Which hormone system regulates blood pressure and sodium balance via angiotensin II and aldosterone?

• A. Sympathetic nervous system
• B. Renin–angiotensin–aldosterone system
• C. Antidiuretic hormone system
• D. Endothelin pathway

Answer: (B)

The regulation of blood pressure and sodium balance is governed by the renin–angiotensin–aldosterone system. When the kidneys sense low blood pressure or reduced sodium delivery, they release renin. Renin converts angiotensinogen to angiotensin I, which is transformed by ACE into angiotensin II. Angiotensin II narrows blood vessels and stimulates the adrenal cortex to release aldosterone. Aldosterone acts on the distal nephron to reabsorb sodium (and water follows), increasing blood volume and pressure. Angiotensin II also reinforces the pressure-restoring response by promoting other water-conserving signals. As pressure and sodium balance return to normal, renin release decreases, dialing the system back.

Other pathways exist, but they don’t form this same sodium-balancing loop. The sympathetic nervous system can raise blood pressure through neural signals but doesn’t use angiotensin II and aldosterone to regulate sodium balance. The antidiuretic hormone system centers on water reabsorption via vasopressin, not the aldosterone-driven sodium reabsorption. The endothelin pathway involves a different vasoconstrictor system and isn’t the primary mechanism that links renin, angiotensin II, and aldosterone to regulate sodium and blood pressure.