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Updated: Apr 25 2022

Branchial Apparatus

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  • Overview
    • Branchial apparatus (pharyngeal apparatus)
      • branchial clefts (branchial grooves)
        • derived from ectoderm located between the arches
      • branchial arches
        • derived from mesoderm (muscles, arteries) and neural crest cells (bones, cartilage)
        • each arch is associated with a cranial nerve
      • branchial pouches
        • derived from endoderm which line the foregut
  • Branchial arch innervation
    • 1st arch derivatives
      • CN V2 and V3: muscles for "chewing"
    • 2nd arch derivatives
      • CN VII: muscles for "facial expression"
    • 3rd arch derivatives
      • CN IX
    • 4th and 6th arch derivatives
      • supplied by CN X: muscles for "swallowing" and "speaking"
    • CN V3, VII, IX, and X are both sensory and motor.
    • CN V2 is only sensory
  • Branchial arch derivatives
      • Deriv.
      • Cartilage
      • Muscles
      • Nerves
      • Arteries
      • Syndromes
      • 1
      • Meckel's cartilage
        • mandible
        • malleus
        • incus
        • sphenomandibular ligament
      • Muscles of mastication
        • temporalis
        • masseter
        • lateral and medial pterygoids
      • Mylohyoid
      • Anterior belly of digastric
      • Tensor tympani
      • Tensor veli palatini
      • Anterior 2/3 of tongue
      • CN V2 and V3
      • Maxillary artery, external carotid artery
      • Treacher Collins syndrome
        • neural crest cells fail to migrate into arch 1
        • results in underdeveloped zygomatic bones, mandibular hypoplasia, lower eyelid colobomas, and malformed earsPierre Robin syndromesmall jaw,tongue falls back into throat causing choking and difficulty breathing
      • Pierre Robin syndrome
        • small jaw,tongue falls back into throat causing choking and difficulty breathing
      • 2
      • Reichert's cartilage
        • stapes
        • styloid process
        • lesser horn of hyoid
        • stylohyoid ligament
      • Muscles of facial expression
      • stapedius
      • stylohyoid
      • posterior belly of digastric
      • CN VII
      • Stapedial artery, hyoid artery
      • Congenital pharyngocutaneous fistula
        • persistence of cleft and pouch
        • fistula between internal tonsillar area and external neck
        • found alonganterior border of sternocleidomastoid
      • 3
      • Cartilage
        • greater horn of hyoid
      • Stylopharyngeus
      • CN IX
      • Common carotid, internal carotid arteries
      • 4-6
      • Cartilages
        • thyroid
        • cricoid
        • arytenoids
        • corniculate
        • cuneiform
      • 4th arch
      • pharyngeal constrictors except stylopharyngeus
      • cricothyroid
      • muscles of soft palate except tensor veli palatini
      • 6th arch
      • intrinsic muscles of larynx except cricothyroid
      • upper muscles of esophagus
      • 4th arch
      • CN X: superior laryngeal branch (swallowing)
      • 6th arch
      • CN X: recurrent laryngeal branch (speaking)
      • 4 - Right: subclavian artery; Left: aortic arch
      • 6 - Right: pulmonary artery; Left: pulomonary artery & ductus arteriosus
  • Branchial cleft derivatives
    • 1st cleft
      • develops into epithelial lining of external auditory meatus
    • 2nd - 4th cleft
      • forms temporary cervical sinuses
      • later obliterated by proliferation of 2nd arch
    • Persistent cervical sinus
      • branchial cleft cyst within lateral neck/angle of mandible
  • Branchial pouch derivatives
    • 1st pouch
      • forms
        • epithelial (endoderm derived) lining of middle ear cavity and eustachian tube
        • mastoid air cells
    • 2nd pouch
      • forms epithelial lining of palatine tonsil
    • 3rd pouch
      • dorsal wings
        • forms inferior parathyroids
      • ventral wings
      • 3rd pouch derivatives end up below the 4th derivatives
    • 4th pouch dorsal wings
      • forms superior parathyroids
    • DiGeorge syndrome (22q11 deletion)
      • 3rd and 4th pouches fail to differentiate into thymus and parathyroid glands
      • Symptoms
        • ↓ PTH due to parathyroid aplasia
          • tetany due to hypocalcemia
        • T cell deficiency due to thymic aplasia
          • recurrent viral/fungal infections
          • cell mediated immunity still functional and can fight bacterial infections
        • congenital heart and great vessel defects
        • absent thymic shadow on CXR
    • MEN 2A
      • mutation of germline RET (neural crest cells)
        • pheochromocytoma
        • parathyroid tumor
          • derived from 3rd/4th pharyngeal pouch
        • medullary thyroid cancer
          • derived from parafollicular cells from the 4th/5th pharyngeal pouch
          • NOTE: 5th pouch degenerates during development
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