High-Yield TM Embryology FIFTH EDITION High-Yield TM Embryology FIFTH EDITION Ronald W. Dudek, PhD Professor Brody School of Medicine East Carolina University Department of Anatomy and Cell Biology Greenville, North Carolina Acquisitions Editor: Crystal Taylor Product Manager: Lauren Pecarich Marketing Manager: Joy Fisher Williams Vendor Manager: Bridgett Dougherty Manufacturing Manager: Margie Orzech Design Coordinator: Terry Mallon Compositor: S4Carlisle Publishing Services Copyright © 2014, 2010, 2007, 2001, 1996 Lippincott Williams & Wilkins, a Wolters Kluwer business. 351 West Camden Street 530 Walnut Street Baltimore, MD 21201 Philadelphia, PA 19106 Printed in China All rights reserved. This book is protected by copyright. No part of this book may be reproduced or transmitted in any form or by any means, including as photocopies or scanned-in or other electronic copies, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotations embodied in critical articles and reviews. Materials appear- ing in this book prepared by individuals as part of their official duties as U.S. government employees are not covered by the above-mentioned copyright. To request permission, please contact Lippincott Williams & Wilkins at 530 Walnut Street, Philadelphia, PA 19106, via email at [email protected], or via website at lww.com (products and services). 9 8 7 6 5 4 3 2 1 Library of Congress Cataloging-in-Publication Data ISBN-13: 978-1-4511-7610-0 ISBN-10: 1-4511-7610-4 Cataloging-in-Publication data available on request from the Publisher. DISCLAIMER Care has been taken to confirm the accuracy of the information present and to describe g enerally accepted practices. However, the authors, editors, and publisher are not responsible for errors or omis- sions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the pub- lication. Application of this information in a particular situation remains the professional responsibility of the practitioner; the clinical treatments described and recommended may not be considered absolute and universal recommendations. The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with the current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new or infrequently employed drug. Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice. To purchase additional copies of this book, call our customer service department at (800) 638-3030 or fax orders to (301) 223-2320. International customers should call (301) 223-2300. Visit Lippincott Williams & Wilkins on the Internet: http://www.lww.com. Lippincott Williams & Wilkins customer service representatives are available from 8:30 am to 6:00 pm, EST. I would like to dedicate this book to my father, Stanley J. Dudek, who died Sunday, March 20, 1988, at 11 A.M. It was his hard work and sacrifice that allowed me access to the finest educational institutions in the country (St. John’s University in Collegeville, MN; the University of Minnesota Medical School; Northwestern University; and the University of Chicago). It was by hard work and sacrifice that he showed his love for his wife, Lottie; daughter, Christine; and grandchildren, Karolyn, Katie, and Jeannie. I remember my father often as a good man who did the best he could. Who could ask for more? My father is missed and remembered by many. Preface The fifth edition of High-Yield™ Embryology includes improvements based on suggestions and comments from the many medical students who have used this book in preparation for the USMLE Step 1 examination and those students who have reviewed the book. I pay close attention to these suggestions and comments in order to improve the quality of this book. The goal of High-Yield™ Embryology is to provide an accurate and quick review of important clinical aspects of embryology for the future physician. Many times in the history of science, certain biological concepts become entrenched and ac- cepted as dogma even though recent evidence comes to light to challenge these concepts. One of these concepts is the process of twinning. Recent evidence calls into question the standard figures used in textbooks on how the process of twinning occurs. In particular, it is becoming increasingly difficult to ignore the fact that dizygotic twins are sometimes monochorionic. Although we by far do not know or attempt to explain exactly how twinning occurs, it seems that the interesting cell and molecular events involved in twinning occur in the first few cell divisions during first three or four days after fertilization. You are not a twin because the inner cell mass splits. The inner cell mass splits because you are a twin. This evidence warrants a new twinning figure (Figure 2-2) that does not comport with the standard figures but tries to embrace recent evidence although many may call it controversial. Progress in our scientific understanding of twinning will never occur if our concept of the twinning process is overly simplistic and reinforced by standard figures repeated over and over in textbooks. Some published references that speak to this twinning issue include Boklage (2009, 2010), Yoon et al. (2005), Williams et al. (2004), and Hoekstra et al. (2008). I understand that High-Yield™ Embryology is a review book designed for a USMLE Step 1 review and that you will not be faced with a question regarding this twinning concept, but I know my readers are sophisticated enough to appreciate the scientific and clinical value of being chal- lenged to question traditional concepts as “grist for the mill” in discussions with your colleagues. I would appreciate receiving your comments and/or suggestions concerning High-Yield™ Embryology, Fifth Edition, especially after you have taken the USMLE Step 1 examination. Your suggestions will find their way into the sixth edition. You may contact me at [email protected]. References Boklage CE. Traces of embryogenesis are the same in monozygotic and dizygotic twins: not compatible with double ovulation. Hum Reprod. 2009;24(6):1255–1266. Boklage CE. How New Humans Are Made: Cells and Embryos, Twins and Chimeras, Left and Right, Mind/Self/Soul, Sex, and Schizophrenia. Hackensack, NJ; London: World Scientific Publishing; 2010. Yoon G, Beischel LS, Johnson JP, et al. Dizygotic twin pregnancy conceived with assisted reproductive tech- nology associated with chromosomal anomaly, imprinting disorder, and monochorionic placentation. J Pediatr. 2005;146:565–567. Williams CA, Wallace MR, Drury KC, et al. Blood lymphocyte chimerism associated with IVF and monocho- rionic dizygous twinning: Case report. Hum Reprod. 2004;19(12):2816–2821. Hoekstra C, Zhao ZZ, Lambalk CB, et al. Dizygotic twinning. Hum Reprod Update. 2008;14(1):37–47. vii