During dialysis, diffusion moves solutes from where to where?

• A. From the dialysate to the blood
• B. From the patient's blood into the dialysate
• C. Equally in both directions
• D. From blood to dialysate

Answer: (B)

Diffusion in dialysis happens because solutes move along their concentration gradient across the dialysis membrane. The blood typically has higher concentrations of waste solutes (like urea and creatinine) than the dialysate, so these small solutes diffuse through the membrane into the dialysate where their concentration is lower. This drives the cleansing of the blood as wastes are carried away with the dialysate flow. In short, solutes move from the blood into the dialysate.