ELECTROLYTES
Definition:
Electrolytes are the chemicals dissolved in the body fluid. The distribution has important
consequences for the ultimate balance of fluids.
Sodium chloride is found mostly in extracellular fluid, while potassium and phosphate are the
main ions in the intracellular fluid.
BODY WATER
A typical adult body contains about 40 L of body fluids.
 25 L of fluids (or 63%) are located inside body cells, called intracellular fluid (ICF).
 15 L of fluids (or 37%) are located outside of body cells, called extracellular fluid (ECF). 80%
of ECF is interstitial fluid (which includes lymph, synovial fluid,
 cerebrospinal fluid, GI tract fluids, and fluids in the eyes and ears), and 20% of ECF is blood
plasma.
 ICF is mostly water and is rich in K+ , Mg++, HPO4 2- , SO4 2- , and protein anions.
 ECF contains more Na+ , Cl- , HCO3 - , and Ca++
 Concentrations of substances dissolved in ICF and ECF are constantly different because the
cell membrane is selectively permeable, which maintains a relatively unchanged distribution of
substances in different body fluids.
 Fluid balance refers to the proper levels of water and electrolytes being in the various body
compartments according to their needs.
 Osmotic pressure (created by the dissolved electrolytes in body fluids) and hydrostatic
pressure (created by the water in body fluids) are the main forces behind any molecular
movement between body compartments.
Compartments of
Body and Distribution of Water by Weight
Plasma 5%
Interstitial 15%
Intracellular 40%
Total 60 % Water
Solids - 40%
fat, protein, carbohydrates,
minerals
ELECTROLYTE DISTRIBUTION
Electrolyte
Extracellular
meq/liter
Intracellular
meq/liter
Function
Sodium
142
10
fluid balance,
osmotic
pressure
Potassium
5
100
Neuromuscular
excitability
acid-base balance
Calcium
5
-
bones, blood clotting
Magnesium
2
123
enzymes
Total Positive ions
154
205
Electrolyte Distribution
Electrolyte
Extracellular
meq/liter
Intracellular
meq/liter
Function
Chloride
105
2
fluid balance, osmotic
pressure
Bicarbonate
24
8
acid-base balance
Proteins
16
55
osmotic pressure
Phosphate
2
149
energy storage
Sulfate
1
-
protein metabolism
Total Negative ions
154
205
WATER BALANCE
 Water is the most abundant constituent in the body, varying from 45% to 75% of body weight.
Water balance occurs when water intake equals water output. A normal adult consumes about
2,500 ml of water daily 1,500 ml in beverages, 750 ml in food, and 250 ml from cellular
respiration and anabolic metabolism. At the same time, this adult is releasing about 2,500 ml of
water daily -- 1,500 ml in urine, 700 ml by evaporation (through the skin and lungs), 100 ml in
the feces, and 200 ml in sweating.