Which statement about arteries and arterioles is true?

• A. Arteries are thick-walled, elastic conduits that carry low-pressure blood.
• B. Arterioles regulate gas exchange in the lungs.
• C. Veins have thick muscular walls that regulate systemic resistance.
• D. Arteries conduct high-pressure blood; arterioles regulate systemic vascular resistance and local blood flow.

Answer: (D)

Understanding how arteries and arterioles handle blood pressure and flow helps explain why this statement is true. Arteries are thick-walled and elastic to withstand the high pressure generated by the heart as blood is ejected; they serve as conduits carrying blood away from the heart under substantial pressure. Arterioles are much smaller vessels with more smooth muscle in their walls; by constricting or dilating, they regulate diameter and thus control resistance to flow. This regulation of resistance by arterioles is what primarily determines systemic vascular resistance and how much blood reaches different tissues at any given moment. Gas exchange happens mainly at the capillaries in the lungs, not at arterioles, and veins have thinner walls and serve as capacitance vessels rather than primary regulators of systemic resistance.