What are the physical effects of the flight or fight response?

Eric Olsen
The late Hans Selye, MD, of Montreal, best described the peculiar aspect of our reactions to stress over 40 years ago in his book The Stress of Life. He called the phenomenon the General Adaptation Syndrome (GAS), better known as the "flight-or-fight" response. His theory is based on the belief that, biologically, we are animals, and that our biology is based on another, quite distant time. Whenever animals encounter situations that place demands on their ability to adapt, a chain of identifiable, predictable physical and mental responses take place, all of them regulated by the hypothalamus, a part of the brain that evolved to cope specifically with the rigors of a rough-and-tumble life in the wilds.

The hypothalamus wants to keep on being a hypothalamus, and as far as the hypothalamus is concerned, the only realistic response to any source of stress is physical action, usually accompanied by quick thinking, perhaps to run, to fight, to walk long and fast to find shelter or warmth, or to search for a new mate. So the hypothalamus responds at once to any stressor by preparing the body for rigorous physical activity. It directs the pituitary and adrenal glands to secrete a veritable Mulligan's stew of hormones and neurotransmitters.

The most immediate and measurable result of all of these surging chemicals is that your blood pressure shoots up, your heart rate increases, your breathing quickens and deepens, and the small, peripheral blood vessels in your skin constrict, diverting more blood to your working muscles while your face goes pale and your hands grow clammy. Still more blood is diverted to the muscles from various internal organs, particularly the stomach, putting digestion on hold.

Your pupils dilate so you can see better. More glycogen stores in your body are broken down to augment blood sugar levels for immediate energy. Your blood chemistry changes subtly to shorten clotting time in case you're injured, while blood flow to the brain increases and the brain's chemistry changes so you can think more quickly. Even the body's processes of cell repair and growth are put on hold temporarily during stress; your hypothalamus, after all, sees no point in expending energy on cell repair if you're being chased by something that wants you for dinner.

All of these changes result in a state of physical and mental arousal for "flight or fight."
Lifefit: An Effective Exercise Program for Optimal Health and a Longer Life

More About this Book

Lifefit: An Effective Exercise Program for Optimal Health and a Longer Life

An easy-to-follow programme for lengthening and improving lives. More than an exercise guide, this text is an effective tool for making meaningful lifestyle decisions to benefit long-term fitness. In...

Continue Learning about Endocrine System

Endocrine System

Your endocrine system works with your nervous system to control important bodily functions. The endocrine systems responsibilities include regulating growth, sexual development and function, metabolism and mood. The endocrine syst...

em also helps give your body the energy it needs to function properly. Endocrine glands secrete hormones into the bloodstream. Hormones are considered chemical messengers, coordinating your body by transferring information from one set of cells to another. Your endocrine system health can be affected by hormone imbalances resulting from impaired glands. A hormone imbalance can cause problems with bodily growth, sexual development, metabolism and other bodily functions. Endocrine system diseases or conditions include diabetes, growth disorders and osteoporosis.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.