- Created by: Samia
- Created on: 23-12-10 20:58
Stress as a bodily response
What is stress?
Individuals experience stress when their perceived environmental, social, and physical demands exceed their percieved ability to cope. This is particularly the case if such demands are seen as threatening a person's well being in some way. The demands of a crucial examination might be a typical example of a tress inducing phenomenon.
A key feature of stress invovles the way individuals perceive situations which can be just as important in the experience of stress as the stressful situation itself.
Early human beings faced different threats in their environment and the bodily changes associated with stress were essential in conditions of flight and fight (an energised readiness to either fight or run away when confronted with a threat)
The evaluation of whether something is a stressor occurs in the higher brain centres- the cerebal cortex. When there's stressor in the environment, these higher areas send a signal to the hypothalamus. This tiny part of the brain makes up for size by having many functions- including controlling the physiological activites involved in stress. in respinse to the higher areas, the hypothalamus triggers two processes in the body.
Two pathways involved in the stress response:
One happens through the nervous system so it is very rapid - SYMPOTHOMEDULLARY
One happens through the blood stream so it is slower- PITUATRY-ADRENAL PATHWAY
The activation of the sympathomedullary pathway
Acute Stress Response Pathway. The initial shock response
Hypothalamus triggers activity in the system of the sympathetic branch of the Autonomic Nervous System ->
Gets the body ready for fight or flight (body becomes more stressed and uses energy) ->
Increase heart rate and lungs ->
Decrease digestive activity ->
Stimulates the adrenal medulla wich releases adrenaline and noradrenaline into the bloodstream.
Activation of the pituitary-adrenal system
Chronic Stress Response Pathway- Countershock Response
Hypothalamus also triggers the release of CRH (corticotropin-releasing hormone)->
CRH stimulates the Pituitary Gland->
Releases ACTH (adrenocorticotropic hormones)->
ACTH travels through the body and then stimulates the Adrenal Cortex->
Adrenal Cortex then releases Cortisol which gives energy by converting fat and protein->
Liver releases stored energy->This energy is needed to replace that used up by the body's initial reaction to the stress.
The Stress Response
When a person appraises an even as stressful, the body undergoes a number of changes that heighten physiological and emotional arousal. First the sympathetic division of the autonomic nervous system is activated. The sympathetic division prepares the body for action by directing the adrenal glands to secrete the hormones adrenaline and noradrenaline. In response, the heart begins to beat more rapidly,muscle tension increases, blood pressure rises, and blood flow is diverted from the internal organs and skin to the brain and muscles. Breathing speeds up, the pupils dilate and perspiration increases. This reaction is sometimes called fight or flight response because it energizes the body to either confront or flee from a threat. Another part of the stress response involves the hypothalamus and the pituitary gland, parts of the brain that are important in regulating hormones and many other bodily functions. In times of stress the hypothalamus directs the pituitary gland to secrete ACTH. This hormone, in turn, stimulates the outer layer cortex of the adrenal glands to release glucocorticoids primarily the stress hormone cortisol. This hormone helps the body access fats and carbohydrates to fuel the fight or flight response.
Illness and Stress- Immune System
Stress has a weakening effect in the immune system.
Kiecolt-Glaser (1984( aimed to see if there was a correlation between immunity and stress. She took blood samples if medical students in periods of low stress i.e before exams and periods of high stress i.e during exams. She was measuring the levels of white blood cells in the blood.
She found that long term stress impairs the effectiveness of the immune system to heal wounds. And that there were less natural killer cells were reduced during high stress and concluded that stress impacts the immune system.
Evaluation-+ Application of findings-> high ecological validity-> relared to the real world +/- Natural Experiment-> can't prove cause and effect- Limited sample
Diffucult to unravel the relationshop for certain. Does stress cause illness or does being ill make you mroe prone to stress? Mediating health behaviours eg smoking
The Immune System
The immune system involves a collection of cells, produced mainly in the spleen, lymph nodes, thymus and bone marrow, which travel through the bloodstream, defending the body against antigens (such as bacteria, viruses and cancerous cells). The major type of immune cells are white blood cells.
Immunodeficiency diseases- such as AIDS involve widespread destruction of the immune syndrome and leaves the body vulneravle to various illnesses/infections.
Autoimmune diseases- Illness caused by the immune system's failure to recognise host tissues and attacking them. Examples include some forms of cancer, diabetes and rheumatoid arthritis.
Research into the effects of acute/cronic stress
Kiecolt-Glaser et al 1984
Natural Experiment (no manipulation of the IV- low stress before exam,high stress during exams)- Do short term stressors such as key exams have an effect on the immune system? Carried out with 75 medical students. Blood samples taken one month (low stress period) before the exams and during the exam period (high stress). The functioning of the immune system was assessed by measuring NK cell activity in the blood samples. NK cell activity was significantly reduced in the second blood sample compaered to the sample taken one month before. This indicates that short term, predictavle stressors reduce the immune system functioning, increasing vulnerability to illness. The participants were also given questionnaires with the aim of assessing the influence of psychological variables such as psychiatric symptoms, loneliness and life events. Immune responses were particularly weak in those students who reported feeling most lonely etc.
Evaluation- +Gender differences were dealt with by repeated measures design. -Can't control all variables, - Demand characteristics.
Sources of Stress
Major changes to life (e.g divorce,death of spouse,moving house) require a person to adapt. This adaptation is stressful and may have an impact on physical health. Life changes involve upheaval and readjustment, this causes stress. Stress causes illnes, therefore you'd expect a correlation betwen life changes and illness.
Holmes + Rahe (1967) used the SRRS scale to measure life changes scores and ill health. Rahe et al (1970) used the SRRS with large sample of Navy personnel. Again, found a positive correlaton between scores and ill health. These studies suggest that life change and ill health are linked.
Correlations, whilst significant, are still very small. Life change only has minor impact on general health. The effect may be explained several ways e.g possibly becoming ill increases exposure to life stressors or maybe being ill makes you more likely to report life changes. SRRS assumes that each stressor affects people the same way. Not true-divorce maybe good. SRRS includes positive life change-increase in income.
Research into the effects of acute/cronic stress
Marucha et al (1998) Acute stress-Does exam related immunity changes affect the rate at which wounds heal?
A punch biopsy was administrated in the mouth of students wither during the summer holidays or three days before an exams. The wounds given before the exams took 40% longer to heal than the wounds given during the holidays.
Kiecolt-Glaser et al (2005) Chronic Stressors- Relationsip stress. How is the immune system affected under conditions of on going stress? Marital conflict can be an example of chronic stress. The research explored wound healing in relation to marital conflict. Blister wounds healed more slowly on the arms of married couples who had been involved in conflicting rather than supportive discussion.
Sources of Stress
Daily Hassles- Critism of life changes is that it doesnt happen everyday. The SRRS has been criticised for having little everyday relevance and the concept of Daily Hassles has been forward as an alternative approach to measuring the amount of stress in people's lives.
Research-Kanner et al (1981) i