Selye and stress
Selye: Discovered that rats + daily injections = stomach ulcers
Showed different stressors all produced the same pattern of physiological responses
∴ NOT due to injection but due to STRESS.
Stressor: A stimulus or situation putting demands on an individual
Transaction model: Originally developed by Cox and Mackay (1978)
Primary appraisal: When one assesses the situation to identify potential threats
Secondary appraisal: When one assesses their ability to cope with a threatening situation.
Stress dependent on : Estimation of pressure or estimation of ability to cope
The body's initial response to stress- SAM pathway
Stress results when someone feels they cannot cope with the demands they have been given.
SAM PATHWAY (Sympathetic Adreno-medullary)
- Brain appraises situation as stressful
- Message to hypothalamus
- Acvtivates SAM PATHWAY
- SNS activates Adrenal Medulla
- Adrenal Medulla releases hormones adrenaline and noradrenaline.
- Prepares body for fight or flight
EFFECTS: ↑ BP, ↑ Perspiration, ↑ Breathing, ↑ Heart rate, ↑ muscle tension ↓ disgestion
Pituitary-adrenal systems's response to stress
- Still stresses after 1-2 hrs, HPA AXIS activated to relaase more energy to keep bodily functions going.
HPA AXIS (Hypothalamic pituitary-adrenal)
- Hypothalamus releases hormone CRH which activates the pituitary gland
- Pituitary gland stimulates release of ACTH travels in bloodstream
- Activates adrenal cortex
- Adrenal cortex releases corticosteroids
Corticosteroid effects: ↑ release of energy reserves (to keep dealing w/ stressor
& suppresses immune system)
GAS Model (general adaptation syndrome)
Selye's GAS model- in response to findings from rats. How body responds to stressors:
Alarm: SAM and HPA activated. Lvls of stress-related hormones surge
Resistance: If stressor persists, body's response systems (SAM & HPA) keep going.
Exhaustion: Long/"chronic" stress eventually exhausts body's response systems.
Stress-related illness and the immune system
Stress & physical illness
- ↑ heart rate → damaged lining of blood vessel or heart muscles
- In chronic stress, ↑ lvls of glucose and free fatty acids → ATHEROSCLEROSIS
- Increases likelihood of heart attacks and strokes
- The weakened immune system leaves body vulnerable to infection
Immune system (protects body against bacteria & viruses that could cause disease)
--Natural immunity: White blood cells that non-specifically attack and ingulf/ingest invading pathogens.
--Specific immunity: White blood cells recognise invading pathogens & produce specific antibodies to destroy them.
Brady et al (1958)- stress and development of ulcers
Kiecolt-Glaser et al (1995)-strss impacts on healing wounds
Cohen (1993) stress increases vulnerability to common cold virus
Kiecolt-Glaser 1984)-stress reduces NK cell activity
Segerstorm and Miller (2004)-Meta-review of stress research
Brady et al (1958)- stress and development of ulce
MONKEYS put in pairs and given electric shocks every 20 secs for 6 hrs.
EXECUTIVE monkey in pair could POSTPONE electric shock if they pushed a lever.
Results: Executive monkeys were more likely to develop ulcers and later die.
Conc: Illness and death not due to shocks but the stress Executives had delaying shock.
Eval: ✘ Unethical due to harming of animals
✘Can't generalise from monkey's to humans
Kiecolt-Glaser et al (1995)- stress impacts on hea
PUNCH BIOPSY on 26 women's arm to create small wound.
13 ppl: Control group 13 ppl: Alzheimer's carers (stressful)
Results: Wounds took on average 9 days longer to heal in Alzheimer's carers.
Conc: Long- term stress impairs immune systems effectiveness at healing wounds.
Eval: ✔ Sweeney (1995) found same thing with dementia carers
✘ Carers may have other differences eg. poor diet, lack of sleep
✘ Small sample size
Choen (1993)-stress increases vulnerability to col
QUESTIONNAIRE on number of stressful life events in past year. (394 participants)
RATINGS on life events and negaive emotions-------------------------------->STRESS INDEX
82% of those expossed became infected.
After 7 days, numbers of those who developed clinical cold were recorded
Results: Strong positive correlation between stress index and those who developed cold.
Conc: Life stress and negative emotions reduce effectiveness of immune system.
Eval: ✔ Although no direct measures of immune function, other studies show similar findings.
✘Independent variable (stress index) not directly manipulated
Kiecolt-Glaser 1984)-stress reduces NK cell activi
75 MEDICAL STUDENTS preparing for final exams were tested for NK cell activity.
Blood samples taken 1] 1 month before exams (↓ stress) 2] During exams (↑ stress)
Quesstionnaires on negative life events and socal isolation
Results: Greatly reduced NK cell activity in highly stressed samples, greastest reduction in students who were socially isolated too.
Conc: Exam stress reduces immune function ∴ more vulnerable to illness etc. Effects more noticeable in those socially isolated too.
Eval: ✔ Similar findings with LT carers and women going through divorce
✘Didn't assess actuall illness outcomes BUT ✔ had direct measure of immune function
✘NK cell activity only 1 component of sophisticated system--may just alter pattern of responses.
Segerstorm and Miller (2004)-Meta-review of stress
Reviewed meta-review on 293 studies looking at effects of different stressors on measures of immune system functioning.
1] Acute time-limited stressors
↑ Natural immunity (eg. increased no. of NK cells) b/c natural immunity is a fast response system so increases quickly to prevemt stressor leading to physical injury.
2] Chronic Stressors
General ↓ in both natural and specific immunity,-------->Global immunosuppression
Supports fact that acute stressors stimulate fight or flight reponse i.e. rapidly occurring natural immunity responses for emergency situations.
Global immunosuppression thought to be result of HPA axis and release of c/steroid