Chapter 17, Problem 15RA

The countercurrent exchange in the vasa recta

$\begin{array}{l}\text{a}{\text{. removes Na}}^{\text{+}}\text{ from the extracellular fluid}\text{.}\hfill \\ \text{b}\text{. maintains high concentrations of NaCl in the extracellular fluid}\text{.}\hfill \\ \text{c}{\text{. raises the concentration of Na}}^{\text{+}}\text{ in the blood leaving the kidneys}\text{.}\hfill \\ \text{d}{\text{. causes large quantities of Na}}^{\text{+}}\text{ to enter the filtrate}\text{.}\hfill \\ \text{e}\text{. does all of these}\text{.}\hfill \end{array}$