Why urea passes through the dialysis tubing into fluid?

Urea passes through the dialysis tubing into fluid due to the process of diffusion. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. In the case of dialysis, the urea concentration is higher in the blood than in the dialysis fluid, so urea molecules move down the concentration gradient and into the dialysis fluid.

The dialysis tubing is made of a semipermeable membrane that allows small molecules like urea to pass through, while blocking larger molecules like proteins. This allows the urea to be removed from the blood without removing other important substances.

The rate of diffusion depends on a number of factors, including the concentration gradient, the temperature, and the surface area of the membrane. In dialysis, the concentration gradient is created by the difference in urea concentration between the blood and the dialysis fluid. The temperature is controlled to keep the patient comfortable, and the surface area of the membrane is maximized by using a large number of small tubes.

By using these principles, dialysis can effectively remove urea and other waste products from the blood of patients with kidney failure.