Which substance diffuses from the patient's blood during dialysis?

During dialysis, urea is a waste product that diffuses from the patient's blood into the dialysis solution, or dialysate. Urea is a nitrogenous waste formed from the breakdown of proteins in the body and is typically cleared from the blood through the kidneys in healthy individuals. However, patients with kidney failure have impaired kidney function, making dialysis necessary to effectively remove urea and other waste products.

The process of dialysis relies on the principle of diffusion, where solutes move from an area of higher concentration, such as the blood, to an area of lower concentration, such as the dialysate. This allows for the removal of urea from the blood, helping to maintain safe levels of waste products and electrolytes in the body.

In contrast, bacteria and proteins are not effectively removed through this diffusion process during dialysis. Bacteria are typically much larger than the pores in the dialysis membrane, which are designed to selectively allow smaller molecules like urea to pass through. Proteins, due to their larger size, also do not diffuse easily across the dialysis membrane; preserving protein levels in the blood is essential for maintaining health. Fluid balance is managed through ultrafiltration rather than diffusion, targeting the excess fluid rather than specific waste solutes.