molecules no longer function. Some chemicals act to disrupt the lipid bilayer of membranes. These chemicals break down the phospholipids that make up the bulk of the membrane, thereby allowing the free passage of molecules into the cell’s internal environment. of cells. For example, during the hypertrophy of tissues mitochondria increase in number in order to meet the increased metabolic demands of the larger cell. Similarly, with atrophy, a decrease in the number of mitochondria occurs. With certain pathological conditions, a change in the size of the mitochondria is seen. With alcoholism, an increase is seen in the size of mitochondria, while some nutritional deficiencies cause a decrease in the size of mitochondria. During some physiological process, there are changes seen in the Like cell membranes, the is susceptible to denaturation in acidic conditions. Once the integrity of the cytoskeleton is compromised many cells cannot carry out their normal function. WBC’s cannot perform cytoplasmic streaming to get to the site of injury or infection, cilia in the respiratory tract cannot function as part of the mucocilliary elevator and sperm lose their motility. are also damaged during cell injury. Once the membrane surrounding a lysosome loses integrity the digestive enzymes contained within the lysosome spill out into the cytosol and begin to digest cellular structures. This is the mechanism by which autophagy occurs. Cellular Adaptations Like there are patterns in inflammation there are patterns seen in the changes cells undergo in response to injury or stress. The type of change seen depends on the type of injury and the type of cell involved. Some changes are reversible while others are irreversible. Atrophy Atrophy is defined as a decrease in the size of a cell or tissue. Atrophy is not always a pathological change and it can be reversible. When a cell or tissue has a decrease in activity the cell breaks down some of its organelles, as there is a decrease in metabolic demand. For example, when an individual stops the metabolic demands of muscle tissue decreases and muscle cells loses mass as they reduce the number of contractile fibres and mitochondria found in each cell. Some cases of atrophy are associated with a pathological state. Any pathological condition that reduces the activity of a tissue will cause atrophy. For example, a requires that a bone or limb be stabilized by a cast, pin or splint. Forced immobility has the effect of decreasing metabolic demands in the muscle tissue of the area. In response to decreased metabolic demands the muscle cells decrease in mass. Some causes of atrophy include:
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