Our professors continually told us that the kidney is the "smartest organ in the body" (still not sure about that). The nephrologists are definitely some of the smartest docs around so take advantage.
Renal Charts and Algorithms (cost $5) - A 14 pg. study aid including Ion Transport Diagrams: convoluted tubules (proximal & distal), thick ascending limb, cortical collecting duct (principle & alpha cells) & Electrolyte Imbalance Algorithms: Na, K, Ca & H/HCO3.
United States Renal Data System - reports, chars and presentations from the national data system that collects, analyzes, and distributes information about end-stage renal disease in the United States.
Renal Calculators (you probably have to memorize the equations for your exam)