[Disorders of sodium metabolism]

We do not know why sodium was chosen to fill the extracellular space while potassium occupies the intracellular area. The sodium/potassium pump was placed in charge of maintaining this separation. The usual sodium blood concentration, in vertebrates, and in all ages, ranges from 135 to 145 mmol/L, although it may decrease with age. The maintenance of its concentration within these limits, as well as the total amount locally deposited are regulated by an intertwined net of sensors and effectors found in the Central Nervous System, in the cardiovascular apparatus including the right auricle, in the kidneys and adrenal glands, or indirectly due to a number of factors which act on the sodium/potassium pump--for examples the thyroid hormone, the digestive system and the skin. The changes in the metabolism and regulation of water and sodium may cause an excess (hypernatremia) or a deficit (hyponatremia) in the concentration of sodium in plasma--either extreme can be fatal. The prompt correction of these changes should include treating the causes while taking into consideration the time they took to occur. The most frequent cause of these changes in children is diarrheal disease and its inadequate treatment. The correct administration of the oral rehydrating solution recommended by the World Health Organization can prevent fatal endings.