Harrison’s Manual of Medicine 19th edition provides 600+ internal medicine topics in a rapid-access format. Download Harrison’s App to iPhone, iPad, and Android smartphone and tablet. Explore these free sample topics:
-- The first section of this topic is shown below --
Disturbances of sodium concentration [Na+] result in most cases from abnormalities of H2O homeostasis, which change the relative ratio of Na+ to H2O. Disorders of Na+ balance per se are, in contrast, associated with changes in extracellular fluid volume, either hypo- or hypervolemia. Maintenance of “arterial circulatory integrity” is achieved in large part by changes in urinary sodium excretion and vascular tone, whereas H2O balance is achieved by changes in both H2O intake and urinary H2O excretion (Table 1-1). Confusion can result from the coexistence of defects in both H2O and Na+ balance. For example, a hypovolemic pt may have an appropriately low urinary Na+ due to increased renal tubular reabsorption of filtered NaCl; a concomitant increase in circulating arginine vasopressin (AVP)—part of the defense of effective circulating volume (Table 1-1)—will cause the renal retention of ingested H2O and the development of hyponatremia.
|What is sensed||Plasma osmolality||Arterial filling|
|Sensors||Hypothalamic osmoreceptors||Carotid sinus|
|Effectors||AVP||Sympathetic nervous system|
|What is affected||Urine osmolality||Urinary sodium excretion|
|H2O intake||Vascular tone|