Stress is a term that refers to the sum of the physical, mental, and emotional strains or tensions on a person. A stressor is defined as a stimulus or event that provokes a stress response in an organism. Stressors can be categorized as acute or chronic.



The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) defines a psychosocial stressor as "any life event or life change that may be associated temporally (and perhaps causally) with the onset, occurrence, or exacerbation (worsening) of a mental disorder".

Hans Selye (1907-1982), a Canadian researcher was a pioneer in studying stress. Selye defined stress, in essence, as the rate of wear and tear on the body. He observed that an increasing number of people, particularly in the developed countries, die of so-called diseases of civilization, or degenerative diseases primarily caused by stress.

In humans, the biochemical response to acute stress is known as the "fight-or-flight"activation of a section of the brain called the hypothalamic-pituitary-adrenal system, or HPA activates the release of steroid hormones which include cortisol, the primary stress hormone in humans. Neurotransmitters known as catecholamines are released which have three effects:

1. They activate the amygdala, an almond-shaped structure in the limbic system that triggers an emotional response to fear.

2. They signal the hippocampus, another part of the limbic system, to store the emotional experience in longterm memory.

3. They suppress activity in parts of the brain associated with short-term memory, concentration, and rational thinking. This suppression allows a human to react quickly to a stressful situation, but it also lowers the ability to deal with complex social or intellectual tasks that may be part of the situation.

The body's physical reaction to stress can cause heart rate and blood pressure to rise, the person breathes more rapidly allowing the lungs to take in more oxygen. Blood flow to the muscles, lungs, and brain may increase by 300-400%. The spleen releases more blood cells which increases the blood's ability to transport oxygen. The immune system redirects white blood cells to the skin, bone marrow and lymph nodes; these are areas where injury or infection is most likely to occur. In chronic stress, the organ systems of the body do not have the opportunity to return fully to normal levels. Different organs become under or over activated on a long-term basis. In time, these abnormal levels of activity can damage an organ or organ system. Stress has negative effects on the Cardiovascular system, the Gastrointestinal system, the Reproductive system and the Musculoskeletal system.

The physical effects of stress on the brain include interference with memory and learning. Acute stress interferes with short-term memory, although this effect goes away after the stress is resolved. People who are under severe stress become unable to concentrate; they may become physically inefficient, clumsy, and accident-prone. Chronic stress is a reaction to a situation that is stressful but ongoing. Chronic stress affects the human immune system and increases a person's risk of getting an infectious illness. Several research studies have shown that people under chronic stress have lower than normal white blood cell counts and are more vulnerable to colds and influenza.

There are 2 major categories of mental disorders directly related to stress-the-post-traumatic syndromes and adjustment disorders. Stress is, however, also closely associated with depression, and can worsen the symptoms of most other disorders. Post traumatic stress disorder and Acute Stress Disorder are defined by their temporal connection to a traumatic event in the individual's life.

Stress is related to substance abuse disorders in that chronic stress frequently leads people to self-medicate with drugs of abuse or alcohol. Substance abuse disorders are associated with a specific type of strategy for dealing with stress called emotion-focused coping. The Diagnostic and Statistical Manual of Mental Disorders defines adjustment disorders as psychological responses to stressors that are excessive given the nature of the stressor; or result in impairment of the person's academic, occupational, or social functioning. The causes of stress may include any event or situation that a person considers a threat to his or her resources or coping strategies.

Acute stress is defined as a reaction to something perceived as an immediate threat. Acute stress reactions can occur to a falsely perceived danger as well as to a genuine threat; they can also occur in response to memories. Social isolation and loneliness can produce chronic stress. A study done in Norway between 1987 and 1993 found that social support networks mad a significant difference in lowering the impact of both acute and chronic stress on mental health.

Another stress factor is sleep deprivation. Many people get only six or less hours of sleep each night even though the National Sleep Foundation estimates that most adults need 8-8-1/2 hours per night for good health. Fatigue due to sleep deprivation causes additional stress.

Lastly, economic trends have produced a "Winner-take-all" economy in which the gap between the well-off and the average family is constantly widening. Socioeconomic status (SES) affects health in a number of ways. Persons of higher SES can afford better health care, are less likely to suffer from exposure to environmental toxins, and generally lead healthier lifestyles. In addition, chronic stress associated with low SES appears to increase morbidity and mortality among persons in these income groups.