Bone Remodeling Affected By Osteoporosis Essay
Bone Remodeling Affected By Osteoporosis Essay
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Introduction
Bone remodeling is a cyclical process in which the mature bone tissues are constantly replaced by the new bone tissues. The process of mature or old bone tissue removal is called bone resorption and the process of new bone tissue formation is called ossification (Long, 2012). Bone Remodeling Affected By Osteoporosis Essay. However, due to osteoporosis the bone remodeling or the reformation of new bone tissues gets affected. While it must be kept within the homeostatic range to minimize the harmful effects of bone thinning. The factors that disrupt the bone remodeling include parathyroid hormone and thyroid hormone (Naylor & Eastell, 2012).
Discussion
The removal of mature bone tissues is both inhibited and enhanced by the signals received from the other parts of the body and the whole process depends on the availability and deficiency of calcium. Parathyroid gland has calcium sensing membrane receptors that senses the level of calcium in the body fluids. When the level of calcium reduces in blood, the parathyroid gland gets stimulated which leads to the secretion of parathyroid hormone. Calcitonin on the other hand reduces the effect of the osteoclasts and inhibits its production. This results in decreased resorption of bone tissues by the osteoclasts (Del Fattore, Teti & Rucci, 2012). Bone Remodeling Affected By Osteoporosis Essay.
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When parathyroid hormone gets secreted by the parathyroid gland, this in turn increases the level of as well as the activity of osteoclasts. The presence of the osteoclasts before the secretion of parathyroid hormone leads to an increased number and activity of the osteoclasts, the effect of the increased levels of osteoclasts are seen as increased resorption of phosphate and calcium ions. High levels of calcium in blood reduces the release of parathyroid gland and in turn reduced activity of the osteoclasts. Whereas, vitamin D helps in the effective absorption of phosphate and calcium from the intestine. The effects of osteoporosis are evident when the bone tissue formation (resorption) outpaces the process of removal of mature bone tissues (ossification). Due to the effect of osteoporosis bones loses it density, and it becomes fragile and porous (Boyce et al., 2012).
The harmful effects of osteoporosis are seen when the effects of osteoblasts in the bone tissue formation falls behind the increased effects of osteoclasts. In the normal and usual bone remodeling cycle, osteoblasts secrete calcium salts and collagen matrix which leads to the formation of new bone tissues. In the next process, the osteoblasts get calcified and its structur
2. The relationship between calcium and bones is that calcium is one of the minerals that make up the bones.…
As the osteoclasts are busy reabsorbing parts of the bone normally the osteoblasts would be going behind them to replace the reabsorbed bone.Bone Remodeling Affected By Osteoporosis Essay. In osteoporosis, the osteoclasts are continuing to do their job reabsorbing bone, but the osteoblasts are unable to keep up with them causing the bones to become brittle. The bone matrix itself remains intact, but the bone mass declines and the bones become porous and light. With the bones becoming more brittle, the possibility of a fracture increases, especially the neck of the thigh bone. If a fracture does occur, it can take longer or require surgical intervention to heal.
5. Scientists know that genetics play a role in who will develop osteoporosis. Being female, especially post-menopausal, is one of the well know genetic risk factors for developing osteoporosis. Others include either being Caucasian or Asian, having a small body frame, low body weight and a family history of maternal
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The bony skeleton is a remarkable organ that serves both a structural function, providing mobility, support, and protection for the body, and a reservoir function, as the storehouse for essential minerals.
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During childhood and adolescence bones are sculpted by a process called modeling, which allows for the formation of new bone at one site and the removal of old bone from another site within the same bone. This process allows individual bones to grow in size and to shift in space.
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Much of the cellular activity in a bone consists of removal and replacement at the same site, a process called remodeling. The remodeling process occurs throughout life and becomes dominant by the time that bone reaches its peak mass (typically by the early 20s). Remodeling continues throughout life so that most of the adult skeleton is replaced about every 10 years. Bone Remodeling Affected By Osteoporosis Essay.
