Calcitonin

Book recommended: Medical Physiology by Jaypee

1. Calcitonin Danish Hassan Lecturer, University of sargodha

2. Calcitonin Secreted by the parafollicular cells or clear cells (C cells), situated amongst the follicles in thyroid gland. In lower animals, the parafollicular cells.

3. Chemistry and Synthesis Calcitonin is a polypeptide chain with 32 amino acids. Its molecular weight is about 3,400. It is synthesized from procalcitonin

4. Plasma Level and Half-life Plasma level of calcitonin is 1 to 2 ng / dL . It has a halflife of 5 to 10 minutes

5. Metabolism Calcitonin is degraded and excreted by liver and kidney

6. Actions Of Calcitonin Plays an important role in controlling the blood calcium level. It decreases the blood calcium level and thereby counteracts parathormone . Calcitonin reduces the blood calcium level by acting on: Bones Kidneys Intestine

7. On bones Calcitonin stimulates osteoblastic activity and facilitates the deposition of calcium on bones. At the same time, it suppresses the activity of osteoclasts and inhibits the resorption of calcium from bones. It inhibits even the development of new osteoclasts in bones

8. On kidney Increases excretion of calcium through urine, by inhibiting the reabsorption from the renal tubules

9. On intestine Prevents the absorption of calcium from intestine into the blood.

10. On Blood Phosphate Level With respect to calcium, calcitonin is an antagonist to PTH. But it has similar actions of PTH, with respect to phosphate. It decreases the blood level of phosphate by acting on: Bones Kidneys

11. On bones Inhibits the resorption of phosphate from bone and stimulates the deposition of phosphate on bones.

12. On kidney Calcitonin increases the excretion of phosphate through urine, by inhibiting the reabsorption from renal tubules

13. Regulation Of Calcitonin Secretion High calcium content in plasma stimulates the calcitonin secretion through a calcium receptor in parafollicular cells. Gastrin also is known to stimulate the release of calcitonin .