Stress Health Article

Definitions

Stress is a term that refers to the sum of the physical, mental, and emotional strains or tensions on a person. Feelings of stress in humans result from interactions between persons and their environment that are perceived as straining or exceeding their adaptive capacities and threatening their well-being. The element of perception indicates that human stress responses reflect differences in personality as well as differences in physical strength or health.

A stressor is defined as a stimulus or event that provokes a stress response in an organism. Stressors can be categorized as acute or chronic, and as external or internal to the organism. The Diagnostic and Statistical Manual of Mental Disorders(DSM-IV-TR) defines a psychosocial stressor as "any life event or life change that may be associated temporally (and perhaps causally) with the onset, occurrence, or exacerbation [worsening] of a mental disorder."

Stress affects the lives of most adults in developed countries in many ways. It is a major factor in rising health care costs; one public health expert maintains that 90% of all diseases and disorders in the United States are stress-related. Stress plays a part in many social problems such as child and elder abuse, workplace violence, juvenile crime, suicide, substance addiction, "road rage," and the general decline of courtesy and good manners. Stress also affects the productivity of businesses and industries. One nationwide survey found that 53% of American workers name their job as the single greatest source of stress in their lives. Furthermore, the overall cost of medical care, time lost from work, and workplace accidents in the United States comes to over $150 million per year.

The neurobiology of stress

One way to understand stress as a contemporary health problem is to look at the human stress response as a biologically conditioned set of reactions that was a necessary adaptation at earlier points in human evolution, but is less adaptive under the circumstances of modern life. Hans Selye (1907-1982), a Canadian researcher, was a pioneer in studying stress. Selye defined stress, in essence, as the rate of wear and tear on the body. He observed that an increasing number of people, particularly in the developed countries, die of so-called diseases of civilization, or degenerative diseases, which are primarily caused by stress. Selye also observed that stress in humans depends partly on people's evaluation of a situation and their emotional reaction to it; thus, an experience that one person finds stimulating and exciting—for example, bungee jumping—would produce harmful stress in another.

The stress response

In humans, the biochemical response to acute stress is known as the "fight-or-flight" reaction. It begins with the activation of a section of the braincalled the hypothalamic-pituitary-adrenal system, or HPA. This system first activates the release of steroid hormones, which are also known as glucocorticoids. These hormones include cortisol, the primary stress hormone in humans.

The HPA system then releases a set of neurotransmittersknown as catecholamines, which include dopamine, norepinephrine, and epinephrine (also known as adrenaline). Catecholamines have three important effects:

• They activate the amygdala, an almond-shaped structure in the limbic system that triggers an emotional response of fear.
• They signal the hippocampus, another part of the limbic system, to store the emotional experience in longterm memory.
• They suppress activity in parts of the brain associated with short-term memory, concentration, and rational thinking. This suppression allows a human to react quickly to a stressful situation, but it also lowers ability to deal with complex social or intellectual tasks that may be part of the situation.

In reaction to stress, heart rate and blood pressure rise, and the person breathes more rapidly, which allows the lungs to take in more oxygen. Blood flow to the muscles, lungs, and brain may increase by 300–400%. The spleen releases more blood cells into the circulation, which increases the blood's ability to transport oxygen. The immune system redirects white blood cells to the skin, bone marrow, and lymph nodes; these are areas where injury or infection is most likely.

At the same time, nonessential body systems shut down. The skin becomes cool and sweaty as blood is drawn away from it toward the heart and muscles. The mouth becomes dry, and the digestive system slows down.

The relaxation response

After the crisis passes, the levels of stress hormones drop and the body's various organ systems return to normal. This return is called the relaxation response. Some people are more vulnerable to stress than others because their hormone levels do not return to normal after a stressful event. An absent or incomplete relaxation response is most likely to occur in professional athletes and in people with a history of depression.