Pharyngeal Arches

Pharyngeal Arches

Pharyngeal arches (branchial arches) provide nerve, artery, bone and muscle to the craniofacial development. This article explores arches, pouches and grooves.

Summary Card


Overview
Ectoderm, endoderm and mesoderm form pharyngeal arches that develop into maxillary, mandibular, frontonasal prominences.

Pharyngeal Arches
I, II, III, IV, and VI paired arches each contain nerve, artery, muscle, and bone

Grooves and Pouches
Arches are connected by internal pouches and external grooves.

Facial Development
During the 4th-8th week of gestation from frontonasal process, paired maxillary and mandibular processes

Flashcards
Evidence-based flashcards to improve your active recall.

Important: Branchial arches are pharyngeal arches.


Overview of Pharyngeal Arches


Key Point

Ectoderm, mesoderm and endoderm form paired pharyngeal arches (I, II, III, IV, VI) that give rise to maxillary, mandibular and frontonasal processes.


There are 6 paired pharyngeal arches containing neural crest cell derivatives: nerve, artery, bone, muscle. These arches are formed by:

  • Ectoderm: nerves, skin, pluripotent neural crest cells.
  • Endoderm: GI and respiratory lining.
  • Mesoderm: bone, cartilage, muscles, vessels.

😎
Fun Fact: There is no 5th branchial arch in humans.


Pharyngeal Arches


Key Point

6 paired pharyngeal arches each contain nerve, artery, bone/cartilage, and muscle. This can be linked to specific congenital conditions.


1st Pharyngeal (Mandibular) Arch

  • Nerve: Trigeminal
  • Artery: Maxillary
  • Bone/Cartilage: mandible, maxilla, greater sphenoid wing, malleus, squamous temporal.
  • Muscle: mastication, tensor veli palitini, tensor tympani, anterior digastric.
  • Syndromes: Treacher Collins, Pierre Robin, Stickler.

The first pharyngeal arch also contains mandibular prominence, maxillary prominence, Meckel’s cartilage, and quadrate cartilage.

2nd Pharyngeal (Hyoid) Arch

  • Nerve: Facial Nerve
  • Artery: Stapedial (corticotympanic artery)
  • Bone/Cartilage: Stapes, upper body of hyoid, lesser cornu, styloid process
  • Muscle: facial expression, posterior digastric, stapedius, stylohyoid
  • Syndrome: Mobius Syndrome (bilateral facial nerve absence).

The second pharyngeal arch also contains Reichert's cartilage.

3rd Pharyngeal Arch

  • Nerve: glossopharyngeal nerve, taste to the posterior 1/3rd of the tongue
  • Artery: common carotid artery and proximal portion of internal carotid artery
  • Bone/Cartilage: lower body and greater horn of the hyoid.
  • Muscle: stylopharyngeus
  • Syndrome: Velocardiofacial (DiGeorge) syndrome

The third pharyngeal arch also develops the thymus and inferior III parathyroids.

4th Pharyngeal Arch

  • Nerve: superior laryngeal branch of the vagus.
  • Artery: proximal subclavian artery (right), aortic arch (left)
  • Bone/Cartilage: laryngeal cartilages
  • Muscles: pharynx constrictors, levator veli palatini, cricothyroid.

6th Pharyngeal Arch

  • Nerve: recurrent laryngeal branch of vagus, diffuse sensory innervation
  • Artery: proximal pulmonary arteries (right), ductus arteriosus (left)
  • Bone/Cartilage: laryngeal cartilages
  • Muscles: intrinsic muscles of the larynx (except for cricothyroid)


Pharyngeal Pouches and Grooves


Key Point

Arches are connected by internal pouches and external grooves. They form specific aspects of the craniofacial skeleton.


Pharyngeal pouches are internal grooves between the arches. Each pouch helps develop specific areas of the head and neck region.

  • 1st pouch forms the middle ear, the internal auditory canal.
  • 2nd pouch forms palatine tonsils.
  • 3rd pouch forms inferior parathyroids and thymus.
  • 4th pouch forms superior parathyroids.
  • 5th pouch forms parafollicular cells of the thyroid

Pharyngeal grooves (clefts) are external connections between the arches.

  • 1st groove forms the external auditory canal and tympanic membrane.
  • 2nd-4th grooves create a cervical sinus.

Failure to obliterate the grooves can result in pharyngeal cysts, sinuses or fistulas.

💡
Tip: pouch III becomes inferior, pouch IV travels superior


Facial Development


Key Point

During the 4th-8th week of gestation from frontonasal process, paired maxillary and mandibular processes.

The face develops during the 4th-8th week of gestation from 5 processes:

  • Paired maxillary processes arising from 1st branchial arch.
  • Paired mandibular process arising from 2nd branchial arch.
  • Frontonasal process arising from mesoderm proliferation.

Maxillary Prominences

  • Arise from 1st branchial arch
  • Migrate medially to form the secondary palate, lateral maxilla and lateral lip
  • Separates the nasal pits and stomodeum
  • Forms nasolacrimal duct system

Mandibular Prominences

  • Arise from 2nd branchial arch
  • Form mandible, lower lip, lower face.

Frontonasal Prominences

The frontonasal prominences are independent of the branchial arteries. They are formed by a proliferating mesoderm that develops into paired placodes.

  • Medial placode forms the medial nasal process, which forms midline structures (philtrum, cupid bow, premaxilla, nasal tip and septum).
  • Lateral placode forms the lateral nasal process, which forms the nasal alae.

😎
Fun Fact: the cranium grows via intramembranous and cartilaginous ossification in response to brain growth


Embryological Failures

Specific conditions arise due to the failure of fusion of the following two structures:

  • Cleft Lip: unilateral medial nasal process with maxillary process.
  • Bilateral Cleft Lip: bilateral medial nasal process with maxillary process.
  • Cleft Palate: medial and lateral palatine processes.
  • Median Cleft Lip or Tessier 0: midline fusion of median nasal prominences
  • Tessier 3: lateral nasal processes and maxillary process at the alar groove.
  • Tessier 7: maxillary and mandibular processes

💡
Tip: anterior 2/3 of tongue arises from pharyngeal arch 1 and posterior 1/3 arises from arches III and IV


Flashcards

Evidence-based flashcards are designed for active recall & spaced repetition using the Feynman Technique.

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