Branchial arches & primitive mouth (dcp)

Embryology (Branchial arches & Primitive mouth)

1. Branchial Arches & Primitive Mouth Dr. Muznah Sultan Dept of Oral Biology DIDC - DUHS

2. When the stomatodeum first forms, it is delimited rostrally by the neural plate and caudally by the cardiac plate. Buccopharyngeal membrane separates it from the foregut. Laterally the stomatodeum becomes limited by the first pair of pharyngeal or branchial arches.

3. Arches are seen as bulges on the lateral aspect of the embryo and are externally separated by small clefts called BRANCHIAL GROOVES. On the inner aspect of the pharyngeal wall are corresponding small depressions called PHARYNGEAL POUCHES separating each branchial arches internally.

4. Fate of grooves and pouches 1 st groove & pouch  formation of external auditory meatus , lymphatic membrane, tympanic antrum , mastoid antrum , eustachian tube. 2 nd ,3 rd & 4 th grooves  obliterated by overgrowth of 2 nd arch. 2 nd pouch  obliterated by the development of palatine tonsil. 3 rd pouch  expands dorsoventrally into: Dorsal component originates inferior parathyroid gland. Vental component  forms thymus by fusing with its counterpart.

5. 4 th pouch  expands dorsoventrally into: Dorsal component  gives origin to superior parathyroid gland Ventral component  gives origin to ultimobranchial body 5 th pouch  rudimentary

6. Anatomy of an arch Inner aspect covered by endoderm and the outer surface by ectoderm (except for 1 st arch-lining is reversed). CENTRAL CORE consists of mesenchyme derived from lateral plate mesoderm which is surrounded by mesenchyme . This mesenchyme condenses to form the arch cartilage.

7. 1 st arch cartilage  MECKEL’S CARTILAGE 2 nd arch cartilage  REICHERT’S CARTILAGE

8. Some of the mesenchyme surrounding the cartilaginous bar develops into striated muscles. 1 st arch musculature  Muscles of mastication 2 nd arch musculature  Muscles of facial expression

9. Each arch also consists of an artery a nerve (motor & sensory components) Nerve of 1 st arch  Trigeminal (V) Nerve of 2 nd arch  Facial (VII) Nerve of 3 rd arch  Glossopharyngeal (IX) Structures derived from any arch carry with them the nerve supply of that arch.