Fluid & Electrolyte Q 63

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The majority of the body’s water is contained in which of the following fluid compartments?

  

    A. Intracellular

    B. Interstitial

    C. Intravascular

    D. Extracellular

    

    

Correct Answer: A. Intracellular

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The intracellular compartment holds two-thirds of total body water. At a cellular level, the distribution of the various fluid compartments in the body is paramount for the maintenance of health, function, and survival. For the average 70 kg man, 60% of the total body weight is water, equaling 42L. The body’s fluid separates into two main compartments: Intracellular fluid volume (ICFV) and extracellular fluid volume (ECFV). Of the 42L of water found in the body, two-thirds of it is within the intracellular fluid (ICF) space, which equates to 28L.

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Option B: The extracellular compartment is the interstitial space plus the intravascular space. Out of the extracellular fluid volume, 75% or 10.5L of the volume is present in the interstitial space, and 25% of that water is in the plasma, which is equivalent to 3.5L.

Option C: Plasma is the only fluid compartment that exists as a real fluid collection all in one space. It differs from the interstitial fluid by its higher protein content and its function in transportation. Plasma is a component of blood and is said to be the “interstitial fluid of the blood” as it bathes the suspended red and white cells, which also reside in the blood.

Option D: The extracellular compartment accounts for one-third of total body water. The ECFV consists of two spaces: The interstitial fluid volume (ISFV) and the plasma volume (PV). One-third of the total body water is the ECFV, which is equivalent to 14L.

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