What are the smallest blood vessels called?

Capillaries are the smallest blood vessels in the circulatory system. They serve as the primary sites for the exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and surrounding tissues. Their thin walls, composed of a single layer of endothelial cells, facilitate this exchange, allowing for efficient transfer of substances at the cellular level.

Veins and arteries are larger vessels that play different roles in the circulatory system, with veins carrying blood back to the heart and arteries transporting blood away from the heart. Arterioles are smaller branches of arteries that lead into capillaries but are still larger than capillaries themselves. Therefore, the correct identification of capillaries as the smallest blood vessels highlights their crucial role in microcirculation and tissue perfusion.