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13.1: Electrolytes

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    Electrolytes are compounds that separate into ions in water. Electrolytes can be separated into 2 classes:

    • Cations: ions that have a positive charge
    • Anions: ions that have a negative charge

    The following table summarizes the major intracellular and extracellular electrolytes by giving their milliequivalents (mEq)/L. Milliequivalents are a measure of charge. Thus, a higher value means that the cation or anion is accounting for more charge.

    Table \(\PageIndex{1}\): Major intracellular and extracellular electrolytes (mEq/L)1,2
    Intracellular Extracellular
    Cations Anions Cations Anions
    Potassium (\(\ce{K+}\)) 150 Phosphate (\(\ce{PO^4-}\)) 104 Sodium (\(\ce{Na+}\)) 142 Chloride (\(\ce{Cl-}\)) 103
    Magnesium (\(\ce{Mg^2+}\)) 40 Proteins 57   Bicarbonate (\(\ce{HCO^3-}\)) 27
      Sulfate (\(\ce{SO4^2-}\)) 20   Proteins 16

    The following figure graphically shows the major intracellular and extracellular cations (green) and anions (red).


    Figure \(\PageIndex{1}\): Major intracellular and extracellular cations (green) and anions (red)2

    Electrolytes and proteins are important in fluid balance. Your body is 60% water by weight. Two-thirds of this water is intracellular, or within cells. One-third of the water is extracellular, or outside of cells. One-fourth of the extracellular fluid is plasma, while the other 3/4 is interstitial (between cells) fluid. Thus, when considering total body water, around 66% is intracellular fluid, 25% is interstitial fluid, and 8% is plasma3,4.

    Fluid distribution between the different compartments are shown below.


    Figure \(\PageIndex{2}\): Distribution of fluid in the body3,4.

    Query \(\PageIndex{1}\)


    1. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw's perspectives in nutrition. New York, NY: McGraw-Hill.
    2. Whitney E, Rolfes SR. (2011) Understanding nutrition. Belmont, CA: Wadsworth Cengage Learning.
    3. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
    4. Adapted from

    This page titled 13.1: Electrolytes is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Brian Lindshield via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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