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We all understand that chronic stress causes harm to our bodies and minds. But do we really know why? I am asked this question very often, so below have summarized some important information we know about the interaction of stress and the immune system.
Walter Cannon was the first to apply the definition of homeostasis to the body’s internal mechanism of regulation. The state of body’s functional stability is also known as equilibrium. When the organism faces various challenges or stressors, it must respond by adjusting physical functions including the hormonal, immune, cardiovascular and other resources. Not only physical challenges may cause the body to respond in an effort to maintain homeostasis. Psychological stressors are known to invoke similar mechanisms. The arousal of the nervous system increases the heart rate, respiration, cortisol and adrenaline production. To counter balance these changes, the body must provide for an adequate response. If the response is not adequate, the organism will start suffering damages leading to further medical problems. Cannon’s concept of homeostasis is very valuable in explaining the effect of acute and chronic physiological and psychological stress responses.
Hans Selye introduced the word “stress” in Cannon’s homeostasis as an effect of environmental challenges and changes requiring the organism to adjust. Selye noted that response to stress happens through integration of multiple bodily systems. The HPA (hypothalamic-pituitary-adrenocortical) axis, according to Selye, played an important role in the activation of endocrine response system and prolonged or chronic stress exposure produce a weakening effect on the wide number of body’s functions, including the endocrine and the immune systems. Selye named the body’s response the General Adaptation Syndrom, which consists of Alarm Reaction, Resistance, and Exhaustion. Alarm Reaction leads the body functions to drop causing compensatory response initiation, known as the Resistance stage. Peak performance is achieved through mobilization of all body’s resources. However, since the mobilization consumes a lot of energy, this phase cannot last indefinitely. The stage of Exhaustion begins when energy levels are depleted. Resistance to stressors is weakened and the body suffers tissue and system’s damage. In chronic stress, body’s ability to adapt and recover from each stressful episode is diminished. Weakened immune system, elevated levels of cortisol and constant high blood pressure damage the organism’s functions and make the body susceptible to illness and cognitive decline. Psychopathology can be caused by chronic stress exposure, where brain tissue damage in the hippocampus and amygdala may lead to increased anxiety or major depression episodes and impairment of cognitive function.
Stress usually leads to higher susceptibility to illness. Stress activates overproduction of adrenaline and cortisol hormones, which reinforce all cycles of physiological processes to allow the human organism to perform under duress. Extended duress or chronic stress wears out all organism functions, including the immune system. In the short term stress, the immune system gears all resources to help the body, but in the chronic stress, the immune system stops recognizing stress as duress and fails to provide protection from the intruding pathogens. Stress also leads to decreased activity of the T-cells and the killer-cells, which further impair the immune system’s ability to detect tumors, and other dangerous developments. Psychological stress impairs many parts of the cellular immune response. Communication between the central nervous system and the immune system occurs through the networks of chemical messengers secreted by nerve, endocrine and immune cells, and psychological stressors can disrupt these networks.