44 & 45 Digestion and absorption I and II Flashcards
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.
Deficiency of Vitamin B12 may result in _______.
Pernicious anemia
6 reasons for malabsorption of Vitamin B12
- Pancreatic exocrine insufficiency
e. g. pancreatitis/ cystic fibrosis
- fail to cause the dissociation of B12-R complex in duodenum - Deficiency in IF secretion by parietal cells
e. g. atrophy, autodigestion of gastric mucosa, autoimmune
- no B12-IF complex - Decreased HCl
e.g. due to use of PPI, causing low pH secretion,
no R-B12 complex - Genetic defect in IF-B12 receptors in the ileum
- Removal of the distal ileum due to inflammatory bowel disease (IBD)
- Intestinal bacterial growth, leading to taking up of B12 (blind loop syndrome)
Water and electrolyte absorption:
Which of the followings is/are correct?
A. Water is excreted from faeces
B. Faeces is rich in K+ , Na+, Cl- and HCO3- ions
A only
B: faeces are only rich in K+ and HCO3- ions
Diarrhea:
A. Hyperkalemia, metabolic acidosis
B. Hyperkalemia, metabolic alkalosis
C. Hypokalemia, metabolic acidosis
D. Hypokalemia, metabolic alkalosis
C
Vomiting:
A. Hyperkalemia, metabolic acidosis
B. Hyperkalemia, metabolic alkalosis
C. Hypokalemia, metabolic acidosis
D. Hypokalemia, metabolic alkalosis
D
Name the route(s) for absorption of ions and water in the small intestine.
Transcellular route
Paracellular route
Which route for absorption of ions and water in the small intestine predominates?
Depends on leakiness and tightness,
In duodenum, as the tight junctions are very leaky, paracellular route predominates.
In ileum, as the tight junctions are much tighter, transcellular route predominates.
Absorption of water is ________ to ions.
A. Primarily
B. Secondarily
B
List the 4 different mechanisms for absorption of Na+ by intestinal cells
- Na/H+ pumps
- Na+/Cl- pumps
- Direct diffusion
- Nutrient dependent
- Na+/glucose
- Na+/AA
- Na+/Di- or Tri-peptide
