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StressBody

Page history last edited by PBworks 13 years, 7 months ago


Sress as a bodily response

 

Introduction

Threatening and aversive stimuli can produce more than emotional reactions. They can actually harm people’s health. Many of these harmful events are caused not by the events themselves, but by our reactions to them. My boss might place impossible demands on me and suggest that I might be demoted (or even sacked) if I fail to meet these demands. Whether his behaviour causes me to have sleepless nights and stomach ulcers will mainly depend on how I respond to the source of stress. Some people have better ways of managing stress (or coping strategies) than others.

 

Activity

 

Stress is a word that is used in a number of different contexts. The word itself is borrowed from engineering — the action of physical forces on mechanical structures, such as strong winds on a bridge. In this way work could be regarded as stress. However, sources of stress are perhaps better referred to as stressors. Stress can also mean the organism’s reaction to stimuli— as in ‘I feel stressed today’. This should really be termed the stress response.

 

 

How the body responds to stress

Stress has also been studied through a variety of attempts to describe, quantify or analyse its effects on people. Humans appear to have inherited certain emotional reactions, which seem to be geared to coping with short-term stressors. For example, if confronted by an aggressive individual, our body’s reaction to stress might help us prepare to threaten or fight them, or to make good our escape. Cannon described this as the fight-or-flight response. Once the threat is over, our physiology can return to normal. It is when the stressor is prolonged that damage to health may ensue. Early research on the stress response was partly stimulated by the recognition, towards the end of the First World War, of ‘shell shock’ — the effects of prolonged exposure to combat. Initial explanations of the sometimes complete physical and mental breakdown experienced by some combatants actually attributed this to the physical effects on the nervous system of the pounding of guns and explosives (hence the name). It is now known to be part of the syndrome known as post traumatic stress disorder (PTSD). (Anxiety disorders such as PTSD are studied in A2, Unit 5.1.2)

The nervous system and stress

Responses to stress are mediated through the nervous system. This is usually described as consisting of three main parts: the central nervous system (CNS) made up of the brain and spinal chord, the autonomic nervous system (ANS) and the endocrine system (ES). The last two are particularly important in stress.

The autonomic nervous system governs the smooth muscles of the internal organs and controls the involuntary functions of the body. The ANS has two branches: sympathetic and parasympathetic. The action of its two branches is conventionally described as antagonistic — one branch increases a particular response variable (e.g., heart rate) whilst the other is responsible for decrease. Although the autonomic nervous system is not normally under voluntary control, some individuals appear to have developed an ability to exercise conscious control over a range of automatic response variables. For example, the relaxation and meditation techniques practised by experienced yogis can drastically reduce heart rate energy consumption by the body. In a classic experiment, Miller and DiCara (1968) showed that rats could be conditioned by means of reinforcements to alter their heart rates. The clinical techniques of biofeedback relay information about autonomic activity to individuals who are attempting to bring phobic or stress reactions under some measure of conscious control (see below).

As well as the autonomic nervous system, the endocrine system also has an important role to play in regulating behaviour. This system is responsible for the production of hormones in the body and is itself stimulated by the action of the autonomic nervous system and the parts of the CNS that control the ANS.

The adrenal glands are particularly interesting in the study of stress because of the central role they play in activating the organism and regulating the availability of energy. They each have two sections — an outer cortex and an inner medulla. The pituitary, through the release of adrenocorticotrophic hormone (ACTH), regulates the adrenal cortex. The cortex produces a range of hormones called corticosteriods that stimulate the liver’s release of stored sugar and promote muscle growth and general resistance to stress (see below: the General Adaptation Syndrome).

The adrenal medulla produces adrenaline and noradrenaline. The former activates the sympathetic branch of the ANS whilst the latter is responsible for raising blood pressure. The action of noradrenaline shows just how interdependent the endocrine system’s various components are. When it reaches the anterior pituitary, via the bloodstream, it can liberate further supplies of ACTH, the hormone that in turn activates the adrenal cortex. (This is an example of a positive feedback mechanism.)

