Sodium and Water Disorders

The balancing of fluids and electrolytes is a core function of the kidneys. There are redundant mechanisms within the body to sense the adequacy of organ perfusion and the composition of body fluids aimed at maintaining hemodynamics and protecting an environment for optimal cellular function. Sodium and water are key components of extracellular fluid and are regulated in response to end-organ perfusion and serum tonicity. Baroreceptors activate the renin-angiotensin-aldosterone system, sympathetic nervous system, vasopressin, and atrial natriuretic peptide to adjust sodium handling to alter extracellular volume. Osmoreceptors affect anti-diuretic hormone release and aquaporin activity in the medullary collecting duct to modify the handling of water. Disordered handling of sodium and/or water may be adaptive or maladaptive, and understanding the stimuli and responses to clinical scenarios assists clinicians in developing appropriate treatment strategies.