Calcitonin ppt.ppt for medical students.

Calcium

2. Introduction

Calcitonin is a hypocalcemic, 32 amino acid polypeptide
hormone.

It is secreted by parafollicular cells of thyroid gland.

It is antagonistic to parathyroid hormone

3. Thyroid Gland

4. Biosynthesis

Human Calcitonin has a molecular weight of 3500.


Two calcitonin genes, and located on 11
th
chromosome.


Two different mRNA molecules are transcribed from gene.


One is translated into the precursor of calcitonin, other
massage is translated into alternative product CGRP.

CGRP has cardiovascular actions and may serve as
neurotransmitter

5. Physiology
It is a single chain peptide with disulfide bridge linking the
cysteine residues in positions one and seven.
Structural features are essential for biological activity.

Residues in middle portion are more variable

6. Regulation of Secretion

Secretion of calcitonin is regulated by plasma calcium concentration.


Multiple forms of calcitonin are found in plasma – high molecular weight
aggregates or cross linked product.


The circulating concentration of calcitonin are
- 15 pgm/ml (male)
- 10 pgm/ml (female)

Circulating half life is about 10 minutes.


Abnormally elevated levels of calcitonin are characteristic of thyroid C-cell
Hyperplasia and Medullary Thyroid Carcinoma.


Secretion is also stimulated by catecholamines, glucagon, gastrin and
cholecystokinin

7. Mechanism of action and receptors

Actions are mediated by calcitonin receptor (CTR).

CTR situated an plasma membrane like other peptide
hormone.


It occurs through adenylyl cylase cyclic AMP second
messanger system pathway.

8. Functions of Calcitonin

9. Plasma Ca
++
And Its Regulation by
Calcitonin

The normal value of calcium is about 9.4 mg/dl which is equivalent to
2.4 mmol Calcium per liter.

Important role in many physiological processes including contraction of
skeletal, cardiac and smooth muscles; blood clotting and transmission of
nerve impulses.

Extracellular calcium is only about 0.1% of total body calcium.

About 1% is in cells and the test is stored in bones.


This precise control of Calcium ions in plasma is maintained by
1- Parathyroid hormone
2- Calcitonin
3- Calcitriol (Vitamin D)

10. Actions

Hypocalcemic and hypophosphataemic effects.


Caused predominantly by direct inhibtion of osteoclastic bone
reabsorption.


Depressed bone reabsorption reduces urinary excretion of ca
++
. Mg
and hydroxyproline.

Other effects

Immediate effect is to decrease absorptive activities of osteoclasts.

The secondary and prolonged effect of calcitonin is to decrease the
formation of new osteoclast

11. Diagnostic Use

Calcitonin is a sensitive and specific marker for the
presence of medullary thyroid carcinoma (MTC).


MTC can be hereditary (25%) or sporadic (75%), and is
present in all patients with the multiple endocrine
neoplasia type 2 (MEN2) syndromes

12. Therapeutics Use

Calcitonin lowers plasma ca
++
and
phosphate con. In patients with
hypercalcemia.

A rise in serum calcium above 12.5
mg/dl produces weakness, loss of
muscle tone and thirst.



Effect results from decreased bone
resorption and is greater in patients
in whom bone turnover rates are
high

13. Salmon calcitonin is used for the treatment
of:

Postmenopausal osteoporosis

Hypercalcemia

Paget’s disease

Bone metastases

Phantom limb pain

14. Osteoporosis

15. Paget’s disease