zona glomerulosa

The adrenal cortex is divided into three histologically and functionally distinct zones (from outer to inner): zona glomerulosa, zona fasciculata, and zona reticularis (mnemonic: GFR - Glomerulosa/Fasciculata/Reticularis corresponds to Salt/Sugar/Sex hormones). The zona glomerulosa consists of small, tightly packed cells arranged in oval clusters (glomeruli-like structures) just beneath the adrenal capsule. It expresses the enzyme aldosterone synthase (CYP11B2), which is unique to this zone and allows conversion of corticosterone to aldosterone. Aldosterone acts on the principal cells of the renal collecting ducts to increase sodium reabsorption and potassium/hydrogen secretion, thereby regulating blood pressure, fluid volume, and electrolyte balance. Regulation of the zona glomerulosa is primarily via the renin-angiotensin-aldosterone system: decreased renal perfusion triggers renin release from juxtaglomerular cells, generating angiotensin II, which stimulates aldosterone secretion. Hyperkalemia also directly stimulates aldosterone release. Clinically, zona glomerulosa dysfunction is relevant in conditions such as primary hyperaldosteronism (Conn syndrome), often due to an adenoma or bilateral hyperplasia of this zone, causing hypertension, hypokalemia, and metabolic alkalosis with suppressed renin. Congenital adrenal hyperplasia (e.g., 21-hydroxylase deficiency) can also affect mineralocorticoid production depending on the enzyme deficiency, since 21-hydroxylase is needed in this zone for aldosterone synthesis pathway as well as glucocorticoid pathway in zona fasciculata.