Atrophy and Hypertrophy Are Two Sides of the Same Coin

Atrophy
Atrophy is the decreased size or function of cells or organs and occurs in both pathologic and physiologic settings.

Thus, for example, atrophy may result from disuse of skeletal muscle or from loss of hormonal signals following menopause.

It may also be an adaptive response whereby a cell accommodates changes in its environment, all the while remaining viable.

However, most commonly atrophy reflects harmful processes, like those involved in some chronic diseases and biological aging.

Atrophy of an organ differs from cellular atrophy. Reduction in an organ’s size may be caused either by reversible cell shrinkage or by irreversible loss of cells.

Hypertrophy
Hypertrophy is an increase in cell or organ size and functional capacity.

When trophic signals or functional demands increase, adaptive changes to satisfy these needs lead to larger cells (hypertrophy) and, in some cases, increased cell number (hyperplasia).

In several organs (e.g., heart, skeletal muscle), such adaptive responses are achieved mainly by increased cell size, which leads to increased organ mass. In other organs (e.g., kidney), cell numbers and cell size may both increase.