The human kidney is comprised of heterogenous cell types. (A) The kidney is comprised of a cortex, medulla, and papilla regions. Nephrons are segmented epithelial subunits of the kidney. (Right nephron) Nephron segments are color-coded to depict the regionalized structure, and show varying lengths of intermediate segments throughout the medulla and papilla region, where tracks of the collecting duct system are also found. (B) Examples of differentiated nephron cell types, which display unique morphological features. Abbreviations are as follows: ATL, ascending thin limb; G, glomerulus; CNT, connecting tubule; DCT, distal convoluted tubule; DTL, descending thin limb; MD, macula densa; PCT, proximal convoluted tubule; PST, proximal straight tubule; TAL, thick ascending limb.