Oncotic pressure

Oncotic pressure

Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system.

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, there will be a reduction in oncotic pressure and an increase in filtration across the capillary, resulting in excess fluid buildup in the tissues (edema).

The large majority of oncotic pressure in capillaries is generated by the presence of high quantities of albumin which constitute approximately 80% of the total oncotic pressure exerted by blood plasma on interstitial fluid. The total oncotic pressure of an average capillary is about 28 mmHg with albumin contributing approximately 22 mmHg of this oncotic pressure. Because blood proteins cannot escape through capillary endothelium, oncotic pressure of capillary beds tends to draw water into the vessels.[1]

Oncotic pressure is represented by the symbol Π or π in the Starling equation and elsewhere.

In intravenous therapy

In the clinical setting, there are two types of fluids that are used for intravenous drips: crystalloids and colloids. Crystalloids are aqueous solutions of mineral salts or other water-soluble molecules. Colloids contain larger insoluble molecules, such as gelatin; blood itself is a colloid.

Colloids preserve a high colloid osmotic pressure in the blood, while, on the other hand, this parameter is decreased by crystalloids due to hemodilution. [2] However, there is still controversy involving the actual difference in efficacy by this difference.[2] Another difference is that crystalloids, in general, are much cheaper than colloids.[2]

References

  1. ^ Guyton, Arthur; Hall, John (2006). "Chapter 16: The Microcirculation and the Lymphatic System". In Gruliow, Rebecca (Book). Textbook of Medical Physiology (11th ed.). Philadelphia, Pennsylvania: Elsevier Inc.. pp. 187–188. ISBN 0-7216-0240-1. 
  2. ^ a b c An Update on Intravenous Fluids by Gregory S. Martin, MD, MSc

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  • oncotic pressure — on·cot·ic pressure ( )äŋ kät ik , ( )än n the pressure exerted by plasma proteins on the capillary wall * * * a pressure represented by the pressure difference that exists between the osmotic pressure of blood and that of the lymph or tissue… …   Medical dictionary

  • oncotic pressure — a pressure represented by the pressure difference that exists between the osmotic pressure of blood and that of the lymph or tissue fluid. Oncotic pressure is important for regulating the flow of water between blood and tissue fluid. See also:… …   The new mediacal dictionary

  • oncotic pressure — (ˈ)än]|käd.ik , (ˈ)äŋ] noun Etymology: oncotic probably International Scientific Vocabulary onco (I) + tic (as in osmotic) : the pressure exerted by plasma proteins on the capillary wall and made up of the osmotic and imbibition pressures of the… …   Useful english dictionary

  • Давление Онкотическое (Oncotic Pressure) — давление, характеризующее разницу между существующим осмотическим давлением крови и давлением лимфы или тканевой жидкости. Это давление играет важную роль в регуляции поступления воды из крови в тканевые жидкости, и наоборот. (Онкотическое… …   Медицинские термины

  • oncotic — Relating to or caused by edema or any swelling (oncosis). * * * adj. 1. characterized by a tumour or swelling. 2. relating to an increase in volume or pressure. * * * on·cot·ic (ong kotґik) 1. pertaining to, caused by, or marked by swelling. 2.… …   Medical dictionary

  • pressure — 1. A stress or force acting in any direction against resistance. 2. (P, frequently followed by a subscript indicating location)In physics and physiology, the force per unit area exerted by a gas or liquid against the walls of its container or… …   Medical dictionary

  • oncotic — adj. 1) characterized by a tumour or swelling. 2) relating to an increase in volume or pressure …   The new mediacal dictionary

  • iso-oncotic — iso on·cot·ic (i″so on kotґik) having the same oncotic pressure …   Medical dictionary

  • ДАВЛЕНИЕ ОНКОТИЧЕСКОЕ — (oncotic pressure) давление, характеризующее разницу между существующим осмотическим давлением крови и давлением лимфы или тканевой жидкости. Это давление играет важную роль в регуляции поступления воды из крови в тканевые жидкости, и наоборот.… …   Толковый словарь по медицине

  • Starling equation — The Starling equation is an equation that illustrates the role of hydrostatic and oncotic forces (the so called Starling forces) in the movement of fluid across capillary membranes.Capillary fluid movement may occur as a result of two processes:… …   Wikipedia

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