 Solution

Modern hypertrophy means enlargement of individual biological cells; hyperplasia means an increase in their number. Both can enlarge an organ, and both can occur together. The historical question requires care because nineteenth-century authors sometimes included “numerical hypertrophy” within the broader discussion of growth. Rudolf Virchow's 1860 English edition explicitly distinguishes enlargement of existing elements from multiplication of elements, using simple and numerical hypertrophy for these different processes.^[ref]

At the minute structural level, true hypertrophy entails increased cellular substance and, in a contractile biological cell, more contractile apparatus. Enlarged cell nuclei can accompany it, but a large cell nucleus alone does not prove a proportional increase in functional tissue. Increased cell number belongs to hyperplasia. Apparent organ enlargement from oedema, fatty infiltration, amyloid or a tumour must be distinguished from a coordinated increase of the organ's working tissue.^[ref]

The clearest early-to-late examples compare adaptation with the possible effects of continued overload:

These illustrations compare different outcomes rather than proposing a universal stage in which every enlarged organ degenerates.^[ref][ref]

A second set illustrates growth in organs whose biological cells can also divide. The pregnant uterus combines marked enlargement of smooth muscle biological cells with an increase in their number; after delivery it undergoes involution. An enlarged remaining kidney after loss of its partner exemplifies compensatory growth. In a modern rat experiment comparing neonatal, weanling and adult animals after removal of one kidney, the younger groups showed greater compensatory growth; that experimental comparison does not make an age-independent prediction for every human kidney.^[ref] Thus organ size alone cannot distinguish the cellular processes: compare cell dimensions, numbers and tissue composition by histology.^[ref]