Fig. 9.

Acid-base transport in the distal nephron under baseline conditions, as predicted by a model of distal nephron acidification (97). The abscissa is distance along the distal nephron (in cm). The elongated ticks mark the boundaries of the distal convoluted tubule (DCT), connecting tubule (CNT), cortical collecting duct (CCD), outer medullary collecting duct (OMCD), and inner medullary collecting duct (IMCD). Left, from top to bottom: lumen pH and concentrations of HCO₃⁻, titrable acid (TA), and NH₄⁺; right from top to bottom: axial flows of net acid, HCO₃⁻, TA, and NH₄⁺. The model predicts that the DCT-CNT is the principal locus for net acid secretion, responsible for 70% of the increase in net acid flow from the DCT to final urine. [From Weinstein (97).]