FETUSEssential elements of embryology 16th Edition ABEDUR RAHMAN MBBS (DMC), M Phil (DU) Editorial Assistant Dr. Farzana Iqbal Afrazul Haque Bhelejan Thakurgaon On behalf of Fetus Publications First published………. September, 1991. Second Edition………. September, 1993. Third Edition………. February, 1995. Fourth Edition………. September, 995. Fifth Edition……….January, 1997 Sixth Edition………. May, 1998 Seventh Edition……….March, 2000 Eighth Edition……….August, 2000 Ninth Edition………. May, 2002 Tenth Edition………. October, 2003 Eleventh Edition………. April, 2004 Twelfth Edition………. December, 2004 Thirteenth Edition………. February, 2006 Fourteenth Edition……….October, 2006 Fifteenth edition ……….January, 2008 Sixteenth edition ……….November, 2008 Published by MD. ABEDUR RAHMAN AII rights reserved. No part of this book may be reproduced or transmitted in any form or by any means without the written permission of the author. Cover Design: Abedur Rahman Price: Taka Three hundred and Twenty (320/-) only. For all kinds of correspondence: DR MD ABEDUR RAHMAN Phone: +88 01819-050041 E-mail:
[email protected] DISTRIBUTORS Ahad Book Center Allied Book Center Bangladesh Book Center Capital Book Center Keya Medical Book Center Mukti Book House New Bengal Library National Book Center Samima Book Center Setu Book Center Taj Medical Books Nilkhet, Dhaka Dedicated to My father for the uncompromising principle that guided his life. ACKNOWLEDGEMENTS I remember Dr. A. Hye Fakir EX-Head of the department of anatomy, BSMMU. Dr. Habibur Rahman. EX Head of the department of anatomy, SBMC Dr. Shahid-UlIah EX-Head of the department of anatomy, RPMC Dr. Kazi Rafiqul Haque Head of the department of anatomy, USTC. Chittogong Late Dr. S.S. Banik. Ex-Associate Professor of anatomy, SSMC. Dr. Motahar Hossain. Ex-Head of the department of anatomy, DMC. Dr. Manjar-e-Shamim. Professor & head of the department of anatomy, BSMMU. Dr. Shamim Ara Head of the department of anatomy, DMC Dr. Shafiq Haider Asst prof. of anatomy, CMC. for their good wishes to this publication Dr. Nazrul Islam Principal, Dinajpur Medical College Dr. Rubaiual Morshed Ex Asst. Professor, Pediatric Surgery, DMCH for their kind efforts in revising this book. I am also grateful to Alauddin (SOMC) and other students who made constructive criticism to make the book more helpful for the students. I want to acknowledge my students Juthy (K-63, DMC) and Sristi (K-63, DMC) for their whole hearted co-operation in editing this 16th edition of the book; Ilias (K-62, DMC), Juwel (K-63, DMC), Pritom (K-63, DMC), Fauzia (NUB) for their constructive criticism for making necessary correction of in this edition. I am also grateful to the doctors and students of different institutions and medical colleges who made constructive criticism to make the book more helpful for the embryology student. Forewords Excellent one I have gone through the book and found that the author has been succeeded in presenting the essential elements of embryology in an excellent manner. The elements served here are authentic. I hope that this humble presentation will serve its purposes well. My best wishes go to the author. Prof. Dr. Md. Nazrul Islam MBBS, M. Phil (DU), MS (Glasgow). MHPED (Australia) Principal, Dinajpur Medical College Ex Vice president, BMA Really charmed to find the simplicity I have gone through the book Fetus by Dr. Abedur Rahman with interest & have been really charmed to find the simplicity of its presentation & diagrams which depict the wide subject of embryology into the small space of this handy volume. Student can peep into the memory of the whole aspect of embryology through this book instantaneously and comfortably even at rest or in leisure like the cow which enjoys the taste of food by cutting its jaw while at rest. I wish the promising young author & his book a glorious success in the days to come. Dr. Kazi Rafiqul Huq Head, dept. of Anatomy USTC, Chittogong. AUTHOR’S SAYINGS “The history of man for nine months preceding his birth would, probably, be far more interesting, and contain events of greater moment than all three score and ten years that follow it.” --- Samuel Taylor Coleridge It is now well proved that ‘Fetus’ is the most read embryology book in our country. The last 15 editions of the book have proven that it is unique in its field. In this edition, I have tried my best to make it more useful for the students making necessary changes elsewhere. New to this edition- Development of different organs at a glance Answers of all first professional SAQ Some new information Some figures and information are modified. All praises for the Almighty. Thanks to all the anatomy teachers and students – past, present, and future. November 2008 Rahman Dr Md Abedur Contents Part-1: Introduction 1. Introduction to embryology 2. Reproduction and Development 3. Some basic concepts in embryology 4. Some historical elements on embryology Part-2: General Embryology 1 3 8 12 5. Gametogenesis: Conversion of germ cells into male & female gamete 21 34 6. Female reproductive cycles and ovulation 7. Pre-embryonic period – I: Fertilization, cleavage and implantation 8. Pre-embryonic period-II: Formation of germ layers (Gastrulation) 9. Embryonic period: Derivatives of germ layers 10. Fetal period Some facts concerning the fetus 11. Fetal membranes and placenta 12. Congenital malformations 13. Developmental genetics Part-3: Systemic Embryology 68 90 115 123 127 155 159 14. Cardiovascular system 15. Digestive system 16. Respiratory system 17. Diaphragm and septum transversum18. Urogenital system 19. Head neck and ear 20. Nervous system 21. Skeletal system 22. muscular system 23. Integumentary system Glossary Fetus 2 contents SAQ in Embryology