MAYOR HEALTH TIP (ISCHEMIA) This is a restriction in blood supply to tissues, causing a shortage of oxygen and glucose needed for cellular metabolism(to keep tissue alive). [ 3 ]Ischemia is generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue. It also meanslocal anemiain a given part of a body sometimes resulting from congestion (such as vasoconstriction, thrombosisor embolism). Signs and symptoms Further information: ischemic cascade, stroke, and heart attack Since oxygen is carried to tissues in the blood, insufficient blood supply causes tissue to become starved of oxygen. In the highly aerobictissues of the heartand brain, irreversible damage to tissues can occur in as little as 3–4 minutes at body temperature. The kidneysare also quickly damaged by loss of blood flow. Tissues with slower metabolic rates may undergo irreversible damage after 20 minutes. Ischemia results in tissue damage in a process known as ischemic cascade. The damage is the result of the build-up of metabolic wasteproducts, inability to maintain cell membranes, mitochondrialdamage, and eventual leakage of autolyzing proteolytic enzymesinto the cell and surrounding tissues. Restoration of blood supply to ischemic tissues can cause additional damage known as reperfusion injurythat can be more damaging than the initial ischemia. Reintroduction of blood flow brings oxygen back to the tissues, causing a greater production of free radicalsand reactive oxygen speciesthat damage cells. It also brings more calcium ions to the tissues causing further calcium overloading and can result in potentially fatal cardiac arrhythmiasand also accelerates cellular self-destruction. The restored blood flow also exaggerates the inflammationresponse of damaged tissues, causing white blood cellsto destroy damaged cells that may otherwise still be viable
Posted on: Mon, 30 Sep 2013 07:33:03 +0000
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