Final answer:
Calcitonin is a hormone produced by the thyroid gland that decreases blood calcium levels by inhibiting osteoclasts and stimulating osteoblasts. Its role is most important in children, during pregnancy, and during prolonged starvation.
Step-by-step explanation:
Calcitonin, a hormone produced by the thyroid gland, decreases blood calcium levels by inhibiting osteoclasts and stimulating osteoblasts. It also stimulates calcium excretion by the kidneys. This hormone helps promote bone growth in children, reduces maternal bone loss during pregnancy, and reduces bone mass loss during prolonged starvation. In healthy adults, the role of calcitonin is unclear.