endocrine and metabolic disorders
Overview of Disorders of Fluid Volume
Introduction
Because sodium is the major osmotically active ion in the extracellular fluid (ECF), total body sodium content determines ECF volume. Deficiency or excess of total body sodium content causes ECF Volume Depletion or Dietary intake and renal excretion regulate total body sodium content. When total sodium content and ECF volume are low, the kidneys increase sodium conservation. When total sodium content and ECF volume are high, sodium excretion (natriuresis) increases so that volume decreases. Renal sodium excretion can be adjusted widely to match sodium intake. Renal sodium excretion requires delivery of sodium to the kidneys and so depends on renal blood flow and glomerular filtration rate (GFR). Thus, inadequate sodium excretion may be secondary to decreased renal blood flow, as in Chronic Kidney Disease or 