Ischemia : is a restriction in blood supply to tissues, causing a shortage of oxygen and glucose needed for cellular metabolism (to keep tissue alive).
Ischemia is generally caused by problemswith blood vessels, with resultant damage to or dysfunction of tissue. It also means local anemia in a given part of a body sometimes resulting from congestion (suchas vasoconstriction, thrombosisor embolism).
Since oxygen is carried to tissues in the blood, insufficient blood supply causes tissue to become starved of oxygen. In the highly aerobic tissues of the heart and brain, irreversible damage totissues can occur in as little as 3–4 minutes at body temperature. The kidneys are also quickly damaged by loss of blood flow. Tissues with slower metabolic rates may undergo irreversible damage after20 minutes.
Ischemia results in tissue damage in a process known as ischemic cascade. The damage is the result of the build-up ofmetabolic waste products, inability to maintain cellmembranes, mitochondrial damage, and eventual leakage ofautolyzing proteolytic enzymes into the cell and surrounding tissues.
Restoration of blood supply to ischemic tissues can cause additional damage knownas reperfusion injury that can be more damaging than the initial ischemia. Reintroduction of blood flow brings oxygen back to the tissues, causing a greater production of free radicals and reactive oxygenspecies that damage cells. It also brings more calcium ions to the tissues causing further calcium overloading and can result in potentially fatal cardiac arrhythmias and also acceleratescellular self-destruction. The restored blood flow also exaggerates the inflammation response of damaged tissues, causing white blood cells to destroy damaged cells that may otherwise still be viable.-------------------------------------------------
Decrease in body temperature reduces the aerobic metabolic rate of the affected cells, reducing the immediate effects of hypoxia. Reduction of...
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