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A hormone, the only known secretory product of the parenchymal or C cells of the mammalian thyroid and of the ultimobranchial glands of lower forms.
In conjunction with the parathyroid hormone, thyrocalcitonin is of prime importance in regulating calcium and phosphate metabolism. Its major function is to protect the organism from the dangerous consequences of elevated blood calcium. Its sole known effect is that of inhibiting the resorption of bone. It thus produces a fall in the concentration of calcium and phosphate in the blood plasma because these two minerals are the major constituents of bone mineral and are released into the bloodstream in ionic form when bone is resorbed. See Bone, Parathyroid gland, Parathyroid hormone
Thyrocalcitonin also causes an increased excretion of phosphate in the urine under certain circumstances, but a question remains as to whether this is a direct effect of the hormone upon the kidney or an indirect consequence of the fall in blood calcium which occurs when the hormone inhibits bone resorption. See Thyroid gland
(calcitonin), a hormone in vertebrate animals and man that decreases the Ca2+ content in the blood plasma. In fishes, amphibians, reptiles, and birds, thyrocalcitonin is secreted by the ultimobranchial bodies, which develop from the last pair of branchial arches. In mammals, this tissue is represented by the C cells of the interfollicular islets of the thyroid gland.
Thyrocalcitonin, which can be isolated from the thyroid glands of swine and man, is a polypeptide containing 32 amino-acid residues. By constantly inhibiting the resorption of Ca2+ from the bones, it promotes homeostasis and the growth of bone tissue. This is important where there is an increased need for Ca2+, such as periods of bone growth in young animals, pregnancy and lactation in mammals, and egg laying in birds. Thyrocalcitonin also increases the excretion of phosphates in the urine. It regulates the content of Ca2+ and phosphates in the body by interaction with the parathyroid hormone, which stimulates the release of Ca2+ from bone tissue into the extracellular fluid.
REFERENCESAleshin, B. V. “Novye dannye o tireokal’tsitonine.” Uspekhi sovremennoi biologii, 1970, vol. 69, issue 1.
Sovremennye voprosy endokrinologii, fasc. 4. Moscow, 1972. (Collection of articles.)
“Symposium on Thyrocalcitonin.” American Journal of Medicine, 1967, vol. 43, no. 5.
Hirsch, P. F., and P. L. Munson. “Thyrocalcitonin.” Physiological Reviews, 1969, vol. 49. no. 3.
L. V. KRIUKOVA