Body fluid compartments

Body fluid compartments are divisions of body water distinguished by location and solute composition. The principal compartments are intracellular fluid inside cells and extracellular fluid outside them.

Connect

Intracellular fluid: The water and dissolved substances inside cells, forming the largest body fluid compartment. It is the principal compartment on one side of the cell membrane.
Osmolality: The concentration of osmotically active particles per kilogram of solvent. Differences in effective osmolality can move water across cell membranes.
Fluid therapy: The clinical administration of fluids to restore or maintain hydration and circulation. Infused fluid distributes among compartments according to its composition and route.
Plasma: The liquid component of blood in which blood cells and dissolved substances are suspended. It is the intravascular part of extracellular fluid, not a separate principal compartment.
Extracellular fluid: The water and dissolved substances outside cells, including plasma and interstitial fluid. It is the principal compartment separated from intracellular fluid by cell membranes.
Tonicity: A solution's effect on cell volume, determined by solutes that cannot freely cross the membrane. It predicts whether extracellular fluid makes cells swell, shrink, or remain stable.
Dehydration: A deficit of body water that can alter fluid volumes and concentrations. Its effects depend on which compartments lose water and how rapidly.
Interstitial fluid: Extracellular fluid occupying spaces between tissue cells. It is distinct from plasma despite exchanging water and solutes with it.
Cell membrane: A selectively permeable boundary that separates a cell's interior from its surroundings. Its selective permeability helps maintain distinct intracellular and extracellular compositions.
Sodium: A positively charged ion that is the main extracellular cation in human body fluids. Its extracellular abundance strongly influences extracellular fluid osmolality and volume.