Physical Responses

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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.
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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.