The small intestine Flashcards
Most lipid digestion occurs in the small intestine
WHY
conditions more favourable than in the stomach
What are into the lumen of small intestine
Bile salts
What surrounds and emulsifies dietary lipids?
Bile salts + lysolecithin & products of lipid digestion
Emulsification produces
small droplets of lipid dispersed in the aqueous solution of the intestinal lumen, creating a large surface area for the action of pancreatic enzymes
What enzymes are secreted into the small intestine to accomplish the digestive work
Pancreatic lipase, cholesterol ester hydrolase, phospholipase A2 & colipase
Pancreatic lipase
- is secreted as active enzyme
- It hydrolyses TG molecules to 1 molecule of monoglyceride & 2 molecules of FA.
Pancreatic lipase is inactivated by
bile salts displacing pancreatic lipase at the lipid- water interface of the emulsified lipid droplets.
Colipase
- is secreted in pancreatic juices in an inactive form, pro-colipase, which is activated in the intestinal lumen by trypsin
- Colipase then displaces bile salts at the lipid-water interface & binds to pancreatic lipase
- With the inhibitory bile salts displaced, pancreatic lipase can proceed with its digestive functions.
Cholesterol ester hydrolase
is secreted as an active enzyme & hydrolyses cholesterol ester to free CH & FAs. It also hydrolyses ester linkages of TG, yielding glycerol.
Phospholipase A2
is secreted as a pro-enzyme is activated by trypsin. Phospholipase A2 hydrolyses phospholipids to lysolecithin & FAs.
The final absorption products of lipid digestion are:
Monoglycerides
FAs
CH
Lysolecithin, & glycerol (from hydrolysis of ester bonds of TGs).
With the exception of glycerol, each end product of lipid digestion is
hydrophobic & not soluble in water.
Now the hydrophobic digestive products must be
solubilized in micelles & transported to the apical membrane of the intestinal cells
Slide 20!!
