- 32 amino acid peptide derived from procalcitonin
- synthesised by parafollicular (C) cells of the thyroid gland
- stimulation for secretion is elevated calcium levels and GI hormones,
mainly gastrin
- clearance occurs in kidney, liver and possibly bone
- in bone causes down-regulation of osteoclastic activity eventually
leading to complete down-regulation of bone turnover
- within days inhibitory effect lost due to down-regulation of calcitonin
receptors in bone (escape phenomenon)
- in kidney leads to increase of renal excretion of calcium, phosphate,
sodium, potassium and magnesium
- may increase 1,25-(OH)2D production by kidney
- acts by increasing cAMP levels in target cells
- used in treatment of Paget's disease
- very little effect of over or under production of calcitonin
1.1.3 Calcitonin — protection against hypercalcaemia,
hyperphosphataemia
| origin thyroid C cells, relation to neural crest |
|
| stimulus: increased plasma calcium |
|
| actions: in bone (and gut) to normalise raised plasma
calcium; |
calcitonin "escape" |
| "dysfunction": lack of major effect of
calcitonin-secreting tumours. |
|
|