Total body water (TBW) in a 70 kg adult male is approximately 60% of body weight (42 L). Two-thirds of TBW constitutes intracellular fluid (ICF). What is the approximate volume of interstitial fluid in this individual?

• A 10.5 L ✓
• B 3.5 L
• C 14 L
• D 28 L

Explanation

TBW = 42 L. ICF = 2/3 × 42 = 28 L. ECF = 1/3 × 42 = 14 L. ECF is subdivided into plasma (~25% of ECF = 3.5 L) and interstitial fluid (~75% of ECF = 10.5 L). Thus, interstitial fluid ≈ 10.5 L. Transcellular fluids (CSF, synovial, pleural, peritoneal) make up a small additional compartment (~1–2 L) within ECF.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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