Capillary exchange drives tissue fluid formation

Steps:

• Recall tissue fluid forms via filtration at capillary arterial end, where hydrostatic pressure pushes fluid out.
• Note water potential gradient: higher in tissues (fewer solutes) than plasma, but hydrostatic pressure dominates outflow.
• Compare labels to standard model: hydrostatic > osmotic at start, reverse at end.
• Identify correct label as the one matching tissue water potential.

Why C is correct:

• Water potential is higher in tissues than capillary plasma due to lower solute concentration (no plasma proteins), per water potential definition ψ = ψ_s + ψ_p, enabling net filtration.

Why the others are wrong:

• A: Hydrostatic pressure decreases along capillary, not increases.
• B: Red blood cells stay in capillaries; only water and small solutes form tissue fluid.
• D: Less blood volume returns to veins due to filtration loss, balanced by lymph.

Final answer: C