Embryology Ronald W. Dudek, PhD Professor Department of Anatomy and Cell Biology Brody School of Medicine East Carolina University Greenville, North Carolina Questions Contributor: H. Wayne Lambert, PhD LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page i Aptara Acquisitions Editor: Crystal Taylor Product Manager: Sirkka E. Howes Marketing Manager: Brian Moody Manufacturing Manager: Margie Orzech Designer: Holly Reid McLaughlin Vendor Manager: Bridgett Dougherty Compositor: Aptara, Inc. Fifth Edition Copyright © 2011, 2008, 2005, 1998, 1994 Lippincott Williams & Wilkins, a Wolters Kluwer business. Back cover images from Tasman W, Jaeger EA. Wills Eye Hospital Atlas of Clinical Ophthalmology. Philadelphia: Lippincott-Raven, 1996, and McMillan JA, DeAngelis CD, Feigin RD, et al., eds. Oski’s Pediatrics. 3rd Ed. 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Lippincott Williams & Wilkins customer service representatives are available from 8:30 am to 6:00 pm, EST. LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page ii Aptara Preface The fifth edition of BRS Embryology has afforded me the opportunity to further fine- tune a work that was already a highly rated course review book as well as an excellent review for the USMLE Step 1. This fine-tuning is a result of the many students who have contacted me by e-mail to point out errors and give suggestions for improve- ment. I appreciate this student feedback very much. In the fifth edition, I have placed clinical images closer to the corresponding text to make reviewing more efficient. As in the previous edition, the Comprehensive Examination at the end of the book reflects the USMLE Step 1 format. I hope that students will continue to find BRS Embryology a clear and thorough review of embryology. After taking the USMLE Step 1, I invite you to e-mail me at dudekr@ecu.edu to convey any comments or to indicate any area that was particu- larly represented on the USMLE Step 1, so that future editions of this book may improve. Ronald W. Dudek, PhD iii LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page iii Aptara Preface iii 1. PREFERTILIZATION EVENTS 1 I. Sexual Reproduction 1 II. Chromosomes 1 III. Meiosis 2 IV. Oogenesis: Female Gametogenesis 2 V. Spermatogenesis: Male Gametogenesis 4 VI. Clinical Considerations 4 Study Questions for Chapter 1 8 Answers and Explanations 10 2. WEEK 1 OF HUMAN DEVELOPMENT (DAYS 1–7) 12 I. Fertilization 12 II. Cleavage and Blastocyst Formation 12 III. Implantation 13 IV. Clinical Considerations 14 Study Questions for Chapter 2 15 Answers and Explanations 17 3. WEEK 2 OF HUMAN DEVELOPMENT (DAYS 8–14) 18 I. Further Development of the Embryoblast 18 II. Further Development of the Trophoblast 18 III. Development of Extraembryonic Mesoderm 18 IV. Clinical Considerations 20 Study Questions for Chapter 3 22 Answers and Explanations 24 4. EMBRYONIC PERIOD (WEEKS 3–8) 26 I. General Considerations 26 II. Further Development of the Embryoblast 26 III. Vasculogenesis (De Novo Blood Vessel Formation) 29 Contents iv LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page iv Aptara Contents v IV. Hematopoiesis (Blood Cell Formation) 31 V. Clinical Considerations 31 Study Questions for Chapter 4 33 Answers and Explanations 35 5. CARDIOVASCULAR SYSTEM 37 I. Formation of Heart Tube 37 II. Primitive Heart Tube Dilations 37 III. The Aorticopulmonary (AP) Septum 39 IV. The Atrial Septum 41 V. The Atrioventricular (AV) Septum 43 VI. The Interventricular (IV) Septum 45 VII. The Conduction System of the Heart 46 VIII. Coronary Arteries 47 IX. Development of the Arterial System 47 X. Development of the Venous System 49 Study Questions for Chapter 5 50 Answers and Explanations 53 6. PLACENTA AND AMNIOTIC FLUID 55 