This document summarizes the digestion, absorption, and transport of dietary lipids in the human body. Dietary lipids undergo limited digestion in the mouth and stomach by lipases before entering the intestine, where pancreatic enzymes emulsify and break down triglycerides, phospholipids, and cholesterol esters into absorbable components. These components are absorbed via micelle transport into intestinal cells and repackaged into chylomicrons that enter the bloodstream. Chylomicrons deliver lipids to tissues and lose triglycerides due to lipoprotein lipase activity before remnants are removed from circulation by the liver.

1. DIGESTION,
ABSORPTION &
TRANSPORT OF
DIETARY LIPIDS
Dr.UsmanSaleem

2. Overview

3. Digestion of
Dietary
Lipids
• Triacylglycerols are the major fat
source in the human diet.
• Limited digestion of these lipids occur
in the mouth and stomach by lipases
(lingual lipase in the saliva and gastric
lipase in the stomach).
• As food enters the intestine,
cholecystokinin is released, which
signals the gallbladder to release bile
acids and the exocrine pancreas to
release digestive enzymes.

4. Digestion of
Dietary
Lipids • Within the intestine, bile salts emulsify
fats, which increase their accessibility
to pancreatic lipase and colipase.
• Triacylglycerols are degraded to form
free fatty acids and 2-monoacylgylcerol
by pancreatic lipase and colipase.

5. Digestion of
Dietary
Lipids
• Dietary phospholipids are hydrolyzed
by pancreatic phospholipase A2 in the
intestine.
• Dietary cholesterol esters (cholesterol
esterified to a fatty acid) are
hydrolyzed by pancreatic cholesterol
esterase in the intestine.

6. Absorption
of Dietary
Lipids
• Micelles, consisting of bile acids and
the products of fat digestion, form
within the intestinal lumen and interact
with the enterocyte membrane.
• Lipid-soluble components diffuse from
the micelle into the intestinal epithelial
cell.
• Bile salts are resorbed farther down the
intestinal tract and returned to the liver
by the enterohepatic circulation.

7. Transport of
Dietary
Lipids in
the Blood
• The intestinal epithelial cells
resynthesize triacylglycerol and
package them into nascent (newborn)
chylomicrons for release into the
circulation.
• Once they are in the circulation, the
nascent chylomicrons interact with
HDL particles and acquire two
additional protein components:
 apoCII and
 apoE.

8. Transport of
Dietary
Lipids in
the Blood
• ApoCII activates lipoprotein lipase on
capillary endothelium of muscle and
adipose tissue, which digests the
triglycerides in the chylomicron.

9. Fate of
Chylomicrons
• The fatty acids released from the
chylomicron enter the muscle for
energy production or the fat cell for
storage.
• The glycerol released is metabolized
only in the liver.
• As the chylomicron loses triglyceride,
its density increases, and it becomes a
chylomicron remnant.

10. Fate of
Chylomicrons
• Chylomicron remnants are removed
from circulation by the liver through
specific binding of the remnant to apoE
receptors on the liver membrane.
• Once it is in the liver, the remnant is
degraded, and the lipids are recycled.