# Human hormones

## Parathyroid hormone

Parathyroid hormone (parathyrin, PTH) is a linear polypeptide of 84 amino acids and a molecular mass of 9,500 $There$. Between the human parathyroid hormone and that from cattle or pigs there are differences in the amino acid sequence in 5-6 positions. Partial synthesis products from 34 amino acids are also biologically active.

PTH causes a number of processes related to mineral metabolism. It increases the mobilization of the calcium bound in the bone as well as the absorption of calcium from the intestine and absorption from the kidneys. The excretion of phosphate in the urine is also increased by PTH. In osteoclasts, the PTH stimulates the membrane-bound adenylate cyclase and the influx of calcium ions. Calcitonin is the antagonist of PTH; the two hormones are important for regulating the calcium and phosphate balance in the body.

### PTH and vitamin D.

PTH causes the release of a hydroxylase (calcidiol-1-monooxygenase, EC 1.14.13.13) in the kidneys, which converts 25-hydroxy-cholecalciferol (calcidiol, calcifediol) into the 1α, 25-dihydroxy derivative calcitriol. This activates vitamin D.3-Hormone, which in turn regulates the calcium level in the blood. Tumors release the PTH-related protein (PTHrP made up of 141 amino acids), which cross-reacts with the PTH receptors in the bones and kidneys, thereby increasing the calcium level in the blood. However, PTHrP is also produced by normal fetal and adult tissue, where it is responsible for smooth muscle tone, organ development and calcium transport through the epithelia.