 

The general adaptation syndrome (GAS)

Our detailed knowledge of the body’s response to stress can be largely traced back to the pioneering work of Selye (1936). He found that a wide variety of stressful experiences including extreme cold, fatigue, electric shocks and injection of different pathogens produced similar responses in his laboratory rats. This response he termed the general adaptation syndrome (GAS). This non-specific response to stressors (usually called the pituitary-adrenal stress syndrome) is essentially an adaptive behaviour, which is both normal and necessary. What we generally refer to as the effects of stress, are the consequences of repeating and prolonging the GAS.

The general adaptation syndrome comprises three stages: alarm reaction, resistance and exhaustion:

  • During the initial alarm stage, perceived threats to the organism result in the hypothalamus activating the sympathetic NS. This in turn stimulates the production of catecholamines (adrenaline and noradrenaline) from the adrenal medulla. As a result the body is activated in many ways (eg increased heart rate) and is so prepared for fight or flight (as described by Cannon).
  • During the resistance stage, the body’s resources are fully mobilised to cope with the stressor. For example, the hypothalamus increases the production of corticotrophic releasing hormone, which in turn stimulates the pituitary’s release of adrenocorticotrophic hormone (ACTH). This acts on the adrenal cortex, which secrete corticosteroids. This reaction is known as the hypothalamic-pituitary-adrenal axis (HPAA).
  • If stressors persist and cannot be overcome, the resistance of the individual sooner or later gives way to exhaustion. The physiological consequences include effects on the adrenal glands, which are enlarged but depleted, and an endocrine system that is generally thrown into disarray. Ultimately all body tissues and processes can be affected and, in extreme cases, become diseased.

 

Useful as Selye’s analysis is, it has been criticised because its inspiration came from studies of animals, not humans. Also, while it may be accurate at the physiological level, it fails to account for psychological factors that mediate the stress response and the psychological consequences of prolonged stress.

 

Psychological effects of stress

Stressful situations lead to powerful, and often rapidly changing emotions. Our reactions can switch back and forth from anger, exhilaration, anxiety and depression. The extent of these reactions depends as much on the effectiveness of our coping mechanisms as it does on the intensity of the stressor. The main psychological responses to stress can be summarised as follows:

  • Anxiety: In extreme cases this can result in the symptoms known as post traumatic stress disorder.
  • Anger and aggression: Laboratory studies have shown that a variety of stressors can lead to aggression, including overcrowding, pain, failure to achieve expected rewards. Children become angry when they are frustrated: the frustration-aggression hypothesis.
  • Apathy and depression: Seligman (1975) showed that animals that experience painful, uncontrollable events can show signs of apathy and depression. Some humans also show this pattern and this has been suggested as a cause of depression.
  • Cognitive impairment: This includes difficulty in concentrating and organising thoughts, and being easily distracted. Highly stressful situations lead people to stick rigidly to established behaviour patterns even when these are no longer appropriate. Some people regress to earlier, childlike behaviour. Existing personality traits such as extreme caution or aggression are exaggerated.

 

The relationship between stress and illness

Selye’s General Adaptation Syndrome (GAS) still influences much contemporary research in this area. As was noted above, persistent exposure to stressors that cannot be overcome will mean that the resistance of the individual sooner or later gives way to exhaustion. Selye believed that the stage of exhaustion was characterised by what he called diseases of adaptation. He identified coronary heart disease (CHD) and ulcers as the main ones.

Since Selye’s time, the list of disorders, both physical and psychological, that are claimed to be stress-related has grown very long. Areas that have been investigated include: effects on the immune system, physical disorders (especially cardiovascular disease), and susceptibility to cancer. But the extent to which stress is a cause of such disorders and how it has its effect remains uncertain. There are a number of ways in which the link between stress and health could be made:

 

*Stress could affect health by the direct route, by producing physiological; and psychological changes conducive to the development of illnesses (such as suppressed activity in the immune system).

*The effects of stress may not be same in all individuals, the interactive route suggests that stress may have little impact on an individual’s blood pressure unless he or she is already genetically predisposed to hypertension.

*Stress it can also affect health in an indirect way, for example people who are stressed may smoke and drink more heavily (the health-behaviour route).

