Stress, whether physiological, biological or psychological, is an organism's response to a stressor, such as an environmental condition or change in life circumstances. When stressed by stimuli that alter an organism's environment, multiple systems respond across the body. In humans and most mammals, the autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are the two major systems that respond to stress. Two well-known hormones that humans produce during stressful situations are adrenaline and cortisol. The sympathoadrenal medullary axis (SAM) may activate the fight-or-flight response through the sympathetic nervous system, which dedicates energy to more relevant bodily systems to acute adaptation to stress, while the parasympathetic nervous system returns the body to homeostasis. The second major physiological stress-response center, the HPA axis, regulates the release of cortisol, which influences many bodily functions, such as metabolic, psychological and immunological functions. The SAM and HPA axes are regulated by several brain regions, including the limbic system, prefrontal cortex, amygdala, hypothalamus, and stria terminalis. Through these mechanisms, stress can alter memory functions, reward, immune function, metabolism, and susceptibility to diseases. Disease risk is particularly pertinent to mental illnesses, whereby chronic or severe stress remains a common risk factor for several mental illnesses.
Psychology
Acute stressful situations in which the stress experienced is severe can cause psychological changes to the detriment of the well-being of the individual, such that symptomatic derealization and depersonalization, and anxiety and hyperarousal, are experienced. The International Classification of Diseases includes a group of mental and behavioral disorders which have their aetiology in reaction to severe stress and the consequent adaptive response. Chronic stress, and a lack of coping resources available, or used by an individual, can often lead to the development of psychological issues such as delusions, depression and anxiety. Chronic stressors may not be as intense as acute stressors such as natural disaster or a major accident, but they persist over longer periods of time and tend to have a more negative effect on health because they are sustained and thus require the body's physiological response to occur daily. This depletes the body's energy more quickly and usually occurs over long periods of time, especially when these microstressors cannot be avoided. When humans are under chronic stress, permanent changes in their physiological, emotional, and behavioral responses may occur. Chronic stress can include events such as caring for a spouse with dementia, or may result from brief focal events that have long term effects, such as experiencing a sexual assault. Studies have also shown that psychological stress may directly contribute to the disproportionately high rates of coronary heart disease morbidity and mortality and its etiologic risk factors. Specifically, acute and chronic stress have been shown to raise serum lipids and are associated with clinical coronary events. However, it is possible for individuals to exhibit hardiness—a term referring to the ability to be both chronically stressed and healthy. Even though psychological stress is often connected with illness or disease, most healthy individuals can still remain disease-free after being confronted with chronic stressful events. This suggests that there are individual differences in vulnerability to the potential pathogenic effects of stress; individual differences in vulnerability arise due to both genetic and psychological factors. In addition, the age at which the stress is experienced can dictate its effect on health. Research suggests chronic stress at a young age can have lifelong effects on the biological, psychological, and behavioral responses to stress later in life.
Etymology and historical usage The term "stress" had none of its contemporary connotations before the 1920s. It is a form of the Middle English destresse, derived via Old French from the Latin stringere, "to draw tight". The word 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, biological and psychological circles occasionally used "stress" to refer to a physiological or environmental perturbation that could cause physiological and mental "strain". The amount of strain in reaction to stress depends on the resilience. Excessive strain would appear as illness. Walter Cannon used it in 1926 to refer to external factors that disrupted what he called homeostasis. But "...stress as an explanation of lived experience is absent from both lay and expert life narratives before the 1930s". Physiological stress represents a wide range of physical responses that occur as a direct effect of a stressor causing an upset in the homeostasis of the body. Upon immediate disruption of either psychological or physical equilibrium the body responds by stimulating the nervous, endocrine, and immune systems. The reaction of these systems causes a number of physical changes that have both short- and long-term effects on the body. The Holmes and Rahe Stress Scale was developed as a method of assessing the risk of disease from life changes. The scale lists both positive and negative changes that elicit stress. These include things such as a major holiday or marriage, or death of a spouse and firing from a job.
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