The kidney filters vast quantities of Na at the glomerulus but excretes a very small fraction of
this Na in the final urine. Although almost every nephron segment participates in the
reabsorption of Na in the normal kidney, the proximal segments (from the glomerulus to the
macula densa) and the distal segments (past the macula densa) play different roles. The
proximal tubule and the thick ascending limb of the loop of Henle interact with the filtration
apparatus to deliver Na to the distal nephron at a rather constant rate. This involves …