Structure of the nephron. Structure of the nephron. The cartoon depicts the cortex (top), outer medulla (middle), and inner medulla (bottom), showing the location of the various substructures of the nephron labeled as follows: 1, glomerulus; 2, proximal convoluted tubule; 3s and 3l, proximal straight tubule in the short-looped nephron (3s) and long looped nephron (3l); 4s and 4l, thin descending limb; 5, thin ascending limb; 6s and 6l, medullary thick ascending limb; 7, macula densa; 8, distal convoluted tubule; 9, cortical collecting duct; 10, outer medullary collecting duct; 11, initial inner medullary collecting duct; and 12, terminal inner medullary collecting duct. Modified from reference 11, with permission of the American Physiological Society. I. David Weiner et al. CJASN 2015;10:1444-1458 ©2015 by American Society of Nephrology