Parathyroid hormone regulates the body’s calcium levels. It controls the calcium in our blood and bones. The thyroid gland regulates the body’s metabolism and has no effect on calcium levels while parathyroid glands control calcium levels and have no consequence on metabolism. Role of the parathyroid hormone in the regulation of blood Ca++:
(1) Bone
(i) Rapid phase;
(ii) Slow phase;
- Activates the osteoclastic cells →
- Activated osteoclasts then decrease deposition of a Ca++ salt on bone →
- This, in turn, increases the blood Ca++ level.
(2) Kidney (main site)
↑ Ca+ reabsorption from distal tubule,
↓ PO43- reabsorption from PT.
(3) Intestine By forming (1,25 dihydroxy-cholecalciferol)
- PTH →↑ 1,25-(OH)2–D3,
- Ca2+ absorption from intestine.
Fig: Parathyroid Hormone in the regulation of Calcium Metabolism
Effect of parathyroidectomy: Parathyroid hormone (PTH) has a very influential control over the cells of your bones by causing them to release their calcium into the bloodstream.
PTH is necessary for life –
(A) A steady decline in blood Ca++ which, results into –
(i) Neuromuscular hyperexcitability,
(ii) Hypocalcemic tetany.
(B) Sometimes phosphate level may (as ↓ plasma Ca2+) increase.
