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.

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

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

6.  Metabolism
 Calcitonin is degraded and excreted by liver and
kidney

7.  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

8.  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

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

10.  On intestine
 Prevents the absorption of calcium from intestine
into the blood.

11.  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:
1. Bones
2. Kidneys

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

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

14.  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.