This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Which of the gland secretes calcitonin for regulation of calcium metabolism? \nSelect and explain. \nA. Thyroid gland, B. Parathyroid gland, C. Both of the above, D. None of the above', 'role': 'user'}, {'content': "Answer: A \nExplanation: Calcitonin is produced by the parafollicular cells of the thyroid gland, which are also known as the clear or C cells. Its secretion is increased when the thyroid gland is exposed to a plasma calcium level of approximately 9.5 mg/dL. The actions of calcitonin are sho-lived because it has a half-life of less than 10 min in humans. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 21. Hormonal Control of Calcium & Phosphate Metabolism & the Physiology of Bone. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.", 'role': 'assistant'}]