an increase in the volume of a body organ or of any of its parts.
Hypertrophy in man (or in animals) may occur either as the result of the enlargement of the individual component elements of an organ (cells and tissues) or as the result of an increase in their quantity (hyperplasia). True hypertrophy and false hypertrophy are distinguished. The former includes enlargement in volume or mass of specific elements as the result of an increased functional load (so-called functional, or compensatory, hypertrophy) or disruption of the regulatory influences of the nervous and endocrine systems. Functional hypertrophy may appear in healthy persons who are occupied with physical labor, such as in athletes (“physiologic hypertrophy” of the muscles). It may also appear upon affection of a part of any organ, such as after heart failure (compensatory hypertrophy) or after the destruction of a paired organ, such as a kidney (vicarious hypertrophy). Compensation for the impaired functions occurs in all instances of functional hypertrophy. Examples of hypertrophy occurring as a result of the disruption of neuroendocrine influences include acromegaly and gynecomastia; in these cases the hypertrophy has no compensatory significance but is accompanied by considerable disturbances of function. False hypertrophy refers to enlargement of the organ as the result of excessive growth of the interstitial, most often the adipose, tissue in response to atrophy of the parenchyma (the functional tissue). Function of the organ in such cases is usually decreased.
L. L. SHIMKEVICH
Hypertrophy of plant organs is the result of an increase in the size of their cells. The hypertrophy may be the effect of increased synthesis of the substances of the cell membrane or cytoplasm, deposits of reserve compounds, or the development of polynucleosis or polyploidy. The causes of hypertrophy include disruption of the synthesis and metabolism of phenol compounds, amino acids, proteins, carbohydrates, and fats, as well as deficiency of trace elements. The condition may also be caused by viruses, bacteria, fungi, invertebrates, and plant parasites. It may accompany many mutations, grafts, and the effects on the plant of ionizing radiation or ultrasound. Hypertrophy is usually interconnected with hyperplasia and disruptions of tissue differentiation in the organs. In many instances (for example, when there is development of tumors or galls) hypertrophy follows cell division; after mechanical injury and physical or chemical effects, however, it is often primary. Hypertrophy is observed in higher as well as in lower plants.
E. I. SLEPIAN