395 Stress Responses FIGURE 10.2 Alarm Resistance Exhaustion The General Adaptation Syndrome Hans Selye found that physical reactions to stressors include an initial alarm reaction, followed by resistance and then exhaustion. During the alarm reaction, the body’s resistance to stress temporarily drops below normal as it absorbs a stressor’s initial impact. Resistance increases and then levels off in the resistance stage, but it ultimately declines if the exhaustion stage is reached. Level of normal resistance Stressor Source: Adapted from Selye (1974). chest pains might trigger the psychological stress response of worrying about a heart attack. Still, it is useful to consider each category of stress responses one at a time. Online Study Center Improve Your Grade Tutorial: Physical Reactions to Stressors—General Adaptation Syndrome general adaptation syndrome (GAS) A three-stage pattern of responses triggered by the effort to adapt to stressors. Physical Responses If you have experienced a near accident or some other sudden, frightening event, you know that the physical responses to stressors include rapid breathing, increased heartbeat, sweating, and, a little later, shakiness. These reactions make up a general pattern known as the ﬁght-or-ﬂight syndrome. As described in the chapters on biology and behavior and on motivation and emotion, this syndrome prepares the body to face or to ﬂee an immediate threat. Once the danger passes, ﬁght-or-ﬂight responses subside. When stressors are longer lasting, however, the ﬁght-or-ﬂight syndrome is only the beginning of a longer sequence of reactions. Observation of animals and humans led Hans Selye (pronounced “SELL-yay”) to suggest that this extended sequence of physical stress responses occurs in a consistent pattern. He called this sequence the general adaptation syndrome, or GAS (Selye, 1956, 1976). The GAS occurs in three stages (see Figure 10.2), and it is activated by efforts to adapt to any stressor, whether it is physical or psychological. The ﬁrst stage, called the alarm reaction, involves some version of the ﬁght-or-ﬂight syndrome. The alarm reaction to a mild stressor, such as a hot room, might be no more than changes in heart rate, respiration, and perspiration that help the body regulate its temperature. More severe stressors prompt more dramatic alarm reactions, rapidly mobilizing the body’s adaptive energy, much as a burglar alarm alerts the police to take action (Kiecolt-Glaser et al., 1998). Alarm reactions are controlled by the sympathetic nervous system through organs and glands that make up the sympatho-adreno-medullary (SAM) system. As shown on the right side of Figure 10.3, stressors trigger a process that begins when the brain’s hypothalamus activates the sympathetic branch of the autonomic nervous system (ANS), which stimulates the medulla (inner part) of the adrenal glands. The adrenals, in turn, secrete catecholamines (pronounced “kat-uh-KOH-luh-meens”)—especially adrenaline and noradrenaline—which circulate in the bloodstream, activating the liver, kidneys, heart, lungs, and other organs. The result is increased blood pressure, muscle tension, and blood sugar, along with other physical changes needed to cope with stressors. Even brief exposure to a stressor can produce major changes in these coordinated regulatory body systems (Cacioppo et al., 1995). As shown on the left side of Figure 10.3, stressors also activate the hypothalamicpituitary-adrenocortical (HPA) system, in which the hypothalamus stimulates the pituitary gland in the brain. The pituitary, in turn, secretes hormones such as adrenocorticotropic hormone (ACTH). Among other things, ACTH stimulates the cortex (outer surface) of the adrenal glands to secrete corticosteroids; these hormones release the body’s energy supplies and ﬁght inﬂammation. The pituitary gland also triggers the release of endorphins, which are some of the body’s natural painkillers.