Chloride ions, Cl-, follow actively transported Na+ ions from the nephron into the blood. would you not expect the Cl- concentration to decrease as fluids are extracted along the nephron? What causes the discrepancy?
Actually, most of the Na+ is not transported through a regular ion channel. It is used to transport glucose back into the blood thorugh a permease(simport transport). Some of the ions ar later absorbed through ion channels. In the permease it is simple: there is no place for the Cl- ion to bind. In the ion channel, if i remember correctly, you have negatively charged aminoacids at the surface that keep those ions out(electrostatic forces do not let them enter)
Good question..
Regards,
Andrew
