Head and Neck Dev 08

7/28/2019 Head and Neck Dev 08

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Embryology of the Head,Face and Oral Cavity

Raj Gopalakrishnan B.D.S., Ph.D.Oral and Maxillofacial Pathology

Dept. of Diagnostic and Biological Sciences

University of Minnesota School of Dentistry


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Prenatal Development

Figure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6 th edition


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Differentiation of the Morula into Blastocyst

Figure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6th edition


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Formation of Two-Layered Embryo (2nd week of gestation)

Figures obtained from Before We Were Born; Moore and Persaud, 6thedition, 2003.

Called bilaminar germ disk

Ectoderm

EndodermPre/prochordal plateFirm union between ectodermal and

endodermal cells occur at prechordal

plate


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Formation of Three-Layered Embryo: Gastrulation (3rd week)


Triploblastic embryo


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Formation of Three-Layered Embryo: Gastrulation (3rd week)



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First 3 weeks: Leads to formation of triploblastic embryo

Next 3-4 weeks: differentiation of major tissues and organs

includes head and face and tissues responsible

for teeth development

differentiation of nervous tissue from ectoderm

differentiation of neural crest cells (ectoderm)

differentiation of mesoderm

folding of the embryo (2 planes-rostrocaudal and lateral)


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Neural tube undergoes massive expansion to form the forebrain,

midbrain and hindbrain

Formation of neural tube and neural groove


Neural groove


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Components of the mesoderm

Along the trunk paraxial mesoderm breaks up into segmented

blocks called somites

Each somite has: sclerotome- 2 adjacent vertebrae and disks

myotome-muscle

dermatome-connective tissue of the skin over the somite

In the head region the paraxial mesoderm only partially fragments to form a series

of numbered somatomeres which contribute to head and neck musculature

Intermediate mesoderm: urogenital system

Lateral plate mesoderm: connective tissue of muscle annd viscera; serous

membranes of the pleura; pericardium and peritoneum; blood and lymphatic cells;

cardiovascular and lympahtic systems, spleen and adrenal cortex.Figure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6 th edition


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In the head, the neural tube undergoes massive expansion to form

the forebrain, midbrain and hindbrain

The hindbrain segments into series of eight bulges called

rhombomeres which play an important role in development of the head


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Folding of the Embryo

Head fold forms a primitive

stomatodeum or oral cavity; leading

to ectoderm lining the stomatodeum

and the stomatodeum separated from

the gut by buccopharyngeal membrane

Onset of folding is at 24 days and

continues till the end of week 4

Embryo just before folding (21 days)



12/71Figure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6th edition


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Neural Crest Cells

Group of cells separate from the neuroectoderm, migrate and

differentiate extensively leading to formation of cranial sensoryganglia and most of the connective tissue of the head

Embryonic connective tissue elsewhere is derived form mesoderm

and is known as mesenchyme

But in the head it is known as ectomesenchyme because of its

origin from neuroectoderm

Look up Fig 2-12 in text book for derivative of the germ layers

and neural crest


14/71Figure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6 th edition

Avian neural crest cells


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Head Formation


Rhombomeres

(one of the first are the

occipital somites)


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Neural Crest Cell Migration



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Pharyngeal arches expand by proliferation of

neural crest cells

Couly et al., 2002

Forebrain(prosencephalon)

Midbrain

(mesencephalon)

Hindbrain

(rhombencephalon)

r3

r5


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Migration of cranial neural crest cellsAnterior midbrain

Posterior midbrain

Anterior hindbrain

Imai et al., 1996

E

E

E

FNM

TG

TG

TG

Md

Md


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Clinical Correlation

Treacher Collins Syndrome is characterized by defects of

structures that are derived form the 1st and 2nd branchial arches andis due to failure of neural crest cells to migrate properly to the

facial region


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Sagittal section through a 25-day embryoFigure from Ten Cates Oral Histology, Ed., Antonio Nanci, 6 th edition

Buccopharyngeal membrane ruptures at 24 to 26 days


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Internal View of the Oral Pit at 3.5 weeks


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26-day embryo


Th h l t


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The Developing Human by Moore & Persaud

groove/cleft

pouch

arch

membrane

esophagus

The pharyngeal apparatus

1 234

Branchial arches form in the pharyngeal wall (which has lateral plate mesoderm sandwiched

between ectoderm and endoderm) as a result of lateral plate mesoderm proliferation and

subsequent migration by neural crest cells


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3 weeks


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Sagittal view of the branchial arches with corresponding grooves between each arch.

