Body water and distribution

Body water and distribution
Water is the largest component of the human body and the total body water content varies from approximately 45 – 70% of the total body mass, corresponding to about 33 to 53 for 75 kg man. Although body water content varies greatly among individuals, the water content of the various tissues is maintained relatively constant. For example, adipose tissue has low water content and lean tissue such as muscle and bone has a high water content, so the total fraction of water is the body is determine largely by the total fat content. In other words, a high fat content is related to a lower total water content as a percentage of body mass.

The body water can be divided into two components – intracellular fluid and extracellular fluids; the intracellular fluid is the major component and composes approximately two thirds of total body water. The extracellular fluids can be further divided into interstitial fluid (that between the cells) and the plasma, with the plasma volume representing approximately one-quarter of the extracellular fluid volume.

A wide range of electrolytes and solutes are dissolves in varying concentrations within the body fluids. An electrolyte can be defined as a compound that dissociates into ions when in solution. The major cations (positively charge electrolytes) in the body water are sodium, potassium, calcium, and magnesium; the major anions (negatively charged electrolytes) are chloride and bicarbonates. Sodium is the major electrolyte present in the extracellular fluid, while potassium is present in a much lower concentration.

In the intracellular fluid, the situation is reversed, and the major electrolyte present is potassium, with sodium found in much lower concentrations. It is critical for the body to maintain this distribution of electrolytes because maintenance of the transmembrane electrical and chemical gradients is of paramount importance for assuring the integrity of cell functions and allowing electrical communications throughout the body.
Body water and distribution