As members of the endocrine system, adrenal glands excrete chemicals, called hormones, to regulate important functions by sending messages through the bloodstream. These various hormones control metabolism, physical development, and stress management. A malfunctioning hypothalamus, which controls the endocrine glands, can make adrenal glands secrete too few or too many hormones resulting in serious disorders.
The two adrenal glands are three-pointed and flat, each one located above a kidney near the lower back. The outer layer of adrenal glands is called the adrenal cortex. The cortex is responsible for synthesizing and secreting hormones essential to digestion and sexual maturity. The inner layer, the adrenal medulla, isn't actually necessary to normal life, but evolved to help us manage moments of stress and improve our quality of life.
The adrenal cortex produces steroidal hormones and chemicals that regulate digestion. Androgenic steroids help develop secondary sex characteristics in males while estrogen and progesterone aid in sexual development in females. These hormones work closely with steroids excreted by the testes and ovaries. For metabolism, aldosterone keeps healthy levels of potassium and salt in the bloodstream. Cortisol helps to metabolize carbohydrates, protein, and fats into glucose.
We handle stressful situations, such as public speaking or being chased by a dog, with greater ease due to the adrenal medulla. It is called a "sympathetic" gland because it responds to external stimuli, such as anxiety with the so-called "fight or flight" instinct. Then it releases adrenaline, or epinephrine, which speeds your heartbeat, thereby increasing circulation, and recirculates stored glucose, which provides a sudden burst of energy and strength. Norepinephrine mildly constricts blood vessels, also raising blood pressure, as well triggering perspiration. This allows to fight, with stronger muscles and quicker reflexes, or take flight, with enough energy to run away. We've adapted this instinct to modern situations, like a job interview.
Also known as the suprarenal glands, adrenal glands can be affected by hormonal imbalances. For example, underactive glands don't produce enough chemicals. Addison's Disease results in low blood sugar and weakened immunity. Overactive adrenal glands, called Cushing's Syndrome, causes high blood pressure and can create problems during adolescent development with exaggerated masculine characteristics. Tumors in the adrenal cortex pose a major health risk, but the adrenal medulla can be removed with minimal effects.