During reabsorption, sodium ions cross the proximal tubule walls into the interstitial fluid principally by means of
A)bulk flow.
B)active transport.
C)countercurrent multiplication.
D)phagocytosis.
E)none of these.

Question

Quizplus · Accepted Answer

Sodium ions are actively transported across the proximal tubule walls and into the interstitial fluid, which creates a concentration gradient that drives their diffusion across the apical membrane of epithelial cells into the tubular lumen for excretion in the urine. Bulk flow refers to the movement of fluids across membranes due to hydrostatic and osmotic pressures, countercurrent multiplication is a process that occurs in the loop of Henle of the nephron, and phagocytosis is the engulfment of particles by specialized cells and not a mechanism for ion transport.

During Reabsorption, Sodium Ions Cross the Proximal Tubule Walls into the Interstitial