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See below - Essay Example From our infancy to our death our bones grow and change characteristics from flexible cartilage to mature â€Å"hard-as-rock† bone, to porous, brittle bones of old age. Two of the most important elements that make up hard, mature bone are Calcium and Phosphate. Calcium is the most abundant element in the body. Aside from maintaining bones and teeth it can also â€Å"enable the contraction of muscles, including the function of the body’s most important muscle, the heart. It is also essential for normal blood clotting, proper nerve impulse transmission, and the appropriate support of connective tissue† (Krapp, 2002, p. 387). Phosphate plays many other roles in the body, mostly as a component of ATP and as a buffer to other compounds. In the bones, Phosphate and calcium ions combine into hydroxyapatite, which is the structural material found in bones. There is a limit to the amount of Calcium and Phosphate in the body. To maintain proper levels of both, the bones co ntinuously undergo bone remodeling. Bone remodeling is the process of bone deposit and bone resorption combined. It involves correcting imbalances between phosphate and calcium levels in the blood. Normally, a human has 9-11 mg of calcium for every 100ml of blood (Marieb & Hoehn, 2006). If it drops below that, calcium is taken from the blood, and if it exceeds it, the extra calcium is absorbed into the blood. The components that make bone remodeling happens are your Parathyroid hormones, your calcitonin, your osteoblasts and your osteoclasts. Parathyroid hormones are hormones released by the Parathyroid gland that stimulates osteoclasts to break down bone. Osteoclasts are made from the same kind of stem cells that turn into macrophages. They â€Å"move along a bone surface, digging grooves as the break down the bone matrix† (Marieb & Hoehn, 2006), transporting the calcium parts of it into the blood. Since there is a very little difference between nine and eleven milligrams of calcium, the body has to make sure the osteoclasts don’t overdo it. This is where calcitonin comes in. When there is an excess of calcium in the blood, calcitonin is secreted by the thyroid gland, and it activates your bones’ osteoblasts. Osteoblasts are the opposite of the osteoclasts. It absorbs calcium from the blood and stimulates calcium salt deposit in the bone, balancing the calcium levels. This cycle goes on and on, perpetually trying to strike that balance. If too much calcium is released to the blood, the bones would be brittle and would break easily, and if too much calcium is absorbed, the heart would not be able to contract correctly, leading to many possible circulatory problems. Bone remodeling through hormonal control is not primarily for the benefit of the bones. Bone integrity is secondary to maintaining a normal amount of calcium in the blood. Bones are just storage space for ionic calcium to be used by the rest of the body. If it needs more, the bo dy will just keep demineralizing the bones until it has enough in the blood, likewise, if there is too much calcium, neither the blood nor the bones can keep all of it. Calcium salt deposits can form in many organs, thereby hampering the function of these organs such as blood vessels, kidneys, etc. There is another way wherein bones are remodeled. That is through mechanical stress. Gravity is a constant. It is always weighing the bones down. The