The surface of an alveolus in a mammal is well supplied with tiny blood vessels known as
- arterioles
- venules
- arteries
-
capillaries
The correct answer is: D
Explanation
The tiny blood vessels found on the surface of the alveolus are called capillaries. Capillaries are so small that red blood cells can only pass through them one at a time.
How capillaries work
- Capillaries are part of a network of arteries and veins that move blood throughout the body.
- The pulmonary artery branches off to deliver blood to the capillaries that surround the alveoli.
- The blood in the capillaries is low in oxygen and high in carbon dioxide.
- Oxygen moves from the air in the alveoli into the blood in the capillaries.
- Carbon dioxide moves from the blood in the capillaries into the air in the alveoli.