Figure 1
The revised Starling principle and equation. Hydrostatic pressures are higher within the vascular lumen (P v ) than within the interstitium (P i ), favouring outward fluid filtration. The endothelial surface layer (ESL) is formed by the endothelial glycocalyx (EG), which binds plasma proteins and excludes them from the subglycocalyx layer (S). This forms an oncotic gradient from the low protein concentration of the subglycocalyx (IIs) to the intravascular space (IIv). This gradient opposes outward fluid filtration. Net transcapillary flow (J v )—dashed arrows—can be expressed using the revised Starling equation: J v  = K f ([P v  − P i ] − σ[π v  − π s ]), where K f is the filtration coefficient and σ is the reflection coefficient (the degree to which the tendency of a macromolecule to cross the endothelial barrier is resisted). EC, endothelial cell. NB: Reproduced with permission from reference [2].