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Old 01-19-2012
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Default PTH Confusion

PTH increases Vit D, which increases Ca++ and P absorption in the gut, while PTH also decreases P reabsorption in the kidney... Yet PTH = Phosphate trashing hormone. Is this because there is a NET loss of P when both are happening? I just want to make sure I'm understanding these hormones correctly. It would be awesome if someone could give me a quick simple explanation of the differences between Vit D and PTH because FA is confusing me >.< Thanks and good luck all!
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Old 01-19-2012
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I remember them this way:
PTH increases the level of only Ca++, by resorption of bone, absorption by intestine, or reabsorption by kidney. VitD increases both Ca and PO4 from those 3 places.
When Ca is low, PTH secretion is stimulated, that will increase Ca, decrease PO4 and induce enzyme 1a-hydroxylase of the proximal tubule. Low Ca, low Po4, enzyme 1 a hydroxylase will increase formation of vitD, which will further increase Ca level, and balance the level of PO4 ( VitD increases both ). That action of vitD will further increase Ca level back to the normal range. When Ca level is back to normal, PTH secretion stops.
Hope it helps.
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Old 01-19-2012
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both have same effect on calcium (increase reabsorption in kidneys) but opposite effect on phosphate in kidneys.

PTH - increases reabsorption of calcium (DCT), decreases reabsorption of calcium (PCT).
Vit.D - increases reabsorption of both.
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