ABSTRACT
As sodium is the most abundant cation of the extracellular fluid (ECF) and sodium salts
account for the most important part of the osmotically active solutes in the plasma and
interstitial fluids, the amount of sodium in the body is a prime determinant of the ECF
volume. Therefore, multiple regulatory mechanisms have evolved in terrestrial animals
to tightly control its concentration in the body. Through the operation of these regulatory
mechanisms, the amount of sodium excreted is adjusted to equal the amount ingested over a
wide range of dietary intakes, allowing individuals to stay in sodium and volume balance.
