Final answer:
Hemodialysis involves the removal of small waste molecules like urea from the blood across a semipermeable membrane within a dialysis machine by creating a concentration gradient where the dialysate in the lower compartment has a lower concentration of waste than the blood in the upper compartment, facilitating diffusion.
Step-by-step explanation:
The process of hemodialysis involves the removal of waste products, such as urea, from the blood of patients with kidney failure. In a dialysis machine, the patient's blood passes through a semipermeable membrane, which allows certain solutes to pass through while retaining larger components like red and white blood cells. Dialysate, a specialized solution that runs opposite to the flow of blood, is designed to facilitate the movement of wastes by diffusion.
In the context of the question about the internal diameter of hemoconcentrators and the removal of solutes of certain sizes, it's important to know how the concentration gradient influences this process. For successful hemodialysis, the upper component containing the patient's blood typically has a higher concentration of solutes such as urea compared to the lower compartment with the dialysate. This concentration gradient allows urea to diffuse down its concentration gradient into the dialysate, effectively removing it from the blood.
The semi-permeable membrane of the hemoconcentrator is designed not to allow larger molecules or complexes, such as those above certain Dalton thresholds, to pass through. This ensures that only smaller waste molecules and excess water diffuse into the dialysate, leaving the necessary blood components intact within the bloodstream.