I thought it might be helpful to people if I excerpted the following from Prof. John Hall's preface to the 12th edition because it deals in part with what revisions he made for the book:
"I worked closely with Dr. Guyton for almost 30 years and had the privilege of writing parts of the 9th and 10th editions. After Dr. Guyton's tragic death in an automobile accident in 2003, I assumed responsibility for completing the 11th edition.
For the 12th edition of the Textbook of Medical Physiology, I have the same goal as for previous editions - to explain, in language easily understood by students, how the different cells, tissues, and organs of the human body work together to maintain life.[...]
A brief explanation is needed about several features of the 12th edition. Although many of the chapters have been revised to include new principles of physiology, the text length has been closely monitored to limit the book size so that it can be used effectively in physiology courses for medical students and health care professionals. Many of the figures have also been redrawn and are in full color. New references have been chosen primarily for their presentation of physiological principles, for the quality of their own references, and for their easy accessibility. The selected bibliography at the end of the chapters lists papers mainly from recently published scientific journals that can be freely accessed from the PubMed internet site at [...]. Use of these references, as well as cross-references from them, can give the student almost complete coverage of the entire field of physiology. The effort to be as concise as possible has, unfortunately, necessitated a more simplified and dogmatic presentation of many physiologic principles than I normally would have desired. However, the bibliography can be used to learn more about the controversies and unanswered questions that remain in understanding the complex functions of the human body in health and disease.
Another feature is that the print is set in two sizes. The material in large print constitutes the fundamental physiologic information that students will require in virtually all of their medical activities and studies.
The material in small print is of several different kinds: first, anatomic, chemical, and other information that is needed for immediate discussion but that most students will learn in more detail in other courses; second, physiologic information of special importance to certain fields of clinical medicine; and, third, information that will be of particular value to those students who may wish to study particular physiologic mechanisms more deeply."