The Physiology of Stress: The Fight-or-Flight Response

There is more than sufficient data demonstrating that stress can lead to physical, emotional, and behavioral maladjustments. But how do changes in our lives lead to ill health? The answer lies in a physiological mechanism known as the fight-or-flight response. The fight-or-flight response is a survival mechanism present in humans and most animals that prepares us to deal with physical danger. Imagine our prehistoric ancestors, cavemen and cavewomen, exploring their terrain, perhaps even enjoying the wonders of their environment, when suddenly out of the corner of their eyes they spot a sabertoothed tiger, licking its lips in anticipation of a tasty human morsel. The fight-or-flight reaction would kick in, preparing their bodies to either fight or flee from the tiger, through a series of instantaneous physiological and psychological changes that prepare the individual to take immediate physical action in the face of danger. These changes and their resulting physical signs are outlined in Table 2.1, Table 2.2, and Figure 2.1.

In short, the fight-or-flight response shows a picture of autonomic hyperactivity. Returning to the example with the cave dwellers, the person's body and mind would be put on “red alert” in order to deal with the impending danger. This activation would not go on for long, however. If the tiger had its way and the cave dweller ended up serving as a meal, he or she would definitely be relaxed, as the deceased tend to show no autonomic activity. If, on the other hand, our friend was lucky enough to escape and tell the story to those back in the cave, his or her physiology would return to a state of homeostasis or balance. After a slight period of recovery, our cave dweller would be no worse for the wear. Visually, this may be represented as shown in Figure 2.2.

Table 2.1. Signs of the Fight-or-Flight Response

Racing thoughts Rapid pulse Gritting of teeth Restlessness Tremors Rapid, shallow breathing Serious, concerned expression Numbness Impulsive behavior Inability to concentrate

Narrowed attention span Pounding heart Muscular tension Clenched jaw Tightened stomach Increased perspiration Narrowed field of vision Cold, clammy hands Gripping emotions Dry mouth

Table 2.2. Anatomy of the Fight-or-Flight Response

The breathing rate becomes more intense and rapid, increasing the oxygen supply in the blood. Breathing becomes more shallow, switching from diaphragmatic to thoracic respiration, again shifting the oxygen/carbon dioxide balance. Muscles tense in preparation for strenuous action. Heart rate speeds up, ensuring sufficient blood supply to needed areas, especially to the brain for optimized control over conscious functions, as well as to major muscles to prepare the individual for action. Peripheral blood vessels constrict to send the bulk of the blood supply and the oxygen it carries to needed areas. Blood-clotting mechanisms are also activated to prevent excess bleeding should the individual be injured. The increased heart rate and constriction of peripheral blood vessels cause blood pressure to soar. Digestion ceases, so blood may be diverted to muscles and the brain. Stored sugar and fats pour into the bloodstream to provide fuel for quick energy. The adrenal glands release the hormones epinephrine (adrenaline) and norepinephrine into the system. Triggered by the pituitary gland, the endocrine system steps up hormone production. All senses are heightened. Pupils dilate, making vision more sensitive. Hearing becomes more acute. Electrical resistivity (perspiration/galvanic action) and skin temperature change. Perspiration increases and saliva decreases. The urethra and anal sphincter muscles (controlling bowel and bladder function) initially loosen, in order to evacuate waste if necessary, but then constrict to prevent waste elimination when running or fighting. So when people say, “I was so scared that I peed in my pants,” there is a physiological mechanism underlying this humiliating phenomenon.

