The Body's Reaction To Stress

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General Reaction to Stress

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The body’s physiological response to stress begins with appraisal of the situation, followed by activation of the two key pathways, the sympathomedullary pathway (SAM) and the hypothalamic pituitary-adrenal pathway (HPA).
The SAM axis has two pathways. The sympathetic branch, which does things such as increasing heart rate, inhibiting saliva and releasing glucose and this triggers the fight or flight response. The parasympathetic branch introduces a calm state with such changes as increased saliva, reducing heart rate to normal and glucose being stored. These branches make up the autonomic nervous system (the ANS).
The fight or flight response engages the sympathetic nervous system and withdrawing the parasympathetic nervous system, thereby enacting cardiovascular, respiratory, gastrointestinal, renal, and endocrine changes.
In modern society we cannot respond to stress with ‘fight or flight’ (as the SAM axis) so the long-lasting stress of the HPA axis can have negative effects on our physical and psyc

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The sympathomedullary pathway (SAM):

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1. Hypothalamus activates the SNS (sympathetic nervous system).
2. Activation of the SNS causes bodily arousal.
3. SNS also activates the adrenal medulla.
4. The adrenal medulla releases adrenaline and noradrenaline into the bloodstream.
5. These hormones have an effect on the body.
6. This is a rapid acting pathway.
7. Fight or flight response.

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The hypothalamic pituitary-adrenal pathway (HPA):

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1. Higher brain centres activate the hypothalamus.
2. Hypothalamus releases CRF – which travels to the pituitary gland.
3. Pituitary releases ACTH – which travels to the adrenal cortex.
4. Adrenal cortex releases corticosteroids (such as cortisol) into the bloodstream.
5. These hormones have an effect on the body.

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General Adaptation Syndrome (GAS):

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Selye,1956:
The short-term flight or flight response includes changes to both digestion and the immune system. The stressed body is better able to quickly digest sugars (food types that can supply a ‘quick fix’ of energy), but slower to digest food sources requiring more prolonged digestion (proteins and fats). Essentially, the digestion process during stress favours processing food from which energy can be released most quickly. The activity of the immune system, also a long-term process, is suppressed. The whole fight or flight response is programmed for immediate survival – long-term bodily processes (such as digestion of proteins and fats and the activity of the immune system) are temporarily neglected.
Selye’s work led to the development of psychoimmunology the study of the relationship between psychological factors and functioning and efficiency of the immune system.
There are 3 stages of GAS.

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1st Stage of GAS:

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The ALARM STAGE is as described in the previous section on the short-term fight or flight response to stressors. It includes negative consequences of low white blood cell production (essential for the immune system), and sometimes stomach ulcers.

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2nd Stage of GAS

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The RESISTANCE STAGE is characterised by attempts to revert to ‘normal’ functioning. There are still the high levels of adrenaline in the blood from stage 1, but the body attempts to cope with the excess and regulate hormone production as it becomes habituated to the stressor.

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3rd Stage of GAS

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The EXHAUSTION (or COLLAPSE) stage involves a return to what appears to be a normal state, as the body has depleted energy and cannot maintain the fight or flight state. However, there is still an unusually high level of adrenaline in the blood, and in this state an animal experiencing a new stressor, even a mild one, will react immediately strongly. The adrenal cortex stops functioning correctly, leaving the body less able to fight infection.