" This feeling of stress triggers a cascade of physiological consequences. The hypothalamus and pituitary gland in the brain release hormones that cause the release of cortisol from the adrenal glands located on the kidneys. Cortisol increases heart rate, among other things, readying the body for “fight” or “flight.” Acutely, the release of cortisol is beneficial and helps you cope with whatever is urgently being demanded of you. But if the stress becomes chronic, maladaptive things begin to happen. Normally, the release of cortisol turns the hypothalamus and pituitary off, stopping the release of hormone, which in turn stops the further release of cortisol from the adrenal glands. It’s a nice, clean, negative feedback loop. But in the chronically stressed, the loop breaks. The brain stops reacting to cortisol. Our natural, automatic shutoff valve stops working. The brain keeps releasing hormone, and the adrenal glands keep dumping cortisol into the bloodstream, even when the stressful thing that initially triggered the stress response is no longer around. Chronic, elevated levels of cortisol have been associated with a weakened immune system, deficits in short-term memory, chronic fatigue syndrome, anxiety disorders, and depression. "
― Lisa Genova , Left Neglected