Bone Mineral Homeostasis

Question 1

What factors regulate bone mineral homeostasis?

Answer 1

PTH, vitamin D, calcitonin

Question 2

What are the actions of PTH?

Answer 2

Increases plasma calcium by:
- increasing calcitriol (vitamin D) synthesis
- mobilising calcium from bone
reducing renal calcium excretion
- favours bone resorption by osteoclasts

Increases osteoblast and osteoclast activity

Question 3

What are the actions of calcitonin?

Answer 3

Binds to receptor on osteoclasts which inhibits its action and decreases resorption from bone
- inhibits calcium reabsorption in kidney

Decreases osteoclast activity

Question 4

What are the actions of calcitriol?

Answer 4

Increase plasma calcium

- increased intestinal absorption, decreased renal excretion and increased osteoclast activity

Question 5

What are the roles of calcium in the body?

Answer 5

• intracellular signal
• structural functions (contribute physical strength to bone matrix and help hold cells together at tight junctions)
• cofactor in blood coagulation
• required for normal excitability of neurons and muscle

Question 6

When is PTH secreted?

Answer 6

In response to low calcium, functions to increase plasma calcium and decrease plasma phosphate

Question 7

When is calcitonin secreted?

Answer 7

When plasma calcium is high, decreases plasma calcium and phosphate
NO ROLE NORMALLY, only works with extreme hypercalcaemia