Human Embryology and Developmental Biology: With STUDENT CONSULT Online Access 5th Edition
As was the case in the preparation of the fourth edition (and for that matter, also the previous editions), the conundrum facing me was what to include and what not to include in the text, given the continuing explosion of new information on almost every aspect of embryonic development. This question always leads me back to the fundamental question of what kind of book I am writing and what are my goals in writing it. As a starting point, I would go back to first principles and the reason why I wrote the first edition of this text. In the early 1990s, medical embryology was confronted with the issue of integrating traditional developmental anatomy with the newly burgeoning field of molecular embryology and introducing those already past their formal learning years to the fact that genes in organisms as foreign as Drosophila could have relevance in understanding the cause of human pathology or even normal development. This is no longer the case, and the issue today is how to place reasonable limits on coverage for an embryology text that is not designed to be encyclopedic.
For this text, my intention is to remain focused both on structure and on developmental mechanisms leading to structural and functional outcomes during embryogenesis. A good example is mention of the many hundreds of genes, mutations of which are known to produce abnormal developmental outcomes. If the mutation can be tied to a known mechanism that can illuminate how an organ develops, it would be a candidate for inclusion, whereas without that I feel that at present it is normally more appropriate to leave its inclusion in comprehensive human genetic compendia. Similarly, the issue of the level of detail of intracellular pathways to include often arises. Other than a few illustrative examples, I have chosen not to emphasize these pathways.
The enormous amount of new information on molecular networks and interacting pathways is accumulating to the point where new texts stressing these above other aspects of development could be profitably written. Often, where many molecules, whether transcription factors or signaling molecules, are involved in a developmental process, I have tried to choose what I feel are the most important and most distinctive, rather than to strive for completeness. Especially because so many major molecules or pathways are reused at different stages in the development of a single structure, my sense is that by including everything, the distinctiveness of the development of the different parts of the body would be blurred for the beginning student. As usual, I welcome feedback ([email protected]) and would be particularly interested to learn whether students or instructors believe that there is too much or too little molecular detail either overall or in specific areas.
In this edition, almost every chapter has been extensively revised, and more than 50 new figures have been added. Major additions of relevant knowledge of early development, especially related to the endoderm, have led to significant changes in Chapters 3, 5, 6, 14, and 15. Chapter 12 on the neural crest has been completely reorganized and was largely rewritten. Chapter 9 (on skin, skeleton, and muscle) has also seen major changes. Much new information on germ cells and early development of the gonads has been added to Chapter 16, and in Chapter 17 new information on the development of blood vessels and lymphatics has resulted in major changes.
For this edition, I have been fortunate in being allowed to use photographs from several important sources. From the late Professor Gerd Steding’s The Anatomy of the Human Embryo (Karger) I have taken eight scanning electron micrographs of human embryos that illustrate better than drawings the external features of aspects of human development. I was also able to borrow six photographs of important congenital malformations from the extensive collection of the late Dr. Robert Gorlin, one of the fathers of syndromology. This inclusion is particularly poignant to me because while we were students at the University of Minnesota in the early 1960s, both my wife and I got to know him before he became famous. This edition includes a new Clinical Correlation on dental anomalies written by Dr. Pranit N. Kantaputra from the Department of Orthodontics and Pediatric Dentistry at Chiang Mai University in Chiang Mai, Thailand. He has assembled a wonderful collection of dental anomalies that have a genetic basis, and I am delighted to share his text and photos with the readers. Finally, I was able to include one digitized photograph of a sectioned human embryo from the Carnegie Collection. For this I thank Dr. Raymond Gasser for his herculean efforts in digitizing important specimens from that collection and making them available to the public. All these sections (labeled) are now available online through the Endowment for Human Development (www.ehd.ord), which is without question the best source of information on human embryology on the Internet. I would recommend this source to any student or instructor.
In producing this edition, I have been fortunate to be able to work with much of the team that was involved on the last edition. Alexandra Baker of DNA Illustrations, Inc. has successfully transformed my sketches into wonderful artwork for the past three editions. I thank her for her patience and her care. Similarly, Andrea Vosburgh and her colleagues at Elsevier have cheerfully succeeded in transforming a manuscript and all the trimmings into a recognizable book. Madelene Hyde efficiently guided the initial stages of contracts through the corporate labyrinth. Thanks, as always, to Jean, who provided a home environment compatible with the job of putting together a book and for putting up with me during the process.
Bruce M. Carlson
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