General Adaptation Syndrome
Dr. Hans Selye, an endocrinologist, developed a three-stage model of the body's response to stress. He called his theory the general adaptation syndrome (GAS). The first phase is an alarm reaction, the second stage is one of resistance or adaptation, and the final stage is one of exhaustion.
In the alarm stage the body responds to a stressor, which could be physical or psychological. Perhaps you are crossing the street and a car suddenly speeds toward you. Your heart begins to beat fast and the release of adrenaline makes you move quickly from the path of the oncoming car. Or another response might include butterflies in your stomach, a rise in your blood pressure, heavy breathing, dilation of your eyes, dry mouth, and the hair on your arms might even stand on end. To help you meet the sudden danger, your blood flows away from the organs not needed to confront the danger, to organs and tissues which are; for example, your heart races, your eyes dilate, your muscles tense up, and you will not be able to concentrate on any kind of problem solving outside the danger confronting you.
During the resistance stage of a stress reaction, your body remains on alert for danger. When this part of the GAS is prolonged, your immune system may become compromised and you may become susceptible to illness. Even within days of becoming stressed and maintaining a stress alertness, changes take place that weaken your body's ability to fight off disease.
The final stage of Selye's GAS is the exhaustion stage. As your body readjusts during this period, hormones are released to help bring your body back to normal, to the state of balance called homeostasis. Until balance is reached, the body continues to release hormones, ultimately suppressing your immune system.