5.2 Stress as a Response

Selye’s original theory of stress treated stress as a

response, or a physiological phenomenon based on experiments performed on rats

This includes changes to

physiological measures such as heart rate and breathing rate

Selye 1983 proposed a three-stage model that described the physiological changes occurring when under stress

a)      Alarm

b)     Resistance

c)      Exhaustion

In the alarm phase

, in response to distress, sympathetic NS activity increases to combat the stressor, Selye observed physiological changes within the first 48 hours including decrease in thymus (immune control), disappearance of fat tissue, loss of muscle tone and loss of lining of digestive tract

In the resistance phase

>48 hours after stressor, the body’s resources are mobilized by the continued release of stress hormones to allow the body to maintain its response to stressor, With continuation of exposure to stressor for 1-3 months organisms may return to normal if stressors are small in strength and intensity

exhaustion phase

With continuation of a strong/intense stressor, organisms lose resistance and enter exhaustion phase- similar to alarm phase, increasing risk of disease, illness or death.

Physiological responses to stress

In response to  a stressor the body release a range of hormones into circulatory system and neurotransmitters into the CNS

These include adrenaline (epinephrine), noradrenaline (norepinephrine) and cortisol

These primary functions of these substances is to prepare the body to respond to a threat- real or perceived