What are the smallest blood vessels known as?

The smallest blood vessels in the circulatory system are referred to as capillaries. These tiny vessels play a crucial role in the exchange of substances between the blood and tissues. Their thin walls consist of a single layer of endothelial cells, which allows for efficient transfer of oxygen, carbon dioxide, nutrients, and waste products. The vast network of capillaries ensures that blood can reach nearly every cell in the body, facilitating essential physiological processes.

While arteries and arterioles are important for transporting blood away from the heart, and veins carry blood back to the heart, they are larger in diameter than capillaries. Capillaries represent the transition between arterioles and venules, where the actual exchange of materials takes place—a key function in maintaining homeostasis within the body.