Review/ Background ● First week Buccopharynge Second Week Prenotochordal cells o Third- 8th week Primitive node X-section at"B" Primitive streak Gastrulation Cloacal membrane A primitive pit Primitive Primitive .Primitive node ● Primitive streak Epiblast Am mniobla notochord(脊索) Invaginating Hypoblast
Review/Background •First Week •Second Week •Third- 8th week –Gastrulation •Primitive pit •Primitive node •Primitive streak •Notochord（脊索）
Expansion and Elongation Migration of Epiblasts to of amni form Endoderm Mesoderm amative Ectoderm 16 days o Expansion of the disk aryngeal Cloacal Notochord mbrane membrane ● Notochord midline rod of mesoderm Yolk sac orientation the germ disc
Expansion and Elongation •Migration of Epiblasts to form –Endoderm –Mesoderm –Ectoderm •Expansion of the disk •Notochord: -midline rod of mesoderm -orientation the germ disc
Differentiation of trilaminar germ disc 3rd -8th weeks embryonic period(胚期): the major body form and organ structure take Bilaminar disc: flat and round elongated with a broad cephalic and a narrow caudal end Trilaminar disc: a pear-shaped appearance
Differentiation of trilaminar germ disc 3 rd –8 th weeks embryonic period（胚期）: the major body form and organ structure take Bilaminar disc: flat and round→elongated with a broad cephalic and a narrow caudal end Trilaminar disc: a pear-shaped appearance
Ectoderm(外胚层)- Neurulation Overlying notochord Antenor neuropore Thickens- Neural plate (神经板) Otic placode eDges- Neural Folds (神经褶) ut edge of amnio Fuse at future neck region p i2 da B Posterior dromore 23 days Zippers shut - Neural Tube(神经管) ●Ant/ Post Neuropores (前/后神经孔) Notochord
Ectoderm （外胚层）- Neuralation •Overlying notochord Thickens – Neural Plate （神经板） •Edges - Neural Folds （神经褶） •Fuse at future neck region •Zippers shut –Neural Tube（神经管） •Ant/Post Neuropores （前/后神经孔）