However they are the principal route of transport for large molecular weight solutes. Diffusion limited solute flux. If the permeability is low, there is no great change in Cp-Ct as the blood passes through an individual capillary. So solute flux is limited by the diffusive capacity of the molecule through the membrane. In this case solute flux is diffusion limited.
Water flows across the capillary wall.
The rate of flow of water depends on the balance of pressures inside and outside the capillaries, and their permeability to water. This relationship was first pointed out by Ernest Starling in 1896, at University College London. Oncotic reflection coefficient. If the molecule is larger than the pore then it will have a reflection coefficient of 1.0. As water moves through the pores it will drag solutes with it.