**Core Concept**
Hypertrophy refers to the enlargement of cells due to an increase in cell size, not cell number or protein content. It is a key pathological process in response to increased workload or stress, such as in the heart or skeletal muscles.

**Why the Correct Answer is Right**
Hypertrophy involves cellular enlargement, where cells grow larger in size due to increased cytoplasmic volume. This occurs through increased protein synthesis and metabolic activity, but without cell division. In cardiac muscle, for example, hypertrophy results from chronic pressure overload, leading to larger myocytes. The increase in size is distinct from hyperplasia (increase in cell number) or protein accumulation.

**Why Each Wrong Option is Incorrect**
Option A: Increased protein content is a *consequence* of hypertrophy, not its definition. Protein content rise occurs due to cell growth, but it does not define hypertrophy.
Option C: Increase in number of cells describes hyperplasia, not hypertrophy. Hyperplasia involves cell multiplication, such as in the endometrium or liver regeneration.
Option D: This is incorrect because option B is accurate and directly defines hypertrophy.

**Clinical Pearl / High-Yield Fact**
Remember: **Hypertrophy = bigger cells**, **Hyperplasia = more cells**. In heart disease, left ventricular hypertrophy is a common adaptation to hypertension, and it can progress to heart failure if unchecked.

✓ Correct Answer: B. Increase in size of cells