Calcitonins and Calcitonin Precursors Peptides

Calcitonin is a significant peptide hormone that plays a pivotal role in maintaining calcium and phosphate balance in the body. It is primarily produced by the thyroid gland, specifically by the parafollicular cells (C cells), and is crucial for controlling blood calcium levels, bone metabolism, and skeletal integrity.

What is Calcitonin?

Comprising thirty-two amino acids, calcitonin is a polypeptide hormone Mostly released in response to rising blood calcium levels, it is generated in the C cells of the thyroid gland. Its main purpose is to reduce blood calcium levels, therefore countering the effects of parathyroid hormone (PTH), which raises them.

Bone health and mineral metabolism are governed by a sophisticated network of hormones including calcitonin. Acting in concert to stimulate bone remodeling and control calcium homeostasis, it is sometimes seen as a "counter-regulating" hormone to PTH. Calcium levels rigorously limit calcitonin generation; so, they are prevented in normal levels and released in too high amounts.

Calcitonin Classification

Calcitonin belongs to the family of hormones known as hypocalcemic hormones, which reduce blood calcium levels. It is divided into two categories according on its source and molecular form:

Human Calcitonin: The thyroid C cells in humans create this kind of calcitonin. Usually, it is used to control the body's metabolism of calcium.

Salmon Calcitonin: The thyroid gland of salmon is the source of this artificial version of calcitonin. Compared to human calcitonin, salmon calcitonin is more powerful and has a longer half-life. It is often used to treat Paget's disease and osteoporosis.

Calcitonin Gene-Related Peptide (CGRP)

Calcitonin gene-related peptide (CGRP) is a neurotransmitter and peptide that shares a gene with calcitonin but has distinct physiological roles.

Although calcium metabolism is the main function of calcitonin, CGRP also has significant influence on other systems: Vasodilation: CGRP is a strong vasodilator that causes blood vessel smooth muscle cells to relax, resulting in blood vessel enlargement. This characteristic is important for controlling blood flow, especially in the brain, and it is linked to the pathophysiology of migraines.

Neurogenic Inflammation: By stimulating the production of pro-inflammatory mediators and boosting immunological responses, CGRP also contributes to neurogenic inflammation.

What does Calcitonin do?

By affecting several organs, such as the kidneys, gastrointestinal system, and bone, calcitonin primarily lowers blood calcium levels. Below is a summary of its main purposes:

Promotion of Calcium Deposition in Bone: Calcitonin indirectly promotes the activity of osteoblasts, the cells that build bones, in addition to suppressing osteoclasts. Calcium serves to improve bone mineralization, which in turn promotes bone strength and structural integrity by reducing bone resorption and maintaining a balance between resorption and creation.

Renal Calcium Excretion: Calcitonin also affects the kidneys by decreasing the renal tubules' ability to reabsorb calcium. This helps avoid hypercalcemia (high blood calcium levels) by encouraging the elimination of excess calcium via the urine. The impact of calcitonin on bone resorption is enhanced by this renal action.

Modulation of Intestinal Calcium Absorption: Although calcitonin primarily affects the gastrointestinal system, it may also affect how well calcium is absorbed from it. Calcitonin may help control blood calcium levels by decreasing the absorption of calcium.

Calcitonin Function

In addition to regulating calcium, calcitonin has a number of additional functions in the model body, some of which are now the subject of ongoing study. Its impacts include:

Calcitonin helps maintain the proper physiological range of calcium and phosphate in the body, which is essential for blood coagulation, muscular contraction, and nerve transmission. It does this by promoting the deposition of calcium in the bones and decreasing calcium levels.

Prevention of Hypercalcemia: In diseases including hyperparathyroidism, Paget's disease, and bone metastases that are linked to high blood calcium levels, calcitonin is especially helpful. It reduces excess calcium in the blood as a natural defensive mechanism.

How does Calcitonin Work?

The main way that calcitonin functions is by attaching itself to calcitonin receptors (CTR) on a variety of target cells, including those found in the kidneys, intestines, and osteoclasts. The actions of calcitonin in each of these tissues are broken out in depth below:

Bone (Osteoclast Inhibition): Calcitonin reduces osteoclast activity by binding to the calcitonin receptor (CTR) on osteoclasts. By reducing bone resorption, this mechanism stops calcium and phosphate from leaving the bone and entering the blood. In diseases like osteoporosis and Paget's disease, inhibiting osteoclast activity is very important to halting bone loss.

Kidneys (Calcium Excretion): Calcitonin in the kidneys promotes calcium excretion via urine by decreasing calcium reabsorption in the renal tubules. This aids in reducing the body's total calcium levels, particularly when hypercalcemia (high calcium levels) is present.

Gastrointestinal system (Calcium Absorption): Although calcitonin may help restrict excessive absorption of calcium from meals, it does not directly affect calcium absorption in the gastrointestinal system. Calcitonin helps maintain the body's overall calcium balance by decreasing the absorption of calcium in the gut.

Effects on Vascular Function and Blood Pressure: There is evidence that calcitonin, particularly calcitonin gene-related peptide (CGRP), has vasodilatory properties that may affect vascular tone and blood pressure. In CGRP, a peptide that is closely linked to calcitonin but has different physiological roles, this impact is more pronounced.

Calcitonin Mechanism of Action

The main way that calcitonin works is via interacting with calcitonin receptors on target cells such as kidneys and osteoclasts. Calcitonin initiates a series of intracellular processes upon binding:

Osteoclast Inhibition: Osteoclasts' resorptive activity is reduced when they bind to CTR, which lowers the amount of calcium released from bones. In diseases like osteoporosis and Paget's disease, this activity helps avoid excessive bone destruction, which is crucial.

Calcium Excretion in the Kidneys: Calcium reabsorption is inhibited by calcitonin in the kidneys, which increases calcium excretion via urine. This aids in lowering hypercalcemia, or excessive calcium levels.

Bone Mineralization: Calcitonin indirectly promotes bone mineralization and osteoblast function by decreasing osteoclast activity, which in turn encourages the growth of new bone tissue.

Neurological System and Blood Pressure: Calcitonin affects the vascular and neurological systems by modulating inflammation and vasodilating them via its related peptide CGRP.