Calcitonin
Hormone · 32 amino acids Acts on osteoclast
A 32-amino-acid peptide from thyroid C cells that inhibits osteoclastic resorption directly and increases urinary calcium excretion. It opposes PTH, but has little part in day-to-day human calcium homeostasis: neither its absence after thyroidectomy nor its gross excess in medullary carcinoma disturbs serum calcium.
Traced from the start
Detail
- Source and structure
- Thyroid parafollicular C cells; 32 amino acids from the CALCA gene, whose alternative splicing also yields calcitonin gene-related peptide
- Bone action
- The calcitonin receptor sits on the osteoclast itself, one of the few hormones acting directly on osteoclasts rather than through osteoblasts; ruffled-border resorption stops within minutes
- Renal action
- Reduces tubular reabsorption of calcium and of phosphate
- Physiological weight
- Minor in adults; more relevant to skeletal protection in pregnancy and lactation, and much more important in other species
When it goes wrong
Severe symptomatic hypercalcaemia needing rapid control
Salmon calcitonin lowers calcium within hours as a bridge to a bisphosphonate, but tachyphylaxis develops within about 48 hours
Medullary thyroid carcinoma
Serum calcitonin is the marker for diagnosis and recurrence, while serum calcium stays normal
Practise this structure
4 questions in the bank tagged Thyroid.
A 42-year-old man was treated with radioactive iodine for Graves disease three days ago. He now reports dry mouth and painful swelling in front of both ears, wo…
Clinical rotations · common
A 34-year-old woman taking carbimazole for Graves disease presents with fever, malaise and two painful oral ulcers. She has a temperature of 38.7°C and mild cer…
Clinical rotations · common
A 35-year-old woman has palpitations and a 9 kg weight loss over 3 months. Her free thyroxine is 48 pmol/L (reference 10–22 pmol/L), TSH is less than 0.01 mIU/L…
Mechanisms of disease · common
A 38-year-old woman presents with two weeks of pain in the front of her neck radiating to her jaw, together with palpitations, sweating and 2 kg of weight loss.…
Clinical rotations · common