Stress is a Response to Stimuli in the Environment 1. Stress can be explained as the stimulus in the environment that triggers a stress response. Psychologists call anything that causes someone to act stressed a ‘stressor’ 2. Stress can be explained as a response to a stimuli 3. ‘The response that occurs when we think we can’t cope with the pressures in our environment’ can lead to stress. HANS SELYE studied this with stressed rats. Hans Selye Explained Stress as a Three Stage Response Hans Selye (1956) found rats became ill when they were given harmless injections.
He concluded that all animals & humans react to stressors through a three stage physiological response. This is called General Adaptation Syndrome (GAS). 1. The Alarm Stage – when we perceive a stressor our arousal levels increase this happens so that we are ready to make any physical response. ‘Fight or Flight’ 2. The Resistance Stage – when exposed to stressor for long time, out bodies adapt to the situation and we can cope in a normal way. However, there would still will a high level of arousal. 3. The Exhaustion Stage – after long time exposure to a stressor our bodies will eventually be unable to continue to cope with the situation.
Alarm stage may return (result in distress). Selye called this ‘diseases of adaptation’. Commentary * The GAS theory offers a single type of response & neglects that the body’s reaction to stress does vary (e. g. how much adrenaline is released depends on how the stressor is perceived). All Selye’s early work was carried out on rats, using physical stressors. There are differences in physiology between rats & humans; humans respond mostly to psychological stressors. The GAS ignores individual differences, such as Type A behaviour & gender, it assumes we all behave the same way.
The Hypothalamus is the Bit of the Brain that Responds to Stress When we perceive a stressor a chain of events if triggered in the body. ‘Hypothalamic-Pituitary-Adrenal Axis’ 1. Evaluation of whether something is a stressor, occurs in higher brain centre (cerebral cortex) 2. When there’s a stressor in the environment, these areas send a signal to the hypothalamus, which starts two processes in the body: a) Signals sent to pituitary gland, which release hormone called ACTH (adrenocorticotrophic hormone) into the blood. b) The Autonomic Nervous System (ANS) is also activated.
This stimulates (arouse), adrenal medulla to release adrenaline & noradrenalin into the bloodstream. To respond successfully to a stressor, we have evolved a ‘fight or flight’ response. However, in modern society stressors are more likely to be psychological than physical & more long-term. Some stress can be positive & exhilarating this is known as eustress. Stress and Physical Illness Long-Term Stress Affect’s Cardiovascular System Cardiovascular is another name for, ‘heart & blood vessels’. A long-term stress response may have effect on this system:
Stored energy (glucose) which is released during a stressful event is re-absorbed by the body after the stressor has gone. If the stress is long-term it will remain in the blood stream, which may lead to blockage, producing heart attack/stroke. 2. Stress causes a high heart rate & blood pressure. Over long time pressure can weaken blood vessels. 3. If blood vessels are damaged/weakened this increases the risk of one breaking, which is called haemorrhage. KRANTZ et al (1991) – Stress & the Heart * 39 participants did one of three stress-inducing tasks (e. g. maths test) while the blood flow to their hearts & their blood pressure were measured.