Ivt

Ultrafiltration

Blood

90 mm Hg

Dialysate

-150 mm Hg

Dialysis membrane

FIGURE 6-1 (Continued)

B, During hemodialysis water moves from blood to dialysate driven by a hydrostatic pressure gradient between the blood and dialysate compartments, a process referred to as ultrafiltration. The rate of ultrafiltration is determined by the magnitude of this pressure gradient. Movement of water tends to drag solute across the membrane, a process referred to as convective transport or solvent drag. The contribution of convective transport to total solute transport is only significant for average-to-high molecular weight solutes because they tend to have a smaller diffusive flux.

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