Thyroid gland calcitonin

Calcitonin is a 32-amino-acid polypeptide hormone that was hrst purihed in 1962 by Copp and Cheney (121). It was originally thought as a product from parathyroid glands, but later it was discovered to be made by the C cells of the thyroid gland. Calcitonin participates in calcium and phosphorus metabolism, lowers plasma calcium and phosphate levels, and it has been used as a drug for bone and mineral disorders for a long time. 

Calcitonin is a 32-amino acid peptide hormone that participates in calcium and phosphorus metabolism. In mammals, the major source of calcitonin is from the parafollicular or C cells in the thyroid gland. Calcitonin contains a single disulfide bond, which causes the amino terminus to assume the shape of a ring. It is used to... 

Calcitonin A polypeptide honnone of 32-amino acid residues that is synthesized in the parafollicular cells (C cells) of the thyroid gland. Calcitonin is seaeted in response to elevated blood Ca levels. 

Factors controlling calcium homeostasis are calcitonin, parathyroid hormone(PTH), and a vitamin D metabolite. Calcitonin, a polypeptide of 32 amino acid residues, mol wt - SGOO, is synthesized by the thyroid gland. Release is stimulated by small increases in blood Ca " concentration. The sites of action of calcitonin are the bones and kidneys. Calcitonin increases bone calcification, thereby inhibiting resorption. In the kidney, it inhibits Ca " reabsorption and increases Ca " excretion in urine. Calcitonin operates via a cyclic adenosine monophosphate (cAMP) mechanism. 

The main role of the human thyroid gland is production of thyroid hormones (iodinated amino acids), essential for adequate growth, development, and energy metaboHsm (1 6). Thyroid underfunction is an occurrence that can be treated successfully with thyroid preparations. In addition, the thyroid secretes calcitonin (also known as thyrocalcitonin), a polypeptide that lowers excessively high calcium blood levels. Thyroid hyperfunction, another important clinical entity, can be corrected by treatment with a variety of substances known as antithyroid dmgs. 

Several years ago, it was discovered that the thyroid gland was also the source of a hypocalcemic hormone having effects in general opposition to those of the parathyroid hormone. This hormone is produced in mammals by the parafollicular C-ceUs and in other vertebrates by the ultimobrachial bodies (45). Originally called thyrocalcitonin, it is now referred to as calcitonin (CT). 

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. 

Methodology. Several radioimmunoassays of human calcitonin (hCT) have been developed In the past 5 years (18-20). Their greatest utility has been In the definitive diagnosis of patients with medullary carcinoma of the thyroid gland (MTC) and, recently. In Identifying family members of these patients who have occult MTC. 

Calcitonin. This hormone, which is also secreted from the thyroid gland, is synthesized by the parafollicular cells (C cells) located between the follicles. The primary effect of calcitonin is to decrease the blood levels of calcium and phosphate. The mechanism of action involves the direct inhibition of osteoclast activity, which decreases bone resorption. This results in less demineralization of the bone and therefore a decrease in the release of calcium and phosphate from the bone into the blood. Calcitonin has no direct effect on bone formation by osteoblasts. 

An alternative therapeutic approach to osteoporosis is through the use of calcitonin (798), a peptide hormone containing 32 amino acids (the sequence is species dependent) secreted by the thyroid gland, which stimulates the production of new bone. Synthetic calcitonins corresponding to human, eel, and salmon variants, and natural calcitonin extracted from pig thyroid, are all used in medicine - they have slightly different efficacies, side effects, and tolerance levels (799). 

Calcitonin is released from the thyroid gland when serum calcium is elevated. Salmon calcitonin is used clinically because it is more potent and longer lasting than the mammalian form. Calcitonin is reserved as a third-line agent because efficacy is less robust than with the other antiresorptive therapies. 

Calcitonin a peptide hormone secreted by the thyroid gland that lowers plasma calcium levels by increasing the deposition of bone. 

Calcitonin, a peptide produced in the C cells of the thyroid gland, inhibits the resorption of both calcium and phosphate ions. The result is an overall reduction in the plasma level of both ions. Calcitonin is thus a parathyrin antagonist relative to Ca ". ... 

Calcitonin is a single chain polypeptide of 32 amino-acids. It is secreted by the parafollicular cells of the thyroid gland. However in the circulation various forms of calcitonin are present, probably including several precursors. Calcitonin inhibits osteoclastic resorption of bone and it increases calcium and... 

Three hormones, thyroxine (3,5,3, 5 -tetraiodothy-ronine, or T4), triiodothyronine (3,5,3 -triiodothyronine, or T3), and calcitonin (see Chapter 66) are secreted by the thyroid gland. The hormones T4 and Tj are iodine-containing amino acid derivatives and are unique in that they have no discrete target tissue. Every tissue in the body is affected in some way by thyroid hormones, and almost all cells appear to require constant optimal amounts for normal operation. 

The regulation of calcitonin synthesis and release from the parafollicular C cells of the thyroid gland is calcium dependent. Rising serum calcium is the principal stimulus responsible for calcitonin synthesis and release. Other hormones, such as glucagon, gastrin, and serotonin, also stimulate calcitonin release. Calcitonin has been isolated in tissues other than the parafollicular C cells (parathyroid, pancreas, thymus, adrenal), but it is not known whether this material is biologically active. 

Thyroid gland secretes two important hormones, thyroxine (TJ and triiodothyronine (Tj). The third hormone, calcitonin secreted from interstitial cells is physiologically different and is responsible for the regulation of calcium metabolism. 

Like calcitonin, CGRP is present in large quantities in the C cells of the thyroid gland. It is also distributed widely in the central and peripheral nervous systems, in the cardiovascular system, the gastrointestinal tract, and the urogenital system. CGRP is found with substance P (see above) in some of these regions and with acetylcholine in others. 

The normal thyroid gland secretes sufficient amounts of the thyroid hormones—triiodothyronine (T3) and tetraiodothyronine (T4, thyroxine)—to normalize growth and development, body temperature, and energy levels. These hormones contain 59% and 65% (respectively) of iodine as an essential part of the molecule. Calcitonin, the second type of thyroid hormone, is important in the regulation of calcium metabolism and is discussed in Chapter 42. 

Thyroid gland function also regulates calcitonin which combats elevated levels of calcium. 

Calcitonin is a peptide hormone produced in the thyroid gland that serves to lower serum calcium and phosphate levels by inhibiting bone resorption. Calcitonin has been used in the treatment of a variety of diseases, such as primary hyperparathyroidism, Paget s disease, and postmenopausal osteoporosis [99,100]. Salmon calcitonin has a longer half-life than human calcitonin. Salmon calcitonin, 3.6 kDa, is available as a nasal formulation that contains only benzalkonium chloride as a preservative, without an absorption enhancer, and as a parenteral product for injection. The direct effect of benzalkonium chloride on the nasal mucosa is under... 

CaR expression is greatest in the parathyroid glands, calcitonin-secreting C-cells of the thyroid gland, and kidney, but the CaR is also found in the two other key organs that participate in calcium homeostasis gut and bone (Brown and MacLeod, 2001). This review will focus on the structure and function of the CaR, its role in normal physiology and in various disorders of Ca -sensing, and the development of CaR-based therapeutics. 

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