However, experiments have shown that if cortisol is absent, the activity of these other two adrenal hormones is reduced. If the source of stress persists for a few hours, one of cortisol's major functions is to increase the supply of glucose to the brain and heart. Cortisol also makes sure that the needs of these two organs take precedence over other needs. The stress hormone accomplishes this by promoting metabolic breakdown of proteins from muscle, bones, and a few other tissues. The amino acids produced by this breakdown go to the liver where enzymes convert them to glucose, a process called gluconeogenesis .
Cortisol even stimulates the synthesis of the liver enzymes that convert amino acids to glucose.
But if the source of stress persists, the brain can override cortisol's message to shut off stress axis activity. Under these circumstances, Watson says, cortisol begins making long-lasting, and occasionally, permanent changes to the body. For example, Watson says, suppose someone receives word that a family member has been in a car crash, but without getting any other details. Quickly, the brain releases CRH, which leads to ACTH release, and then cortisol, which in turn immediately begins to shut off this cascade. Now, five minutes later, this person hears that the accident was only a fender bender and all is well.