Development of Different organ at a Glance 165 190 231 237 241 279 304 325 329 332 339 Look for the other books by the same author 1. D”P evW †cÖmvi: cÖwZKvi I cÖwZ‡iva 2.Medical Genetics 3.Research methodology 4.How to Write a thesis 5.Essentials of Biostatistics Sample Chapter 3 Some Basic Concepts in Embryology He that useth many words for the explaining of any subject, doth like the cuttle-fish hide himself---- in his own ink. John Ray (A naturalist of the 17th century) Differentiation It means formation of new type of cells or tissues. The differences of the cells or tissues that are formed is irreversible to those from which they are formed. For example, from the cells of the mesoderm bones develop or more clearly from the fertilized ovum the whole tissues or cells of the body develop. [see Gray. 37th P-107) Self and dependent differentiation (DU, Regular-81) Differentiation in which the fates of the earlier cells or tissues have been determined is called self differentiation. The differentiation in which the earlier cells or tissues suffer a stepwise restriction in their possible fates is called dependent differentiation. In the former, as the name suggests, a fragment (of developing tissue) when transplanted to an apparently indifferent region of the blastula or more critically into salt solution, proceeded to develop into the tissues it would have formed if undisturbed. Regions with dependent differentiation, however, it transplanted early, failed to continue development and only did so if combined with some neighboring mass of cells. If such a region, which at an early stage showed dependent differentiation, was not transplanted until a later stage, it was often found to have become self-differentiating. [Gray] Totipotent An embryonic cell capable of differentiating into a large variety of cells is called totipotent. The fertilized ovum has this ability [Taber’s]. Totipotent character may be retained upto 8 cell state of cleavage division of the zygote. (Datta) . Pluripotent Following repeated cleavage division of the zygote, the cells of morula lose the totipotent character but are succeeded by a plastic phase with reduced potencies. Plastic phase is denoted by pluripotent character of cells in which groups of cells produce specific type of tissue. [Datta] Thus, an embryonic cell that can differentiate into different (several) kinds of cell is called pluripotent. [Taber’s] Organiser and Induction Plastic phase of differentiation is followed by a phase of chemo-differentiation. Chemo-differentiation is probably a physio-chemical process and appears first in the cells of the dorsal lip of blastopore which corresponds with the primitive streak of higher vertebrates. These localized areas of the embryo induce directly tissue differentiation by liberating some chemical substances and are known as Organiser or inductor. By definition, “Embryonic tissues which have the organising capacity to differentiate neighboring tissues are called organiser or inductor and the process of such differentiation is called induction.” The dorsal lip of the blastopore or primitive streak acts as primary organiser and induces the development of notochord and secondary mesoderm. Notochord in turn acts as a secondary organiser and induces the development of brain and spinal cord from the overlying neuro-ectodermal plate. The neural tube (comes from this plate to form brain & spinal cord) again acts as a tertiary organiser and gives rise to somite formation of paraxial mesoderm. In this way, the entire embryonic area is mapped out into various individuation fields’. [Datta, 3rd, P-5, Singh 5th P.-382] Stem Cell Stem cells are commonly defined as undifferentiated cells. They have the ability to differentiate into virtually all kinds of cell types, a capacity that becomes progressively restricted with development. As shown in Figure below, they have two important characteristics that distinguish them from other types of cells. • First, as unspecialized cells, they can proliferate and renew themselves for long periods through cell division. • The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions. As the matter of fact, they provide a theoretically inexhaustible supply of cells that, depending on type can give rise to some or all body tissues. Figure: Definition of a stem cell. Stem cells are typically found in the embryo and fetus. In the adult body, they have been identified in various tissue niches, including bone marrow, brain, liver, and skin, as well as in the circulation. They have been termed "adult stem cells". Embryonic stem cells (ESC) Pluripotent murine (murine = pertaining to, derived from, or characteristic of mice or rats) stem cells are derived from two main embryonic sources: ESC from the blastocyst and embryonic germ (EG) cells from the gonadal ridge of the embryo after gastrulation. The successful derivation of murine ESC from the inner cell mass of mouse blastocytes was achieved in 1981 (Martin, 1981), while embryonic germ (EG) cells have been isolated and cultured from primordial germ cells (Stewart et al., 1994). Integration It is the process by which different tissues are brought together and combined to form organs. [Ref. Embryology by Cragmyle] Primordium It means cellular beginning of a future tissue, organ or part For example, arm bud is the primordium of arm. [Ref. Aids to Embryology by Samit publ.] Replication The process of duplication of genetic material is called replication. Terms of position In embryology, the terms dorsal and ventral are used to describe the back and front of the body respectively In embryology the terms cranial (cephalic) and caudal are used to denote relationships to the head and tail, respectively.