Which component of the RAAS primarily increases systemic vascular resistance?

• A. Aldosterone
• B. Renin
• C. Bradykinin
• D. Angiotensin II

Answer: (D)

The main idea is that a specific RAAS component directly controls vascular tone to raise systemic vascular resistance. Angiotensin II acts on AT1 receptors in vascular smooth muscle, causing contraction by increasing intracellular calcium. This direct vasoconstriction narrows arterioles and raises systemic vascular resistance, which increases blood pressure. It also triggers aldosterone release, which expands blood volume, but the immediate rise in resistance comes from the vasoconstrictive effect. Bradykinin promotes vasodilation, reducing resistance, and renin initiates the cascade rather than causing constriction by itself. Aldosterone mainly affects volume rather than immediate vessel tone. Therefore, Angiotensin II is the primary driver of increased systemic vascular resistance.