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

1. REGULATION OF
PLASMA-CALCIUM
LEVEL.
G R O U P : D
S H R I YA S M A H A R J A N

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
Calcitoni
n

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.

7. 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+

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

9. 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.

10. 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.

11.  Originally synthesized as:
 The release of PTH is under negative
feedback of serum Calcium level.
PreproPTH ProPTH PTH

12. Mechanism of PTH
PTH
Receptor
protein
Activates
adenylat
e cyclase
Release
of cAMP
Increases
intracellul
ar
Calcium
level
BIOLOGICAL
ACTIONS

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

14. 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.

15. 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.

16. 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.

17. SUMMARY

18. Calcitriol
SUMMARY

19. THANK YOU