Question

Which of the following events are critical in development of irreversible cell injury:
A. Loss of membrane integrity
B. Loss of mitochondrial function
C. Lipid accumulation
D. Calcium influx
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, B and C only
• C. B, C, and D only
• D. A and C only

Hint:

To remember this concept, think of the "membrane-calcium-mitochondria" triad. Together, they define irreversible injury. Fatty change (lipid accumulation) and cellular swelling are classic reversible changes.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Cell injury progresses through a reversible stage before reaching a point of no return, resulting in irreversible injury and cell death (necrosis or apoptosis).
Two main phenomena consistently characterize the transition to irreversibility: the inability to reverse mitochondrial dysfunction and profound disturbances in membrane function.

Step 2: Detailed Explanation:
Let us analyze each event to determine its role in irreversible cell injury:
1. Loss of membrane integrity (A):
This is a critical event in irreversible injury.
Damage to lysosomal membranes releases hydrolytic enzymes (RNases, DNases, proteases, phosphatases) into the cytoplasm, which degrade cellular components.
Damage to the plasma membrane leads to the loss of essential cellular proteins, coenzymes, and metabolites, while allowing extracellular fluids and ions to flood the cell.
Therefore, A is correct.
2. Loss of mitochondrial function (B):
The inability to reverse mitochondrial dysfunction (such as the formation of the mitochondrial permeability transition pore) prevents ATP synthesis via oxidative phosphorylation.
Persistent ATP depletion impairs all energy-dependent cellular processes, making cell survival impossible.
Therefore, B is correct.
3. Lipid accumulation (C):
Intracellular lipid accumulation (fatty change or steatosis) is a classic morphological feature of reversible cell injury.
If the noxious stimulus is removed, hepatocytes or myocardial cells can metabolize or export the accumulated lipids and return to normal function.
Therefore, C is incorrect.
4. Calcium influx (D):
Ischemia and toxins cause a massive influx of extracellular $Ca^{2+}$ across the damaged plasma membrane, alongside the release of $Ca^{2+}$ from mitochondrial and endoplasmic reticulum stores.
This high concentration of cytosolic calcium activates several destructive enzymes, including:
- Phospholipases (which further degrade membrane lipids).
- Proteases (which degrade cytoskeletal proteins).
- ATPases (which accelerate ATP depletion).
- Endonucleases (which cause chromatin fragmentation).
This enzymatic cascade drives the cell into irreversible death.
Therefore, D is correct.
Thus, the critical events are A, B, and D.

Step 3: Final Answer:
The critical events that mark the transition to irreversible cell injury are the loss of membrane integrity (A), loss of mitochondrial function (B), and calcium influx (D).
Therefore, the correct answer is option (A).