The tongue develops from endodermal and ectodermal tissues originating from the pharyngeal arches. The thyroid gland develops from an endodermal diverticulum that descends in the neck and remains connected to the tongue via the thyroglossal duct. The face develops from five prominences, with the nose forming from the frontal prominence and medial and lateral nasal prominences. The palate develops as the palatine shelves rotate and fuse in the midline. Congenital anomalies can affect structures developing from the pharyngeal arches, including cleft lip/palate and thyroglossal duct cysts.

1. Dr shittu LAJ

2.  Describe the development of the
tongue and the thyroid gland.
 Describe the development of the face,
palate, and nasal cavity.
 Describe the congenital anomalies
associated with the development of the
pharyngeal apparatus, face and palate.

3.  The first endocrine gland to appear in embryonic
development.
 - 24 days after fertilization
 - Median endodermal thickening
 - Thyroid diverticulum
 - Thyroid glossal duct
 Becomes functional at about end of first trimester of
preg. With formation of follicular cells/follicles
containing colloid for production of T3 and T4.
 Also C-cells secreting cacitonin (ultimobrachial body-
4th
/5th
arch)

5.  is a diverticulum that originates at the level of the first
pouch.
 It arises from the floor of the pharynx and migrates
caudally to a position ventral and inferior to the larynx.
 This diverticulum forms a right and left lobe with an
isthmus of thyroid tissue between.
 During development, the thyroid gland continues to
retain a connection with the pharyngeal lumen. This
connection is known as the thyroglossal duct
 Ordinarily, the thyroglossal duct closes off, leaving only
an enlarged pit on the tongue (the foramen cecum)
to mark its point of origin.

6.  begins as a downward growth from the floor of the
pharynx called the thyroid diverticulum.
 As it descends down the neck to lie below the larynx
and anterior to the trachea,
 it remains connected to the tongue via the
thyroglossal duct.
 In the adult, a remnant of this duct persists in the tongue
as the foramen cecum.

7.  - foramen caecum
 - Isthmus
 - Pyramidal lobe

10.  The endodermal derivatives of all the pharyngeal arches
give rise to its formation in the region where the
stomodeum and primitive pharynx meet.
 It is seen initially as a proliferation of mesenchyme
(mesoderm).
 The stomodeum is lined by ectoderm
 NB: The lateral lingual swellings- which forms most
part of the body of the tongue, is lined by ectoderm.

11.  Near the end of the fourth week.
 Median triangular elevation in the floor of the primitive
pharynx.
 Median tongue bud - Tuberculum Impar- First Arch
 Distal tongue bud
 Copula and Hypobranchial eminence - Third Arch

12.  The tuberculum impar- at the caudal level
of the first arch,
 forms part of the body of the tongue and is
covered by endoderm.
 The root of the tongue develops from a
primitive swelling - the hypo-branchial
eminence (copula),
 at the levels of the second, third and fourth
pharyngeal arches.
 At the level of the fourth arch, an epiglottic
swelling arises which lies cephalic to the
laryngotracheal groove.

13.  A small nodule- the tuberculum impar, first appeared in the
developing tongue in the floor of the pharynx.
 This is later covered over by the lingual swellings, one on each
side, derived from the first branchial arch.
 They both fused in the midline to form the definitive anterior two-
thirds of the tongue supplied by V and reinforced by chorda
tympani (special sensory).
 Posteriorly, this mass meets the copula (or hypobranchial
eminence), a central swelling in the pharyngeal floor, which
represents the 2nd, 3rd and 4th arches to form the posterior one-
third of the tongue (nerve supply IX and X).
 The tongue muscles are derived from the occipital myotomes,
which migrate forward dragging with them their nerve supply (XII-
the hypoglossal nerve).

