User talk:Abdullahjkj

Cell death Cells can die via one of the following two ways: 1. Necrosis 2. Apoptosis 1. Necrosis In necrosis, excess fluid enters the cell, swells it, & ruptures its membrane which kills it. After the cell has died, intracellular degradative reactions occur within a living organism. Necrosis does not occur in dead organisms. In dead organisms, autolysis & heterolysis take place. Necrosis occurs by the following mechanisms: A. Hypoxia B. Free radical-induced cell injury C. Cell membrane damage D. Increased intracellular calcium level 19 A. Hypoxia Hypoxia is decreased oxygen supply to tissues. It can be caused by: 1. Ischemia Ischemia is decreased blood flow to or from an organ. Ischemia can be caused by obstruction of arterial blood flow – the most common cause, or by decreased perfusion of tissues by oxygen-carrying blood as occurs in cardiac failure, hypotension, & shock. 2. Anemia Anemia is a reduction in the number of oxygen-carrying red blood cells. 3. Carbon monoxide poisoning CO decreases the oxygen-capacity of red blood cells by chemical alteration of hemoglobin. 4. Poor oxygenation of blood due to pulmonary disease. The cell injury that results following hypoxia can be divided into early & late stages: 1. Early (reversible) stages of hypoxic cell injury At this stage, hypoxia results in decreased oxidative phosphorylation & ATP synthesis. Decreased ATP leads to: a. Failure of the cell membrane Na – K pump, which leads to increased intracellular Na & water, which cause cellular & organelle swelling. Cellular swelling (hydropic change) is characterized by the presence of large vacuoles in the cytoplasm. The endoplasmic reticulum also swells. The mitochondria show a low amplitude swelling. All of the above changes are reversible if the hypoxia is corrected. b. Disaggregation of ribosomes & failure of protein synthesis. 2. Late (irreversible) stages of hypoxic cell injury. This is caused by severe or prolonged injury. It is caused by massive calcium influx & very low pH, which lead to activation of enzymes, which damage the cell membrane& organelle membranes. Irreversible damage to the mitochondria, cell membranes, & the nucleus mark the point of no return for the cell, that is after this stage, the cell is destined to die.