Calcium Handling in the Nephron

Question 1

majority of calcium in blood is transported via; what forces it’s way into binding with albumin, releasing Ca?

Answer 1

albumin; protons

Question 2

what percentage of total Ca in serum is filterable?

Answer 2

60% (50% free, 10% bound to small anions, e.g. phosphate, citrate, bicarb, sulfate)

Question 3

what is PTH’s primary role?

Answer 3

to prevent death from hypocalcemia; maintenance of calcium levels in the blood

Question 4

how does PTH carry out its role? Ca and Phosphate mechanisms (and the other one)

Answer 4

distal reabsorption of calcium; Vitamin D mediated bone resorption; GI tract reabsorption of Ca and PO4 (to replace bone loss); increases phosphate secretion in the proximal tubule; decreases proximal bicarb reabsorption

Question 5

how is PTH regulated?

Answer 5

1 Ca sensing receptor mediates release of PTH
2 Vit D can block transcription
3 increased PO4/decreased Ca increase 1/2 life of PTH mRNA

Question 6

what other electrolyte does Ca reabsorption shadow?

Answer 6

sodium

Question 7

what’s the mechanism of proximal tubule reabsorption of

Answer 7

paracellular reabsorption (80%) dependent on ECF volume and concurrent flow of Na/water (inc. ECF volume inc. Ca conc. thereby inc. rate of passive diffusion (paracellular transport))

Question 8

what’s the mechanism of calcium reabsorption in the thick ascending limb?

Answer 8

driven by the electrical gradient, which is maintained by the NKCC and ROMK channels; still paracellular

Question 9

what’s the regulation of the TAL reabsorption maintained by? what’s it susceptible to?

Answer 9

calcium sensing channel that inhibits the activity of ROMK, thereby blocking the maintenance of the electrical gradient, thus blocking calcium from getting in
susceptible to both inactivating and activating mutations; magnesium activation and aminoglycosides (anti-Gram neg. aerobic antibiotics)

Question 10

what’s the intermediate that the calcium sensing receptor uses to block ROMK?

Answer 10

20-HETE

Question 11

what’s the pathway for Ca reabsorption in the DCT and CT?

Answer 11

transcellularly, through TRPV5, V6 into the cell, binds to calbindin; out the other side via NCX (main) and Ca-ATPase (minor)

Question 12

what amplifies the effect of DCT/CT absorption?

Answer 12

bicarb, PTH; this explains why PTH blocks bicarb reabsorption in the PCT