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

• The sympathomedullary pathway (SMP) is made up of the sympathetic nervous system (SNS) and the sympathetic adrenal medullary system (SAM) 

• The SNS is the division of the autonomic nervous system 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

  • The SAM stimulates the release of adrenaline and noradrenaline into the bloodstream from the adrenal glands in the adrenal medulla 

  • The SNS and the SAM prepare for ‘fight-or-flight’  by boosting the supply of oxygen and glucose to the brain and muscles through raising the heart rate and blood pressure

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

• After the acute stressor is dealt with, the body returns to homeostasis through activation of the parasympathetic branch of the nervous system, conserving energy and resting 

• The Hypothalamic Pituitary-Adrenal system (HPA) is responsible for arousing the ANS in response to a stressor 

• 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 a chemical (corticotropin-releasing factor, CRF) which causes the pituitary gland to release adrenocorticotropic hormone (ACTH)  into the bloodstream 

• Once the adrenal cortex detects the ACTH in the bloodstream, it releases cortisol, another stress hormone, which restores energy to help the body cope with the stress

• High cortisol levels trigger a reduction in CRF and ACTH, and once the stressor is removed, the cortisol levels also drop

Cortisol & the stress response

• Because of its immunosuppressive properties, over a period of 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 and found lower levels of these immunity-protecting cells in the second sample taken in a stressful situation

• 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) found that acute stress produces the fight-or-flight response in men but a different 'Tend-and-befriend' response in women, demonstrating a gender difference in the activation of the SMP

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 response to stress.

Limitations

• Research fails to consider the effect of psychological processes on how we physically respond to stress, as it could be that those with more resilience respond in a different physiological way

• Most of Selye’s research was on rats and his theory assumes that the response remains the same to all stressors, which is not the case with humans, who have individual responses depending on the stressor

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