- Chronic Stress
- Stressor is detected by hypothalamus which releases CRF (Corticotrophin-releasing factor)
- This activates the pituitary gland which stimulates the release of ACTH (Adrenocoricotrophic hormone)
- The adrenal cortex then is activated which releases corticosteriods into the bloodstream, including cortisol
- Wich enables the body conserve glucose for neural tissues, elevate or stabilize blood glucose, mobilise protein reserves and preserve salts and water - stimulates liver conversion of glucagon to glucose
- Cortisol also slows wound-healing and suppresses the immune system
- The glucose helps to provide a continuous supply of energy to respiring tissues
- Acute stress
- Stressor detected by hypothalamus
- Activates the sympathetic branch of the ANS (Autonomic Nervous System)
- Sends messages via neurons to glands and organs
- Adrenal medulla stimulated to release adrenaline and noradrenaline
- Heart and respiratory rates speed up, sweating, pupils dilate
- Blood diverted from stomach to skeletal muscles
- Oxygen, glucose supply to muscles and brain boosted, digestion suppressed
- After a few minutes, parasympathetic branch activated to calm and relax
- Heart/ respiratory rates return to normal, no more adrenaline/noradrenaline so homeostasis achieved
Evaluation of stress response
- One strength is that it has research to support it. Baxter found that people who did not have adrenal glands, and therefore could not produce cortisol had to be given additional quantities if stressed in order to survive.
- A limitation of the biological explaination is that it does not consider gender differences. For example, evolutionary theory suggests that if a female reacted this way it could put the offspring in danger. Taylor argues that the fight or flight response is a biologically male response to acute sress and that neurophysiological mechanisms in the female brain inhibit this and promote attachment behaviour in the "tend or befriend" repsonse.
- Another limitation of the explanation is that is reductionist as it fails to consider that individual differences may affect the stress response.
The Immune System
- Main defence against infection by foreign agents
- Cells and chemicals seek and destroy antigens (virus, bacteria, fungi)
- White blood cells (manufactured in bone marrow) come in two types, Phagocytes and Lymphocytes which provide 3 mechanisms for immunity:
-Non-specific - Phagocytes surround and ingest particles, e.g macrophages, which destory invaders, and activate helper T cells
- Cell-Based - Lymphocytes (T Cells) are manufactured in the thymus gland seek and destroy foreign cells and those infected with antigens. Helper T cells activate Cytoxic T cells which destroy infected body cells and activate the B cell.
- Antibody-based - B cells which mature in the bone marrow, destroy invading agents in bloodstream, by forming plasma cells which produce antibodies- attach and slow down, making it easier for destruction by phagocytes and cytoxic.
Effects of Stress on Immune Health
- During stress the digestive system is supressed. After stress digestive activity is increased. This can affect digestive health and cause ulcers (which adrenaline can also cause)
- Stress raises blood pressure
- High levels of corticosteriods shrink the thymus gland - which means less T cells can be produced
- Lifestyle changes due to stress e.g stress -> smoking -> CHD/lung cancer
- ACTH signals production of anti-inflammatory hormones, which makes skin condtions like eczema worse and inhibits immune functioning
- Increase in blood cholesterol levels, through adrenaline and noradrenaline on the release of free fatty acids.
The SRRS (Social Readjustment Rating Scale)
- Measures relationship between life changes and wellbeing
- When a psychological adjustment must be made - this causes stress
- Researchers made a list of life events based on work as clinicians
- Asked 100s of men and women from various backgrounds to rate events in terms of adjustment they would take
- Death of a spouse came out top, and was assigned the artibtary life change unit of 100
- A house move was 20 and a holiday was 13
- They found using both reterospective and prospective studies, that a combined score of 150 increased chances of stress related illness by 30%
- A score of over 300 increased the chances by 50%
Validity of the SRRS
- Population validtiy: Scale was developed in the USA, critics argue it is difficult to use within other culutres (e.g a change in church activities may not be relevant in a more secular society). Therefore the scale should be adapted for each culutre. It is also more focused on changes that affect males, so a modern scale should focus on issues for both genders
- Temporal validity: Scale produced in 1960s so some of the items may not be relevant today. For example, divorce may not carry the same implications as it did 5 decades ago.
- Causality: no way of knowing if life changes cause ill health or if they are a symptom of health issues or if a third factor influences both.
- Self Report (Social desirability bias): Self reports are unreliable, participants have a tendency to complete them differently each time (based on research) therefore we can never be certain the results are consistent with what has actually happened. Also people may want to appear in a positive light to researchers and so not put down the truth.