At its most basic level, stress is a survival mechanism, an evolutionary adaptation to a world filled with life-threatening dangers. The cascade of responses — increased blood sugar, heart rate, and energy available to the muscles — are perfectly suited to fighting or fleeing from physical danger. But today's stressors — traffic, work pressures, family obligations and tensions — are of a different sort than those faced by our ancestors. And the responses that worked so beautifully when confronting a brief physical attack can fail when the stresses are emotional and constant.
The body's response to stress follows a prescribed sequence that begins in the brain as soon as we perceive danger. The senses send a message to the cortex, which processes the signal and sends a message to another part of the brain, the amigdala, which recognizes threats in the environment. The amigdala then activates the hypothalamus. Located at the base of the brain, the hypothalamus stimulates the center of the adrenal gland, called the adrenal medulla, to release adrenaline.
Adrenaline, also called epinephrine, is critical to the stress response: it raises blood sugar, increases heart rate and boosts the amount of energy available to your muscles. Simultaneously, the pituitary gland stimulates the outside of the adrenal gland, called the adrenal cortex, to release a second key stress hormone, cortisol. Cortisol, known as the "fight or flight" hormone, acts to maintain high level of both blood pressure and blood sugar.
While cortisol has short-term benefits, such as providing essential bursts of energy during critical periods, scientists have become concerned about the hormone's long-term effects on our health. Evidence shows that extended exposure to cortisol weakens bones, causes nerve cells in the brain to degenerate or perhaps even die, and compromises the immune system, making us more vulnerable to infection. High blood pressure, depression, skin problems, headaches, back pain, insomnia, digestive disorders, heart disease and stroke have all been related to extended periods of stress.