a. Secretion of PAH occurs from peritubular capillary blood into tubular fluid (urine) via carriers in the proximal tubule.
b. At low plasma concentrations of PAH, the secretion rate increases as the plasma concentration increases.
c. Once the carriers are saturated, further increases in plasma PAH concentration do not cause further increases in the secretion rate (Tm).
Figure 5-6. Para-aminohippuric acid (PAH) titration curve. PAH filtration, excretion, and secretion are shown as a function of plasma [PAH], Tm = transport maximum.
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