parathormooni

Parathormooni, also known as parathyroid hormone (PTH), is a peptide hormone produced by the chief cells of the parathyroid glands. It is a key regulator of calcium and phosphate homeostasis in humans. Human PTH consists of 84 amino acids; the N-terminal region (PTH 1-34) mediates most biological effects and serves as the active fragment in some therapies.

Secretion is controlled primarily by serum ionized calcium through the calcium-sensing receptor (CaSR). Low calcium stimulates PTH release, while high calcium inhibits it. PTH also responds to phosphate levels and, to a lesser extent, to magnesium status.

Actions: In bone, PTH stimulates osteoblasts to express RANKL, promoting osteoclast formation and bone resorption, which releases calcium and phosphate into the bloodstream. In the kidney, PTH increases calcium reabsorption in distal tubules and decreases phosphate reabsorption in proximal tubules, increasing phosphate excretion. It also stimulates renal 1-alpha-hydroxylase, raising production of calcitriol (1,25-dihydroxyvitamin D3), which enhances intestinal absorption of calcium and phosphate.

Physiological role: Through these effects, parathormooni maintains serum calcium within a narrow range and coordinates calcium and phosphate balance, particularly during growth, pregnancy, and bone remodeling. It interacts with vitamin D signaling and calcitonin in a complex regulatory network.

Clinical significance: Abnormal PTH secretion underlies disorders such as primary hyperparathyroidism (excess PTH with hypercalcemia), secondary hyperparathyroidism (often due to chronic kidney disease), and hypoparathyroidism (insufficient PTH with hypocalcemia). Diagnosis commonly involves measuring intact PTH alongside calcium levels.

Therapeutic notes: Recombinant PTH fragments (for example, teriparatide, PTH 1-34) are used in osteoporosis treatment and in some cases of hypoparathyroidism under medical supervision.