Fundamentals of Epithelial Na+ Absorption

Abstract

The maintenance of electrolyte balance is essential for the control of many functions in the human body. Na + , K + , and Cl À are key electrolytes that contribute to a variety of processes ranging from the maintenance of cellular membrane potential to the regulation of cell volume and extracellular fluid volume. Fundamentals of epithelial Cl À and K + transport are discussed in the preceding and following chapters and will be only briefly touched upon here. Na + absorption occurs across the epithelial barriers of many organs, including the lung, gastroin-testinal tract, exocrine glands, and kidney. Na + is the primary determinant of blood volume, and a number of physiological mechanisms that control blood pressure mediate their effects by adjusting Na + balance in the kidney. This chapter describes classical fundamentals of epithelial Na + absorption and highlights some recent mechanisms involved in physiological regulation of Na + transport in specific epithelia with a particular emphasis on the kidney.