Question 11

 Describe the body fluid compartments.

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College Answer

This question was answered poorly. Many answers provided incorrect facts relating to the body fluid compartments, their approximate sizes, the factors that regulate and contribute to those sizes and their constituents. Total body water was often incorrectly calculated and associated with limited explanation as to the factors that may affect it.


Some bare minimum would probably have consisted of something like this:

  • Total body water: 42 L (60% of total body mass)
    • 50% for women; and usually
    • Higher in obesity, but as a lower proportion of body mass, as adipose tissue is only 10-20% water
  • Intracellular Fluid = 33% ( 23.1 litres) ; this volume is regulated by the movement of free water.
  • Extracellular Fluid = 27% (18.9 litres); this volume is regulated by the movement of sodium.
    • Plasma volume (2.8L)
    • Interstitial and lymph fluid 
    • Dense connective tissue and bone
    • Adipose tissue
  • Transcellular fluid: ~1.5% (1050ml); fluid formed by the secretory activity of cells,
    • communicates with the intracellular fluid, rather than the interstitial fluid.
    • exists within epithelium-lined spaces.
      • Synovial fluid
      • CSF
      • Aqueous humour
      • Bile
      • Bowel contents
      • Peritoneal fluid
      • Pleural fluid
      • Urine in the bladder


Bhave, Gautam, and Eric G. Neilson. "Body fluid dynamics: back to the future." Journal of the American Society of Nephrology 22.12 (2011): 2166-2181.

Snyder, W. S., et al. "Report of the task group on reference man." Report Prepared for International Commission on Radiological Protection 23: 46-57.