Overview

The adrenal glands are complex polyfunctional organs whose secretions are required for maintenance of life. Without adrenal hormones, deranged electrolyte or carbohydrate metabolism leads to circulatory collapse or hypoglycemic coma and death. The hormones of the outer region, or cortex, are steroids and act at the level of the genome to regulate the expression of genes that govern the operation of fundamental processes in virtually all cells. The inner region, the adrenal medulla, is actually a component of the sympathetic nervous system and participates in the wide array of regulatory responses that are characteristic of that branch of the nervous system. The three major categories of adrenal steroid hormones are mineralocorticoids, whose actions defend the body content of sodium and potassium; glucocorticoids, whose actions affect body fuel metabolism, responses to injury, and general cell function; and androgens, whose actions are similar to the hormone of the male gonad. We focus on actions of these hormones on the limited number of processes that are most thoroughly studied, but the reader should keep in mind that adrenal cortical hormones directly or indirectly affect almost every physiologic process and hence are central to the maintenance of homeostasis. Secretion of mineralocor-ticoids is primarily controlled by the kidney through secretion of renin and the consequent production of angiotensin. Secretion of glucocorticoids and androgens is controlled by the anterior pituitary gland through secretion of ACTH.

The adrenal cortex and the medulla often behave as a functional unit and together confer a remarkable capacity to cope with changes in the internal or external environment. Fast-acting medullary hormones are signals for physiologic adjustments, and slower acting cortical hormones maintain or increase sensitivity of tissues to medullary hormones and other signals; they also maintain or enhance the capacity of tissues to respond to such signals. The cortical hormones thus tend to be modulators rather than initiators of responses.

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