Embryology of Teeth Tongue Thyroid Dr Shivaram Bhat

Embryology of Teeth, Tongue, Thyroid Dr Shivaram Bhat

Learning objectives • Embryology of teeth from dental lamina • Development of tongue from floor of pharyngeal pouches • Development of thyroid from thyroid diverticulum • Applied embryology related to above organs

Questions • Embryology & anomalies thyroid • Embryology & Anomalies of tongue • Embryology & nerve supply of tongue • Development of teeth • • Anomalies of tongue Thyroglossal duct Thyroglossal cyst Anomalies of thyroid

Time line of events • • 4 weeks – lingual swellings and tuberculum impar 5 weeks – hypopharyngeal eminence, thyroid 6 weeks – dental lamina 7 weeks – thyroid in definitive position 8 – 10 weeks – enamel organs 6 months – enamel, dentine, tongue 9 months – cementum Birth – periodontal ligaments

TEETH

Dental lamina

Stages

Stages

Deciduous teeth

Dental buds for permanent teeth

Permanent teeth

Embryological origin • Ectoderm – Ameloblasts – Enamel • Mesoderm ( neural crest ) – Odontoblasts – Dentine • Mesenchyme – Cementoblasts – Cementum, Periodontal ligament

Morphology

Applied aspects • • Anodentia Gemination Natal teeth Amelogenesis imperfecta Dentinogenesis imperfecta Tooth impaction Dentigerous cyst

TONGUE

Floor of primitive pharynx

Nerve supply

Nerve supply

To summarise • Anterior 2/3 rd - 2 lateral lingual swellings and 1 median lingual swelling • Posterior 1/3 rd - hypobranchial eminence • Posterior most part – 4 th pharyngeal arch • Muscles of tongue – occipital myotomes

Anomalies of tongue • • Aglossia. Microglossia Macroglossia Ankyloglossia Cleft tongue Bifid tongue Lingual thyroid

THYROID GLAND

Thyroid development

Floor of primitive pharynx

Caudal pharyngeal complex

To summarise Thyroid develops from • Thyroid diverticulum from foramen cecum at the junction of tuberculum impar and copula • Caudal pharyngeal complex from 4 th arch and also probably disappearing 5 th arch. • Starts functioning by 3 -4 months

• Absence of isthmus, + 1 lobe • Presence of pyramidal lobe • Levator glandulae thyroidae

THYROID GLAND- Pyramidal lobe