44 & 45 Digestion and absorption I and II Flashcards
(33 cards)
What are the 3 sources of lipases ?
○ Food bearing lipase: e.g. milk lipase in breast milk
○ Salivary and gastric lipase (pH3-6)
○ Pancreatic lipase ( very pH dependent)
§ lipase-colipase (pH 8,acid sensitive)
§ Phospholipase A2
§ Cholesterol esterase (non specific)
What are the 4 major dietary fats?
- Triglyceride
- Cholesterolester
- 2 monoglyceride
- Phospholipid/ lecithin
What is the product of triglyceride? What enzyme is involved?
- Triglyceride > 2 monoglyceride (FA at 1st and 3rd position are released); by pancreatic lipase
What is the product of cholesterolester? What enzyme is involved?
Cholesterol;
Choelsterolester hydrolase
What is the product of 2 monoglyceride? What enzyme is involved?
Glycerol (water soluble, not participating in micelles);
Cholesterol esterase (non-specific)
What is the product of phospholipid/lecithin ? What enzyme is involved?
Lysolecithin;
Phospholipase A2
In the churning action of gastric peristalsis, fat globules are being emulsified by bile salt.
_______ act as a detergent, and the emulsion droplets become _______ soluble aggregates.
Phospholipids;
water
What are the 2 main purposes of of emulsification?
- Reduce re-aggregation because duodenum is an aqueous environment in which fat droplets might re-aggregate tgt
- Increase surface to volume ratio
Lipase is needed for the formation of micelles. _________ serves as an anchor for lipase to prevent the inactivation of lipase by bile salts.
Co-lipase
Ratio of co-lipase and lipase is 1:1.
What does a water-soluble aggregate micelle contains?
- Monoglyceride
- Fatty acid
- Cholesterol
- Fat soluble vitamins
Micelles can go through the unstirred layer, can be absorbed into the intestinal epithelium by A. Active transport B. Carrier-mediated transport C. Facilitated diffusion D. Simple diffusion
D. Simple diffusion
__________ can also go through the unstirred layer, as they are also water soluble and not micelle-dependent.
Short and medium fatty acids.
The size of an emulsion droplet is ________ than a micelle.
Larger
What are the 3 products after triglyceride meets pancreatic lipase?
Glycerol
Free fatty acids
Monoglyceride
Glycerol + short and medium fatty acids are water soluble and enters capillaries via ______________without involving micelle.
A. Active transport
B. Carrier-mediated transport
C. Facilitated diffusion
D. Simple diffusion
B
What are the 2 processes after micelle enters enterocytes (intracellular processing)?
- Re-synthesis of triglycerides
2. Formation of chylomicron
What are the 2 pathways in re-synthesis of triglycerides?
Major pathway: Monoglyceride acylation pathway
2 monoglycerides+ Co-A activated fatty acids > Triglyceride
Minor pathway: Phosphatidic acid pathway
Phosphorylated glycerol + Co-A activated fatty acids > Triglyceride
What does a chylomicron contain?
It is a lipoprotein containing cholesterol, vitamin A,D,E,K and triglyceride.
How chylomicrons are formed?
Apo-protein + phospholipids + triglycerides (justed formed from re-synthesis) + cholesterol + fat soluble vitamin > lipoprotein > chylomicron
Failure to synthesize apoprotein B prevents?
Chylomicron formation, thus build up of fats within enterocytes, fat malabsorption
Abetalipoproteinemia describes a condition that:
Malabsorbed triglycerides go back to GI lumen, results in fatty stool.
Which of the following is/are true?
A. Vitamins can be from both endogenously and exogenously.
B. Vitamins can act as co-factors/co-enzymes for metabolic reactions
C. The absorption of vitamins depends on fat-soluble/ water-soluble
D. Vitamins are absorbed by carrier mediated transport only.
B & C only.
A. Vitamins are not synthesized in body, obtained from diet
B. True
C. Absorption based on fat-soluble (chylomicron/micelle dependent) (A,D,E,K) / water-soluble
D. Simple diffusion and
carrier mediated transport
Which of the followings is/are false?
A. Vitamin A: carotene for vision
B. Vitamin B12 = cobalamin, for RBC maturation
C. Vitamin C is an anti-oxidant.
D. Vitamin E is for blood clotting.
E. Vitamin D - Anti-rickets.
F. Vitamin K is an anti-oxidant
G. Niacin (nicotinic acid) is an anti-pellagra
D and F are wrong, swapped.
Describe the process of Vitamin B12 absorption.
4 steps
vegetarian has high risk of deficiency.
- Vitamin B12/ Cbl (Cobalamin) and R protein from saliva and gastric juice comes down to the stomach
- B12 in protein-bound animal foodstuffs is released in stomach by HCl/pepsin; and binded to R protein
>R-Cbl complex
- Low pH favours binding of B12 to R protein rather than IF
3. In duodenum, pancreatic proteases and HCO3- secretion free B12. High pH favours binding og B12 to IF > IF-Cbl complex.
4. IF-Cbl receptor can only recognize this complex and absorb it at distal ileum.
