Figure 61

Diffusional and convective flux in hemodialysis. Dialysis is a process whereby the composition of blood is altered by exposing it to dialysate through a semipermeable membrane. Solutes are transported across this membrane by either diffusional or convective flux. A, In diffusive solute transport, solutes cross the dialysis membrane in a direction dictated by the concentration gradient established across the membrane of the hemodialyzer. For example, urea and potassium diffuse from blood to dialysate, whereas bicarbonate diffuses from dialysate to blood. At a given temperature, diffusive transport is directly proportional to both the solute concentration gradient across the membrane and the membrane surface area and inversely proportional to membrane thickness.

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