Embryology

• Embryology


  The study of the development of an organism from fertilization through birth
• Flexion


  • Curvature of the embryo that starts at the end of week 3
• Pharyngeal arches


  • Transverse elevations that form on the lateral walls of the foregut and move medially until they join
• Primary palate


  The anterior - most portion of the maxilla that forms from the fusion of the maxillary and medial nasal processes
• Secondary palate


  The majority of the hard palate including the palatine process of the maxilla that forms from the maxillary processes
• Failure of one or more of the fusions to occur can result in a cleft lip, cleft palate or both
• Tongue must descend for palate to fuse


  Anatomical issues may prevent or delay the tongue from descending, which can prevent or delay palate fusion
• Prenatal substance exposure, such as alcohol (FASD) and tobacco, can cause craniofacial anomalies
• Birth prevalence estimates for FASD vary from 9-10 per 1000 to 15 per 1000 in families with foster children, which is high compared to other congenital syndromes
• Embryonic disk forms 10-13 days post conception from inner cell mass, forms into three groups: endoderm, mesoderm, ectoderm

  
• Facial development

  1. Frontonasal process

  2. Maxillary processes

  3. Mandibular arch

  4. Hyoid arch
• The hard palate forms from the primary and secondary palate
• Embryology is relevant to understanding how human organs take form, basis for understanding number of disorders and abnormalities that arise before birth
• Greater than 25% of syndromes in humans have some manifestation in craniofacial region
• Blastocyst: Cell division during 6-7 days after fertilization, fluid filled sphere with cell mass at one end, surrounded by trophoblasts
• Endoderm will eventually become visceral organs (digestive tract, lungs)
• Ectoderm will eventually develop into skin and nervous system (epidermis, tooth enamel, nervous system, hair, nails)
• Mesoderm will eventually produce cells that differentiate into structural and circulatory systems (bones, muscles, tissue, blood)
• Nervous system starts to develop at about 18 days
• Neural plate develops neural groove, plate rolls up around groove to form neural tube, lasts about 10 days
• Mandibular arch: Arise from pharyngeal arches, mandible, maxilla, palatine bones, muscles of mastication
• Hyoid arch: Arise from pharyngeal arches, upper body and lesser horns of hyoid, muscles of facial expressions
• Arches 3, 4, & 6: Arise from pharyngeal arches, laryngeal cartilages, intrinsic laryngeal muscles
• During week 5, face can begin to be divided into 4 primordial areas:

  1. Frontonasal process
  2. Maxillary process
  3. Mandibular arch
  4. Hyoid arch
• Frontonasal process will develop into the forehead, bridge and tip of nose, primary palate
• Maxillary processes will develop into cheek, upper lip and most of the upper jaw
• Weeks 7 through 10 are important in development of palate
• Failure of one or more fusions (lateral nasal processes, maxillary and medial nasal processes, secondary palate arising from maxillary processes) to occur can result in cleft lip, cleft palate or both
• Early in secondary palate formation, tongue high and fills most of oral cavity, extending into nasal cavity
• Between weeks 7 and 9, mandibular development permits tongue to descend from nasal cavity
• •Fusion takes place in anterior to posterior direction
• •Soft palate closure complete by 10th week
• Tongue must descend for palate to fuse, anatomical issues may prevent or delay tongue from decending
• Narrow time window for tongue descent to occur
• Prenatal substance exposure can also cause craniofacial anomalies