About the Book

As the study of embryology continues to be integrated with a range of
disciplines, this textbook remains the ideal solution for students who need to
quickly learn the basics. Fully updated by the world’s foremost embryologists,
Before We Are Born provides concise guidance on human embryology at
every stage of development, using rich illustrations and photographs designed
to further explain content.

About the Author

KEITH L. MOORE Recipient of the inaugural Henry Gray/Elsevier Distinguished Educator Award in 2007 —the American Association of Anatomists ’ highest award for excellence in human anatomy education at the medical/dental, graduate, and undergraduate levels of teaching; the Honored Member Award of the American Association of Clinical Anatomists (1994) for signifi cant contributions to the fi eld of clinically relevant anatomy; and the J.C.B. Grant Award of the Canadian Association of Anatomists (1984) “in recognition of meritorious service and outstanding scholarly accomplishments in the fi eld of anatomical sciences.” In 2008 Professor Moore was inducted as a Fellow of the American Association of Anatomists . The rank of Fellow honors distinguished AAA members who have demonstrated excellence in science and in their overall contributions to the medical sciences. In 2012 Dr. Moore received an Honorary Doctor of Science degree from The Ohio State University; The Queen Elizabeth II Diamond Jubilee Medal honoring signifi cant contributions and achievements by Canadians; and the Benton Adkins Jr. Distinguished Service Award for an outstanding record of service to the American Association of Clinical Anatomists. T.V.N. (VID) PERSAUD Recipient of the Henry Gray/Elsevier Distinguished Educator Award in 2010 —the American Association of Anatomists ’ highest award for excellence in human anatomy education at the medical/dental, graduate, and undergraduate levels of teaching; the Honored Member Award of the American Association of Clinical Anatomists (2008) for signifi cant contributions to the fi eld of clinically relevant anatomy; and the J.C.B. Grant Award of the Canadian Association of Anatomists (1991) “in recognition of meritorious service and outstanding scholarly accomplishments in the fi eld of anatomical sciences.” In 2010 Professor Persaud was inducted as a Fellow of the American Association of Anatomists . The rank of Fellow honors distinguished AAA members who have demonstrated excellence in science and in their overall contributions to the medical sciences. In 2003 Dr. Persaud was a recipient of the Queen Elizabeth II Golden Jubilee Medal , presented by the Government of Canada for “signifi cant contribution to the nation, the community, and fellow Canadians.” MARK G. TORCHIA Recipient of the Norman and Marion Bright Memorial Medal and Award and the Silver Medal of the Chemical Institute of Canada in 1990 for outstanding contributions. In 1993 he was awarded the TIMEC Medical Device Champion Award . In 2008 and in 2014 Dr. Torchia was a nominee for the Manning Innovation Awards , for innovation talent. Dr. Torchia ’ s most cherished award has been the Award for Teaching Excellence in 2011 from the Faculty of Medicine, University of Manitoba, and being asked to address the graduating class of 2014.

