The lungs consist of many small air sacs and blood vessels, which greatly increase surface area and improve the transfer of substances through their walls. The structures in the digestive system most similar in function to these air sacs and capillaries are the __________.

• A. esophagus
• B. gastric glands
• C. cecum
• D. sphincters
• E. villi and microvilli

Answer: (E)

Verified step by step guidance

1. Understand the function of the lungs: The lungs contain alveoli, which are small air sacs that increase the surface area for gas exchange. This is crucial for efficient transfer of oxygen and carbon dioxide between the air and the blood.
2. Identify the structures in the digestive system that have a similar function: In the digestive system, the goal is to maximize the absorption of nutrients. Structures that increase surface area for absorption are key.
3. Learn about villi and microvilli: Villi are small, finger-like projections in the small intestine that increase the surface area for nutrient absorption. Microvilli are even smaller projections on the villi that further increase the surface area.
4. Compare the functions: Just like alveoli in the lungs, villi and microvilli in the small intestine increase the surface area to enhance the transfer of substances—in this case, nutrients from the digestive tract into the bloodstream.
5. Conclude the comparison: The villi and microvilli in the digestive system are most similar in function to the alveoli and capillaries in the lungs because they both serve to increase surface area for efficient transfer of substances.