The way in which a cell responds to a pathogen is governed by the of pathogen involved as well as by the cell type. By understanding the mechanisms used by various types or classes of pathogens one can predict the responses that will be generated in the cell. Causes of Cellular Injury Some major types of cellular injury include hypoxic injury, chemical injury, physical injury, biological injury, immune-mediated responses, genetic mutations, age related injury & nutritional imbalances. 1. Hypoxia Hypoxia is the most common mechanism of cellular injury. Hypoxia is defined as a decrease in the oxygenation of tissues and has its most profound effect on aerobic cellular metabolism. The cells must rely on anaerobic energy production which results in decreased energy production, decreased protein synthesis, lipid deposition and an increasingly acidic environment.
There are three general causes for hypoxia:
1.
The first is
. Ischemia is a reduction in tissue perfusion. Ischemia can be
caused by arterial constriction, venous congestion, or haemorrhage.
2. The second cause of hypoxia is decreased intake of oxygen from the . This occurs in cases where the environment has little or no oxygen, such as under water or at very high altitudes, or in cases of respiratory failure or disease. 3. The third scenario in which hypoxia occurs is instances where the blood has a decreased capacity to oxygen. Anemia is a reduction in the number of circulating red blood cells (RBC’s). The effect of anemia is that the blood cannot carry a normal amount of oxygen as haemoglobin molecules located inside RBC’s is the major carrier of oxygen in the blood. Anemia can be caused by genetic disease, hormonal imbalances, or insufficient dietary intake of iron. Another cause for a reduction in the carrying capacity of blood for oxygen is carbon monoxide poisoning. Haemoglobin has a greater affinity for carbon monoxide than it does for oxygen and therefore binds more readily to carbon monoxide molecules than to oxygen molecules. 2. Chemical Damage Chemical agents can contain molecules that interfere with membrane integrity or alter the function of membrane transport proteins, disrupt osmotic balance or enzyme/cofactor function ultimately hampering the control of the content of the ICF, and thereby disrupting homeostasis. Chemical damage can be caused by a wide variety of substances, many of which may not be normally considered “chemicals”. Substances such as poisons, venoms and drugs, and even molecules like glucose or vitamins if they are present in excess can affect homeostasis.
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