Stress Physiology

Contributors
David McQuillan (2008), Otago Polytechnic

Learning Objective
In this learning module you will learn about how stress affects the body.

The fight or flight response
The stress response is mobilised primarily via two body systems
 * Nervous system
 * Endocrine system (hormones)

Read through these learning resources to gain an understanding of...
 * How stress affects the nervous system
 * How stress affects the endocrine system

Coordination of Neurological and hormonal components
From what you've read so far it would be easy to think that the stress response was a result of hormones that were triggered by the nervous system. This is not exactly true.

In the initial stages of the stress response, activation of the sympathetic nervous system causes all of the effects that we relate to the fight or flight response.
 * Eyes dilate
 * Skeletal muscle tone increases
 * Attention focusses
 * Breathing and heart-rate increase

This is why we can react so quickly. Hormones take a bit longer to propagate through the bloodstream. The sympathetic nervous system initiates the fight or flight response. The hormones take over the job, and provide more long-term effects.

The experience of someone who's almost had a car crash is a good illustration of the lag between stimulus and hormonal response. It's not uncommon for someone who's had a near car crash to feel pretty stressed immediately following the near accident, then to calm down and get on the road only to be overcome with shaking, a pounding heart, etc. after about ten minutes. The sympathetic nervous system kicks in during the event providing the focus and speed required to avoid the accident. The release of hormones is also triggered, but the effect of these hormones are not felt until about ten minutes later when they reach the organs that they are targetting.

Chronic stress
The fight or flight response is designed to combat short-term stressors. Short-term stress and recovery from stress is managed well by negative feedback cycles, because cortisol inhibits the production of cortiocosteroid-releasing hormone. (Marieb, 2004)

When a stressor is chronic, these feedback cycles are thought to break down resulting in neurotransmitter and hormonal imbalances. In the modern environment many stressors are emotional/mental in nature, and stress can become constant, having many detrimental effects.


 * The effects of chronic stress on the body