Dietary Lipids Metabolism Flashcards
What are lipids?
Heterogenous group of hydrophobic organic molecules
Where are lipids found?
1) Compartmentalized
2) Transported in plasma in lipoprotein or albumin
What are some lipid functions?
- Major source of energy
- Provide hydrophobic barriers
- Fat-soluble vitamins
- Regulatory or coenzyme fx
- Prostaglandins (from eicosanoids, mediate pain, BP, cell damage)
- Steroid hormones (derived from cholesterol)
What are the power house of fats?
Fatty acids
- Need to be carried (albumin)
- Long hydrocarbon chain + single acidic carboxylic group
What is triacylglycerol (TAG)?
FA in an ester bond w/ glycerol in position 1, 2, and 3
-Animals store fat as TAG in adipose cells
What is glycerolphospholipid?
Glycerol + FA on C-1 and 2 and phosphate group attached to position #3
-In many membranes
What is sphinoglycolipid?
Sphinosine as backbone instead of glycerol + a sugar attached to them
-Think in the CNS
In USA, over 90% intake of lipids is from what?
TAG
What is the enzyme that begins digestion?
Lingual lipase (glands at back of tongue) -Mainly milk fat
What does pancreatic lipase degrade?
Degrades TAG by removing FA at C1 and C3 -> 2-monoacylglycerol + 2 free FAs
-Substrate = TAG
What does colipase do?
Restores activity to lipase in presence of inhibitory bile salts that bind the micelles
What does cholesterol esterase (pancreatic cholesteryl ester hydrolase) degrade?
Cholesteryl esters (10-15% of dietary cholesterol) hydrolyzed to remove FA from OH position of cholesterol -> free cholesterol ( w/ 1 OH) + free FA
What does phospholipase A2 degrade?
Removes a FA from C2 -> Lysophospholipid
What can FA at C1 be removed by?
Lysophospholipase
What is Orlistat?
Antiobesity drug inhibits gastric and pancreatic lipases
-Lowers fat absorption -> weight loss
What are bile salts conjugated to?
Glycine or taurine
Where are bile salts made and stored?
Made in liver; stored in gall bladder
Why do conjugated bile salts serve as detergents?
They are amphipathic (hydrophobic and hydrophilic) derivatives of cholesterol
What is lipid digestion controlled by?
Hormones
What is the role of peptide hormone cholecystokinin in control of lipid digestion?
In response to presence of lipids:
- Gallbladder -> release bile
- Pancreas -> release digestive enzymes
- Stomach -> decrease gastric motility -> slower release of contents into small intestine
What is the role of small peptide hormone secretin in control of lipid digestion?
In response to low pH:
- Pancreas -> release bicarbonate -> neutralizes acidity of stomach
- Without bicarbonate none of the enzymes will work
How are lipids absorbed by intestinal mucosal cells (enterocytes)?
- In lumen, soluble mixed micelles created that facilitate uptake (micelle = free FAs, cholesterol, 2-monoacylglycerol, bile salts, fat-soluble vitamins A, D, E, K)
- Approach brush border membrane of enterocytes -> absorbed
Where are bile salts absorbed? What percentage is lost in feces?
In terminal ileum; 5% lost in feces
How are TAGs resynthesized?
By fatty acyl-Coenzyme A (CoA Synthetase)
-Take FA and add a CoA to it to add FA in position 1 and 3 -> TAG