Table of Contents:
1. Introduction to Human Development Importance of and Advances in Embryology Descriptive Terms Clinically Oriented Questions 2 Human Reproduction Reproductive Organs Female Reproductive Organs Male Reproductive Organs Gametogenesis Meiosis Spermatogenesis Oogenesis Comparison of Male and Female Gametes Female Reproductive Cycles Ovarian Cycle Menstrual Cycle Transportation of Gametes Oocyte Transport Sperm Transport Maturation of Sperms Viability of Oocytes and Sperms Clinically Oriented Questions 3 First Week of Human Development Fertilization Phases of Fertilization Results of Fertilization Cleavage of Zygote Formation of Blastocyst Clinically Oriented Questions 4 Second Week of Human Development Formation of Amniotic Cavity, Embryonic Disc, and Umbilical Vesicle Development of Chorionic Sac Implantation Sites of Blastocysts Clinically Oriented Questions Third Week of Human Development Gastrulation: Formation of Germ Layers Primitive Streak Notochordal Process and Notochord Neurulation: Formation of the Neural Tube Neural Plate and Neural Tube Neural Crest Formation Development of Somites Development of Intraembryonic Coelom Early Development of Cardiovascular System Vasculogenesis and Angiogenesis Development of Chorionic Villi Clinically Oriented Questions 6 Fourth to Eighth Weeks of Human Development Folding of Embryo Head and Tail Folds Lateral Folds Germ Layer Derivatives Control of Embryonic Development Estimation of Embryonic Age Highlights of the Fourth to Eighth Weeks Fourth Week Fifth Week Sixth Week Seventh Week Eighth Week Clinically Oriented Questions 7 Fetal Period: The Ninth Week to Birth Highlights of Fetal Period Nine to Twelve Weeks Thirteen to Sixteen Weeks Seventeen to Twenty Weeks Twenty-One to Twenty-Five Weeks Twenty-Six to Twenty-Nine Weeks Thirty to Thirty-Eight Weeks Expected Date of Delivery Factors Infl uencing Fetal Growth Procedures for Assessing Fetal Status Ultrasonography Diagnostic Amniocentesis Chorionic Villus Sampling Cell Cultures Percutaneous Umbilical Cord Blood Sampling Magnetic Resonance Imaging Fetal Monitoring Alpha-Fetoprotein Assay Noninvasive Prenatal Diagnosis Neonatal Period Clinically Oriented Questions 8 Placenta and Fetal Membranes Placenta Decidua Development of Placenta Fetomaternal Junction Intervillous Space Amniochorionic Membrane Placental Circulation Parturition Stages of Labor Placenta and Fetal Membranes after Birth Umbilical Cord Amnion and Amniotic Fluid Signifi cance of Amniotic Fluid Umbilical Vesicle Signifi cance of Umbilical Vesicle Allantois Multiple Pregnancies Twins and Fetal Membranes Other Types of Multiple Births Clinically Oriented Questions 9 Body Cavities, Mesenteries, and Diaphragm Embryonic Body Cavity Mesenteries Division of Embryonic Body Cavity Development of Diaphragm Septum Transversum Pleuroperitoneal Membranes Dorsal Mesentery of Esophagus Muscular Ingrowth from Lateral Body Walls Positional Changes and Innervation of the Diaphragm Clinically Oriented Questions 10 Pharyngeal Apparatus, Face, and Neck Pharyngeal Arches Pharyngeal Arch Components Pharyngeal Pouches Derivatives of Pharyngeal Pouches Pharyngeal Grooves Pharyngeal Membranes Development of Thyroid Gland Development of Tongue Lingual Papillae and Taste Buds Nerve Supply of Tongue Development of Salivary Glands Development of Face Development of Nasal Cavities Paranasal Sinuses Development of Palate Primary Palate Secondary Palate Clinically Oriented Questions 11 Respiratory System Development of Larynx Development of Trachea Development of Bronchi and Lungs Maturation of Lungs Clinically Oriented Questions 12 Alimentary System Foregut Development of Esophagus Development of Stomach Development of Duodenum Development of Liver and Biliary Apparatus Development of Pancreas Development of Spleen Midgut Rotation of Midgut Loop Cecum and Appendix Hindgut Cloaca Anal Canal Clinically Oriented Questions 13 Urogenital System Development of Urinary System Development of Kidneys and Ureters Positional Changes of Kidneys Changes in Blood Supply of Kidneys Development of Urinary Bladder Development of Urethra Development of Suprarenal Glands Development of Genital System Development of Gonads Development of Genital Ducts Development of External Genitalia Development of Inguinal Canals Relocation of Testes and Ovaries Descent of Testes Descent of Ovaries Clinically Oriented Questions 14 Cardiovascular System Early Development of Heart and Blood Vessels