The main electrolytes that are measured in chemistry profiles are:
Sodium: The major determinant of effective circulating volume and tonicity. Changes in fluid (loss or gain of fluid) influences sodium concentrations and triggers body responses as outlined in the fluid changes page.
Because electrolytes are essential to proper functioning of cells, the body maintains their concentrations within fairly narrow limits. The main mechanisms to consider for changes in electrolyte concentrations are:
Changes in free water: This particularly affects sodium and chloride.
Intake of electrolytes: This minimally affects sodium and chloride but is substantial for potassium.
Translocation: This means the electrolyte moves across cellular membranes, from inside cells to the extracellular fluid or vice versa. This primarily affects potassium since sodium (and chloride) concentrations are tightly regulated with higher concentrations outside than inside the cells.
Excretion/loss: This occurs through various routes, mainly the gastrointestinal system (feces, saliva) and kidneys (urine) but also respiratory system (panting with evaporative water loss) and skin (sweat, burns).