201 13.1 Electrolytes
Electrolytes are compounds that separate into ions (molecules with a charge) 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 13.11 Major intracellular and extracellular electrolytes (mEq/L)1,2
Intracellular Extracellular
| Cations | Anions | Cations | Anions |
| Potassium (K+) 150 | Phosphate (PO4-) 104 | Sodium (Na+) 142 | Chloride (Cl-) 103 |
| Magnesium (Mg2+) 40 | Proteins 57 | Bicarbonate (HCO3-) 27 | |
| Sulfate (SO42-) 20 | Proteins 16 |
The following figure graphically shows the major intracellular and extracellular cations (green) and anions (red).
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.
References & Links
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 http://www.netterimages.com/image/21248.htm