I. Formation of the Placenta 55 II. Placental Components: Decidua Basalis and Villous Chorion 55 III. Placental Membrane 58 IV. The Placenta as an Endocrine Organ 59 V. The Umbilical Cord 60 VI. Circulatory System of the Fetus 60 VII. Amniotic Fluid 62 VIII. Twinning 62 IX. Clinical Considerations 64 Study Questions for Chapter 6 67 Answers and Explanations 69 7. NERVOUS SYSTEM 70 I. Overview 70 II. Development of the Neural Tube 70 III. Neural Crest Cells 72 IV. Placodes 74 V. Vesicle Development of the Neural Tube 74 VI. Histogenesis of the Neural Tube 75 VII. Layers of the Early Neural Tube 77 VIII. Development of the Spinal Cord 77 IX. Development of the Myelencephalon 78 X. Development of the Metencephalon 79 XI. Development of the Mesencephalon 80 LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page v Aptara vi Contents XII. Development of the Diencephalon, Optic Structures, and Hypophysis 81 XIII. Development of the Telencephalon 82 XIV. Development of the Sympathetic Nervous System 84 XV. Development of the Parasympathetic Nervous System 84 XVI. Development of the Cranial Nerves 84 XVII. Development of the Choroid Plexus 85 XVIII. Congenital Malformations of the Central Nervous System 86 Study Questions for Chapter 7 93 Answers and Explanations 96 8. EAR 98 I. Overview 98 II. The Internal Ear 98 III. The Membranous and Bony Labyrinths 98 IV. Middle Ear 100 V. External Ear 100 VI. Congenital Malformations of the Ear 101 Study Questions for Chapter 8 104 Answers and Explanations 105 9. EYE 106 I. Development of the Optic Vesicle 106 II. Development of Other Eye Structures 109 III. Congenital Malformations of the Eye 110 Study Questions for Chapter 9 113 Answers and Explanations 114 10. DIGESTIVE SYSTEM 115 I. Overview 115 II. Derivatives of the Foregut 115 III. Derivatives of the Midgut 123 IV. Derivatives of the Hindgut 127 V. Anal Canal 130 VI. Mesenteries 130 Study Questions for Chapter 10 131 Answers and Explanations 133 11. RESPIRATORY SYSTEM 134 I. Upper Respiratory System 134 II. Lower Respiratory System 134 Study Questions for Chapter 11 142 Answers and Explanations 144 LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page vi Aptara Contents vii 12. HEAD AND NECK 145 I. Pharyngeal Apparatus 145 II. Development of the Thyroid Gland 145 III. Development of the Tongue 147 IV. Development of the Face 148 V. Development of the Palate 149 VI. Development of the Mouth 150 VII. Development of the Nasal Cavities 150 VIII. Clinical Considerations 151 Study Questions for Chapter 12 154 Answers and Explanations 155 13. URINARY SYSTEM 156 I. Overview 156 II. Development of the Metanephros 156 III. Relative Ascent of the Kidneys 157 IV. Blood Supply of the Kidneys 158 V. Development of the Urinary Bladder 159 VI. Development of the Female Urethra 159 VII. Development of the Male Urethra 160 VIII. Clinical Considerations 161 IX. Development of the Suprarenal Gland 165 Study Questions for Chapter 13 169 Answers and Explanations 170 14. FEMALE REPRODUCTIVE SYSTEM 171 I. The Indifferent Embryo 171 II. Development of the Gonads 171 III. Development of the Genital Ducts 173 IV. Development of the Primordia of External Genitalia 175 V. Tanner Stages of Female Sexual Development 176 VI. Clinical Considerations 176 Study Questions for Chapter 14 180 Answers and Explanations 181 15. MALE REPRODUCTIVE SYSTEM 182 I. The Indifferent Embryo 182 II. Development of the Gonads 182 III. Development of the Genital Ducts 184 IV. Development of the Primordia of External Genitalia 186 V. Tanner Stages of Male Sexual Development 186 VI. Clinical Considerations 186 VII. Summary 191 Study Questions for Chapter 15 192 Answers and Explanations 193 LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page