Question

Movement of urea from blood to dialysing fluid occurs due to

• A. temperature difference
• B. concentration gradient
• C. both a and b
• D. none of the above

Answer 1

The correct option is B concentration gradient

Patients suffering from kidney failure can undergo haemodialysis to remove wastes from the body.
Hemodialysis unit has a coiled cellophane tube (dialyzer) with the dialysing fluid. Dialysing fluid is similar to blood plasma in composition except for the nitrogenous waste.
Patient’s blood is pumped into the cellophane tube. Cellophane tubes are made of porous membranes which are semi permeable in nature. Blood and dialysing fluid are circulated across the membrane. Due to the concentration gradient between blood and dialysing fluid (lacks urea and other nitrogenous waste), nitrogenous wastes move from plasma to dialysing fluid. The purified blood is transferred back to the patient's body.

Tubular portion of the dialyser