Oncotic pressure

In blood plasma, the dissolved compounds have an osmotic pressure. A small portion of the total osmotic pressure is due to the presence of large proteinmolecules; this is known as the colloidal osmotic pressure, or oncotic pressure. Because large plasma proteins can't easily cross through the capillarywalls, their effect on the osmotic pressure of the capillary interiors will, to some extent, balance out the tendency for fluid to leak out of the capillaries. In conditions where plasma proteins are reduced, e.g. from being lost in the urine (proteinuria) or from malnutrition, the result of the too low oncotic pressure can be oedema- excess fluid buildup in the tissues.

Related to hydrostatic pressure.

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It uses material from the http://en.wikipedia.org/wiki/Oncotic+pressure Wikipedia article Oncotic pressure.