Pharyngeal Apparatus – Embryology

Pharyngeal apparatus consists of three structures. They are…

  • Pharyngeal arches
  • Pharyngeal clefts
  • Pharyngeal pouches


Pharyngeal apparatus begins to develop at 4 week of gestation and responsible for the development of structures of the head and neck region.


Pharyngeal Arches

  • At first pharyngeal arches grows forward from both sides to meet in the midline to fuse with its’ opposite partner to form a tube
  • Superior and inferior tubes fuse with each other as well
  • Each pharyngeal arches are identical at first
  • There are six pharyngeal arches, but the fifth pharyngeal arch regress soon after development, resulting in only five pharyngeal arches
  • But external only four are visible in an embryo


Each Pharyngeal Arch Consist Of….

  • Mesenchymal core
    • Blood vessel
    • Nerve
    • Connective tissues
  • Membrane
    • Ectoderm (Outer lining) 
    • Endoderm (Inner lining)  

  
Pharyngeal Clefts

  • Pharyngeal arches are separated externally by pharyngeal clefts 
  • Lined by ectoderm
  • There are four pharyngeal clefts
  • Only the first pharyngeal cleft remains and the rest fades out
  • Rest become obliterated 



Pharyngeal Pouches

  • Pharyngeal arches are separated internally by pharyngeal pouches
  • Lined by endoderm



Components Of Pharyngeal Arches

Each pharyngeal arch is responsible for the development of a….

  • Cranial nerve
  • Artery 
  • Skeletal components
  • Muscular components
 
First Pharyngeal Arch
  • Muscular components
    • Muscles of mastication 
      • Temporalis
      • Masseter
      • Pterygoid
    • Anterior belly of digastric
    • Tensor veli palatini
    • Tensor tympani
  • Skeletal components
    • Maxilla
    • Malleus 
    • Incus
    • Part of temporal bone
    • Zygomatic bone
    • Meckel’s cartilage
  • Artery
    • Part of maxillary artery, a branch of the external carotid artery
  • Nerve
    • Mandibular branch of trigeminal nerve


Second Pharyngeal Arch

  • Muscular components
    • Muscles of facial expression
    • Posterior belly of digastric
    • Stylohyoid
  • Skeletal components
    • Stapes
    • Styloid process of temporal bone
    • Hyoid bone
      • Lesser horns
      • Upper body
    • Stapedius
  • Artery
    • Stadedial artery
  • Nerve
    • Facial nerve
 
Third Pharyngeal Arch
  • Muscular components
    • Stylopharyngeus
  • Skeletal components
    • Hyoid bone
      • Greater horns
      • Lower body
  • Artery
    • Common carotid artery
    • Proximal part of the internal carotid artery
  • Nerve
    • Glossopharyngeal nerve


Fourth Pharyngeal Arch

  • Muscular components 
    • Muscles of the soft palate – Except tensor veli palatini
    • Muscles of the pharynx – Except stylopharyngeus
    • Cricothyroid
    • Cricopharyngeus
  • Skeletal components
    • Laryngeal cartilages (In contribution with sixth pharyngeal arch)
      • Thyroid
      • Cricoid
      • Arytenoid
      • Corniculate 
      • Cuneiform
  • Artery
    • Right – Subclavian artery (Proximal part)
    • Left – Aortic arch
  • Nerve
    • Vagus nerve – Superior laryngeal nerve
 
Sixth Pharyngeal Arch

  • Muscular components
    • Intrinsic muscles of larynx – Except cricothyroid
    • Skeletal muscles of oesophagus
  • Skeletal components (In contribution with fourth pharyngeal arch)
    • Thyroid
    • Cricoid
    • Arytenoid
    • Corniculate 
    • Cuneiform
  • Artery
    • Right – Pulmonary arteries (Proximal part) 
    • Left – Ductus arteriosus
  • Nerve
    • Vagus nerve – Recurrent laryngeal nerve
Components Of Pharyngeal Clefts
 
Only the first pharyngeal pouch gives rise to permanent structures 
 
First Pharyngeal Cleft
  • External auditory meatus
  • Tympanic membrane
 
 
Components Of Pharyngeal Pouch
 
First Pharyngeal Pouch
  • Internal auditory canal 
  • Eustachian tube
 
Second Pharyngeal Pouch
  • Primitive palatine tonsil
 
Third Pharyngeal Pouch
  • Dorsal portion  – Inferior parathyroid gland
  • Ventral portion – Thymus
 
Fourth Pharyngeal Pouch
  • Dorsal portion  – Superior parathyroid gland
  • Ventral portion – Ultimopharyngeal body later differentiate into parafollicular cells
 
 
Development Of Tongue
  • Anterior 2/3rd of tongue
    • Formed by first pharyngeal arch
  • Posterior 1/3rd of tongue
    • Formed by 3rd and 4th pharyngeal arches
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