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
Calcitonin is secreted by: 
Select and explain. 
A. Thyroid gland, B. Parathyroid gland, C. Adrenal glands, D. Ovaries
A: Thyroid gland
Answer: A: Thyroid gland 
Explanation: Calcitonin is primarily secreted by the parafollicular C cells of the Thyroid gland. It is a hormone secreted in response to elevated blood calcium. It stimulates calcium deposition in bone and calcium excretion by the kidneys, thus reducing blood calcium. Ref: Essentials of Pharmacology By K D Tripathi, 5th, Edition, Page 301; Ganong's Review of Medical Physiology, 22nd Edition, Page 393.