Why is urine calcium low in osteomalacia?

[GomerPyle]

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Hi all.

In osteomalecia, you have low vitamin D so I thought that urine calcium would be higher than normal since you wouldn't be allowed to reabsorb it. Why is this not the case?

Thanks for your time!

 

[zhopv10]

Osteomalacia you have a def of vit D or calcium so your calcium is low. This leads to an increase in PTH in an attempt to normalize serum calcium. PTH acts in the kidney to increase calcium reabsorption. Thus, in osteomalacia: calcium is low, alk phos is highish (bone turnover), PTH is high and urine calcium is low.


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[GomerPyle]

But I thought parathyroid acts on the kidneys by activating vitamin D (1a-hydroxylase). Since there's no vitamin D, how is it acting on the kidneys?

 

[dirty630]

But I thought parathyroid acts on the kidneys by activating vitamin D (1a-hydroxylase). Since there's no vitamin D, how is it acting on the kidneys?

It acts through the Gs/cAMP/PKA pathway.

 

[zhopv10]

It acts on the DCT to increase direct reabsorption of calcium. It up regulates the transporters in the DCT. There is also the effect on vit D but that is an effect on synthesis of Vit d.


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[zhopv10]

And there's the molecular mech from dirty630 🙂


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[GomerPyle]

Doh...didn't follow the chart in first aid...that would have helped haha. Thanks guys!