Extracellular fluid (ECF) contains the cation , and and as its anions. ECF is one-third of total body water and is composed of interstitial fluid and plasma. Plasma is one-fourth of the ECF, thus it is one-twelfth of total body water (TBW).

Intracellular fluid (ICF) provides two-thirds of TBW. Its major cations are and . The major anions of ICF are proteins and organic phosphates (ATP, ADP, AMP). Note that DNA also carries a net negative charge, and is intracellular, but not dissolved.

Total body water is approximately 60% of body weight. The percentage of total body water is highest in newborns and adult males, and lowest in adult females and in adults with large amounts of adipose tissue (fat). Intracellular fluid is 40% of body weight, and extracellular fluid is 20% of body weight (60-40-20 rule).

Intracellular fluid (ICF) is two-thirds of total body water. Its major cations are and . The major anions of ICF are proteins and organic phosphates (ATP, ADP, AMP). Also, most proteins carry a net negative charge at physiological pH. Major cations of extracellular fluid (ECF) are , its anions are and . Remember that the sodium potassium pump works continuously to pump three sodium ions out of the cell and two potassium ions into the cell, thus concentrating these species in their respective compartments.

Because women have smaller urethras, bacteria and other pathogens have a shorter distance to travel in order to cause infections in the body. In addition, the proximity of the anus to the urethral opening in women is much closer compared to men, resulting in a closer proximity to bacteria.