Embryonic Development Stages

Embryonic Development Stages

• Gastrulation: a process where a single-layered blastula transforms into a trilaminar structure consisting of three germ layers: ectoderm, mesoderm, and endoderm
• The three germ layers give rise to various tissues and organs in the body

Facial Development

• Frontonasal Process: arises from the ectoderm and plays a crucial role in facial development, giving rise to the forehead, bridge of the nose, and primary palate
• Maxillary Process: derived from the first pharyngeal arch, contributes to the development of the cheek and upper jaw
• Mandibular Arch: also derived from the first pharyngeal arch, gives rise to the lower jaw

Palate Formation

• Primary Palate: develops from the frontonasal process
• Secondary Palate: arises from outgrowths of the maxillary processes

Ossification

• Occurs through intramembranous ossification
• The mandible develops secondary growth cartilages, such as the condylar and coronoid cartilages

Facial Development Processes

• Olfactory Pit: initial depression in the surface ectoderm marking the beginning of facial development, surrounded by pharyngeal arches and the frontal process of the brain
• Frontal Process: gives rise to the forehead, bridge of the nose, and primary palate, derived from the ectoderm
• Maxillary Process: develops laterally to the olfactory pit, contributing to the development of the cheeks
• Mandibular Arch: located below the olfactory pit, gives rise to the lower jaw through intramembranous ossification
• Stomodeum: initial depression of the surface ectoderm forming the primitive oral cavity, separated from the primitive pharynx by the oropharyngeal membrane
• Nasal Placode: thickening of the surface ectoderm on each side of the frontonasal prominence, gives rise to the nasal pits

Palatal Development Processes

• Early Palatal Development (Weeks 6-7):
  • Formation of the Primary Palate
    • Medial nasal prominences begin to form during the sixth week and merge to form the intermaxillary segment
  • Formation of the Secondary Palate
    • Maxillary prominences develop from the internal aspects of the maxillary prominences and give rise to the palatal shelves during the seventh week
• Middle Palatal Development (Weeks 7-8):
  • Elevation of the Palatal Shelves
    • Mandible growth and tongue descent help lower the position of the tongue
    • Horizontal movement of the palatal shelves
  • Fusion of the Palatal Shelves
    • Midline contact and adhesion
    • Epithelial seam formation and breakdown through apoptosis and epithelial-mesenchymal transition
• Late Palatal Development (Weeks 9-12):
  • Completion of Palatal Fusion
    • Continuous layer formation creates a continuous layer of mesenchyme, which later ossifies