**Core Concept:** Reversible cell injury refers to temporary damage to cells that can be reversed or repaired with proper intervention. The primary concern is maintaining cellular integrity and function.

**Why the Correct Answer is Right:** Option D, "altered cellular function," is not a feature of reversible cell injury because altered cellular function refers to long-term changes in cell behavior, often due to irreversible damage or disease conditions. Reversible cell injury is characterized by temporary disruptions in cell function, which can be restored with proper treatment.

**Why Each Wrong Option is Incorrect:**

A. **Increased cellular permeability:** While increased cellular permeability can be seen in reversible cell injury, it is more commonly associated with irreversible cell damage. In reversible cell injury, the permeability issue can be resolved through appropriate interventions.

B. **Necrosis:** Necrosis represents irreversible cell death, not a feature of reversible cell injury. Reversible cell injury involves temporary damage that can be repaired or reversed.

C. **Necrosis:** Similar to option B, necrosis is the irreversible destruction of cells and tissues, and does not apply to reversible cell injury.

**Clinical Pearl:** Understanding the distinction between reversible and irreversible cell injury is crucial for appropriate treatment decisions. In reversible cell injury, prompt recognition and intervention can prevent progression to irreversible damage.

**Correct Answer:** D (altered cellular function) is not a feature of reversible cell injury, as it refers to long-term changes in cell behavior due to irreversible damage or disease conditions. Reversible cell injury is characterized by temporary disruptions in cell function that can be restored with proper treatment.