Body Fluid Electrolyte Distribution

The body's water can be divided into two primary categories: intracellular fluid and extracellular fluids. The larger segment is the intracellular fluid, comprising approximately two-thirds of the total body water. Further division of extracellular fluids includes interstitial fluid, found between cells, and plasma, which accounts for roughly one-quarter of the extracellular fluid volume.

Within bodily fluids, there exist varying concentrations of different electrolytes and solutes. An electrolyte is a substance that dissociates into ions when dissolved in a solution. In the body's water composition, positively charged electrolytes (referred to as cations), such as sodium, potassium, calcium, and magnesium, are notable, while negatively charged electrolytes (anions) encompass chloride and bicarbonates. Particularly, sodium takes on the role of the primary electrolyte in extracellular fluid, in contrast to the relatively lower levels of potassium.

However, within intracellular fluid, this pattern is reversed. Potassium assumes prominence as the predominant electrolyte, while sodium maintains a lower presence. Maintaining this distribution of electrolytes is of utmost importance for the body. This equilibrium is critical because it supports the preservation of cell functions and facilitates electrical communication across the body by upholding transmembrane electrical and chemical gradients. Ultimately, this balance is indispensable for overall bodily health and functionality.
Body Fluid Electrolyte Distribution

Body fluids: Intracellular and extracellular fluids

Human beings are creatures that are primarily composed of water. It is the essence of life and the aqueous base solution in which all essential biochemical processes occur that produce life.

The body water can be divided into two components – intracellular fluid (ICF) and extracellular fluids (ECF); the intracellular fluid is the major component and composes approximately two thirds of total body water (TBW).

The ICF volume represents the fluid content within the body's cells. This volume cannot be measured directly but is calculated as the difference between the measured TBW and the measured ECF volume. Potassium provides the osmotic skeleton for the ICF in much the same way that sodium provides the osmotic skeleton for the ECF. In general, ICF are stable and do not readily adjust rapidly to changes.

The proportion of ECF is much greater than that of ICF in preterm infants and reaches 60% of TBW at term. The membranes retaining this fluid allow the passive diffusion of water, whereas active transport mechanisms maintain an internal solute milieu different from that found outside the cells. K+, P2-, and Mg2+ are intracellular ions, and Na+ and Cl- are predominantly extracellular.

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.

Interstitial fluid flow is the movement of fluid through the extracellular matrix of tissues, often between blood and lymphatic vessels. This flow provides a necessary mechanism for transporting large proteins through the interstitium and constitutes an important component of microcirculation.
Body fluids: Intracellular and extracellular fluids