Stress (biology)
Stress, whether physiological, biological or psychological, is an organism's response to a stressor such as an environmental condition.[1] When stressed by stimuli that alter an organism's environment, multiple systems respond across the body.[2] In humans and most mammals, the autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are the two major systems that respond to stress.[3] Two well-known hormones that humans produce during stressful situations are adrenaline and cortisol.[4]
For other kinds of stress, see Stress.
The sympathoadrenal medullary (SAM) axis 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.[3] Through these mechanisms, stress can alter memory functions, reward, immune function, metabolism and susceptibility to diseases.[5]
Disease risk is particularly pertinent to mental illnesses, whereby chronic or severe stress remains a common risk factor for several mental illnesses.[6][7]
Etymology and historical usage[edit]
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".[19] 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 the term to refer to a mental strain or to a harmful environmental agent that could cause illness.[20][21]
Walter Cannon used it in 1926 to refer to external factors that disrupted what he called homeostasis.[22] But "...stress as an explanation of lived experience is absent from both lay and expert life narratives before the 1930s".[23] 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.[24]
The Holmes and Rahe stress scale was developed as a method of assessing the risk of disease from life changes.[25] 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.
Biological need for equilibrium[edit]
Homeostasis is a concept central to the idea of stress.[26] In biology, most biochemical processes strive to maintain equilibrium (homeostasis), a steady state that exists more as an ideal and less as an achievable condition. Environmental factors, internal or external stimuli, continually disrupt homeostasis; an organism's present condition is a state of constant flux moving about a homeostatic point that is that organism's optimal condition for living.[27] Factors causing an organism's condition to diverge too far from homeostasis can be experienced as stress. A life-threatening situation such as a major physical trauma or prolonged starvation can greatly disrupt homeostasis. On the other hand, an organism's attempt at restoring conditions back to or near homeostasis, often consuming energy and natural resources, can also be interpreted as stress.[28] The brain cannot sustain an equilibrium under chronic stress; the accumulation of such an ever-deepening deficit is called chronic stress.[13]
The ambiguity in defining this phenomenon was first recognized by Hans Selye (1907–1982) in 1926. In 1951 a commentator loosely summarized Selye's view of stress as something that "...in addition to being itself, was also the cause of itself, and the result of itself".[29][30]
First to use the term in a biological context, Selye continued to define stress as "the non-specific response of the body to any demand placed upon it". Neuroscientists such as Bruce McEwen and Jaap Koolhaas believe that stress, based on years of empirical research, "should be restricted to conditions where an environmental demand exceeds the natural regulatory capacity of an organism".[31] The brain cannot live in an harsh family environment, it needs some sort of stability between another brain. People who have reported being raised in harsh environments such as verbal and physical aggression have showed a more immune dysfunction and more metabolic dysfunction.[13] Indeed, in 1995 Toates already defined stress as a "chronic state that arises only when defense mechanisms are either being chronically stretched or are actually failing,"[32] while according to Ursin (1988) stress results from an inconsistency between expected events ("set value") and perceived events ("actual value") that cannot be resolved satisfactorily,[33] which also puts stress into the broader context of cognitive-consistency theory.[34]
Biological background[edit]
Stress can have many profound effects on the human biological systems.[35] Biology primarily attempts to explain major concepts of stress using a stimulus-response paradigm, broadly comparable to how a psychobiological sensory system operates. The central nervous system (brain and spinal cord) plays a crucial role in the body's stress-related mechanisms. Whether one should interpret these mechanisms as the body's response to a stressor or embody the act of stress itself is part of the ambiguity in defining what exactly stress is.
The central nervous system works closely with the body's endocrine system to regulate these mechanisms. The sympathetic nervous system becomes primarily active during a stress response, regulating many of the body's physiological functions in ways that ought to make an organism more adaptive to its environment. Below there follows a brief biological background of neuroanatomy and neurochemistry and how they relate to stress.[36]
Stress, either severe, acute stress or chronic low-grade stress may induce abnormalities in three principal regulatory systems in the body: serotonin systems, catecholamine systems, and the hypothalamic-pituitary-adrenocortical axis. Aggressive behavior has also been associated with abnormalities in these systems.[37]
Assessment[edit]
Health risk factors[edit]
Both negative and positive stressors can lead to stress. The intensity and duration of stress changes depending on the circumstances and emotional condition of the person with it (Arnold. E and Boggs. K. 2007). Some common categories and examples of stressors include:
History in research[edit]
The current usage of the word stress arose out of Hans Selye's 1930s experiments. He 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 programs and publication efforts.[74]
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 lecture tours. He wrote for both non-academic physicians and, in an international bestseller entitled 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 civilization. Selye coined the term "eustress" for positive stress, by contrast 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.[74] He also coined the term stressor to refer to the causative event or stimulus, as opposed to the resulting state of stress.
Selye was in contact with the tobacco industry from 1958 and they were undeclared allies in litigation and the promotion of the concept of stress, clouding the link between smoking and cancer, and portraying smoking as a "diversion", or in Selye's concept a "deviation", from environmental stress.[75]
From the late 1960s, academic psychologists started to adopt Selye's concept; they 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 also 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. The US military became a key center of stress research, attempting to understand and reduce combat neurosis and psychiatric casualties.[74]
The psychiatric diagnosis post-traumatic stress disorder (PTSD) was coined in the mid-1970s, in part through the efforts of anti-Vietnam War activists and the Vietnam Veterans Against the War, and Chaim F. Shatan. The condition was added to the Diagnostic and Statistical Manual of Mental Disorders as posttraumatic stress disorder in 1980.[76] PTSD was considered a severe and ongoing emotional reaction to an extreme psychological trauma, and as such often associated with soldiers, police officers, and other emergency personnel. The stressor may involve threat to life (or viewing the actual death of someone else), serious physical injury, or threat to physical or psychological integrity. In some cases, it can also be from profound psychological and emotional trauma, apart from any actual physical harm or threat. Often, however, the two are combined.
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, and stress management techniques were developed. The term also became a euphemism, a way of referring to problems and eliciting sympathy without being explicitly confessional, just "stressed out". It came to cover 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 American Psychological Association's 2015 Stress In America Study[77] found that nationwide stress is on the rise and that the three leading sources of stress were "money", "family responsibility", and "work".