Pharyngeal arch derivatives

1. Overview of
Pharyngeal arch
Derivatives
Prepared by- Bisrat G. / ORL-HNS (R1)
Moderator- Dr Alene /ORL-HNS Surgeon/
Jan. 2018 GC

2. OUTLINE
 General Embryology
 Definition of terms
 Pharyngeal Arches
 Pharyngeal Pouches
 Pharyngeal Membranes

3. Definition
 Groove --- invagination of ectoderm.
 Pouch ---- evagination of endoderm.
 Arch – bulge/ swelling
 Diverticuli --- evagination through a wall of a tubular organ.

4. GENERAL EMBRYOLOGY
 Development begins with fertilization when the sperm and oocyte, each haploid
with 23 chromosomes, unite to form the diploid zygote containing 46
chromosomes.
 The zygote divides, producing a morula which cavitates to form a blastocyst
that implants in the endometrium during the second week.
 Initially the inner cell mass forms a bilaminar germ disc which then, by
gastrulation, leads to a trilaminar disc comprised of ecto-, meso- and endoderm
layers in week 3
 Weeks 3-8 comprise the embryonic period

5. Embryo at the End of 3rd wk….

6. The Developing Head

7. PHARYNGEAL ARCHES
 Arches of mesenchyme derived from paraxial and lateral plate
mesoderm and neural crest cells appear in the fourth and
fifth weeks of development.
 They are covered externally by ectoderm, which forms clefts
between successive arches, and internally by endoderm
which forms pouches between arches.

8. Providence of Pharyngeal Arches
 A typical pharyngeal arch contains ;
 A pharyngeal arch artery
 A cartilaginous rod
 A muscular component
 Sensory and motor nerves

9. First pharyngeal arch
 The first arch has a dorsal maxillary process and a ventral
mandibular process.
 The maxillary process gives rise to the premaxilla, maxilla,
zygomatic bone, the zygomatic process and squamous part of the
temporal bone by intramembranous ossification.
 The mandibular process / Meckel's cartilage which persists as the
malleus, anterior ligament of malleus, incus and
sphenomandibular ligament.

10. Cont…
 The trigeminal (V) nerve supplies sensation to the first arch
connective tissues via its ophthalmic, maxillary and
mandibular branches.
 Only the mandibular division has a motor root and supplies
eight first arch muscles:
 Four muscles of mastication (temporalis, masseter, medial and lateral
pterygoid),
 Two tensors (tympani and palati), mylohyoid and the anterior belly of
digastric.

12. Second pharyngeal /Hyoid Arch/Reichert’s
cartilage
 The second arch gives rise to the
 Dorsal Part -- stapes, styloid process of the temporal bone,
 Middle -- stylohyoid ligament,
 Ventral -- lesser cornu and upper body of the hyoid bone.
 The facial (VII) nerve supplies sensation to second arch connective
tissue in the external auditory canal, but is mainly motor supplying:
stapedius, stylohyoid, posterior belly of digastric, occipitofrontalis and the
muscles of facial expression.

13. Third pharyngeal arch
 The third arch gives rise to the greater cornu and lower body
of the hyoid bone.
 The glossopharyngeal (IX) nerve supplies sensation to third
arch connective tissues in the posterior third of the tongue
and is motor to glossopharyngeus.

14. Fourth and sixth pharyngeal arches
 The cartilagenous components of the fourth and sixth arches fuse to form the
laryngeal cartilages: thyroid, cricoid, arytenoid, corniculate and cuneiform.
 The superior laryngeal branch of the vagus (X) supplies sensation to fourth arch
connective tissue from the valleculae and epiglottis to the true vocal cords and
is motor to levator palati, pharyngeal constrictors (partially) and cricothyroid.
 The recurrent laryngeal branch of the vagus supplies sensation to sixth arch
derivatives, notably the infraglottic larynx:, and is motor to the other muscles of the
larynx.

16. Derivatives of pharyngeal arch arteries
 1st Arch – Maxillary Artery
 2nd Arch – Stapedial A. + Ext.
Carotid
 3rd Arch – CCA and Proximal ICA
 4th Arch -- Left – part of arch of
Aorta
Right –proximal part of
Subclavian a.
6th Arch – Left – Ductus Arteriosus
Right – Pulmonary Artery

17. Primitive Aortic Arch

19. Pharyngeal arch muscles

20. Chronology

22. PHARYNGEAL POUCHES
 On each side, between the six arches, lie five pharyngeal pouches lined by
endoderm
 The first pouch extends laterally to form the Eustachian tube, the middle ear
cavity and the tubotympanic recess, which extends as far as the tympanic
membrane.
 Distal portion of tubotympanic recess expands upward to become middle ear
cavity or tympanic cavity
 Proximal part becomes eustachian (auditory, pharyngotympanic) tube

24. Cont…
 The second pouch forms the bed of the palatine tonsil.
 The third pouch forms ventral and dorsal wings.
 The epithelium of the ventral wing differentiates into the
thymus, while that of the dorsal wing forms the inferior
parathyroid gland.

