USMLE题库Cardiology(一)1-10.pptx

Cardiology 1 题库 Q 1 A 54-year-old Caucasian male comes to the emergency room with retrosternal chest pain of 30 minutes duration. The patient also complains of sweating and mild dyspnea. A single tablet of nitroglycerin is delivered sublingually, and the patient’s pain decreases significantly. The patient has experienced several similar episodes of pain over the last 12 hours, all of which resolved spontaneously. Which of the following ultrastructural changes would most likely indicate irreversible myocardial cell injury in this patient? A. Myofibril relaxation B. Disaggregation of polysomes C. Mitochondrial vacuolization D. Disaggregation of nuclear granules E. Triglyceride droplet accumulation F. Glycogen loss A 1: Correct answer: C The appearance of vacuoles and phospholipid-containing amorphous densities within mitochondria generally signifies irreversible injury, and implies a permanent inability to generate further ATP via oxidative phosphorylation. When the mitochondria are injured irreversibly, the cell cannot recover. Simple mitochondrial swelling may be associated with reversible cellular injury, however. (Choice A) Myofibril relaxation is an early sign of reversible injury in cardiac myocytes, which occurs within the first 30 minutes of severe ischemia. Myofibril relaxation corresponds with intracellular ATP depletion and lactate accumulation due to anaerobic glycolysis during this period. (Choice B) Disaggregation of polysomes denotes the dissociation of rRNA from mRNA in reversible ischemic/hypoxic injury. Depletion of intracellular ATP is thought to promote the dissolution of polysomes into monosomes as well as the detachment of ribosomes from the rough endoplasmic reticulum. Disaggregation of polysomes results in impaired protein synthesis. (Choice D) Disaggregation of granular and fibrillar elements of the nucleus is associated with reversible injury. Another common nuclear change associated with reversible cell injury is clumping of nuclear c