In the systemic circulation, which segment has the highest vascular resistance?

• A. Vena cava
• B. Aorta
• C. Capillaries
• D. Arterioles

Answer: (D)

The segment that contributes most to systemic vascular resistance is the arterioles. These small, muscular vessels sit right before the capillary beds and contain a lot of smooth muscle that can constrict or dilate in response to neural, hormonal, and local metabolic signals. Because resistance depends extremely strongly on radius (small changes in radius cause large changes in resistance), the arterioles’ ability to adjust their diameter makes them the major determinant of total peripheral resistance and thus the pressure drop across the systemic circulation.

Capillaries, while numerous, are arranged in parallel across the network, so their combined effect lowers the overall resistance despite each one having a small radius. The vena cava are large, compliant veins with relatively low resistance and function mainly as capacitance vessels, not as the primary resistance sites. The aorta is a large-diameter elastic vessel with high conductance and likewise presents low resistance compared with the arterioles.