Why have another book in the bone-calcium field? When the idea was first raised that this important area of biomedical research should be given more attention in the review literature, we felt that comprehensive texts recently published and in press were directed at more general audiences and did not address in detail some of the important areas of current investigation. As this field has grown and matured, information has accumulated at such a rapid rate that it has become impossible to keep abreast of all areas by reading the original articles in the scientific literature. Accordingly, we believed there was a void which could be filled by a collection of essays on specific topics in which significant progress had recently been made. Thus, this book is meant to be an up-to-date account of specific topics by investi­ gators at the forefront of their areas of research. We have tried to review major areas of basic science in the field which have an impact on our understanding of the diseases of bone and mineral. We hope that you will agree that the authors have done an outstanding job, and will find the volume as stimulating to read as we have. San Antonio, TX, USA GREGORY R. MUNDY Melbourne, Australia T. JOHN MARTIN Spring 1993 Contents CHAPTER 1 Calcium Homeostasis A. M. PARFITI. With 12 Figures 1 A. Introduction and Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 B. Concepts of Homeostasis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 C. Extracellular Fluid Free Calcium: The Controlled Variable. . . . . .