Fluid and Electrolyte Balance

The main fluid in the body is water. Total body water is 60% of body weight. The water is distributed in three main compartments separated from each other by cell membranes. The intracellular compartment is the area within the cell. The extracellular compartment consists of the interstitial area (between and around cells) and the inside of the blood vessels (plasma).

Compartments of Body and Distribution of Water by Weight Plasma 5% Interstitial 15% Intracellular 40% Total 60 % Water Solids - 40%  fat, protein, carbohydrates, minerals

Electrolytes are the chemicals dissolved in the body fluid. The distribution has important consequences for the ultimate balance of fluids.

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

Sodium chloride is found mostly in extracellular fluid, while potassium and phosphate are the main ions in the intracellular fluid.

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