Phosphate Homeostasis

Question 1

What effect does low Phosphate have on the body?

Answer 1

Poor mineralisation of bone –> Rickets, osteomalacia, pain and fractures

Question 2

Give 3 dietary sources of phosphate?

Answer 2

1) Nuts/Seeds
2) Dairy
3) Protein

Question 3

What are the 3 regulators of phosphate?

Answer 3

1) FGF-23 (Main Regulator)
2) PTH
3) 1,25 dihydroxyvitD

Question 4

What effect does PTH have with phosphate homeostasis?

Answer 4

Increases phosphate absorption at intestine

Decreases phosphate reabsorption at the kidney

Question 5

What causes release of FGF-23?

Answer 5

1) High phosphate levels
2) PTH
3) 1,25 dihydroxyvitD

Question 6

What action does FGF-23 have?

Answer 6

1) Increases phosphate excretion at kidneys

2) Decrease 1-hydroxylase so less 1,25 dihydroxyvitD produced and less phosphate absorbed from intestine

Question 7

What role does PHEX have?

Answer 7

Breaks down FGF-23 when phosphate levels are low so (FGF V as phosphate levels ^)

Question 8

What happens if loss of function of PHEX?

Answer 8

FGF-23 not broken down, so phosphate levels in serum very low and urinary phosphate levels high (Osteomalacia as can’t mineralise bone)

Question 9

What effect would vitamin D deficiency have on FGF-23

Answer 9

Low phosphate levels as less absorbed from intestine and FGF-23 low as high phosphate levels triggers its action

Question 10

What is the role of Klotho?

Answer 10

Transmembrane protein modifying FGF receptors so specific for FGF-23