Physiology of Stress

‘Stress’ can have a number of different meanings, one of which is the body’s response in stressful situations (considered below). Other meanings can include things that trigger this response (often referred to as stressors), and the perception of a lack of ability to cope with the demands of life.

General Adaptation Syndrome(GAS)

This was proposed by Selye (1936), who saw the boy’s response as a way of adapting to stressful situations. Over a short term (acute stress) this is helpful, but it can be damaging if the response continues for a long time (chronic stress). The body’s response goes through three stages:

  • Alarm reaction: a stressor is perceived and the body’s response prepared
  • Resistance: the body attempts to adapt to the stressful situation by releasing stress hormones, which helps to cope with the situation but requires a large investment of resources. If a stressor becomes chronic, the parasympathetic nervous system is activated to conserve energy
  • Exhaustion: the resources needed to respond to chronic stress become depleted, and the symptoms seen when the stressor first emerged appear again, for example, raised blood pressure and heart rate, sweating, and so on. The immune system becomes compromised and stress-related illness is more likely to occur.

Stress, figure 1


  • Selye found that when introducing stressors of various kinds to rats, their bodily response was the same in each case. This lends support to the idea that there is a general response to any stressful situation.
  • Mason (1971) found that in monkeys, differing stress responses were shown. For instance, cortisol levels increased in response to excessive cold, decreased in in response to extreme heat, and did not change in response to excessive exercise. This weakens the suggestion that the stress response is the same in all situations.

Physiological Response to Stress

Acute stress: The sympathomedullary pathway (SAM) deals with acute stress by activating the fight-or-flight response.

A stressor is perceived, and the hypothalamus activates the sympathetic branch of the autonomic nervous system (ANS). Messages are sent to the adrenal medulla (the central part of the adrenal glands, situated above the kidneys), stimulating the release of the hormones adrenaline and noradrenaline. The effects of these include raised heart rate, dilation of pupils, tension of muscles, and the conversion of glycogen to glucose, to provide energy. Once the stressor passes, the parasympathetic branch of the ANS is activated. This reverses the effects of the sympathetic branch, returning the person to a state of calmness.

Chronic stress: The hypothalamic-pituitary-adrenal (HPA) system deals with chronic stress. This takes longer to activate than the SAM system, but the effects last for longer.

A stressor is perceived, and the hypothalamus releases corticotropin releasing factor (CRF). This sends a message to the pituitary gland in the brain, causing the release of adrenocorticotropic hormone (ACTH) into the bloodstream. This travels to the adrenal cortex (the outer part of the adrenal gland), stimulating the release of the hormone cortisol. The effects of cortisol include providing long-term energy supplies to deal with a stressor. It can also have a negative effect on the immune system.

The HPA system is self-regulating, via a ‘negative feedback loop’. Levels of cortisol are monitored by the brain, and if high levels are detected, the levels of CRF and ACTH are lowered, leading to a reduction in cortisol levels.


  • The fight or flight response may be less applicable to females. This is because preparing to run away from danger would be helpful to survival for males, but less so for females (as their offspring may be abandoned). It has been argued that females respond with a ‘tend and befriend’ characteristic, in order to protect offspring in times of stress. This means the fight or flight response could be an example of a male-centric viewpoint in psychology.
  • Physiological explanations are often researched using animals, and therefore the cognitive aspect of stress is not considered. It is argued that humans cognitively ‘work out’ whether a situation poses a threat/is stressful, therefore there is more to the stress response than the simple perception of threat by the hypothalamus.


There is research to suggest that the stress response prevents the immune system functioning properly, leading to an increased likelihood of illness. The effect of chronic stress was investigated by Kiecolt-Glaser et al (1984):

Aim: To investigate the effect of chronic stress on the immune system.

Stress, figure 1

Procedure: 75 medical students gave a blood sample one month before an exam period (low-stress), and another on the day of their first exam (high-stress). They also completed questionnaires on sources of stress and physiological symptoms.

Findings: The activity of Natural Killer (NK) and killer T cells, which help fight infection by identifying and destroying antigens (foreign bodies such as a virus), was lowered between the first and second blood samples. This was most evident in students who reported more sources of stress, such as a negative life event.

Conclusion: Stress has a negative effect on the working of the immune system, making illness more likely.

Kiecolt-Glaser also carried out a longitudinal study in 1991, finding that participants who experienced long-term stress (they were caring for a relative with Alzheimer’s) showed decreased immune system functioning and more instances of illness, including depression, than a control group.

Cardiovascular Disorders(CVDs)

CVDs include any disorder of the heart or blood vessels, which includes strokes.

Aim of study 1- Wilbert-Lampen et al (2008): To investigate the effects of short-term stress on CVDs.

Procedure: Researchers looked at instances of heart attacks in Germany during football matches played in the 1996 World Cup.

Findings: When Germany played, there was a 2.66 increase in the number of cardiac emergencies on that day, compared with days when Germany were not playing.

Conclusion: Acute stress, such as watching your team play an important football match, doubles the risk of a cardiovascular event.

Aim of study 2- Yusuf et al (2004): To investigate the effects of long-term stress on CVDs.

Procedure: Participants from 52 countries of differing cultures were included. 15000 people who had had a heart attack (‘MI’) were compared with a similar number who had not.

Findings: Several chronic stressors were linked with MIs, for example workplace stressors and stressful life events. Stress not only caused the CVDs in the first place, but made existing conditions worse.

Conclusion: Chronic stress contributes to the onset of, and severity of, CVDs.


