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calcitonin

calcitonin

Introduction

Chemistry:

  • Calcitonin is a 34AA polypeptide (MW 3500) synthesised and secreted by the parafollicular (or clear cells) cells of the thyroid and in small amounts elsewhere:
  • “Calcitonin gene” ⇒ preprocalcitonin (thyroid) ⇒ calcitonin ⇒ katacalcin
    • ⇒ calcitonin-gene related peptide (G\CGRP) (brain);
  • Plasma half life = 10 min.

Regulation:

Calcitonin secretion:

Actions:

Calcitonin receptors in bone & kidneys:

  • inhibits osteoclasts & bone resorption;
  • increases Ca renal excretion;
  • THUS: ⇒ decr. [Ca] & decr. [P]

Disease:

  • Thyroidectomy does not significantly alter bone density or [Ca] as long as parathyroid glands are intact ⇒ exact physiologic role of calcitonin is still uncertain;
    • ? protects agains post-prandial hypercalcaemia;
    • ? protects from XS Ca loss in pregnancy and lactation;
  • Medullary Ca thyroid causes very high [calcitonin] but no symptoms due to the hormone!
calcitonin.txt · Last modified: 2009/09/24 17:29 (external edit)