What is the tiniest blood vessel?

The tiniest blood vessel is called a capillary. Capillaries are microscopic blood vessels that form networks to connect arterioles and venules in order to facilitate the exchange of oxygen and carbon dioxide between the blood and the tissues. Capillaries have thin, single-layered walls which enable an efficient exchange of small molecules and substances like water, oxygen, carbon dioxide, glucose, and waste products through the blood-tissue barrier. The endothelial cells that line the walls of capillaries play a crucial role in regulating this exchange and maintaining the integrity of the circulatory system.