Presentation on theme: "Stress and GAS- Hans Selye"— Presentation transcript:
1Stress and GAS- Hans Selye Selye (1956)– administered ‘noxious’ agents to rats and he found that they had same physiological responseCould be the same with humans & stress?Different sources of stress – same ‘non-specific’ physiological response occurs – which can be harmfulSelye (1956) Called this ‘General Adaptation Syndrome’ (GAS)
2The transactional model of stress Most popular model for studying stress today – stress as a lack of fit between the perceived demands of a situation and the person’s ability to copeIn this model any stimulus which produces physical signs of a stress response is a stressorE.g. Exams – some overestimate the demands? may be very stressed and do wellSome underestimate the demands,and do badlySo there is a cognitive elementand there are individual differences in this
3The body’s response to stressors Two main responses – both involve the adrenal glandsTwo adrenal glands – just above the kidneys : each one made up from:Adrenal cortex & adrenal medulla: these release different types of hormones into the blood stream, and are controlled by two different pathways which are the hypothalamic-pituitary adrenal cortex (HPAC) pathway and hypothalamic-ANS-Adrenal medulla pathway
4The hypothalamic-pituitary adrenal cortex pathway (HPAC) Controlled by the hypothalamus and pituitary glandHypothalamus is a small structure at the base of the brainPituitary gland ‘master gland’ as it releases many hormones into the bloodstreamWhen we are confronted with a stressor - it releases ACTH hormone and this travels to the adrenal cortex and triggers the release of corticosteroids – a vital part of the stress response – mobilising energy reserves – heart rate & blood flowThe HPAC pathway is activated when higher brain centres evaluate a situation as stressful and instruct the hypothalamus to release the CRH hormone to stimulate the release of ACTH from the pituitary gland
5The red arrows show the hypothalamic-pituitary adrenal cortex (HPAC) pathway StressorHigher Brain Centres(cortex & limbic systems)HypothalamusCRH HormoneMetaboliceffects on the body(higher heart rate & bloodpressure toget oxygen to muscles)BrainstemPituitary glandACTH hormone inbloodstreamNeural controlvia autonomicnervous systemCorticosteroidsIn bloodstreamAdrenal cortexAdrenal medullaEpinephrine (adrenaline) andNorepinephrine (nor-adrenaline)In bloodstream
6The hypothalamic- autonomic nervous system (ANS) adrenal medulla pathway The autonomic nervous system (ANS) is a network of nerve pathways running from the lower part of the brain (the brainstem) to the body’s organs.Circulatory (blood) systemVarious glands- including theAdrenal medullaHeartDigestive systemThe ANS is controlled by the higher brain structures, especially the hypothalamus
7The green arrows show the hypothalamic-ANS-Adrenal medulla pathway StressorHigher Brain Centres(cortex & limbic systems)ActivatesThe ANS sympatheticsubdivisionVia the brainstemHypothalamusCRH HormoneBrainstemPituitary glandMetaboliceffects on the bodyACTH inbloodstreamNeural controlvia autonomicnervous systemCorticosteroidsIn bloodstreamAdrenal cortexAdrenal medullaAdrenaline andNoradrenaline inBloodstream (increases heartRate & blood pressure)
8Activating the body’s stress response Selye identified the HPAC & hypothalamic-ANS-adrenal medulla pathways as the main components of the body’s response to stressorsHe then thought about why they become activatedBoth systems prepare the body for energy expenditure – normally hypothalamus and ANS does this without of conscious involvement – making sure the body is functioning properlybut we also need higher brain centres when things happen in the world which we have to respond to quickly.Cannon (1914) called this the -‘FIGHT OR FLIGHT RESPONSE’
10Fight or Flight Response Increaseoxygen intakeRelease storedglucoseDivert resourcesaway fromdigestionReady to expend energy,either by fighting or by running away
11Fight or Flight and your Body Sympathetic(Pumps you up)Parasympathetic (chill out)PupilsLungsHeartLiverStomachSalivaActivity: fill out this sheet with the effect of stress on these parts of the body
12The thin arrows show the hypothalamic-ANS-Adrenalmedulla pathway(colour in green)The thick arrows show thehypothalamic-pituitaryadrenal cortex (HPAC)Pathway (colour in red)StressorHigher Brain Centres(cortex & limbic systems)ActivatesThe ANS sympatheticsubdivisionVia the brainstemHypothalamusCRH HormoneMetaboliceffects on the body(higher heart rate & bloodpressure toget oxygen to muscles)BrainstemPituitary glandACTH inbloodstreamNeural controlvia autonomicnervous systemCorticosteroidsIn bloodstreamAdrenal cortexAdrenal medullaAdrenaline andNoradrenaline inBloodstream (increases heartRate & blood pressure)Activity: make your own diagram
13Stress response systems activated The three phases of the General Adaptation Syndrome (GAS) (Selye, 1956)Phase 1: AlarmStress response systems activatedPhase 2: ResistanceBody copes with stressPhase 3: ExhaustionStress related illness may develop
14The General Adaptation Syndrome (GAS) (Selye, 1956) The GAS has three phases1st phase – The alarm phase, the presence of a stressful event is registered – could be a threat from an outside or physical stressor – such as an injury or illness affecting the body - the hypothalamic-pituitary adrenal cortex (HPAC) pathway and hypothalamic-ANS-Adrenal medulla pathway prepare the body for energy expenditure (fight or flight) – nowadays many of the stressors are psychological
15The General Adaptation Syndrome (GAS) (Selye, 1956) 2nd phase is resistance – the body’s stress response is fully activated and coping with the stressor, so from the outside things appear to be back under controlHowever, the body enters the 3rd phase of exhaustion if the stressor is long lasting and chronic. Hormone levels are depleted, and stress related conditions such as raised blood pressure, ulcers, depression and anxiety may develop as stress systems become exhausted
