Adrenals - The Cortex - Aldosterone

This is a 'mineralocorticoid' (a cortical hormone that regulates salt balance) and has a narrower range of action than cortisol. It acts principally to maintain blood pressure.

Specifically it causes:

1. Retention of sodium and water by the kidney, resulting in a rise in blood pressure.
2. Excretion of potassium and hydrogen ions by the kidney.

Aldosterone is produced in the last step of a pathway initiated by a fall in blood pressure. This system is known as the renin-angiotensin system. Low blood pressure causes a release of the enzyme renin from the kidney. Renin converts angiotensinogen to angiotensin I. Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II in the lung. Angiotensin II travels in the bloodstream to the adrenal cortex causing aldosterone release from the zona glomerulosa. The release of aldosterone then increases blood pressure.

Diagram illustrating the control of aldosterone production - click to enlarge

Aldosterone release is also stimulated by high potassium levels and to a more limited extent, by ACTH from the pituitary.