**Core Concept**
Cell injury can be reversible or irreversible, depending on the severity and duration of the insult. Ultrastructural changes are key to distinguishing between these two types of injury. In reversible cell injury, the cell membrane remains intact, and the cell undergoes adaptive changes to maintain homeostasis. In contrast, irreversible cell injury is characterized by severe ultrastructural damage.

**Why the Correct Answer is Right**
Ultrastructural findings of irreversible cell injury include damage to the cell membrane, disruption of the cytoskeleton, and fragmentation of the mitochondria. The cell membrane becomes permeable, leading to the loss of cellular contents, including enzymes and organelles. The mitochondria, which are responsible for energy production, undergo swelling and fragmentation, further compromising cellular function. These changes are indicative of irreversible cell injury and are often associated with cell death.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option may refer to the early changes seen in reversible cell injury, such as swelling of the endoplasmic reticulum and Golgi apparatus. However, these changes are not indicative of irreversible injury.
* **Option B:** This option may refer to the changes seen in apoptosis or programmed cell death. While apoptosis is a form of cell death, it is a regulated process that involves distinct ultrastructural changes, including nuclear fragmentation and chromatin condensation.
* **Option C:** This option may refer to the changes seen in necrosis, which is a form of cell death that occurs due to severe injury or infection. However, necrosis is not the same as irreversible cell injury, which is a more general term that encompasses a range of ultrastructural changes.

**Clinical Pearl / High-Yield Fact**
Remember that ultrastructural changes are a key indicator of cell injury, and irreversible cell injury is characterized by severe damage to the cell membrane, cytoskeleton, and mitochondria. These changes are often associated with cell death and can be seen in various disease states, including ischemia, toxins, and infections.

**Correct Answer:** D.