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Overview of the Endocrine System

Author(s): Center for Educational Outreach, Baylor College of Medicine.

Adrenal Glands

The adrenal glands, which sit above the kidneys, are made up of two regions: the outer adrenal cortex and central adrenal medulla. The adrenal medulla secretes epinephrine and norepinephrine, which give the body a rapid energy boost as part of the “fight-or-flight” response. Specific effects of epinephrine and norepinephrine include: increased blood glucose due to glycogen breakdown, increased blood pressure, increased breathing rate, and a change in blood flow patterns that increases alertness and decreases digestive activity. 

Like the adrenal medulla, the adrenal cortex also reacts to stress. Stressful stimuli cause the anterior pituitary to release ACTH, which stimulates the adrenal cortex to synthesize a family of steroids, called corticosteroids. The two main types of corticosteroids in humans are glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone). Glucocorticoids effect the breakdown and conversion of proteins and fats to glucose, leading to increased blood glucose, and in some cases suppressing the immune system. Mineralocorticoids promote retention of sodium and water by the kidneys, and increased blood volume and blood pressure.