Stress (biology)

For other uses, see Stress.

Stress is an internal response to stimuli or pressures that challenge an organism's ability to adapt or cope, disrupting homeostasis (internal balance). Stress may be mental, physiological, anatomical or physical. Stressful stimuli, also known as stressors, range from chemical agents to medical illnesses to a hectic lifestyle. Psychologically, the level of stress can depend on the emotional or cognitive appraisal that a person makes of a situation and of himself. Stress typically involves activation of the fight-or-flight response. Stress has been shown to cause neurochemical, hormonal and physiological changes.

Stress can be seen as a positive phenomenon, an evolved adaptive response that can activate internal resources to help overcome challenges and achieve realistic goals. However, chronic stress may develop if stressors are excessive and unavoidable and too many demands are placed on an organism's internal resources. There are also individual differences in sensitivity to stressors and the propensity to the stress response. Severe or chronic stress has been linked to states of exhaustion and correlated with a greater incidence of health conditions and problems with functioning.

The term 'stress' in this sense was first used by the endocrinologist Hans Selye in the 1930s. Originally defined in terms of the physiological response of laboratory animals, the concept was expanded and popularized by Selye to include the perceptions and responses of people as they sought to adapt to challenges, including in war, in work, in society and in life in general.

Models of Stress

General Adaptation Syndrome

Hans Selye researched the effects of stress on rats and other animals by exposing them to unpleasant or harmful stimuli. He found that all animals showed a very similar series of reactions, broken into three stages. He describes this universal response to the stressors as the General Adaptation Syndrome, or GAS, in 1936.

• Alarm

This is the 1st stage. When the threat or stressor is identified or realized, the body's stress response is a state of alarm. During this stage adrenaline will be WALSHY produced in order to bring about the fight-or-flight response. There is also some activation of the HPA axis, producing cortisol.

• Resistance

This is the 2nd stage. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. Although the body begins to try to adapt to the strains or demands of the environment, the body cannot keep this up indefinitely, so its resources are gradually depleted.

• Exhaustion

This is the 3rd stage. In the final stage in the GAS model, all the body's resources are eventually depleted and the body is unable to maintain normal function. At this point the initial autonomic nervous system symptoms may reappear (sweating, raised heart rate etc.). If stage three is extended, long term damage may result as the capacity of glands, especially the adrenal gland, and the immune system is exhausted and function is impaired resulting in decompensation. The result can manifest itself in obvious illnesses such as ulcers, depression, trouble with the disgestive system or even cardiovascular problems, along with other mental illnesses.

Lazarus

Richard Lazarus published in 1974 a model dividing stress into eustress and distress. Where stress enhances function (physical or mental, such as through strength training or challenging work) it may be considered eustress. Persistent stress that is not resolved through coping or adaptation, deemed distress, may lead to anxiety or withdrawal (depression) behavior. The difference between experiences which result in eustress or distress is determined by the disparity between an experience (real or imagined), personal expectations, and resources to cope with the stress. Alarming experiences, either real or imagined, can trigger a stress response. Therefore, Lazarus's model argues that cognitive processes of appraisal are central in determining whether a situation is potentially threatening or harmful.

Zajonc

Robert B. Zajonc (1984), somewhat in opposition to the Lazarus model of stress, argued that emotional reactions occur before cognitive reactions, and in fact, may be at odds with cognitive responses. This belief was consonant with the previous James-Lange hypothesis (1890, 1922), which held that the body's emotional reaction to stress occurred prior to and resulted in conscious responses.

The debate has underscored the existence of two modes of reactivity, one conscious and under volitional control, and the other automatic and uncontrollable. Scholars such as Aldwin have argued for a simultaneous, parallel processing approach rather than a sequential neurological processing model where emotions come first followed by cognition, or vice versa.

Neurochemistry and Physiology

The neurochemistry of the stress response is now believed to be well understood, although much remains to be discovered about how the components of this system interact with one another, in the brain and throughout in the body.

In response to a stressor, corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP) are secreted into the hypophyseal portal system and activate neurons of the paraventricular nuclei (PVN) of the hypothalamus. The locus ceruleus and other noradrenergic cell groups of the medulla and pons, collectively known as the LC/NE system, also become active and use brain epinephrine to execute autonomic and neuroendocrine responses, serving as a global alarm system.

The autonomic nervous system provides the rapid response to stress commonly known as the fight-or-flight response, engaging the sympathetic nervous system and withdrawing the parasympathetic nervous system, thereby enacting cardiovascular, respiratory, gastrointestinal, renal, and endocrine changes.

The so-called hypothalamic-pituitary-adrenal axis (HPA), a major part of the neuroendocrine system involving the interactions of the hypothalamus, the pituitary gland, and the adrenal glands, is also activated by release of CRH and AVP. This results in release of adrenocorticotropic hormone (ACTH) from the pituitary into the general bloodstream, which results in secretion of cortisol and other glucocorticoids from the adrenal cortex. These corticoids involve the whole body in the organism's response to stress and ultimately contribute to the termination of the response via inhibitory feedback.

Stress can significantly affect many of the body's immune systems, as can an individual's perceptions of, and reactions to, stress. The term psychoneuroimmunology is used to describe the interactions between the mental state, nervous and immune systems, as well as research on the interconnections of these systems.

