Questions: Cell Injury and Adaptation

Question 1

Which morphologic feature best indicates that cell injury has become irreversible?

• A. Cellular swelling (hydropic change)
• B. Fatty change in hepatocytes
• C. Plasma membrane disruption with nuclear fragmentation
• D. Loss of microvilli on renal tubular epithelium

Answer: (C)

Plasma membrane rupture and nuclear dissolution (pyknosis, karyorrhexis, karyolysis) mark the point of no return. Cellular swelling, fatty change, and loss of microvilli are all reversible changes that reflect early metabolic stress but do not by themselves constitute irreversible injury.

Question 2

Metaplasia, in which one differentiated cell type is replaced by another (e.g., columnar to squamous epithelium in the esophagus), is classified as a form of irreversible cell injury.

• T. True
• F. False

Answer: False

Metaplasia is an adaptive response, not cell injury. The cell population changes to better withstand an altered environment—for instance, squamous epithelium better tolerates acid exposure than columnar epithelium does. It is reversible if the stimulus is removed and, while it increases cancer risk over time, the change itself is a controlled adaptation rather than injurious necrosis or apoptosis.

Question 3

Why is ATP depletion so central to most forms of cell injury, regardless of the specific initial cause?

Model answer: ATP powers the Na⁺/K⁺-ATPase that maintains ion gradients; without it, sodium and water flood into the cell causing swelling. ATP is also required for calcium extrusion, protein synthesis, membrane repair, and mitochondrial function. When ATP falls below a critical threshold, these interlinked systems fail together, rapidly amplifying damage beyond the cell's capacity to recover.

Many disparate injuries—ischemia, toxins, radiation—converge on ATP depletion because energy is required to maintain virtually every homeostatic mechanism. This explains why mitochondrial dysfunction (the primary site of ATP production) is the common final pathway in most forms of lethal cell injury.