Cobalamin revision questions - week 10 Flashcards
Food source
animals foods, fortified ready to eat breakfast cereals
Absorption - only vitamin B which was asked about absorption
- bound to protein in food
- free cobalamin released by action of HCL and pepsin in stomach
- free cobalamin binds to R-protein (from salivary cells and parietal cells)
- in SI pancreatic proteases release cobalamin from R-protein
- free cobalamin binds to intrinsic factors (IF) from parietal cells
- IF + B12 travel to and are absorbed by endocytosis in the terminal ileum
Transport
- taken to liver and body cells bound to trans-cobalamin
- released into bile
Storage
liver (enough to 2 yrs, approx 2500ug)
Excretion
- little in urine
- most recycled via enterohepatic circulation
coenzyme form
methylcobalamin
main fucntion
coenzyme affecting folate metabolism, homocysteine metabolism
RDI
2.4ug
for >50yrs supplements recommended
UL
none
toxicity
none
deficiency
pernicious anemia
bioavailability from food sources
- 11% in liver
- 24-40% in egg-fish
- > 60% in mutton /chicken
absorption increased with
increased uptake
very small amount absorbed via
passive diffusion
1%
methyl cobalamin
- formed when 5 methyl THF donates methyl group to cobalamin
homocysteine
An amino-acid not found in the diet, and not one of the 20 amino acids used in anabolism
Homocysteine concentration >15 μM was associated with:
- Increased rate of heart attack x 3
- Endothelial cells damage, blood clotting mechanisms
disruption (increased clotting)
- Promotion of smooth muscle cells growth
- Decline in cognition function
- Lower cerebral white matter
