Hormone. The chief cells of the parathyroids secrete a hormone called parathyroid hormone (PTH) or parathormone or also called Collip's hormone after the name of its discoverer.
- This hormone regulates the calcium and phosphate balance between the blood and other tissues.
- PTH inhibits collagen synthesis by osteoblasts and bone resorption by osteoclasts. It mobilises the release of calcium into the blood from the bones.
- PTH increases calcium absorption from the intestines. It increases calcium resorption from the nephrons (and inhibits phosphate resorption) of the kidneys.
- Parathormone regulates the metabolism of calcium and phosphate.
- Parathyroids are under the feeding back control of blood calcium level. A fall in blood calcium stimulates them to secrete parathormone, a rise in blood calcium inbihits parathormone secretion from them.