Fig. 1

Fluid filtration according to the classic Starling model. Fluid filtration is mainly guided by the difference between the hydrostatic gradient [hydrostatic capillary pressure (Hcp) and hydrostatic interstitial pressure (Hip) multiplied by K (permeability index)] and oncotic gradient [oncotic capillary pressure (Ocp) and oncotic interstitial pressure (Oip) multiplied by δ (reflection coefficient)]. The interstitial space (IS) is considered to have a low protein concentration [Ptn]. Residual fluids situated in the IS would return to the plasma compartment guided mainly by Ocp; little fluid would return through the lymph vessels