Downside of the Fight-or-Flight Response

The fight-or-flight response is clearly an adaptive response to the presence of physical danger. The problem is that the response is triggered not only by actual physical danger, but by perceived danger. The tigers that chase modern humans are not made of flesh and blood; they are things like deadlines; unpaid bills; confrontations with others; rush-hour traffic; and demands from children, spouses, and bosses. All these and many more trigger the fight-or-flight response in the person of today. But it gets worse, for not only are the tigers the actual events, but also those events remembered and anticipated by us. So not only does the act of asking the boss for a raise lead to increased autonomic activity, but also our anticipation of the meeting, along with the recollection of the event, particularly if we didn't obtain the desired results. The predicament lies in the fact that the fight-or-flight reaction prepares us to fight or run away, and neither of these responses is particularly useful nor adaptive for dealing with most of the stresses we face in our modern world. To further aggravate the situation, our cave dweller's stresses had a distinct beginning and a definite ending, whereas the tigers we face today seem to be much more ongoing. No sooner have we begun to recover from fight-or-flight activation when another event, real or imaginary, triggers the response again. Thus, we never really have the chance to fully recover and return to homeostatic balance before we are faced with the onslaught of new or old stressors recurring in our environment. This can be expressed visually as shown in Figure 2.3.

Day after day we are faced with a continuous barrage of stressors. We get some relief at night when we sleep, but even in our sleep we might dream about our stressors, again triggering the fight-or-flight response, and the next day we awaken with our physiology just a bit above homeostasis, to begin the whole cycle over again. After years of this pattern we forget what relaxation really feels like, as we habituate to a state of autonomic arousal. This state feels relaxed in comparison to full blown fight-or-flight activation, but in reality it is higher than true homeostasis, which we need to maintain health. This is illustrated in Figure 2.4.

Thus a person under chronic stress is like a car with its idle set too high. Imagine for a moment a car whose engine is idling just a little too fast. What would happen to it? For one thing, it would use more gas, just as we tend to spend more energy for diminishing returns when we are under stress. In addition, the engine would wear out prematurely, which similarly appears to happen to our bodies. Stress researcher Hans Selye, mentioned earlier, described this phenomenon as a three-stage process, which he named the General Adaptation Syndrome (GAS), which is illus trated in Figure 2.1. The first stage of GAS, called the alarm reaction, is basically the fight-or-flight response. If the stressor continues, as is typical of modern-day tigers, we enter the stage of resistance, where our bodies habituate to the specific stressors. Overt signs of the fight-or-flight reaction disappear or go underground, but subtle signs persist (our neural and glandular systems remain hyperactive), leaving us overstimulated and vigilant. The last phase, the stage of exhaustion, occurs when stressors are prolonged despite our best attempts at coping. Just as we have to rest, so must our glandular system rest in order to regain balance. Without rest it wears down and eventually out, resistance deteriorates, and stress-related symptoms resurface. Clearly, if there is no relief, even death is possible (Selye, 1982).

Stress Sensitization

To make matters even worse, before the stage of exhaustion overtakes us, recent research indicates that we can become sensitized, or acutely sensitive, to stress. That is, we may respond to stress as we do to an allergy (Carpi, 1996). Once that happens, even the slightest stress can trigger a torrent of chemical reactions in both our brain and body that besiege us from within, making stress the psychological equivalent of ragweed. Even though at some level we realize that what we are facing is a normal, everyday stressor, our brain is signaling our body to overreact. We may not think we are getting worked up over running late for an appointment, but our brain is responding as though it were a life-or-death situation. Years of research have demonstrated that people become sensitized to stress, and this sensitization actually alters physical patterns in the brain. We may produce too many excitatory chemicals or too few calming ones; either way, we are responding inappropriately.

The fact that stress itself lowers our ability to cope with further stress leads to yet another distressing finding: Sensitization to stress may occur before we are old enough to prevent it ourselves. New studies suggest that animals ranging from rodents to monkeys to humans may experience still-undetermined developmental periods during which exposure to extreme stress is more damaging than in later years. For example, we have known that losing a parent when you are young is much harder to handle than if your parent dies when you are an adult. What we now believe is that a stress of that magnitude occurring in childhood may rewire your brain's circuitry, throwing the system off kilter, leaving you less able to handle normal, everyday stress. So clearly, stress does not just grab us for a time and then release us. It changes us by altering our bodies and our brains.