What happens to the body when high stress levels are prolonged? Hans Selye studied this issue by subjecting laboratory animals to a variety of stressors such as very high or low environmental temperatures, X rays, insulin injections, and exercise over a long period of time. He also observed people who experienced stress from being ill. Through this research, he discovered that the fight-or-flight response is only the first in a series of reactions the body makes when stress is long-lasting. Selye called this series of physiological reactions the general adaptation syndrome (GAS). As the diagram shows, the GAS consists of three stages:
1. Alarm Reaction.
The first stage of the GAS is like the fight-or-flight response to an emergency— its function is to mobilize the body’s resources. At the very beginning of the alarm reaction, arousal— as measured by blood pressure, for example drops below normal for a moment, but then rapidly rises to above normal. This last- increasing arousal results from activation of the hypothalamus pituitary adrenal axis: the hypothalamus triggers the pituitary gland to secrete ACTH, which causes the adrenal glands to release epinephrine, nor- epinephrine, and cortical into the bloodstream. By the end of this stage in the GAS, the body is fully mobilized to resist the stressor strongly. But the body cannot maintain this intense arousal for very long. Some organisms that have experienced a continuous and unrelieved alarm reaction to an extremely intense stressor have died within hours or days.
2. Stage of Resistance.
If a strong stressor continues but is not severe enough to cause death, the physiological reaction enters the stage of resistance. In this stage, the body tries to adapt to the stressor. Physiological arousal declines somewhat but remains higher than normal, and the body replenishes the hormones released by the adrenal glands. Despite this continuous physiological arousal, the organism may show few outward signs of stress. But the ability to resist new stressors may be impaired for long periods of time. According to Selye, one outcome of this impairment is that the organism becomes increasingly vulnerable to health problems he called diseases of adaptation. These health problems include ulcers, high blood pressure, asthma, and illnesses that result from impaired immune function.
3. Stage of Exhaustion.
Prolonged physiological arousal produced by severe long-term or repeated stress is costly. It weakens the immune system and depletes the body’s energy reserves until resistance is very limited. At this point, the stage of exhaustion begins. If the stress continues, disease and damage to internal organs are likely, and death may occur.
Two lines of evidence support the long-term effects the GAS describes. First, people who experience chronically high levels of stress show greater reactivity to stressors they encounter: compared with other people, individuals under chronic stress respond to a stressor with greater increases in blood pressure and decrements in immune function.
Second, having to adapt repeatedly to intense stressors may take a high physiologic toll that accumulates over time in a process called allostatic load. Studies of chronic stress have confirmed that high levels of allostatic load are related to poor health in children and the elderly.