Understanding the natural stress response

When you encounter a perceived threat — such as a large dog barking at you during your morning walk — your hypothalamus, a tiny region at your brain's base, sets off an alarm system in your body. Through a combination of nerve and hormonal signals, this system prompts your adrenal glands, located atop your kidneys, to release a surge of hormones, including adrenaline and cortisol.

Adrenaline increases your heart rate, elevates your blood pressure and boosts energy supplies. Cortisol, the primary stress hormone, increases sugars (glucose) in the bloodstream, enhances your brain's use of glucose and increases the availability of substances that repair tissues.

Cortisol also curbs functions that would be nonessential or harmful in a fight-or-flight situation. It alters immune system responses and suppresses the digestive system, the reproductive system and growth processes. This complex natural alarm system also communicates with the brain regions that control mood, motivation and fear.