the osmotic pressure difference. The second Kedem–Katchalsky equation explains the trans endothelial transport of solutes, . The equation The classic Starling equation reads as follows: where: is the trans endothelial solvent filtration volume per second (SI units of m3·s−1). is the net driving force (SI units of Pa = kg·m−1·s−2, often expressed as mmHg), is the capillary hydrostatic pressure is the interstitial hydrostatic pressure is the plasma protein oncotic pressure is the interstitial oncotic pressure is the hydraulic conductivity of the membrane (SI units of m2·s·kg−1, equivalent to m·s−1·mmHg−1) is the surface area for filtration (SI units of m2) the product · is defined as the filtration coefficient (SI units of m4·s·kg−1, or equivalently in m3·s−1·mmHg−1) is Staverman's reflection coefficient (adimensional) By convention, outward force is defined as positive, and inward force is defined as negative. If Jv is positive, solvent is leaving the capillary (filtration). If negative, solvent is entering the capillary (absorption). Applying the classic Starling equation, it had long been taught that continuous capillaries filter out fluid in their arteriolar section and reabsorb most of it in their venular section, as shown by the diagram. However, empirical evidence shows that, in most tissues, the flux of the intraluminal fluid of capillaries is continuous and, primarily, effluent. Efflux occurs along the whole length of a capillary. Fluid filtered to the space outside a capillary is mostly returned to the circulation via lymph nodes and the thoracic duct. A mechanism for this phenomenon is the Michel-Weinbaum model, in honour of two scientists who, independently, described the filtration function of the glycocalyx. Briefly, the colloid osmotic pressure πi of the interstitial fluid has been found to have no effect on Jv and the colloid osmotic pressure difference that opposes filtration is now known to be π'p minus the subglycocalyx π, which is close to zero while there is adequate filtration to flush interstitial proteins out of the interendothelial cleft. Consequently, Jv is much less than previously calculated, and the unopposed diffusion of interstitial proteins to the subglycocalyx space if and when filtration falls wipes out the colloid osmotic pressure difference necessary for reabsorption of fluid to the capillary. The revised Starling equation is compatible with the steady-state Starling principle: where: is the trans endothelial solvent filtration volume per second. is the net driving force, is the capillary hydrostatic pressure is the interstitial hydrostatic pressure is the plasma protein oncotic pressure