What is the primary mechanism by which PD removes waste products from the body?

• A. Osmosis only without diffusion
• B. Active transport of solutes via peritoneal enzymes
• C. Diffusion of solutes and osmosis of water across the peritoneal membrane, using dialysate in the peritoneal cavity.
• D. Filtration by renal-like nephrons

Answer: (C)

In peritoneal dialysis, waste removal happens mainly through diffusion of small solutes and osmosis of water across the peritoneal membrane, using dialysate placed in the abdominal cavity. Small waste molecules like urea and creatinine move from the blood (where their concentration is higher) into the dialysate, following the concentration gradient. At the same time, water is drawn from blood into the dialysate by an osmotic gradient created primarily by the glucose in the dialysate (or other osmotic agents), pulling excess fluid with it. The peritoneal membrane acts as a semipermeable barrier, enabling these two processes to clear waste and remove fluid. This is distinct from active transport or renal-like filtration, which do not occur in peritoneal dialysis.