How a dialysis machine works - Higher tier only
- Blood is removed from the patient and flows into the dialyzer where it is kept separated from dialysis fluid by a Also called semi-permeable. A partially permeable membrane allows water and other small molecules to pass through, but not larger molecules such as starch. membrane.
- The dialysis fluid contains the same concentration of glucose and salts as normal blood plasma so there is no net movement of glucose out of the blood by diffusion.
- Excess salts diffuse into the dialysis fluid.
- The dialysis fluid contains no urea, so all of the urea diffuses from the blood in to the dialysis fluid from the high concentration in the blood to the lower concentration in the dialysis fluid.
- The blood and dialysis fluid move in opposite directions across the membrane (a Where one substance moves along a surface in the opposite direction to another.) in order to maintain concentration gradients all the way along.
- The clean blood is returned to the patient and the waste dialysis fluid is disposed of.