Adrenal Hormone Physiology

The adrenal glands sit above the kidneys, but their cortical hormones affect nearly every organ system. The cortex has three functionally distinct layers: - Zona glomerulosa produces aldosterone, which retains sodium and water while promoting potassium excretion in the distal nephron. - Zona fasciculata produces cortisol, which supports vascular responsiveness to catecholamines, helps maintain blood glucose during fasting or illness, and regulates immune and inflammatory activity. - Zona reticularis produces adrenal androgens. The adrenal medulla is separate from the cortex and releases catecholamines. Cortisol from the cortex helps blood vessels respond appropriately to those catecholamines. Without enough cortisol, epinephrine and norepinephrine may be present, yet vascular tone can still fail. This is one reason severe cortisol deficiency can produce hypotension that responds poorly to fluids or vasopressors alone. Aldosterone is controlled mainly by the renin-angiotensin-aldosterone system and serum potassium. Cortisol is controlled through the hypothalamic-pituitary-adrenal axis: hypothalamic corticotropin-releasing hormone stimulates pituitary ACTH release, and ACTH stimulates the adrenal cortex to produce cortisol. Rising cortisol normally suppresses further ACTH release through negative feedback.