Stress (biology)

Stress (English for 'pressure, tension'; from Latin stringere 'to tense') refers on the one hand to mental and physical reactions in living beings caused by specific external stimuli (stressors), which enable them to cope with particular demands, and on the other hand to the resulting physical and mental strain.

According to the current allostasis concept, stress plays a central role in adapting physically and psychologically to changing environmental conditions. Stress can also have an evolutionary effect, with the consequence that stresses are better tolerated or ultimately neutralized by a corresponding stress tolerance. Thus, stress can cause adaptation and ultimately speciation through selection advantages of single individuals. Through genetic fixation of traits that cause selection advantages, certain hereditary traits can prevail evolutionarily. Examples of such traits are succulence in plants in arid regions or sickle cell anaemia in humans in malaria regions.

The term stress was first used by Walter Cannon (1914, cited in Lazarus & Folkman, 1984) in relation to alarm situations (fight-or-flight). Based on this work, Hans Selye (1936, cited in Lazarus & Folkman, 1984) formulated stress as a physical state under stress, which was characterized by tension and resistance to external stimuli (stressors) - the general adaptation syndrome (GAS). Hans Selye had borrowed the term from physics to name the "non-specific reaction of the body to any demand". In materials science, stress refers to the change in a material caused by the application of external force: this is followed by tension, distortion and bending. With the cognitive turn, appraisal (appraisal) and stress management (coping) of psychological stress have been assigned a central role (Lazarus and Folkman, 1984). To date, there is no agreement on a definition and a conceptual operationalization of stress (Kahn and Byosiere, 1992). Depending on the conceptualization of the term stress, a variety of definitional attempts exist (Väänänen et al., in press).

The occurrence of stress requires a sensory perception of the stress-triggering stimulus as well as a nervous transmission of such a stimulus to a stimulus-processing region of the body. Accompanying symptoms on a biochemical level are usually the release of stress hormones and other secretions from glands.

Basics

The starting point was the confrontation of an animal with an acute dangerous situation, for example the encounter with a predator or an intraspecific aggressor or a physical danger such as forest fire or only an alarming noise etc. The animal must then be in a heightened state of readiness to act, which concerns both the readiness of its musculature and its circulatory system or its central nervous attention and readiness to make decisions. The animal must then be in a heightened state of readiness for action, which concerns both the readiness of its musculature and circulation and its central nervous attention and readiness to make decisions. Therefore, the release of the adrenal hormone adrenaline, for example, triggers a vegetative chain of effects that ultimately increases blood pressure and blood sugar as well as general muscle tone.

In the brain, the relatively slow processing of the cerebrum is pushed back in its influence, and schematic decision patterns of the brain stem are used with priority. This occurs through altered patterns of release of depressing serotonin and stimulating norepinephrine in the relevant parts of the brain. The animal can then react more quickly, albeit with a greater margin of error.

With the precise assessment of the situation by the cerebrum, an appropriate reaction in the acute dangerous situation would often be life-threateningly slow.

For this reason, the initial detection of a dangerous situation often does not preferentially take place via the cerebrum, but via schematized trigger patterns, to which evolutionary old brainstem mechanisms react: sudden sound or sudden change of brightness, shrill sounds (screams) etc.. Such trigger patterns occur frequently in the modern everyday life of many people. They are then called non-specific stressors, and each time they occur they produce a physical reaction to the perceived danger (fight-or-flight). In the case of long-term stress, other stress hormones are also released. In addition to the classic stress hormones, the body's own neuropeptides, such as substance P, opioid peptides and others, also play a role in the stress reaction. If a person is permanently under stress, the physical reactions can cause damage to health (general adaptation syndrome).

Stress in humans

Definition: Stress is understood to be the strain (effect of strain) placed on a person by internal and external stimuli or pressures (objective factors acting on a person as well as their magnitudes and time periods). These can be both artificial and natural, both biotic and abiotic, can affect both the body and the psyche of the human being and can ultimately be perceived as positive or negative or have an effect. Coping with stress depends on the personal (including health) characteristics and cognitive abilities of the individual person; dealing with a threat is also called coping. Behaviours that can be used include aggression, escape, behavioural alternatives, acceptance, changing the condition or denial of the situation.

Positive stress" or eustress (the Greek prefix εὖ (eu) means "well, good, right, easy") is the term used to describe those stressors that strain the organism but have a positive effect. Positive stress increases alertness and promotes maximum efficiency of the body without harming it. Eustress occurs, for example, when a person is motivated to perform certain tasks, then has time and opportunities to prepare for them, or also when a (possibly also longer or more severe) crisis situation or illness can nevertheless be approached positively, overcome (see coping strategy) and overcome. As a result, moments of happiness can even be experienced. Eustress also has a positive effect on the mental or physical functioning of an organism when it occurs frequently over a longer period of time.

Stress is only perceived negatively when it occurs frequently or permanently and cannot be compensated for physically and/or psychologically and is therefore judged to be unpleasant, threatening or overwhelming. In particular, negative effects can occur if the individual person (also through his interpretation of the stimuli) sees or has no way of coping with the situation. Examples of this are exams without the time or ability to study, an illness that is unclear or unrecognized despite a visit to the doctor (cf. Semmelweis reflex), an apartment that is unbearable due to noise without the possibility of moving, or the like. In this case, lasting negative stress (also disstress or dysstress; the Greek prefix δύς (dys) means "bad") can, if necessary, be prevented by appropriate help or stress management strategies.

Abiotic stress factors would be, for example, of a physical nature, such as cold, heat, noise, exhaust fumes and natural and artificial radiation. The latter include strong and excessively long exposure to sunlight or other radiation, such as radiofrequency, radioactive or electromagnetic radiation. Furthermore, toxic substances, e.g. softeners such as diethylhexyl phthalate (DEHP) in PVC floor coverings or children's toys; (cigarette) smoke and the substances it contains; contamination of drinking water; excessive and regular alcohol consumption; diets low in vital substances or the pesticides increasingly used in a variety of agricultural products and application methods (e.g. "herb regulation" by glyphosates) - and thus absorbed into the human body.

Biotic factors would be, for example, stresses caused by pathogens or tumours, also chronic and autoimmune inflammatory processes, which are, however, in turn influenced by the abiotic factors mentioned above (stressors with effects on cell metabolism and immune system). On an emotional level, psychological stresses such as bullying, certain of a person's own attitudes and expectations or, for example, those of his parents, and further fears can also be stressors (see psychosocial stress factors).

Stress is therefore first of all the strain placed on the body by such stressors. This is followed by a reaction and, if necessary, adaptation of the body to these factors, if necessary with external help. Disstress leads to a strongly increased tension of the body (release of certain neurotransmitters and hormones, e.g. adrenaline and noradrenaline, activation of the sympathetic nervous system) and in the long run to a decrease in attention and performance. Stress or dis-stress only has a damaging effect on the human organism when stress exceeds the range of possible adaptation and repair functions (see e.g. DNA repair) of the individual human being or his organism according to his individual physique and psyche or health condition (chronic stress/duration of exposure; excess; possibly multiple factors).

In this case, the above-mentioned factors can lead to an impairment of the metabolism (see metabolic stress; oxidative stress) and thus to a generalised impairment of healing processes or (immune) reactions to infections and impacts of all kinds and/or in this way also to cell mutations, i.e. cancer, unhindered by the immune system (see medical aspects).