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Renal > Renal Calcium Phosphorus Magnesium Balance > Flashcards

Renal Calcium Phosphorus Magnesium Balance Flashcards

1
Q

What is the main reservoir of body calcium and phosphorus?

A

Bone and intracellular

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2
Q

To what ion is phosphorus regulation linked?

A

Calcium

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3
Q

How is calcium and phosphorus maintained in the body?

A

GI, bone, kidneys

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4
Q

What excretes the most calcium?

A

Bowel

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5
Q

What three hormones regulate calcium plasma levels?

A
  1. Parathyroid hormone
  2. Vitamin D3 - calcitriol
  3. Fibroblast growth factor- 23
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6
Q

What produces parathyroid hormone?

A

Parathyroid glands

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7
Q

When is PTH produced?

A

In response to..

  1. Low free plasma calcium levels
  2. High plasma phosphate levels
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8
Q

When is production of PTH inhibited?

A

In response to…

  1. High free plasma calcium levels?
  2. High calcitriol/Vitamin D3 levels
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9
Q

On which organs does PTH work?

A

Bones & kidneys

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10
Q

What effect does PTH have on bone?

A
  1. Increase calcium release

2. Increase phosphate release

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11
Q

What effect does PTH have on the kidneys?

A
  1. Increase calcium reabsorption
    2, Increase phosphate excretion
  2. Increase calcitriol production (to repay calcium debt from bone)
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12
Q

What three factors activate the kidney to produce calcitriol?

A
  1. Low serum calcium
  2. Low serum phosphate
  3. High PTH
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13
Q

What three organs are involved in calcitriol synthesis?

A
  1. Skin
  2. Liver
  3. Kidney
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14
Q

What are the effects of calcitriol?

A
  1. Suppress PTH release from parathyroid glands
  2. Increase absorption of calcium and phosphate from GI
  3. Increase calcium and phosphate release from bone
  4. Increase calbindin-D and TRPV5 expression in the distal tubule to facilitate increased calcium reabsorption
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15
Q

What secretes FGF-23?

A

Bone osteoclast

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16
Q

When is FGF-23 secreted?

A

In response to …

  1. Elevated serum phosphate
  2. Elevated calcitriol levels
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17
Q

What are the actions of FGF-23

A
  1. Increase phosphorus secretion via kidneys
  2. Decrease PTH
  3. Decrease calcitriol production
18
Q

Where is phosphorus reabsorbed in the nephron?

A

Na-phosphate co-transporter in the proximal convoluted tubule

19
Q

What occurs in response to high plasma phosphate?

A
  1. Parathyroid glands produce PTH

2. Bone produces FGF-23 (most important)

20
Q

In what conditions is hyperphosphatemia seen?

A
  1. Renal failure
  2. Hypoparathyroidism
  3. Vitamin D excess
21
Q

In what conditions is hypophosphatemia seen?

A
  1. Dietary deficiency
  2. Hyperparathyroidism
  3. Vitamin D deficiency
  4. Proximal Tubule Diseases
22
Q

How does calcium get reabsorbed in the proximal convoluted tubule?

A

Paracellularly via Claudin 2 Calcium Channel

23
Q

What drives calcium reabsorption?

A

Sodium reabsorption

24
Q

What class of diuretic will increase calcium reabsorption in the proximal convoluted tubule?

A

Thiazide diuretics

25
Q

What class of diuretics decrease calcium reabsorption in the thick ascending limb of the loop of henle?

A

Loop diuretics

26
Q

How does the basolateral calcium/magnesium sensing receptor regulate calcium absorption in the ascending limb of the loop of henle?

A

When interstitial calcium levels rise, calcium/magnesium sensing receptor will shut down ROMK leading to decreased potassium cycling therefore decreased sodium absorption via NKCC2 therefore decreased calcium absorption

27
Q

How does calcium absorption in the distal tubule differ than other sites?

A

Calcium moves via TRPV5 channel rather than trancellularly - binds calbindin-D to maintain gradient

28
Q

How does calcitriol affect calcium absorption in the distal tubule?

A

Increases calcium reabsorption by increasing TRPV5 and calbindin-D

29
Q

Most common cause of hypercalcemia

A

Primary hyperparathyroidism (malignancy in 90%)

30
Q

Three causes of hypercalcemia

A
  1. Primary hyperparathyroidism
  2. Loss of function mutation in calcium sensing receptors
  3. Thiazide diuretics
31
Q

Causes of hypocalcemia

A
  1. Hypoparathyroidism
  2. Vitamin D deficiency
  3. Loop diuretics
  4. Gain of function in calcium sensing receptors
32
Q

Where is the body’s store of magnesium?

A

Bones

33
Q

Which ion is not under any hormonal regulation?

A

Magnesium

34
Q

At what segment of the nephron is most of the magnesium reabsorbed?

A

Thick ascending limb of the loop of henle

35
Q

How is Mg absorbed in the thick ascending loop of henle?

A

Paracellulary via claudin 16, like Ca.

36
Q

How is Mg reabsorbed in the distal tubule?

A

Via TRPM6 channel

37
Q

Three causes of hypomagnesemia?

A
  1. Renal tubular defects
  2. Diuretics
  3. Malabsorption
38
Q

Two causes of hypermagnesemia?

A
  1. Renal failure

2. Overdose

39
Q

How much calcium is absorbed by the proximal convoluted tubule?

A

65%

40
Q

How does acid/base balance affect calcium absorption

A

Intracellular alkalosis promotes TRPV5 insertion and increased calcium reabsorption - acidosis = internalization of TRPV5 = reduced calcium reabsorption

Renal (11 decks)

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