Bone metabolism is significantly influenced by the activity of osteoblasts and osteoclasts, the calciotropic hormones 1,25-dihydroxy vitamin D, parathyroid hormone and calcitonin, as well as the extracellular calcium concentration.
Parathyroid hormone (PTH) is a peptide hormone which is synthesised in the parathyroid glands. The main function of PTH is to increase the concentration of calcium in the blood plasma. Intact PTH (iPTH) is the biologically active form and is secreted when the calcium level is low. iPTH is eliminated from the circulation after a half-life of less than four minutes.