How does angiotensin II affect extracellular fluid volume?

• A. Inhibits thirst and urine production
• B. Triggers secretion of aldosterone
• C. Decreases sodium retention
• D. Increases urine output

Answer: (B)

Angiotensin II plays a significant role in regulating extracellular fluid volume, primarily through its effect on the secretion of aldosterone. When angiotensin II levels increase, they stimulate the adrenal cortex to release aldosterone, a hormone that promotes sodium reabsorption in the kidneys. This sodium retention leads to an increase in extracellular fluid volume because water follows sodium by osmosis. As a result, the overall blood volume increases, enhancing blood pressure and improving tissue perfusion, which are critical for maintaining homeostasis in the body.

This action of aldosterone, induced by angiotensin II, is essential during states of low blood pressure or volume depletion, ensuring that the body retains necessary fluids and electrolytes. Hence, the choice indicating that angiotensin II triggers the secretion of aldosterone is accurate, as it directly relates to how angiotensin II manages fluid balance through hormonal regulation.