When science looks at stress, the focus is on the body/mind interaction or, more precisely, on its psychological and physiological mechanisms. Our genes and the environment in which we grow up (in which our genes are expressed) determine how we respond to stress as adults. Our genetic and environmental differences (the nature or nurture of who we are) help explain how individuals exposed to the same stressful situation can have an entirely different reaction. Some can adapt successfully to the stressor (albeit not without discomfort), while others experience more severe immediate trauma and long-term emotional problems, such as PTSD.
During specific developmental periods, such as infancy, puberty, adolescence, adulthood, or maturity, certain stressors are almost certain to occur and are understood to be typical and appropriate to the process of maturation and change. The earliest such stressor is the effect of caregiving styles, which stems from the parents’ psychological state. An attentive and nurturing style produces vastly different effects on the child’s later adaptation to stress than a harsh, unforgiving or neglectful one. In adolescence, patterns of behavior and emotional reactivity—including the stress reaction—begin to crystallize and become fully set in early adulthood.
Later in life, the natural aging process causes certain systems to soften and become more vulnerable to emotional reactivity and stress, due not in small part to the equally natural decline in physical strength and resiliency. Again, an individual’s genetic make-up comes into play as it did in infancy and childhood. The mature individual is as much influenced by genes and early environmental stressors, and patterns or behavior are carried through well into late adulthood. The saying that you can’t change a leopard’s spots may very well be updated to, you can’t change nature or nurture. In fact, the younger the age when certain stressors were experienced, the more likely it is that their effects will be felt throughout a person’s life.
The stress reaction is produced in multiple body systems. Its effects are most readily observable in the brain (the nervous system, the limbic system and the amygdala), the endocrine system (the hormones that are released into the blood stream) and the immune system (our primary mechanism of defense against disease).
The endocrine system is powerfully activated by stressors. Within milliseconds of the perception of a danger, the excitatory hormones norepinephrine (a.k.a. adrenaline) and epinephrine are released into the blood stream. Their immediate effect is to stimulate the cardiovascular system (elevating blood pressure and heart rate), the respiratory system (the rapid, shallow breathing of hyperventilation), the musculature (tensing long muscles), as well as to inhibit gastrointestinal activity. In addition to the epinephrines, glucocorticoids (e.g. cortisol) are also released, producing an almost instantaneous increase in metabolic rate (our overall alertness and readiness) and at the same time reducing the inflammatory response. In simpler terms, the entire organism is primed for action as well as for the management of possible injury or pain—all quite automatically and without conscious effort.
It is interesting to note that the exact same effects can be produced intentionally, in a positive way (through physical exercise, or by the application of social support) or in a negative way (by the use of stimulating substances, conflict or deprivation).
The persistence of stress has significant effect on the nervous system, and on brain structures and functions, including the hippocampus, the amygdala, the cingulate cortex, the medial prefrontal cortex, and the dorsolateral prefrontal cortex—all structures that are involved in our highest-order brain functions such as judgment, memory and decision-making.
Severe stressors and the stress response they produce are almost invariably physically and mentally exhausting. In addition to the effects of such a powerful mobilization of the heart, lungs, muscles and other organs, the mind is also heavily taxed in thinking about the stressor, how it will affect us and our loved ones, how to defuse it or eliminate it, or how to best adapt to it. In times of stress, many functions take a back seat to its effects: self-care behaviors such as eating a balanced diet, adhering to a prescribed medical regimen, limiting the intake of drinking or nicotine or other substances, or getting a good night’s sleep are postponed, neglected, or altogether abandoned.
The suppression of our immune responses in the presence of a stressor is an adaptive mechanism designed to resolve quickly and return to a normal state. When the stressor is not resolved, a prolonged activation of the nervous system, the continuous circulation of hormones, and immune suppression become counterproductive. Negative emotions, depressed mood, heightened anxiety, fear, terror, pervasive worry and other emotionally excited states maintain a constant state of alertness that can have very serious health consequences.
Several theories explain the value and function of stress as an alert mechanism, but also describe the deleterious effects of chronic stress. Among the most frequent are post-traumatic stress disorder, the type A behavior pattern (particularly its most nefarious manifestations, such as anger and hostility), high life stress, poor interpersonal relationships, elevated risk of acute cardiovascular events and long-term coronary artery disease, and the metabolic syndrome (comprised of essential hypertension, type 2 diabetes, hyperlipidemia, and obesity.)
High circulating cortisol indicates a disruption of normal endocrine levels. These elevated values are characteristic of depressive disorders, which helps establish a clear link between chronic stress and depression. Anxiety is experienced often in the body as tachycardia, hyperventilation, and sweating and the emotional experience of intense arousal, derealization, and difficulty concentrating.