Pharyngeal Apparatus

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Pharyngeal Apparatus
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• The term pharyngeal arch is now used instead of
  branchial arch when describing the development of
  the head and neck regions of human embryos.
• The pharyngeal apparatus consists of
• pharyngeal arches, pharyngeal pouches, pharyngeal
  grooves, pharyngeal membranes.
• These embryonic structures contribute to the
  formation of the head and neck.

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Pharyngeal groove
1st pharyngeal arch
2nd pharyngeal pouch
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• -Pharyngeal arches begin to develop early in the
  fourth week as neural crest cells migrate into
  the future head and neck regions.
• -By the end of the fourth week four pairs of
  pharyngeal arches are visible externally.
• -fifth and sixth arches are rudimentary and are
  not visible on the surface of the embryo.
• -The pharyngeal arches are separated from each
  other by fissures - the pharyngeal grooves.
• -Like the pharyngeal arches, the grooves are
  numbered in a craniocaudal sequence.

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• The first pharyngeal arch (mandibular arch),
  develops two prominences
• 1) The maxillary prominence gives rise to the
  maxilla (upper jaw), zygomatic bone, and part of
  the temporal bone.
• 2) The mandibular prominence forms the mandible
  (lower jaw).
• The first pair of pharyngeal arches plays a major
  role in facial development.
• The second pharyngeal arch (hyoid arch)
  contributes to the formation of the hyoid bone.
• The pharyngeal arches support the lateral walls
  of the primordial pharynx, which is derived from
  the cranial part of the foregut.
• The primordial mouth or stomodeum initially
  appears as a slight depression of the surface
  ectoderm

1)
2)
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1st pharyngeal arch (mandibular arch)
Forms maxilla
(Forms mandible)
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Fate of Pharyngeal Arches

• The pharyngeal arches contribute extensively to
  the formation of the
• face,
• nasal cavities,
• mouth,
• larynx,
• pharynx, and
• neck
• During the fifth week, the second pharyngeal arch
  enlarges and overgrows the third and fourth
  arches, forming an ectodermal depression - the
  cervical sinus
• By the end of the seventh week, the second to
  fourth pharyngeal grooves and the cervical sinus
  have disappeared, giving the neck a smooth
  contour.

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During 4th week
During 5th week
End of 7th week
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Derivatives of Pharyngeal Arch Cartilages

• dorsal end of 1st arch cartilage (Meckel
  cartilage) ? ear and ossifies to form two middle
  ear bones, the malleus and incus
• middle part regresses, but perichondrium forms
  the anterior ligament of malleus and the
  sphenomandibular ligament.
• Ventral parts of the 1st arch cartilages form the
  horseshoe-shaped primordium of the mandible and
  guide its early morphogenesis.
• dorsal end of the 2nd arch cartilage (Reichert
  cartilage), ossifies to form the stapes of the
  middle ear and the styloid process of the
  temporal bone
• The part of cartilage between the styloid process
  and hyoid bone regresses its perichondrium forms
  the stylohyoid ligament.
• The ventral end of the 2nd arch cartilage
  ossifies to form the lesser cornu and the
  superior part of the body of the hyoid bone
• The 3rd arch cartilage, located in the ventral
  part of the arch, ossifies to form the greater
  cornu and the inferior part of the body of the
  hyoid bone.
• The 4th and 6th arch cartilages fuse to form the
  laryngeal cartilages except for the epiglottis
  (mesenchyme in the hypopharyngeal eminence from
  3rd4th).
• The 5th pharyngeal arch is rudimentary and has no
  derivatives.

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Derivatives of Pharyngeal Arch Cartilages
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• A typical pharyngeal arch contains
• an aortic arch
• a cartilaginous rod that forms the skeleton of
  the arch
• a muscular component that differentiates into
  muscles in the head and neck
• a nerve that supplies the mucosa and muscles
  derived from the arch

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During the fifth week, the second pharyngeal arch
enlarges and overgrows the third and fourth
arches, forming an ectodermal depression - the
cervical sinus
By the end of the seventh week, the second to
fourth pharyngeal grooves and the cervical sinus
have disappeared, giving the neck a smooth contour
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Muscles derived from the pharyngeal arches
4 weeks
20 weeks
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• Each arch is supplied by its own cranial nerve
  (CN)
• -first arch ? CNV (trigeminal nerve)
• Maxillary division
• Mandibular division
• -second arch ? CN VII (facial nerve)
• -third arch ? CN IX (glosspharyngeal nerve)
• -fourth to sixth arches ? CN X (vagus nerve)

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Sagittal section of the fetal head and neck,
showing the deep distribution of sensory fibers
of the nerves to the teeth and mucosa of the
tongue, pharynx, nasal cavity, palate, and larynx.
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Pharyngeal pouches

• Notice the relationship between the pharyngeal
  arches, grooves, pouches and their germ layer
  derivatives
• Fig. A ? 5 weeks
• Fig. B ? 6 weeks

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Derivatives of Pharyngeal Pouches

• Primitive pharynx at 7 weeks
• Note that 1st pair of pouches contribute to the
  formation of the tympanic membranes

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Pharyngeal Pouch Derivatives at 20 weeks

• Remember DiGeorges Syndrome?

