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Renal Final > Regulation of Ca, Pi, and Mg balance > Flashcards

Regulation of Ca, Pi, and Mg balance Flashcards

1
Q

What are the forms that calcium exists in the body?

A

ionized, bound to plasma proteins, complexed in non-ionized form

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2
Q

Where is calcium stored in the body?

A

99% in bone, 1% in ICF, 0.1% in ECF

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3
Q

What is the total plasma level of calcium?

A

5.0 mEq/L

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4
Q

What is the biologically active plasma calcium level?

A

2.4 mEq/L

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5
Q

What percent of calcium excretion is through the feces?

A

90%

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6
Q

What is the effect of hyoalbuminemia on calcium levels?

A

increases plasma Ca2+

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7
Q

What is the effect of hyperalbuminemia on calcium levels?

A

lowers plasma Ca2+

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8
Q

What is the effect of acidosis on calcium levels?

A

more free calcium in circulation

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9
Q

What is the effect of alkalosis on calcium levels?

A

more calcium bound to plasma proteins
predisposition to hypocalcemic tetany
acute alkalosis can induce symptoms mimicking hypocalcemia

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10
Q

What is the other name for vitamin D?

A

calcitriol

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11
Q

What does calcitriol act with on the bone?

A

PTH

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12
Q

What is the overall effect of calcitriol?
bone?
intestine?
kidney?

A

overall: increases serum calcium and phosphate
bone: promotes osteoid mineralization and osteoclast mediated bone resorption
intestine: increases calcium absorption (30% absorbed); increases phosphorus absorption
kidney: increases phosphate reabsorption; increases calcium reabsorption

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13
Q

What is the receptor for calcitriol?

A

Vitamin D receptor which is widely expressed

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14
Q

What is a calcitriol deficiency thought to contribute to?

A

chronic pain

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15
Q

What does calcitonin act on? What does it regulate?

A

bone and kidney

level of calcium

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16
Q

What does calcitonin inhibit?

A

bone resorption

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17
Q

What does calcitonin lower with high doses?

A

calcium and phosphate levels

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18
Q

What does calcitonin promote?

A

renal excretion of calcium and phosphate

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19
Q

What does calcitonin oppose?

A

PTH

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20
Q

What is calcitonin stimulated by?

A

hypercalcemia

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21
Q

What is the effect of calcitonin overall?
bone?
kidney?

A

overall: regulates Ca2+ and Pi concentrations
bone: inhibits osteoclast resorption
kidney: promotes calcium and phosphate excretion

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22
Q

What are pharmacologic doses of calcitonin used to treat?

A

osteoporosis
Paget’s disease
hypercalcemia

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23
Q

What is the effect of PTH overall?
bone?
intestines?
kidney?

A

overall: increases serum calcium and decreases serum phosphate
bone: increases osteoclastic resorption
intestine: increases calcium and phosphate absorption indirectly via calcitriol production
kidney: promotes reabsorption of calcium in DCT; decreases reabsorption of phosphate in PCT; decreases activity of Na+/H+ antiporter; decreases bicarbonate reabsorption

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24
Q

What can excess PTH cause?

