adrenals

Adrenals, or adrenal glands, are small endocrine glands located on top of each kidney. Each gland consists of two distinct regions: the outer cortex and the inner medulla, with separate embryological origins and functions.

The adrenal cortex produces corticosteroids, including mineralocorticoids (primarily aldosterone), glucocorticoids (primarily cortisol), and adrenal androgens. Aldosterone helps regulate electrolyte balance and blood pressure through the renin-angiotensin system. Cortisol influences metabolism, immune function, and the body’s response to stress. Adrenal androgens contribute to sex characteristics and are modest in adults.

The adrenal medulla produces catecholamines, mainly epinephrine and norepinephrine, which mediate the fight-or-flight response. These hormones increase heart rate and blood pressure, dilate airways, and mobilize energy stores.

Regulation of adrenal activity involves multiple pathways. The hypothalamic-pituitary-adrenal axis coordinates cortisol production: the hypothalamus releases corticotropin-releasing hormone, stimulating the pituitary to secrete adrenocorticotropic hormone, which prompts the cortex to synthesize cortisol and other steroids. Aldosterone secretion is primarily regulated by the renin-angiotensin-aldosterone system and plasma potassium levels. The adrenal medulla is controlled by sympathetic nervous system input.

Clinical notes include disorders such as adrenal insufficiency (primary Addison's disease or secondary pituitary failure), Cushing syndrome from excess cortisol, primary hyperaldosteronism causing hypertension and hypokalemia, and pheochromocytoma, a catecholamine-secreting tumor. Management varies and may involve hormone replacement, surgical removal of tumors, or medications to modulate hormone production or action.