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oxygen deprivation

Sunday 29 January 2006

- Hypoxia is a deficiency of oxygen, which causes cell injury by reducing aerobic oxidative respiration. Hypoxia is an extremely important and common cause of cell injury and cell death. It should be distinguished from Ischemia.

- Ischemia is a loss of blood supply from impeded arterial flow or reduced venous drainage in a tissue resulting in oxygen deprivation and hypoxia.

But Ischemia compromises the supply not only of oxygen, but also of metabolic substrates, including glucose (normally provided by flowing blood). Therefore, ischemic tissues are injured more rapidly and severely than are hypoxic tissues.

- One cause of hypoxia is inadequate oxygenation of the blood due to cardiorespiratory failure. Loss of the oxygen-carrying capacity of the blood, as in anemia or carbon monoxide poisoning (producing a stable carbon monoxyhemoglobin that blocks oxygen carriage), is a less frequent cause of oxygen deprivation that results in significant injury.

- Depending on the severity of the hypoxic state, cells may adapt, undergo injury, or die. For example, if the femoral artery is narrowed, the skeletal muscle cells of the leg may shrink in size (atrophy).

- This reduction in cell mass achieves a balance between metabolic needs and the available oxygen supply. More severe hypoxia induces injury and cell death.