Pharyngeal pouches are seen in the wall of the pharynx. The aortic arch vasculature

leads from the heart dorsally through the arches to the face


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Fate of the Pharyngeal Grooves and Pouches

First groove and pouch: external auditory meatus

tympanic membrane

tympanic antrum

mastoid antrum

pharyngotympanic or eustachian tube

2nd, 3rd and 4th grooves are obliterated by overgrowth of the secondarch forming a cervical sinusif persists forms the branchial fistula

that opens into the side of the neck extending form the tonsillar sinus

2nd

pouch is obliterated by development of palatine tonsil

3rd pouch: dorsally forms inferior parathyroid gland

ventrally forms the thymus gland by fusing with the

counterpart from opposite side


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4th pouch: dorsal gives rise to the superior parathyroid gland

ventral gives rise to the ultimobranchial body (which

gives rise to the parafollicular cells of the thyroid gland)

5th pouch in humans is incorporated with the 4th pouch


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(A) Tissue from arch II and V growing towards each other (arrows) to make branchial

arches and grooves disappear

(B) Resulting appearance following overgrowth

(C) Contribution of each pharyngeal pouch


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Anatomy of the Branchial Arches

Cartilage of 1starch: Meckels

Cartilage of 2nd

arch: ReichertsOther arches not named

Some mesenchyme around cartilage

gives rise to striated muscle

Each arch also has an artery and nerve

Nerve: two components (motor and

sensory)

Sensory nerve divides into 2 branches:

1. Posttrematic branch: covers the anteriorhalf of the arch epithelium

2. Prettrematic: covers the posterior half

of the arch epithelium



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Meckels cartilage: Has a close relationship with the

developing mandible BUT DOES NOT CONTRIBUTE TO IT

Indicates the position of the future mandible.

The mandible develops by intramembranous ossification.The malleus and the incus develop by endochondral ossification of

the dorsal aspect of this cartilage.

Innervation: V cranial nerve

Reicherts: Dorsal end: stapes and styloid process

Ventral end: lesser horns of hyoid bone and superior

part of the body of the hyoid bone

Innervation: VII cranial nerve

Cartilage of the 3rd arch: inferior part of the body and greater

horns of the hyoid bone

Cartilage of 4

th

and 6

th

arches: fuse to form the laryngeal cartilage


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Table obtained from Before We Were Born; Moore and Persaud, 6thedition, 2003.


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Aortic Vasculature Development

(A) At 4 weeks the anterior vessels have passed through each branchial arch tissue

and have disappeared. The pouches project laterally between each arch.

(B) At 5 weeks the 3rd branchial arch vessel becomes the common carotid, which

supplies the face by means of the internal carotid and stapedial arteries.

Face, Neck and Brain are supplied by the common carotid through internal carotid.

But by 7 weeks the circulation of face and neck shifts from the internal carotid to

external carotid. The internal carotid continues to supply the brain.


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Details of the aortic arch changes during early development. Aortic arch vessels numbers

1,2 and 5 disappear . Arch 3 becomes the common carotid artery. Arch 4 becomes the

dorsal aorta and enlarges so that the common carotid arises from the aorta. Arch 6 becomes

the right and left pulmonary arteries


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Shift in the vascular supply to the face

(A)Face and brain are supplied first by the internal carotid artery

(B) Facial vessels detach from the internal carotid and attach to the

external carotid


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Muscle cells in the first arch become apparent

during the 5th week and begin to spread within

the mandibular arch into each muscle sitesorigin in the 6th and 7th week. These form the

muscles of masticationmasseter, medial

pterygoid, lateral pterygoid and temporalis

muscle. They all relate to the developing mandible

By 7 weeks the muscles of 2nd arch growupward to form the muscles of face.

