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Download Early Embryogenesis - Week 3 - Stony Brook University School of
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Early Embryogenesis - Week 3 The audio narrations of these slides have been transcribed verbatim and can be downloaded from http://www.anat.sunysb.edu/HBA531/Embryology/ 2 weeks old connecting stalk prochordal plate remants of primary yolk sac amnion amniotic cavity primitive streak yolk sac extraembryonic coelom Jack Stern 2003 cranial (head) right left caudal (tail) Jack Stern 2003 Jack Stern 2003 connecting stalk amniotic cavity primitive streak amnion extraembryonic coelom extraembryonic coelom yolk sac Jack Stern 2003 Jack Stern 2003 primitive groove Jack Stern 2003 intraembryonic mesoderm extraembryonic mesoderm Jack Stern 2003 Jack Stern 2003 amnioblast nonproliferating ectoderm epiblast Jack Stern 2003 Jack Stern 2003 endoderm Jack Stern 2003 Jack Stern 2003 prochordal plate (oropharyngeal membrane) ectoderm primitive (Hensen’s) node primitive pit primitive groove primitive streak cloacal membrane Jack Stern 2003 Migration of Intraembryonic Mesoderm Jack Stern 2003 intraembryonic mesoderm ectoderm endoderm Jack Stern 2003 endoderm of orophrayngeal membrane prechordal mesoderm intraembryonic mesoderm notochord endoderm of cloacal membrane Jack Stern 2003 Jack Stern 2003 15-16 days orophrayngeal membrane connecting stalk amniotic cavity primitive pit primitive node amnion cloacal membrane prechordal mesoderm notochord intraembryonic mesoderm coming from primitive streak yolk sac Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 connecting stalk Jack Stern 2003 allantoic diverticulum Jack Stern 2003 grow Jack Stern 2003 grow Jack Stern 2003 Jack Stern 2003 intraembryonic mesoderm from primitive streak notochord Jack Stern 2003 endoderm of prochordal plate intraembryonic mesoderm from primitive streak notochord Jack Stern 2003 Jack Stern 2003 15-16 days amniotic cavity mesenchyme intraembryonic mesoderm yolk sac notochord extraembryonic mesoderm Jack Stern 2003 intermediate paraxial lateral plate Jack Stern 2003 neural groove neural folds Jack Stern 2003 neural plate Jack Stern 2003 grow Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 grow Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 Changes in Intraembryonic Mesoderm During Third Week Jack Stern 2003 15-16 days amniotic cavity paraxial intermediate lateral plate yolk sac Jack Stern 2003 Jack Stern 2003 notochord lateral plate mesoderm paraxial mesoderm Jack Stern 2003 notochord lateral plate mesoderm paraxial mesoderm Jack Stern 2003 notochord lateral plate mesoderm paraxial mesoderm Jack Stern 2003 20 days somites Jack Stern 2003 Jack Stern 2003 somite Jack Stern 2003 amniotic cavity somite microdroplets of intercellular fluid lateral plate yolk sac notochord Jack Stern 2003 microdroplets of intercellular fluid microdroplets of intercellular fluid Jack Stern 2003 Jack Stern 2003 intraembryonic coelom Jack Stern 2003 left channel of the intraembryonic coelom right channel of the intraembryonic coelom Jack Stern 2003 mesothelium mesothelium Jack Stern 2003 mesothelium Jack Stern 2003 Jack Stern 2003 bend at the front of the intraembryonic coelom amniotic acvity neural fold primitive streak allantoic diverticulum notochord yolk sac cardiogenic mesoderm Jack Stern 2003 3D View of Mesothelial Wall of Coelom oropharyngeal membrane Jack Stern 2003 heart tubes (form at 18-19 days) Jack Stern 2003 Jack Stern 2003 amniotic cavity bend at the front of the intraembryonic coelom yolk sac heart tubes Jack Stern 2003 oropharyngeal membrane Jack Stern 2003 aorta (left) aortic arch (left) umbilical arteries Jack Stern 2003 Jack Stern 2003 amniotic cavity yolk sac aortae intraembryonic coelom Jack Stern 2003 Two Days After Heart Tubes Form Jack Stern 2003 amniotic cavity bend at the front of the intraembryonic coelom yolk sac heart tube Jack Stern 2003 A Little Later Jack Stern 2003 amniotic cavity yolk sac aorta Jack Stern 2003 Jack Stern 2003 vitelline vein Jack Stern 2003 umbilical vein Jack Stern 2003 cardinal vein Jack Stern 2003 21 days Jack Stern 2003 cardinal vv. Jack Stern 2003 Changes in Neural Folds During Third Week Jack Stern 2003 Jack Stern 2003 crests of neural folds Jack Stern 2003 Jack Stern 2003 neural crest neural tube Jack Stern 2003 Neural tube closure begins on the first day of the 4th week (i.e., day 22). It starts in the middle of the embryo and sweeps forward toward the head and backward toward the tail. It takes 2 –3 days to reach the front of the brain and another couple of days to reach the tip of the tail, so it is completed by the end of the 4th week. Jack Stern 2003 One More Change in the Coelom Jack Stern 2003 ? ? amniotic cavity ? ? ? ? yolk sac intraembryonic coelom Jack Stern 2003 extraembryonic coelom Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 Jack Stern 2003 3D View of of Coelom oropharyngeal membrane Jack Stern 2003 Bottom Line At the end of the 3rd Week • embryonic disc is still flat, but now it is much longer than wide, and it has three layers rather than two • fundamental segmentation of the embryo has begun, as seen in somites and neural crest clumps • circulation of blood has begun • a U-shaped intraembryonic coelom has formed and its side arms open to the extraembryonic coelom in the region caudal to the oropharyngeal membrane • neural folds are just beginning to touch in the vicinity of what will become the neck Jack Stern 2003
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