Ok, Webby, close but no cigar. Of course, I should cut you a little slack - 1913 is a ways back..
In chemistry, electrolytes are substances that in solution conduct electricity and are electrolyzed (decomposed) by it. These are substances that are ionized when dissolved, such as salt (positive sodium ion, negative chloride ion).
In medicine, an electrolyte is one of the major ionic compounds found in the blood. These are sodium+, potassium+, chloride-, calcium+, phosphate-, magnesium+, hydrogen+, and bicarbonate (HCO3-)(although the last two are generally treated separately under acid-base balance).
These ions are balanced through respiration, metabolism and excretion.There is a relatively narrow range within which these electrolytes can vary without causing problems. Interestingly enough, the symptoms of excess and insufficient electrolytes are often strikingly similar, so a good diagnostic workup with bloodwork and EKG is essential, as is a thorough patient history.
The body is very good at maintaining homeostasis, i.e. keeping its systems in balance. However, dietary or metabolic problems as well as many different diseases (and medications, such as vitamin or mineral supplements, diuretics, and many, many more) can interfere with the regulatory mechanisms. Breathing problems can cause retention of CO2, increasing the acidity of the blood, or can blow off too much CO2, causing the blood to become too alkaline. Kidney problems play a major role in the development of electrolyte imbalances, as the kidneys are the major regulatory excretory organ. Pituitary, thyroid, parathyroid gland problems can all throw the system off balance, as can simply dehydration or excess water (water intoxication).
Boy, aren't you glad your body takes care of all this stuff without conscious input from you? :-)