What is the primary function of angiotensin II?

The primary function of angiotensin II is to cause vasoconstriction and increase blood pressure. It plays a pivotal role in the body's renin-angiotensin-aldosterone system (RAAS), which is crucial for regulating blood pressure and fluid balance. When blood pressure drops, the kidneys release renin, which converts angiotensinogen into angiotensin I. Angiotensin I is then converted to angiotensin II by the enzyme ACE (angiotensin-converting enzyme).

Once formed, angiotensin II has several critical effects: it constricts blood vessels, leading to increased vascular resistance and, consequently, elevated blood pressure. Additionally, it stimulates the release of aldosterone from the adrenal glands, which promotes sodium and water retention, further increasing blood volume and pressure.

While vasodilation and decreased blood pressure are contrary to the effects of angiotensin II, other choices related to stimulating aldosterone secretion and enhancing renal blood flow, while true to some extent, do not capture the immediate and primary action of angiotensin II, which is primarily vasoconstriction and raising blood pressure.