Final answer:
Osteoblasts and osteoclasts react to Ca2+ levels in the blood stream to regulate calcium homeostasis. When blood Ca2+ levels increase, calcitonin is released to inhibit osteoclast activity, reducing the release of calcium into the blood. Conversely, when blood Ca2+ levels decrease, parathyroid hormone (PTH) is released to stimulate osteoclasts, increasing the release of calcium into the blood.
Step-by-step explanation:
Osteoblasts and osteoclasts are bone cells that react to Ca2+ levels in the blood stream to maintain calcium homeostasis. When blood Ca2+ levels decrease, parathyroid hormone (PTH) is released, which stimulates osteoclasts to resorb bone and release calcium into the blood. This increases the blood Ca2+ levels. On the other hand, if blood Ca2+ levels increase, calcitonin is released, which inhibits osteoclast activity. This reduces the resorption of bone and therefore, reduces the release of calcium into the blood, lowering the blood Ca2+ levels.