Chapter 19: The Adrenal Medulla & Adrenal Cortex

The adrenal medulla acts as a modified sympathetic ganglion, secreting catecholamines such as epinephrine and norepinephrine to coordinate the body’s systemic response to acute stress through interactions with alpha and beta-adrenergic receptors. In contrast, the adrenal cortex is organized into three specialized zones that convert cholesterol into vital steroid hormones: the zona glomerulosa produces the mineralocorticoid aldosterone, the zona fasciculata primarily secretes the glucocorticoid cortisol, and the zona reticularis synthesizes adrenal androgens. The discussion details the complex enzymatic pathways, primarily involving cytochrome P450 enzymes, and the crucial transport roles of plasma proteins like corticosteroid-binding globulin. A significant portion of the material is dedicated to the regulation of these hormones, highlighting the hypothalamic-pituitary-adrenal axis for cortisol and the renin-angiotensin system for aldosterone. The physiological impact of these hormones is vast, ranging from the maintenance of electrolyte balance and blood pressure to the management of carbohydrate metabolism and immune suppression. The chapter also provides deep clinical insights into endocrine disorders, contrasting the symptoms of hormone excess—such as the muscle wasting and fat redistribution in Cushing syndrome—with the consequences of hormone deficiency, exemplified by the hypotension and metabolic crises found in Addison disease. Additionally, it examines the genetic basis of enzyme deficiencies that cause congenital adrenal hyperplasia and the unique "escape" mechanisms the body employs to manage mineralocorticoid levels.