Regulation of Ca2+, Pi, and Mg Balance

Question 1

What percentage of Ca+ is filtered by the glomerulus?

Answer 1

60%

Ionized Ca+ = 45%

Diffusable Ca+ complexes = 15%

Question 2

How does hyperalbuminemia effect plasma Ca2+ levels?

Answer 2

Decreases free Ca2+ levels

Question 3

How does acidosis effect free Ca2+ serum levels?

Answer 3

Increases free Ca2+

Question 4

What effect does Vitamin D (Calcitrol) have on the phosphate and calcium?

Answer 4

Acts synergistically with PTH to resorb bone

Increases absorption of calcium and phosphorous in the intestine

Increases reabsorption in the kidney

Question 5

What is the effect of Calcitonin on the body?

Answer 5

Lowers serum Ca+ and Pi levels

Promotes renal excretion of calcium and phosphate

Decreases resorption of bone

Question 6

What diseases can be treated with Calcitonin?

Answer 6

Osteoporosis

Paget’s disease

Hypercalcemia

Question 7

What effects does PTH elicit on the kidney?

Answer 7

Increases resabsorption of Ca2+ primarily in the distal convoluted tubule.

Upregulates TRPV5

Decreases reabsorbtion of Pi in the PCT

Decreases the Na/H antiporter

Decreases bicarbonate reabsorption

Question 8

How does a volume contraction effect Ca2+ reabsorption?

Answer 8

Increases, parallel with Na+

Question 9

What is the thick ascending limb dependent on for Ca2+ and Mg+ absorption?

What kind of movement is here?

Answer 9

The Trans Epithelial Potential Difference (TEPD) for a positive voltage difference.

Paracellular

Question 10

How is the lumen-negative transepithelial voltage of the distal tubule overcame in Ca transport?

Answer 10

Through apical TRPV5 or TRPV6

Crosses the basolateral membrane via NCE - Na/Ca+ exchanger

Question 11

How is TRPV5 stimulated?

Answer 11

Vitamin D

Question 12

What prevents an influx of calcium from inducing apoptosis?

Answer 12

Calbindin

Question 13

How does acidemia influences Ca2 excretion/reabsorption?

Answer 13

Inhibits TRPV5 ⇒ Increases Ca2+ excretion

Question 14

How does a decrease in ECV effect Ca2+ reabsortion?

Answer 14

Stimulates SNS which increases Na+ and Ca+ reabsorption

Question 15

How does phosphate enter the peritubular capilary from the lumen?

Answer 15

Driven by an Na-K-ATPase, the Na-Pi symporter allows entry into the lumenal cells.

The mechanism of how Pi gets through the basolateral membrane is unkown.

Question 16

What negatively regulates Phosphate absorption?

Answer 16

FGF-23

Question 17

What converts the inactive form of vitamin D into calcitriol?

Answer 17

Renal 1alpha-hydroxylase

Question 18

What channels does PTH inhibit?

Answer 18

Inhibits Na-Pi symporter and Na-H+ antiporter.

Question 19

What stimulates the release of FGF-23?

Answer 19

Secreted by bone in response to:

PTH

Calcitriol

Hyperphosphetemia

Question 20

How much magnesium is reabsorbed in the proximal tubule, TAL, and distal tubule respectively?

Answer 20

20%

70%

10%

Question 21

How does Mg cross the following structures into circulation?

Proximal Tubule

TAL

DIstal Tubule

Answer 21

PT = paracellular, dependent on the uptake of Na+ and K+

TAL = paracellular and dependent on uptake of Na+ and K+ via NKCC2 (dependent on lumen positive voltage)

Distal Tubule = crosses apical membrane via TRPM6, intracellular and basolateral transport unkown.

Question 22

What factors increase magnesium reabsorption?

Answer 22

Dietary depletion

PTH

Metabolic alkalosis

ECF volume contraction