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MP - BR > Chapter 7 Calcium, Mg, Phos Excretion > Flashcards

Chapter 7 Calcium, Mg, Phos Excretion Flashcards

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1
Q
A
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2
Q

Where is most calcium stored in the human body?

A

In bone

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3
Q

What percentage of filtered calcium is reabsorbed by the kidney?

A

Approximately 98-99%

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4
Q

What hormone reduces claudin-14 expression in the TALH to promote calcium reabsorption?

A

Parathyroid hormone (PTH)

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5
Q

Which form of vitamin D is biologically active?

A

1α,25-dihydroxyvitamin D3

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6
Q

What is the effect of metabolic acidosis on calcium reabsorption?

A

It decreases calcium reabsorption in the distal tubule

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7
Q

What channel mediates calcium reabsorption in the distal tubule?

A

TRPV5 and TRPV6 channels

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8
Q

What percentage of calcium in plasma is ionized?

A

Approximately 50%

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9
Q

What is the normal daily urinary calcium excretion?

A

Approximately 250 mg/day

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10
Q

Which tight junction protein mediates paracellular calcium transport in the PT?

A

Claudin-2

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11
Q

What stimulates the synthesis of 1α,25(OH)2D3 in response to hypocalcemia?

A

Parathyroid hormone (PTH)

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12
Q

Where is the calcium-sensing receptor (CaSR) primarily located in the nephron?

A

On the basolateral membrane of the TALH

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13
Q

What protein helps trap TRPV5 in the membrane to sustain its activity?

A

Klotho

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14
Q

How do loop diuretics affect urinary calcium?

A

They increase urinary calcium excretion

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15
Q

How do thiazide diuretics affect urinary calcium?

A

They decrease urinary calcium excretion

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16
Q

What is the primary site for magnesium reabsorption in the nephron?

A

Thick ascending limb (TALH)

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17
Q

What protein complex forms the paracellular channel for magnesium in TALH?

A

Claudin-16 and claudin-19

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18
Q

What transporter maintains the Na gradient used by the Na/Ca exchanger in the DT?

A

Na-K-ATPase

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19
Q

What is the role of TRPM6 and TRPM7 in the distal tubule?

A

They form the apical magnesium channel complex

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20
Q

Which cation sensing receptor regulates paracellular calcium transport via claudin-14?

A

Calcium-sensing receptor (CaSR)

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21
Q

What is the daily filtered load of calcium by the kidney?

A

9000–10,000 mg/day

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22
Q

What happens to claudin-14 expression during high calcium intake?

A

It is upregulated, reducing calcium reabsorption

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23
Q

What is the effect of estrogen on renal calcium transport?

A

Increases TRPV5 expression, reducing urinary calcium

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24
Q

Which nephron segment has active calcium transport mediated by TRPV channels?