vii Aptara viii Contents 16. INTEGUMENTARY SYSTEM 194 I. Skin 194 II. Hair and Nails 198 III. Mammary, Sweat, and Sebaceous Glands 201 IV. Teeth 203 Study Questions for Chapter 16 205 Answers and Explanations 206 17. SKELETAL SYSTEM 207 I. Skull 207 II. Vertebral Column 211 III. Ribs 216 IV. Sternum 216 V. Bones of the Limbs and Limb Girdles 216 VI. Osteogenesis 217 VII. General Skeletal Abnormalities 217 Study Questions for Chapter 17 220 Answers and Explanations 221 18. MUSCULAR SYSTEM 222 I. Skeletal Muscle 222 II. Smooth Muscle 223 III. Cardiac Muscle 224 IV. Clinical Considerations 224 Study Questions for Chapter 18 226 Answers and Explanations 227 19. UPPER LIMB 228 I. Overview of Development 228 II. Vasculature 228 III. Musculature 230 IV. Nerves: The Brachial Plexus 230 V. Rotation of the Upper Limb 231 VI. Skeletal 232 Study Questions for Chapter 19 234 Answers and Explanations 235 20. LOWER LIMB 236 I. Overview of Development 236 II. Vasculature 236 III. Musculature 238 IV. Nerves: The Lumbosacral Plexus 238 LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page viii Aptara [...]... include abnormalities of the epididymis, abnormalities of the vas deferens, and defective ejaculation 4 Hypothalamic-pituitary disease (1%–2% of cases) This includes congenital idiopathic hypogonadotropic hypogonadism caused by a defect in gonadotropin-releasing factor (GRF) secretion from the hypothalamus, acquired hypogonadotropic hypogonadism caused by a pituitary macroadenoma, surgical therapy for... nondisjunction Clinical findings include moderate mental retardation, microcephaly, microphthalmia, colobomata, cataracts and glaucoma, flat nasal bridge, epicanthal folds, protruding tongue, Brushfield spots, simian crease in the hand, increased nuchal skin folds, congenital heart defects, and an association with a decrease in ␣-fetoprotein LWBK507-c01_p01-11.qxd 11/01/2010 08:45 AM Page 5 Aptara Chapter... period (LNMP age) In this book, age is presented as the fertilization age 12 LWBK507-c02_p12-17.qxd 11/01/2010 01:08 PM Page 13 Aptara Chapter 2 Week 1 of Human Development (Days 1–7) 13 considered totipotent (capable of forming a complete embryo) up to the 4- to 8-cell stage (important when considering monozygotic twinning) 2 Blastomeres form a morula by undergoing compaction, that is, tight junctions... structures from each of the three primary germ layers: for example, colon glandular tissue (endoderm), cartilage (mesoderm), and squamous epithelium (ectoderm) 3 TTC also contains undifferentiated pluripotent stem cells called embryonic carcinoma (EC) cells 4 TTC is associated with elevated ␣-fetoprotein levels 5 TTC can be experimentally produced by implanting a blastocyst in an extrauterine site The... mitochondria present within the secondary oocyte (maternal) remain in the fertilized zygote 8 C This scenario would result in four genetically identical children Blastomeres at the 4to 8-cell stage are totipotent, that is, capable of forming an entire embryo Since blastomeres arise by mitosis of the same cell (zygote), they are genetically identical This phenomenon is important in explaining monozygotic . Designer: Holly Reid McLaughlin Vendor Manager: Bridgett Dougherty Compositor: Aptara, Inc. Fifth Edition Copyright © 2011, 2008, 2005, 1998, 1994 Lippincott Williams & Wilkins, a Wolters. student feedback very much. In the fifth edition, I have placed clinical images closer to the corresponding text to make reviewing more efficient. As in the previous edition, the Comprehensive Examination. 8:30 am to 6:00 pm, EST. LWBK507-FM-i-x.qxd 11/01/2010 07:38 PM Page ii Aptara Preface The fifth edition of BRS Embryology has afforded me the opportunity to further fine- tune a work that was already