2. Lipids:
Any of a class of organic compounds that are fatty acids or their
derivatives.
Examples:
Butter, ghee, vegetable oil, cheese, cholesterol and other
steroids, waxes, phospholipids, and fat-soluble vitamins.
Properties:
Lipids are hydrophobic, and thus are
poorly soluble in the aqueous
environment of the digestive tract.
3. Source of Energy:
Lipids are mainly composed of hydrocarbons in their most reduced form, making them an
excellent form of energy storage.
Because one triglyceride molecule yields three fatty acid molecules , fat molecules
yield more energy than carbohydrates and are an important source of energy for the human body.
Fats are incredibly important for energy storage:
1g lipid= 9calories
1g carbo= 4calories
4.
5.
6. Challenges in Lipid Digestion:
Lipid digestion pose some special challenges.
Triglycerides are large molecules.
Not water-soluble.
Because of this, they like to cluster together in large droplets
when they’re in a watery environment like the digestive tract.
Transportation around the body, which again requires some
special handling since lipids are not water-soluble and do not
mix with the watery blood.
7. SPECIAL ADAPTATIONS FOR LIPID DIGESTION IN
INFANTS:
Lipids are an important part of an infant’s diet.
Mother milk=4 %fat
Cow’s milk= 4 %fat
But infants are born with low levels of bile and
pancreatic enzyme secretion?? So, how do babies digest diet?
Adaptation:
Infants have plenty of lingual and gastric lipases right
from birth.
Second, breast milk actually contains lipase enzymes that
are activated in the baby’s small intestine.
In other words, the mother makes lipases and sends
them in breast milk to help her baby digest the milk fats.
8. Digestion of lipids.
Typical diet consist of 25-160 gm of lipids.
Triaceylglycerides(TAG) are major lipid components in diet (90%).
TAGs is composed of three fatty acid esterified to glycerol molecule.
9.
10. Enzyme for lipids digestion
* Lipase is an enzyme the body uses to break down fats in food
so they can be absorbed in the intestines.
11. Steps in Lipid Digestion:
At following parts digestion take place.
Digestion in mouth
Digestion in stomach
Digestion in small intestine
Absorption in small intestine
12. Digestion of lipid in mouth
Food mix sliva and lingual lipase.
Mechanical Digestion of food
This enzyme is secreted by ebner's gland
optimum pH for this enzyme is 4.0 to 4.5
Lingual lipase converts triglycerides into diglycerides and free fatty
acids.
Lingual lipase cannot start digestion of fat in mouth
due to shorter stay of food in mouth and difference
in optimum PH for enzyme action.
13. Digestion in Stomach
The heat of the stomach liquidizes the lipids.
Emulsification of lipids starts in the stomach by peristaltic contraction.
Lingual lipase swallowed with food and enter stomach.
Highly acidic environment of stomach activate the lingual lipase .
Gastric lipase is secreted by chief cells of gastric mucusa.
Both enzymes break down short and medium chain triglycerides.
lingual and gastric lipases hydrolyse 25–30% of ingested triglycerides into diglycerides and free
fatty acid
14. Digestion in stomach
They play important role in lipid digestion in individuals with
pancreatic insufficiency such as those with cystic fibrosis.
Short chain triglycerides (SCT) are present In milk, butter, ghee
ete.
So , the action of these lipase is significant in newborn.
15. 3. LIPID DIGESTION IN THE SMALL INTESTINE:
Emulsification of lipids.
Enzymatic action on lipids.
what is emulsification ?
Is the process of dispersion of lipids into small droplets by reducing surface tension.
Emulsification is essential for the digestion of lipids
Emulsification is done by
Bile salt
Peristalsis
16. Bile salt
Bile salts are called biological detergents.
They helps in emulsification of lipids by forming micelle
synthesized from cholestrol in the liver.
Secreted with bile in the intestine.
Chemically these are …
Sodium glycocholate
Sodium tourochlate
Along with bile salts phospholipids also helps in emulsifiction.
