Did you know that the emotions associated with stress actually cause physical changes in your body? A Hungarian scientist and physician named Hans Selye identified this response in 1936 while experimenting on mice. Although he injected the animals with various kinds of fluids, they all developed ulcers, swelling glands, and depleted immune systems. (The body’s immune system helps fight infection.) The mice’s bodies changed, or adapted, in the same way.
Selye called this response general adaptation syndrome. Later, as he expanded his work on general adaptation syndrome, he began referring to it as stress. At the time, physicists used the term, which comes from a Latin word meaning “to pull apart,” to describe elasticity.
According to a colleague of Selye’s, the word strain was closer to the idea of what the researcher was trying to describe. (Strain refers to an injury to the body caused by extreme physical tension.) If Selye had been more proficient in English, people today might be talking about “strain relief” instead of “stress relief”! But the name stress stuck, and others began researching the subject as well.
So exactly how does stress affect people? Actually, it’s all in your head—more specifically, in your brain. The physical reaction to stress is triggered by a part of your brain called the hypothalamus. Although the hypothalamus is only about the size of a marble, it affects your entire body. This tiny region of the brain is a control center that sparks many complex chemical reactions. Among them is the release of hormones—special chemical substances that signal other body cells to action. In emergency situations, the hypothalamus sets off an alarm resulting in the release of two important hormones—adrenaline and cortisol—into the bloodstream. They cause changes to quickly occur in the body: the muscles tense and breathing becomes rapid.
“Stress is like an iceberg. We can see one-eighth of it above, but what about what’s below?”
—Anonymous
This stress reaction is called the “fight-or-flight” response—your body is prepared to fight the perceived danger or flee from it. The fight-or-flight instinct is a natural response that dates to prehistoric times, when humans had to struggle for survival.
Although you probably don’t have to face mortal danger on a regular basis today, you still experience fight-or-flight moments. The stress response can occur when your emotions cause your body to react as it would in an actual emergency, even when there is no physical danger.
Once the stressful event or threat that set off your hypothalamus alarm has passed, the levels of adrenaline and cortisol decrease in the bloodstream. Your body returns to normal.
Adrenaline and cortisol are produced by the adrenal glands—two boomerang-shaped glands located near your kidneys. Adrenaline increases the heart rate and raises your blood pressure. Cortisol regulates metabolism, which is the process in which the body breaks down substances so the cells can use them. Both adrenaline and cortisol increase the amount of sugar in the bloodstream, which results in feeling a rush of energy.