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Both genes and the environment contribute to bone health. Some elements of bone health are determined largely by genes, and errors in signaling by these genes can result in birth defects. External factors, such as diet and physical activity, are critically important to bone health throughout life, and these factors can be modified.
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The growth of the skeleton, its response to mechanical forces, and its role as a mineral storehouse are all dependent on the proper functioning of a number of systemic or circulating hormones that respond to changes in blood calcium and phosphorus. If calcium or phosphorus are in short supply, the regulating hormones take them out of the bone to serve vital functions in other systems of the body. Too many withdrawals can weaken the bone.
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Many things can interfere with the development of a strong and healthy skeleton. Genetic abnormalities can produce weak, thin bones, or bones that are too dense. Nutritional deficiencies can result in the formation of weak, poorly mineralized bone. Many hormonal disorders can also affect the skeleton. Lack of exercise, immobilization, and smoking can also have negative effects on bone mass and strength.
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Osteoporosis, the most common bone disease, typically does not manifest until late in life, when bone loss begins due to bone breakdown and decreased levels of bone formation. Loss of bone mass leads to the development of structural abnormalities that make the skeleton more fragile. Bone Remodeling Affected By Osteoporosis Essay.
The purpose of this chapter is to provide an overview of bone biology that will help the reader to understand:
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why humans have bones;
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how bones work;
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how bones change during life;
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what keeps bones healthy;
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what causes bone disease, including the most common form, osteoporosis; and
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the future of bone biology and what it means for preventing and treating bone disease.
While dealing with a subject that is highly technical in nature, this chapter attempts to explain bone biology in terms that a lay person can generally understand. It is intended to provide the reader with the background needed to understand the basis for some of the preventive, diagnostic, and treatment approaches related to bone disease that are discussed in detail later in this report. Those interested in a more detailed review of bone biology and bone disease can consult any of a number of recent texts (Bilezikian et al. 2001, Marcus et al. 2001, Favus 2003). Bone Remodeling Affected By Osteoporosis Essay.
Why Do We Have Bones?
The bony skeleton is a remarkable organ that serves both a structural function—providing mobility, support, and protection for the body—and a reservoir function, as the storehouse for essential minerals. It is not a static organ, but is constantly changing to better carry out its functions. The development of the bony skeleton likely began many eons ago, when animals left the calcium-rich ocean, first to live in fresh water where calcium was in short supply, and then on dry land where weight bearing put much greater stress on the skeleton. The architecture of the skeleton is remarkably adapted to provide adequate strength and mobility so that bones do not break when subjected to substantial impact, even the loads placed on bone during vigorous physical activity. The shape or structure of bone is at least as important as its mass in providing this strength.
The skeleton is also a storehouse for two minerals, calcium and phosphorus, that are essential for the functioning of other body systems, and this storehouse must be called upon in times of need. The maintenance of a constant level of calcium in the blood as well as an adequate supply of calcium and phosphorus in cells is critical for the function of all body organs, but particularly for the nerves and muscle. Therefore, a complex system of regulatory hormones has developed that helps to maintain adequate supplies of these minerals in a variety of situations. Bone Remodeling Affected By Osteoporosis Essay. These hormones act not only on bone but on other tissues, such as the intestine and the kidney, to regulate the supply of these elements. Thus one reason that bone health is difficult to maintain is that the skeleton is simultaneously serving two different functions that are in competition with each other. First, bone must be responsive to changes in mechanical loading or weight bearing, both of which require strong bones that have ample supplies of calcium and phosphorus. When these elements are in short supply the regulating hormones take them out of the bone to serve vital functions in other systems of the body. Thus the skeleton can be likened to a bank where we can deposit calcium or phosphorus and then withdraw them later in times of need. However, too many withdrawals weaken the bone and can lead to the most common bone disorder, fractures.
