Final answer:
Calcitonin is a hormone that lowers blood calcium levels by stimulating osteoblasts and promoting calcium absorption in bones.
Step-by-step explanation:
Calcitonin is a hormone synthesized by the parafollicular cells of the thyroid gland. It acts primarily on osteoblasts, stimulating calcium absorption and deposition in bone, which helps lower blood calcium levels. Calcitonin works synergistically with calcitriol, an active form of vitamin D, to maintain calcium homeostasis in the body.