The Physiology of Stress
'Stress' refers to life events, both physical and psychological, that challenge
our ability to cope, and to the uncomfortable consequences of our efforts to
cope. Stress certainly affects us physiologically, and excessive stress can be
harmful to health. Stress can exacerbate almost any illness.
There are two main pathways by which the brain effects changes in the body in
response to stressors:
The Autonomic Nervous System (ANS)
The ANS has two branches, known as the sympathetic and parasympathetic nervous
systems. In their affect on the body's arousal level, they work something like a
car's accelerator and brake respectively. The sympathetic system is associated
with the acute stress response ("fight or flight") while the parasympathetic
calms us down again. Over-predominance of the parasympathetic is sometimes
associated with fatigue and low energy.
Hormones
The main stress hormones are secreted by the adrenal glands. Adrenalin helps the
body prepare for action ("fight or flight" response) for example by raising
heart rate. Cortisol has similar effects but stays in the system much longer (up
to several hours). It helps us recover from stress and return to normal but
persistently high levels of cortisol can cause harm.