In dialysis, if the blood has a higher solute concentration than the dialysate, diffusion causes solutes to move in which direction?

• A. From the dialysate to blood
• B. Neither
• C. Both
• D. From blood to dialysate

Answer: (D)

Diffusion relies on a concentration gradient, moving solutes from where they are more concentrated to where they are less concentrated. In a dialysis setting, the dialyzer membrane is permeable to small solutes but not to large proteins. When the blood has a higher solute concentration than the dialysate, those solutes diffuse across the membrane into the dialysate, helping to cleanse the blood. If the dialysate had a higher concentration, the diffusion would reverse. So the movement occurs from blood to dialysate.