4/5. Calciferol (vit D) Flashcards

4. Structure and metabolism of calciferol (vitamin D). Conversion of provitamin to calciferol. 5. Biochemical role and deficiency of calciferol (vitamin D). Toxicity of vitamin D (hypervitaminosis).

1
Q

Vit D2, name and structure

A

Ergocalciferol

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2
Q

Vit D3, name and structure

A

Cholecalciferol

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3
Q

what is the difference between D2 and D3?

A

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

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4
Q

Metabolism of vit D

A

-

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5
Q

Biochemical role of vitamin D in general?

A

-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.

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6
Q

Biochemical role in intestine:

A

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.

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7
Q

Biochemical role in bones:

A

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

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8
Q

Biochemical role in kidney:

A

Increased Ca and P reabsorption which will increase the circulation.

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9
Q

Other Biochemical roles:

A

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

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10
Q

Deficiency:

A

-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.

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11
Q

Hypervitaminosis:

A

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.

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