Step I Chronic renal failure

[aspiringmd1015]

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why does po4 build up, but ca2+ become lower? simply just bc of vitamin D? but that would effect both ca2+ and po4 absorption in the gut. why is ca2+ being preferentially lost in the urine and gut? could it be bc you cant secrete + so you lose the paracellular absorption of ca2+ in the TAL?

 

[pathologyDO]

Po4 binds calcium in serum. You lose serum free calcium when phosphate levels increase. Is there another reason? Maybe, but that's one explanation

 

[aspiringmd1015]

right, drives it into tissues, mets calcification and the whole shish kabob, so in that case ca2+ and po4 would both have to be high initially, adn then po4 would lower serum ca2+, but with CRF you lose vit D activation, so you should be losing po4 in your gut along w/ca2+

 

[pathologyDO]

You also lose the ability to excrete phosphate, so although you take up less in the gut the degree of decreased excretion is greater, so phosphate is still high

 

[aspiringmd1015]

where in the tubules is p04 excreted? i know most i think 85% of po4 is reabsorbed in the PCT, but dont know where its excreted

 

[aspiringmd1015]

side question: what's the stimulus for EPO release? is it hypoxia, hypoxemia, or what?