Download STRESS AS A BODILY RESPONSE

AQA PSYCHOLOGY: PHYSIOLOGICAL PSYCHOLOGY
Unit of learning 1
Stress as a bodily response
LEARNING OBJECTIVES :
YOU WILL BE ABLE TO:
1.
Outline the body’s response to stress, including the pituitary-adrenal system
and the sympathomedullary pathway.
2.
Explain how stress may affect the immune system.
Introduction
Stress is experienced when a person’s perceived environmental, social, and physical demands
exceed their perceived ability to cope, particularly when these demands are seen as
endangering the person’s well-being in some way. For example, a person who has built up an
examination to be something that is incredibly demanding, and yet knows they have done very
little revision, will experience stress, but only if failing the exam will result in unpleasant
consequences for them. It is clear from this definition that the experience of stress is as
strongly influenced by our perception of a situation as it is by the actual situation itself
(transactional model). People are constantly evaluating events in their life (exams, jobs,
relationships etc.), deciding whether they threaten well-being (primary appraisal) and
determining whether they have the resources available for meeting the demands posed by
them (secondary appraisal). The stress response was especially important for our ancestors
because the bodily changes associated with stress were essential in conditions of fight or flight,
helping them deal with stressors that were current at the time. Nowadays, however, although
the stress response has stayed the same, the nature of the stressors we typically face has
clearly changed.
The body’s response to stress involves two major systems, one for acute (i.e. sudden)
stressors such as a personal attack, and the second for chronic (i.e. ongoing) stressors such as
a stressful job.
1. ACUTE STRESS RESPONSE – SYMPATHOMEDULLARY PATHWAY (SAM) (Also known as
sympathetic adrenal medullary system)
The autonomic nervous system (ANS) is divided into the sympathetic branch and the
parasympathetic branch.
The sympathetic branch arouses the body when threatened – for fight or flight.
Neurons from the sympathetic branch of the ANS travel to virtually every organ and gland within the
body including the adrenal medulla (top of kidney) which releases adrenaline. The result is increased
heart rate, blood pressure, dilated pupils, metabolic changes such as mobilisation of fat and glycogen
(sugar) in the blood stream. This helps to boost the supply of oxygen and glucose to the brain and
muscles. Non-emergency processes such as digestion are suppressed.
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AQA PSYCHOLOGY: PHYSIOLOGICAL PSYCHOLOGY
Unit of learning 1
Stress as a bodily response
2. CHRONIC STRESS RESPONSE
hypothalamic-pituitary adrenal axis )
–
PITUITARY-ADRENAL
SYSTEM
(HPA)
(AKA the
When stressors are perceived by the higher centres of the brain, a message passes to the
hypothalamus which is the control system for most of the body’s hormonal systems. In response to this,
the pituitary gland releases adrenocorticotrophic hormone (ACTH) which travels to the adrenal cortex
(also top of kidney). The adrenal cortex releases cortisol which has several effects in the body both
positive (bursts of energy, lower sensitivity to pain) and negative (impaired cognitive performance,
higher blood pressure, lowered immune response).
Prolonged release of ACTH causes the adrenal cortex to increase in size in order to cope with
increased cortisol production.
Cortisol levels rise sharply about 20 minutes after the initial perception of an acute stressor.
The system regulates itself quite efficiently.
Both the hypothalamus and pituitary gland have special receptors that monitor circulating cortisol levels.
If these rise above normal levels, they initiate a reduction in ACTH which helps to bring the cortisol level
back to normal.
STRESS-RELATED ILLNESS: THE IMMUNE SYSTEM
Both HPA and SAM have been shown to have a direct effect on the immune system.
The main function of the immune system is to protect the body from antigens, e.g. Bacteria, Viruses
Toxins, Parasites
Note that this is more information than you will need for an exam answer. It is important to just
have a general awareness of how the immune system works.
It operates in two ways:
1
it creates a barrier that prevents antigens from entering the body
2
if an antigen (such as a virus) succeeds in getting into the body, the immune system tries to
detect and eliminate it quickly.
3
if the virus reproduces and starts to cause problems, the immune system tries to eliminate it.
The cells of the immune system
White blood cells (leucocytes) which are produced in the bone marrow.
Some stay in the bone marrow while others travel to the thymus gland, spleen or lymph nodes for
storage.
Those remaining in the bone marrow are known as B cells.
Those travelling elsewhere are known as T cells.
Macrophages are another kind of cell in the immune system which act as scavengers, because they
pick up and ingest foreign materials. They present antigens to B and T cells for extermination.
Th1 and Th2 immunity
Th 1 immunity = aggressive form of immunity, detect, bump, destroy antigens including cancers
Th2 immunity = a specific B cell is produced to eliminate a particular antigen.
Cytokines are produced to help regulate Th1 and Th2 immunity so that their action is efficient.
YOU WILL NOT BE EXAMINED ON THIS DIRECTLY
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AQA PSYCHOLOGY: PHYSIOLOGICAL PSYCHOLOGY
Unit of learning 1
Stress as a bodily response
Research 1.
Cohen et al. (1993) investigated the role of general life stress on vulnerability to the common cold
virus.
Procedure 395 participants completed questionnaires on the number of stressful life events they
experienced in the previous year.
They rated their degree of stress and their level of negative emotions such as depression.
The three scores combined into a ‘stress index’.
The participants were exposed to the common cold virus.
Findings
82% were infected with the virus. After 7 days a record was made of the participants who had
developed a cold. The chance of developing a cold, was significantly correlated with stress index
scores, i.e. the higher the stress levels on the questionnaires, the more chance of getting a cold.
Conclusion
Life stress and negative emotions reduce the effectiveness of the immune system, making people less
able to resist viral infections.
Evaluation of method
1.
there were no direct measures of immune function. However, there is supporting evidence from
other studies (Evans and Edgerton (1991)
2
There was no direct manipulation of the independent variable (the stress index) and so it is
impossible to establish cause and effect, e.g. questionnaires involve self-report rather than
objective measurement.
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this study does not tell us which element of the stress index is most important.
Research 2
Kiecolt-Glaser et al. (1984) investigated naturalistic life stressors and their impact on measures of the
immune function.
Procedures
75 medical students preparing for the end of first year exams.
Natural killer cell activity was measured from a blood test taken one month before exams (low stress)
and during the exam period (high stress).
Participants completed questionnaires on experience of negative life events and social isolation.
Findings
NK cell activity was significantly reduced in the high stress samples.
The greatest reductions were in students reporting higher levels of social isolation.
Evaluation of method
1.
it might be that the significant reductions seen in this study are still too small to increase the
chances of stress-related illness. The measure taken was of Killer cells rather than illness.
2.
This study uses medical students and it could be argued that results should not be generalised.
However, other research has found effects with different types of people, e.g. Kiecolt-Glaser’s
work with women caring for Alzheimer patients.
3.
Natural killer cell activity was measured, but is only one component of the immune system which
is very complex.
4.
Cause and effect cannot be established as there was not manipulation of the independent
variable (exam stress). However, a range of findings from a number of different studies suggests
a relationship between life stress and reduced immune function.
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