ATROPHY

When confronted with a decrease in work demands or ad­verse environmental conditions, most cells are able to re­vert to a smaller size and a lower and more efficient level

 

 

UNIT II Cell Function and Growth

Change in cell size or number

Change in cell type

Normal

Dysplasia

Atrophy

Adaptive tissue (large circles) and cell responses involving a change in number (hyperplasia), cell size (hypertrophy and atrophy), cell type (metaplasia), or size, shape, and organization (dysplasia).

of functioning that is compatible with survival. This de­crease in cell size is called atrophy. Cell size, particularly in muscle tissue, is related to workload. As the workload of a cell declines, oxygen consumption and protein synthesis decrease. Cells that are atrophied reduce their oxygen con­sumption and other cellular functions by decreasing the number and size of their organelles and other structures. There are fewer mitochondria, myofilaments, and endo-plasmic reticulum structures. When a sufficient number of cells are involved, the entire tissue or muscle atrophies.

The general causes of atrophy can be grouped into five categories: (1) disuse, (2) denervation, (3) loss of endocrine stimulation, (4) inadequate nutrition, and (5) ischemia or decreased blood flow. Disuse atrophy occurs when there is a reduction in skeletal muscle use. An extreme example of

CELLULAR ADAPTATIONS

Cells are able to adapt to increased work demands or threats to survival by changing their size (atrophy and hypertrophy), number (hyperplasia), and form (metaplasia).

Normal cellular adaptation occurs in response to an appro­priate stimulus and ceases once the need for adaptation has ceased.

disuse atrophy is seen in the muscles of extremities that have been encased in plaster casts. Because atrophy is adaptive and reversible, muscle size is restored after the cast is removed and muscle use is resumed. Denervation atrophy is a form of disuse atrophy that occurs in the mus­cles of paralyzed limbs. Lack of endocrine stimulation produces a form of disuse atrophy. In women, the loss of estrogen stimulation during menopause results in atrophic changes in the reproductive organs. With malnutrition and decreased blood flow, cells decrease their size and energy requirements as a means of survival.