Introduction
Calcitonin is a peptide (a molecule with two or more amino acids) hormones secreted by the thyroid gland primarily responsible for the regulation of calcium levels in the body. The C-cells of the thyroid gland produce this hormone. This hormone acts as a primary regulator of the resorption process of the bones. This article will discuss the link between the hormone calcitonin and bone.
What Is Calcitonin?
The small butterfly-shaped gland located in the front of the neck is the thyroid gland. It is a vital hormone gland and plays an important role in the endocrine system of the body by producing and secreting hormones. The thyroid gland's parafollicular cells are responsible for the hormone calcitonin synthesis and secretion.. It is a peptide hormone made up of 32 amino acids. When there is a high level of calcium in the blood, the presence of gastrin triggers the release of calcitonin from the thyroid glands. They act as an antagonist to the parathyroid hormone released from the parathyroid gland, which increases the calcium levels in the blood.
What Are the Essential Functions of Calcitonin?
As mentioned earlier, they are triggered by the increase of calcium levels in the blood, and they act by inhibiting osteoclast activities (the bone cells responsible for breaking down bone tissues). During an osteoclastic activity, the bone cells called the osteoclasts break down the bone tissue, which releases calcium into the bloodstream. Therefore, by inhibiting the actions of osteoclasts, calcitonin decreases the calcium level entering the bloodstream. Additionally, calcitonin lowers the level of calcium in the blood by increasing calcium excretion and decreasing calcium reabsorption in the kidney.
What Is the Role of Calcitonin in Bone Disorders?
Based on the mechanism of calcitonin on osteoclast activities, they are used to treat various bone disorders.
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Paget’s Disease: A chronic condition of bone is Paget's disease. Generally, in the body, a process of breaking down the old bone and reforming a new bone happens. Whereas in this disorder, this process is disrupted, leading to excessive and disordered bone turnover resulting in excessive bone resorption and reduced bone mineral density. Over time the patients are highly likely to undergo fractures. Bisphosphonates are the first line of treatment in these patients. However, in patients who developed a tolerance for bisphosphonates, calcitonin is used as the second line of treatment. Calcitonin helps in reversing the symptoms of bone pain and neurological deficits. It has a peak effect on the osteoclast within 24 to 48 hours of therapy. The patients are given 50 to 100 units of calcitonin through the intramuscular route daily in the initial days and tapered later. Calcitonin helps in reducing the alkaline phosphatase, which is a marker of bone remodeling and turnover.
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Osteoporosis: Osteoporosis is an age-related chronic bone disease affecting more females than males due to the decline of bone mineral density in females after menopause. It is caused due to loss of bone mass and density or the presence of any structural abnormalities in the bone. This condition often results in brittle bones and weakened bones. By acting on osteoclastic activity, calcitonin reduces the loss of bone mineral density and thereby reduces the risk of osteoporosis. A dosage of 200 units of calcitonin through the nasal route daily has been shown to reduce the risk of vertebral fractures by 33 percent in patients with osteoporosis. The recommended dosage is 200 units through intra-nasal spray or 100 units through intramuscular or subcutaneous injection.
What Is the Mechanism of Calcitonin in Bone?
Synthetic salmon-derived calcitonin is a 32-amino acid polypeptide that has greater potency than human calcitonin. The most important mechanism of calcitonin is on the osteoclasts and the tubular epithelial layer of the kidney.
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In bone, calcitonin reduces the mobility of osteoclasts by contracting them and disrupts the ability to reabsorb bone. The osteoclasts tend to retract and break out from the effects of calcitonin. However, the peak effects of calcitonin in the first 24 to 48 hours inhibit osteoclastic activity.
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Also, calcitonin inhibits the carbonic anhydrase Ⅱ, which promotes an optimal acidic environment for osteoclastic activity.
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Calcitonin also prevents the precursors of osteoclasts from developing into a mature form.
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The result of all these reactions leads to a decrease in bone resorption and a reduction of calcium levels in the bloodstream.
What Is the Effect of Calcitonin on Bone Health?
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Several studies have been conducted since the early 1960s focusing on the effect of calcitonin on bone health. Recent studies show evidence that calcitonin produced in response to the intake of meals helps in storing calcium by intestinal absorption into bone fluids. Here calcitonin uses phosphate to store calcium temporarily between the oral intake of foods with calcium. Thereby reducing the parathyroid hormone-induced bone destruction during continuous fasting periods.
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Women lose around six to ten percent of bone mineral content during lactation. During pregnancy and lactation, the body demands an increased calcium level to transfer maternal calcium to the fetus. Surprisingly calcitonin has been shown to stimulate the production of 1,25-dihydroxy vitamin D in the kidney through reabsorption. Vitamin D synthesis is essential for maintaining the bone cells (osteoclasts, osteoblasts, and osteocytes). Additionally, Studies have shown the role of calcitonin in protecting the body’s skeletal tissues from excessive loss of bone minerals during high times of demand, such as lactation.
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Too much calcium in the blood can result in weakened bones. The condition of hypercalcemia can cause the bone to release excessive amounts of calcium from the bone, which leaves the bone deficient. Administering calcitonin has shown to be effective in inhibiting bone osteoclastic activity to treat hypercalcemia. The “escape” of osteoclasts from the effects of calcitonin is prevented by prolonged administration of calcitonin.
Conclusion
Calcitonin is a peptide hormone that plays a major role in regulating the calcium levels in the body. They are produced and secreted by the small endocrine gland located in the neck called the thyroid gland. This hormone has been approved by the Federal Agency of Food and Drug Administration (FDA) for 25 years to treat osteoporosis, a bone disorder that results in low bone mineral density. Various studies have demonstrated the effectiveness of calcitonin in preserving and increasing bone mineral density. It also reduces the risk of vertebral fractures in patients with osteoporosis.
