190 MHR • Unit 2 Homeostasis
Selye’s Legacy
Selye described the anti-inflammatory properties
of adrenal steroid hormones, such as cortisol. He
discovered that steroid hormones regulated the
activity of many lymphatic structures, such as the
thymus, spleen, and lymph nodes.
In 1936, Selye, whose photograph appears in
Figure 6.21, produced a paper that first described
what he termed the General Adaptation Syndrome
(GAS). He stated that the GAS was the body’s
“non-specific” response to any stressor that placed
a demand on the sympathetic nervous system,
adrenal gland, ADH production, and production of
rennin and angiotensin. Selye suggested that the
human body produces a similar response to most
types of stressors.Figure 6.21Dr. Hans SelyeBriefly, the GAS was a three-stage response by
the body to stress. The first stage was the “Alarm
Reaction,” in which some form of physical or
mental trauma would trigger an immediate stress
response in the body. This reaction depressed
immune system activity, leaving the body more
susceptible to infection and disease. This wasfollowed by the “Resistance” stage, in which the
body adapted to a state of stress. In this stage, the
body draws on fat and protein energy reserves to
strengthen the body’s defences. The final stage was
“Exhaustion,” in which there is a sharp decline in
immune system function and other homeostatic
mechanisms.
Chronic stress can lead to diarrhea, migraine
headaches, insomnia, bruxism (grinding of the
teeth), emotional instability, heart palpitations,
trembling or nervous ticks, inability to concentrate,
and increased frequency of urination. Ignoring such
warning signs of stress can lead to the onset of
serious illness.
Recently, the GAS concept has met with
considerable criticism in the medical community.
For example, it is now known that the body tends
to produce specific, rather than general, responses
to a particular type of stressor, such as infection,
extreme exercise, or pain.
Selye was also unable to develop a physiological
definition of “stress.” One dilemma he faced was
that stress is a highly subjective experience. He
knew that the same situation could elicit a wide
range of emotional responses, from pleasure to
irritation, anger or fear, in different individuals. For
some people, rock climbing is an exhilarating
activity, while others may regard it as terrifying.
In addition, Seyle’s theories were often based on
relatively crude experimental observations, such as
the visual study of stomach ulcers. Also, much of
his research focussed on the physiological action of
cortisol. Current research methods and technology
are considerably more advanced than those on
which Selye based many of his theories.
However, Selye’s innovative ideas did prompt
mainstream medicine to focus more intensely on
the link between psychological stress and general
health, including immune system function. Thus,
despite its shortcomings, Seyle’s body of work did
make a major contribution to the scientific
understanding of the impact of stress on the
physiology of the endocrine and immune systems
in the body.
In this section, you learned how hormones of the
adrenal gland regulate metabolism and control the
body’s response to stressful situations. You also
examined the negative effects of chronic stress on
the immune system and other body functions. In
the next section, you will see how the endocrine
system controls development and function of the
male and female reproductive systems.