All About Cortisol, the Master Stress Hormone
If you've been paying attention throughout the first two chapters, then you already know the basic relationship between stress and cortisol. For those who missed it, stress makes cortisol levels go up. You also understand that cortisol can be both a "good thing" and a "bad thing," depending on how much cortisol is present in the body and how long it "hangs around." In very general terms, cortisol turns "bad" when you either have too much of it or are exposed to it on a regular basis. The discussion that follows provides a closer look at the dynamics of cortisol metabolism.
The Endocrine System
The vast network of hormones and glands in the body is known as the endocrine system. This system is made up of specialized tissues (glands) that play an integral part in our overall response to stress. Through our senses of sight, sound, smell, and even our thoughts, the brain collects information and uses both the nervous system and the endocrine system to respond to what it "observes" in the environment. When we encounter a stressor, whether through our physical or our psychological senses, the endocrine system jumps into action to set things right. Through the coordinated actions of two glands in the brain, the hypothalamus and the pituitary, along with another set of glands that sit just above the kidneys, the adrenal glands, stress causes a cascade of hormonal signals to be set into motion. These hormonal signals involve epinephrine (adrenaline), norepinephrine, cortisol, and numerous intermediary hormones that interact to help regulate important aspects of physiology, such as cardiovascular function, energy metabolism, immune-system activity, and brain chemistry.
The Adrenal Glands
The two adrenal glands are located just above the kidneys (Figure 3.1). Each adrenal gland is made up of two parts: the inner medulla, which produces adrenaline, and the outer cortex, which produces cortisol and aldosterone, another steroid hormone that is important in salt/water balance and blood pressure. Cortisol and other glucocorticoids are secreted in response to stimulation of the adrenal glands by adrenocorticotropic hormone (ACTH, also known as corticotropin) from the pituitary gland. Secretion of ACTH is under the control of another hormone from the hypothalamus called corticotropin-releasing hormone (CRH).
It is easy to see how closely the central nervous system is linked with the endocrine (hormone) system. The brain perceives stress; it responds by secreting CRH from the hypothalamus in the brain; CRH stimulates the pituitary gland (also in the brain) to secrete ACTH; and ACTH travels to the adrenal glands (on top of the kidneys) to stimulate cortisol production.
Cortisol levels typically fluctuate in a fairly rhythmic fashion throughout the day, with the highest levels present in the morning and the lowest present at night. It is important to note, however, that cortisol rhythms can be disrupted by a wide variety of factors, such as emotional and physical stress, inadequate sleep, and various illnesses.