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                    Hypoxia is a reduction in oxygen supply to one or more areas 
                    of the body. Total absence of oxygen is called anoxia. Cells 
                    throughout the body depend on oxygen to survive; when the 
                    oxygen supply is reduced, cells begin to starve and eventually 
                    die.   The brain, which is the body's single largest 
                    consumer of oxygen. Although the brain represents only about 
                    2% of the body's weight, it utilizes about 20% of the body's 
                    oxygen. As a result, the brain is especially sensitive to 
                    hypoxia. After about 4 to 6 minutes without oxygen, large 
                    numbers of brain cells begin to die. Prolonged hypoxia (e.g. 
                    suffocation) results in death.   Shorter intervals of hypoxia may result 
                    in lesser degrees of brain damage. The effects of hypoxia 
                    are especially severe in the hippocampus. 
                    Individuals who survive an hypoxic episode often sustain hippocampal 
                    damage and anterograde 
                    amnesia.  Ischaemic hypoxia is caused by a circulatory 
                    problem. Normally, oxygen is carried throughout the body via 
                    the bloodstream. When the flow of blood is reduced or blocked, 
                    cells which depend on that bloodflow are deprived of oxygen 
                    (and other nutrients). Ischaemic hypoxia can be caused by 
                    a variety of conditions including cardiac arrest, stroke 
                    or aneurysm, and 
                    massive bleeding.   Anemic hypoxia occurs when oxygen levels 
                    in the blood fall below normal levels. In this case, bloodflow 
                    continues to reach its target areas, but does not bring the 
                    needed oxygen with it. Anemic hypoxia can be caused by conditions 
                    including carbon monoxide poisoning, respiratory failure or 
                    obstruction (e.g. choking or near-suffocation), sleep 
                    apnea, or anesthesia overdose.  Further Reading: "Arrested 
                    Memories" by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain
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