Urea transporters along the nephron. Urea transporters along the nephron. The cartoon and histology show the urea transporters (UT-A1/UT-A3, UT-A2, and UT-B1) along the nephron. UT-B1 is found chiefly in the vasa recta, UT-A2 is found in the thin descending limb of the loop of Henle, and UT-A1 (apical) and UT-A3 (basolateral) are found in the inner medullary collecting duct. Modified from reference 12, with permission. I. David Weiner et al. CJASN 2015;10:1444-1458 ©2015 by American Society of Nephrology