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The calcitonin receptor (CT) is a G protein-coupled receptor that binds the peptide hormone calcitonin and is involved in maintenance of calcium homeostasis, [5] particularly with respect to bone formation and metabolism. [6] [7] [8]
Parafollicular cells secrete calcitonin, a hormone that participates in the regulation of calcium metabolism. Calcitonin lowers blood levels of calcium by inhibiting the resorption of bone by osteoclasts , and its secretion is increased proportionally with the concentration of calcium.
The calcitonin receptor is a G protein-coupled receptor localized to osteoclasts [20] as well kidney and brain cells. It is coupled to a G s α subunit , thus stimulating cAMP production by adenylate cyclase in target cells.
When osteoclast-inducing cytokines are used to convert macrophages to osteoclasts, very large cells that may reach 100 μm in diameter occur. These may have dozens of nuclei, and typically express major osteoclast proteins but have significant differences from cells in living bone because of the not-natural substrate.
Calcitonin is a hormone secreted by the thyroid in humans. Calcitonin decreases osteoclast activity, and decreases the formation of new osteoclasts, resulting in decreased resorption. [4] Calcitonin has a greater effect in young children than in adults, and plays a smaller role in bone remodeling than PTH. [4]
At the same time, the parathyroid glands reduce the secretion of parathyroid hormone (PTH), also a polypeptide hormone, into the blood. The resulting high levels of calcitonin in the blood stimulate osteoblasts in bone to remove calcium from blood plasma and deposit it as bone. The reduced levels of PTH inhibit removal of calcium from the skeleton.
In the brain, osteocalcin plays an important role in development and functioning, including spatial learning and memory. [ 17 ] An acute stress response (ASR), colloquially known as the fight-or-flight response, stimulates osteocalcin release from bone within minutes in mice, rats, and humans.
Calcitonin gene-related peptide (CGRP) is a member of the calcitonin family of peptides consisting of calcitonin, amylin, adrenomedullin, adrenomedullin 2 and calcitonin‑receptor‑stimulating peptide. Calcitonin is mainly produced by thyroid C cells whilst CGRP is secreted and stored in the nervous system. [1]