What is the role of the renin-aldosterone system?

• A. It causes vasodilation
• B. It regulates BP and fluid balance by promoting sodium retention and increasing blood volume.
• C. It decreases urinary sodium reabsorption
• D. It reduces thirst

Answer: (B)

The renin-angiotensin-aldosterone system works to keep blood pressure and fluid balance stable. When kidney perfusion or sodium delivery drops, renin is released and triggers a cascade that produces angiotensin II. Angiotensin II causes vasoconstriction and stimulates aldosterone release. Aldosterone acts on the distal nephron to increase sodium reabsorption, so water follows by osmosis, expanding blood volume. The overall effect is higher blood pressure and preserved circulating volume. It does not promote vasodilation or decrease sodium reabsorption; while it can influence thirst, the main role is regulation of BP and fluid balance through sodium retention and volume expansion.