6.7: Hemodialysis
- Apply the process of diffusion to hemodialysis.
The main function of the kidneys is to filter the blood to remove wastes and extra water, which are then expelled from the body as urine. Some diseases rob the kidneys of their ability to perform this function, causing a buildup of waste materials in the bloodstream. If a kidney transplant is not available or desirable, a procedure called dialysis can be used to remove waste materials and excess water from the blood.
In hemodialysis , a patient’s blood is passed though a length of tubing that travels through an artificial kidney machine (also called a dialysis machine ). A section of tubing composed of a semipermeable membrane is immersed in a solution of sterile water, glucose, amino acids, and certain electrolytes. This solution called the dialysis solution is an isotonic solution that is formulated to contain many of the same solutes that is in the blood. The concentration of waste molecules such as urea are high in the blood of the patient and so the wastes move via diffusion from the blood to the dialysis solution. The dialysis solution is continually replenished. Red and white blood cells are too large to pass through the membrane, so they remain in the blood. After being cleansed in this way, the blood is returned to the body.
Dialysis is a continuous process, as the diffusion of waste materials and excess water takes time. Typically, 5–10 lb of waste-containing fluid is removed in each dialysis session, which can last 2–8 hours and must be performed several times a week. Although some patients have been on dialysis for 30 or more years, dialysis is always a temporary solution because waste materials are constantly building up in the bloodstream. A more permanent solution is a kidney transplant.