Answer:
Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semi-permeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane.
Basically, ultrafiltration is the removal of fluid from a patient and is one of the functions of the kidneys that dialysis treatment replaces. Ultrafiltration occurs when fluid passes across a semipermeable membrane (a membrane that allows some substances to pass through but not others) due to a driving pressure.