Which of the following enhances the exchange of substances between capillary walls and the interstitial spaces?

• A. Continuous tight junctions between endothelial cells
• B. Thick basement membrane
• C. Fenestrations (pores) in capillary endothelial cells
• D. Decreased capillary surface area

Answer: (C)

Verified step by step guidance

1. Understand the function of capillaries: Capillaries are small blood vessels where the exchange of substances (like oxygen, nutrients, and waste products) occurs between the blood and surrounding tissues. Their structure is specialized to facilitate this exchange.
2. Analyze the structural features of capillaries: Capillaries can have different types of endothelial cell arrangements, such as continuous, fenestrated, or sinusoidal. Fenestrations (pores) in endothelial cells are small openings that enhance permeability, allowing substances to pass more easily between the blood and interstitial spaces.
3. Evaluate the role of fenestrations: Fenestrations increase the efficiency of exchange by providing direct pathways for substances to move across the capillary wall. This is particularly important in tissues requiring rapid exchange, such as the kidneys and intestines.
4. Compare fenestrations to other features: Continuous tight junctions limit permeability, thick basement membranes reduce exchange efficiency, and decreased capillary surface area lowers the overall capacity for substance exchange. Fenestrations are uniquely suited to enhance exchange.
5. Conclude why fenestrations are the correct answer: Fenestrations in capillary endothelial cells are specialized adaptations that enhance the exchange of substances by increasing permeability and facilitating movement between the blood and interstitial spaces.