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Unformatted text preview: www.brain101.info 1 THE THORAX AND EARLY EMBRYOLOGY Early Embryologic Development Bones / General Regions of the Thorax The Breast Musculature of the Thorax Nerve and Blood Supply to the Intercostals Embryological Partitioning of Body Cavities The Lungs Fundamentals of Radiology Embryology of the Heart Pericardium and Positioning of the Heart The Heart The Superior Mediastinum Tetralogy of Fallot EARLY EMBRYONIC DEVELOPMENT Morula: The name of the embryo at the 16 to 32 cell stage. Blastocyst : At about day 5 after implantation. Cells are divided into the inner cell mass and trophoblast. Inner Cell Mass: The cells on the inside. Trophoblast: The cells surrounding the outside. Implantation: Blastocyst travels from ampulla ------> oviduct ------> uterus to implant in the uterus. Implantation occurs around day 5. Trophoblast forms two cell-layers. Syncytiotrophoblast: The cell mass at the embryonic pole (nearest the uterine wall). Cytotrophoblast: The cell mass jutting out from the pole. Will form the extraembryonic membranes. Inner Cell Mass: Form two layers of cells, epiblast and hypoblast. A Bilaminar Embryonic Disc is formed. Epiblast Cells: From inner cell mass, will ultimately give rise to the three germ layers and the entire embryo. Amniotic Cavity : Forms as the space between the Epiblast and cytotrophoblast.. Hypoblast Cells: These cells are the first to migrate and eventually disintegrate. Progression of events after implantation: Each item represents simultaneous events. The epiblast cells grow deeper into the wall of the uterus. o The amniotic cavity begins to form in the epiblast layer . Amnioblasts differentiate from the epiblasts and migrate to the inner amniotic layer. o Heuser's Membrane is formed from hypoblasts (interior of cytotrophoblast layer). It will differentiate into the yolk sac. o Trophoblastic Lacunae are openings that form in the syncytiotrophoblast. Maternal blood enters the lacunae. o Extraembryonic Reticulum forms. Primary Yolk Sac: Epiblasts form mesoderm on the exterior of Heuser's Membrane. Definitive Yolk Sac: New Hypoblast cells migrate to displace Heuser's membrane, pushing back the primary yolks sac to form the new definitive yolk sac. o Chorionic Cavity forms in the ECM. www.brain101.info 2 The Placenta is formed from a network of villi (trophoblast cells). Villi form from trophoblast in the following order of maturation: o Primary Villus : Cytotrophoblast + a layer of syncytiotrophoblast grow into the lacunae. o Secondary Villus : Extraembryonic mesoderm grows into the primary villus. o Tertiary Villus : Extraembryonic mesoderm gives rise to blood vessels. Exchange of nutrients is now possible with mother ....
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