In the lumen of the proximal tubule, Na⁺ concentration ________ the Na⁺ concentration inside the cells of the tubule wall.
A) is much higher than
B) is slightly higher than
C) is about the same as
D) is slightly lower than
E) is much lower than

Question

Quizplus · Accepted Answer

The proximal tubule actively reabsorbs Na⁺ from the filtrate into the interstitial fluid and peritubular capillaries. This is achieved by Na⁺/K⁺ ATPase pumps located in the basolateral membrane of the tubule epithelial cells. The pumps move Na⁺ out of the cytoplasm, creating a concentration gradient that drives the passive diffusion of Na⁺ into the cells from the lumen of the tubule. Therefore, the Na⁺ concentration in the lumen of the proximal tubule is much higher than the Na⁺ concentration inside the cells of the tubule wall.

In the Lumen of the Proximal Tubule, Na⁺ Concentration ________