Disorders of Extracellular Fluid Volume: Basic Concepts
In Chap. 3, we discussed how NaCl and water are handled by various segments of the nephron. Since Na+ is the major extracellular electrolyte, the total amount of this electrolyte and its accompanying anion (Cl−) determine the extracellular fluid (ECF) volume. Therefore, retention or excretion of Na+ by the kidneys is critical for the regulation of ECF volume. This regulation of NaCl is precise in normal individuals. In a steady state, urinary Na+ approximates dietary Na+, as the kidneys are the major excretory organs of Na+ besides gastrointestinal tract and skin. Low salt intake results in low excretion of Na+. Conversely, high salt intake results in high excretion of Na+. Any disturbance in this regulation activates or inhibits neural and hormonal mechanisms, leading to appropriate change in Na+ excretion by the kidneys. This chapter discusses the basic concepts that characterize ECF volume depletion, and conditions that are associated with the development of volume expansion and edema formation.
KeywordsDisorders of extracellular fluid volume Extracellular fluid volume Effective arterial blood volume Edema formation
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