TOTAL BODY WATER

SUMMARY

TBW
1. In an adult male 18% of body weight (BW) is protein (& related substances), 7% mineral, 15% fat
2. Remaining 60% is water: total body water (TBW) is ~60% of his BW
3. TBW (60% of BW) = ECF (20% of BW or 14L) + ICF (40% of BW)

ECF
4. Remember: TBW = ECF + ICF, where ECF = interstitial fluid + plasma + lymph
5. 75% of ECF is in interstitial fluid (i.e. 15% of BW), 25% is in plasma (i.e. 5% of BW), only a negligible amount of lymph
6. Total blood volume (TBV) is 8% of BW

Reference(s)

Barrett, K.E., Barman, S.M., Boitano, S., Brooks, H.L., Weitz, M., Brian Patrick Kearns, Ganong, W.F. and Mcgraw-Hill Education (Firm (2016). Ganong’s review of medical physiology. 25th ed. New York: Mcgraw Hill Education.
Hall, J.E. and Hall, M.E. (2020). Guyton And Hall Textbook Of Medical Physiology. 14th ed. S.L.: Elsevier - Health Science.
West, J.B. and Luks, A.M. (2021). West’s Pulmonary Pathophysiology. Lippincott Williams & Wilkins.