STRESSOR
stimulates
Hypothalamus
Pituitary Gland
Produces
Corticotropin releasing
hormone (CRH)
Glucocorticoids
accumulate
PROBLEMS
Aerobic exercise
produces Adreno
Cortico Tropic
Hormone
(ACTH)
Immune system and
body metabolism
are put in a high
state of alert
NORMAL
Adrenal Glands
Burns up
glucocorticoids
Fight or Flight
?eld” in the Journal of Human Stress. He suggested a
model that divided stress into ‘eustress’ and ‘distress’.
He suggested that where stress enhances function (and
this could be physical or mental resulting from strength
training or challenging work) it can be thought of as
eustress. Negative stress – distress – is what most people
think of as stress, and this may lead to problems. But
basically Selye’s conclusion was that what doesn’t kill
you makes you stronger!
Selye’s research led him to a three-stage theory
known as GAS (General Adaptation Syndrome):
1.
2.
3.
Alarm - when a threat or stressor is ?rst
identi?ed, the body’s ?ght or ?ight response
kicks in with the production of adrenaline.
At the same time some cortisol is produced
from what’s called the HPA axis (see later).
Resistance If the stressor continues, the
body tries to cope with it, but, even so, resources
are gradually used up.
Exhaustion – the body’s resources are used up
and this can lead to illness such as ulcers,
depression, diabetes, digestive system issues,
and cardiovascular problems.
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Adrenal cortex
releases cortisol
Adrenal medulla
releases adrenaline
Figure 1: HPA axis
Normally a stressor will come and then go. The
body will activate its ?ght or ?ight response when it
?rst identi?es the stressor and then (slowly) return to
normal once the stressor has gone.
Fight or ?ight symptoms: [v]
? Dilation of the pupils, for
maximum visual perception.
? Constriction of the arteries to
maximize blood pressure to muscles.
? Adrenal glands produce cortisol,
adrenaline, and noradrenaline.
Let’s take a more detailed look at what happens
with that ?ght or ?ight response (often extended to
freeze, ?ght, or ?ee) – see Figure 1. Firstly, a stressor
occurs – our old friend the polar bear appearing – and
the (paraventricular nucleus of the) hypothalamus
produces Corticotropin-Releasing Hormone (CRH),
which used to be known as Corticotropin-Releasing
Factor (CRF). This (with vasopressin) stimulates the
(anterior lobe of the) pituitary gland to produce ACTH
(AdrenoCorticoTropic Hormone). This triggers the