Chapter 50: The Adrenal Gland

The adrenal cortex, comprising three functional zones, synthesizes steroid hormones through a series of enzymatic reactions beginning with cholesterol uptake and conversion. The zona glomerulosa produces mineralocorticoids, particularly aldosterone, which regulates sodium reabsorption and potassium excretion in the kidney to maintain blood pressure and osmotic homeostasis. The zona fasciculata generates glucocorticoids, primarily cortisol, which promote gluconeogenesis, inhibit inflammation, and mediate the body's response to physical and psychological stress through hypothalamic-pituitary-adrenal axis signaling. The zona reticularis secretes androgens that contribute to sexual development and maintenance. The adrenal medulla, derived from neural crest tissue, functions as a neuroendocrine organ producing catecholamines—epinephrine and norepinephrine—which increase heart rate, blood pressure, and metabolic rate during sympathetic nervous system activation. The chapter details the synthesis pathways of steroid hormones, involving cytochrome P450 enzymes and the role of adrenocorticotropic hormone in stimulating cortisol production. Regulation of adrenal function occurs through multiple feedback mechanisms: cortisol provides negative feedback to suppress adrenocorticotropic hormone release, while the renin-angiotensin-aldosterone system controls mineralocorticoid secretion in response to blood pressure and electrolyte changes. Clinical pathologies are discussed, including Addison's disease resulting from adrenal insufficiency, Cushing's syndrome from excessive glucocorticoid exposure, primary hyperaldosteronism from aldosterone excess, and pheochromocytoma from catecholamine-secreting tumors. The chapter integrates molecular mechanisms with systemic effects to illustrate how adrenal hormones coordinate essential physiological functions across multiple organ systems.