Both the amount of bone and its architecture or shape are determined by the mechanical forces that act on the skeleton. Much of this is determined genetically so that each species, including humans, has a skeleton that is adapted to its functions. However, there can be great variation within a species, so that some individuals will have strong bones and others will have weak bones, largely because of differences in their genes (Huang et al. 2003). Moreover, bone mass and architecture are further modified throughout life as these functions and the mechanical forces required to fulfill them change. In other words, bones will weaken if they are not subjected to adequate amounts of loading and weight bearing for sufficient periods of time. If they are not (such as in the weightless condition of space travel), rapid bone loss can occur. In other words, as with muscle, it is “use it or lose it” with bone as well. Conversely, the amount and architecture of the bones can be improved by mechanical loading. However, as described in Chapter 6, some types of exercise may be better than others in strengthening the skeleton. Bone Remodeling Affected By Osteoporosis Essay.
To respond to its dual roles of support and regulation of calcium and phosphorus, as well as to repair any damage to the skeleton, bone is constantly changing. Old bone breaks down and new bone is formed on a continuous basis. In fact, the tissue of the skeleton is replaced many times during life. This requires an exquisitely controlled regulatory system that involves specialized cells that communicate with each other. These cells must respond to many different signals, both internal and external, mechanical and hormonal, and systemic (affecting the whole skeleton) and local (affecting only a small region of the skeleton). It is not surprising that with so many different tasks to perform and so many different factors regulating how the skeleton grows, adapts, and responds to changing demands, there are many ways that these processes can go astray.
How Bones Work
Bone is a composite material, consisting of crystals of mineral bound to protein. This provides both strength and resilience so that the skeleton can absorb impact without breaking. A structure made only of mineral would be more brittle and break more easily, while a structure made only of protein would be soft and bend too easily. The mineral phase of bone consists of small crystals containing calcium and phosphate, called hydroxyapatite. This mineral is bound in an orderly manner to a matrix that is made up largely of a single protein, collagen. Collagen is made by bone cells and assembled as long thin rods containing three intertwined protein chains, which are then assembled into larger fibers that are strengthened by chemical connections between them. Bone Remodeling Affected By Osteoporosis Essay. Other proteins in bone can help to strengthen the collagen matrix even further and to regulate its ability to bind mineral. Very small changes in the shape of the bone can act on the cells inside bone (the osteocytes), which produce chemical signals that allow the skeleton to respond to changes in mechanical loading. Abnormalities in the collagen scaffold can occur as a result of a genetic disorder called osteogenesis imperfecta, while the failure of mineral deposition can be the result of rickets and osteomalacia, conditions that result in marked weakening of the skeleton (see below and Chapter 3).
To provide the body with a frame that is both light and strong, bones are hollow. The outer dense shell is called cortical bone, which makes up roughly three-quarters of the total skeletal mass. Inside the cortical shell is a fine network of connecting plates and rods called trabecular bone that makes up the remaining 25 percent (Figure 2-1). Most bones are hollow structures in which the outer cortical bone shell defines the shape of the bone. This cortical shell is essential because it provides strength, sites for firm attachment of the tendons, and muscles and protection without excessive weight. The inner trabecular network has two important functions. It provides a large bone surface for mineral exchange. In addition, trabecular bone helps to maintain skeletal strength and integrity, as it is particularly abundant in the spine and at the ends of the long bones, sites that are under continuous stress from motion and weight-bearing. Fractures are common at these sites when the bone is weakened (Kontulainen, Sievanen et al. 2003). The rods and plates of trabecular bone are aligned in a pattern that provides maximal strength without too much bulk, much in the way that architects and engineers design buildings and bridges. The shape and size of both cortical and trabecular bone can respond to different kinds of stress produced by physical activity. For example, in most people the cortex of their dominant arm is larger than that of their non-dominant arm. The difference in cortex size is even larger for tennis players and other athletes who routinely use a dominant arm in their sporting activities. Bones do not work in isolation, but rather are part of the musculoskeletal system, providing the “lever” that allows muscles to move (by pulling on the lever). Bone Remodeling Affected By Osteoporosis Essay. Thus muscle activity is important for the normal function of the bone. When the mechanical force produced by muscle is lost—for example, in patients with muscular dystrophy or paralysis—bone mass and strength are also rapidly lost. Many bones in the skeleton also have connecting joints that provide greater flexibility of movement. These joints are sites of great mechanical stress and are subject to injury and to degeneration with aging. The most common type of joint degeneration is osteoarthritis, a painful, degenerative condition that affects the hip, knees, neck, lower back, and/or small joints of the hand. These joint diseases result from very different causes and require very different management than do bone diseases, and consequently they are not covered in this report. However it is important to recognize that the bones, joints, and muscles are the key parts of an integrated “musculoskeletal system.” Problems with any one component of this system can affect the other components. Thus, weakness of the muscles can lead to loss of bone and joint damage, while degeneration of the joints leads to changes in the underlying bone, such as the bony spurs or protuberances that occur in osteoarthritis. Bone Remodeling Affected By Osteoporosis Essay.
