Embryology Lecture 4 (Week 2 Development) PDF
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Helwan University
Dr. Eman El Sawaf
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Summary
These lecture notes cover the events of the second week of human development, focusing particularly on the development of the blastocyst on Days 8 and 9. This includes details about the trophoblast differentiation into cytotrophoblast and syncytiotrophoblast layers, and how the inner cell mass or embryoblast forms the hypoblast and epiblast.
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Dr. Eman El Sawaf Anatomy & Embryology Department Faculty Of Medicine, Helwan University Basic Medical Science I Module Anatomy General Embryology General Embryology Objectives By the end of this lecture student should be able to: Mention the events in the 2nd week of...
Dr. Eman El Sawaf Anatomy & Embryology Department Faculty Of Medicine, Helwan University Basic Medical Science I Module Anatomy General Embryology General Embryology Objectives By the end of this lecture student should be able to: Mention the events in the 2nd week of development (Bilaminar germ disc) (Day 8 & 9) Contents -Day 8 blastocyst -Day 9 blastocyst Placenta Embryo Day 8 Blastocyst Implantation Day 8 The blastocyst is partially embedded in the endometrial stroma. 2- Endometrial stroma 2 1 1- Surface epithelium (Epithelial cells) Implantation Day 8 The blastocyst is partially embedded in the endometrial stroma. Implantation Day 8 Trophoblast Day 8 In the area over the embryoblast, the trophoblast differentiate into two layers. Trophoblast Day 8 Inner layer Outer layer Cyto Syncytio trophoblast trophoblast Syncytio Mononucleated Multinucleated trophoblast cells zone without clear cell boundaries Cyto trophoblast Day 8 Syncytio trophoblast Cytotrophoblast Day 8 Trophoblast Day 8 The cells in the cytotrophoblast divide and migrate into the syncytiotrophoblast. Syncytiotrophoblast Cytotrophoblast Embryoblast Day 8 The cells of the inner cell mass or embryoblast differentiate into two layers. Embryoblast Day 8 Hypoblast Epiblast layer layer Small High cuboidal columnar cells near cells near to to the the blastocyst amniotic cavity cavity The 2 layers form a flat disc. Epiblast Hypoblast Blastocyst cavity Day 8 Epiblast Hypoblast Blastocyst cavity Day 8 Epiblast Hypoblast Bilaminar embryonic disc Embryoblast Day 8 -Small cavity appears within the epiblast. -This cavity enlarges to become the amniotic cavity. -The epiblast cells near to the cytotrophoblast are called amnioblasts. Amnioblast Amniotic cavity Epiblast Hypoblast Blastocyst cavity Day 8 Amnioblast Amniotic cavity Epiblast Hypoblast Blastocyst cavity Day 8 Blastocyst Partially embedded in the endometrial stroma. Trophoblast Embryoblast Differentiate into two layers: Differentiate into two layers: Cytotrophoblast Syncytiotrophoblast Hypoblast Epiblast layer layer Mononucleated Multinucleated zone Small High columnar cuboidal The cells in the Small cavity cytotrophoblast appears within divide and migrate the epiblast into the (The amniotic syncytiotrophoblast. cavity). Day 9 Blastocyst Implantation Day 9 The penetration defect in the Blastocyst is surface deeply embedded epithelium is in the closed by a fibrin endometrium. coagulum. Implantation Day 9 Endometrium Blastocyst is deeply embedded in the endometrium. The penetration defect in the surface epithelium is closed by a fibrin coagulum. Day 9 Trophoblast Day 9 Vacuoles appear in the syncytiotrophoblas (Syncytium) Trophoblast Day 9 When the vacuoles fuse they form Large lacunae Lacunar stage Day 9 Embryoblast Day 9 The hypoblast form a thin membrane, the exocoelomic (Heuser) membrane (flattened cells). Hypoblast Abembryonic pole Embryoblast Day 9 The hypoblast form a thin membrane, the exocoelomic (Heuser) membrane (flattened cells). Exocoelomic membrane Exocoelomic cavity (primitive yolk sac) Hypoblast Day 9 Exocoelomic membrane Exocoelomic cavity Hypoblast (primitive yolk sac) Day 9 Blastocyst Deeply embedded in the endometrium. Penetration defect in the surface epithelium is closed by a fibrin coagulum. Trophoblast Embryoblast Cytotrophoblast Syncytiotrophoblast Hypoblast layer Epiblast layer -Vacuoles appear in the The hypoblast form syncytiotrophoblas a thin membrane, (Syncytium). the exocoelomic -The vacuoles fuse to (Heuser) membrane form large lacunea. (flattened cells) Exocoelomic cavity (primitive yolk sac) MCQ - Regarding the day 8 blastocyst, which one of the following statements is correct? a. It is deeply embedded in the endometrium. b. The exocoelomic membrane appears. c. The amniotic cavity appears. d. The syncytiotrophoblast show the lacunae. MCQ - Regarding the day 8 blastocyst, which one of the following statements is correct? a. It is deeply embedded in the endometrium. b. The exocoelomic membrane appears. c. The amniotic cavity appears. d. The syncytiotrophoblast show the lacunae. MCQ - The Heuser,s membrane originates from which one of the following cells? a. The syncytiotrophoblast. b. The cytotrophoblast. c. The epiblast. d. The hypoblast. MCQ - The Heuser,s membrane originates from which one of the following cells? a. The syncytiotrophoblast. b. The cytotrophoblast. c. The epiblast. d. The hypoblast. Reference -Langman’s Medical Embryology 13th Edition, T.W. Sadler. Images: - Langman’s Medical Embryology - https://www.pinterest.com/pin/204350901824989137/ - 8 weeks pregnant: fetal development Approved by the BabyCentre Medical Advisory Board -https://webpath.med.utah.edu/FEMHTML/FEM200.html -File:Early development stages with names.gif - From Wikimedia Commons, the free media repository -BGDA Practical 3 - Early Cell Division -File:Human embryo day 5 label.gif -3RD WEEK OF PREGNANCY -C WWW.PROYECTO-BEBE.COM - ANIMATION: MANUEL HERNANDO -General Embryology - Detailed Animation On Second Week Of Development Thank You
