Which of the following is an example of physiologic hypertrophy?

Physiologic hypertrophy refers to an increase in the size of an organ or tissue as a normal, adaptive response to a stimulus, promoting beneficial effects. In this context, the enlargement of muscle mass due to exercise exemplifies physiologic hypertrophy because it occurs as a result of increased demand placed on the muscles. When an individual engages in regular exercise, particularly resistance training, the muscle fibers experience stress that leads to their growth and increased strength. This type of hypertrophy is a healthy and reversible process, allowing the muscle to adapt to the higher levels of activity without any underlying pathology.

In contrast, the other options describe pathological processes. Heart enlargement due to valvular disease and increased heart size from hypertension reflect maladaptive responses to stressors that can lead to dysfunction of the heart muscle over time. Similarly, fatty liver from alcohol ingestion represents a pathological change in the liver due to the toxic effects of alcohol, leading to the accumulation of fat and potential liver damage. These conditions are typically associated with disease and can result in negative health outcomes, unlike the healthy adaptations seen in physiologic hypertrophy.