MudPhud20XX

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So the way Kaplan explained it makes sense:

Vit D deficiency --> hypocalcemia --> secondary hyperparathyroidism --> increased bone breakdown --> increased Ca2+ --> metastatic calcification leading to renal osteodystrophy

Now FA says that hyperphosphatemia also independently decrease serum Ca2+ by causing tissue calcificaion.

Isn't hyperphosphatemia simply the result of increased PTH due to secondary hyperparathyroidism? I don't get the explanation from FA. Can anyone enlighten me?
 

nguyen1025

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Renal failure → 1) Decreased Vitamin D due to less 1-α hydroxylase activity 2) Decreased phosphate excretion, both these lead to decreased serum calcium → secondary hyperparathyroidism

It is in renal failure that you uniquely get increased serum phosphate and decreased serum calcium as a driver for hyperparathyroidism.
 

Apoplexy__

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Isn't hyperphosphatemia simply the result of increased PTH due to secondary hyperparathyroidism?
Just wanted to say: PTH decreases phosphate levels in the serum. I think FA has the mnemonic "Phosphate-Trashing Hormone" for PTH to help you remember that key fact.
 
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swoopyswoop

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i believe phosphate also binds up serum Ca2+, thus both lowering serum Ca2+ and allowing for deposition in tissues. but i may be wrong.