Final answer:
The tiny blood vessels surrounding the alveoli in the lungs are called capillaries, which facilitate the exchange of oxygen and carbon dioxide between the lungs and blood.
Step-by-step explanation:
The tiny blood vessels that surround the alveoli in the lungs are called capillaries. Capillaries are the smallest and thinnest blood vessels in the body, and they connect the smallest branches of arteries and veins. Their thin walls allow for the exchange of gases, such as oxygen and carbon dioxide, between the blood and the tissues. The alveoli are thin-walled structures where gas exchange occurs, as they are in direct contact with these capillaries. This allows oxygen to diffuse from the alveoli into the blood and carbon dioxide to move from the blood into the alveoli to be exhaled. The large surface area of the alveoli, estimated at around 100 m², is akin to half a tennis court, facilitating efficient gas exchange.