Embryology 1.pptx

Early Embryology Embryology Lecture Objectives • In general, what happens in the first and second phases of the embryonic period? • What happens during week 1 and 2? • Describe the main events in gastrulation. • How does the neural tube form, and what happens to it? Embryology Lecture Objectives...

Early Embryology Embryology Lecture Objectives • In general, what happens in the first and second phases of the embryonic period? • What happens during week 1 and 2? • Describe the main events in gastrulation. • How does the neural tube form, and what happens to it? Embryology Lecture Objectives • What is the fate of the endoderm, mesoderm and ectoderm? • What are the pharyngeal arches? What structures arise from each arch, groove, and cleft? • What structures do neural crest cells form? major stuff forms from pouches? Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 • Formation of neural tube • Differentiation of mesoderm • Folding of embryo Embryology Lecture Outline General overview of prenatal development Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization Fetus Phase 3 Growth and maturation 40 Delivery This YouTube video is explaining early embryonic development: http://www.youtube.com/watch?v=rN3lep6roRI Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization Fetus Phase 3 Growth and maturation 40 Delivery Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk Week 1: Differentiation of Morula into Blastocy Morula Blastocy st Week 2: Formation of Bilaminar Germ Disk epiblas t hypobla st Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) "It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life.” - Lewis Wolpert (1986) Gastrulation: formation of primitive streak primitive streak primitive node epiblast Gastrulation: movement and differentiation of epiblast cells Bilaminar germ disk Primitive streak Epibla st Hypobla st Endoder m Ectoderm Mesoder m Endoderm Epiblast cells give rise to all three germ cell layers! (the hypoblast does NOT turn into endoderm) Gastrulation: formation of notochord The notochord is super important because it tells the three layers what to do next. Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization Fetus Phase 3 Growth and maturation 40 Delivery Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 • Formation of neural tube Formation of Neural Tube Formation of the Neural Tube Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 • Formation of neural tube • Differentiation of mesoderm Differentiation of mesoderm Paraxial mesoderm forms bones and muscles of most of the body (except head), pharyngeal arches, and connective tissue Intermediate mesoderm forms urogenital system Lateral plate mesoderm forms hematopoietic system, heart, pharyngeal arches, and connective tissue Central nervous system Cranial nerves Bones and connective tissue of head Pharyngeal arches Neuroectode rm Urogenital system Neural crest Intermediate plate mesoderm Know this! Surface ectoderm Paraxial mesoderm Epidermis Bones and muscles of body (except head) Pharyngeal arches Connective tissue Endoderm Lining of GI tract Lateral plate mesoderm Heart Hematopoietic system Pharyngeal arches Connective tissue Clinical Correlation: Treacher Collins Syndrome Neural crest cells don’t migrate properly to the facial region. Structures derived from 1st and 2nd pharyngeal arches don’t develop properly. Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 • Formation of neural tube • Differentiation of mesoderm • Folding of embryo Folding of the Embryo Lateral Folding of the Embryo Lateral plate mesoderm splits in two. One part remains near the ectoderm. The other part follows the endoderm. Lateral Folding of the Embryo Endodermal layer (lined by mesoderm) bends, the edges reaching towards each other, meeting in front to form the gut. Ectodermal layer (lined by mesoderm) grows forward, reaches around the gut, and zips up the front to form the Lateral Folding of the Embryo Back, with ectoderm overlying neural tube Amnion (and amniotic cavity) comes along for the ride, eventually surrounding entire embryo. Gut (lined by endoderm, surrounded by mesoderm) Anterior thoracic wall (mesoderm covered with ectoderm) Head-Tail Folding of the Embryo Head-Tail Folding of the Embryo Day 24 Before folding Stomatodeu m Day 26 Day 28 What happens to the neural tube? It turns into the brain (forebrain, midbrain and hindbrain) and the spinal cord. Hey, what’s that mesoderm doing there? It’s forming: • Somatomeres (which turn into muscles of the head and neck) • Somites (which turn into the bones and muscles of the back). Embryo, day 23-26 Neural tube still open Neural tube closed Somites Neural tube still open Embryo, day 26-30 Neural tube closed Somites Neural tube still a little bit open Embryo, day 26-30 Embryology Lecture Outline General overview of prenatal development Embryonic period phase 1 • Formation of bilaminar disk • Formation of trilaminar disk (gastrulation) Embryonic period phase 2 • Formation of neural tube • Differentiation of mesoderm • Folding of embryo Formation of Pharyngeal Arches Pharyngeal Arch Anatomy Arches have a core that’s derived from lateral and paraxial mesoderm and neural crest cells. They are covered with ectoderm on the outside and lined by endoderm on the inside. Each arch has its own cartilage, artery, and nerve. Migration of Neural Crest Cells Neural crest cells live next to the midbrain and rhombomeres. Some of them migrate to the cores of the pharyngeal arches. For the boards, know which midbrain/rhombomere region supplies neural crest cells to which arch! (no joke) 1 2 3 4 Formation of Pharyngeal Arches 25-day-old embryo No arches yet Buccopharyngeal membrane intact 35-day-old embryo Arches and pouches nicely formed Mouth now open to esophagus 26-day-old embryo showing stomatodeum and first two arches Embryo, day 26-30 Frontal prominence 1 2 3 Somites Optic placode Nasal placode Maxillary Stomatode um 1 Mandibular Heart 2 3 4 Somite s First four arches in a 32-day-old embryo Pharyngeal arches, grooves, pouches Wait, are they branchial or pharyngeal arches? have branchial (“gill”) arches, with slits in between for water Humans don’t have gills. So our arches are called pharyngea Groove/cleft Arch Pouch Pharyngeal arches, grooves/clefts and pouches Know the stuff in red! Arc h Nerve Muscles Skeleton V (trigeminal) Mastication muscles Mylohyoid, anterior digastric Tensors tympani and veli palatini Meckel’s cartilage (malleus, incus) 2 VII (facial) Facial expression muscles Posterior digastric Stylohyoid Stapedius Reichert’s cartilage (stapes, styloid, lesser hyoid) 3 IX (glossopharynge al) Stylopharyngeus Greater hyoid 1 4-6 X (vagus) Larynx muscles Cricothyroid Laryngeal Important! Levator veli palatini cartilages Meckel’s cartilage indicates Constrictors of pharynx where the mandible will develop – but it does not turn into the mandible! What happens to the pouches and grooves? • • • • • 1st groove and pouch -> ear stuff Rest of grooves disappear 2nd pouch obliterated by tonsil 3rd pouch -> inferior parathyroid, thymus 4th and 5th pouches -> superior parathyroid, Head and Neck Anomalies From Improper Groove Closure Pharyngeal sinuses and cysts Auricular sinuses and cysts Prenatal Development Embryo Phase 1 Fetus Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization We covered this in this lecture. Phase 3 Growth and maturation 40 Delivery Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fetus Phase 3 Growth and maturation 40 Delivery Fertilization We covered some of this in this lecture. Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization Fetus Phase 3 Growth and maturation 40 Delivery You’ll learn more details about head and neck development (e.g., tooth development) in oral Prenatal Development Embryo Phase 1 Phase 2 Cellular Differentiation proliferation of internal & external and structures migration 0 1 2 3 4 5 6 7 8 Fertilization Fetus Phase 3 Growth and maturation 40 Delivery We’ll talk about the development of other,