Filtration

Filtration occurs when water and any dissolved particles are pushed through cell membranes or pore systems by a hydrostatic pressure difference. Pores occur, for instance, when there are small spaces between endothelial cells (intercellular clefts) or holes (fenestrations) in the cell membranes. Such a process is found in the capillaries of the tissues. The term ultrafiltration is used when, in the course of filtration processes such as that in the capillaries of the renal corpuscles, larger blood components are retained or dissolved molecules are separated out because of their size or charge.