Selye's began his research in the 1930s, when he noticed that rats given repeated daily injections developed similar stress-related symptoms, such as gastric (stomach) ulcers.
On the basis of many studies he developed a three-stage model of how the body responds to stressors:
Stage 1. Alarm
A stressor is percieved and the pituitary-adrenal system and the sympathomedullary pathway are activated. Levels of stress-related hormones surge, heart rate and blood pressure increase, and energy reserves are mobilised.
Stage 2: Resistance
If the stressor persists the body's response systems maintain their activation, with levels of stress related hormones and bodily arousal remaining high.
Stage 3: Exhaustion
Long periods of stress ('chronic' (long lasting) stress) eventually exhaust the body's defense systems and its ability to maintain high levels of circulating stress hormones. This is the stage when stress-related illnesses may develop.
- Selye's work has been extremely influential in developing the whole area of research into stress. He emphasised the central roles of the pituitary-adrenal system and the sympathomedullary pathway, and the links between chronic stress and illness.
- Selye emphasised that the GAS (General Adaptation Syndrome) was a common response to all stressors, i.e. he took a response-based approach to stress, which ignores individual differences and the cognitive elements of perception and appraisal.