All of the following are features of reversible cell injury EXCEPT:

Explanation

## Reversible vs Irreversible Cell Injury: Ultrastructural Features ### Key Distinction **Key Point:** Reversible cell injury is characterized by structural and functional changes that can be restored to normal if the injurious stimulus is removed. Once plasma membrane integrity is lost with leakage of intracellular contents (particularly enzymes like LDH, AST, CK), the injury becomes irreversible. ### Ultrastructural Features of Reversible Injury | Feature | Reversible | Irreversible | |---------|-----------|---------------| | Cellular swelling | Present (cytoplasmic edema) | Severe, progresses to lysis | | Mitochondrial changes | Swelling, cristae disruption | Swelling with amorphous densities, calcification | | Plasma membrane | Intact, blebs form | **Loss of integrity, rupture** | | Ribosomes | Detach from RER | Detach from RER | | ER changes | Dilation, ribosome loss | Dilation, fragmentation | | Nucleus | Intact, may show pyknosis | Pyknosis → karyorrhexis → karyolysis | | Leakage of contents | Minimal | **Massive leakage of enzymes/ions** | ### Why Option 2 Is Correct **High-Yield:** Irreversible loss of plasma membrane integrity with leakage of intracellular contents (LDH, AST, troponin, myoglobin) is the **hallmark of irreversible injury**, not reversible injury. This represents the "point of no return" — once the cell membrane ruptures, homeostasis cannot be restored and the cell undergoes necrosis. ### Why Other Options Are Correct Features of Reversible Injury 1. **Cellular swelling (Option 0):** Results from Na+/K+-ATPase dysfunction → Na+ accumulation → osmotic water influx. This is reversible if ATP is restored. 2. **Mitochondrial swelling with cristae disruption (Option 1):** Occurs early in reversible injury due to impaired oxidative phosphorylation and Ca²+ overload. Mitochondria can recover if energy supply is restored. 3. **Ribosome detachment (Option 3):** Occurs in both reversible and early irreversible injury. Detachment from rough ER leads to polysome disaggregation and reduced protein synthesis — reversible if stimulus is removed. ### Clinical Pearl **Clinical Pearl:** In acute myocardial infarction, reversible injury occurs within the first 20–30 minutes of ischemia (ultrastructural changes only). After 60–90 minutes, irreversible changes (sarcolemmal rupture, mitochondrial calcification, myofibrillar loss) begin. This is why the "golden window" for reperfusion therapy is critical. ### Mnemonic **Mnemonic:** **CRISP** = Changes Reversible In Structural Pathology - **C**ellular swelling (cytoplasmic edema) - **R**ibosomes detach - **I**ncreased mitochondrial volume - **S**arcolemma/membrane intact - **P**yknosis (nuclear condensation) — early, reversible Once **MEMBRANE RUPTURE** occurs → irreversible. [cite:Robbins 10e Ch 2]