lecture 3

• Organogenesis


  The process of organ formation during embryonic development

  
• Germ layers


  • Endoderm
  • Mesoderm
  • Ectoderm
• Gastrulation


  Embryo (blastocysts) transforms from epithelial cells (blastula) into a multilayered, multidimensional structure called gastrula
• Endoderm


  • Gives rise to liver, GI tract (digestive), respiratory organs
• Mesoderm


  • Gives rise to cardiovascular system, muscles, bone
• Ectoderm


  • Precursor of nervous system and most CNS

  
• Neural tube development


  1. Notochord secretes Sonic Hedgehog protein as signal molecule

  2. Ectoderm differentiates into neuroectoderm

  3. Neuroectoderm becomes neural plate

  4. Neural plate becomes neural tube
• Neurulation


  The process of neural tube formation

  
• Primary brain vesicles


  • Forebrain (prosencephalon)
  • Midbrain (mesencephalon)
  • Hindbrain (rhombencephalon)

  
• Secondary brain vesicles


  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon

  
• Neural tube defect


  Problem during neurulation

  
• Neural tube defects


  • Spina bifida
  • Anencephaly

  
• Spina bifida


  Caudal neuropore does not close posteriorly, bones do not close around spinal cord/meninges, can cause complications in lower half of body
• Anencephaly


  Rostral neuropore does not close anteriorly, major portions of brain or skull are absent, infant fails to develop, haemorrhaging of meninges or brain, stillbirth / death shortly after birth

  
• Holoprosencephaly (HPE)


  Forebrain fails to develop normally, left/right hemispheres fail to separate
• Cephalic disorders are malformations of the forebrain