What is the microscopic vessel through which exchanges take place between blood and cells?

The microscopic vessel that facilitates the exchange of substances between blood and cells is the capillary. Capillaries have thin walls composed of a single layer of endothelial cells, allowing for efficient diffusion of oxygen, carbon dioxide, nutrients, and waste products. Their small diameter and extensive networks throughout tissues enable close proximity to cells, promoting optimal exchange processes.

In contrast, arterioles are small arteries that regulate blood flow into capillaries but do not directly participate in exchange. Venules, on the other hand, are small veins that collect blood from capillaries but are primarily involved in transporting blood back to the heart, rather than in the exchange itself. The aorta, as the main artery of the body, carries oxygenated blood away from the heart and is not involved in exchange processes at the cellular level. Thus, capillaries are uniquely suited for this critical function in the circulatory system.