The Body's Response to Stress

& immune system

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  • Created by: Amy
  • Created on: 26-05-12 12:41

When you're stressed:

The sympathetic nervous system increases physiological arousal and prepares the body to respond quickly to threatening situations.

The activation of the sympathetic nervous system is a vital part in the body’s response to stressful stimuli.

When you’re not stressed:

The parasympathetic nervous systems slows the body down when we are not in a state of stress this system is activated. 

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The hypothalamus is an important part of the brain that is responsible for many physiological functions, including thirst, hunger and stress. 

When we are experiencing stress, the hypothalamus is responsible for activating the sympathetic branch of the autonomic nervous system and pituitary gland.

Adrenaline:

Increases the amount of energy to the muscles, increases heart rate, breathing rate, blood pressure, sweating and slows down digestion (to conserve resources for fight or flight).

Noradrenaline:

Increases breathing rate, blood pressure, blood flow to the muscles, slows down digestion and releases sugar from the liver.

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Cortisol:

Important for coping with long term stress as it maintains a steady supply of blood sugar for increased energy.

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The sympatheticomedullary pathway:

·         Higher brain centres evaluate a situation as stressful. They instruct the hypothalamus to trigger the Sympathetic branch of the autonomic nervous system.

·         This in turn stimulates the adrenal medulla (via nerves).

·         This releases adrenaline and noradrenaline into the blood stream.

·         Adrenaline and noradrenaline increase heart rate and blood pressure.

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The pituitary-adrenal system:

·         The hypothalamus is activated when higher brain centres evaluate a situation as stressful and instruct the hypothalamus to stimulate the pituitary gland.

·         The pituitary gland releases ACTH – Adrenocorticotrophic hormone which travels to the adrenal cortex and stimulates the release of hormones called corticosteroids (specifically Cortisol) into the bloodstream.

·         Cortisol suppresses the immune system and mobilises fat stores so they can be used as energy.

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Immune System

Natural Immunity:

Primitive system comprising of white blood cells e.g. natural killer cells that non-specifically destroy invading pathogens.

Specific immunity:

More sophisticated system – lymphocyte cells have the ability to recognise invading pathogens and produce specific antibodies to destroy them

- Cellular immunity- a variety of T lymphocytes attack intracellular pathogens. (attack alien cells harbouring viruses)

- Humoral immunityB lymphocytes release antibodies to attack and destroy extracellular pathogens. (involved in infection control)

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Effects of stress on the immune system

Kiecolt-Glaser et al:

Aim: To investigate whether the stress of important examination examinations has an effect on the functioning of the immune system

Procedure: They used 75 students and took their blood, one month before their final examinations and during their examination period. Their immune function was assessed by measuring NK cell lymphocyte activity in the blood samples. Moreover, the students were also given questionnaires to assess psychological variables such as life events and loneliness Findings: NK cell activity was significantly reduced in the second blood sample, taken during their final examinations, compared with the first sample (taken one month before their final examinations). NK cell activity was most reduced in participants who also reported high levels of life events and loneliness.

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Conclusion: Examination stress reduces immune function, potentially leaving the individual vulnerable to illness and infections. Immune function is also affected by psychological variables such as the stress of life events and feelings of loneliness. These long-term stressors may make individuals more vulnerable to the added effect of short-term stressors such as examinations

Evaluation

Bad points:

  • This study only used medical students, who might be considered a non-representative group. This limits the extent to which these results can be generalised to other groups in society. (external validity)
  • Low internal validity - does not take into account other EVs such as daily hassles
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Good points:

  • External validity is quite high as the IV is not manipulated – could apply to other cases of exam stress
  • They did use a questionnaire to try to rule out the effects of life events
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Cohen et al

Aim:

Cohen was interested in how stress may increase vulnerability to the common cold.

Method:

394 participants, completed questions (stress index)

- Stressful life events

- Degree of stress

- Level of negative emotion

Then exposed to one of 5 cold viruses via nasal drops. After 7 days, doctors assessed symptoms of the cold.

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Findings:

82% became infected. There was a correlation between the intensity of symptoms and levels of stress. High stress – high symptoms.

Evaluation:

- Social desirability bias

- Self report techniques – could make mistakes, forget things or misinterpret the questions

- Tried to improve validity by controlling: age, gender, smoking, weight, diet, etc.

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