 

Another and rather intriguing possibility is that stress affects illness behaviour without actually causing illness. Stress produces a range of symptoms such as anxiety, depression, fatigue, lack of appetite and insomnia) that could be mistaken for physical illness. People may even learn that a way of coping with stress is to feign illness, i.e. to gain attention or to avoid going in to work. This means that conducting research into illness and stress is difficult because it is not clear if one is measuring actual illness or just illness behaviour.

 

Effects of stress on the immune system

It has been suggested that the excessive production of corticosteroids interferes with the creation of antibodies – the natural opponents of any antigens (bacteria, viruses or other invaders of the body). One class of antibody, secretory immunoglobulin A (sIgA), covers the mucosal surfaces in the respiratory and gastrointestinal tract and acts as a barrier to invading micro organisms. Because it can be measured in saliva, it has been widely used in studies of the immune system.

Such studies have shown that the immune system is not affected in the same way by all stressors. Only chronic stressors (e.g. bereavement, marital disharmony, serious problems at work) tend to result in impaired functioning of the immune system. To investigate this relationship between stress and immune system functioning, Keicolt-Glaser et al. (1995) used caring for a relative with Alzheimer’s disease as an indicator of chronic stress and the progress of wound healing as an indication of the effect on the immune system. The caregivers were matched to a control group of similar ages and income levels. The researchers assessed the progress of wound healing in the two groups and found that it took an average of nine days longer in the caregivers than the controls. Similarly, Sweeney (1995) showed that wounds resulting from small skin biopsies took significantly longer for the body to repair in individuals who were known to be stressed as a result of caring for relatives suffering dementia, than they did in a control group.

Acute stressors do not have the same effect. One study showed that students asked to present a paper to the class actually showed an increase in sIgA (Evans, et al., 1994). It is also known to be raised during periods of examinations (Jemmott & Magloire, 1988). Acute stress appears to increase the number of natural killer cells as well as the levels of sIgA.

Evidence that susceptibility to virus infections such as influenza can be increased by the effects of stress on the production of immunoglobulin A, the line of first defence against infection by this virus, is provided by the study by Stone et al (1987).

 

Stress and cardiovascular disorders

A number of cardiovascular disorders have at some time been associated with stress. Because of prolonged increased blood-flow and the consequent strains placed on the tissues of the circulatory system, proneness to heart attacks and other cardiovascular disorders is increased in individuals who are highly-stressed for long periods. The most researched stress-related condition is that of hypertension (high blood pressure) which is chronic amongst many sufferers of prolonged stress.

However not everyone subjected to chronic stress develops coronary heart disease (CHD). It has been suggested that this may be because the relationship between stress and CHD could be a consequence of a certain personality type (i.e. Type A). However, the research evidence on this is inconclusive. Personality as a mediator of stress is discussed in the next section.

A large amount of research has focused on suppressed hostility (or rage) as a cause of CHD. However, finding valid measures of suppressed rage, but it is also possible that it only has an influence when other risk factors are present. One study that has tried to disentangle the complex set of factors involved in CHD is by Harburg et al. (1973).

 

Susceptibility to cancer

It is the immune system that guards against disease causing antigens, but there is also evidence to show that it may produce chemical responses to the formation and reproduction of cancer cells. Many studies of cancer patients have revealed abnormally high stress levels prior to onset, but such findings are unreliable because of the essentially retrospective nature of the investigations. Even if a relationship existed however, the extent to which stress is an actual cause of any disorder is open to argument. Most studies are correlational, and stress could be one amongst a host of interacting factors. There is good reason to believe that it is also a consequence of illness (i.e. ill-heath is itself a cause of stress).

 

Stress and mental health

Stress is also related to psychological disorders. Cooper includes constant irritability, loss of sense of humour and difficulty in concentrating in a long list of mental symptoms of stress. Such symptoms must interact with the physiological effects of stress, adding to the complexity of how to deal with stress in the individual. According to the diathesis-stress theory of schizophrenia, there are people who are genetically vulnerable to this disorder but the symptoms will only develop when they are subjected to stress (through relationship/family problems, poverty, etc.).

 

References

 

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