ultrafiltration

Filtration through a semipermeable membrane or any filter that separates colloid solutions from crystalloids or separates particles of different size in a colloid mixture.

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ul·tra·fil·tra·tion .əl-trə-fil-'trā-shən n filtration through a medium (as a semipermeable capillary wall) which allows small molecules (as of water) to pass but holds back larger ones (as of protein)

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n.

filtration under pressure. In the kidney, blood is subjected to ultrafiltration to remove the unwanted water, urea, and other waste material that goes to make up urine.

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ul·tra·fil·tra·tion (ul″trə-fil-traґshən) filtration through filters with minute pores, which allows separation of extremely minute particles. It occurs naturally, as in the filtration of plasma at the capillary membrane, and is also performed clinically and in the laboratory, such as in hemodialysis. In hemodialysis it involves bulk movement of solute and solvent across a membrane down pressure gradients and is usually performed under pressure to accelerate the process.