Fertilized cell early development

Fertilized cell early development

1. Week 2

   • Trophoblast forms and has 2 layers:
     • 1. cytotrophoblast (makes cells)
       • 2. syncytiotrophoblast: forms syncytium = responsible for invasion of the blastocyst into the uterine endometrium and production of hormones
   • the germ disc (embryoblast) forms and has 2 layers:
     • 1. epiblast
       • 2. hypoblast
   • Three cavities form:
     • 1. amniotic = dorsal to epiblast
       • 2. yolk sac = ventral to hypoblast
         • Later in the week...
           • 3. chorionic cavity forms
   • Extraembryonic mesoderm forms around the outside of the amnion and yolk sac splits into two layers:
     • 1. somatic
       • 2. splanchnic

2. Week 1

   • 1. Fusion of pronuclei
   • 2. Blastomeres divide
   • 3. Morula forms
   • 4. Blastocyst forms
     • Consists of a fluid filled cavity, an inner cell mass = embryo, and an outer cell mass = trophoblast (fetal contribution to the placenta)

3. Week 3

   • Gastrulation
     • The process of making the 3 germ layers:
       • ectoderm
         • skin, CNS, PNS, eyes, internal ear, neural crest cells(bones & connective tissue of the face and part of the skull)
       • mesoderm
         • blood, bones, connective tissue, urogenital system, cardiovascular system
       • endoderm
         • gut, gut derivatives (liver, pancreas, lungs, etc.), parenchyma of glands
   • Notochord formation
     • helps induce the CNS
     • eventually forms the nucleus pulposus in intervertebral discs.