This volume is part of a series of books that presents fundamental concepts of medicine in a self-teaching format. Each book in the series contains three to five chapters covering individual concepts integrally related to each other. Concepts in the series are chosen from those thought to be most difficult by medical students. The authors write their chapters according to a specific, self-teaching format designed to help the student gain an understanding of these challenging concepts. Each chapter stands by itself as a complete teaching unit on a particular subject, though each chapter also leads the reader to an understanding of the position of the particular concept within the greater body of medical knowledge. The format reinforces problem solving skills across the basic science and clinical disciplines and therefore represents an important study aid for the revised problem-oriented board examination.