Chronic stress has also been shown to impair developmental growth in children by lowering the pituitary gland's production of growth hormone, as in children associated with a home environment involving serious marital discord, alcoholism, or child abuse.

Common sources of stress

Both negative and positive stressors can lead to stress. Some common categories and examples of stressors include:

• Sensory: pain, bright light
• Life events: birth and deaths, marriage, and divorce
• Responsibilities: lack of money, unemployment
• Work/study: exams, project deadlines, and group projects
• Personal relationships: conflict, deception
• Lifestyle: heavy drinking, insufficient sleep
• Environmental: Lack of control over environmental circumstances, such as food, housing, health, freedom, or mobility
• Social: Struggles with conspecific individuals and social defeat can be potent sources of chronic stresses
• Adverse experiences during development (e.g. prenatal exposure to maternal stress, poor attachment histories, sexual abuse) are thought to contribute to deficits in the maturity of an individual's stress response systems.

One evaluation of the different stresses in people's lives is the Holmes and Rahe stress scale.

Adaptation to stress

Main article: Stress management

Responses to stress include adaptation, psychological coping such as stress management, anxiety, and depression. Over the long term, distress can lead to diminished health or illness; to avoid this, stress must be managed.

History and Usage

The term "stress" had none of its current general senses before the 1950s. As a semi-psychological term referring to hardship or coercion, it dated from the 14th century. It is a form of the Middle English destresse, derived via Old French from the Latin stringere – to draw tight. It had long been in use in physics to refer to the internal distribution of a force exerted on a material body, resulting in strain.

In the 1920s and 30s, the term was occasionally being used in psychological circles to refer to a mental strain or unwelcome happening, and by advocates of holistic medicine to refer to a harmful environmental agent that could cause illness. Walter Cannon used it in 1934 to refer to external factors that disrupted what he called "homeostasis". But a new scientific usage developed out of Hans Seyle's reports of his laboratory experiments in the 1930s. Selye started to use the term to refer not just to the agent but to the state of the organism as it responded and adapted to the environment. His theories of a universal non-specific stress response attracted great interest and contention in academic physiology and he undertook extensive research programmes and publication efforts.

However, while the work attracted continued support from advocates of psychosomatic medicine, many in experimental physiology concluded that his concepts were too vague and unmeasurable. During the 1950s Selye turned away from the laboratory to promote his concept through popular books and lectures tours. The US military became a key center of stress research, attempting to understand and reduce combat neurosis and psychiatric casualties. Seyle wrote for both non-academic physicians and, in an international bestseller titled "Stress of Life", for the general public. A broad biopsychosocial concept of stress and adaptation offered the promise of helping everyone achieve health and happiness by successfully responding to changing global challenges and the problems of modern civilisation. He coined the term "eustress" for positive stress, by constrast to distress. He argued that all people have a natural urge and need to work for their own benefit, a message that found favor with industrialists and governments. He also coined the term "stressor" to refer to the causative event or stimulus, as opposed to the resulting state of stress.

From the late 1960s, Selye's concept started to be taken up by academic psychologists, who sought to quantify "life stress" by scoring "significant life events", and a large amount of research was undertaken to examine links between stress and disease of all kinds. By the late 1970s stress had become the medical area of greatest concern to the general population, and more basic research was called for to better address the issue. There was renewed laboratory research into the neuroendocrine, molecular and immunological bases of stress, conceived as a useful heuristic not necessarily tied to Selye's original hypotheses. By the 1990s, "stress" had become an integral part of modern scientific understanding in all areas of physiology and human functioning, and one of the great metaphors of Western life. Focus grew on stress in certain settings, such as workplace stress. Stress management techniques were developed.

Its psychological uses are frequently metaphorical rather than literal, used as a catch-all for perceived difficulties in life. It also became a euphemism, a way of referring to problems and eliciting sympathy without being explicitly confessional, just "stressed out". It covers a huge range of phenomena from mild irritation to the kind of severe problems that might result in a real breakdown of health. In popular usage almost any event or situation between these extremes could be described as stressful. The most extreme events and reactions may elicit the diagnosis of Posttraumatic stress disorder.

See also

• Jon Kabat-Zinn
• Burnout (psychology)
• Hypothalamic-pituitary-adrenal axis
• Oxidative stress
• Compassion fatigue

References

• Petersen, C., Maier, S.F., Seligman, M.E.P. (1995). Learned Helplessness: A Theory for the Age of Personal Control. New York: Oxford University Press. ISBN 0-19-504467-3
• Seligman, M.E.P. (1975). Helplessness: On Depression, Development, and Death. San Francisco: W.H. Freeman. ISBN 0-7167-2328-X
• Seligman, M.E.P. (1990). Learned Optimism. New York: Knopf. (Reissue edition, 1998, Free Press, ISBN 0-671-01911-2).
• Holmes, T.H. and Rahe, R.H. (1967). The social readjustments rating scales. Journal of Psychosomatic Research 11:213-218.

External links

• The American Institute of Stress
• University of Massachusetts Medical School Stress Reduction Program
• "Research on Work-Related Stress", European Agency for Safety and Health at Work (EU-OSHA)
• "Working on Stress", European Agency for Safety and Health at Work (EU-OSHA)
• "Taming Stress", Scientific American, September 2003