This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
A patient is on low calcium diet for 8 weeks. Following increases to maintain serum calcium levels 
Select and explain. 
A. PTH, B. Calcitonin, C. Active 24,25 dihydroxy cholecaliferol, D. Serum phosphate level
A: PTH
Answer: A: PTH 
Explanation: Parathyroid hormone (PTH), also called parathormone or parathyrin, is a hormone secreted by the parathyroid glands that is impoant in bone remodeling, which is an ongoing process in which bone tissue is alternately resorbed and rebuilt over time.Ref: Ganong&;s review of medical physiology: 24th edition; page no: 377