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 germ layers 
 
Ectoderm
  • Surface ectoderm
    • adenohypophysis 
    • lens of the eye
    • sensory organs 
      • ear
      • olfactory epithelium
    • epithelial linings
      • oral cavity
      • lower anal canal
      • external auditory meatus
    • epidermis, hair, and nails
    • mammary, sweat, and salivary glands
  •  Neuroectoderm - CNS and brain
    • brain - all neurons within brain and spinal cord/CNS
      • neurohypophysis
      • oligodendrocytes
      • astrocytes
      • ependymal cells
      • pineal gland
    • retina
  • Neural Crest - PNS and nearby non-neural structures
    • ANS
    • ganglia (dorsal root, cranial, and autonomic)
    • cranial nerves
    • celiac ganglion
    • melanocytes  
    • chromaffin cells of adrenal medulla
    • enterochromaffin cells
    • parafollicular (C) cells of thyroid
    • Schwann cells
    • pia and arachnoid
    • bones of the skull
    • odontoblasts
    • laryngeal cartilage
    • aorticopulmonary septum
Endoderm
  • Epithelium lining of
    • respiratory: trachea, bronchi, and lungs
    • urinary: urinary bladder, female urethra, and majority of male urethra
    • GI tract
    • biliary system
    • lower 2/3 of vagina
    • middle ear cavity and auditory tube
  • Liver
  • Parathyroid
  • Thyroid follicular cells
  • Thymus
  • Pancreas
Mesoderm
  • Muscle (smooth, cardiac, and skeletal)
  • Dermis and subcutaneous layers of skin
  • Bone, cartilage, and connective tissue
  • Dura mater
  • Serous linings of body cavities
    • peritoneum
  • Spleen
  • Cardiovascular structures
  • Lymphatics
  • Blood: RBCs, WBCs, Kupffer cells, and microglia
  • Urogenital structures
    • male: testes, epididymis, ductus deferens, seminal vesicle, and ejaculatory duct
    • female: ovaries, uterus, uterine tubes, and upper 1/3 of vagina
  • Kidneys
  • Adrenal cortex
Defects
  • Types of errors
    • malformation vs. deformation 
      • malformation is intrinsic embryological disruption during the embryonic period
      • deformation is extrinsic disruption, occurs after embryonic period
    • agenesis vs. hypoplasia vs. aplasia
      • agenesis = organ is absent because of absent primordial tissue
        • e.g., renal agenesis - failure of one or both kidneys to develop
      • hypoplasia = organ develops incompletely with remnant primordial tissue
        • e.g., microorchidism in Klinefelter syndrome
      • aplasia = organ absent but primordial tissue present
        • e.g., thymic aplasia in DiGeorge syndrome
  • Craniopharyngioma
    • benign Rathke's pouch tumor containing cholesterol crystals and calcifications, tends to compress the optic chiasm 
  • Mesodermal defects VACTERL 
    • Vertebral defects: usually small hypoplastic vertebrae or hemivertebrae, only half of the bone is formed
    • Anal atresia/imperforate anus 
    • Cardiac defects: ventricular septal defect, atrial septal defect, and Tetralogy of Fallot
    • Tracheo-Esophageal fistula
    • Renal defects: incomplete formation of one or both kidneys
    • Limb defects: absent or displaced thumbs, polydactyly, and syndactyly
 

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