Parathormone parathyroid

Parathyroid hormone (parathormone) Parathyroid gland Ca " mobilization... 

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

A nontrophic hormone acts on nonendocrine target tissues. For example, parathormone released from the parathyroid glands acts on bone tissue to stimulate the release of calcium into the blood. Aldosterone released from the cortical region of the adrenal glands acts on the kidney to stimulate the reabsorption of sodium into the blood. 

Four small parathyroid glands are embedded on the posterior surface of the thyroid gland as it wraps around the trachea. Parathyroid hormone (PTH, parathormone) is the principal regulator of calcium metabolism. Its overall effects include ... 

The polypeptide parathormone is released from the parathyroid glands when plasma Ca + level falls. It stimulates osteoclasts to increase bone resorption in the kidneys, it promotes calcium reabsorption, while phosphate excretion is enhanced. As blood phosphate concentration diminishes, the tendency of calcium to precipitate as bone mineral decreases. By stimulating the formation of vit D hormone, parathormone has an indirect effect on the enteral uptake of Ca + and phosphate. In parathormone deficiency, vitamin D can be used as a substitute that unlike parathormone, is effective orally. 

Parathyrin (parathyroid hormone, parathormone, PTH) is secreted by the parathyroid glands. A peptide of 84 amino acids, it has two precursors during its biosynthesis, a... 

The changes in calvarial phosphatase activities observed in animals treated with 25-(OH)D3 are totally different from those obtained with either 1.25-(OH)2D3 or 24.25—(OH)2D3. This fact indicates that physiological doses of 25-(OH)D3 may have an effect on cellular activity, independent of the conversion of this metabolite into these dihydroxyderivatives. The various effects of these vitamin D3 metabolites cannot be correlated with changes in serum calcium and/or phosphate concentrations. Among those factors other than serum calcium and phosphate concentrations that may be involved in the mechanism of action of vitamin D3 metabolites on bone phosphatase activities, the parathyroid hormone is of importance. This hormone is known to be a potent activator of bone phosphatases223,224,228. Parathormone increases the content of alkaline, neutral and acid phosphatases in mouse calvaria in vitro. Calcitonin does not prevent the increase of those enzymes while dichloromethylene diphosphonate causes a decrease in acid phosphatase and pyrophosphatase226. ... 

A 72-year-old woman received calcitonin 100 IU twice a week intramuscularly, calcitriol 0.25 micrograms bd, and daily calcium supplements for 3 years, before presenting with a raised calcium concentration (2.7 mmol/ 1) and linear calcification in the knee joints. The parathormone concentration was raised (151 pg/ml reference range 7-53) and a parathyroid adenoma was demonstrated on ultrasound (15). 

Parathormone (protein) Parathyroid Bones Transfer Ca2+ from bone to blood... 

All the pharmacological and behavioural effects elicited by dopamine agonists and antagonists in the brain can only be explained if such an interaction occurs at the level of the dopamine receptor (D2 receptor site) the site still remains in search of a function. Bovine parathyroid cells were reported to possess dopamine sites which should be involved in the control of parathormone secretion. However, the very poor pharmacological characterization and the lack of in vivo evidence do not allow to assess the dopaminergic nature of this hormone secretion. Dopamine-sensitive adenylate cyclase is thus not a receptor directly implicated in the dopaminergic neurotransmission it is an enzyme which could have an important role in the control of long term metabolic effects such as the synthesis of neuronal constituents. 

In 1977, Brown et al. (15) reported that dopamine (10-8 M) stimulates by 2-4 fold the secretion of parathormone from dispersed bovine parathyroid cells. 

ADTN and other dopamine agonists mimicked this effect which was antagonized by a- and B-flupenthixol, the a-isomer being 100 times more potent. In a similar way, dopamine caused a rapid 20-30-fold increase in cellular cAMP in dispersed bovine parathyroid cells. The potency of a series of dopaminergic agonists and antagonists on adenylate cyclase activity paralleled the effects of these ligands on CAMP accumulation and parathormone secretion (16). It was concluded that bovine parathyroid cells possess dopamine sites which are involved in the control of parathormone secretion. 

Compounds which can regulate (+) or not (-) cAMP production and parathormone secretion in parathyroid cells... 

In hypocalcemia, the parathyroid increases its secretion of parathormone, resulting in enhanced liberation of Ca2+. Calcitonin transfers active osteoclasts into a resting state. Calcitonin given therapeutically relieves pain associated with neoplastic bone metastases and vertebral body collapse. Estrogens diminish bone resorption by (a) inhibiting activation of osteoclasts by osteoblasts and (b) promoting apoptosis of osteoclasts. 

The major function of the parathyroid hormone (PTH parathormone) is to regulate the concentration of extracellular calcium. PTH is heterogeneous and circulates as an intact polypeptide and as fragments. The major circulating biologically active peptide is intact PTH, which is rapidly cleared from the circulation (half-life less than 10 min). The N-terminal portion is responsible for its biologic activity. 

Not all calcium present in the diet is absorbed by the small intestine and mechanisms are present to ensure only amounts appropriate to body needs are absorbed. These processes are complex and involve the interaction of special transport protein, vitamin D and parathormone. Thus, abnormalities of calcium metabolism may result from many different disease processes. Diseases affecting the bowel may prevent normal absorption, diseases of the parathyroid gland may result in inappropriate levels of parathormone for calcium requirement and a nutritionally inadequate diet may cause vitamin D deficiency with consequent disordered calcium absorption. 

Calcium is essential for the normal growth and development of the body, especially (in the form of calcium phosphate) of the bones and teeth. Its level in the blood is regulated by the opposing actions of the thyroid hormone calcitonin, and the parathyroid hormone parathormone. Its uptake from food is enhanced by vitamin D (calciferol). Forms of calcium used therapeutically include the folinic acid supplement calcium foiinate, and the mineral supplements calcium bicarbonate, calcium carbonate, calcium gluconate and calcium lactate. 

The free calcium ions in blood and extracellular fluid are critical for building and maintaining an adequate bone mass, and also for preventing excessive calcification. The sensor that regulates the free calcium ion concentration of plasma is within the parathyroid glands, where it controls the secretion of parathormone (PTH). This 84 amino acid peptide is split from a large, precursor protein and retained in secretory vesicles. If the concentration of free calcium ions drops below a critical level in blood plasma, the gland is activated to secrete PTH into the bloodstream. 

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