PTH

PTH, also known as parathormone or parathyrin, is a peptide hormone produced by the parathyroid glands that regulates serum calcium levels through its actions on the bone, kidney, and intestine. PTH has an effect on bone remodelling, which is a continuous process in which bone tissue is resorbed and repaired. PTH is produced in response to low calcium (Ca2+) levels in the blood serum. In order to raise a low serum calcium level, PTH indirectly induces osteoclast activity within the bone matrix (osteon). Despite the ever-present problems of metabolism, stress, and nutritional fluctuations, the bones operate as a (metaphorical) “bank of calcium” from which the body can make “withdrawals” as needed to keep the amount of calcium in the blood at optimal levels. 

Function of the Perathyroid Hormone:

• Regulation of Serum Calcium 

The effects of parathyroid hormone on bone, kidney, and gut influence serum calcium: PTH increases the release of calcium from the vast calcium store found in bones. PTH indirectly stimulates bone resorption, which is the normal degradation of bone by osteoclasts. Because osteoclasts lack a receptor for PTH, stimulation is indirect; instead, PTH attaches to osteoblasts, the cells responsible for bone formation. Binding encourages osteoblasts to boost RANKL expression while inhibiting osteoprotegerin production (OPG). As a decoy receptor, free OPG competes with RANKL, preventing RANKL from binding with RANK, a RANKL receptor. The binding of RANKL to RANK (facilitated by the reduced quantity of OPG available for binding the excess RANKL) causes monocyte-derived osteoclast precursors to merge.

• Regulation of Serum Phosphate

PTH inhibits phosphate reabsorption in the proximal tubule of the kidney, causing more phosphate to be discharged in the urine.

PTH, on the other hand, increases phosphate uptake into the blood from the gut and bones. The breakdown of bone releases slightly more calcium than phosphate in the bone. Absorption of calcium and phosphate is mediated in the intestines by an increase in activated vitamin D. Phosphate absorption is not as reliant on vitamin D as calcium absorption. PTH release causes a slight net decrease in phosphate concentration in the blood.

PTH Secretion Regulation:

Through negative feedback, serum ionised calcium concentration determines parathyroid hormone secretion. Calcium-sensing receptors are found on the cell surface of parathyroid cells. When [Ca2+] falls, PTH is released (calcitonin is secreted when serum calcium levels are elevated). G-protein-coupled calcium receptors bind extracellular calcium and are located on the surface of many different cells in the brain, heart, skin, stomach, C cells, and other organs. High levels of extracellular calcium activate the Gq G-protein coupled cascade in the parathyroid gland, which is mediated by phospholipase C.

Disorders of Parathyroid Hormone:

Hyperparathyroidism, or the presence of abnormally high levels of parathyroid hormone in the blood, can originate in two ways. Primary hyperparathyroidism is caused by the parathyroid gland’s autonomous, aberrant hypersecretion of PTH, whereas secondary hyperparathyroidism is caused by an adequately high PTH level as a physiological reaction to hypocalcemia. Hypoparathyroidism is a low amount of PTH in the blood caused by injury to or removal of the parathyroid glands during thyroid surgery.

Measurement of PTH

Intact PTH, N-terminal PTH, mid-molecule PTH, and C-terminal PTH can all be tested in the blood, and different tests are employed in different clinical settings. The amount may be expressed in pg/dL or pmol/L (often abbreviated mmol/L); to convert from pg/dL to pmol/L, multiply by 0.1060.

According to a US source, the average PTH level is 8–51 pg/mL. The biological reference range in the United Kingdom is 1.6-6.9 pmol/L. The normal range for total plasma calcium is 8.5 to 10.2 mg/dL (2.12 mmol/L to 2.55 mmol/L).

Conclusion:

PTH is a hormone produced and released by your parathyroid glands to regulate the amount of calcium in your blood, not your bones. Calcium is one of your body’s most significant and ubiquitous minerals. PTH regulates phosphorus (a mineral) and vitamin D (a hormone) levels in your blood and bones. Hormones are chemicals that communicate with your organs, muscles, and other tissues in your body to coordinate diverse processes.

PTH receptors are divided into two categories. The 34 N-terminal amino acids of PTH activate parathyroid hormone 1 receptors, which are abundant on bone and kidney cells. The central nervous system, pancreas, testes, and placenta all have high numbers of parathyroid hormone 2 receptors.  PTH has a half-life of roughly 4 minutes.