Carrier-mediated transport particle

A - transcellular passive diffusion B - carrier mediated transport C - transcellular diffusion by endocytosis D - paracellular passive diffusion E - transcellular diffusion by lipid particles F - paracellular passive diffusion via modulation of T.J. 

Profiles in which this latter profile can be found are electrodialysis, per/aporation, gas separation, dialysis, diffusion dialysis, facilitated transport or carrier mediated transport and membrane contactors. The extent of the boundary layer resistance varies from process to process and even for a specific process it is quite a lot dependent on application. Table Vn.2 summarises the causes and consequences of concentration polarisation in various membrane processes. The effect of concentration polarisation is very severe in microfiltration and ultrafiltration both because the fluxes (J) are high and the mass transfer coefficients k (= EV8) are low as a result of the low diffusion coefficients of macromolecuiar solutes and of small particles, colloids and emulsions. Thus, the diffusion coefficients of macromolecules are of the order of lO ° to 10 m /s or less. The effect is less severe in reverse osmosis both because the flux is lower and the mass transfer coefficient is higher. The diffusion coefficients of low molecular weight solutes are roughly of the order of 10 m /s. In gas separation and pervaporation the effect of concentration polarisation is low or can be neglected. The flux is low and the mass transfer coefficient high in gas separation (the diffusion coefficients of gas molecules are of the... 

In addition to passive diffusion, channels, and carrier proteins, a fourth mechanism of breaching biological membranes is provided by vesicle-mediated transport, which can also be used for drug delivery. Endocytosis refers to the uptake of cell surface constituents by the formation of vesicles from the plasma membrane. This process can be subclassified into phagocytosis, the engulfment of particles, and pinocytosis, the engulfment of fluid. 

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