The calcitonin receptor is found within thyroid cells that produce calcitonin. This receptor binds calcium ions in the blood, which increase in number as calcium is absorbed from food. This process releases the calcitonin hormone that prevents calcium levels from building too quickly by stopping calcium ions from being absorbed by the small intestine and from being released by bone cells. These receptors are classified as class B, G protein-coupled receptors (GPCRs), and are similar to the secretin, calcitonin receptor-like, and parathyroid hormone receptors.
Control of calcitonin release is important in regulating bone metabolism. This hormone is synthesized within parafollicular cells, or C cells, within the thyroid gland. Calcitonin is a 32 amino acid long substance that belongs to a family of hormones, including amylin, a product of insulin in the pancreas; calcitonin gene-related peptide (CGRP), a blood vessel dilator; and adrenomedullin, which also regulates the dilation of blood vessels.
Closely affiliated with the calcitonin receptor is the amylin receptor, which is formed by the interaction of the receptor for calcitonin with receptor activity modifying proteins. The stimulation of CGRP does not cause a change in vascular function, heart rate, or blood pressure, and calcitonin itself inhibits the breakdown of bone cells by osteoclast cells. This in turn prevents calcium from being transferred from bone fluid into the blood stream.
Aside from the function of the calcitonin receptor, calcitonin can be used as a medical treatment for conditions such as osteoporosis. It can be administered by inhalation, and a commercially available nasal spray is available for this purpose. Calcitonin is digestible, so swallowing it is not an effective method.
Hyperparathyroidism, a condition in which the receptors are unable to stop calcium from building up in the blood, is a disorder involving the calcitonin receptor. Another type of receptor mutation causes hypoparathyroidism, which leads to low calcium in the blood and high levels of calcium in urine. Autoimmune disorders, tumors, injuries, and inherited defects can also negatively impact the function of the calcitonin receptor.
Many conditions that affect the receptors can be treated by calcium supplements as well as with calcitrol, a variant of vitamin D. The calcitonin receptor has a direct influence on bone health, and its state can be monitored by measuring the deviation of calcium levels in the blood from normal. This can aid detection and successful treatment of thyroid disorders and other health conditions.