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  1. #1
    Roxanita is offline Senior Member
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    Q-2) Vitamins N*

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    Q.- The absorption of Calcium from the intestinal tract results principally from the direct action of which of the following?

    A) Calcitonin

    B) Cyclic AMP

    C) 1,25-Dihydroxycholecalciferol

    D) 25-Hydroxycholecalciferol

    E) Parathyroid hormone

  2. #2
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    Asclepius1 is offline Ultimate Member 537 points
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    i think i would narrow it down to either c or e. both pth and 1, 25 dihyroxycholecalciferol increase calium resorption from bone, so not sure which one to pick. i guess that 1,25-Dihydroxycholecalciferol is the active form of vit D, so that would be my guess, but not sure.

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    Roxanita is offline Senior Member
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    c) 1,25-Dihydroxycholecalciferol

    Vitamin D and Ca++
    Hypocalcemia will stimulate release of PTH, which binds to Receptors (R) in PCT in the glomerulus, R coupled through cAMP to activate "1 Alpha Hydroxylase" to
    convert Vit D >>to>> 1,25-DHCC(Dihydroxycholecalciferol or calcitriol)

    1,25-DHCC acts on Duodenum, its intracellular R (Zn finger protein ) will induce
    Ca++binding proteins which will stimulate CALCIUM UPTAKE from GI tract. It
    also facilitates Ca reabsorption in kidneys and mobilizes calcium from bone when PTH is also present; and all these actions will bring Ca back to normal levels.
    * Calcitonin main function is to lower the Ca: "calcitonin= toning ca" in plasma by decreasing the osteoclastsactivity.

    PTH:
    - as a rapid or direct function: increases Ca reabsorptionin the kidney
    - as a slower or indirect function: increases theOsteoclasts activity and also
    - increases the formation of Vit D in the PCT>>1,25 DHCC (whichthen leads to incr absorpt Ca and PO4 from the small intestines)


    Check kaplan pg145

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