Physiology of water balance and pathophysiology of hyponatremia

Abstract

The understanding of hyponatremic disorders requires a knowledge of normal water balance and how this relates to the maintenance of normal sodium concentrations despite large variations of water intake. This chapter thus reviews the physiology of water homeostasis and describes the components of the normal renal diluting and concentrating mechanisms. The quantitation of water excretion is also reviewed in order to more appropriately approach the pathogenesis and treatment of disorders of water excretion. Emphasis is placed on the central role of vasopressin in the maintenance of water balance. Finally an overall approach to hyponatremic patients is put forth to be discussed in greater detail in forthcoming chapters.