Renal physiology is one of the most sophisticated courses in medicine . Kidney is a vital organ which has been highly adapted during evolution to cope with its various physiological functions . In this book, which is the fourth one among the " cases in nephrology " series, the author has tried to integrate basic physiological concepts with their clinical applications by using the usual format of the series, namely real clinical scenarios .This book depicts major issues in a rather new style, with the aim of transferring educational materials to its readers in a more durable and more attractive way. Study of this book is highly recommended to medical students in all levels, residents of internal medicine and junior clinicians interested in the field of "renal physiology" .