4/5. Calciferol (vit D)

Question 1

Vit D2, name and structure

Answer 1

Ergocalciferol

Question 2

Vit D3, name and structure

Answer 2

Cholecalciferol

Question 3

what is the difference between D2 and D3?

Answer 3

double bond and an extra methyl group on D2. They bare both steroid derivatives.

Question 4

Metabolism of vit D

Answer 4

-

Question 5

Biochemical role of vitamin D in general?

Answer 5

-Maintain Ca and P levels. -Stimulate intestinal calcium and phosphate absorption and mobilization (allowing calcification) -Improve renal absorption of Ca and P -Act as a steroid hormone, but must undergo biochemical change before it can function.

Question 6

Biochemical role in intestine:

Answer 6

binds to nucleus receptor which stimulates RNA polymerase 2, mRNA synthesis will be promoted and a special calcium binding protein will be transported to ribosomes. This will lead to the synthesis of CaBP, which promotes the movement of Ca from intestinal lumen to portal vein.

Question 7

Biochemical role in bones:

Answer 7

It will stimulate mobilization of Ca and P from bone to protein synthesis and PTH. Will result in increased plasma Ca and P concentration.

Question 8

Biochemical role in kidney:

Answer 8

Increased Ca and P reabsorption which will increase the circulation.

Question 9

Other Biochemical roles:

Answer 9

Inhibitory action on citrate oxidation in the bones, the elevated levels will then promote the bone promotion.

Question 10

Deficiency:

Answer 10

-Rickets (soft bones) formation of collagen matrix, but incomplete mineralization. -Low plasma conc –> stimulate PTH –> increase bone dissolution, Ca and P are released into plasma and demineralization of bone will happen. -In elderly, fragile bones, demineralization of pre-existing bones.

Question 11

Hypervitaminosis:

Answer 11

THE MOST TOXIC ONE!!! - It is very well stored and are very slowly metabolized. - Will increase the Ca absorption and bone will dissolve. -Hypercalcemia and hyperphosphatemia will happen, which can lead to calcification of other tissues, like arteries. -Fragile and deformed bones.