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As part of the endocrine system, the most important adrenal gland function is to produce and secrete hormones. Each adrenal gland can be thought of as two separate glands. The adrenal medulla primarily secretes epinephrine, also known as adrenaline, which prepares the body for the so-called flight or fight response. The adrenal cortex produces a class of hormones called steroids, which are released in response to states like anxiety or decreased food supply. These hormones all help the body deal with stressful situations, which is an important adrenal gland function.
The production of epinephrine and norepinephrine, which occurs in the adrenal medulla, is a major adrenal gland function. Epinephrine plays a number of roles in preparing the body to deal with dangerous situations. It causes the heart to pump more blood to the skeletal muscles and reduces blood flow to organs not involved in physical activity. Shifting resources to the muscles under voluntary control readies the body for physical exercise, which could include fighting or running away. Epinephrine also releases some of the body's fat stores to provide extra energy in such situations.
Norepinephrine is produced in smaller amounts than epinephrine. It's actually a precursor to epinephrine, but has similar effects of its own. In contexts where epinephrine is called adrenaline, norepinephrine may be called noradrenaline.
The adrenal cortex has a somewhat different adrenal gland function. It produces three types of hormones, all of which are steroids. These are called glucocorticoids, mineralocorticoids, and androgens.
The glucocorticoids have a number of effects on inflammation, metabolism, and development. The most important glucocorticoid is cortisol. In stressful situations, cortisol directs the muscles and organs to use proteins and fats for energy, instead of the more usual glucose. This saves glucose for the brain, which is by far its most important fuel. Cortisol also reduces inflammation and is similar to the drug cortisone. Cortisone lowers the overactive inflammation response in autoimmune disorders.
Of the mineralocorticoids, aldosterone is produced in the greatest amounts. This hormone is released in response to drops in blood pressure that occur in cases of bleeding. It also helps the body conserve water in cases like diarrhea, which limits dehydration.
The class of adrenal cortex hormones known as androgens promote secondary characteristics in sexual development. In females, this leads in part to the development of body hair and plays a role in sexual behavior. In males, this adrenal gland function is much less important because the major androgens are produced by the testes.