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Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine. [5] PTH influences bone remodeling, which is an ongoing process in which bone tissue is alternately resorbed and rebuilt over
reabsorption in response to PTH and ↑ reabsorption with Thiazide Diuretics. – Magnesium: Calcium and magnesium compete, and an excess of one can lead to excretion of the other. reabsorption: reabsorption (thick ascending) reabsorption – Phosphate: Excreted as titratable acid. reabsorption (85%) via sodium/phosphate cotransporter. [3]
The low levels of PTH have several other effects: there is increased loss of calcium in the urine, but more importantly, the loss of phosphate ions through urine is inhibited. Phosphate ions will therefore be retained in the plasma where they form insoluble salts with calcium ions, thereby removing them from the ionized calcium pool in the blood.
phosphate: approximately 80%: Parathyroid hormone reduces reabsorption of phosphate in the proximal tubules, but, because it also enhances the uptake of phosphate from the intestine and bones into the blood, the responses to PTH cancel each other out, and the serum concentration of phosphate remains approximately the same. citrate: 70%–90% [12]
PTH increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium conservation (reabsorption) by the kidneys. [12] Phosphate. PTH is the major regulator of serum phosphate concentrations via actions on the kidney. It is an inhibitor of proximal tubular reabsorption of phosphorus.
PTHrP shares the same N-terminal end as parathyroid hormone and therefore it can bind to the same receptor, the Type I PTH receptor . [12] PTHrP can simulate most of the actions of PTH including increases in bone resorption and distal tubular calcium reabsorption, and inhibition of proximal tubular phosphate transport.
PTH normally inhibits reabsorption of phosphate by the kidney. Therefore, without enough PTH there is more reabsorption of the phosphate leading to a high phosphate level in the blood. [citation needed] Chronic kidney failure: When the kidneys are not working well, there will be increased phosphate retention. [citation needed]
Continued elevation of PTH levels increases the abundance of osteoclasts. This leads to a greater resorption of calcium and phosphate ions. [4] High levels of calcium in the blood, on the other hand, leads to decreased PTH release from the parathyroid gland, decreasing the number and activity of osteoclasts, resulting in less bone resorption.