SYSTEMIC EMBRYOLOGY

SYSTEMIC EMBRYOLOGY: PHARYNGEAL ARCHES

Formation of Pharyngeal Arches

The pharyngeal arches are six paired structures that develop early in embryonic life and eventually give rise to various structures of the head and neck. They are formed by the migration of mesenchymal cells between the first to the sixth pharyngeal pouches. The pharyngeal arches are initially solid but later become hollow and develop into various structures.

Derivatives of Pharyngeal Arches

• First Pharyngeal Arch
  • Mandible
  • Maxilla
  • Malleus and incus bones
  • Anterior portion of the external auditory meatus
• Second Pharyngeal Arch (Hyoid Arch)
  • Styloid process
  • Lesser horn and upper part of the hyoid bone
  • Stapes bone
  • Muscles of facial expression
  • Hyoglossus muscle
  • Stylohyoid ligament
  • Posterior belly of the digastric muscle
• Third Pharyngeal Arch
  • Lesser cornu of the hyoid bone
  • Lower part of the hyoid bone
  • Posterior belly of the digastric muscle
  • Cricothyroid muscle
• Fourth Pharyngeal Arch
  • Upper laryngeal muscles
  • Lower laryngeal muscles
• Sixth Pharyngeal Arch
  • C1-C6 vertebrae
  • Muscles of the neck

Formation of Tongue

The tongue is formed from the first and second pharyngeal arches. The lingual swellings fuse to form the tongue. The lingual swellings eventually give rise to the anterior two-thirds of the tongue. The posterior one-third of the tongue arises from the third pharyngeal pouch.

1 → Lingual swellings → Fusion of lingual swellings → Tongue formation

Formation of Thyroid Gland

The thyroid gland is formed from the endoderm of the second pharyngeal pouch. The thyroid gland develops from the thyroid diverticulum, which grows upwards to reach the base of the tongue. The thyroid diverticulum eventually forms the thyroid gland.

1 → Second pharyngeal pouch → Thyroid diverticulum → Thyroid gland formation