14. ◦ Contributions from all arches
◦ which changes with time
◦ begins as swelling rostral to foramen cecum
◦ median tongue bud - Tuberculum Impar
 Arch 1
◦ oral part of tongue (ant 2/3)
 Arch 2
◦ initial contribution to surface is lost
 Arch 3
◦ pharyngeal part of tongue (post 1/3)
 Arch 4
◦ epiglottis and adjacent regions
 Salivary Glands
◦ epithelial buds in oral cavity (wk 6-7),
◦ extend into mesenchyme

16.  4th week facial promordia appear around the
stomodeum.
 Under inductive influence - Proliferation of Neural crest
cells.
 Involvement of 1st
pharyngeal arch and the whole
process takes about 4-10 wks of development.
 5 Facial Promordia develop
 Single Median Fronto nasal Prominence - V1
 Paired Maxillary Prominence - V2
 Paired Mandibular Prominence - V3

18.  FNP Vesicles
 Nasal Placodes
 Nasal Pits
 Medial (MP) and Lateral Nasal Prominences (LNP)

19.  During the fifth week, the nasal placodes invaginate to
form nasal pits.
 Then, we have a ridge of tissue that surrounds each pit
and forms the nasal prominences.
 The prominences on the outer edge of the pits are
 the lateral nasal prominences;
 those on the inner edge are the medial nasal
prominences

20. 1. Philtrum
2. Premaxillary part of Maxilla (carries the 4
incissors)
3. Primary Palate

21.  the frontonasal process which projects down from the
cranium.
 Two olfactory pits develop in it and rupture into the
pharynx to form the nostrils.
 this process hence forms the nose, the nasal septum,
nostril, the philtrum of the upper lip (the small midline
depression) and the premaxilla
 —the V-shaped anterior portion of the upper jaw which
usually bears the four incisor teeth;

22.  the maxillary processes on each side, which fuse
with the frontonasal process and become:
 the cheeks,
 upper lip (exclusive of the philtrum),
 Upper jaw and
 palate (apart from the premaxilla);

23.  nasolacrimal groove
 nasolacrimal duct-canalized groove
 MP + LNP fusion, leads to the connection of the
nasolacrimal duct from the medial side of the eye
to the inferior meatus of the nasal cavity.
 Ear Auricles -
◦ form from 6 auricular hillocks (week 5)
◦ 3 on each of arch 1 and 2

24.  the mandibular processes, which meets in the
midline form the lower jaw/mandible.

25.  The nose is formed from five facial prominences :
 the frontal prominence gives rise to the bridge;
 the merged medial nasal prominences-provide the crest
and tip; and
 the lateral nasal prominences form the sides
 (alae)

30.  Intermaxillary segment of the
maxilla
 Premaxillary part of the maxilla

31.  By wk 7-The floor of the nasal cavity at this stage is a
posterior extension of the intermaxillary process known
as the primary palate.
 The medial walls of the maxillary swellings begin to
produce a pair of thin medial extensions, 'palatine
shelves', which grow inferiorly on either side of the
tongue.
 By wk 8-The tongue moves downward and the palatine
shelves rapidly rotate upwards towards the midline,
growing horizontally.
 By wk 9- The palatine shelves begin to fuse
ventrodorsally with each other, the primary palate and
the inferior nasal septum.

33.  Lateral Palatine Processes
 Nasal Septum
 Hard and Soft Palate
 By wk 10- The ventral secondary palate becomes the
bony hard palate through mesenchymal condensations
(endochondral ossification).
 The dorsal secondary palate becomes the soft palate
 through myogenic mesenchymal condensation

38.  Nasal placodes - become nasal pits
 Oronasal/bucconasal membrane
 The Conchae - Superior
 Middle
 Inferior-

39.  The maxillary and medial nasal processes
bulge forward together and the epithelium on
their surfaces fuse to form a sheet, the nasal
fin.
 Subsequently this nasal fin breaks down such
that both maxillary and medial nasal
mesenchyme now intermingle.
 The epithelial fins behind this fusion are
stretched out laterally to form the bucconasal
membranes and this also break down to form
the nasal choanae that is connecting the
nasal pits and the stomatodeum/stomodeum.

41.  The tissues below the nasal pits now form the
primary palate or intermaxillary segment.
 The posterior part will form -the premaxillary
part of the definitive palate,
 the intermediate zone -premaxillary alveolar
process and teeth,
 the anterior zone- the medial portion of the
upper lip.

