(1) A high pressure filtration through a semipermeable membrane in which colloidal particles are retained while the small sized solutes and the solvent are forced to move across the membrane by hydrostatic pressure forces.
(2) The process of separating particles of one size from particles of another size in a suspending medium using a filter (of particular pore size), especially used in industry and scientific research for purifying and concentrating macromolecular (103 - 106 Da) solutions.
Ultrafiltration is a vital process that takes place in the kidneys. With ultrafiltration, large molecules (such as cells and proteins) that are essential are separated or filtered out to be reabsorbed. The ultrafiltrate, in turn, is passed through the proximal tubule, the loop of Henle, the distal convoluted tubule, and a series of collecting ducts to form urine.