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Cervical sinus

• The 2nd pharyngeal arch tends to grow over the
  3rd and 4th arches
• Normally, the sinus disappears by the 7th week of
  development

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Patient with cervical sinus cyst

• Enlarged painless swelling often located inferior
  to the angle of the mandible

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• Pharynx comes from endoderm of the pouches which
  are located next to the strernum, and migration
  of tissue takes place there.
• the beauty is the c-shape of the embryo which
  it tend to grow,
• thyroid gland, thymus, and parathyroid glands,
  illustrating various congenital anomalies that
  may occur.

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INFERIONTIAL GROWTH, from the 2-3 pouches we
get the palatine tonsillymphoid tissue,
endodermis derivation, epithelium component, that
covers it as endodermis derivation, underline
migration of the cell to complete the derivation,
population of cell in the tonsil come from the
bone mirror. Thyroid gland granular in nation,
sub epithelium derivation.From the pouches 3
and 4 we get the thyroid and thymus,
Development of the thyroid gland. A, B, and C,
Schematic sagittal sections of the head and neck
regions of embryos at 4, 5, and 6 weeks, which
illustrating successive stages in the development
of the thyroid gland. D, Similar section of an
adult head and neck showing the path taken by the
thyroid gland during its embryonic descent
(indicated by the former tract of the
thyroglossal duct).
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1)Desent to the parathyroid and to the
population of lymphoid tissue indicate here, as
the cell migrate down to the parathyroid, and
thyroid downward making the descend come from the
3-4 pouches get attached to the capsule of the
thyroid gland. 2) migration of cell is not a
great distances 3) this picture showing the
possible locations of thyroglossal duct cysts.
4) thyroglossal duct sinus is also illustrated
( the broken line indicates the course taken by
the thyroglossal duct during descent of the
developing thyroid gland from the foramen cecum
to its final position in the anterior part of
the neck.) b, illustrating lingual and cervical
thyroglossal duct cysts.5)most thyroglossal
duct cysts are located just inferior to the hyoid
bone.
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The broken line indicates the path followed by
the thyroid gland during its descent and the
former tract of the thyroglossal duct.
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Development of the Tongue Anterior 2/3

• Near the end of the fourth week
• First, the median tongue bud (tuberculum impar)
  appears
• Second, two oval distal tongue buds (lateral
  lingual swellings) develops on each side of the
  median tongue bud
• The distal buds rapidly increase in size, merge
  (midline of the tongue), over grow the median
  tongue bud
• This is formed by the first pair of pharyngeal
  arches and makes up the anterior 2/3 of the
  tongue
• Note Innervated by the lingual branch of the
  mandibular division of the trigeminal nerve (CN
  5), except the taste buds are innervated by the
  chorda tympani branch of the facial nerve (CN 7)
  and the vallate papillae is the glossopharyngeal
  nerve (CN 9)

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Development of the Tongue Posterior 1/3

• Formation of the posterior third (pharyngeal
  part) of the tongue is indicated by two
  elevations that develop caudal to the foramen
  cecum
• The copula forms by fusion of the ventromedial
  parts of the second pair of pharyngeal arches
• The hypopharyngeal eminence (hypobranchial
  eminence) develops caudal to the copula from
  mesenchyme in the ventromedial parts of the third
  and fourth pairs of arches
• As the tongue develops the copula is gradually
  overgrown by the hypopharyngeal eminence and
  disappears. As a result, the pharyngeal part of
  the tongue develops from the rostral part of the
  hypopharyngeal eminence
• The line of fusion of the anterior and posterior
  parts of the tongue is roughly indicated by a
  V-shaped groove - the terminal sulcus
• Note Innervated by glossopharyngeal nerve (CN
  9), except the epiglottis is innervated by vagus
  nerve (CN 10)

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Congenital Anomaly of Tongue

• Ankyloglossia (Tongue-Tie) the lingual frenulum
  normally connects the inferior surface of the
  tongue to the floor of the mouth. Sometimes the
  frenulum is short and extends to the tip of the
  tongue. This interferes with its free protrusion
  and may make breast-feeding difficult.
  Ankyloglossia (tongue-tie) occurs in about one in
  300 North American infants but is usually of no
  functional significance. A short frenulum usually
  stretches with time, making surgical correction
  of the anomaly unnecessary

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Development of the Tongue

• Where the teeth and lower lip will be formed in
  relation to the floor of the mouth