Development of Veins Associated with Embryonic Heart Pharyngeal Arch Arteries and Other Branches of the Dorsal Aorta Fate of Vitelline and Umbilical Arteries Later Development of Heart Circulation through Primordial Heart Partitioning of Primordial Heart Changes in Sinus Venosus Primordial Pulmonary Vein and Formation of Left Atrium Partitioning of Primordial Ventricle Partitioning of Bulbus Cordis and Truncus Arteriosus Development of Cardiac Valves Conducting System of Heart Birth Defects of Heart and Great Vessels Derivatives of Pharyngeal Arch Arteries Derivatives of First Pair of Pharyngeal Arch Arteries Derivatives of Second Pair of Pharyngeal Arch Arteries Derivatives of Third Pair of Pharyngeal Arch Arteries Derivatives of Fourth Pair of Pharyngeal Arch Arteries Fate of Fifth Pair of Pharyngeal Arch Arteries Derivatives of Sixth Pair of Pharyngeal Arch Arteries Pharyngeal Arch Arterial Birth Defects Fetal and Neonatal Circulation Fetal Circulation Transitional Neonatal Circulation Derivatives of Fetal Vessels and Structures Development of the Lymphatic System Development of Lymph Nodes Development of Spleen and Tonsils Clinically Oriented Questions 15 Musculoskeletal System Skeletal System Development of Cartilage and Bone Histogenesis of Cartilage Histogenesis of Bone Development of Joints Fibrous Joints Cartilaginous Joints Synovial Joints Development of Axial Skeleton Development of Vertebral Column Cartilaginous Stage of Vertebral Development Bony Stage of Vertebral Development Development of Ribs Development of Sternum Development of Cranium Development of Appendicular Skeleton Muscular System Development of Skeletal Muscle Development of Smooth Muscle Development of Cardiac Muscle Development of Limbs Early Stages of Limb Development Final Stages of Limb Development Cutaneous Innervation of Limbs Blood Supply of Limbs Clinically Oriented Questions 16 Nervous System Development of Nervous System Development of Spinal Cord Development of Spinal Ganglia Development of Spinal Meninges Positional Changes of Spinal Cord Myelination of Nerve Fibers Birth Defects of Spinal Cord Development of Brain Brain Flexures Hindbrain Myelencephalon Metencephalon Choroid Plexuses and Cerebrospinal Fluid Midbrain Forebrain Congenital Anomalies of Brain Development of Peripheral Nervous System Spinal Nerves Cranial Nerves Development of Autonomic Nervous System Sympathetic Nervous System Parasympathetic Nervous System Clinically Oriented Questions 17 Development of Eyes and Ears Development of Eyes and Related Structures Development of Retina Development of Choroid and Sclera Development of Ciliary Body Development of Iris Development of Lens Development of Aqueous Chambers Development of Cornea Development of Eyelids Development of Lacrimal Glands Development of Ears Development of Internal Ears Development of Middle Ears Development of External Ears Clinically Oriented Questions 289 18 Integumentary System Development of Skin and Appendages Epidermis Dermis Development of Glands Development of Hairs Development of Nails Development of Mammary Glands Development of Teeth Bud Stage of Tooth Development Cap Stage of Tooth Development Bell Stage of Tooth Development Tooth Eruption Clinically Oriented Questions 19 Human Birth Defects Teratology: Study of Abnormal Development Birth Defects Caused by Genetic Factors Numerical Chromosomal Abnormalities Structural Chromosomal Abnormalities Birth Defects Caused by Mutant Genes Birth Defects Caused by Environmental Factors Principles of Teratogenesis Human Teratogens Environmental Chemicals as Teratogens Infectious Agents as Teratogens Radiation as a Teratogen Maternal Factors as Teratogens Mechanical Factors as Teratogens Birth Defects Caused by Multifactorial Inheritance Clinically Oriented Questions 20 The Cellular and Molecular Basis of Development Intercellular Communication Gap Junctions Cell Adhesion Molecules Morphogens Retinoic Acid Transforming Growth Factor-ß/Bone Morphogenetic Protein Sonic Hedgehog Wnt/ß-Catenin Pathway Receptor Tyrosine Kinases 325 Common Features Regulation of Angiogenesis by Receptor Tyrosine Kinases Notch-Delta Pathway Transcription Factors Hox/Homeobox Proteins Pax Genes Basic Helix-Loop-Helix Transcription Factors Epigenetics DNA Methylation Histone Modifications Stem Cells: Differentiation versus Pluripotency Summary of Common Signaling Pathways Used during Development Bibliography and Suggested Reading Answers to Clinically Oriented Questions Index