Role of PTH , Calcitonin , Calcitriol in Regulation of Plasma-Calcium Level

Contents :
~Plasma Calcium level
~Calcitriol
~Parathyroid hormone
~Calcitonin
~Summary

1. REGULATION OF PLASMA-CALCIUM LEVEL. GROUP: D Shriyas Maharjan

2. OUTLINE Plasma Calcium level Calcitriol Parathyroid hormone Calcitonin Summary

3. PLASMA CALCIUM LEVEL Normal concentration of plasma or serum Ca is 9-11mg/dl. (Narrow range) 2+

4. Factors Regulating Plasma Ca Level Calcitriol PTH Calcitonin

5. CALCITRIOL It is an active form of VITAMIN- D (1,25-Dihydroxycholecalciferol). Its action is similar to steroid hormones. It binds to a receptor in the cytosol and the complex acts on DNA to stimulate the synthesis of Calcium binding protein.

6. Action On Small Intestine Activates synthesis of CaT (Ca transporter) and Calbindin D. Calcitriol increases the intestinal absorption of calcium as well as phosphate. Calcium absorption: In duodenum. Phosphate absorption: In jejunum and ileum. 2+

7. Action On Bone AT NORMAL LEVELS: Stimulates osteoblasts ; increases concentration of ALP and osteocalcin . AT HIGH LEVELS: Increases bone resorption .

8. Action On Kidney Increases the tubular reabsorption of Calcium and Phosphate. ACTION ON PARATHYROID GLAND Increases the concentration of calcium sensing receptors ( CaSR ). Parathyroid glands are sensitized to calcium inhibition.

9. PARATHYROID HORMONE PTH is secreted by 2 pairs of parathyroid glands that are closely associated with the thyroid glands. Synthesis : By chief cell of parathyroid gland It is a single chain polypeptide containing 84 amino acids.

10. Originally synthesized as: The release of PTH is under negative feedback of serum Calcium level.

11. Mechanism of PTH

12. Action on Bone Demineralization is brought out by PTH stimulated increased activity of enzymes: COLLAGENASE and PYROPHOSPHATASE . Increase of serum calcium level occurs.

13. Action On Kidney PTH increase the calcium reabsorption from DCT Decreases reabsorption of phosphate. Activates 1 - α - hydroxylase enzyme required for the synthesis of calcitriol . Action On Intestine The action of PTH is indirect, since it promotes the synthesis of calcitriol .

14. CALCITONIN It is a peptide containing 32 amino acids. Secreted by parafollicular cells of thyroid gland. It shows antagonistic action to that of PTH on calcium metabolism. Used pharmacologically as an inhibitor of bone resorption .

15. Action On Bone It promotes calcification by increasing the activity of osteoblast . It decreases resorption of bone Action On Kidney It increases the excretion of calcium in urine .

16. SUMMARY

17. Calcitriol SUMMARY

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