Embryology Quiz

• Session 1 covers the embryology of the head, face, and oral cavity, using a self-directed workbook.
• The assessment for embryology includes formative workbooks, quizzes, and discussions during the consolidation session.
• A summative e-assessment contributes to the Biomedical Sciences module grade.
• The goals are to outline embryogenesis phases, define embryonic origins, and explain developmental interruption consequences.

Definitions

• Embryology is the study of tissue development.
• Oral embryology focuses on the development of oral tissues.
• Embryogenesis is the process of embryological development and the formation of tissues and organs.
• Embryonic origins refer to the three tissue layers: ectoderm, mesoderm, and endoderm.
• Derivatives are the structures formed from the embryonic origins/tissue layers.

Key Phases of Embryogenesis

• Fertilization, cleavage, proliferation, migration, and differentiation are the key phases.
• Early embryogenesis occurs from weeks 1-4, involving the blastocyst, three embryonic origins, neural crest cells, and pharyngeal arches.
• Embryogenesis from weeks 5-8 involves the development of all tissues, including the face, palate, tongue, jaws, and skull.
• Fetal development spans from week 9 to term, focusing on growth and maturation of the fetus.

Early Embryogenesis: Week 1

• Features the zygote, cleavage, proliferation, migration, and differentiation stages.

Early Embryogenesis: Weeks 2-3

• The embryoblast differentiates into a bilaminar embryonic disc, comprising the ectoderm and endoderm.
• The bilaminar disc transforms into a trilaminar disc, introducing the mesoderm.
• The ectoderm, mesoderm, and endoderm form the embryonic origins.

Early Embryogenesis: Weeks 3-4

• Key stages in development occur during these weeks, including the development of neuroectoderm, the neural tube, neural crest cells, and somites.

Early Embryogenesis: Neural Crest Cells Derivatives

• Neural crest cells are important for the development of the head, face, and oral cavity.
• Neural crest cells are highly specialised.
• Neural crest cells migrate throughout the embryo.
• They give rise to cranial nerves, the peripheral nervous system, and teeth.
• Ectomesenchyme gives rise to connective tissue in the head, face, and oral cavity, however not enamel.

Early Embryogenesis: Week 4

• The embryo starts forming: the stomodeum (primitive mouth), the bucco-pharyngeal membrane, and the primitive gut.
• The bucco-pharyngeal membrane ruptures, allowing communication between the stomodeum and gut.
• Pharyngeal arches (branchial arches) develop, with each arch having its nerve supply, blood supply, and cartilage.

Pharyngeal Arches

• The 1st Mandibular arch has the Trigeminal nerve, 1st aortic arch blood vessel, Muscles of mastication, Merkel's cartilage, forming the Mandible, Maxilla, zygomatic bones.
• The 2nd Hyoid arch has the Facial Nerve, 2nd aortic arch blood vessel, Muscles of facial expression, Reichert's Cartlidge, forming part of the hyoid bone, body of hyoid, styloid process, stapes.
• The 3rd arch has the Glossopharyngeal Nerve, 3rd aortic arch blood vessel, Stylopharyngeal muscle (supports swallowing), forming part of the hyoid bone and body.
• The 4th arch has the Superior laryngeal branch of Vagus nerve, 4th aortic arch blood vessel, Laryngeal muscles, Cartlidge of the larynx, forming the Thyroid, corniculate and cuneiform.

Embryogenesis: Weeks 5-8

• Development of the head, face, and oral cavity, including jaws, tongue, palate, and skull occurs.

Development of the Face: Weeks 4-6

• The face is formed through the fusion of prominences.
• These include the frontonasal prominence (1), maxillary prominences (2), and mandibular prominences (2).

Development of the Primary Palate: Weeks 6-7

• Forms at the same time as the face.
• It involves the fusion of the frontonasal prominence and the medial nasal prominences.
• The tongue fills the space where the secondary palate would form, so the primary palate forms first.

Development of the Secondary Palate: Weeks 7-8

• The palatine shelves develop around the tongue.
• The palatine shelves fuse along the midline with the primary palate and nasal septum.
• The incisive foramen forms at the midline between the secondary and primary palates.

Development of the Tongue: Weeks 4-7

• The tongue develops from the 1st, 2nd, and 4th pharyngeal arches.
• The anterior 2/3 of the tongue forms from the lateral lingual swellings (1st arch) and the tuberculum impar (2nd arch).
• The posterior 1/3 of the tongue forms from the copula/hypobranchial eminence.
• Cellular apoptosis allows the tongue to separate from the mouth floor, anchored by the frenulum.

Development of Alveolar Bone: Week 7

• Maxilla and mandible ossification is similar to normal.
• Jaws develop a neural and alveolar portion and secondary cartilages promoting tooth development and bone growth.

Development of the Skull

• Occurs in 3 sections of the Cranial vault brain case, Cranial base, and Facial bones.
• Skull bones derive from neural crest cells and mesoderm.
• Cranial vault bones fully fuse at 6-7 years to allow brain growth.

Fetal Development: Week 9 to Birth

• Focuses on the growth of the fetus, where the structures already formed continue to develop and mature.
• Begins after first 8 weeks.

Clinical Significance of Embryology

• Embryogenesis is a complex set of processes susceptible to malfunctions or interruptions, resulting in developmental anomalies.
• Such anomalies can impact health and quality of life.
• The aetiology includes genetic and environmental (congenital) factors like infections, radiation, hormones, and nutritional deficiencies.

Cleft Lip and Palate

• Facial clefts (space/gap) are congenital anomalies affecting the face and oral cavity.
• Presentation varies: complete or incomplete, unilateral or bilateral.
• The most common facial cleft in the UK is cleft lip and palate, which occurs in approximately 1 in 700 live births.
• There are 3 variations of cleft lip/ palate, including cleft lip (CL), cleft palate (CP), and cleft lip and palate (CLP)
• Management is usually a multidisciplinary team for early intervention.

Management of Cleft Lip and Palate

• Early diagnosis and effective treatment can reduce the impact on patients.
• Patients may face a higher risk of oral disease due to the impact on tooth development.
• Treatment with multidisciplinary teams.

Test your knowledge of embryological development with this quiz. Questions cover key stages, germ layers, and the formation of various structures. Topics include pharyngeal arches and facial development.