Cobalamin revision questions - week 10

Question 1

Food source

Answer 1

animals foods, fortified ready to eat breakfast cereals

Question 2

Absorption - only vitamin B which was asked about absorption

Answer 2

• 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

Question 3

Transport

Answer 3

• taken to liver and body cells bound to trans-cobalamin

- released into bile

Question 4

Storage

Answer 4

liver (enough to 2 yrs, approx 2500ug)

Question 5

Excretion

Answer 5

• little in urine

- most recycled via enterohepatic circulation

Question 6

coenzyme form

Answer 6

methylcobalamin

Question 7

main fucntion

Answer 7

coenzyme affecting folate metabolism, homocysteine metabolism

Question 8

RDI

Answer 8

2.4ug

for >50yrs supplements recommended

Question 9

UL

Answer 9

none

Question 10

toxicity

Answer 10

none

Question 11

deficiency

Answer 11

pernicious anemia

Question 12

bioavailability from food sources

Answer 12

• 11% in liver
• 24-40% in egg-fish
• > 60% in mutton /chicken

Question 13

absorption increased with

Answer 13

increased uptake

Question 14

very small amount absorbed via

Answer 14

passive diffusion

1%

Question 15

methyl cobalamin

Answer 15

• formed when 5 methyl THF donates methyl group to cobalamin

Question 16

homocysteine

Answer 16

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