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The adrenal gland is actually two endocrine organs, one wrapped around the other. The outer adrenal cortex secretes many different steroid hormones, including glucocorticoids such as cortisol, mineralocorticoids such as aldosterone, and androgens, chiefly dehydroepiandrosterone (DHEA). The glucocorticoids help to regulate carbohydrate, protein, and fat metabolism. The mineralocorticoids help to regulate Na+ and K+ balance and extracellular fluid volume. The glucocorticoids and mineralocorticoids are essential for survival, but no essential role of adrenal androgens has been determined. The inner adrenal medulla, discussed in Chapter 12, secretes catecholamines (epinephrine, norepinephrine, and dopamine).
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Mainly because of their potent immunosuppressive and anti-inflammatory effects, glucocorticoids are used commonly in pharmacologic doses to treat diseases such as autoimmune disorders. Interestingly, while the deleterious effects of glucocorticoids in states of hypercortisolism and the beneficial effects of their use in pharmacotherapy are rather well understood, the actual role of endogenous glucocorticoids in metabolic homeostasis during times of minimal stress remains somewhat enigmatic.
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The major disorders of the adrenal cortex (Table 21–1) are characterized by excessive or deficient secretion of each type of adrenocortical hormone: hypercortisolism (Cushing syndrome), adrenal insufficiency (Addison disease), hyperaldosteronism (aldosteronism), hypoaldosteronism, and androgen excess.
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Normal Structure & Function of the Adrenal Cortex
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The adrenal glands are paired organs located in the retroperitoneal area near the superior poles of the kidneys (Figure 21–1). They are flattened, crescent-shaped structures, which together normally weigh about 8–10 g. Each is covered by tight fibrous capsules and surrounded by fat. The blood flow to the adrenals is copious.
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Grossly, each gland consists of two concentric layers: The yellow peripheral layer is the adrenal cortex,...