MEDizzy - A 54-year-old man develops a thrombus in his left anterior

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General Pathology (I)

A 54-year-old man develops a thrombus in his left anterior descending coronary artery. The area of myocardium supplied by this vessel is irreversibly injured. The thrombus is destroyed by the infusion of streptokinase, which is a plasminogen activator, and the injured area is reperfused. The patient, however, develops an arrhythmia and dies. An electron microscopic (EM) picture is taken of the irreversibly injured myocardium. Which one of the listed EM findings is most characteristic of irreversible ischemic cell damage?

ExplanationSevere damage to mitochondria is a characteristic finding of irreversible cellular injury. With prolonged ischemia, certain cellular events occur that are not reversible, even with restoration of oxygen supply. These cellular changes are referred to as irreversible cellular injury. In addition to severe damage to mitochondria, this type of injury is characterized by extensive damage to plasma membranes and nuclei, and rupture of lysosomes. Irreversible damage will result in the influx of calcium ions into the mitochondria and the subsequent formation of large, amorphic (flocculent) densities. These flocculent densities are characteristically seen in irreversibly injured myocardial cells that undergo reperfusion soon after injury. Less severe changes in mitochondria, such as mitochondrial swelling, are seen with reversible injury. Subsequently, cytochrome c released from damaged mitochondria can induce apoptosis, a process through which irreversibly injured cells can shrink and increase the eosinophilia of their cytoplasm. These shrunken apoptotic cells (apoptotic bodies) may be engulfed by adjacent cells or macrophages.