Renal Calcium Phosphorus Magnesium Balance

Question 1

What is the main reservoir of body calcium and phosphorus?

Answer 1

Bone and intracellular

Question 2

To what ion is phosphorus regulation linked?

Answer 2

Calcium

Question 3

How is calcium and phosphorus maintained in the body?

Answer 3

GI, bone, kidneys

Question 4

What excretes the most calcium?

Answer 4

Bowel

Question 5

What three hormones regulate calcium plasma levels?

Answer 5

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

Question 6

What produces parathyroid hormone?

Answer 6

Parathyroid glands

Question 7

When is PTH produced?

Answer 7

In response to..

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

Question 8

When is production of PTH inhibited?

Answer 8

In response to…

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

Question 9

On which organs does PTH work?

Answer 9

Bones & kidneys

Question 10

What effect does PTH have on bone?

Answer 10

1. Increase calcium release

2. Increase phosphate release

Question 11

What effect does PTH have on the kidneys?

Answer 11

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

Question 12

What three factors activate the kidney to produce calcitriol?

Answer 12

1. Low serum calcium
2. Low serum phosphate
3. High PTH

Question 13

What three organs are involved in calcitriol synthesis?

Answer 13

1. Skin
2. Liver
3. Kidney

Question 14

What are the effects of calcitriol?

Answer 14

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

Question 15

What secretes FGF-23?

Answer 15

Bone osteoclast

Question 16

When is FGF-23 secreted?

Answer 16

In response to …

1. Elevated serum phosphate
2. Elevated calcitriol levels

Question 17

What are the actions of FGF-23

Answer 17

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

Question 18

Where is phosphorus reabsorbed in the nephron?

Answer 18

Na-phosphate co-transporter in the proximal convoluted tubule

Question 19

What occurs in response to high plasma phosphate?

Answer 19

1. Parathyroid glands produce PTH

2. Bone produces FGF-23 (most important)

Question 20

In what conditions is hyperphosphatemia seen?

Answer 20

1. Renal failure
2. Hypoparathyroidism
3. Vitamin D excess

Question 21

In what conditions is hypophosphatemia seen?

Answer 21

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

Question 22

How does calcium get reabsorbed in the proximal convoluted tubule?

Answer 22

Paracellularly via Claudin 2 Calcium Channel

Question 23

What drives calcium reabsorption?

Answer 23

Sodium reabsorption

Question 24

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

Answer 24

Thiazide diuretics

Question 25

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

Answer 25

Loop diuretics

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

How does calcitriol affect calcium absorption in the distal tubule?

Answer 28

Increases calcium reabsorption by increasing TRPV5 and calbindin-D

Question 29

Most common cause of hypercalcemia

Answer 29

Primary hyperparathyroidism (malignancy in 90%)

Question 30

Three causes of hypercalcemia

Answer 30

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

Question 31

Causes of hypocalcemia

Answer 31

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

Question 32

Where is the body's store of magnesium?

Answer 32

Bones

Question 33

Which ion is not under any hormonal regulation?

Answer 33

Magnesium

Question 34

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

Answer 34

Thick ascending limb of the loop of henle

Question 35

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

Answer 35

Paracellulary via claudin 16, like Ca.

Question 36

How is Mg reabsorbed in the distal tubule?

Answer 36

Via TRPM6 channel

Question 37

Three causes of hypomagnesemia?

Answer 37

1. Renal tubular defects 2. Diuretics 3. Malabsorption

Question 38

Two causes of hypermagnesemia?

Answer 38

1. Renal failure | 2. Overdose

Question 39

How much calcium is absorbed by the proximal convoluted tubule?

Answer 39

65%

Question 40

How does acid/base balance affect calcium absorption

Answer 40

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