HYPERTROPHY, a term in medicine implying increase in size of an organ or component tissue of the body, where such enlargement involves the natural elements of the part and is not the result of the presence of some extraneous morbid material. Thus, a lung in pneumonia, a liver full of cancer, is enlarged but not hypertrophied. Further, the word implies life, an uncut nail or excessive length of hair is not hypertrophy. The enlargement may consist in the presence of a normal number of elements each of excessive size (true hypertrophy) or an excessive number of ele ments, each of normal size (hyperplasia). Frequently both con ditions are present.
Hypertrophy may be physiological or pathological. Physio logical hypertrophy is due either to work (e.g., the muscles of an athlete), or is compensatory when one of paired organs is absent or removed) . For hypertrophy to occur the functional activity demanded must be well within its powers, otherwise atrophy occurs. Pathological hypertrophy is seen in leucocythae mia, where the spleen is enormously enlarged; lymphadenoma, where lymphatic glands are enlarged; acromegaly, where bone is affected, etc. Physiological hypertrophy occurs under patho logical conditions. The hypertrophy of the left ventricle in aortic obstruction, of the bladder in stricture of the urethra, of the stomach in pyloric obstruction are examples of work hypertrophy.
The causes of hypertrophy are largely the converse of those causing atrophy (q.v.), but as is shown by acromegaly, endocrine activity plays a part not observed in atrophy, and the growth of tissues in dermoid cysts or in monsters without brain or spinal cord (see MONSTERS) is clearly independent of the nervous sys tem. As hypertrophy is essentially growth carried beyond normal limits the conditions underlying it are those underlying growth. These are (I) an inherent power of growth on the part of the cell; (2) an excessive supply of nutriment ; (3) a stimulus.
A spurious hypertrophy is observed in the rare disease pseudo hypertrophic muscular paralysis, in which the calves, buttocks and muscles of the back are greatly enlarged but excessively feeble. The enlargement is due to interpolation of fatty connec tive tissue between the muscular bundles which themselves are greatly atrophied. (W. S. L.–B.)