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Renal-1 > Regulation of Ca, Pi, and Mg > Flashcards

Regulation of Ca, Pi, and Mg Flashcards

1
Q

How does PTH affect bone?

A

increases resorption

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2
Q

How does low and high albumin affect plasma Ca levels?

A

hypoalbuminemia = increases plasma Ca

hyperalbuminemia = decreases plasma Ca

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3
Q

How does calcitonin work overall?

A

lowers serum calcium and phosphate levels

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4
Q

How is calcium reabsorbed in the proximal tubule?

A

primarily paracellularly

some transcellular = diffuses down gradient from lumen –> exits via Ca-ATPase and Na-Ca antiporter

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5
Q

How do chronic acidosis and alkalosis affect Pi excretion?

A

chronic acidosis: increases Pi excretion

chronic alkalosis: decreases Pi excretion

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6
Q

What is FGF-23 and what does it do?

A

secreted by bone in response to PTH, calcitriol, and hypoerphosphetemia –> inhibits Na-Pi symporter –> decreases Pi reabsorption in early PT

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7
Q

Where is calcium reabsorbed in the nephron?

A

PT: 65-70% reabsorbed; mostly passive and follows Na and H2O

Thick ascending limb: lumen positive voltage drives Ca reabsorption via paracellular path

Distal tubule: reabsorbs 8%, but major site of regulation via Vit D

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8
Q

How does PTH affect the intestines?

A

Increases Ca/Pi absorption indirectly via Vit D

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9
Q

How does PTH affect the Kidneys?

A

promotes Ca reabsorption, primarily in the DCT

decreases reabsorption of Pi in PCT

decreases Na/H antiporter action

decreases bicarbonate reabsorption

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10
Q

In general, what does vitamin D/Calcitriol do?

A

works with PTH to resorb bone (stimulate osteoclasts)

increases Ca and Pi plasma levels

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11
Q

Where is the active form of Vit D made?

A

made by proximal tubule epithelial cells via 1 alpha-hydroxylase

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12
Q

How does calcitriol affect the intestines?

A

increases calcium and phosphorus absorption –> increases serum Ca and Pi levels

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13
Q

How is most calcium excreted from the body?

A

90% excreted through feces

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14
Q

What things affect production/expression of calcitriol?

A

low Ca, low Pi, and high PTH –> upregulate 1 alpha hydroxylase expression

High calcium –> CaSR –> inhibits 1 alpha hydroxylase

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15
Q

How does insulin affect phosphate?

A

lowers serum Pi levels by shifting Pi into cells

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16
Q

How does ADH affect Ca reabsorption in the TAL?

A

increases NaCl reabsorption in TAL –> Ca follows and therefore also is reabsorbed more

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17
Q

What is the % filterability load of calcium?

What does this number mean?

A

60%

45% is ionized Ca and 15% is in diffusible complexes

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18
Q

What is the other name for vitamin D?

A

calcitriol

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19
Q

How does calcitriol affect the kidneys?

A

increases Ca and Pi reabsorption –> increases Serum levels

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20
Q

What does the Calcium sensing receptor do?

A

monitors calcium levels in IF (in kidney)

If plasma/IF Ca is high –> inhibits NKCC –> Ca can’t be reabsorbed paracellularly

21
Q

How does calcitonin affect bone?

The Kidneys?

A

bone: inhibits osteoclast-mediated resorption
kidney: promotes phosphate and excretion

22
Q

How is Mg reabsorbed in the distal tubule?

A

10%

electrical potential is primary driver

crosses apical border via TRPM6

basolater border cross = unknown

23
Q

How do ECF expansion and contraction affect Mg reabsorption?

A

expansion = decreases

contraction = increases

24
Q

How does acidemia affect Ca excretion?

Alkalemia?

A

acidemia = inhibits TRPV5 in DT –> increases Ca excretion

Alkalemia stimulates TRPV5 –> decreases Ca excretion

25
What does calbindin do?
binds influxing calcium (especially important in the distal tubule) and prevents excessive intracellular levels that might lead to apoptosis
26
How is Ca reabsorbed in the distal tubule?
DT has a **lumen negative** TEPD Ca reabsorption is active = crosses apical membrane via TRPV5 and basolateral via Na-Ca exchanger
27
How is Pi reabsorbed in the early PT?
via Na-Pi symporter on the apical surface or via Pi-H antiporter on apical surface basolateral surface = unknown transporter
28
How does volume contraction affect Ca reabsorption in the proximal tubule?
increases Ca reabsorption bc Na and Ca parallel each other (volume expansion has opposite effect)
29
What does PTH do, in general?
increases serum Ca and decreases serum Pi
30
Where is Mg reabsorbed in the nephron?
20% in Proximal tubule 70% thick ascending limb 5% distal tubule
31
How is Mg reabsorbed in the proximal tubule?
20% paracellularly following Na and water
32
How is Ca reabsorbed in the thick ascending limb?
primarily paracellular reabsorption parallels Na dependent upon TEPD (lumen positive charge)
33
What is the relationship btw calcium and hydorgen?
compete for binding sites on plasma albumin
34
How does PTH affect magnesium reabsorption?
increases reabsorption
35
Where in the kidney is Phosphate reabsorbed?
80% reabsorbed by PT
36
How do metabolic acidosis and alkalosis affect Mg reabsorption?
acidosis = decreases reabsorption alkalosis = increases reabsorption
37
Is Ca secreted in the kidney?
No!
38
What is the normal total plasma level of calcium?
5.0 mEq/L
39
What is the most important hormone that regulates Pi excretion? How does it work?
PTH inhibits the Na-Pi transporters and Na-H antiporter in apical membrane of PT cells uses cAMP to do so
40
How does alkalosis affect free calcium levels?
decreases free calcium (bc fewer H+ to bind albumin, so Ca binds to it) predisposes to hypocalcemic tetany acute alkalosis can induce symptoms mimicking hypocalcemia
41
How do thiazide diuretics affect the distal tubule?
inhibit Na reabsorption and stimulate TRPV5 to increase Ca reabsorption PTH, Vit D, and Calcitriol also stimulate TRPV5
42
How is Mg reabsorbed in the TAL?
70% paracellular depends on function of NKCC, which depends on lumen-positive voltage of TAL
43
Where is calcium stored in the body?
99% in bone 1% in ICF 0.1% in ECF
44
How does acidosis affect free calcium levels?
increases free calcium (H+ has used up all the binding sites on albumin)
45
How does calcitriol affect bone?
promotes osteoclastic-mediate bone resorption
46
How do loop diuretics affect Ca reabsorption?
inhibits NKCC --\> reduces magnitude of lumen-positive TEPD --\> reduces Ca paracellular reabsorption = lowers plasma Ca
47
How does increased Calcium intake affect Pi?
Increased Ca decreases Pi absorption in GI --\> decreases serum Pi
48

Renal-1 (14 decks)

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