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Concepts of Stress
- Stress recently has been defined as the state of affairs arising when a person relates to (i.e., interacts or transacts with) situations in a certain way. How he or she appraises and reacts to situations is important.
- Hans Selye identified three structural changes in rats subjected repeatedly to noxious stimuli (stressors): (1) enlargement of the cortex of the adrenal gland, (2) atrophy of the thymus gland and other lymphoid tissues, and (3) gastrointestinal ulceration.
- Selye believed that the three changes were caused by a nonspecific physiologic response to any long-term stressor. He called this response the general adaptation syndrome (GAS).
- The GAS occurs in three stages: (1) the alarm stage, (2) the stage of resistance or adaptation, and (3) the stage of exhaustion. Diseases of adaptation develop if the stage of resistance or adaptation does not restore homeostasis.
- Selye identified three components of physiologic stress: the stressor, the physiologic or chemical disturbance produced by the stressor, and the body’s adaptational response to the stressor.
- Other investigators have shown that the physiologic stress response also occurs in response to psychologic or emotional stress.
- Psychologic stressors can be anticipatory and triggered by anticipation of an upcoming stressor or it can be reactive to a stressor. Both of these psychologic stressors are capable of eliciting a physiologic stress response.
The Stress Response
- The stress response involves the nervous system (sympathetic branch of the autonomic nervous system), the endocrine system (pituitary and adrenal glands), and the immune system.
- The stress response is initiated when a stressor is present in the body or perceived by the mind.
- The neuroendocrine response to stress consists of sympathetic stimulation of the adrenal medulla to secrete catecholamines (norepinephrine, epinephrine, neuropeptide Y) and stressor-induced stimulation of the pituitary to secrete ACTH, which in turn stimulates the adrenal cortex to secrete steroid hormones, particularly cortisol.
- In general, the catecholamines prepare the body to act, and cortisol mobilizes energy (glucose) and other substances needed to fuel the action.
- Epinephrine exerts its chief effects on the cardiovascular system. Epinephrine increases cardiac output and increases blood flow to the heart, brain, and skeletal muscles by dilating vessels that supply these organs. It also dilates the airways, thereby increasing delivery of oxygen to the bloodstream.
- Norepinephrine’s chief effects complement those of epinephrine. Norepinephrine constricts blood vessels of the viscera and skin; this has the effect of shifting blood flow to the vessels dilated by epinephrine. Norepinepherine also increases mental alertness.
- Cortisol’s chief effects involve metabolic processes. By inhibiting the use of metabolic substances while promoting their formation, cortisol mobilizes glucose, amino acids, lipids, and fatty acids and delivers them to the bloodstream. Cortisol at low levels consistent with stress increase humoral immunity, may activate proinflammatory mediators, and decrease cellular immunity. Cortisol at high levels (e.g., therapeutic levels) decreases both humoral and cellular immunity and is anti-inflammatory.
- The nervous, endocrine, and immune systems communicate through the common use of signal molecules and their receptors, which in turn regulate the behavior of cells in each system during stress challenge.
- There are direct and indirect pathways of influence among the nervous, endocrine, and immune systems. Neuropeptides have direct effects on immune cells, as well as indirect influences through neurologically mediated endocrine modulation of immune function. Endocrine products (cortisol) also influence neurologic cell behavior. Immune cell products affect both nervous and endocrine cell function, reflecting an adaptive role for the immune system as a “signal” organ to alert other systems of threatening stimuli.
- Other hormones are affected by the stress response; these include increased circulating levels of β-endorphins, growth hormone, prolactin, oxytocin, and antidiuretic hormone. Testosterone decreases during the stress response.
Stress, Personality, Coping and Illness
- Stress is a system of interdependent processes that are moderated by the nature, intensity, and duration of the stressor and coping efficacy of the affected individual, all of which in turn mediate the psychologic and physiologic response to stress.
- Personality characteristics are associated with individual differences in appraisal and response to stressors.
- Coping styles associated with altered immunity include repression, denial, escape-avoidance, and concealment.
- Many studies have linked psychologic distress with altered immune function, and there is now evidence that strengthens the association of stress with potential for illness in humans.
Aging & Stress-Age Syndrome
- With aging, often a set of neurohormonal and immune alterations including tissue and cellular changes occur. These changes are collectively called stress-age syndromes.
- The changes are numerous, with some being adaptational whereas others are potentially damaging.