Question

Which finding on electron microscopy indicates irreversible cell injury?

• A. Dilatation of endoplasmic reticulum
• B. Dissociation of ribosomes from rough endoplasmic reticulum
• C. Flocculent densities in mitochondria
• D. Myelin figures

Hint:

Reversible changes involve ER and ribosomes; irreversible injury shows severe, permanent mitochondrial damage.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which change seen under the electron microscope tells us that a cell has crossed the point of no return and cannot recover, that is irreversible injury.

Step 2: Key Formula or Approach:
Cell injury is graded as reversible or irreversible based on structural changes. Reversible injury shows swelling of the cell and organelles, ER dilation, ribosome detachment, and chromatin clumping, all of which can return to normal if the stress is removed. Irreversible injury adds severe mitochondrial damage that cannot be undone, most classically large amorphous flocculent densities inside the mitochondrial matrix.

Step 3: Detailed Explanation:
Dilatation of the endoplasmic reticulum happens early in cell injury and is fully reversible once normal oxygen and ATP supply return.
Dissociation of ribosomes from the rough endoplasmic reticulum is also an early, reversible change, it reduces protein synthesis but the ribosomes reattach if the cell recovers.
Flocculent densities in mitochondria are large, amorphous, cottonwool like deposits that form inside a severely swollen and damaged mitochondrion. This change appears only after the cell has lost the ability to recover and is taken as a marker of irreversible injury.
Myelin figures are whorled membrane fragments that can appear in both reversible and irreversible injury, since they simply mark membrane damage and phospholipid rearrangement, so they do not by themselves point to irreversible injury.

Step 4: Final Answer:
The finding that specifically marks irreversible cell injury is flocculent densities in the mitochondria.