Embryology Lecture 1: From Fertizilation to Gastrulation

Embryology Lecture 1: From Fertizilation to Gastrulation

1. Bottom Line

   • Fertilization in ampulla of uterine tube
     • fusion of pronuclei -> division of blastomeres -> MORULA -> compaction of blastomeres so fluid into center -> BLASTOCYST w/fluid filled cavity & inner cell mass = EMBRYO; outer cell mass = TROPHOBLAST
     • pregnancy -> syncytiotrophoblast secretes hCG -> maintains corpus luteum -> makes progesterone -> maintain pregnancy
   • Infertility 15-30%; ART ^ prematurity, low birth weight, & birth defects
     • no fertilization -> no hCG -> corpus luteum regresses -> no progesterone -> menstruation & prep for next cycle
   • 2nd Week
     • Trophoblast
       • Cytotrophoblast (makes cells)
       • Syncytiotrophoblast (forms syncytium - blastocyst into uterine endometrium))
     • Inner cell mass @ one pole of blastocyst -> germ disc (epiblast & hypoblast)
     • 2 cavities - amniotic (dorsal to epiblast); yolk sac (ventral to hypoblast)
     • syncytio - this whole part - ASK QUESTIONS WHAT IS HAPPENING
     • "Week of 2s" - 2 layers trophoblast (synctio- and cytotrophoblast), 2 layers embryoblast (epiblast & hypoblast), 2 cavities (amniotic & yolk sac - then chorionic cavity), 2 layers extraembyonic mesoderm (somatic & splanchnic)
   • 3rd Week - GASTRULATION
     • 3 Germ Layers from epiblast
       • Ectoderm
         • Skin, CNS, PNS, eyes, internal ear, neural crest cells
       • Mesoderm
         • bones, connective tissue, urogenital system, cardiovascular system
       • Endoderm
         • gut & gut derivatives (liver, pancreas, lungs, etc)
     • 3 cavities - amniotic, yolk sac, chorionic