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# [Embriologia] Langman

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Contents
part one
General Embryology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
chapter 1
Gametogenesis: Conversion of Germ Cells Into Male and
Female Gametes ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
chapter 2
First Week of Development: Ovulation to Implantation ............ . . . . . . . 31
chapter 3
Second Week of Development: Bilaminar Germ Disc ............ . . . . . . . . . . 51
chapter 4
Third Week of Development: Trilaminar Germ Disc ............. . . . . . . . . . . 65
chapter 5
Third to Eighth Week: The Embryonic Period ............... . . . . . . . . . . . . . . . . 87
chapter 6
Third Month to Birth: The Fetus and Placenta ................... . . . . . . . . . . . . 117
chapter 7
Birth Defects and Prenatal Diagnosis ................... . . . . . . . . . . . . . . . . . . . . . 149
part two
Special Embryology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
chapter 8
Skeletal System ............................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
ix
x Contents
chapter 9
Muscular System ........................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
chapter 10
Body Cavities ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
chapter 11
Cardiovascular System ......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
chapter 12
Respiratory System ........................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
chapter 13
Digestive System ........................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
chapter 14
Urogenital System .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
chapter 15
Head and Neck ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
chapter 16
Ear ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
chapter 17
Eye ................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
chapter 18
Integumentary System .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
chapter 19
Central Nervous System ......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
part three
Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
Answers to Problems .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
Figure Credits .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
Index ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
Preface
established by the original publication\u2014it provides a concise but thorough de-
scription of embryology and its clinical signi\ufb01cance, an awareness of which is
essential in the diagnosis and prevention of birth defects. Recent advances in ge-
netics, developmental biology, maternal-fetal medicine, and public health have
signi\ufb01cantly increased our knowledge of embryology and its relevance. Because
birth defects are the leading cause of infant mortality and a major contributor to
disabilities, and because newprevention strategies have been developed, under-
standing the principles of embryology is important for health care professionals.
To accomplish its goal, Langman\u2019s Medical Embryology retains its unique ap-
proach of combining an economy of text with excellent diagrams and scanning
electron micrographs. It reinforces basic embryologic concepts by providing
numerous clinical examples that result from abnormalities in developmental
processes. The following pedagogic features and updates in the ninth edition
help facilitate student learning:
Organization of Material: Langman\u2019s Medical Embryology is organized into two
parts. The \ufb01rst provides an overview of early development from gametogenesis
through the embryonic period; also included in this section are chapters on
placental and fetal development and prenatal diagnosis and birth defects. The
second part of the text provides a description of the fundamental processes of
embryogenesis for each organ system.
Molecular Biology: New information is provided about the molecular basis of
normal and abnormal development.
Extensive Art Program: This edition features almost 400 illustrations, includ-
ing new 4-color line drawings, scanning electron micrographs, and ultrasound
images.
Clinical Correlates: In addition to describing normal events, each chapter con-
tains clinical correlates that appear in highlighted boxes. This material is de-
signed to provide information about birth defects and other clinical entities that
are directly related to embryologic concepts.
vii
viii Preface
Summary: At the end of each chapter is a summary that serves as a concise
review of the key points described in detail throughout the chapter.
Problems to Solve: These problems test a student\u2019s ability to apply the infor-
mation covered in a particular chapter. Detailed answers are provided in an
appendix in the back of the book.
Simbryo: New to this edition, Simbryo, located in the back of the book, is
an interactive CD-ROM that demonstrates normal embryologic events and the
origins of some birth defects. This unique educational tool offers six original
vector art animation modules to illustrate the complex, three-dimensional as-
pects of embryology. Modules include normal early development as well as
head and neck, cardiovascular, gastrointestinal, genitourinary, and pulmonary
system development.
Connection Web Site: This student and instructor site (http://connection.
labus designed for use with the book. The syllabus contains objectives and
de\ufb01nitions of key terms organized by chapters and the \u201cbottom line,\u201d which
provides a synopsis of the most basic information that students should have
mastered from their studies.
I hope you \ufb01nd this edition of Langman\u2019s Medical Embryology to be an
excellent resource. Together, the textbook, CD, and connection site provide a
user-friendly and innovative approach to learning embryology and its clinical
relevance.
Twin Bridges, Montana
1
p a r t o n e
General
Embryology
c h a p t e r 1
Gametogenesis: Conversion
of Germ Cells Into Male and
Female Gametes
Primordial Germ Cells
Development begins with fertilization, the pro-
cess by which the male gamete, the sperm, and the
female gamete, the oocyte, unite to give rise to a zygote.
Gametes are derived from primordial germ cells (PGCs)
that are formed in the epiblast during the second week
and that move to the wall of the yolk sac (Fig. 1.1). During
the fourth week these cells begin to migrate from the yolk
sac toward the developing gonads, where they arrive by the
end of the \ufb01fth week. Mitotic divisions increase their number
during their migration and also when they arrive in the gonad.
In preparation for fertilization, germ cells undergo gametogenesis,
which includes meiosis, to reduce the number of chromosomes and
cytodifferentiation to complete their maturation.
C L I N I C A L C O R R E L A T E
Primordial Germ Cells (PGCs) and Teratomas