Embryology of head, face and oral cavity revision notes quiz

Embryology and Oral Embryology

• The study of tissue development is known as embryology.
• Oral embryology focuses on the development of oral tissues.
• Embryogenesis is the process of embryonic development, responsible for tissue and organ formation.

Embryonic Origins

• The trilaminar embryonic disc, composed of three tissue layers (ectoderm, mesoderm, and endoderm), is the origin of all tissues in the body.
• Derivatives are the structures that form from the origin/tissue layers.

Stages of Embryogenesis

• Early Embryogenesis (Week 1-4):
  • Week 1 – Formation of a blastocyst through fertilization, cleavage, proliferation, migration, and differentiation. (Zygote – Morula – Blastocyst)
  • Weeks 2-3 – Formation of the three embryonic origins (ectoderm, mesoderm, endoderm), creating the trilaminar embryonic disc.
  • Weeks 3-4 – Highly specialized neural crest cells, derived from ectoderm and neuroectoderm, play a crucial role in the development of the head, face, and oral cavity.
  • Week 4 – The embryo begins to take shape through the development of folds and bulges, including the stomodeum, the buccopharyngeal membrane, the primitive gut, and pharyngeal arches. These structures are the building blocks for the face and oral cavity.
• Embryogenesis (Week 5-8):
  • Development of all tissues, organs, and structures.
  • Weeks 4-6 – The face starts to form through the fusion of prominences, including the frontonasal, maxillary, and mandibular prominences.
  • Weeks 4-7 – The tongue develops from the 1st, 2nd, and 4th pharyngeal arches. The anterior 2/3rd of the tongue originates from the 1st and 2nd arches, while the posterior 1/3rd develops from the 4th arch. Cellular apoptosis occurs during the development of the tongue, allowing it to separate from the floor of the mouth. The frenulum acts as an anchor.
  • Weeks 6-7 – The primary palate develops from the fusion of the frontonasal and medial nasal prominences.
  • Weeks 7-8 – The secondary palate develops as the palatine shelves grow and fuse together at the midline with the primary palate and nasal septum. The tongue retracts to create space, leading to the formation of the incisive foramen at the midline, situated between the primary and secondary palates.
  • Week 7 – The maxilla and mandible jaws undergo ossification, each developing a neural and alveolar portion. These structures support the development of teeth and secondary cartilages, further supporting bone growth.

Fetal Development (Week 9 – Birth) & Clinical Significance

• Development, maturation, and growth of previously formed structures, organs, and body systems occur during this period.
• The embryo is now considered a fetus.
• Fingernails, eyelashes, and hair begin to grow.
• The fetus can move its limbs.
• Embryogenesis is a complex and delicate set of processes.
• Malfunctions or interruptions in embryogenesis can lead to developmental anomalies.
• Aetiology of anomalies can be genetic or environmental (congenital). Congenital causes include exposure to radiation, medications, illness, hormones, and nutritional deficiencies.
• If cellular apoptosis did not occur during tongue development, an individual might have ankyloglossia (‘tongue-tied’), impacting feeding, speech, oral hygiene, and breathing.
• If tissues do not fuse together properly during development, individuals may have cleft lip and/or palate, impacting feeding, speech, hearing, tooth development, and oral hygiene.
• Anomalies increase the risk of oral disease.

Pharyngeal Arches

• Arch | Innervation | Muscles | Artery | Cartilage or Bones
• I | Trigeminal nerve (Cranial nerve V) | Muscles of mastication | Aortic arch 1 | Merkel’s cartilage. Mandible, maxilla, zygomatic, squamous portion of temporal and malleus and incus of ear.
• II | Facial nerve (Cranial nerve VII) | Muscles of facial expression | Aortic arch 2 | Reichert’s cartilage. Hyoid bone.

Tissue Layers

• Ectoderm: Outer layer for protection. (Skin, hair, nails, enamel, neural)
• Mesoderm: Middle layer for support. (Muscles, blood, bone, connective tissues)
• Endoderm: Inner layer for specialist organs. (Respiratory, digestive systems etc.)

This quiz covers the fundamental concepts of embryology, focusing specifically on oral embryology and the stages of embryogenesis. It explores the trilaminar embryonic disc and the significance of embryonic layers in tissue development. Test your understanding of the processes involved in the formation of oral tissues and other body structures.