Stress (medicine)

In the medical world, stress is defined as one of the following:

An applied force or system of forces that tends to strain or deform a body,
The resisting force set up in a body as a result of an externally applied force, or
A physical or psychological stimulus that can produce mental tension or physiological reactions that may lead to illness.''The American Heritage® Stedman's Medical Dictionary

Stressors

Any factor that causes stress is called a "stressor." There are two kinds of stressors: processive stressors and systemic stressors.

Processive stressors

Processive stressors are elements in the environment (for example, elevated sound levels or bright light) perceived by the organism as potential dangers. These do not cause damage directly, but are processed in the cerebral cortex. The processed information is then sent via the limbic system in the hypothalamus, where they activate the supreme centers of the autonomic nervous system. This results in the fight-or-flight (or sympathetico-adrenal) response.

Systematic stressors

Systemic stressors cause a disturbance in the organism's homeostasis, as well as tissue necrosis, hypotension and/or hypoxia. Often both types of stressors occur simultaneously. They are usually accompanied by pain and/or intensive emotions.

Neurochemistry and physiology

The neurochemistry of the general adaptation syndrome is now believed to be well understood, although much remains to be discovered about how this system interacts with others in the brain and elsewhere in the body.

The body reacts to stress first by releasing the catecholamine hormones, epinephrine and norepinephrine, and the glucocorticoid hormones, cortisol and cortisone.

The hypothalamic-pituitary-adrenal (HPA) axis is a major part of the neuroendocrine system, involving the interactions of the hypothalamus, the pituitary gland and the adrenal glands. The HPA axis is believed to play a primary role in the body's reactions to stress, by balancing hormone releases from the adrenaline-producing adrenal medulla and from the corticosteroid-producing adrenal cortex.

Folklore of stress

About the time of Selye's work, the gradual realization dawned that such concepts as anxiety, antagonism, exhaustion, frustration, distress, despair, overwork, pre-menstrual tension, over-focusing, confusion, mourning and fear could all come together in a general broadening of the meaning of the term stress. The popular use of the term in modern folklore expanded rapidly, spawning an industry of popular psychology, self-help, personal counselling, and sometimes quackery.

The use of the term stress in serious and recognized cases such as those of post-traumatic stress disorder and psychosomatic illness has scarcely helped clear analysis of the generalized "stress" phenomenon. Nonetheless, some varieties of stress from negative life events, or distress, and from positive life events, or eustress, can clearly have a serious physical impact distinct from the troubles of what psychotherapists call the "worried well". Stress activates the sympathetic nervous system and release of stress hormones including adrenaline/epinephrine and cortisol.

Sympathetic nervous output tends to divert bloodflow to the large muscles - the body 'thinks' it has to run away from something or fight something: the so-called 'fight or flight' response of ancient evolutionary heritage - and bloodflow is correspondingly less to the bowel and other non-muscle organs. We all recognise the effects: dry mouth, motor agitation, sweating, pallor, enlarged pupils and insomnia. Our modern lifestyle tends to cause continual sympathetic nervous system activation with very little opportunity for the parasympathetic (also called 'vegetative') nervous system to activate. When this system is active, the bowel and other non-muscle organs receive good blood-flow, the pupils constrict, the glands all function well and secrete their various compounds. Absence of parasympathetic activation leads to poor digestion and probably also to poor healing and organ function. It is vital to take time out from our modern lifestyles to allow for rest and proper parasympathetic action in our bodies.

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