Arterioles are best described as?

• A. The smallest and thinnest arteries that regulate blood pressure and flow
• B. The largest arteries
• C. Venules that drain capillaries
• D. Capillaries that exchange gases

Answer: (A)

The key idea is that arterioles regulate how much blood reaches tissues by changing resistance. They are the smallest arteries equipped with a substantial smooth muscle layer that can constrict or dilate in response to nerves, hormones, and local tissue factors. This ability to tighten or relax controls both tissue perfusion and overall blood pressure, which is why arterioles are described as the small arteries that regulate blood pressure and flow.

The other vessel types don’t fit this role: the largest arteries carry blood at high pressure from the heart; venules drain blood from capillaries; capillaries are the sites of gas and nutrient exchange.