CEA Nursing Practice Exam

What concept explains the use of hemodialysis for cleaning blood?

1. Blood forced across a filter under pressure

2. Blood cleaned by diffusing across a semipermeable membrane

3. Water drawn to dirty blood to dilute waste

4. None of these are correct

The correct answer is: Blood cleaned by diffusing across a semipermeable membrane

The use of hemodialysis for cleaning blood is fundamentally based on the principle of diffusion across a semipermeable membrane. In this process, blood is drawn from the patient and circulated through a dialyzer, which contains a semipermeable membrane. This membrane allows smaller waste molecules, such as urea and creatinine, to pass through while retaining larger molecules such as proteins and blood cells. The dialysate, a special fluid, is present on one side of this membrane and has a lower concentration of waste products than the blood. As a result, substances in the blood diffuse through the membrane into the dialysate, effectively removing these harmful waste products from the blood. This process is driven by the concentration gradient, where molecules move from an area of higher concentration (the blood) to an area of lower concentration (the dialysate). This diffusion process is essential in treating patients with kidney failure, as it mimics the natural function of healthy kidneys, which would normally filter and cleanse the blood of toxins and excess substances.