25. Cont,,,
 The dorsal wing of the fourth pouch differentiates into parathyroid tissue
which descends to lie posterior to the superior pole of the ipsilateral
thyroid lobe.
 The ventral wing of the fourth(fifth pouch) forms the ultimobranchial
body, which is incorporated into the thyroid gland· and gives rise to
parafollicular calcitonin secreting cells.

27. Summary

28. Pharyngeal diverticulum
 The structural weakness between thyropharyngeus and
cricopharyngeus, Killian's dehiscence, may be the site of an
acquired pulsion diverticulum which may be described
erroneously as a 'pharyngeal pouch'.

29. PHARYNGEAL CLEFTS
 The 5-week embryo is characterized by the presence of four pharyngeal
clefts
 On each side, between the first five arches, lie four pharyngeal clefts lined by
ectoderm.
 Normally, only the first cleft persists and its dorsal end gives rise to the external
auditory meatus, separated from the first pouch by the tympanic membrane.
 the second, third, and fourth clefts lose contact with the outside
 The clefts form a cavity lined with ectodermal epithelium, the cervical sinus,
but with further development, this sinus disappears.

30. Clinical correlate
 The second arch overgrows the second, third and fourth clefts, forming the
cervical sinus which then resorbs.
 However, if this sinus persists, it gives rise to cervical cysts along the anterior
border of sternocleidomastoid.
 If the cysts communicate with the skin, they form external branchial fistulae.

31. Branchial Fistula
 An abnormal canal that opens internally into the tonsillar sinus and externally in the
side of the neck
 This canal results from persistence of parts of the second pharyngeal groove and
second pharyngeal pouch
 The fistula passes between the internal and
external carotid arteries and opens into the tonsillar sinus.

32. Pharyngeal membranes
 Pharyngeal membranes appear in the floor of the pharyngeal grooves
 These membranes form where the epithelia of the grooves and pouches approach
each other
 The endoderm of the pouches and ectoderm of the grooves are soon separated by
mesenchyme
 Only first pharyngeal membrane becomes the tympanic membrane, others
obliterate.

33. Tongue
 The tongue appears in embryos of approximately 4 weeks in the form of
two lateral lingual swellings and one medial swelling, the tuberculum
impar
 These three swellings origínate from the first pharyngeal arch.
 As the lateral lingual swellings increase in size, they overgrow the
tuberculum impar and merge, forming the anterior two-thirds, or body,
of the tongue

34. Cont,,,
 Because the mucosa covering the body of the tongue
originates from the first pharyngeal arch, sensory
innervation to this area is by the mandibular branch of the
trigeminal nerve.
 The body of the tongue is separated from the posterior
third by a V-shaped groove, the terminal sulcus

35. Cont…
 The posterior part, or root, of the tongue originates from the
second, third, and parts of the fourth pharyngeal arch.
 The fact that sensory innervation to this part of the tongue is
supplied by the glossopharyngeal nerve indicates that tissue of the
third arch overgrows that of the second.
 The epiglottis and the extreme posterior part of the tongue are
innervated by the superior laryngeal nerve, reflecting their develop-
ment from the fourth arch.

36. Cont…
 Some of the tongue muscles probably differentiate in situ, but most are derived
from myoblasts originating in occipital somites. Thus, tongue musculature is
innervated by the hypoglossal nerve.

37. Clinical correlates
 Tongue-Tie / Ankyloglossia/
 Frenulum extends to the tip of the tongue.
 Normally extensive cell degeneration occurs, and the frenulum is the only tissue
that anchors the tongue to the floor of the mouth.

38. THYROID GLAND
 The thyroid gland appears as an epithelial proliferation in the floor of
the pharynx between the tuberculum impar and the copula at a point
later indicated by the foramen cecum.
 Subsequently, the thyroid descends in front of the pharyngeal gut as a
bilobed diverticulum.
 During this migration, the thyroid remains connected to the tongue by a
narrow canal, the thyroglossal duct. This duct later disappears.

39. Cont…
 With further development, the thyroid gland descends in
front of the hyoid bone and the laryngeal cartilages. It reaches
its final position in front of the trachea in the seventh week.
 The thyroid begins to function at approximately the end
of the third month.

41. Clinical correlates
 Thyroglossal cyst
 it is a cystic remnant of the thyroglossal duct.
 50 % - close to or just inferior to the Hyoid bone.
 May also be found at the base of the tongue.
 Aberrant thyroid tissue
 Any where along path of descent.

43. References
 Langman’s Medical Embryology 13th ed.
 Scott Brown ORL- HNS 7th ed.
 Medscape

44. THANK
YOU