Branchial apparatus

The branchial (or pharyngeal) apparatus is the complex region in the developing embryo between the head and chest that develops in the fourth week and provides bilateral ridges and valleys that subsequently develop into numerous anatomic structures of the head, face, palate and anterior neck. The development of structures from the apparatus helps explain the complex cranial nerve distribution in some regions. 

The apparatus resembles the branchia (gills) of fish and amphibians, which obviously don't form in the human. Hence the description of pharyngeal arches etc. is more correct and advised.

Structure

The apparatus consists of paired symmetrical pharyngeal arches, pouches, grooves and membranes that develop from the ectoderm and in part from the pharyngeal part of the primitive foregut (see figure 1). They start forming in week 4 and by about week 7 the differentiation and migration of structures from the branchial apparatus is complete.

  • pharyngeal arches are transverse swellings that laterally border the proximal foregut, each is separated from adjacent arches by the branchial clefts
    • contains both mesoderm (forming muscles and vessels) and mesenchyme (neural crest cells which form bones)
    • each arch has a cranial nerve associated with it, along with a cartilage piece and artery associated with aortic arch development, some of which obliterate
    • the fifth arch doesn't develop but for comparative anatomy reasons, the sixth arch retains its name
  • pharyngeal pouches form as endodermal invaginations from the lateral wall of the proximal primitive foregut
    • these penetrate the mesenchyme but do not form an open communication with the external clefts
  • pharyngeal or branchial clefts (or grooves) form as ectodermal invaginations on the external surface of the embryo, between the arches
  • pharyngeal membranes are formed between the pharyngeal pouch and groove
Pharyngeal arches
Pharyngeal pouches
  • the first pharyngeal pouch forms as a diverticulum called the tubotympanic recess and gives rise to the epithelium of the auditory tube and middle ear cavity
  • the second pharyngeal pouch gives rise to the epithelium of the palatine tonsil
  • the third pharyngeal pouch has ventral and dorsal wings and gives rise to the thymus (from the ventral wing) and inferior parathyroid gland (from the dorsal wing)
  • the fourth pharyngeal pouch gives rise to the superior parathyroid gland
  • the fifth pharyngeal pouch is atypical and often considered to be part of the fourth pouch. It gives rise to the ultimobranchial body which contributes to the parafollicular (C) cells of the thyroid gland responsible for the secretion of calcitonin.
Pharyngeal cleft
  • the first pharyngeal cleft forms the epithelium of the external auditory meatus and the external epithelium of the tympanic membrane
  • the second to fourth pharyngeal clefts fuse and form the cervical sinus, which typically obliterates
Pharyngeal membranes
  • the first pharyngeal membrane forms the tympanic membrane
  • the second to fifth pharyngeal membranes are obliterated

Related pathology

Anatomy: Head and neck

Anatomy: Head and neck

Article information

rID: 77393
System: Head & Neck
Section: Anatomy
Synonyms or Alternate Spellings:
  • Pharyngeal apparatus
  • Pharyngeal cleft
  • Pharyngeal groove
  • Pharyngeal arch

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Cases and figures

  • Figure 1: pharyngeal arches (creative commons diagram)
    Drag here to reorder.
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