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

This question tests the difference between reversible and irreversible cell injury as seen under the electron microscope. Reversible changes are ones the cell can undo once the harmful stimulus is removed, irreversible changes mean the cell is already committed to death.

1. Dilatation of endoplasmic reticulum: This is an early change from loss of ATP and calcium pump failure. It reverses fully once normal metabolism is restored, so it does not mark irreversible injury.
2. Dissociation of ribosomes from rough endoplasmic reticulum: This lowers protein synthesis but is also an early, reversible event tied to falling ATP levels.
3. Flocculent densities in mitochondria: These are large, amorphous, cotton like deposits inside a badly swollen mitochondrion. They appear only once the mitochondria are damaged beyond repair, so pathologists use this finding as the structural sign of irreversible injury.
4. Myelin figures: These whorled membrane structures come from damaged cell and organelle membranes, but they can be seen in both reversible and irreversible injury, so they are not a specific marker on their own.

The option that specifically points to a cell that cannot recover is flocculent densities in mitochondria, since they reflect permanent structural collapse of the mitochondria.

Let's summarize:

• ER dilation and ribosome loss are early, reversible changes.
• Myelin figures occur in both reversible and irreversible injury.
• Flocculent mitochondrial densities are the electron microscopy hallmark of irreversible injury.

So the correct answer is flocculent densities in mitochondria.