The net effect is an increase in extracellular volume (greater than the volume of fluid added), a decrease in intracellular volume, and a rise in osmolarity in both compartments. Again, almost all the added sodium chloride remains in the extracellular compartment, and fluid diffuses from the cells into the extracellular space to achieve osmotic equilibrium. If a hypertonic solution is added to the extracellular fluid, the extracellular osmolarity increases and causes osmosis of water out of the cells into the extracellular compartment (see Figure 25–6 B). The sodium and chloride largely remain in the extracellular fluid because the cell membrane behaves as though it were virtually impermeable to the sodium chloride.

The only effect is an increase in extracellular fluid volume (Figure 25–6 A).

If an isotonic saline solution is added to the extracel-lular fluid compartment, the osmolarity of the extra-cellular fluid does not change therefore, no osmosis occurs through the cell membranes. Effect of Adding Saline Solution to the Extracellular Fluid With these basic principles in mind, we can analyze the effects of different abnormal fluid conditions on extracellular and intracellular fluid volumes and osmolarities. Water moves rapidly across cell membranes therefore, the osmolarities of intracellular and extracellular fluids remain almost exactly equal to each other except for a few minutes after a change in one of the compartments.Ĭell membranes are almost completely impermeable to many solutes therefore, thenumber of osmoles in the extracellular or intracellular fluid generally remains constant unless solutes are added to or lost from the extracellular compartment. One can calculate both the changes in intracellular and extracellular fluid volumes and the types of therapy that should be instituted if the following basic principles are kept in mind: Some of the different factors that can cause extracellular and intracellular volumes to change markedly are ingestion of water, dehydration, intravenous infusion of different types of solutions, loss of large amounts of fluid from the gastrointestinal tract, and loss of abnor-mal amounts of fluid by sweating or through the kidneys. Volume and Osmolality of Extracellular and Intracellular Fluids in Abnormal States

Extracellular fluid volume