Oncotic pressure
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Oncotic pressure in the circulatory system is a form of osmotic pressure exerted by proteins in blood plasma that normally tends to pull water into the circulatory system. Another name for oncotic pressure is colloid osmotic pressure.
Throughout the body, dissolved compounds have an osmotic pressure. Because large plasma proteins cannot easily cross through the capillary walls, 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 other words, the oncotic pressure tends to pull fluid into the capillaries. In conditions where plasma proteins are reduced, e.g. from being lost in the urine (proteinuria) or from malnutrition, the result of low oncotic pressure can be edema – excess fluid buildup in the tissues.
Oncotic pressure is represented by the symbol π in the Starling equation and elsewhere.
