Pharyngeal archesPharyngeal arches

The pharyngeal (Branchial) The pharyngeal (Branchial) apparatus :apparatus :

It consists of :It consists of : 1-pharyngeal arches. 1-pharyngeal arches. 2-pharyngeal pouches. 2-pharyngeal pouches. 3-pharyngeal grooves. 3-pharyngeal grooves. 4-pharyngeal membranes. 4-pharyngeal membranes.

These embryonic structures These embryonic structures contribute tocontribute to the development of the head & neckthe development of the head & neck regions.regions.

Drawings illustrating the human pharyngeal apparatus.A, dorsal view of cranial part of an embryo.

B to D, lateral views showing later development of pharyngeal arches.

E to G, ventral or facial views, illustrating the relationship of the first pharyngeal arch to the stomodeum. -Maxillary prominence of 1st arch lies lateral to stomodeum. -Mandibular prominence of 1st arch lies caudal to stomodeum.

H,horizontal S.of cranial part of emb.

I, horizontal S. illustrating the arch components + floor of pharynx.

J, sagittal S.illustrating the openings of pharyngeal pouches in the lateral wall of the primordial pharynx.

Pharyngeal archesPharyngeal archesThey begin to develop early in the 4th week as neural crest cells migrate into the future head & neck regions.

By the end of 4th week, 4 pairs of pharyngeal arches are visible externally

The 5th & 6th arches are rudimentary and not visible on surface of embryo.

Pharyngeal arches are separated externally by fissures- the pharyngeal grooves, which numbered cranio-caudally as the arches.

The arches appear along lateral wall of primordial pharynx.

The primordial mouth (stomodeum) is temporarily closed by oropharyngeal bilaminar membrane (ectoderm & endoderm), which ruptures at about 26 days.(during 4th week).

Fronto-nasal prominence

Pharyngeal archesPharyngeal arches

2- A ventral portion, the mandibular process, which gives rise the mandible ( lower jaw).

-1st pair of pharyngeal arches plays a major role in facial development.

2nd pharyngeal arch (hyoid arch) : contributes to the formation of hyoid bone.

1st pharyngeal arch (mandibular arch), the primordium of jaws consists of : 1- A dorsal portion, the maxillary process, which gives rise to the maxilla (upper jaw), zygomatic bone, and squamous part of temporal bone.

Pharyngeal ArchesPharyngeal ArchesA, By the end of the 4th week (28days), 4 pairs of pharyngeal arches are developed.

B, Drawing showing pharyngeal pouches + aortic arches, that supplies the pharyngeal arches and arise from truncus arteriosus, then enter the dorsal aorta.

The derivatives of aortic arches : are the adult arteries of head & neck.

C, Horizontal section showing the floor of primordial pharynx and germ layer derivatives of the pharyngeal arch components : each arch consists of a core of mesenchyme, which is covered externally by ectoderm and internally by endoderm.

Pharyngeal Arch Pharyngeal Arch ComponentsComponentsEach arch consists of a core of mesenchyme that is

covered externally by ectoderm and internally by endoderm.

A core of mesenchyme derived from the original mesenchyme - mesoderm during 3rd week + neural crest cells (neuroecto-dermal origin) during 4th week that migrate into the arches.

Skeletal musculature & vascular endothelia are derived from the original mesenchyme in the arches.

A typical pharyngeal arch contains : 1-an aortic arch artery : arises from truncus arteriosus of primordial heart to enter the dorsal aorta. 2-a cartilaginous rod : that forms the skeleton of arch. 3-a muscular components : to give ms. of head & neck. 4-a nerve : to supply mucosa & ms. of arch.

Fate of Pharyngeal Fate of Pharyngeal ArchesArches A, lateral view of embryo at 5th week

(32 days) showing pharyngreal arches + cervical sinus.

B, section illustrating growth of 2nd arch over 3rd & 4rth arches.

C, embryo of about 33 days.

D, section illustrating early closure of the cervical sinus during 5th week.

E, embryo of 41 days (end of 6th w.).

F, section showing the transitory cystic remnant of cervical sinus.

G, drawing of 20-week fetus illustrating the area of face derived from the 1st pair of pharyngeal arches.

Fate of Pharyngeal ArchesFate of Pharyngeal ArchesThey contribute to the development of face, nasal cavities, mouth,larynx, pharynx, and neck.

During 5th week, 2nd arch enlarges to overgrow the 3rd & 4th arches, forming ectodermal depression- the cervical sinus. B,D

By the end of 7th week, 2nd to 4th pharyngeal grooves + the cervical sinus have disappeared, giving the smooth contour to the neck

Derivatives of Pharyngeal Derivatives of Pharyngeal Arch Cartilages :Arch Cartilages :

A, lateral view of 4-week embryo, illustrating location of cartilages in pharyngeal arches.

B, 24-week fetus illustrating adult dreivatives of arch cartilages : 1-Note development of mandible by intramembranous ossification of mesenchymal tissue surrounding the ventral part of 1st arch cartilage (Meckel’s cartilage) + development of malleus & incus (middle ear bones) dorsally + anterior ligament of malleus & sphenomandibular ligament in the middle part. 2-Note, the 2nd arch cartilage (hyoid or Reichert’s cartilage) gives rise dorsally stapes & styloid process, in the middle stylohyoid ligament, and ventrally lesser cornu + upper part of body of hyoid bone.

Derivatives of Pharyngeal Derivatives of Pharyngeal Arch Cartilages :Arch Cartilages :

B, 3- Note also derivatives of the 3rd arch cartilage which ossifies to form : greater cornu (horn) + inferior part of the body of hyoid bone. 4- Cartilaginous components of 4th & 6th pharyngeal arches fuse to form most of laryngeal cartilages (thyroid + cricoid + arytenoid + corniculate + cuneiform), EXCEPT the cartilage of epiglottis which develops from the mesenchyme of the caudal part of hypopharyngeal eminence lying in the floor of primordial pharynx and derived from 3rd & 4th pharyngeal arches.

The 5th arch is often absent, if present it is rudimentary and has No derivatives.

Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch Muscles :Muscles :

A, lateral view of 4-week embryo showing the muscles derived from the pharyngeal arches, the arrow showing the pathway of myoblasts from the occipital myotomes to form the muscles of tongue.

B, sketch of head & neck of 20-week fetus, showing the 1st pharyngeal arch forms ms. of mastication & other ms./ 2nd arch forms ms. of facial expression, post.belly of digastric & other ms. / 3rd arch forms stylopharyngeus./ 4th arch forms cricothyroid, levator veli palatini + constrictors of pharynx. / 6th arch forms interinsic ms. of larynx + striated ms of esophagus.

Derivatives of Pharyngeal ArchesDerivatives of Pharyngeal Arches

Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch NervesNerves A, lateral view of head &neck and thorax of

4-week embryo showing the cranial nerves : Trigeminal N.(V), Facial N.(VII), Glossopharyngeal N.(IX), and Vagus N.(X)—supplying 1st ,2nd , 3rd & caudal (4th + 6th ) pharyngeal arches, respectively.

B, sketch of head & neck of 20-week fetus showing the 2 branches of 1st arch nerve (CNV), maxillary & mandibular branches of trigeminal N

C, Sagittal section of fetal head & neck showing the sensory nerves of trigeminal N., which is the principal sensory N. of head & neck supplying face, teeth & m.m. of nasal cavity, palate, mouth & tongue, and is the motor N. for ms. of mastication.

C, The nerves from 2nd to 6th pharyngeal arches have little sensory nerves, however, they innervate m.m. of post.tongue, pharynx & larynx.