A

hypercalcemia
hypophosphatemia
hypercholermic metabolic acidosis

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25
What is the function of the calcium sensing receptor (CaSR)?
monitors calcium levels when calcium levels are high, CaSR in the thick ascending limb senses this and is activated on the interstitial space side of the cell, which inhibits calcium reabsorption on the apical membrane (NKCC2 channels) which decreases calcium paracellular diffusion
26
What are the effects of decreased plasma calcium?
increased PTH - bone: increased resorption of calcium and Pi - kidney: increased Pi excretion, decreased Ca2+ excretion, increased calcitrol production - intestines: increased calcium and Pi absorption
27
What is the filtered load equation?
GFR x plasma concentration x filterability
28
What is the filterability of calcium?
60%
29
When is calcium not filterable?
plasma proteins
30
What percent of calcium is reabsorbed in which parts of the nephron?
65-70% proximal tubule ~20% thick ascending limb 8% distal tubule
31
Describe calcium reabsorption in the proximal tubule
most paracellular (follows Na+ and water) some transcellular -diffusion down gradient into cell - exits cell via Ca2+-ATPase and Na-Ca2+ antiporter
32
What is the effect of volume contraction on calcium reabsorption?
increases calcium reabsorption b/c calcium follows Na and water
33
What is the effect of volume expansion on calcium reabsorption?
decreases calcium reabsorption
34
Describe calcium reabsorption in the thick ascending loop (TAL)
paracellular (paralleling Na+) dependent on TEPD (lumen positive voltage) stimulated by ADH
35
What does ADH do?
1. increasing NaCl reabsorption via thick ascending limb --> increases hypertonicity of medullary interstitium 2. regulates collecting duct water permeability allowing removal of water from the tubule fluid via diffusion
36
How do loop diuretic work?
low yield inhibits Na+ reabsorption by thick ascending loop -reduces magnitude of lumen-positive transepithelial voltage -reduces calcium paracellular reabsorption (increases calcium excretion) -can treat hypercalcemia
37
Describe calcium reabsorption in the distal tubule
- DT has lumen negative transepithelial voltage - reabsorption is active transcellular transport - crosses apical membrane via TRPV5 - crosses basolateral membrane via Na+-Ca2+ exchanger (NCE)
38
Where is TRPV5?
distal tubule apical membrane | calcium reabsorption
39
Where is NCE?
Na+-Ca2+ exchanger in the basolateral membrane of distal tubule
40
How do thiazide diuretics work?
low yield inhibit Na+ reabsorption in DT and stimulate Ca2+ reabsorption -reduces calcium excretion in urine -used to treat calcium containing kidney stones
41
What stimulates calcium reabsorption?
``` PTH and calcitriol (vitamin D) (high yield) thiazide diuretics (low yield) ```
42
What do PTH and calcitriol do?
stimulate reabsorption of calcium
43
What is the effect of acidemia on calcium?
increases calcium excretion by inhibiting TRPV5
44
What is the effect of alkalemia on calcium?
decreases calcium excretion by stimulating TRPV5
45
Is calcium secreted in the kidney?
NO
46
How much plasma calcium is filtered at the glomerulus? | What percent of filtered calcium is reabsorbed?
60% filtered | 99% reabsorbed
47
``` What are the basic functions in regards to calcium: PTH vit D/calcitriol calcitonin decreased ECV metabolic alkalosis ```
PTH: upregulates TRPV5, Na-Ca exchanger vit D/calcitriol: upregulates TRPV5 calcitonin: opposes PTH, stimulated by hypercalcemia, decreases serum phosphorus and calcium concentrations decreased ECV: increased sympathetics --> Na reabsorption in PCT; calcium reabsorption depends on transepithelial voltage and solvent drag, which depend on Na+ reabsorption metabolic alkalosis: increases calcium reabsorption by acting on TRPV5/6
48
What is the filterability of phosphate?
100%
49
How much phosphate is reabsorbed by PT? | What is involved in the phosphate reabsorption in the PT?
80% | Na+-Pi symporter, PTH and Ca2+, FGF-23
50
What is Na uptake across the apical membrane coupled with in the early proximal tubule?
SYMPORTERS: primarily HCO3-, glucose, amino acids, Pi, and lactate ANTIPORTERS: reabsorbed in exchange for H+ or organic solutes
51
How does Pi cross the basolateral membrane?
its own transporter; mechanism unknown
52
How does Pi cross the apical membrane?
Na+-Pi symporter
53
Describe FGF-23's role in phosphate regulation
secreted by bone in response to PTH, calcitriol, and hyperphosphetemia FGF-23 receptors on the basolateral membrane inhibits NaPi symporters on apical membrane promotes Pi excretion
54
What is the effect of PTH on Pi?
inhibits NaPi symporter on apical membrane | promotes Pi excretion
55
Where is calcitriol made?
proximal tubule epithelial cells
56
What converst vitamin D to its active form?
renal 1alpha-hydroxylase
57
What upregulates 1alpha-hydroxylase expression?
low calcium low phosphate high PTH
58
What inhibits renal 1alpha-hydroxylase expression?
high calcium sensed by CaSR
59
Is vitamin D filtered at the glomerulus?
some is filtered, but it is endocytosed by PT cells and reabsorbed
60
What are the major regulatory factors of phosphate?
FGF-23 - fibroblast growth factor 23 released by bone to increase phosphate excretion PTH - lowers serum phosphate by increasing renal excretion 1,25(OH)2D3 - increases serum phosphate by increasing intestinal phosphate absorption insulin - loswers serum levels by shifting phosphate into cells dietary - phosphate intake renal function
61
What is the most important hormone that regulates Pi excretion?
PTH | inhibits the NaPi transporters and NaH antiporter of PT cells
62
What is the effect of chronic acidosis on Pi excretion? | chronic alkalosis?
chronic acidosis: increases Pi excretion | chronic alkalosis: decreases Pi excretion
63
How much Mg2+ is reabsorbed in the PT?
20% | paracellular and follows Na and water
64
How much Mg2+ is reabsorbed in the TAL?
70% | paracellular and depends on uptake of Na+ and K+ via NKCC2 which depends on lumen-positive voltage of TAL
65
How much Mg2+ is reabsorbed in the distal tubule?
10%, site of fine-tuning | driven by electrical potential
66
How does Mg2+ cross the apical border in the DT? basolateral border?
TRPM6; unknown mechanism
67
Is magnesium reabsorption increased or decreased: dietary depletion (60%; does not meet dietary requirements) PTH metabolic acidosis metabolic alkalosis ECF volume expansion ECF volume contraction
dietary depletion (60%; does not meet dietary requirements): increased, promotes retention; increases paracellular permeability of Mg PTH: increased metabolic acidosis: decreased, decreased paracellular permeability of Mg metabolic alkalosis: increased, enhances paracellular permeability of Mg ECF volume expansion: decreased ECF volume contraction: increased

Renal Final (7 decks)

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