Final answer:
Calcitonin, produced by the thyroid gland, lowers blood calcium levels by inhibiting osteoclasts, decreasing kidney reabsorption, and stimulating osteoblasts, maintaining calcium homeostasis.
Step-by-step explanation:
In calcium homeostasis, calcitonin plays a crucial role by lowering the levels of calcium in the blood when they become too high. This hormone, produced by the parafollicular or C cells of the thyroid gland, inhibits the activity of osteoclasts—the bone cells that resorb bone and release calcium into the blood—and also decreases calcium reabsorption by the kidneys. Furthermore, calcitonin stimulates the activity of osteoblasts, which are cells that help build bone by incorporating calcium into the bony matrix. The actions of calcitonin result in a decrease of blood calcium levels, thus helping to maintain calcium homeostasis.