Biological Explanations of Stress (HL IB Psychology)

General Adaptation Syndrome (GAS)

• When we are under threat, our body immediately begins to prepare itself for either fighting the threat or running away: the fight or flight response

• The fight or flight response is an inherited physiological response designed to protect us from danger

• Hans Selye (1956) developed the General Adaptation Syndrome (GAS) to explain the fight/flight response, proposing that the body reacts in the same way to all stressors

• Selye experimented on rats, but GAS has been supported by research into human stress 

• GAS is still used today to explain how stress leads to an exhaustion of the body’s resources, leaving us vulnerable to illness

• Stage 1 - Alarm

  • the hypothalamus activates the sympathetic nervous system (SNS) and the adrenal glands

  • corticosteroids (adrenaline, noradrenaline and cortisol ) are released into the bloodstream

  • heart rate and blood pressure increase in readiness for a physical fight-or-flight response

• Stage 2 - Resistance

  • if the stressor continues, the fight-or-flight response ceases but output of cortisol from the adrenal cortex continues and the adrenal glands may become enlarged

  • because one of the results of the activation of the SNS is the suppression of the immune system, the body is not able to fight off colds and flu during this time.

• Stage 3 - Exhaustion

  • if the stressor continues for a long time, the body’s resources are reduced and alarm signs, such as increased blood pressure, may return

  • the immune system is depleted

  • it is in this stage that major health effects, such as cardiovascular disease, may be seen

Prolonged stress can affect the immune system 

Evaluation of the General Adaptation Syndrome

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 on health

• Research into GAS has had positive implications for helping people cope with stress, especially with its contribution to the development of medicines 

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

• Physiological measurements of cortisol, blood pressure and white cell counts reduce the individual experience of stress to simplistic single-factor biological measurements.

Cortisol and stress

• Cortisol is a hormone which is produced in the adrenal cortex through the activation of the hypothalamus-pituitary-adrenal axis (HPA) when subject to a chronic stressor

• The immune system comprises mainly white blood cells, which travel through the bloodstream to defend the body against antigens like bacteria, viruses and cancerous cells 

• Cortisol regulates the body’s immune system to suppress inflammation, which ordinarily is a good thing

• However when too much cortisol is in the bloodstream for a long period, then the suppression of the immune system lowers resistance to illness

• So stress does not directly cause infections, but with chronic stress the immune system’s ability to fight off antigens is reduced and infection becomes more likely

• This reduction in the immune system’s ability to fight off infection when under chronic stress is thought to be why many people get a cold around exam time

The hypothalamus-pituitary-adrenal axis

Research which investigates the General Adaptation Syndrome and cortisol and stress

• Kiecolt-Glaser et al (1984) found that stress has a direct effect on the immune system by suppressing natural killer cell activity

• Fernald et al. (2008) found that repeated exposure to social stressors like maternal depression and poverty resulted in a reduced (exhausted) cortisol stress response in young children

Both Kiecolt-Glaser et al. (1984) and Fernald et al. (2008) are available as ‘Two Key Studies of Biological Explanations of Stress’’ – just navigate to the next section of the Biological Explanations of Stress topic