In Conn's syndrome, the aldosterone-producing tumor is located in which adrenal cortex zone?

• A. Zona fasciculata
• B. Zona glomerulosa
• C. Zona reticularis
• D. Adrenal medulla

Answer: (B)

Aldosterone comes from the zona glomerulosa, the outer layer of the adrenal cortex. This zone specializes in mineralocorticoids, with aldosterone driving sodium reabsorption and potassium excretion in the distal nephron. In Conn's syndrome, an aldosterone-secreting tumor arises in this layer, causing autonomous aldosterone production that expands extracellular fluid and raises blood pressure, while promoting potassium loss and metabolic alkalosis. The other adrenal zones produce different steroids—fasciculata makes cortisol and some androgens, reticularis makes androgens, and the adrenal medulla makes catecholamines—so they are not the source of the aldosterone excess seen in Conn's syndrome.