Body Fluid Compartments
Start with the big picture
Total body water is divided mainly into intracellular fluid (ICF) and extracellular fluid (ECF). The ECF includes interstitial fluid, plasma, and transcellular fluid, each with distinct roles and measurement approaches. Differences in ions, osmolarity, and effective osmoles help explain how water shifts between compartments, while plasma proteins and capillary Starling forces influence vascular fluid volume and filtration. The lesson also introduces the Gibbs-Donnan effect, indicator-dilution methods for estimating fluid volumes, and regulation by ADH, thirst, RAAS, and ANP. These foundations support understanding of isotonic, hypertonic, and hypotonic fluid imbalance, as well as edema when filtration exceeds lymphatic return.
What you'll learn
- Distinguish ICF, ECF, and the major subdivisions of ECF.
- Explain how osmolarity and effective osmoles influence water movement between compartments.
- Describe how plasma proteins and Starling forces affect capillary filtration.
- Identify methods used to measure total body water, ECF, and plasma volume.
- Relate fluid regulation and capillary imbalance to dehydration, overhydration, and edema.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
