Page:The Principles and Practice of Medicine.djvu/89

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nutrition of a texture may be increased, diminished, or perverted.

Increased nutrition—Hypertrophy.—Hypertrophy must be distinguished from mere enlargement, which often occurs with- out increase of nutrition, as in the distension of a hollow organ by gas, blood, and other fluids, or the swelling of a solid organ by congestion or abnormal deposit. On the other hand, there may be hypertrophy and yet no enlargement this happens when the density of an open tissue is increased, or the walls of cavities, being thickened, encroach upon the interior. Hyper- trophy is well seen in the increased development of a muscle under exercise, as in the biceps of persons who are engaged in such occupations as require constant and laborious exercise of the arms. The muscular tissue is actually added to, the fibres being larger and more numerous. Examples of hyper- trophy are also met with in the walls of hollow muscular organs, whenever there is impediment to the passage of their contents, as in the left ventricle of the heart in disease of the aortic valves, or in the bladder in stricture of the urethra. Sometimes hypertrophy is compensatory ; one kidney being destroyed or absent, the other becomes hypertrophied. Hypertrophy can hardly be viewed as a disease, but it is often the result of disease, and sometimes the cause of it. Of the first, thickening of the walls of the heart from valvular disease is an example ; of the last, the pressure of a hypertrophied thyroid body upon the neighbouring structures. For the most part, however, hypertro- phy is to be considered as conservative. It is most common in the muscular, glandular, and adipose tissues, and in certain of the ductless glands, as the thyroid. Hypertrophied parts or organs may remain for long unchanged, but they are predis- posed to fatty degeneration.

Causes.—Undue functional activity, leading to increased accumulation in the local blood supply of those materials which the organ appropriates for its nutrition or secretion.