Prostaglandins and steroid hormones play major roles in the control of body’s
homeostasis.
• Give shape to the body and protect internal organs by providing a cushioning
effect.

4. DIETARY FAT COMPOSITION
• More than 95% are triglycerides, the other are
• Cholesterol
• Cholesteryl esters
• Phospholipids
• Unesterified fatty acids.

5. DIETARY SOURCES OF LIPIDS
Animal Sources-
• Dairy products-
Meat, butter,
ghee Meat and
Fish, Pork, eggs
Vegetable Sources
• Cooking oils- Sun
flower oil,
Mustard oil,
Ground nut oil
Fats from other
vegetable sources

6. DIGESTION OF LIPIDS
• Lipids are insoluble in aqueous solution.
• The digestive enzymes are present in aq. Medium.
• This leads certain problem in digestion & absorption of lipids.
• This is overcomes by
Increasing the surface area of lipids for digestion.
Emulsification of lipids by bile salts.
Solubilizing the digested product for absorption.

8. Digestion in Mouth
• The body begins breaking down fat in the mouth, using enzymes in
saliva.
• Chewing increases the surface area of foods, allowing the enzymes to
break down food more effectively.
• The most important chemicals that help with fat digestion in the mouth
are lingual lipase and phospholipids, which turn fats into small drops.

9. Digestion in Stomach
• The heat of the stomach liquidizes the lipids.
• Emulsification of lipids starts in the stomach by peristaltic contraction.
• Both lingual lipase and gastric lipase acts on short chain triglycerides
(SCT).
• Short chain triglycerides (SCT) are present in milk, butter, ghee.
• So, the action of these lipase is significant in newborns.

10. Digestion in Intestine
• Emulsification of lipids.
• Enzymatic (pancreatic) action on lipids
• Emulsification is essential for the digestion of lipids
• Emulsification is done by
Bile salts
Peristalsis.
Emulsification- It is the
process of dispersion of
lipids into small droplets
by reducing surface
tension.

11. Cont….
Bile salts
• Bile salts are called biological detergents.
• They helps in emulsification of lipids by forming micelle (Transport Vehicle )
Colloidal solution
• Synthesized from cholesterol in the liver.
• Secreted with bile in the small intestine.
• Chemically these are
 Sodium glycocholate
Sodium taurochlate
• Along with bile salt phospholipids also helps in emulsification.

12. Cont….
Digestion of lipids by pancreatic enzymes
• Three enzymes which digest the lipids are
Pancreatic lipase
(for TGL)
Triglyceride
Cholesteryl
esterase
(Cholesteryl esters)
Phospholipase-A2
(Phospholipids).

13. Cont….
Digestion of dietary triacylglycerols.
• Pancreatic lipase hydrolyse fatty acids in the 1 & 3 positions of TGL, producing 2
monoacylglycerol (2- MAG) & 2 free fatty acids. These are the major end
products of TGL digestion.
• An isomerase shift the ester bond from position 2 to 1
• This is then hydrolysed to glycerol & free fatty acid.
• major end products of TGL digestion are
• 2-MAG (78%) , 1-MAG (6%), Glycerol & fatty acids (14%)

14. Hydrolysis of TGL by lipase

15. Digestion of dietary phospholipids.
• Phospholipase-A2 hydrolyse fatty acids at the 2-
position of glycerophospholipid, producing
lysophospholipids.
• lysophospholipids being detergents, helps in
emulsification and digestion of lipids.

16. Hydrolysis of phospholipid

17. Digestion of dietary Cholesterol ester.
• Cholesteryl esters are hydrolysed by pancreatic
Cholesterol ester hydrolase (C. esterase) to produce
cholesterol and free fatty acids.
Cholesteryl esterase
• Cholesteryl esters Cholesterol
H2O fatty acid.

18. Products of Lipid Digestion
Following are the end products of lipid digestion
Free fatty acids.
2-MAG (Monoacylglycerols), 1-MAG
Glycerol
Free Cholesterol
Lysophospholipids
• These together with bile salt form mixed micelles
• Fat soluble vitamins (A,D,E & K) are also packaged in these
micelles and are absorbed.

19. ABSORPTION OF LIPIDS
Mixed micelles are spherical particles with hydrophilic exterior and
hydrophobic interior core.
Micelles are attached at the microvilous surface of upper part of small
intestine.
All the digested products passively diffuse in to mucosal cell.
Short & medium chain fatty acids do not require bile salt for there
absorption.
They absorbed directly in to intestinal cells and they enter portal blood
rather than lymph & transport to the liver bound to serum albumin.

20. ENTEROHEPATIC CIRCULATION OF BILE
SALT
• Bile salt of the micelles are not absorbed along
with digested product of lipids.
• They reabsorbed in the lower part of the small
intestine and retune to the liver by portal
circulation for resecretion in to the bile.
• This is called as Enterohepatic circulation of bile
salt.

21. Synthesis of Lipids in the intestinal cells
• 1-MAG ( monoacylglycerol ) are further hydrolyzed to
glycerol & FFA (Free Fatty Acids)
• Long chain fatty acids are activated by Thiokinase to
fatty acyl coA.
• This acyl coA combine with 2-MAG to give TAG
(Triacylglycerol).

22. Cont….
• The absorbed cholesterol & lysophospholipids are
recycled to regenerate cholesterylester and
phospholipids.
• Free glycerol released in the lumen of the intestine is
not reutilized but passes directly to portal vein.
• However, the glycerol 3-phosphate, formed within
intestinal cells by glucose, can reutilized for TAG
synthesis.

23. Transport of lipids
• The resynthesized lipids in intestinal mucosal cells
along with fat soluble vitamins are hydrophobic in
nature. So, they all packed in lipoprotein called
chylomicrons.
• Chylomicrons are composed of
Triacylglycerols (85-90%)
Cholesterol & cholesteryl ester (5%)
Phospholipids (7%)
Protein (apolipoprotein) (1-2%)

24. Cont….
• Chylomicrons pass from lymph into the blood through
the thoracic duct.
• After a fatty meal, the plasma appears milky due to
the presence of these particles.

25. Abnormalities in lipid digestion & absorption
Lipid malabsorption
• Loss of lipid in the faeces results Lipid malabsorption.
(loss may be as much as 30 gm/day )
• This includes fat soluble vitamin & essential fatty
acids.

26. Cont….
Steatorrhea-
• It is a condition characterized by the loss of lipids in the
feces.
• It may be due to
 Bile salt deficiency occurs in liver disease or due to
obstruction in the bile duct.
Pancreatic enzyme deficiency occurs in pancreatitis or
cystic fibrosis.
defective chylomicron synthesis occurs in congenital
abetalipoproteinaemia

27. Cholesterol stones
• Cholesterol stone formation in gall-bladder (gall
stones) is a frequent health complication.
• It is found more frequently in females than in males
often in association with obesity.
• Cholesterol gall stones are formed when liver secretes
bile (containing phospholipids, bile acids etc.),
supersaturated with respect to cholesterol.

28. Obesity and Fat Absorption
• Obesity is a major problem in many parts of the world
as the availability of food is generally abundant and
overeating is common.
• Intake of lipids largely contributes to obesity.
• In recent years, pharmacological interventions to
prevent

29. Expected Questions
Essay/ Situational type
Explain the digestion and absorption of Lipids.

30. THANK YOU