FETUSEssential elements of embryology

16th Edition

ABEDUR RAHMAN MBBS (DMC), M Phil (DU)

Editorial Assistant

Dr. Farzana Iqbal

Published byAfrazul 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, 2000Eighth Edition……….August, 2000

Ninth Edition………. May, 2002 Tenth Edition………. October, 2003 Eleventh Edition………. April, 2004

Twelfth Edition………. December, 2004Thirteenth Edition………. February, 2006Fourteenth Edition……….October, 2006Fifteenth edition ……….January, 2008

Sixteenth edition ……….November, 2008

MD. ABEDUR RAHMANAII 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: abeddmc@yahoo.com

DISTRIBUTORS

Ahad Book CenterAllied Book Center

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Keya Medical Book CenterMukti Book House

New Bengal LibraryNational Book CenterSamima Book Center

Setu Book CenterTaj Medical Books

Nilkhet, Dhaka

Dedicated to

My father

for the uncompromising

principle that guided his life.

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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.

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Prof. Dr. Md. Nazrul Islam MBBS, M. Phil (DU), MS (Glasgow). MHPED (Australia) Principal, Dinajpur Medical College Ex Vice president, BMA

Dr. Kazi Rafiqul Huq Head, dept. of Anatomy USTC, Chittogong.

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Forewords

Excellent oneI 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.

Really charmed to find the simplicityI 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.

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AUTHOR’S SAYINGS

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“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 Dr Md Abedur Rahman

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Contents

Part-1: Introduction

1. Introduction to embryology 1

2. Reproduction and Development 33. Some basic concepts in embryology 84. Some historical elements on embryology 12

Part-2: General Embryology

5. Gametogenesis: Conversion of germ cells into male & female gamete

21

6. Female reproductive cycles and ovulation 347. Pre-embryonic period – I: Fertilization, cleavage and implantation 688. Pre-embryonic period-II: Formation of germ layers (Gastrulation) 909. Embryonic period: Derivatives of germ layers 11510. Fetal period Some facts concerning the fetus 12311. Fetal membranes and placenta 12712. Congenital malformations 15513. Developmental genetics 159

Part-3: Systemic Embryology

14. Cardiovascular system 16515. Digestive system 19016. Respiratory system 23117. Diaphragm and septum transversum- 23718. Urogenital system 24119. Head neck and ear 27920. Nervous system 30421. Skeletal system 32522. muscular system 32923. Integumentary system 332Glossary 339

Fetus 2 contentsSAQ in EmbryologyDevelopment of Different organ at a Glance

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Look for the other books by the same author

1. D”P evW †cÖmvi: cÖwZKvi I cÖwZ‡iva

2. Medical Genetics3. Research methodology4. How to Write a thesis5. Essentials of Biostatistics

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Sample Chapter

3Some 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 areformed. 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

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differentiation, was not transplanted until a later stage, it was often found to have become self-differentiating. [Gray]

TotipotentAn 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 CellStem 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.

      

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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.]

ReplicationThe 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

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In embryology the terms cranial (cephalic) and caudal are used to denote relationships to the head and tail, respectively.

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