Calcium Homeostasis

Question 1

What hormones regulate calcium levels?

Answer 1

1. Calcitonin: Released from C cells of the parathyroid gland when Ca2+ levels are too high.
   - Inhibits osteoclast activity in the bones and renal reabsorption of Ca2+ + phosphate.
2. Parathyroid hormone (PTH): Stimulated by chief cells in the parathyroid gland when Ca2+ levels are too low.
   - Increases bone reabsorption and the synthesis of 1,25-dihydroxyvitamin D3 + calcium reabsorption (both in the kidneys).
   - PTH and calcitonin act as feedback loops for one another.
3. 1,25-dihydroxyvitamin D3 (calcitriol): Formed from dietary vitamin D and cholesterol.
   - Calcitriol is the active form of vitamin D which absorbs Ca2+, it acts like a steroid hormone by binding to specific nuclear receptors of DNA producing calbindin.
   - This increases phosphate uptake and the calcification of bones.

Question 2

What are the effects of bad calcium regulation.

Answer 2

1. Hypocalcaemia: Convulsions, arrhythmias
   - Caused by hyperthyroidism or lack of UV.
   - When combined with lack of vitamin D it can lead to poor bone formation and rickets.
2. Hypercalcaemia: Abdominal pains, dehydration or anxiety.
   - Caused by excessive release of PTH or to much vitamin D in the diet.