Formation of calcitonin: The hormone of the thyroid gland calcitonin consists of protein and is therefore a peptide hormone. In contrast to T3 – T4 hormone, this hormone is produced in the C-cells of the thyroid (parafollicular cells). The effect of this hormone unfolds on the bones, in which the bone-destroying cells (osteoclasts) are inhibited.
Furthermore, calcium is increasingly incorporated into the bones. Regulation of Calcitonin: The level of the hormone is determined by the calcium content of the blood. If the blood calcium level is high (hypercalcemia), the hormone is released so that it can be absorbed and incorporated into the bone.
Some gastrointestinal hormones also increase the release of calcitonin, so that calcium absorbed with food can be directly incorporated into the bones under the influence of the hormone. The hormone calcitonin is related to the calcium balance, which it regulates. Its antagonist is the parathyroid hormone produced in the parathyroid glands.
Mode of operation
Calcitonin belongs to the hormones produced by the thyroid gland. More precisely, it is synthesized by the C-cells (“C” for calcitonin) of the thyroid gland. The release of this hormone depends on the concentration of calcium ions in the blood.
If this is increased, calcitonin is released to inhibit osteoclast activity. The main task of osteoclasts is to resorb bone substance. If their activity is inhibited, as is the case with the hormone calcitonin, no more calcium is released from the bone into the blood.
In addition, calcitonin also increases the excretion of calcium, phosphate, magnesium, potassium and sodium via the kidneys, although this plays a subordinate role compared to the inhibition of osteoclast activity. Finally, calcitonin also reduces the absorption of calcium in the intestine. It is precisely the concentration of calcium ions that can stimulate the release of calcitonin by gastrointestinal hormones such as pentagastrin. It is important that the administration of calcitonin in the case of normocalcemia, i.e. a calcium concentration in the blood that is in the normal range, does not cause a too low calcium concentration in the blood, as one might actually expect.
Preparations and application
Synthetic human calcitonin and synthetic salmon calcitonin are used for therapeutic purposes. Human calcitonin disappears from the blood faster and is not as effective as salmon calcitonin. As the hormone calcitonin is a protein (to be precise a polypeptide), it cannot be taken perorally, i.e. by mouth.
It must be taken parenterally, which literally means by-passing the intestine. Possibilities of application are therefore subcutaneous injection (administered under the skin), intramuscular injection (administered into a skeletal muscle) and intravenous injection (administered into a vein). Until 2012, it was used for certain diseases in the form of a nasal spray.