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Stress: Selye's GAS model
Transcript of Stress: Selye's GAS model
‘Stress’ describes the way you feel when under pressure – when the perceived demands of a situation are greater than your perceived ability to cope – particularly when these demands are seen as endangered your well-being in some way.
It is the physical and psychological response to the threat. Knowing what you do about the biological approach, can you guess how it explains stress? The stress response is adaptive – it has evolved to help us to survive. The bodily changes associated with stress are essential in conditions of fight or flight.
Without the stress response, we are in danger of being run over by a car, or being attacked by an angry dog.
Much of our understanding of stress can be tracked back to the pioneering work of Hans Selye. Became interested in how animals are able to resist the effects of various challenges to their homeostasis, such as heat, cold, infection and toxic substances.
He observed that certain reactions always occur – including a decrease in the size of the thymus gland and other immune system organs, ulcers in the gastrointestinal tract and enlargement of the adrenal glands.
The stress response, although severe in its manifestations is recognised as necessary for survival.
Furthermore, repeated exposure to moderate stressors, Selye recognised, could increase the ability of the organism to withstand more prolonged and severe exposure. Selye Is Stress always bad? The sympathetic nervous system Prepares the body for action in situations where a person is threatened.
For example, if you are walking home alone on a dark night, an unusual noise may scare you. The autonomic nervous system prepares you for flight (run away) or fight (stay and confront what is there).
It does this by diverting blood from the stomach to the muscles, increasing heart rate, dilating the pupils of the eyes and making the hairs on your body stand on end. Dilates pupils
Inhibits saliva production
Increases rate of breathing
Relaxes the bladder (increases urination)
Increases heart rate
Increases actions of adrenal glands
Generally, prepares the body to expend energy for flight or fight What is the General Adaptation Syndrome? According to Selye, GAS represents the body’s defence against stress.
The body responds in the same way to any stressor, whether it’s environmental or arises from within the body itself. Environmental stressors may include:
Excessive heat or cold
Sleep and water deprivation
Electric shock Changes here are caused by the nervous system – they help to prepare us for action
The hypothalamus triggers the production of adrenaline.
Adrenaline causes increased heart rate, sweaty palms, fast breathing, dilated pupils, etc – this readies the body for ‘fight or flight’ 1. The Alarm Stage If the threat subsides, the parasympathetic system will return the body to normal. If the stressor isn’t removed, the state of alarm cannot be maintained by adrenaline – other hormones are released to sustain the body’s defence mechanisms. They include:
Cortisol (makes more energy available through breakdown of fats and release of glucose from liver)
Aldosterone (maintains elevated blood pressure)
Thyroxine (maintains elevated heart and breathing rate, allows energy from food to be used quickly and efficiently) 2. Resistance 3. Exhaustion Selye observed that whatever the cause of stress, if the threat persisted, his animals became sick and died.
At this stage, the body can no longer function properly
The adrenal glands may be damaged from previous over-activity
The immune system may not be able to cope because production of necessary proteins (eg cortisol) have been slowed in favour of other needs.
Blood glucose levels drop
Psychophysiological disorders develop – these include high BP (hypertension), coronary heart disease, depression, asthma and peptic ulcers. Selye called these – ‘the diseases of adaptation’ Joe is a student in his AS year and is under a lot of pressure to complete his homework. As he experiences this stress and begins to tolerate it during the year, his cortisol levels rise.
What stage of the GAS would he be in? Joe is also trying to learn to drive but is finding it really difficult. He can’t cope with this source of stress at all and wants to scream at his instructor and abandon his lessons.
How would Selye explain Joe’s ability to cope with one source of stress, but not another? The release of which hormone would be associated with each of the following situations?
Nearly being hit by a car?
A long spell of unemployment?
Waiting in the wings before a performance? Recently bereaved people often find they get ill. Why might this be? Selye's research Selye worked in a hospital, and noticed that all patients shared a common set of symptoms (aches and pains, loss of appetite, etc) no matter what was actually wrong with them.
He later conducted research on the effects of hormones on rats, and noticed that the rats also had this ‘generalised response’
No matter what substance the rats were injected with, they produced a similar response.
He suggested that there was one internal mechanism for dealing with ‘noxious agents’ which he called ‘stressors’ Rats were exposed to various noxious agents:
Production of spinal shock (cutting the spinal cord)
Excessive muscular exercise
Intoxications with sub-lethal doses of drugs (morphine, formaldehyde, etc) The results support Selye’s GAS model – Selye suggested that the responses observed in rats to noxious agents might be similar to general defence reactions to illness De Groot et al, 2002 Injected rats with a virus and exposed some of them to a social stressor.
The stressed individuals produced fewer antibodies and virus-specific interleukins to fight the infection. Herbert & Cohen, 1993 Showed that the activity of special lymphocytes (natural killer cells) that attack cancerous cells is impaired by prolonged stress. Using Selye's GAS model, how would
you explain this man's escape from injury or death?