  • Dharbhar (2008) found that, in rats, mild stressors had a positive impact on the immune system, as the body was prepared for physical damage. This suggests that stress (some forms of acute stress, at least) does not always have a negative impact on the immune system.
  • Pereira et al (2003) found that women who were HIV-positive were more likely to develop pre-cancerous lesions in the cervix if they experienced several stressful life events, compared to those with fewer stressful life events. This supports the link between stress and weakened immune system functioning.
  • The evidence that stress causes CVDs is mixed. There is more evidence that people with existing CVDs are more affected by stress. Therefore, stress may be one of a number of factors contributing to CVDs, weakening the suggestion that it is the initial cause.

Sources of Stress: Life Changes

Sources of stress refers to what factors in the environment lead to a triggering of the stress response. One factor is life changes, which are major, but relatively rarely-occurring, events in our lives, for example moving house, or the death of a close family member. They require a large amount of psychological energy to adjust to, which can lead to stress. The greater the number of life events experienced, the more stress is likely to be caused. It is thought that this is the case for positive and negative life events, as in both cases psychological readjustment is needed.

Stress, figure 1

Link between life changes and illness: To assess whether there is a link, Holmes and Rahe (1967) developed the ‘Social Readjustment Rating Scale’ (SRRS), which assigned a score out of 100 (100 being most stressful) to a series of life events. Early research using this showed that when participants indicated which events they had experienced in the past year, an LCU (life change unit) score of 300 or more meant there was an 80% likelihood of that person also reporting illnesses in the next year. A score of 150-300 meant a 50% likelihood of reporting illness.

Rahe et al (1970): Researchers investigated the link between life changes and illness using the SRRS. US navy personnel were studied, having to complete an early version of the SRRS considering the 6 months before they went on a tour of duty. Whilst on the tour of duty, illness was recorded for each participant by getting them to report every time they felt unwell to a medical officer, who made records of illnesses, calculating a score (considering frequency and seriousness of illness). Participants and medical officers were unaware of the aims of the study. The findings were that there was a positive correlation of .118 between LCU scores and illness scores. Due to the high number of participants, this correlation was statistically significant. The conclusion was that life changes are linked with illness.


  • Lietzen et al (2011) found that high levels of life changes were a predictor for the onset of asthma in 160,000 participants, none of whom had asthma before. This supports the links between life changes and illness, and supports Rahe’s study.
  • Measures such as the SRRS do not account for the fact that individuals will perceive the event in very different ways. For example, the death of a spouse will be highly stressful if they are young and die unexpectedly. However, the expected death of a spouse following a long illness may not provoke the same intensity of feeling. This weakens the validity of the life changes-stress link as individual differences are not considered.
  • There is evidence that negative life changes are more likely to cause stress than positive ones. This weakens the original proposal of the link between life changes and stress, which was that it is the amount of readjustment needed which causes stress, rather than if the event is positive or negative.

Sources of Stress: Daily Hassles

Daily hassles are minor, fairly frequently-occurring events which cause frustration and stress. The effect of these is cumulative, as if lots of daily hassles are experienced at a similar time, the greater the likelihood of stress being experienced. Lazarus et al (1980) proposed that daily hassles are more likely to be a cause of stress than life events due to the fact that life events are quite rare, but everyone experiences daily hassles quite frequently. Hassles include train delays, traffic, losing something, and so on.

Stress, figure 1

Lazarus suggested that when a daily hassle is experienced, the person engages in ‘primary appraisal’- considering how threatening the event is to well-being. If it is judged as threatening, the person then engages in ‘secondary appraisal’- considering if they can cope with it.

Life changes and daily hassles: There is a link between these two, in that if a person is experiencing a major life event (or has done recently), this will amplify the effect of daily hassles. What were previously minor irritations that could be ignored become significant sources of stress.

Kanner et al (1981): Researchers investigated whether daily hassles were a more significant source of stress than life events. Participants completed a ‘Hassles Scale’ of 117 items, where they indicated what hassles they experienced each month for 9 months. They also completed a measure similar to the SRRS to consider life changes experienced just before starting the study and 10 months into it. Finally, they completed the Hopkins Symptom Checklist, measuring how anxious and depressed they were. The findings were that there were significant positive correlations between the amount of hassles experienced and measures of anxiety/depression, for men and women. Hassles were more of a reliable predictor for signs of psychological illness than life events, suggesting hassles are a more significant source of stress.


  1. Ivancevich (1986) found that daily hassles were better predictors than life events for poor health, worse job performance, and more time off work. This supports the link between daily hassles and stress, and supports that they are more significant than life changes.
  2. The research into daily hassles often involves retrospective recall, for example keeping a diary of hassles experienced that day/yesterday/last week/last month. As hassles are minor events, they may be easily forgotten or misremembered. This questions the validity of the findings of research into daily hassles, so weakens the link between hassles and stress.
  3. It is hard to establish a cause-effect link with hassles and stress, as research is correlational. Therefore, it could be that feelings of depression and anxiety lead a person to report more hassles, and experience them more negatively, rather than the hassles causing the depression. This weakens the proposed link between hassles and stress.

Stress, figure 2

Exam Question

Walter and Jesse are waiting to be seen by a GP in a surgery as they have both been feeling unwell recently. ‘How’s your day been?’ the GP asks Walter. ‘A bit annoying actually, my train was late so I was late for work this morning, again. Also, my son keeps hiding my house keys two or three times a day, so it takes me ages to find them.’ Jesse is next in, and the GP asks him the same question. ‘It’s been ok,’ Jesse replies, ‘although I’ve got to sort out the arrangements for my sister’s funeral today. I started a new job two weeks ago so there’s been quite a lot going on.’

Use your knowledge of sources of stress to explain why Walter and Jesse have been feeling unwell. (6 marks- 2-3 paragraphs)
Your answer should include: Daily / Hassles / Life / Events