Figure 2-1
Frontal Longitudinal Midsection of Upper Femur. Source: Gray 1918.
How Bones Change Throughout Life
Throughout life, bones change in size, shape, and position. Two processes guide these changes—modeling and remodeling. When a bone is formed at one site and broken down in a different site its shape and position is changed. This is called modeling (Figure 2-2). However, much of the cellular activity in a bone consists of removal and replacement at the same site, a process called remodeling. The remainder of this section explains why and how these processes occur.
Figure 2-2
Modeling and Remodeling. Note: In modeling, osteoblast and osteoclast action are not linked and rapid changes can occur in the amount, shape, and position of bone. In remodeling, osteoblast action is coupled to prior osteoclast action. Net changes in (more…)
Why We Need Modeling and Remodeling
During childhood and adolescence bones are sculpted by modeling, which allows for the formation of new bone at one site and the removal of old bone from another site within the same bone (Seeman 2003) (Figure 2-2). This process allows individual bones to grow in size and to shift in space. During childhood bones grow because resorption occurs inside the bone while formation of new bone occurs on its outer (periosteal) surface. At puberty the bones get thicker because formation can occur on both the outer and inner (endosteal) surfaces.Bone Remodeling Affected By Osteoporosis Essay. As people get older, resorption occurs on inner surfaces while formation occurs on outer surfaces, which can partially compensate for the loss of strength due to the thinning of the cortex. The size and shape of the skeleton follows a genetic program, but can be greatly affected by the loading or impact that occurs with physical activity. Ultimately bones achieve a shape and size that fits best to their function. In other words, “form follows function.”
The remodeling process occurs throughout life and becomes the dominant process by the time that bone reaches its peak mass (typically by the early 20s). In remodeling, a small amount of bone on the surface of trabeculae or in the interior of the cortex is removed and then replaced at the same site (Figure 2-2). The remodeling process does not change the shape of the bone, but it is nevertheless vital for bone health, for a variety of reasons. First, remodeling repairs the damage to the skeleton that can result from repeated stresses by replacing small cracks or deformities in areas of cell damage. Remodeling also prevents the accumulation of too much old bone, which can lose its resilience and become brittle. Remodeling is also important for the function of the skeleton as the bank for calcium and phosphorus. Resorption (the process of breaking down bone), particularly on the surface of trabecular bone, can supply needed calcium and phosphorus when there is a deficiency in the diet or for the needs of the fetus during pregnancy or an infant during lactation. When calcium and phosphorus supplies are ample the formation phase of remodeling can take up these minerals and replenish the bank.
Modeling and remodeling continue throughout life so that most of the adult skeleton is replaced about every 10 years. While remodeling predominates by early adulthood, modeling can still occur particularly in response to weakening of the bone. Thus with aging, if excessive amounts of bone are removed from the inside, some new bone can be laid down on the outside, thus preserving the mechanical strength of the bone despite the loss of bone mass. Bone Remodeling Affected By Osteoporosis Essay.
