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Physiological stress is a particular form of stress which refers to the consequences of the failure of a human or animal body to respond appropriately to the load of a physical stimulus.[1] It includes a state of alarm and adrenaline production, short-term resistance as a coping mechanism, and exhaustion. It refers to the inability of a human or animal body to cope with the demands the physical factors place on it. This is different from psychological stress which is results from an overload of psychological factors.

Some of the signs and symptoms are similar. Common stress symptoms include irritability, muscular tension, inability to concentrate and a variety of physical reactions, such as headaches and accelerated heart rate.[2]

The term "stress" was first used by the endocrinologist Hans Selye in the 1930s to identify physiological responses in laboratory animals. In Selye's terminology, "stress" refers to the reaction of the organism, and "stressor" to the perceived threat. Stress in certain circumstances may be experienced positively. Eustress, for example, can be an adaptive response prompting the activation of internal resources to meet challenges and achieve goals.


Models Edit

General Adaptation Syndrome Edit

Hans Selye researched the effects of stress[3] on rats and other animals by exposing them to unpleasant or harmful stimuli. He found that all animals presented a very similar series of reactions, broken into three stages. In 1936, he described this universal response to the stressors as the general adaptation syndrome, or GAS.[4][5]

Alarm is the first 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 produced in order to bring about the fight-or-flight response. There is also some activation of the HPA axis, producing cortisol. Resistance is the second 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 is the third and final stage in the GAS model. At this point, all of 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 digestive system or even cardiovascular problems, along with other mental illnesses.

Selye: eustress and distressEdit

Hans Selye published in 1975 a model dividing stress into eustress and distress.[6] 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.[7]


Neurochemistry and physiologyEdit

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 adrenal 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.[8]

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.[8] The 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.[8]

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.[9]

Common sourcesEdit

Both negative and positive stressors can lead to stress. Some common categories and examples of stressors include: sensory input such as pain, bright light, or environmental issues such as a lack of control over environmental circumstances, such as food, housing, health, freedom, or mobility.

See alsoEdit

References Edit

  1. The Stress of Life, Hans Selye, 1956.
  2. EHealthMD: What is stress Retrieved September 3, 2008.
  3. Selye, Hans (1950). Diseases of adaptation. Wisconsin medical journal 49 (6): 515–6.
  4. Seyle, Hans (1936). A syndrome produced by diverse nocuous agents. Nature 138: 32.
  5. "Selye Biologic Reaction to Stress chart", Chronic Fatigue Unmasked, by Dr. Gerald E. Poesnecker, February 1999 (ISBN 0916285618)
  6. {{cite journal |author=Selye |title=Confusion and controversy in the stress field| year=197|5 journal=Journal of Human Stress| volume = 1| pages=37-44|
  7. Ron de Kloet, E, Joels M. & Holsboer F. (2005). Stress and the brain: from adaptation to disease. Nature Reviews Neuroscience 6 (6): 463–475.
  8. 8.0 8.1 8.2 Tsigos, C. & Chrousos, G.P. (2002). Hypothalamic-pituitary-adrenal axis, neuroendocrine factors, and stress. Journal of Psychosomatic Research, 53, 865-871.
  9. Powell, Brasel, & Blizzard, 1967.
  • 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.


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