Calcium and bone physiology

Question 1

What is the effect of PTH on the kidney?

Answer 1

Excretion of phosphate

Question 2

What is the effect of PTH on vitamin D?

Answer 2

PTH is required to have the proximal tubules in the kidney convert 25,-hydroxy vitamin D to 1,25-hydroxy vitamin D

Question 3

What is the effect of PTH on bone?

Answer 3

1. Stimulates osteoclast activity 2. Binds to receptors on osteoblasts and causes them to release OPGL, which activates receptors on preosteoclasts

Question 4

Which form of calcium is filtered in the glomerulus? Which form is present in 50% of total calcium?

Answer 4

1. 20% of the ionized form 2. Free or ionized

Question 5

What is the role of OPGL and OPG?

Answer 5

1. OPGL - bone resorption 2. OPG - acts as decoy to inhibit bone resorption

Question 6

Where are vitamin D precursors transformed into vitamin D3? Where is vitamin D3 converted to its active form?

Answer 6

1. Skin (D3), liver (25-hydroxy) 2. Proximal tubule of kidney (1,25-hydroxy)

Question 7

What are the causes and symptoms of 1) hyperparathyroidism, 2) hypoparathyroidism, and 3) pseudohypoparathyroidism?

Answer 7

1. Adenoma - hypercalcemia, hypophosphatemia , kidney stones, weak bones, constipation, excessive urination 2. Parathyroidectomy - steady decline in calcium, neuromuscular hyperexcitability, hypocalcemic tetany 3. PTH receptor abnormality - decrease in tissue response to PTH

Question 8

How / why can renal disease cause osteomalacia?

Answer 8

“Renal rickets” - due to failure of damaged kidney to produce the active form of vitamin D

Question 9

How does alkaline pH affect protein bound calcium? Acidic pH?

Answer 9

1. Alkaline pH - more calcium bound to protein 2. Acidic pH - less bound to protein