gastrulation

• What divides into outer syncytiotrophoblasts and inner cytotrophoblasts during implantation?

  Outer trophoblast mass
• What does the inner embryoblast divide into?

  Epiblast and hypoblast
• When does a cavity appear in the epiblast layer?

  Day 8
• What are the key stages in the formation of the embryonic germ layers?

  • Week 2: Bilaminar disc from epiblast + hypoblast
  • Week 3: Gastrulation begins
  • Bilaminar disc becomes trilaminar disc
  • Formation of ectoderm, mesoderm, endoderm
• What is gastrulation?

  First stage of morphogenesis in embryogenesis
• What is established during gastrulation?

  Basic organization of the organism
• What begins with the formation of the primitive streak?

  Gastrulation
• What are the components of the primitive streak?

  • Groove
  • Primitive (Hensen's) node
  • Primitive pit
• What does the anterior part of the primitive streak represent?

  Cranial end
• What does the posterior part of the primitive streak represent?

  Caudal end
• What are the three germ layers formed within the primitive streak?

  Endoderm, mesoderm, ectoderm
• How do endoderm cells integrate during gastrulation?

  They displace the hypoblast
• What happens to epiblast cells during gastrulation?

  They roll over and involute into the groove
• How do cells migrate during gastrulation?

  By ingression
• What are the characteristics of epithelial cells in the primitive streak?

  • Well-differentiated and polarized
  • Apical and basal surfaces
  • Connected via tight junctions, gap junctions, desmosomes
• What are the characteristics of mesenchymal cells in the primitive streak?

  • Poorly differentiated
  • Mobile and not connected to adjacent cells
  • In contact with extracellular matrix via focal adhesions
• What are the types of epithelial-mesenchymal transition (EMT)?

  • Type 1: Development
  • Type 2: Wound healing
  • Type 3: Cancer invasion
• How are tumors viewed in relation to normal developmental processes?

  As corrupted normal developmental processes
• What is a common feature of genes important in embryonic development?

  They frequently cause cancer
• What structures are derived from the ectoderm?

  • CNS: brain + spinal cord
  • PNS
  • Sensory epithelia of eye, ear, nose
  • Epidermis + appendages: hair + nails
  • Mammary glands + pituitary glands
• What structures are derived from the mesoderm?

  • Connective tissue: cartilage, bone, blood
  • Striated + smooth muscle
  • Heart, blood + lymphatic vessels
  • Kidneys, ovaries, testis, spleen
  • Serous membranes lining cavities
• What structures are derived from the endoderm?

  • Epithelial lining of GIT
  • Respiratory tract, bladder + urethra
  • Thyroid + parathyroid glands
  • Liver, pancreas
• What are the results of gastrulation?

  • Primary germ layers formed
  • Germ layers organized into proper locations
  • Creation of body axes: anterior-posterior, dorsal-ventral, left-right