Parathyroid hormone (PTH) secreted from four parathyroid gland situated behind the thyroid gland, functions in regulating ionised calcium and phosphate within the reference range by stimulating specific receptor-mediated responses in cells throughout the body.
- parathyroid hormone secretion is increased in response to a decrease in circulating ionised calcium via calcium-sensing receptor (CaSR) located on the surface of the chief cells in parathyroid gland. This in turn results in restoring the normal circulating calcium concentration by
- receptor-mediated tubular reabsorption of calcium from kidney
- stimulation of osteoclast resorption to release skeletal calcium from bone
- increasing activity of renal 1 hydroxylase, resulting in production of 1,25-dihyroxyvitamin D and increasing calcium absorption from bowel (1)
Hyperparathyroidism is a condition in which there is excessive secretion of parathyroid hormone.
Hyperparathyroidism can be
- primary - when one or more parathyroid glands produce excess PTH
- secondary - PTH is secreted excessively in response to decreased ionised calcium (due to kidney liver or bowel disease)
- tertiary - autonomous secretion of PTH as a result of longstanding chronic kidney disease (1)
Clinically, there may be effects of both hypercalcaemia and of hypocalcaemia.
Investigations should include serum calcium and phosphate, and parathyroid hormone.
Treatment depends on the cause.