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11 Cards in this Set
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Calcitonin Lowers circulating ca levels by reducing PTH release Lowers the po4 levels in blood Inhibits bone resorption Decreases the ca excreted in urine Increases the formation of 1,25DHCC
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What is calcitonin |
Calcitonin is a hormone formed by parafollicular cells (so-called C-cells) of the thyroid gland. From the chemical point of view it is a 32 amino acid long peptide and the whole molecule determines its biological activity. By an alternative splicing of its gene another peptide is formed – termed CGRP (calcitonin gene related peptide). The half-life of calcitonin is about 10 minutes |
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What are the functions of calcitonin |
Calcitonin decreases the plasma level of calcium through 3 main mechanisms: 1) Inhibition of ionized calcium absorption from intestines 2) Inhibition of calcium reabsorption in renal tubuli 3) Inhibition of osteoclasts activity The secretion of calcitonin is increased during hypercalcemia, a state of increased plasmatic calcium. The extent of its physiological impact is disputed, because the above-mentioned effects occur in vitro only at concentrations that are not commonly found within the human body. |
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What is calcitonin |
Calcitonin is produced and released by parafollicular cells of the thyroid (”the C cells”). Multiple forms of circulating calcitonin have been found in the serum of healthy and diseased individuals. They all are referred as “circulating immunoreactive calcitonin.” Calcitonin is derived from larger precursors.
It is known to act on the bones, kidneys, and gastrointestinal tract.
Although some clinical studies suggest that the serum calcium concentration may be unaffected in patients with total thyroidectomy, others suggest that medullary thyroid carcinoma (MTC) and excess calcitonin can lead to marked hypocalcemia. Calcitonin induces increased renal clearance of calcium and phosphate. [5]Indications/ApplicationsA calcitonin assay is helpful in identifying patients with nodular thyroid disease. [6, 7, 8] It is often performed in the hope of identifying early MTC, which may be seen in the setting of multiple endocrine neoplasia (MEN) type 2. Successful treatment of MTC depends on early detection; late detection confers a poor prognosis. [9] Slight elevations in calcitonin with subsequent surgical exploration of the thyroid may allow the clinician to identify this lesion in its early, nonpalpable stage of development.In the United States, routine testing for calcitonin in patients with nodular thyroid disease was long considered not to be cost-effective. In Europe, however, studies have shown that this practice is in fact cost-effective. One analysis performed in the United States concluded that routine calcitonin testing in patients with nodular thyroid disease was as cost-effective as other screening tests, such as those for thyroid-stimulating hormone, breast cancer (mammography), and colon cancer (colonoscopy). [10]The specificity of calcitonin testing increases with provocative testing. Pentagastrin stimulation before a calcitonin assay increases diagnostic sensitivity for MTC. Plasma or serum calcitonin levels higher than 100 pg/mL should raise the index of suspicion for this aggressive neoplasm. |
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Regulation of calcium |
The full spectrum of calcitonin regulation is not completely understood, but its secretion is primarily regulated by the ionized calcium concentration, with increases in ionized calcium leading to increases in calcitonin, |
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Actions of calcitonin |
pharmacological doses of calcitonin reduce serum calcium and phosphate concentrations by inhibiting osteoclastic bone resorption and reducing renal tubular reabsorption. |
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What increase calcitonin secretion |
Other potent calcitonin secretagogues include the gastrointestinal peptide hormones, gastrin in particular. A mild postprandial increase in calcitonin concentration occurs. Calcitonin's precise physiologic role in humans remains to be elucidated. |
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What is the action of calcitonin on osteoclasts |
Calcitonin binds directly to osteoclasts, thereby directly inhibiting osteoclastic bone resorption, an effect that is observed within minutes after calcitonin administration. Although this inhibition may be important in short-term control of calcium loads, it is transient and probably plays an insignificant role in overall calcium homeostasis. |
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What is the role of calcitonin on PTH |
Calcitonin also inhibits the action of parathyroid hormone and vitamin D. |
