Final answer:
The bones store excess calcium, and when calcium levels in the blood drop, PTH is released, stimulating the release of calcium from the bones, increasing dietary calcium absorption, and promoting calcium reabsorption in the kidneys. Vitamin D supports intestinal absorption of calcium, while calcitonin helps to lower blood calcium levels when they are too high.
Step-by-step explanation:
The process of calcium storage in bone and its release into the bloodstream involves a tightly regulated system that ensures a balance, or homeostasis, of calcium levels in the body. Bones serve as the main storage sites for calcium, housing more calcium than any other organ. When blood levels of calcium fall too low, parathyroid hormone (PTH) is released, prompting the mobilization of calcium from the bones into the bloodstream. This includes stimulating osteoclasts to reabsorb bone and release calcium, increasing absorption of dietary calcium in the intestines, and promoting reabsorption of calcium in the kidneys. Vitamin D assists by enhancing dietary calcium absorption, while calcitonin, released from the thyroid gland when blood calcium levels are high, opposes the actions of PTH, reducing osteoclast activity and promoting the activity of osteoblasts to incorporate calcium into the bone matrix, thereby lowering blood calcium levels.