Final answer:
Bone storage maintains calcium by storing it, and PTH maintains it by releasing it when necessary. PTH and calcitonin work together to regulate blood calcium levels.
Step-by-step explanation:
Correct calcium ion concentration in blood and bone is maintained by bone storage, which stores calcium, and parathyroid hormone (PTH), which releases it. Bones serve as the primary reserves for calcium and phosphorus. When blood levels of calcium decrease, PTH is secreted by the parathyroid glands, which increases calcium levels by stimulating osteoclasts to resorb bone and release calcium into the blood. Conversely, when blood calcium levels are too high, calcitonin is secreted from the thyroid gland to lower blood calcium levels by inhibiting osteoclast activity and encouraging osteoblasts to incorporate calcium into bone.