Ischemia

Overview
  • Ischemia refers to a combined deficiency in both oxygen and nutrient delivery to a tissue.
Pathogenesis
  • Elimination of both oxygen and nutrient delivery to cells results in a complete inability to produce ATP either from cellular respiration or glycolysis. Consequently, ischemia results in catastrophic declines in cellular ATP stores and the capacity of the cell to continue energy-dependent cellular processes. Derangement of membrane permeability is the primary biochemical sequelae of Ischemia (See: Cell Injury Biochemistry). However, because in ischemic scenarios loss of ATP is rapid, injury to the cell membrane quickly reaches a point of irreversibility and thus induces cell death. The macroscopic, tissue-level manifestation of wide-spread ischemic cell death is termed Infarction. Unfortunately, restoration of blood flow to ischemic tissues which have not reached the point of irreversible injury can often be detrimental due to Reperfusion Injury.
Etiology
  • A reduction in the blood supply of a tissue may occur due to a sudden blockage of its vasculature or arise due to catastrophic decline in blood pressure. Sudden narrowing of vasculature may occurs if the vessel undergoes thrombosis or becomes occluded by an embolism which in most cases is a thromboembolism. Acute local declines in blood pressure may occur downstream of a hemorrhaging artery. However, catastrophic cases of shock may also reduce systemic blood pressure, leading to widespread ischemia.