1) Lipids undergo digestion into monoglycerides, fatty acids, cholesterol, and phospholipids. These products associate with bile salts to form mixed micelles that transport the lipids across the intestinal cells. 2) Inside the intestinal cells, the lipids are reformed into triglycerides and assembled into chylomicrons along with proteins. Chylomicrons enter the lymphatic system and eventually the blood. 3) Short and medium chain fatty acids do not require micelle formation or re-esterification and enter the blood directly to be used for energy or transported to the liver. Long chain fatty acids in chylomicrons are taken up by tissues for storage or used for energy.

1. ABSORPTION
OF
LIPIDS
Absorption of lipids 1

2. Products of digestion
2-MAG
FA
Cholesterol
Phospholipids
Lysophosholipids
Absorption of lipids 2

3. ABSORPTION OF LONG CHAIN
FATTY ACIDS
LCFA (>14C) - not directly to blood
- absorbed to the lymph
Absorption of lipids 3

4. MIXED MICELLE FORMATION
• After digestion, monoglycerides
and FA associate with bile salts
and PL to form molecular
aggregates called micelle.
• Micelles are much smaller than
emulsion droplets (4-7nm v/s
1µm for emulsionlipids
Absorption of
droplets).
4

5. • Most fat absorption takes place in
the jejununal mucosa
• Micelles are transport the poorly
soluble monoglycerides and fatty
acids to the to the brush border
surface of the enterocyte where they
can be absorbed by passive
diffusion.
Absorption of lipids 5

6. • Complex of lipid materials
soluble in water.
• They are spherical particles
with a hydrophillic exterior and
hydrophobic interior core.
Absorption of lipids 6

7. Mixed micelle formed by
bile salts, triacylglycerols and pancreatic lipase.
Absorption of lipids 7

8. • Bile salts help in the formation of
these aggregates due to their
detergent action
• Bile salts are absorbed in the
ileum (enterohepatic circulation)
Absorption of lipids 8

9. Enterohepatic circulation of
bile salts
The bile salts left behind
are re-absorbed further
down the gastrointestinal
tract (in the ileum),
transported to the liver,
and finally recycled and
secreted back into the
digestive tract
Absorption of lipids 9

10. INTESTINAL
CELL WALL
CHYLOMICRON
SMALL
INTESTINE
LUMEN
LIVER TAG
MIXED MICELLE FFA ,
2MAG
LACTEALS
ENTEROHEPATIC
CIRCULATION OF BILE
ACIDS
RELEASED BILE ACIDS
SHORT/ MEDIUM CHAIN
FFA
PORTAL VEIN
RE-ABSORBED BY
CAPILLARIES
Absorption of lipids
ILEUM 10

11. Re-esterification inside
the mucosal cells
Inside the enterocytes, monoglycerides
and free fatty acids are reformed into
TG.
• The fatty acids are activated to fatty
acyl coA by Acyl coA synthetases by
using 2 high energy phosphates.
• 2 such activated fatty acids react with
MAG to form TAG.
Absorption of lipids 11

12. Micelle Formation
Absorption of lipids 12

13. • Free glycerol absorbed from
the intestinal lumen directly
enters into the blood stream.
• So free glycerol is not available
for re-esterification
Absorption of lipids 13

14. • inside the cell, they become
CHYLOMICRONS.
• The triglycerides, cholesterol,
phospholipids along with
apoprotein B4 and apoprotein A
forms the chylomicrons and
enter the lymph system.
Absorption of lipids 14

15. Lipid Absorption
Absorption of lipids 15

16. • The chyle (milky fluid) from the
intestinal mucosa loaded with
chylomicrons are transported
through the lacteals into the
thoracic duct and emptied into
lymph cirulation.
• Serum appears milky within a few
hours after high fat meal ( post
prandial lipemia) due to the
presence of Chylomicron uptake by
tissues. Absorption of lipids 16

17. Absorption of lipids 17

18. Fate of chylomicrons
• The absorbed (exogeneous) TG are
transported in blood as
Chylomicrons.
• They are taken up by adipose tissue
and liver.
• Liver synthesizes endogeneous TG
which are transported as VLDL ,
deposited in adipose tissue.
Absorption of lipids 18

19. Starvation
• TG in adipose are hydrolized to
free fatty acids.
• Transported complexed with
Albumin
• FFA are then oxidized to get
energy.
Absorption of lipids 19

20. ABSORPTION OF SCFA
• Short chain fatty acids (SCFA)-
milk, butter, ghee
• Medium chain fatty acids (MCFA)-
coconut oil, mother’s milk
DO NOT REQUIRE
RE-ESTERIFICATION!
Absorption of lipids 20

21. Directly enter into blood vessels
Portal vein
LIVER
(immediately used as energy!!
Rapid asorption) 21
Absorption of lipids

22. Overview of Fatty Acid Uptake
• Short- and medium-chain fatty acids
– Enter portal blood directly from
enterocytes
– Bound to albumin in blood
• Albumin–FFA complex
– Oxidized in liver or elongated and used for
triglyceride formation
• Long-chain fatty acids
– Form chylomicrons
– Drain into the lymphatics
– Enter bloodstream at the thoracic duct
• Slow entry into the blood
Absorption of lipids 22

23. Abnormalities in lipid absorption
1.Defective digestion:
“STEATORRHEA”
Fat excretion ; >6g/day in faeces
Unsplit fat seen.
Chronic diseases of pancreas.
Absorption of lipids 23

24. 2. Defective absorption:
Split fat seen in stools as fatty acids and
monoglycerides.
Maybe due to:
• Coeliac diseases, sprue, crohn’s diseas
• Surgical removal of intestine
• Bile duct obstruction due to gall stones,
tumour of head of pancreas, enlarged lymph
nodes etc causing deficiency of bile salts.
Absorption of lipids 24

25. • TG with SCFA and MCFA face no
problem in digestion as they do not
require micellerisation for absorption.
• Hence in MALABSORPTION
SYNDROMES, milk fat and coconut oil are
used therapeutically (MCT)
Absorption of lipids 25

26. 3.CHYLURIA
• Appearance of chyle in urine
• Milky appearance due to lipid droplets.
• Due to abnormal connection between
urinary tract and lymphatic drainage.
Absorption of lipids 26

27. INTESTINAL
CELL WALL
CHYLOMICRON
SMALL
INTESTINE
LUMEN
LIVER TAG
MIXED MICELLE FFA ,
2MAG
LACTEALS
ENTEROHEPATIC
CIRCULATION OF BILE
ACIDS
RELEASED BILE ACIDS
SHORT/ MEDIUM CHAIN
FFA
PORTAL VEIN
RE-ABSORBED BY
CAPILLARIES
Absorption of lipids
ILEUM 27

28. tHanK
yoU
Absorption of lipids 28

29. Overview
of Lipid
Digestion
Absorption of lipids 29