NURSING 2LA2 Study Guide - Midterm Guide: Plasma Osmolality, Extracellular Fluid, Oliguria
28 Nov 2016
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Fluid balance at capillary level: 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. Capillary hydrostatic pressure (cid:862)push(cid:863): at the arterial end of the capillary, hydrostatic pressure is higher than oncotic pressure so fluid moves out into interstitial space. Interstitial hydrostatic pressure has a small negative value and contributes slightly to movement of fluid from capillary to tissue. Capillary colloidal osmotic pressure (cid:862)pull(cid:863): 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 move from the vessel into the interstitial space and create interstitial colloidal osmotic pressure, pulling a small amount of fluid into the interstitial space.
