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The Biology of Stress

Harry Mills, Ph.D., Natalie Reiss, Ph.D. and Mark Dombeck, Ph.D.

The first person to study stress scientifically was a physiologist named Hans Selye. Dr. Selye spent many years studying the physical reactions of animals to injury and disease. Based on his research, Selye concluded that human beings and animals share a specific and consistent pattern of physiological responses to illness or injury. These changes represent our body's attempt to cope with the demands imposed by the illness or injury process.

First is the alarm reaction, which is a stage of physiological (bodily) excitation and preparation for fighting the illness or injury. Heart rate, blood pressure and breathing quicken in order to supply the muscles and the brain with more oxygen. More blood is sent to the skeletal muscles and the brain, while blood flow decreases to the stomach, kidneys, skin and liver. Sexual and immune (i.e., disease fighting) functions are suppressed. Body chemicals that act as natural painkillers are released into the blood stream in order to relieve pain. The body's fuel sources, in the form of natural fats and sugars, are actively mobilized to supply us with extra energy. Our attention focuses on the alarming event (if one can be identified), and in general, our senses become sharper. All of these highly coordinated reactions occur very quickly. The alarm reaction phase usually lasts a few seconds, although sometimes it may be shorter than a second in duration.

The physiological changes characteristic of the alarm reaction allow us to quickly react to threats, and in some cases, resolve those threats. In other situations, the alarm reaction allows us to get far enough away from threats that they are no longer an immediate concern. However, some injuries or illnesses cannot be resolved or escaped from, and continue to be a problem over time.

The alarm reaction is very 'expensive' to our bodies; it requires a great deal of energy to produce and maintain, and it is not practical or useful to continue over time in response to extended threats. When faced with an extended threat (that cannot be quickly resolved or avoided), the body shifts away from the alarm mode towards an stage of trying to adjust to the demands of the ongoing threat. In this second stage, called adaptation, the effects of the alarm phase lessen (although the alarm symptoms continue to persist long after the stressor has disappeared). The body continues to fight the illness or injury, but the physiological systems that are aroused to do this work function at a more moderate pace.

While not as energy intensive as the alarm reaction, the adaptation phase still requires a significant amount of energy to sustain. If the illness or injury does not abate after a period of time, the body will enter into a third phase, exhaustion, and start to show evidence of wear and tear. Usually, exhaustion is reversible rather than permanent. Given enough rest and relaxation, the body is typically able to recover fully from the exhaustion phase.

However, if the stressor is too strong, extreme exhaustion can result in death. Prolonged, frequent, or intense stress reactions can also cause permanent stress-related health disorders such as ulcers, high blood pressure, arteriosclerosis, arthritis, kidney disease, and allergic reactions. We will talk more about the relationship between stress and disease in a later section of this document.

Selye called this common pattern of body responses to illness characterized by the alarm, adaptation and finally exhaustion phases the 'General Adaptation Syndrome' or GAS. Importantly, Selye also noted that the GAS was a generalized way that the body tended to respond to any taxing life demand and was not just limited to illness or injury. He used the term "stressor' to describe any event capable of causing the GAS to occur (e.g., any event capable of producing a stress reaction). He also repeatedly noted that the body's reactions to stress were a normal part of the life of animals (including people). He characterized these responses as neutral in quality, rather than being inherently good or bad.

Dr. Selye was one of the first scientists to suggest that stress could weaken the body's ability to resist infection and increase the likelihood of developing diseases. Today, we all take this idea for granted. In the 1950's, however, this was a revolutionary idea. Back then, the conventional wisdom was that disease was solely caused by germs.

Selye is often considered the "father" of stress research, as he was one of the first scientists to concentrate on this area. The many subsequent stress researchers have expanded on Selye's initial work and have studied how our bodies react to stressors that don't involve germs and illness. We know today that our bodies have built-in responses to all types of stressors. Unfortunately, there is often a mismatch between our body's response and the actual demands of the stressors we encounter in the modern world. We are designed to respond efficiently to the types of stress that our prehistoric ancestors experienced; not the type that we face today in our contemporary, technological society.

We are far more adapted to avoid a charging herd of buffalo or physically fight a rival for food than we are to deal with a malfunctioning computer or the incessant ringing of our cell phones. Unfortunately, however, our bodies respond to these modern stressors in exactly the same way as our ancient forebears responded to predators or other physical threats; through a series of four stages. And we do it, as they did: automatically, and without thought.