aldosterone in RAAS

Aldosterone is the “salt-saving” final step of the blood-pressure cascade. After the system has sensed low pressure and sent its chemical signals, aldosterone is the hormone that actually carries out the order at the kidney: keep sodium in, and water will follow.

It is a steroid hormone made in the outermost layer of the adrenal cortex (the zona glomerulosa). Within the renin-angiotensin-aldosterone system its release is driven mainly by angiotensin II, and separately by a high blood-potassium level. Acting on mineralocorticoid receptors in the kidney’s distal tubule and collecting duct, it increases the number and activity of sodium channels and pumps, so more sodium is reabsorbed into the blood and more potassium and acid are excreted. Because sodium pulls water with it, blood volume and pressure rise.

This is the “aldosterone” you meet specifically as the effector arm of the system, distinct from aldosterone studied as a general adrenal steroid. Too much of it — for example from an adrenal tumor (primary aldosteronism) — causes hard-to-control high blood pressure with low potassium, which is why aldosterone-blocking drugs such as spironolactone are valuable treatments.