The General Adaptation Syndrome (GAS) is a cluster of bodily responses to severe, prolonged stressors that was described by Hans Selye. Selye observed that rats exposed to a wide variety of noxious agents exhibited a nonspecific syndrome consisting of enlargement of the adrenal cortex; shrinkage of the thymus, spleen, and lymph glands; and the appearance of ulcers in the stomach and small intestine. This response was seen in animals exposed to extreme cold and heat, intense sound or light, forced exercise, injections of various organ extracts or formalin, or a variety of other intense biological challenges to normal homeostatic function. Selye suggested that the GAS consisted of three phases of response to a stressor. The initial stage consisted of an alarm reaction during which the adrenal cortex enlarged and released large amounts of the adrenoglucocorticoid hormone cortisol into the bloodstream, the lymphatic tissues shrunk, the number of white blood cells declined, the gastrointestinal tract developed ulcers, heart rate and blood pressure increased, and the animals lost weight. During the second stage, the stage of resistance, the adrenal cortex remained enlarged, but instead of releasing cortisol, the gland retained the hormone, other tissues and physiological functions appeared relatively normal, and the body weight returned to near normal levels. With continued application of the severe stressor, according to the GAS, the animals eventually entered a third stage, called the stage of exhaustion. Here again, similar to the body's responses during the alarm reaction, substantial amounts of cortisol were released into the blood, lymphatic tissues shrank, and body weight again fell. This stage ended with the animal's death.
Selye's GAS and the research that followed from this early notion of a nonspecific response to challenges from the environment was an important idea that launched the study of biological stress. Indeed, Selye himself used the term stress, which he had borrowed from physics to refer to this syndrome of responses to a noxious agent. However, more recent studies of the concept of stress have broadened the definition of stressors to include less potent challenges to an organism's normal function, including psychological stressors. Thus, it is now clear that the GAS does not occur following all events that one would reasonably consider stressors and does not occur in all individuals. As Selye himself noted, organisms may not experience all three stages of the GAS and stressors sometimes may produce only limited features of the alarm reaction (e.g., cortisol release without gastric ulceration). Thus, the GAS does not appear to apply to any but the most intense, prolonged, and painful physical stressors. Despite these criticisms, Selye's GAS was an important concept in the history of research on stress because it suggested that in addition to the specific, finely tuned bodily changes induced by aversive physical challenges to homeostasis, there was also a more generalized bodily response elicited by any one of a diverse array of intense stressors that threatened the organism's survival.
Selye, H. (1936). A syndrome produced by diverse nocuous agents.
Nature, 138, 32. Selye, H. (1956). The stress of life. New York: McGraw-Hill. Weiner, H. (1992). Perturbing the organism: The biology of stressful experience. Chicago: Chicago University Press.
Karen S. Quigley
University of Medicine and Dentistry of New Jersey New Jersey Medical School and East Orange VA Medical Center
See also: Homeostasis
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