Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland. It plays a crucial role in calcium homeostasis by opposing the action of parathyroid hormone (PTH). While PTH raises blood calcium levels, calcitonin works to lower them.
1. Physiology of Calcitonin
Source: Calcitonin is produced by the thyroid gland’s parafollicular cells (C cells).
Function:
Calcium Regulation: Calcitonin helps regulate calcium and phosphate homeostasis by opposing the action of parathyroid hormone (PTH).
Bone Deposition: Calcitonin inhibits calcium resorption from bones, promoting calcium deposition into the bone matrix.
Renal Calcium Excretion: It increases calcium excretion in the urine, reducing serum calcium levels.
Control:
Stimulation: Calcitonin secretion is stimulated by high levels of serum calcium.
2. Pathological Role of Calcitonin
Hypercalcemia: While calcitonin lowers blood calcium levels, its role in addressing hypercalcemia is generally considered less significant than parathyroid hormone (PTH). Excess calcitonin production rarely leads to pathological conditions.
Medullary Thyroid Carcinoma: In some cases, tumors of the thyroid C cells, known as medullary thyroid carcinoma (MTC), can produce excessive amounts of calcitonin, leading to elevated blood levels. MTC is a rare but serious form of thyroid cancer.
3. Clinical Uses of Calcitonin
Osteoporosis Treatment:
Salmon Calcitonin: Synthetic calcitonin, derived from salmon, has been used to treat osteoporosis. It helps to slow bone loss and may have a modest effect in reducing fracture risk.
Limited Use: The use of calcitonin for osteoporosis has diminished over time due to the availability of more effective treatments.
Pain Management in Hypercalcemia:
Limited Role: Calcitonin may be a short-term measure for managing acute pain associated with hypercalcemia, especially caused by conditions like malignancy.
Not a Primary Treatment: It is not considered a primary treatment for hypercalcemia but may provide some symptomatic relief.
4. Considerations in Treatment
Calcitonin Nasal Spray:
Administration: Calcitonin can be administered as a nasal spray.
Adverse effects are generally mild and may include nasal irritation.
Alternative Therapies:
Bisphosphonates: More commonly, bisphosphonates are preferred for treating osteoporosis and hypercalcemia due to their greater efficacy.
Calcitonin, though playing a role in calcium regulation, is not the primary hormone in maintaining calcium homeostasis. Its clinical use, especially for osteoporosis, has diminished over time due to the availability of more effective treatments. However, it remains a part of the therapeutic armamentarium in certain clinical scenarios, such as short-term pain management in hypercalcemia. The primary physiological function of calcitonin is to counterbalance the effects of PTH and contribute to the regulation of calcium metabolism.
