Pathomechanism of hyperplasia, examples

1. Definition

• Hyperplasia = ↑ cell number, only in tissues capable of replication (cells move G0 → G1).
• Can coexist with hypertrophy. Controlled proliferation — contrast neoplasia (uncontrolled). Pathological hyperplasia can be fertile soil for neoplasia (e.g. endometrium).

2. Causes & Examples

Hormonal stimulation

• Endometrial hyperplasia: excess estrogen unopposed by progesterone → excessive proliferation → risk of adenocarcinoma.
• Benign prostatic hyperplasia (BPH): men >50; relative ↑estrogen / androgens (DHT) → adenomuscular hyperplasia → urinary obstruction.

Increased functional demand

• Polycythemia: ↑RBCs (hypoxia, blood loss, hemolysis) → bone marrow hyperplasia (widened medullary cavities, thinned cortices).
• Lymph node hyperplasia: follicular (B-cell) or paracortical (T-cell) reactive proliferation.

Chronic inflammation

• Chronic cystitis (recurrent UTI) → bladder epithelial hyperplasia (protective).

💡 High-yield: Hyperplasia = more cells (needs dividing-capable tissue); hypertrophy = bigger cells. It is regulated/reversible — unlike neoplasia. Classic examples: endometrial hyperplasia (unopposed estrogen, premalignant), BPH, compensatory liver regeneration.