Calcitonin and the parathyroid hormone

Calcitonin and parathyroid hormone (PTH) are crucial regulators of calcium levels in the body. While calcitonin helps to lower blood calcium levels, PTH works to increase them. Together, they maintain the delicate balance of calcium necessary for various physiological functions. In this article, we’ll delve into the roles of calcitonin and PTH, their effects on calcium metabolism, and the implications of their dysregulation.

Calcitonin: The Bone Guardian

Calcitonin is a hormone primarily produced by the parafollicular cells (also known as C cells) of the thyroid gland. Its main function is to regulate calcium levels in the blood by inhibiting bone resorption, the process by which bone is broken down and calcium is released into the bloodstream.

When blood calcium levels rise, calcitonin is released to promote calcium deposition into the bones, thereby lowering blood calcium levels. While its role in calcium regulation is significant, calcitonin is not considered essential for life, as its functions can be compensated for by other hormones.

Parathyroid Hormone (PTH): The Calcium Controller

Parathyroid hormone (PTH) is produced by the parathyroid glands, four small glands located behind the thyroid gland. PTH plays a crucial role in maintaining calcium homeostasis by stimulating the release of calcium from bone, increasing calcium reabsorption in the kidneys, and enhancing the absorption of calcium in the intestines.

Additionally, PTH indirectly stimulates the production of calcitriol, the active form of vitamin D, which further promotes calcium absorption from the intestines. Together, these actions help elevate blood calcium levels when they fall below the normal range.

Calcitonin vs. Parathyroid Hormone: Balancing Act

While calcitonin and PTH have opposing effects on calcium metabolism, they work together to maintain calcium homeostasis. When blood calcium levels rise above the normal range, calcitonin is released to promote calcium deposition into the bones, while PTH secretion is suppressed.

Conversely, when blood calcium levels drop, PTH is released to stimulate calcium release from bone and increase calcium reabsorption in the kidneys, while calcitonin secretion is inhibited. This delicate balance ensures that blood calcium levels remain within a narrow range to support vital physiological functions.

Dysregulation of Calcitonin and PTH: Implications

Dysregulation of calcitonin and PTH can lead to various disorders affecting calcium metabolism. Hypocalcemia, or low blood calcium levels, may result from decreased PTH secretion or resistance to its effects, leading to symptoms such as muscle cramps, tingling sensations, and convulsions.

On the other hand, hypercalcemia, or high blood calcium levels, can occur due to excessive PTH secretion, as seen in conditions like primary hyperparathyroidism, or from other causes such as certain cancers. Hypercalcemia can manifest as fatigue, nausea, constipation, and bone pain, and if left untreated, it can lead to severe complications such as kidney stones, bone fractures, and cardiac arrhythmias.


Calcitonin and parathyroid hormone play pivotal roles in maintaining calcium balance in the body. While calcitonin acts to lower blood calcium levels by promoting calcium deposition into bones, PTH works to increase blood calcium levels by stimulating calcium release from bone and enhancing calcium reabsorption in the kidneys and intestines.

Together, these hormones ensure that blood calcium levels remain within a narrow range to support optimal physiological function. Understanding the roles of calcitonin and PTH and their implications for calcium metabolism is crucial for the diagnosis and management of disorders affecting calcium homeostasis.

In conclusion, calcitonin and PTH are essential regulators of calcium metabolism, and their dysregulation can lead to various disorders affecting calcium homeostasis. By understanding the roles of these hormones and their effects on calcium balance, healthcare professionals can effectively diagnose and manage conditions such as hypocalcemia and hypercalcemia, ultimately improving patient outcomes.

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