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Calcium in extracellular fluid must be very tightly regulatd: why?

close to level at which it will precipitate.


how much serum Ca is free vs. bound?



consequences of hypocalcemia?

long-term: bone weakening. shorter term: arrythmias due to lowered threshold, increased muscle excitability.


consequences of hypercalcemia?

decreased muscle excitability, increased BP.


minority of reabsorption of Ca in the nephron is done where and how?

in prox tubule and loop, paracellular.


majority of Ca reabsorption is done where?

distal tubule. active transcellular route. prime site of regulation. via calbindin.


why calbindin?

intracellular Ca needs to be kept low, therefore bind it to protein to transport


relationship between Na and Ca reabsorption in the prox tubule and loop?

they are transported together. due to + lumen voltage, they go paracellularly.


relationship between Na and Ca reabsorption in the distal tubule?

they oppose each other: if too much Na reabsorption in the cell, too positive for Ca entry as well.


Thiazide diuretics block what transporter, and do what to Ca levels?

block the Na/Cl cotransporter, and can lead to hyper Ca.


Will binding of Ca to albumin increase or decrease at alkalotic pH?

increase. normally albumin binds H and Ca, and if there is less H there is more binding capacity for Ca. this leads to a decrease in free Ca.


chronic metabolic acidosis does what to Ca levels?

inhibits Ca reabsorption directly.


the distribution of phosphate between cells and extracellular fluid is dependent upon what?

acid/base balance and carbohydrate status. alkalosis results in P shift INTO cells, acidosis results in P shift OUT of cells


where is most of P reabsorped?

in Prox tubule in cotransport with Na.


what sill stimulate a releae of PTH?

a decrease of plasma Ca.


how does a decrease of plasma Ca lead to a release of PTH?

CaSR receptor: inhibits release of PTH until a state of hypocalcemia. Then inibibtion is lifted.


4 actions of PTH?

increases Ca reabsorption. decreases P reabsorption. induces Ca and Pi release from bone. converts Vit D into active form


how does the kidney guard against stones in lumen or interstitium?

sites of regulation of reabsprption for 3 minerals (P, Ca, Mg) are different. Pi = prox tubule, Ca = distal tubule, Mg = early part of distal tubule.
Also: well placed CaSRs on lumen side of TALH. increase in local Ca will yield decreased Ca reabsorption.