Single-Celled Zygote

Single-Celled Zygote

1. Undergoes mitotic divisions to form

   • Blastomeres
     • Which after compaction and dividing form a
       • Morulla
         • Forms on Day 3 & is made up of 16 cells
         • Inner cell Mass
           • Embryoblast
             • In blastocyst
             • Hypoblast
               • Gives rise to exocoelomic cavity (primitive yolk sac)
               • Disappears
             • Epiblast
               • Endoderm
                 • Gut
                 • Gut derivatives
                   • Liver, pancreas, lungs, etc.
               • Mesoderm
                 • Bones
                 • Connective tissue
                 • Urogenital Tissue
                 • Cardiovascular System
               • Ectoderm
                 • Skin
                 • CNS
                 • PNS
                 • Eyes
                 • Internal ear
                 • Neural Crest Cells
                   • Bones & Connective tissue of face
                   • Part of skull
                 • Cells that interact with outside world
         • Outer Cell Mass
           • Will form Placenta
           • Trophoblast
             • In blastocyst, penetrates endometrium. Has L-Selecin that interacts with carbohydrate receptors on endometrium.
             • Cytotrophoblast
               • Mitotic divisions
               • Project into Syncytium forming
                 • Primary villi
                   • Add mesoderm core
                     • Secondary Villi
                       • Add villous capillary system
                         • Tertiary Villi
             • Syncytiotrophoblast
               • Forms syncytium. Implants in endometrium.
               • Lacunae connect with maternal sinusoids
                 • Uteroplacental circulation