The Physiological Response to Stress (AQA A Level Psychology): Revision Note

General Adaptation Syndrome (GAS)

• Selye (1956) developed the General Adaptation Syndrome (GAS) model to explain how the body responds to prolonged stress

• He proposed that the body initially adapts to stress and protects itself in the short term (acute stress)

• However, when stress becomes prolonged or chronic, it can lead to serious damage, including stress-related illnesses

• The GAS model outlines the body’s adaptation to a stressor in three distinct stages:

The sympathomedullary pathway & the hypothalamic pituitary-adrenal system

Sympathomedullary pathway

• The sympathomedullary pathway (SMP) is made up of the

  • sympathetic nervous system (SNS)

  • adrenal medulla

• The SNS is the division of the autonomic nervous system (ANS) that produces localised adjustments (such as sweating as a response to an increase in temperature) and automatic adjustments of the cardiovascular system, and a state of heightened emotion and arousal

  • Sympathetic arousal stimulates the adrenal medulla, the central part of the adrenal gland, to release adrenaline and noradrenaline into the bloodstream

  • Adrenaline and noradrenaline cause the heart to beat faster, muscles to tense, and the liver to convert stored glycogen into glucose, which is released into the bloodstream to provide energy to fuel the fight or flight response

• Thus, the SMP is the physiological system that responds to acute short-term stressors

• Once the stressor is no longer a threat, the parasympathetic system is activated and the physiological arousal associated with fight or flight decreases, prioritising energy conservation over expenditure

  • This pattern of activity is sometimes called the rest and digest response

Hypothalamic pituitary-adrenal system

• The hypothalamic-pituitary-adrenal system (HPA) is the body's response to long-term or chronic stress

  • It takes longer than the SMP to activate, but can persist for several hours or longer

• The HPA response happens at the same time as the SMP is activated, but the whole process takes much longer and is longer-lasting

• The hypothalamus produces corticotropin-releasing factor (CRF), which is detected by the anterior lobe of the pituitary gland, causing it to release adrenocorticotropic hormone (ACTH) into the bloodstream

• Once the adrenal cortex detects ACTH in the bloodstream, it releases cortisol, a glucocorticoid which helps the body cope with the stressor by mobilising and restoring energy supplies

  • However, cortisol also suppresses the immune system, which is damaging to the body if stress is not resolved

• The HPA is self-regulating via a negative feedback loop

  • Cortisol levels in the bloodstream are monitored at the pituitary and the hypothalamus, and high levels trigger a reduction in CRF and ACTH, producing a corresponding reduction in cortisol

Cortisol & the stress response

• Because of its immunosuppressive properties, over time, cortisol can damage the immune system

• This damage happens if stress passes from the acute stage to a longer-lasting chronic stage, such as stage 3 of Selye’s GAS, when increased levels of cortisol reduce the production of antibodies to fight infection

• Prolonged stress has also been linked to heart disease and strokes

Research which investigates the physiological response to stress

• Kiecolt-Glaser et al. (1984) measured natural killer cells (that protect against infection) in blood samples from American college students one month before their exams and then during the exams

  • They found lower levels of these immunity-protecting cells in the second sample, taken during the stressful exam period

• Timio et al. (1988) conducted a longitudinal study comparing nuns (who are protected from chronic stress by their lifestyle) with working women and found the nuns’ blood pressure was unchanged while the working women had raised blood pressure, suggesting long-term stress has a physical effect on health

• Taylor et al. (2000) argue that fight or flight is characteristic of males, and that a more adaptive response in females is 'tend and befriend', in which a threat is met with tending of offspring and befriending of other females to provide social support

Evaluation of the physiological response to stress

Strengths

• GAS was the first theory to explain the physiological effects of stress, influencing many later theories and a lot of research, especially into the negative effects of stress upon health

• Research into the physiological response to stress has had positive implications for helping people cope with stress, especially with its contribution to research into and the development of medicines to reduce the physiological stress response

Limitations

• Physiological accounts of the stress response ignore psychological factors such as cognitive appraisal

  • Lazarus (1999) argues that we make appraisals of a stressor by assessing whether it is a threat (primary appraisal) and whether we have the resources to cope with it (secondary appraisal)

  • Speisman et al. (1964) showed students a film of a primitive medical procedure and found that changes in heart rate depended on the soundtrack students heard, with rates increasing if the procedure was framed as traumatic and decreasing if it was framed as voluntary and joyful

    • This suggests humans are not as passive in the face of stressors as physiological theories assume

• Mason (1971) replicated Selye's procedures using seven stressors in studies of monkeys rather than rats, and measured levels of urinary cortisol, finding varied effects depending on the stressor; extreme cold increased cortisol levels, extreme heat reduced them, and excessive exercise produced no change

  • This challenges a central concept of Selye's theory by showing that specific stressors can produce specific patterns of response, rather than the same non-specific response to all stressors

Issues & Debates

• Much of the early research into stress responses was conducted on male animals or participants, assuming findings would apply to females (beta bias)

  • Taylor et al. (2000) showed that females may respond to stress with a ‘tend and befriend’ response rather than ‘fight or flight’, suggesting gender differences were overlooked in early physiological stress theories

• Explanations of the stress response are reductionist as they simplify the complex experience of stress to purely bodily systems (e.g. cortisol, adrenaline), ignoring psychological and social factors

  • This limits our understanding of stress, as it overlooks how cognitive processes like coping strategies or appraisal can influence physiological responses