As these muscles grow and expand they

forms sheet over the face and forms the

muscles of facial expression


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Facial muscles grow from

the 2nd branchial arch to cover

the face, scalp and posterior

to the ear

Masticatory muscles of the mandibular arch


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Cranial Nerves growing into Branchial Arches


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Cartilages derived from the

branchial arches

Arch 1: Meckels cartilage and incus

Arch 2: Stapes, stylohyoid and lesser

hyoid

Arch 3: Greater hyoid

Arch 4 and 6 thyroid and

laryngeal cartilage


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Congenital auricular sinuses and cysts

Branchial cysts

Branchial sinuses

Branchial fistula

Branchial vestiges(cartilaginous or bony remnants)

Branchial cysts

Anomalies of the head and neck

Dermatlas

Dermatlas


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Apparent fusion of facial processes by

elimination of furrowsTrue fusion of facial processes by

breakdown of surface epithelium


Development of the Face


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Development of the Face

The face develops between the 24th and 38th days of gestation

On 24th day, the 1st branchial arch divides into maxillary and

mandibular arches



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Frontonasal process



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Middle portion of the upper lip: Formed by the fusion of the medial

nasal process of both sides along with the frontonasal process

Lateral portion of the upper lip: Fusion of the maxillary processes

of each side and medial nasal process

Lower lip: Formed by the fusion of the two mandibular processes

Formation of the Lips

Unusual fusion between maxillary process and lateral nasal process

leading to canalization and formation of the nasolacrimal duct


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Human embryo at 7 weeks


Cleft Lip


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Cleft Lip


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Derivation and Terminology of the Pituitary Gland

Oral Ectoderm Adenohypophysis Pars distalis

(hypophysial diverticulum (glandular portion) Pars tuberalis

from roof of stomodeum) Pars intermedia

Neuroectoderm Neurohypophysis Pars nervosa(neurohypophysial (nervous portion) Infundibular stem

diverticulum from Median eminence

floor of diencephalon)

Clinical Significance: Craniopharyngiomas develop from remnants

of stalk of hypophysial diverticulum (in pharynx of sphenoid bone)


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Formation of the palate (weeks 7 to 9)

Palate develops from the primary palate and the secondary palate

The primary palate develops at about 28 days of gestation

Primary palate develops from the frontonasal and medial nasal

processes and eventually forms the premaxillary portion of the maxilla

The secondary palate develops between 7th and 8th week of gestation

and completes in the 3rd month

The critical period of palate development is from the end of 6th

weektill the beginning of 9th week

Formation of the secondary palate


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Formation of the secondary palate(starts between 7 to 8 weeks and completed around 3 months)



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Cleft Palate


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Cleft Palate

Formation of the Tongue


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Formation of the Tongue

The tongue begins to develop at about 4 weeks. The oral part (anterior

two-thirds) develops from two distal tongue buds (lateral lingual

swellings) and a median tongue bud (tuberculum impar) [1st branchialarch].

Innervation: V nerve

The pharyngeal part develops from the copula and the hypobranchial

eminence [2nd, 3rd and 4th branchial arches].Innervation: IX cranial nerve

The line of fusion of the oral and pharyngeal parts of the tongue is

roughly indicated in the adult by a V-shaped line called the terminal

sulcus.

At the apex of the terminal sulcus is the foramen cecum.

Muscles of the tongue develop form the occipital somites and

innervated by hypoglossal nerve


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Lingual swelling

Tuberculum impar



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The lingual papillae appear by the end of 8th week

Vallate and foliate papillae appear first, fungiform andfiliform (10-11 weeks) papillae appear later

Taste buds develop during the 11 to 13 weeks by inductive

interaction between epithelial cells of the tongue and invadinggustatory nerve cells from chorda tympani, glossopharyngeal

and vagus nerves


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Thyroid gland development (4 to 7 weeks)



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Thyroglossal duct cyst

Lingual thyroid


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Development of Jaw Bones


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Development of Jaw Bones

Development of Mandible


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p


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Fate of Meckels Cartilage

Posteriormalleus of the inner ear

Sphenomandibular ligament

Anteriorly, may contribute to mandible

by endochondral ossification (some evidence)

Rest are resorbed completely

S d C til


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Three secondary (growth) cartilages govern further growth of

mandible until birth

1. Condylar cartilage (most important)

2. Coronoid cartilage

3. Symphysial cartilage

Secondary Cartilages


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Appears during 12th week and occupies most

of the ramus and is quickly ossified by

endochondral ossification, with a very thin

layer of cartilage present in the condylar head.This remnant persists until 2nd decade of life

and is important for growth of mandible

Appears at 4 months and

disappears immediately



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Development of Maxilla

Develops from one center of ossification in maxillary process of

the 1st branchial arch

Center of ossification is angle between the divisions where the

anterosuperior dental nerve is given off from inferior orbital nerve

from where it spreads posteriorly, anteriorly and superiorly

No arch cartilage is present, so maxilla develops in close

association with the nasal cartilage

One secondary cartilage also contributes to maxilla

development: zygomatic cartilage


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Head and Neck Dev 08

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