16Evaluation of GASExperimental support – first systematic attempt to explain the body’s response to stress based on experimental data – also the first to emphasise the role of the hypothalamic-pituitary adrenal cortex (HPAC) pathway and hypothalamic-ANS-Adrenal medulla pathwaysUse of non human animals – Research carried out on rats, using physical stressors. Differences between the physiology of rats and humans, so its difficult to generalise his work to humans, however, his later work was done with humansIndividual differences- GAS ignores individual differences, e.g. Type A behaviour (Highly driven people who thrive in stressful situations). It assumes that we all respond the same way to stress, but personality and gender can also play role
17Questions to check your understanding What are the two divisions of the nervous systemHow does communication occur in the endocrine system?Which is the faster method of communication? The NS or the Endocrine system?What does the Sympathetic and Para-Sympathetic subdivisions of the ANS do?Hormones travel through our…………….The ‘pea sized governor’ is also known as the …………………Give a definition of stressWhat is a stressor?How does the body respond to stress through the hypothalamic-pituitary adrenal cortex (HPAC) pathway9) How does the body respond to stress through the hypothalamic-ANS-Adrenal medulla pathway10) What is the fight or flight response?11) What is the first stage of GAS? – What pathways are activated?12) What is the second stage of GAS?13) What is the third stage of GAS?
18Energy mobilisationNowdays stress comes from psychological sources such as the workplace/ relationshipsPhysical activity rare in the response to stress – but GAS response preparing us for fight or flightGlucose and fatty acids produced to prepare for fight or flight cant all be re-absorbed into the body if stress is chronic, and the ‘furring up of the cardiovascular system (hypertension & atherosclerosis)
19Stress and Physical Illness Principle of the biological LOA demonstrated: there is a relationship between our stress response system (which works through and our nervous/endocrine system and is usually activated by psychological stressors) which then has an effect on our immune system causing illness (this is a biological correlate of behavior)
20Stress and physical illness The immune system is a very complex system of cells and chemicals which protect the body from infection by viruses and bacteria.But during stress all resources are geared to escape, so protection and tissue repair can wait till laterIts an excellent survival mechanism – but long term activation can lead to the shutting down of other systems which are also important
21Walk and talkUsing the note-card provided gather as many ideas as you can about the immune system and stress.You need to use the ‘popcorn partner’ idea- only one fact from each person and it needs to be a new one; you need to exchange with each person in the class.When you have finished your quest for facts write an answer to the following questionsHow do steroids relate to stress?How does a persistent flow of steroids affectone’s physical health?
22The Immune SystemStructures and mechanisms that allow the body to resist and fight off infection by:BacteriaViruses (aka antigens)White blood cells provide mechanisms of immunity(white blood cell) (white blood cell)T-Lymphocyte Phagocyte
23Non specific immunity - Surround and ingest foreign particles whenever they find them (white blood cell) PhagocyteCell-based immunity –produced in the thymus gland they search & destroy foreign cells and cells infected with antigens such as bacteria(white blood cell) T-Lymphocyte
24Suppression of the immune system Immune system very complex & stress- response can affect it directlyE.g. high levels of corticosteroids can shrink the thymus gland – preventing the development of T-Lymphocyte cellsLong term stress causes long term reductions in immune function (Willis et al. 1987)Diet, exercise, and social support can improve immune function and it will recover if the stressful situation is resolved (Sapolsky, 1994)
25Stress & Immune Function Cohen & Herbert (1996)Stress associated with increased susceptibility to cold, flu, herpes virus, chickenpoxBartrop et al (1977)Immune suppression followed loss of intimate relationship through death or divorceLevy et al (1989)PPs who scored high on a scale of daily hassles had lower natural killer (immune) cell activity
26Stress & Immune Function Evidence supports a weak link between stress and immune functioningThe relationship is mediated by:Personality & coping styleSocial supportLifestyleCompared to impact of e.g. age, genes, nutrition stress is relatively unimportant
27Other effectsStress hormones such as corticosteroids may influence the pituitary gland ‘the master gland’ (which controls many bodily functions)The pituitary gland controls sexual and reproductive functions – In males, testosterone in males declines in the stress response. In females, the menstrual cycles can be disruptedGrowth hormones are also controlled by the pituitary gland – some children suffer from ‘stress dwarfism’
28EvaluationSuppression of immune functioning need not lead to illness and disease, you still need to be exposed to an infectious agent for illness to developCorrelations often small but significantConclusion: there is a relationship between stress and physical illness, and this may be due to immunosuppression, and can also be explained by Selye’s (1956) GAS.
29Stress stimulates production of steroids. Steroids suppress the immune systemLittle effect when secretion is intermittentPersistent secretion decreases inflammation (increased blood flow to any injured area resulting in redness and increase in white blood cellsInterferes with formation of anti-bodies therefore become susceptible to illnesses
30Studies relating to stress and lifestyle i Studies relating to stress and lifestyle i.e the effect of the environment on physiological processesIn your group write up notes regarding the assigned study.Join another group and share details ensure that you have exchanged with all groups.