Which vessel type contributes most to peripheral resistance?

• A. Veins
• B. Arterioles
• C. Capillaries
• D. Venules

Answer: (B)

Peripheral resistance is determined mainly by the arterioles because their small diameter combined with a thick, muscular wall gives them the greatest ability to resist blood flow and actively regulate that resistance. The physics of flow shows resistance rises dramatically as radius decreases (a small drop in radius makes a big jump in resistance), so the narrow, muscular arterioles become the primary site where the body can fine‑tune pressure and flow. Capillaries are tiny as well, but they exist in an enormous parallel network; this arrangement lowers the overall resistance of the capillary bed even though each vessel is small, making their collective effect on total peripheral resistance less than that of arterioles. Veins have a much larger radius and primarily serve as capacitance vessels, storing blood and buffering pressure, so their contribution to resistance is comparatively small. In short, the arterioles’ combination of tiny radius and strong, adjustable muscular control makes them the main determinant of peripheral resistance.