Let’s look at the physiology of stress.
When you encounter a perceived threat, say, getting attacked by a sabre-toothed tiger, your hypothalamus goes to work. It lives for this stuff. It sends out nerve and hormonal signals to your adrenal glands (which are at the top of your kidneys, for those of you who don’t remember biology class). The adrenals get excited, because this is their entire raison d’etre, and they release a surge of hormones and neurotransmitters, which include adrenaline and cortisol. Adrenaline increases your heart rate, elevates your blood pressure, and boosts your energy supplies. Your ability to fight the sabre-toothed tiger (bad idea) or run away (better idea) has been increased, which means you have a better chance of surviving the attack. Cortisol increases glucose levels in the bloodstream (more energy), enhances your brain’s ability to use that glucose (faster decision making ability, so you can figure out that running is a better option), and increases the availability of those things that help you repair tissue (theoretically created by running away really fast, rather then being eaten by the tiger, because that’s harder to repair). Cortisol also shuts down or significantly diminishes the non-essential systems in the body. If you were a spaceship, you’d be shutting down the replicators in favor of keeping life support going, but you are not a spaceship. So, instead, your immune system is supressed, your digestive and reproductive systems get put on hold, and growth is repressed. Your body chemistry also has a strong effect on the areas of the brain that handle motivation (ignore it if it’s not life threatening), fear (you’re going to be eaten by a tiger!), and mood (nothing but the stress matters right now).
Once you get back to your cave (or gated community or some other safe haven), and the threat is over, your hormone levels return to normal and your body starts working the way it’s supposed to. Unless, of course, you are now being stalked by a sabre-toothed tiger, or your boss, or your children. When you are under constant stress, this process doesn’t shut off. Which means your glucose levels are high (tasty tasty diabetes), your blood pressure is high (which leads to doctors yelling at you), your brain is on overdrive (you know that committee in your head? They’ve all just had double espressos!), your cellular growth might be pushing itself too hard, your immune system is sub-par, you are having trouble digesting things, you’re not conceiving or growing babies the way you should, and, if you’re still growing, you’re not growing anymore. Oh, also, your motivation is shot, you’re in an unfocused state of fear (which we frequently interpret as worry), and you’re depressed.
Two things will effect how you respond to stress – genetics and life experience. Studies have recently suggested that if your parents and grandparents had experiences in their lives that were stressful, it may have altered their genes. This may mean that people who come from high-stress blood-families are predisposed to being high-stress themselves, even if they were adopted at birth. If your life experiences have been stressful (childhood abuse or neglect, high-crime neighborhood, big accidents, war, etc.), your overall reaction to stress may be higher.
On a chemical level, the intensity of your response if governed by glucocorticoids. These are the steroids produced by your body; they control metabolism (mostly of carbohydrates, but they do have some effect on your ability to metabolize fats and proteins); cortisol is a glucocorticoid. Even if you don’t think that your life should be stressing you out, three things will increase your production of cortisol and, therefore, cause your body to have a stress reaction: sleep deprivation, alcohol consumption, and caffeine intake. It is also important to note that fully 50% of people who are clinically depressed have been found to have elevated cortisol levels.
When you combine your genetics, life experience, and intensity of reaction, it can take anywhere from 30 minutes to several days to “destress” after a stressful event. If you have more stress before the relaxation effect kicks in, you end up with long-term stress, which can cause shrinkage in the hippocampus, which is the area of the brain that stores memories. You might deduce from all of the above, that long term stress also suppresses the immune system, raises blood pressure and blood sugar levels, affects your metabolism and reproductive systems, and can contribute to depression; you would be correct.
Next week, I will be going in depth into the relaxation response
Dartmouth Undergraduate Journal of Science: The Physiology of Stress: Cortisol and the Hypothalamic-Pituitary-Adrenal Axis (Read this article for all of the science about what cortisol does)