= Solution
\b[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.<Cellular Pathology by Rudolf Virchow (1860)>[Lecture III, pp. 93–95, Hypertrophy and Hyperplasy and Degenerative New Formations]{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>.<Cellular Pathology in Pathology: The Big Picture>[Hypertrophy and Hyperplasia; morphological distinction and increased contractile protein in pressure-loaded myocardium]{ref}
The clearest early-to-late examples compare adaptation with the possible effects of continued overload:
* In the <heart>, sustained <hypertension> or <aortic stenosis> makes the <left ventricle> work against greater resistance. Initially its <cardiomyocytes> enlarge and the wall thickens, with enlarged <cell nuclei> and increased contractile <proteins>. With prolonged pathological stress there may be <fibrosis>, loss of <cardiomyocytes>, ventricular dilatation and <heart failure>. The late enlarged failing <heart> need not have a uniformly thick wall; <hypertrophy> and dilatation describe different structural changes.<Stress Kinase Signaling in Cardiac Myocytes>[Cardiac hypertrophy, physiological adaptation versus pathological hypertrophy and progression to heart failure]{ref}
* In the <urinary bladder>, persistent outflow obstruction increases the work of the <detrusor muscle>. Enlargement of <smooth muscle> bundles thickens the wall and can produce <bladder trabeculation>. With prolonged obstruction, <fibrosis>, dilatation and incomplete emptying can coexist with the initial growth. This is a progression possible under sustained pathological load. Human studies describe early <hypertrophy> and subsequent compensation or decompensation; progression is not an inevitable fate of all enlarged <smooth muscle>.<Progressive bladder remodeling due to bladder outlet obstruction>[Results; Discussion, proposed three-stage model and its evidential limits]{ref}
* In <skeletal muscle>, increased use enlarges existing fibres through additional contractile material. Later development of this physiological response produces larger, stronger fibres; it does not inherently require fatty degeneration. If an apparent muscular enlargement is mainly fat or <connective tissue>, that is <pseudohypertrophy>.
These illustrations compare different outcomes rather than proposing a universal stage in which every enlarged organ degenerates.<Hypertrophy and hyperplasia in Underwood's Pathology: a Clinical Approach>[Adaptive responses to increased demand; physiological hypertrophy and hyperplasia]{ref}<Cellular Pathology in Pathology: The Big Picture>[Hypertrophy, physiological and pathological examples]{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>.<Age-dependent characteristics of compensatory renal growth>[Abstract, comparison of neonatal, weanling and young adult rats]{ref} Thus \b[organ size alone cannot distinguish the cellular processes]: compare cell dimensions, numbers and <tissue> composition by <histology>.<Hypertrophy and hyperplasia in Underwood's Pathology: a Clinical Approach>[Physiological hypertrophy and hyperplasia, uterine growth; compensatory growth]{ref}
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