What are the smallest blood vessels in the body?

Capillaries are indeed the smallest blood vessels in the body. They serve a crucial role in the circulatory system by facilitating the exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and the tissues. Their walls are only one cell thick, which allows for this efficient diffusion of substances. Capillaries connect arterioles (small arteries) and venules (small veins), forming an extensive network throughout the body.

In contrast, veins and arteries are larger blood vessels that serve different primary functions. Arteries carry oxygenated blood away from the heart (with the exception of the pulmonary arteries, which carry deoxygenated blood to the lungs), while veins return deoxygenated blood back to the heart. Lymph vessels, although they are part of the circulatory system, are involved in returning lymph (a fluid containing infection-fighting white blood cells) to the bloodstream and are not classified as blood vessels.