Irreversible cell injury is primarily due to which of the following?

Question

Accepted Answer

Irreversible damage to essential cellular components, such as membranes and proteins. The transition from reversible to irreversible cell injury is defined by the "point of no return." While many biochemical changes occur during cell injury, the hallmark of **irreversibility** is the profound and permanent structural damage to cellular membranes and proteins [1].

**1. Why Option B is Correct:**
Irreversible injury is characterized by two critical phenomena: **the inability to reverse mitochondrial dysfunction** (lack of ATP generation even after restoration of oxygen) and **profound disturbances in membrane function** [1]. Damage to the plasma membrane leads to the leakage of intracellular enzymes and cofactors; damage to lysosomal membranes results in the leakage of acid hydrolases into the cytoplasm, leading to enzymatic digestion of the cell (autolysis) [1].

**2. Why Other Options are Incorrect:**
*   **Option A:** A decrease in ATP is the *initial* event in most types of cell injury (especially hypoxia) [1]. However, if oxygen is restored, ATP levels can recover, making this a feature of reversible injury [1].
*   **Option C:** Myelin figures are whorled phospholipid masses derived from damaged cell membranes. While they are more prominent in irreversible injury, they can also be seen in reversible injury as the cell attempts to sequester damaged lipids [1].
*   **Option D:** Cellular swelling (hydropic change) is the **first manifestation** of almost all forms of cell injury [1]. It is a reversible process caused by the failure of energy-dependent ion pumps (Na+/K+ ATPase) [1].

**NEET-PG High-Yield Pearls:**
*   **Morphological Hallmarks of Irreversibility:** Severe mitochondrial vacuolization, amorphous nutrient-rich densities in the mitochondrial matrix, and nuclear changes (Pyknosis → Karyorrhexis → Karyolysis) [1].
*   **Clinical Marker:** The leakage of intracellular proteins across damaged membranes is the basis for blood tests that detect tissue-specific injury (e.g., **Troponins** in MI, **ALT/AST** in hepatitis) [1].
*   **Free Radicals:** Reactive Oxygen Species (ROS) are the primary mediators of membrane damage via lipid peroxidation.

**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 49-62. [Practice more Pathology questions on OnCourse]

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