Hyperplasia

Definition

An increase in tissue or organ mass resulting from elevated cell proliferation, as distinct from hypertrophy (enlargement of individual cells). In arthropods and other invertebrates, hyperplasia occurs in normal development—such as the massive proliferation of imaginal disc cells during insect metamorphosis—and as a pathological response to injury, infection, or parasitism. The process maintains normal cellular architecture and is typically reversible, though chronic or aberrant hyperplasia may precede neoplasia.

Etymology

Greek hyper- (over, above) + plasis (formation, molding)

Example

In the silkworm Bombyx mori, hyperplasia of the silk gland epithelium during the final larval instar increases cell numbers approximately 40-fold, enabling massive silk protein production before pupation; pathological hyperplasia also occurs in honey bee colonies infected with Malpighamoeba mellificae, where protist invasion triggers proliferation of Malpighian tubule epithelial cells.

Synonyms

• hypergenesis

Related Terms

• Hypertrophy
• neoplasia
• metaplasia
• dysplasia
• Imaginal disc
• cell proliferation
• epithelial proliferation

Usage Notes

Distinguish carefully from hypertrophy: hyperplasia reflects more cells, hypertrophy reflects bigger cells. Both may coexist. In entomological literature, 'hyperplasia' sometimes describes tissue responses to parasitoid infection or viral pathogens (e.g., baculovirus-induced hypertrophy/hyperplasia in lepidopteran larvae). The term implies non-neoplastic proliferation; however, sustained hyperplasia can represent a pre-neoplastic state. When describing insect development, specify whether the hyperplasia is hormonally induced (ecdysone-driven imaginal disc expansion) or mechanically triggered (compensatory regeneration).