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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
Q

What does calbindin do?

A

binds influxing calcium (especially important in the distal tubule) and prevents excessive intracellular levels that might lead to apoptosis

26
Q

How is Ca reabsorbed in the distal tubule?

A

DT has a lumen negative TEPD

Ca reabsorption is active = crosses apical membrane via TRPV5 and basolateral via Na-Ca exchanger

27
Q

How is Pi reabsorbed in the early PT?

A

via Na-Pi symporter on the apical surface

or via Pi-H antiporter on apical surface

basolateral surface = unknown transporter

28
Q

How does volume contraction affect Ca reabsorption in the proximal tubule?

A

increases Ca reabsorption

bc Na and Ca parallel each other

(volume expansion has opposite effect)

29
Q

What does PTH do, in general?

A

increases serum Ca and decreases serum Pi

30
Q

Where is Mg reabsorbed in the nephron?

A

20% in Proximal tubule

70% thick ascending limb

5% distal tubule

31
Q

How is Mg reabsorbed in the proximal tubule?

A

20%

paracellularly following Na and water

32
Q

How is Ca reabsorbed in the thick ascending limb?

A

primarily paracellular

reabsorption parallels Na

dependent upon TEPD (lumen positive charge)

33
Q

What is the relationship btw calcium and hydorgen?

A

compete for binding sites on plasma albumin

34
Q

How does PTH affect magnesium reabsorption?

A

increases reabsorption

35
Q

Where in the kidney is Phosphate reabsorbed?

A

80% reabsorbed by PT

36
Q

How do metabolic acidosis and alkalosis affect Mg reabsorption?

A

acidosis = decreases reabsorption

alkalosis = increases reabsorption

37
Q

Is Ca secreted in the kidney?

A

No!

38
Q

What is the normal total plasma level of calcium?

A

5.0 mEq/L

39
Q

What is the most important hormone that regulates Pi excretion? How does it work?

A

PTH

inhibits the Na-Pi transporters and Na-H antiporter in apical membrane of PT cells

uses cAMP to do so

40
Q

How does alkalosis affect free calcium levels?

A

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
Q

How do thiazide diuretics affect the distal tubule?

A

inhibit Na reabsorption and stimulate TRPV5 to increase Ca reabsorption

PTH, Vit D, and Calcitriol also stimulate TRPV5

42
Q

How is Mg reabsorbed in the TAL?

A

70%

paracellular

depends on function of NKCC, which depends on lumen-positive voltage of TAL

43
Q

Where is calcium stored in the body?

A

99% in bone

1% in ICF

0.1% in ECF

44
Q

How does acidosis affect free calcium levels?

A

increases free calcium

(H+ has used up all the binding sites on albumin)

45
Q

How does calcitriol affect bone?

A

promotes osteoclastic-mediate bone resorption

46
Q

How do loop diuretics affect Ca reabsorption?

A

inhibits NKCC –> reduces magnitude of lumen-positive TEPD –> reduces Ca paracellular reabsorption = lowers plasma Ca

47
Q

How does increased Calcium intake affect Pi?

A

Increased Ca decreases Pi absorption in GI –> decreases serum Pi

48
Q
A

Renal-1 (14 decks)

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