Adrenal Glands

One adrenal gland (uh-DREE-nuhl gland) is located above each kidney, as shown in Figure 50-6. Each adrenal gland has an inner core, the medulla, and an outer layer, the cortex. The medulla and cortex function as separate endocrine glands. Secretion of hormones in the medulla is controlled by the nervous system, whereas hormones in the anterior pituitary regulate secretion of hormones in the cortex.

Adrenal Medulla

The adrenal medulla produces two amino acid-based hormones: epinephrine (EP-uh-NEF-rin) and norepinephrine (NAWR-EP-uh-NEF-rin), also known as adrenaline (uh-DREN-uh-lin) and noradrenaline (NOR-uh-DREN-uh-lin), respectively. These hormones orchestrate the nervous system's reaction to stress and its "fight-or-flight" response to danger. When a person is stressed, the medulla secretes epinephrine and norepinephrine into the bloodstream. These hormones increase heart rate, blood pressure, blood glucose level, and blood flow to the heart and lungs. Epinephrine and norepinephrine also stimulate enlargement of the bronchial tubes and dilation of the pupils.

Adrenal Cortex

The adrenal cortex responds to adrenocorticotropic (uh-DRE-noh-KOHR-ti-koh-TROH-pik) hormone (ACTH), which is secreted by the anterior pituitary. Stress causes the hypothalamus to secrete ACTH-releasing hormone. ACTH then stimulates the adrenal cortex to produce the steroid hormone cortisol (KOHRT-uh-SAWL) and aldosterone. Cortisol promotes the production of glucose from proteins making usable energy available to cells. Aldosterone (al-DAHS-tuh-ROHN), helps raise blood pressure and volume by stimulating salt and water retention by the kidneys.

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