home | stress | biology of stress

biology of stress


The body's reaction to stress is based on the fight-or-flight response, which is a relic of our evolutionary heritage for dealing with danger. In the past it served us well, allowing us to survive attacks by predators and other natural threats.

When we sense danger a surge of adrenaline is released, triggering a cascade of bodily changes such as increased heart rate and breathing, strengthening muscles, and closing down systems that are not immediately needed, such as digestion and the immune system. This reaction is healthy and normal - some people seek to trigger it by participating in dangerous sports for example, because they enjoy the feelings of exhilaration which follow.



As well as adrenaline a second hormone called cortisol is secreted - this takes longer to be released and stays in the blood stream longer than adrenaline. As the cortisol level increases it turns off adrenaline helping the body to settle back to a resting state. The body's response to a single stressful event can be represented by the first graph shown in the panel to the right.



The problem comes when our bodies are subjected to a continuous barrage of stress, a situation that modern society creates. Repeated episodes of stress create a state of continuous arousal in which the level of cortisol keeps rising.



At first this can seem very exhilarating, like being on a roller-coaster ride, but if repeated for weeks and months eventually the body’s capacity for recovery starts to become depleted. We experience sleepless nights, tiredness during the day and difficulty concentrating.



After being exposed to chronic stress for extended periods a third stage can occur when the body’s can no longer produce enough cortisol to regulate adrenaline. The result is a very unpleasant state variously described as burnout, breakdown or major depression. There may be panic attacks, insomnia, bouts of worry, and an inability to cope with the slightest stress. Recovery from this state may require many months of rest.