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 \(\PageIndex{1}\)

References

Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw's perspectives in nutrition. New York, NY: McGraw-Hill.
Whitney E, Rolfes SR. (2011) Understanding nutrition. Belmont, CA: Wadsworth Cengage Learning.
Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
Adapted from http://www.netterimages.com/image/21248.htm