What does microcirculation generate in terms of interstitial fluid?

• A. More interstitial fluid due to diffusion than ultrafiltration
• B. More interstitial fluid due to ultrafiltration than diffusion
• C. No interstitial fluid production
• D. Interstitial fluid is decreased

Answer: (A)

The key idea is how fluid moves across capillary walls in the microcirculation. Fluid exchange is driven mainly by ultrafiltration, a bulk flow pushed out of capillaries by capillary hydrostatic pressure, which creates interstitial fluid. Diffusion handles the movement of solutes and water at the molecular level, not the large-scale production of interstitial fluid. So, more interstitial fluid is generated by this outward, filtration-driven process than by diffusion.