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ANAT 1502 Embryology Chapter 1-5 Review

ANAT 1502 Embryology Chapter 1-5 Review - Embryology Review...

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Embryology Review of Ch 1 - 5 Chapter 5 The Third Week of Human Development Development of embryo from embryonic disc in 3rd week characterized by: appearance of primitive streak development of neural tube and notochord differentiation of 3 germ layers (ectoderm, endoderm, mesoderm) development of somites development of chorionic villi early development of cardiovascular system (vasculogenesis and angiogenesis) development of intraembryonic coelom Gastrulation: Formation of Germ Layers The process by which the bilaminar embryonic disc is converted into a trilaminar disc The beginning of morphogenesis Begins with formation of primitive streak Summary: cells of epiblast, through gastrulation, give rise to 3 germ layers in embryo, which are the primordia of all tissues and organs 3 germ layers of embryonic disc: 1. Ectoderm : >> epidermis, CNS, PNS, retina of eye 2. Endoderm : >> epithelial linings of respiratory passages and gastrointestinal tract, glandular cells of related organs (e.g., liver, pancreas) 3. Mesoderm : >> smooth muscular coats, connective tissues, tissue and organ vessels, most of cardiovascular system, blood cells, bone marrow, striated muscles, reproductive and excretory organs
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Primitive Streak Thickened, linear band of epiblast dorsally and caudally in median plane (cells migrate/proliferate from epiblast to median plane) Cranial end proliferates to form a primitive node Primitive groove develops in primitive streak that connects to depression in primitive node ( primitive pit ) Appearance of primitive streak allows one to ID the craniocaudal axis, dorsal/ventral surfaces, right and left Primitive groove & pit result from invagination of epiblastic cells Mesenchyme cells migrate from the primitive streak to form 3 layers: embryonic mesoderm embryonic endoderm embryonic ectoderm Notochordal Process and Notochord Some mesenchyme cells migrate cranially to form notochordal process This process soon forms a lumen ( notochordal canal ) Notochordal process grows cranially, between ectoderm and endoderm until it hits the prechordal plate Cells of the notochordal process and prechordal plate fuse to form the oropharyngeal membrane (future oral cavity) Mesenchymal cells from primitive streak migrate on both sides of primitive streak and around the prechordal plate and meet cranially to form the cardiogenic mesoderm in the cardiogenic area
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