A

Distal tubule

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25
Which vitamin D metabolite promotes calcium and phosphate absorption in the intestine?
1α,25(OH)2D3
26
What is the primary mode of magnesium reabsorption in the proximal tubule?
Paracellular transport
27
What happens to magnesium reabsorption in magnesium depletion?
It increases
28
What type of receptor is the vitamin D receptor (VDR)?
A steroid hormone receptor
29
What is the role of calbindin D9K and D28K in calcium transport?
They bind calcium intracellularly to aid transcellular transport
30
What effect does metabolic alkalosis have on calcium reabsorption?
It increases calcium reabsorption in the DT
31
Which form of phosphorus is most commonly measured clinically?
Inorganic phosphate (Pi)
32
What is the primary site of phosphate reabsorption in the nephron?
Proximal tubule
33
What is the role of FGF-23 in phosphate metabolism?
It promotes phosphate excretion and inhibits 1α-hydroxylase
34
What transporters are downregulated by FGF-23 to cause phosphaturia?
NaPi-IIa and NaPi-IIc cotransporters
35
What is the effect of phosphate depletion on vitamin D metabolism?
Increases 1α,25(OH)2D3 synthesis
36
What condition is caused by claudin-16 and -19 mutations?
Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC)
37
What effect does calcitonin have on calcium reabsorption in TALH?
Stimulates calcium reabsorption
38
What vitamin D-dependent protein mediates apical calcium uptake in the intestine?
TRPV6
39
What effect does hypercalcemia have on CaSR?
Activates CaSR to reduce calcium reabsorption
40
What is the function of the Na+/Ca2+ exchanger in renal epithelial cells?
Extrudes calcium from the cell to the interstitial space
41
What is the daily intake of dietary calcium in a typical human?
1000 mg
42
Where is TRPV5 localized in the kidney?
Apical membrane of distal tubule cells
43
What is the function of PMCA in calcium transport?
Pumps calcium out of the cell at the basolateral membrane
44
What enzyme converts 25(OH)D3 to the active 1α,25(OH)2D3?
25-hydroxyvitamin D3-1α-hydroxylase
45
What regulates PTH secretion?
Serum calcium via the calcium-sensing receptor (CaSR)
46
What is the role of ROMK in the TALH?
Recycles K+ to help generate lumen-positive voltage for Ca2+ reabsorption
47
What is the major driving force for paracellular Ca2+ transport in TALH?
Lumen-positive transepithelial voltage
48
What is the effect of sclerostin on renal calcium reabsorption?
Inhibits calcium reabsorption (increases calciuria)
49
What happens to urinary calcium in Sost-/- mice?
It decreases due to increased calcium reabsorption
50
How is 25(OH)D3 formed from vitamin D3?
By 25-hydroxylase in the liver
51
What condition results from 1α-hydroxylase deficiency?
Vitamin D–dependent rickets type I
52
What is the daily filtered load of magnesium in humans?
Approximately 3000 mg/24 hr
53
What is the primary site of magnesium reabsorption in the nephron?
Thick ascending limb of Henle (TALH)
54
What proteins form the paracellular channel for magnesium in the TALH?
Claudin-16 and claudin-19
55
Which magnesium channel is localized apically in the distal tubule?
TRPM6 (with TRPM7)
56
What factor promotes TRPM6 trafficking to the plasma membrane?
Epidermal growth factor (EGF)
57
What potassium channel determines the voltage gradient in the DT for magnesium entry?
Kv1.1
58
What percentage of filtered magnesium is reabsorbed in the proximal tubule?
15–20%
59
What transporter may mediate basolateral Mg2+ extrusion in the distal tubule?
CNNM2 or SLC41A1
60
Which gene mutation causes isolated dominant hypomagnesemia?
FXYD2
61
What is the role of Kir4.1 in magnesium reabsorption?
Recycles K+ to support Na-K-ATPase function in the DT
62
How does hypermagnesemia affect renal magnesium reabsorption?
It reduces reabsorption
63
What happens to urinary magnesium in magnesium depletion?
It decreases
64
Which gene encodes the apical Na-K-Cl cotransporter in the TALH?
SLC12A1 (NKCC2)
65
What is the function of ROMK in the TALH?
Recycles K+ to sustain NKCC2 activity and lumen positivity
66
What is the primary driving force for paracellular Mg2+ reabsorption in the TALH?
Lumen-positive voltage
67
What syndrome is caused by Kir4.1 mutation?
SeSAME or EAST syndrome
68
How does volume depletion affect calcium reabsorption?
It increases Ca2+ reabsorption in the proximal tubule
69
What is the mechanism by which furosemide increases calcium excretion?
Inhibits NKCC2, reducing lumen positivity
70
What is the effect of thiazide diuretics on urinary calcium?
They decrease calcium excretion (hypocalciuria)
71
What protein is downregulated by PTH to increase TALH calcium reabsorption?
Claudin-14
72
What effect does CaSR activation have on claudin-14?
It increases claudin-14 expression
73
What is the result of claudin-10b deletion in mice?
Hypermagnesemia and increased calcium permeability
74
What is the role of NaPi-IIa and NaPi-IIc in phosphate transport?
They mediate renal phosphate reabsorption
75
What factor inhibits NaPi-IIa and NaPi-IIc expression?
FGF-23
76
What hormone stimulates both calcium and phosphate absorption in the intestine?
1α,25-dihydroxyvitamin D3
77
What are the three major regulators of phosphate homeostasis?
PTH, 1α,25(OH)2D3, FGF-23
78
What happens to phosphate reabsorption in hypophosphatemia?
It increases
79
What is the normal range of inorganic serum phosphate?
2.56–4.16 mg/dL
80
How does high dietary phosphate affect PTH levels?
It increases PTH secretion
81
What does FGF-23 do to 1α-hydroxylase?
It inhibits it, decreasing 1α,25(OH)2D3 synthesis
82
How much phosphorus is typically absorbed daily from the diet?
Approximately 1100 mg
83
Where in the intestine is most phosphate absorbed?
Jejunum
84
What is the typical daily urinary excretion of phosphate?
900 mg
85
What percentage of phosphorus in the body is in bone?
0.85
86
What effect does metabolic alkalosis have on renal magnesium handling?
It increases reabsorption
87
How do calcitonin and PTH affect magnesium excretion?
They increase reabsorption
88
What is the effect of aldosterone on magnesium reabsorption?
It increases Mg reabsorption
89
Which segment reabsorbs phosphate in the nephron?
Proximal tubule
90
What effect does phosphate depletion have on calcium levels?
It increases ionized calcium
91
How does hypophosphatemia affect PTH secretion?
It decreases PTH secretion

MP - BR (8 decks)

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