Pharyngeal Apparatus

Pharyngeal Apparatus


PHARYNGEAL APPARATUS

  • Pharyngeal apparatus includes the structures which form the neck and some structures of head region. Pharyngeal apparatus consists of:
  1. Pharyngeal (branchial) arches, a series of mesodermal thickening lined on outside by ectoderm and on inside by endoderm, which appear in the wall of cranial most part of developing foregut. Initially there are six arches, but soon fifth arch disappears and only five are left.
  2. Pharyngeal pouches (endodermal pouches) refer to the outward bulging of endoderm (i.e. bulging of endoderm from inside out), which separates two pharyngeal arches internally.
  3. Pharyngeal clefts or grooves (ectodermal clefts or branchial cleft) refer to inward dipping of ectoderm b/w two arches. Pharyngeal clefts lie opposite to pharyngeal pouches and thus in this area the ectoderm and endoderm lie close to each other without any intervening mesoderm.
  4. Pharyngeal membrane are thus formed where the ectoderm of pharyngeal clefts contacts the endoderm of pharyngeal pouches. Only one membrane (first pharyngeal membrane) contribute formation of adult structures. First pharyngeal membrane (along with intervening mesenchyme) becomes tympanic membrane. 

Thus each pharyngeal arch has 3 parts:

  1. ectodermal cleft (pharyngeal cleft) from ectoderm, 
  2. mesodermal element (mesenchyme),and 
  3. endodermal pouch (pharyngeal pouch) from endoderm.

Hence structures derived from pharyngeal arches can be divided into:-

  1.  Ectodermal derivatives: From ectodermal cleft.
  2.  Endodermal derivatives: From endodermal pouch.
  3.  Mesodermal derivatives: From mesenchyme. 

The mesenchyme of each pharyngeal arch forms following components:

  1. Skeletal component
  2. Muscular components
  3. Arterial component
  4. Nerve supply 
IMPORTANT POINTS ABOUT PHARYNGEAL APPARATUS
  • First pharyngeal arch (mandibular arch) develops two prominences: smaller maxillary prominence (forms maxilla, zygomatic bone, squamous temporal bone) and larger mandibular prominence (forms mandible).
  • Tympanic membrane derived from first pharyngeal membrane (which seperates 1st pharyngeal groove from 1st pharyngeal pouch) represents all three layers of embryonic disc. It develops from three sources.
  1. External very thin skin is derived from ectoderm of 1st pharyngeal groove.
  2. Mesoderm of 1st and 2nd pharyngeal arches.
  3. Internal lining is derived from endoderm of tuotympanic recess ( a derivative of 1st pharyngeal pouch).
  • Tongue muscles originate from myoblast of occipital somites (occipital myotomes).
  • Anterior 2/3 of tongue develops from 1st (lingual swelling) and tuberculum impar.
  • Posterior 1/3 is developed from 3rd arch (cranial part of hypobronchial eminence).
  • Posterior most part develops from 4th arch (dorsal part of hypobronchial eminence).
Exam Question
  •  Pierre Robin sequence is caused by defect in development of first (1st) pharyngeal arch.
  • Branchial cyst derived from 2nd branchial cleft (2nd pharyngeal cleft).
  • First pharyngeal arch (mandibular arch) develops two prominences: smaller maxillary prominence (forms maxilla, zygomatic bone, squamous temporal bone) and larger mandibular prominence (forms mandible).
  • Tympanic membrane derived from first pharyngeal membrane (which seperates 1st pharyngeal groove from 1st pharyngeal pouch) represents all three layers of embryonic disc. 
  • Parafollicular ‘C’ cells develop from Ultimobranchial body.
  • Tongue muscles originate from myoblast of occipital somites (occipital myotomes).
  • Anterior 2/3 of tongue develops from 1st (lingual swelling) and tuberculum impar.
  • Posterior 1/3 is developed from 3rd arch (cranial part of hypobronchial eminence).
Don’t Forget to Solve all the previous Year Question asked on Pharyngeal Apparatus

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