Bone Remodeling through Hormonal Control - Essay Example

?Bone Remodeling The human body is amazing. From the amazing feats of strength, flexibility and endurance it can do on the outside (e.g. athletes, gymnasts, soldiers, etc.), to the minute processes that take place inside keeping us alive, our bodies are complex creations doing dozens of processes and activities at the same time, almost 24/7 from birth until death. It is a cacophony of chemicals flowing and acting upon each other, striving to keep the balance, homeostasis, which keeps us healthy. Some of those chemical reactions can be seen through the process of bone remodeling. Our bones make up the supportive structure that keeps our shape and allows us to move. From our infancy to our death our bones grow and change characteristics from flexible cartilage to mature “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 “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 continuously 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 “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 body 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 other form of stress is the pull of our own muscles. As we move, our muscles pull at our bones, creating ambulation. Both the constant pull of gravity and the intermittent, yet sometimes forceful pulls of our muscles create a situation wherein our bones are continually under tension and compression of different magnitudes at different parts of different bones. To put this into perspective, it would be accurate to compare the stress experienced by the bone to a long bridge during a strong earthquake. The stress and the weight would most likely break the bridge in half. But after the earthquake, engineers would rebuild and try another design that could handle an earthquake, making the bridge stable. That is the same as bone remodeling. Human beings are bipeds, and we are designed with the bones to move efficiently as bipeds. The shapes of our bones hold a functionality that keeps it secure under all the stress. Like the repaired bridge, our bones are designed to be strong where it needs to be strong, so that it may withstand the stress. The law that governs this phenomenon is called the Wolff’s Law. It states “that a bone grows or remodels in response to the demands placed on it” (Marieb & Hoehn, 2006). An example of this is a typical human femur. This long bone is subject to the weight of the human body from the hips upwards, adding to that, it is surrounded by some of the largest and strongest muscles used for movement. The amount of strain would have been bone-shattering. The weight of the body doesn’t push down parallel to the bone, but rather at an angle. This causes the bone to bend wherein the proximal side of the femur is compacted, the distal side is stretched, while the middle of the bone experiences no stress because it is canceled out by the opposing forces around it. Because of this, the long bone can be hollow on the inside yet solid on the outside and still be able to hold our body weight. The process of bone remodeling, whether through hormones or through mechanical stress, is an adaptive and essential bodily function that keeps us standing. All the minute details that go into the balancing of calcium in the body and the maintenance of bone integrity gives insight into how amazing our body truly is, both from the inside and out. References Krapp, K. (Ed.). (2002). The Gale encyclopedia of nursing and allied health (Vol. 4). Farmington Hills, MI: Gale Group. Marieb, E. N., & Hoehn, K. (2006). Human anatomy and physiology (7th ed.). San Francisco, CA: Benjamin Cummings. Read More