lab6 - 6 Histopathology Objectives In this chapter we will...

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35 6 Histopathology Objectives In this chapter we will study some of the factors leading to cellular injury and necrosis; the effects of cell damage or cell death on tissues and organs; and how histotechnologists and histopathologists study diseased tissues. Cellular Injury and Tissue Damage Cells are vulnerable to injury by such chemical and physical factors as oxygen deprivation (hypoxia), free radicals, toxic chemicals, nutritional imbalances, temperature extremes, acids and bases, trauma, and radiation. Cells can often respond to such disturbances by making homeostatic adjustments in their metabolism, but severe disturbances may cause structural changes that can be observed microscopically. The study of such structural changes and the diagnosis of disease from histological evidence—that is, the clinical applica-tion of histology—is called histopathology. Irreversible damage to cell structure and function leads to cell and tissue necrosis— pathological death, as compared to apoptosis, the “programmed death” of cells that were destined to die in the service of normal bodily development and function. Some of the causes of cellular injury are described here. Hypoxia Hypoxia, or oxygen deficiency, is the most common cause of cell death. It can result from ischemia (deficient blood flow to a tissue), respiratory disorders such as emphysema that interfere with oxygen pickup by the blood, or various kinds of poisoning that interfere with the blood’s ability to transport oxygen (carbon monoxide poisoning) or the tissues’ ability to use the oxygen they receive (cyanide poisoning). Hypoxia forces cells to shift to anaerobic fermentation, which may be harmful in two ways: (1) It may produce too little ATP to meet the cell’s needs, causing the cell to die from a shortage of usable energy, and (2) hypoxia produces lactic acid, which lowers the pH of the cell, especially in ischemic tissues where blood flow is inadequate to remove the lactic acid from the tissue. Free Radicals Free radicals are produced as a normal, toxic by- product of cell metabolism (especially aerobic respiration) and by exposure to radiation and some chemicals. Free radicals can kill cells in three ways: lipid peroxidation (destruction of unsaturated fatty acids), protein fragmentation , and DNA alterations. Of the three, lipid peroxidation is probably the most destructive. When the free radical (usually OH•) reacts with the double bond of an unsaturated fatty acid, the reaction generates peroxide. The peroxide then initiates a series of reactions that damage the plasma membrane and the membranes of the cell’s organelles, killing the cell. In protein fragmentation, peroxide reacts with specific amino acid side chains and irreversibly disrupts the secondary and tertiary structures of the protein, leading to fragmentation.
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This note was uploaded on 11/16/2011 for the course SCIENCE Anatomy an taught by Professor Tory during the Spring '11 term at Kennesaw.

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lab6 - 6 Histopathology Objectives In this chapter we will...

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