Digestion and absorption of lipids

1. Digestion and absorption
of lipids

2. Lipid Digestion
Digestive enzymes from the
pancreas are activated by
bile salts to convert
Triglyceride to fatty acids
Intestinal cells resynthesize
triglyceride and export
chylomicrons into circulation
Most of the bile salts are
returned to the liver for reuse

3. BileAcids and
BileSalts
Bile acids and bile salts are made in the
liver from cholesterol
The gall bladder delivers bile salts to the
gut for emulsification
Bacteria modify the bile salts and most is
reabsorbed by intestinal cells

4. Refers to
the circulation of biliary
acids, bilirubin, drugs or
other substances from
the liver to the bile,
followed by entry into the
small intestine,
absorption by the
enterocyte and transport
back to the liver.
Enterohepatic Circulation

5.  Intestinal cells package dietary fat
(mostlyTG) into chylomicrons
 Chylomicrons pick up proteins from
High Density Lipoprotein
 Lipoprotein lipase (LPL) removes
Triglyceride for use in tissues (Apo-
C-II activates LPL)
 Chylomicron remnants are taken up
by the liver
Transport of Dietary Fat to the Liver

6.  Triglyceride and cholesterol is
exported from the liver asVery
Low Density Lipoprotein
 Very Low Density Lipoprotein
picks up proteins from high
density lipoprotein
 Lipoprotein lipase (LPL) removes
TG for use in tissues (Apo-C-II
activates LPL)
 Very Low Density Lipoprotein is
transformed to low density
lipoprotein during circulation
 low density lipoprotein delivers
cholesterol to tissues by receptor
mediated uptake
Export of Fat from the Liver

7.  Nascent high density
lipoprotein is exported from
liver and intestinal cells
 Free cholesterol is picked up
from cells and other
lipoproteins, along with other
components
 Lecithin-cholesterol
acyltransferase converts
cholesterol to cholesterol
esters (CE)
 CE is transferred to other
lipoproteins
 High density lipoprotein
returns cholesterol to the liver
Role of HDL in Lipid Metabolism

8. ABSORPTION
OF LIPIDS
 Mixed micelle formation
 Bile salts and soaps formed in the intestinal
lumen and bicarbonate of pancreatic and
intestinal juices collect the higher fa, mono and
diglycerides, lecithins, cholesterol in the form
of water soluble molecular aggregates called
“micelles”.

9. Micelles are absorbed mainly from
duodenum and jejunum
Bile salts are absorbed in the lower part
of the intestine and return to liver via
portal vein and resecreted into the bile.
Known as enterohepatic circulation.

10. CHYLOMICRO
NS
Inside the epithelial cell triglycerides are
resynthesized in smooth endoplasmic
reticulum, protein component is
synthesized in rough endoplasmic is
incorporated and chylomicrons are
formed.

11. ABNORMALIT
IES
1.Defective digestion:
STEATORRHOEAS
 Increased fat content in faeces
 Obstruction in bile flow
2.Defective absorption due to
 coeliac disease, sprue, crohn’s disease
 surgical removal of intestine
 obstruction of bile duct