Extracellular Fluid Volume and Electrolyte Balance

Extracellular fluid volume and electrolyte balance refers to the physiological regulation of the amount and composition of fluid outside the body's cells and the concentrations of dissolved ions (electrolytes) such as sodium, potassium, and chloride. This balance is maintained via integrated neurohormonal systems—including the renin-angiotensin-aldosterone system (RAAS), vasopressin (antidiuretic hormone, ADH), and natriuretic peptides—which act through several effectors (notably the kidneys) and molecular targets (such as sodium channels and hormone receptors). It is a functional concept involving many different molecules, receptors, and transporters, and not a single, actionable target itself.