In the lungs, which type of blood vessel forms the dense network that surrounds (covers) the alveoli to allow rapid gas exchange?

• A. Venules
• B. Arterioles
• C. Elastic arteries
• D. Capillaries

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the function of alveoli in the lungs. Alveoli are tiny air sacs where gas exchange occurs between the air and the blood.
2. Step 2: Recognize that for efficient gas exchange, blood vessels must be very thin-walled and form a dense network around the alveoli to maximize surface area contact.
3. Step 3: Identify the types of blood vessels: venules and arterioles are small vessels but do not form the dense network directly surrounding alveoli; elastic arteries are larger vessels that conduct blood away from the heart and are not involved in gas exchange.
4. Step 4: Recall that capillaries are the smallest blood vessels with thin walls, allowing oxygen and carbon dioxide to diffuse easily between the alveoli and the blood.
5. Step 5: Conclude that capillaries form the dense network covering the alveoli, enabling rapid gas exchange due to their thin walls and extensive surface area.