NURSING 2LA2 Lecture Notes - Lecture 5: Starling Equation, Water–Electrolyte Imbalance, Extracellular Fluid
25 Aug 2016
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Document Summary
Fluid balance at the level of the capillary relies on a balance between opposing forces: the pushing force of hydrostatic pressure, and the pulling force of oncotic pressure. At the arterial end of the capillary, hydrostatic pressure is higher than oncotic pressure in the capillary so fluid moves or is pushed out into the interstitial space. Current research shows that interstitial hydrostatic pressure has a small negative value and contributes slightly to the movement of fluid from the capillary to the tissue. Toward the venous end of the capillary much of the fluid has moved to the interstitial space, leaving the solutes in particular, the plasma proteins behind. This creates higher capillary osmotic pressure which effectively pulls fluid from the interstitial space back into the vessel. Some particles such as glucose and electrolytes move from the vessel into the interstitial space and create interstitial colloidal osmotic pressure, pulling a small amount of fluid into the interstitial space.
