Ca2+ and phosphate regulation

Question 1

What organs are involved in vit D synthesis?

Answer 1

Skin
Liver
Kidney

Question 2

What is the 1st stage of vit D synthesis?

Answer 2

7-dehydrocholesterol —> vit D3, using UVB photons

Question 3

Where is vit D3 found?

Answer 3

In skin

Question 4

Where is vit D2 found?

Answer 4

From foods (salmon, cod liver oil, mushrooms)

Question 5

What is the 2nd stage of vit D synthesis?

Answer 5

Vit D3 —> 25 (OH) Vit D3, using 25 hydroxylase

Question 6

What is the 3rd stage of vit D synthesis?

Answer 6

25 (OH) Vit D3 —> 1, 25 (OH)2 Vit D3 (calcitriol), using 1 alpha hydroxylade

Question 7

What is another name for activated vit D?

Answer 7

Calcitriol

Question 8

What does PTH do? (3)

Answer 8

Kidneys:
Increased Ca2+ reabsorption (decreased phosphate reabsorption)
Activated vit D synthesis
Bone:
Increased bone resorption

Question 9

What does activated vit D do?

Answer 9

Increases Ca2+ absorption from the GI tract

Question 10

What does FGF-23 do? How? (3)

Answer 10

Decreases serum phosphate
Kidneys:
Decreases activated vit D synthesis
Decreases phosphate reabsorption

Question 11

PTH is secreted in response to what? (2)

Answer 11

Low serum Ca2+

High serum phosphate

Question 12

What is the antagonist for PTH?

Answer 12

Calcitonin

Question 13

What is the antagonist for FGF-23?

Answer 13

PHEX

Question 14

What does calcitonin do? (3)

Answer 14

• Decreases bone resorption
• Decreases Ca2+ reabsorption (kidneys)
• Increases phosphate reabsorption (kidneys) thus decreases Ca2+

Question 15

In which part of the gut is Ca absorbed actively? (2)

Answer 15

Duodenum

Jejunum

Question 16

In which part of the gut is Ca passively absorbed? (2)

Answer 16

Ileum

Colon

Question 17

In which part of the nephron is Ca passively reabsorbed? (2)

Answer 17

PCT

Ascending LoH

Question 18

In which part of the nephron is Ca actively reabsorbed?

Answer 18

DCT