43.  5 facial prominences
 Bridge-frontal prominence
 Crest and tip- merged MNPs
 Side alar/labie-LNPs

44.  During the sixth week, the nasal pits deepen
considerably, partly due to growth of the surrounding
nasal prominences and partly their penetration into the
underlying mesenchyme.
 At first the oronasal /bucco-nasal membrane
separates the pits from the primitive oral cavity by way
of the newly formed foramina, the primitive
choanae.
 These choanae lie on each side of the midline and
immediately behind the primary palate.
 Later, with formation of the secondary palate and
further development of the primitive nasal chambers,
 the definitive choanae lie at the junction of the
nasal cavity and the pharynx.

46.  Paranasal air sinuses develop as diverticula
of the lateral nasal wall and
 extend into the maxilla, ethmoid, frontal, and
sphenoid bones.
 They reach their maximum size during puberty
and
 contribute also to the definitive shape of the face.

48.  First Arch Syndrome
◦ 2 major types, both result in extensive facial abnormalites
◦ Teacher Collins`s Syndrome
◦ Pierre Robin`s Syndrome
 Cervical Fistulas and Cysts - Incomplete fusion or
remnants of the walls of the cervical sinus (second
branchial groove).
 The internal openings of fistulas are at the sites of the
pharyngeal membranes;
 the external openings are along the anterior border of
the sternocleidomastoid muscle.

49. Bifid Tongue - A midline split in the anterior two-thirds
of the tongue
 due to improper fusion of the lateral lingual swellings.
 Thyroglossal Duct Cyst - A cyst of remnants of all or
part of the thyroglossal duct.
 In removing this cyst, a portion of the body of the hyoid
bone is often removed, because the hyoid bone grows
around the developmental path of this structure.
 Retention and enlargement of that portion of the
thyroglossal duct in contact with the thyroid results in the
formation of a pyramidal lobe.

50.  DiGeorge`s Syndrome
◦ absence of thymus and parathyroid glands
◦ 3rd and 4th pouch do not form
◦ disturbance of cervical neural crest migration.
 Holoprosencephaly
◦ shh abnormality
 NB: SHH genes
◦ expressed in arches
◦ regulates midface formation
 Pax-3 genes expressed in placode cells
◦ contribute to the CNV
◦ ophthalmic branch
 Maternal Effects
◦ Retinoic Acid
 present in skin ointments
 1988 associated with facial developmental abnormalities
 Abnormalities from the Maternal Effects

51.  Cleft Lip and Palate
◦ 300+ different abnormalities
◦ different cleft forms and extent
◦ upper lip and ant. maxilla
◦ hard and soft palate
 Etiology is again multifactorial, with the same teratogens as for
cleft lip
 an x-linked cleft palate syndrome has
 1. Cleft lip
◦ Unilateral
◦ Bilateral
 2. Median Cleft Lip-complete/incomplete


52.  due to alcohol in early development (week 3+)
 facial and neurological abnormalities
 lowered ears, small face, mild retardation
 Microcephaly - leads to small head circumference
 Short Palpebral fissure - opening of eye
 Epicanthal folds - fold of skin at inside of corner of eye
 Flat mid face
 Low nasal bridge
 Indistinct Philtrum - vertical grooves between nose and mouth
 Thin upper lip
 Micrognathia - small jaw
 exposure of embryos in vitro to ethanol simulates premature
differentiation of prechondrogenic mesenchyme of the facial
primordial (1999)

53.  these are pleuripotent cells that develop from the
neural folds and migrate widely in the embryo to give
rise to many nervous structures:
 Spinal ganglia (dorsal root ganglia)
 Ganglia of the autonomic nervous system
 Ganglia of some cranial nerves
 Sheaths of peripheral nerves
 Meninges of brain and spinal cord
 Pigment cells
 Suprarenal medulla
 Skeletal and muscular components in the head

54.  - Mandibulo-facial dysostosis results from a symmetrical loss
 of neural crest cells destined to migrate by the longer posterior route into the
face (Poswillo)
 There is hypoplasia of the zygomatic bone and a deficiency
 or absence of the arch. As a result there is an antimongoloid slant to the
palpebral fissure.
 There may be a coloboma of the lower eyelid with absence of lashes lateral
to the notch and hypoplasia of the mandible resulting in a lack of chin and
an anterior open bite.
 The ears are set low and the auricles and middle ear structures may be
deficient in severe cases.
 The abnormality tends to run in families.