A dialyzer is a medical device used in the process of dialysis, which helps filter waste products and excess fluids from the blood. It is often referred to as an "artificial kidney" because it mimics the function of healthy kidneys. Dialyzers contain a semipermeable membrane that allows small molecules, like urea and creatinine, to pass through while retaining larger molecules, such as proteins and blood cells. During hemodialysis, blood is drawn from the body, passed through the dialyzer, and then returned to the bloodstream. This process is essential for individuals with kidney disease or those whose kidneys are not functioning properly, helping to maintain a balance of electrolytes and fluids in the body.