(1)

• Origin of human tissues:

  • Sperm + Ovum (fertilization) = Zygote (fertilized egg) = Morula (ball of cells) = Blastocyst
  • Gastrula has two cavities divided by embryonic disk and three distinct cell layers:

  1. Ectoderm (inner cavity): will form outer body covering

  2. Endoderm (outer cavity): will give rise to neural plate, neural tube, brain, spinal cord, and linings of gastrointestinal system

  3. Embryonic disk: mesodermal/mesenchymal cells will form muscles, skeleton, and blood cells
• Development of the oropharynx:

  • At the 4th week of development, the human embryo appears like a flat disk and the brain expands, pushing the heart beneath it to create a pit called the stomodeum or primitive oral cavity
  • The oral pit deepens to form the oral cavity, with the deepest extent known as the oropharyngeal membrane/buccopharyngeal membrane, which ruptures along the 5th week opening the oral cavity to the tubular gut
  • Pharyngeal arches/branchial arches are formed, appearing as bars of tissues at the side of the pharynx, with different arches serving specific functions
• Development of the face and the palate:

  • 4th week: frontal processes bulge forward and laterally, maxillary process develops as swellings of tissue from the mandibular arch below it, and the mandibular arch appears divided or constricted
  • 5th week: nasal placodes thicken and develop into nostrils, nasal pits open into the oral pit forming the frontonasal process, eyes become prominent at each side of the head, and the mandibular arch loses constriction
  • 6th week: broadening of the face due to lateral growth of the brain, eyes and maxillary process begin to come into the front of the face, mouth slits widen, and the upper lip is formed by the fusion of the median nasal process and maxillary process