From Fertilization to Gastrulation

From Fertilization to Gastrulation

1. Week 1

   • Fertilization: ampulla of uterine tube
     • pronuclei fusion
   • blastomere division
     • morula
   • compaction of blastomeres
     • blastocyst
       • fluid filled cavity
       • inner cell mass
         • embryo
       • outer cell mass
         • trophoblast

2. Week 2

   • Trophoblast: 2 layers (forms villi for placenta)
     • cytoctrophoblast
       • makes cells
     • syncytiotrophoblast
       • forms syncytium
   • inner cell mass: forms germ disc
     • epiblast
     • hypoblast
   • 2 cavities
     • amniotic
     • yolk sac
     • chorionic later in week
   • extraembryonic mesoderm
     • somatic
     • splanchnic
   • embryo penetrates uterine vessels (12-14 days)

3. Week 3

   • epiblast: forms 3 germ layers
     • Gastrulation
       • ectoderm
         • skin, CNS
       • mesoderm
         • blood, bones, connective tissue
       • endoderm
         • gut, gut derivatives, parenchyma of glands
   • hypoblast disappears
   • primitive streak
     • node = organizer (cranial end of streak)
     • preochordal plate & notochord form
   • cranial-caudal axis
     • Anterior Visceral Endoderm (AVE)
       • head formation