Bile salts have both a hydrophobic and a hydrophilic side, so that they are attracted to both fats and water.
This makes them effective emulsifiers,
Emulsification makes lipids more accessible to digestive enzymes by increasing the surface area for them to
act.
17. Digestion of lipids by Pancreatic
Enzymes
Three enzymes which digest the lipids are..
Pancreatic lipase (for TGL)
Cholesteryl esterase (Cholesteryl esters)
Phospholipase-A2 ( Phospholipids).
18. 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 product of TGL digestion .
major end products of TGL digestion are…
* 2-MAG (78%)
* 1-MAG (6%)
* Glycerol & fatty acids (14%)
19. Digestion of dietary phospholipids
Phospholipase-A2 hydrolyse fatty acids at the 2- position of
glycerophospholipid, producing lysophospholipids.
Lysophospholipids being detergents, helps in emulsification and digestioin of
lipids.
20.
21. Digestion of dietary Cholestrole ester,
Cholesteryl esters are hydrolysed by pancreatic cholesterol hydrolase (C,
esterase ) to produce cholesterol and free faty acids.
Cholestryl esters……cholesteryl esterase ..cholesetrole
H2O fatty acid
22. Products of lipids digestion.
Following are the end product of lipid digestion
Free fatty acids
2-MAG
1-MAG
Glycerole
Free Cholesterol
Lysophospholipids
These toghether with bile salt form mixed micelles.
23.
24. 4.
LIPID ABSORPTION FROM THE SMALL INTESTINE:
Absorption of lipid lipid absorption involved hydrolysis of dietary fats in the lumen of intestine
followed by takeoff hydrolyzed products by by enterocytes. Lipids are resynthesized in the
endoplasmic reticulum and are either secreted with chylo microns and high density
lipoproteins or stored as cytoplasmic lipid droplets about 95% lipids are absorbed in small
intestine.
Micelles
*micelles are spherical particle with hydrophyllic
exterior and hydrophobic anterior core micelles
are attached at the micro villou surface of upper
part of small intestine.
25. All the digestive products passively diffuse into mucosal cell.Micelles are soluble in
the aqueous environment of the intestinal lumen .The micelles approach the brush
border membrane of the enterocytes .Micelles is essential for the absorption of fat
soluble vitamin A D and k. Short and medium chain fatty acidDo not required bile
salts for their absorption.They absorb directly into intestinal cells and they inter
portal blood rather than lymph and transport to the liver bound to serum albumin.
Short and medium chain fatty acid
Do not required bile salts for their absorption.They absorb directly into intestinal
cells and they inter portal blood rather than lymph and transport to the liver
bound to serum albumin.
Enterohepatic circulation
Of bile salts*of micelles are not absorb along with digestive product of lipids.They
reabsorb in the lower part of small intestine and re tune to the liver by portal
circulation for resecretion into the bile.This is called as enterohetic circulation of
26. • Synthesis of lipids in ‘the intestinal cells.’
• One mono acyl glycerides are further hydrolyz to glycerol and FFA. .
• Long chain fatty are activated by *thiokinase to
fatty acyl COA.This acyleCOA combine with
2 MAG to give TAG.The absorb cholesterol and
lysos phospholipids are reacyled to regenerate
cholesterylester and phospholipids.
Free glycerol release in the lumen of the
intestine is not reutilize but passes directly
to portal vein.However that glycerol three
phosphate form within intestinal cells
by glucose can reutilize for TAG synthesis.
27. Transport of lipids
The resynthesize lipids in intestinal mucosal cells along with fat soluble vitamins
are hydrophobic in nature.So they all packed in lipoprotein called chylomicrons
CHYLIOMICRONS :
A small fat soluble composed of protein and lipids.Chylomicrons are found in the
blood and lymphatic fluidwhere they serve to transport fat from its port of entry in
the intestine to the liver and to adipose tissue.
The world chylo micron is made up of chylo
means milky micron means small means small
milky means small milky. of intestine.
Chylomicrons are synthesize in the mucose
of the intestine.
