Final answer:
The capillaries have the greatest total cross-sectional area compared to other blood vessels, due to their expansive and numerous nature, despite each being very narrow.
Step-by-step explanation:
The blood vessels with the greatest total cross-sectional area in the body are the capillaries. These tiny blood vessels form expansive networks called capillary beds. While each individual capillary is quite small and narrow, allowing only one red blood cell through at a time, there are so many capillaries that their total cross-sectional area far surpasses that of other blood vessels.
Arteries and arterioles, in contrast, have smaller total cross-sectional areas but thicker walls to handle the higher pressure of blood pumped from the heart. The arterioles, in particular, are known as resistance vessels because they offer the greatest resistance to blood flow, influencing blood pressure significantly through vasodilation and vasoconstriction mechanisms. However, as vast as the network of capillaries is, they collectively provide the largest area through which blood flows, making them essential for efficient exchange of substances between blood and tissues at a micro-environmental level.