Which vessels are responsible for exchanging nutrients and oxygen with cells?

The correct answer is capillaries because these tiny blood vessels are uniquely designed for the critical function of nutrient and oxygen exchange between the blood and the body's cells. Capillaries have very thin walls, consisting of just a single layer of endothelial cells, which facilitates the diffusion of oxygen, carbon dioxide, nutrients, and waste products. This makes them ideal for connecting the arterial and venous systems and ensures that essential substances can easily move in and out of the bloodstream to meet the metabolic needs of tissues.

In contrast, arteries primarily transport oxygen-rich blood away from the heart to the various tissues; they have thicker, muscular walls to accommodate higher pressure. Veins are responsible for carrying deoxygenated blood back to the heart, and while they may have valves to prevent backflow, they are not directly involved in nutrient and oxygen exchange. Venules, which are small vessels that connect capillaries to veins, play a role in collecting deoxygenated blood from the capillaries to transport it to the veins but do not engage in the direct exchange of nutrients and oxygen themselves. Thus, capillaries are specifically structured for this essential exchange process.