Branchial arches

• Forms the anatomical bases for head & neck development
• Related to gill (brachial system) & located near the developing pharynx (pharyngeal) of the embryo.

The branchial apparatus consists of:

• Branchial (pharyngeal) arches
  • mesoderm
• Branchial (pharyngeal) clefts
  • ectoderm
• Pharyngeal pouches
  • endoderm
  • Simultaneous with the development of the arches & clefts
    • a number of outpocketings arise in the lateral wall of the pharyngeal gut
  • these pouches penetrate the surrounding mesoderm
    • but do not make open communication with the external clefts
• Branchial membranes
  • ectoderm
  • endoderm

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Branchial (Pharnygeal) arches

• Develop during the 4th week as rounded ridges on each side of the future head & neck region
• 4 arches appear by the end of 4th week
  • separated from each other externally by grooves – branchial clefts
• Function
  • support the lateral walls of the primitive pharynx
  • play an important role in formation of the face & neck
• The mouth initially appears as a slight depression in the surface ectoderm
  • stomodaeum
  • at 1st separated from the primitive pharynx by the buccopharyngeal membrane

Branchial arches – Components

Each arch has a mesodermal core covered externally by ectoderm & internally by endoderm.

Neural crest cells migrate into the arches & give rise to skeletal components. The mesoderm of each arch gives rise to muscles.

A typical arch contains the following

• A cartilaginous bar
• A muscle element
• An artery
• A nerve

* REFER PRINTED NOTES ON THE ARCHES, CLEFTS, POUCHES, TONGUE & THYROID GLAND FORMATION

1) 1st branchial arch (Mandibular arch)

Clinical anatomy

• Malformations result from deficiencies in components of the arch (primarily neural crest migration)
  • Treacher-Collins Syndrome (mandibulofacial dyostosis)
    • no ossification
      • abnormal external, middle and inner ear
    • no development of mandible
      • mandibular & malar hypoplasia
    • lower eyelid defects
  • Pierre Robin Syndrome
    • Mandibular hypoplasia
    • Cleft palate *
    • Eyes & ear defect
  • DiGeorge Syndrome
    • Absense of the thymus
    • Malformations of the mouth
    • Nasal clefts
    • Glossoptosis*
      • tongue displaced downwards
    • Cardiac abnormalities

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– The rest read from printed notes.

Formation of tongue
http://embryology.med.unsw.edu.au/Notes/head6.htm