A researcher uses inulin dilution to measure a body fluid compartment in a healthy adult. Which compartment is correctly measured by inulin?

• A Total body water
• B Plasma volume
• C Intracellular fluid
• D Extracellular fluid ✓

Explanation

Inulin is a polysaccharide that distributes throughout the extracellular fluid but does not cross cell membranes, making it a classic marker for ECF measurement. Total body water is measured by deuterium oxide or tritiated water. Plasma volume requires markers confined to the vascular space such as Evans blue dye or radiolabeled albumin. Intracellular fluid is calculated as TBW minus ECF, not measured directly by any single indicator.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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