Electron microscopy of a cardiomyocyte undergoing early reversible ischemic injury shows amorphous densities in the mitochondrial matrix. What is the biochemical significance of these densities?

• A They represent denatured proteins from loss of oxidative phosphorylation and indicate irreversibility
• B They are lipid droplets indicating shift to anaerobic glycolysis
• C They are calcium-phosphate flocculent densities marking irreversible injury ✓
• D They represent glycogen granules deposited during energy deficit

Explanation

Flocculent amorphous densities in the mitochondrial matrix on electron microscopy represent calcium-phosphate aggregates and are the hallmark of irreversible cell injury, indicating that mitochondrial membrane permeabilization has occurred and calcium has flooded into the matrix. These densities appear after about 20–40 minutes of ischemia in myocardium and mark the transition from reversible to irreversible injury. Contraction bands (due to calcium-mediated sarcomere hypercontraction) are seen in reperfused myocardium and also indicate irreversibility. Lipid droplets in ischemic cells appear as small vacuoles, not amorphous densities.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.