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Renal 2 > Ca and P Regulation > Flashcards

Ca and P Regulation Flashcards

1
Q

H+ and Ca2+

A

Compete for binding sites on plasma albumin

hyperalbuminemia–decreases plasma Ca2+
hypoalbuminemia–increases plasma Ca2+

In acidosis, there is more free calcium in circulation

In alkalosis, more calcium is bound to plasma proteins

  • predisposed to hypocalcemic tetany
  • acute alkalosis can induce sx mimicking hypocalcemia
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2
Q

Calcitriol/Vit D

A

Acts synergistically with PTH to resorb bone (stims osteoclasts)

Increases serum Ca2+ and Pi levels

Increases Ca2+ and phosphate plasma concentration via bone resorption

signals thru VDR (widely expressed)

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3
Q

Calcitriol acting on bone

A

Promotes osteoid mineralization

Osteoclastic-mediated bone resorption

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4
Q

Calcitriol acting in GI

A

Increases Ca2+ absorption (30% dietary calcium is absorbed)

Increases Pi absorption

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5
Q

Calcitriol acting in kidney

A

Increase Pi reabsorption

increase Ca2+ reabsorption

Upregs TRPV5

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6
Q

Calcitonin

A

Decreases serum Pi and Ca2+ concentrations

Acts on bone and kidney
Lowers serum calcium and phosphate levels by inhibiting bone resorption (high doses required to elicit effect)

Stimed by hypercalcemia

Decreases activity and number of osteoclasts

Promotes renal excretion of calcium and phosphate

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7
Q

PTH

A

Increases serum Ca and decreases serum Pi

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8
Q

PTH acting on bone

A

Increases osteoclastic resorption

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9
Q

PTH acting on GI

A

Increases Ca2+/Pi absorption indirectly via Vit D (Calcitriol) production

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10
Q

PTH acting on kidney

A

Increased reabsorption of Ca2+, primarily in DCT

decreased reabsorption of Pi in PCT

Decreased Na+/H+ antiporter activity
Upregs TRPV5 and Na+/Ca2+ exchanger

Decreased bicarb reabsorption

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11
Q

Calcium sensing receptor (CaSR)

A

Monitors calcium levels

Inhibits Ca2+ reabsorption

When plasma calcium is high, CaSR is activated on the interstitial space side of the cell, which inhibits reabsorption on the apical membrane

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12
Q

Proximal Tubule and Ca2+

A

65-7-% of filters calcium absorbed here
Transport is mostly passive and follows the local Na+ and water reabsorption

Primarily paracellular, some transcellular
-Exits cell via Ca2+ ATPase and Na+/Ca2+ antiporter

Volume contraction increases Ca2+ reabsorption

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13
Q

Thick ascending limb (TAL)

A

Lumen positive voltage that drives Ca2+ reabsorption via paracellular path (Primarily paracellular movement)

  • Paracellular pores that conduct Ca2+ and Mg2+
  • Have CaSR along their basolateral surface; increase in peritubular Ca2+ decreases Ca2+ reabsorption

ADH stims reabsorption

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14
Q

Loop diuretics inhibit Na+ reabsorption by TAL

A

Reduces magnitude of lumen positive transepithelial voltage

Reduces Ca2+ excretion, thus used to treat hypercalcemia

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15
Q

Distal Tubule

A

DT has a lumen negative transepithelial voltage

Ca2+ reabsorption is active transcellular transport

Crosses apical membrane via TRPV5 or 6

Crosses basolateral membrane via Na+/Ca2+ exchanger

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16
Q

Thiazide Diuretics

A

Inhibit Na+ reabsorption in DT and stim Ca2+ reabsorption

  • Reduces Ca2+ excretion in urine
  • Used to treat Ca2+ containing kidney stones

PTH and Calcitriol stim reabsorption

17
Q

Acidemia

A

Increases Ca2+ excretion

Acidosis inhibits TRPV5

18
Q

Alkalemia

A

Decreases Ca2+ excretion

Alkalosis stims TRPV5

19
Q

Pi Reabsorption

A

Na+/Pi symporter

Na+ uptake across the apical membrane is couple with movement of another molecule (Pi)
-Driven by Na/K pump

Pi moves across BL membrane thru unknown transporter

20
Q

PTH and Pi regulation

A

PTH inhibits the Na+/Pi transporters and Na+/H+ antiporter in apical membrane of TP cells

Chronic acidosis increases Pi excretion

Chronic alkalosis decreases Pi excretion

21
Q

Regulatory Factors of Pi

A

FGF-23: Fibroblast growth factor 23 released by bone to increase Pi excretion
PTH: Lowers serum Pi by increasing renal excretion
1,25(OH)2D3: Increases serum phosphate by increasing intestinal Pi absorption
Insulin: Lowers serum levels by shifting Pi into cells
Dietary: Pi consumption
Renal function

22
Q

Mg2+ reabsorption in PT

A

20% reabsorbed

Paracellular and follows Na+ and H2O

23
Q

Mg2+ reabsorption in TAL

A

70% reabsorbed

Paracellular and depends on the uptake of Na+ and K+ via NKCC2, which depends on lumen-positive voltage of TAL

24
Q

Mg2+ reabsorption in DT

A

10% reabsorbed, site of fine-tuning

Mg concentration is the same inside and outside the cell, so electrical potential is primary driver of cellular Mg2+ influx

Crosses apical border via TRPM6

Intracellular shuttling not well understood

Crosses BL membrane via unknown mechanism

Renal 2 (7 decks)

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