| 
Cellular Injury During Ischemia
Inadequate Energy Supply
 Lack
of glucose and oxygen deplete the cellular energy stores required
to maintain electrical potentials and ion gradients.
In ischemic brain tissue, the membrane that
surrounds each affected neuron becomes "leaky,"
and the cell loses potassium and adenosine triphosphate (ATP),
the tissue's medium for energy exchange.
Energy failure is not the immediate cause of
cell death; however, since all brain cells tolerate loss of
ATP for several minutes. In humans, it appears that
5 to 10 minutes of complete occlusion is required for irreversible
brain damage. In actuality, most strokes do not involve
a complete occlusion of blood flow, but even a partial occlusion,
if allowed to continue for a sufficient time, may produce
irreversible brain damage.
Once blood flow to cerebral neurons diminishes,
one or more branching mechanisms may independently lead to
brain cell death. These mechanisms may involve deterioration
of ion gradients or the effects of anaerobic metabolism.
With respect to the latter, anaerobic glycotic
pathways are utilized in the affected region to compensate
for the loss of oxygen and provide a source of energy.
However, this produces damaging by-products, including lactic
acid and hydrogen ions, which accumulate in tissue in proportion
to the carbohydrate stores present at the outset of ischemia.
Toxicity of hydrogen ions, especially their ability to facilitate
ferrous-iron-mediated free-radical mechanisms, appears to
irreversibly affect neuronal integrity.
|
Stroke Education
