atrophy

the decrease in the size of an organ or tissue of the living organism of animals and man, accompanied by a disorder or cessation of functions. Atrophy is the result of a predominance of dissimilation over the processes of assimilation.

Atrophy can be physiological and pathological, systemic and local. Physiological atrophy is a function of the growth changes of an organism (atrophy of the thymus during puberty, atrophy of the sex glands, skin, and bones in old people, and so on). General pathological atrophy (emaciation, cachexia) appears in cases of insufficient nutrition, chronic infection or intoxication, or disorders of the endocrine glands or of the central nervous system. Local pathological atrophy arises from various causes—from a disorder in the regulation of the trophic nerves (for example, atrophy of the skeletal muscles during poliomyelitis), from insufficient supply of blood (for example, atrophy of the brain cortex during atherosclerosis of the blood vessels of the brain); dysfunctional atrophy (for example, atrophy of the optic nerve after removal of an eye), as a result of pressure (for example, atrophy of the kidney in cases of embolism of the urether and accumulation of urine in the renal pelvis), from lack of use (for example, atrophy of the muscles in the extremities after long immobilization), or from the effects of physiological and chemical factors (for example, atrophy of the lymphoid tissue from the effects of solar energy, atrophy of the thyroid gland upon application of iodine preparations).

When an organ atrophies it diminishes in size but subsequently sometimes appears larger as a result of the expansion of fat tissue which replaces the atrophied cellular elements. Pathological atrophy is, up to a certain stage, a reversible process. Treatment consists of the elimination of the causes producing atrophy.