Which hormone is primarily produced in medullary thyroid carcinoma?

• A. Calcitonin
• B. Thyroxine
• C. Insulin
• D. Parathyroid hormone

Answer: (A)

Medullary thyroid carcinoma (MTC) primarily produces calcitonin, which is a hormone secreted by the parafollicular cells, also known as C cells, of the thyroid gland. In MTC, there is a malignant transformation of these C cells, leading to elevated levels of calcitonin in the serum. Calcitonin plays a role in regulating calcium levels by inhibiting osteoclast activity, which decreases bone resorption and lowers blood calcium levels.

Thyroxine is produced by the follicular cells of the thyroid gland and is responsible for regulating metabolism, while insulin is secreted by the pancreas and is crucial for glucose metabolism. Parathyroid hormone, on the other hand, is produced by the parathyroid glands and is involved in regulating calcium levels in the blood, working in opposition to calcitonin. Thus, in the context of medullary thyroid carcinoma, calcitonin's production is the key feature that sets it apart from other hormone disorders.