ABSTRACT
The kidneys are responsible for day-to-day acid-base homeostasis, with the lungs regulating PaCO2 on a minute-to-minute basis. This renal regulation is accomplished by recapturing filtered HCO3
and excretion of ‘‘nonvolatile’’ or ‘‘fixed’’ acids. The terms ‘‘nonvolatile’’ or ‘‘fixed’’ acids refer to all dietary or endogenously produced acid except CO2, the ‘‘volatile’’ acid excreted by the lungs. Each day, a large amount of HCO3
is filtered (some 4300mEq=day at a glomerular filtration rate (GFR) of 120mL=min), and loss of even a fraction of this HCO3
would represent a major loss of body alkali stores. Acid excretion is much smaller in magnitude, some 50-100mEq=day, but is equally vital for acid-base homeostasis and is carefully regulated to maintain acid-base balance. This chapter addresses the transport processes along the renal tubules that reabsorb HCO3
and excrete acid. The results of these two processes are summarized in Fig. 1. As discussed in what follows, both processes are accomplished primarily by Hþ
secretion by tubule epithelial cells, and much of the chapter is devoted to the nature and regulation of these Hþ transport events. The references are selective with emphasis on more recent papers, which will refer the reader to older papers.
