HYPERTROPHY AND ATROPHY, (vvsg, super,a,priv., and 7g694,,nutrio),(in morbid ana tomy). When any organ or tissue has acquired a certain increase of developement, without any manifest alteration of its natural structure, it is said to be in the state of hypertrophy— the increase being due to a greater activity of the nutritive process in the part affected. A familiar example of hypertrophy, although not morbid, is afforded by the augmentation which muscular fibre acquires in consequence of increased action. If the biceps muscle of one arm be actively exercised, while that of the other does not undergo any considerable degree of action, the former acquires a great increase of size, it becomes denser and firmer, and manifests the physical and vital phenomena of the muscular tissue with more than ordinary energy.
There is no texture in the body which does not occasionally exhibit evidence of the hyper trophous condition. The circumstances which favour its production are an abundant and a free afflux of blood to the part, an energetic nervous influence and an increased demand upon the organ, or increased exercise if it be muscular; and indeed these are the almost in variable conditions under which hypertrophy is manifested. The heart becomes hypertrophous under an exalted nervous influence, or from a necessarily increased exercise from the effort to overcome some obstacle to the free circulation of the blood through its cavities ; one kidney acquires a great increase of size if the other one be incapable of performing its function. It may be said that the liver is in a state of hypertrophy in the foetus in utero, for it has a larger supply of blood than in extra-uterine life, and the lungs have not as yet begun to share with it in the office of decarbonizing the venous blood. The bladder also, like the heart, acquires an enormous developement of its muscular coat, when any obstacle obstructs the free flow of the urine from it. The physi cal condition, then, of a hypertrophous organ differs but in degree from that of the part in its normal state. There are, in general, in
crease of size, of weight, and of consistence, with more or less alteration of shape consequent upon the former ; an increased supply of blood, and a consequent heightening of colour. To judge therefore how far an organ has experi enced hypertrophy, the anatomist must care fully compare its present condition, as regards size, weight, colour, consistence, and supply of blood, with the average state of the parts in health.
Atrophy is not only opposite in its nature to hypertrophy, but it results from causes of an entirely opposite kind. A defective state in the nutritive process is its immediate cause : the affected part shows manifest signs of wast ing; it diminishes in size and in consistence ; it loses its colour from the deficient supply of blood ; its physical and vital properties are manifestly altered, and are fully developed. When the wasting has gone to its greatest ex tent, the natural texture disappears, or is so altered as to present but few of the characters of its normal condition. As frequent exercise and use favour the production of hypertrophy, so on the other hand disuse and inactivity give rise to atrophy. Neither the vascular nor the nervous systems of such parts affiard their wonted supplies ; and those physical characters which are present in hypertrophy in an exalted condition, are in atrophy either absent altoge ther, or but feebly developed. The muscles of paralytic limbs, the hearts of old persons which have been overloaded with fat, the diminution in size and almost total disappear ance of the thymus gland in the adult, the diminution of the left lobe of the liver in extra uterine life, the obliteration and conversion into a fibrous cord of certain disused venous and arterial canals, and the wasting of the optic nerve where the eye is destroyed, are examples of atrophy of every day's occurrence. (See the articles on the morbid anatomy of the different textures and organs.) (R. B. Todd.)