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Transcript
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
Prenatal Development
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Differentiation of the Morula into Blastocyst
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Formation of Two-Layered Embryo (2nd week of gestation)
Called bilaminar germ disk
Ectoderm
Pre/prochordal plate
Endoderm
Firm union between ectodermal and
endodermal cells occur at prechordal
plate
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Formation of Three-Layered Embryo: Gastrulation (3rd week)
Triploblastic embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Formation of Three-Layered Embryo: Gastrulation (3rd week)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
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)
Formation of neural tube and neural groove
Neural groove
Neural tube undergoes massive expansion to form the forebrain,
midbrain and hindbrain
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
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 Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
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
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)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Neural Crest Cells
Group of cells separate from the neuroectoderm, migrate and
differentiate extensively leading to formation of cranial sensory
ganglia 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
Avian neural crest cells
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Head Formation
(one of the first are the
occipital somites)
Rhombomeres
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Neural Crest Cell Migration
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Pharyngeal arches expand by proliferation of
neural crest cells
Midbrain
(mesencephalon)
Hindbrain
(rhombencephalon)
Forebrain
(prosencephalon)
r3
r5
Couly et al., 2002
Migration of cranial neural crest cells
Anterior midbrain
FNM
E
TG
Posterior midbrain
E
TG
Md
Anterior hindbrain
E
TG
Md
Imai et al., 1996
Clinical Correlation
Treacher Collins Syndrome is characterized by defects of
structures that are derived form the 1st and 2nd branchial arches and
is due to failure of neural crest cells to migrate properly to the
facial region
Buccopharyngeal membrane ruptures at 24 to 26 days
Sagittal section through a 25-day embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Internal View of the Oral Pit at 3.5 weeks
26-day embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
The pharyngeal apparatus
pouch
arch
groove/cleft
membrane
34
2
1
esophagus
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
The Developing Human by Moore & Persaud
3 weeks
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
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 second
arch forming a cervical sinus – if 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
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
(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
Anatomy of the Branchial Arches
Cartilage of 1st arch: Meckel’s
Cartilage of 2nd arch: Reichert’s
Other 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 anterior
half of the arch epithelium
2. Prettrematic: covers the posterior half
of the arch epithelium
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Meckel’s 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
Reichert’s: 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 4th and 6th arches: fuse to form the laryngeal cartilage
Table obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
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.
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
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
Muscle cells in the first arch become apparent
during the 5th week and begin to spread within
the mandibular arch into each muscle site’s
origin in the 6th and 7th week. These form the
muscles of mastication – masseter, medial
pterygoid, lateral pterygoid and temporalis
muscle. They all relate to the developing mandible
By 7 weeks the muscles of 2nd arch grow
upward 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
Masticatory muscles of the mandibular arch
Facial muscles grow from
the 2nd branchial arch to cover
the face, scalp and posterior
to the ear
Cranial Nerves growing into Branchial Arches
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
Anomalies of the head and neck
•Congenital auricular sinuses and cysts
•Branchial cysts
•Branchial sinuses
Dermatlas
•Branchial fistula
•Branchial vestiges
(cartilaginous or bony remnants)
•Branchial cysts
Dermatlas
Apparent fusion of facial processes by
elimination of furrows
True fusion of facial processes by
breakdown of surface epithelium
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
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
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Frontonasal process
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Formation of the Lips
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
Unusual fusion between maxillary process and lateral nasal process
leading to canalization and formation of the nasolacrimal duct
Human embryo at 7 weeks
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Cleft Lip
Pituitary Gland Development
Ectodermal in origin and develops from 2 sources:
1. An upgrowth from the ectodermal roof of the stomatodeum
called hypophysial diverticulum (Rathke’s Pouch) - adenohypophysis
2. A downgrowth from the neuroectoderm of the diencephalon
called the neurohypophysial diverticulum – neurohypophysis
During the 4th week of development, a hypophysial diverticulum
(Rathke’s pouch) projects from the roof of the stomatodeum and lies
adjacent to the floor (ventral wall) of the diencephalon. By the 5th
week, this pouch has elongated and has become constricted
at its attachment to the oral epithelium and is in contact with the
infundibulum (derived from the neurohypophysis)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Derivation and Terminology of the Pituitary Gland
Oral Ectoderm
Adenohypophysis
(hypophysial diverticulum (glandular portion)
from roof of stomodeum)
Neuroectoderm
(neurohypophysial
diverticulum from
floor of diencephalon)
Neurohypophysis
(nervous portion)
Pars distalis
Pars tuberalis
Pars intermedia
Pars nervosa
Infundibular stem
Median eminence
Clinical Significance: Craniopharyngiomas develop from remnants
of stalk of hypophysial diverticulum (in pharynx of sphenoid bone)
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 week
till the beginning of 9th week
Formation of the secondary palate
(starts between 7 to 8 weeks and completed around 3 months)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Cleft Palate
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 branchial
arch].
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
Lingual swelling
Tuberculum impar
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
The lingual papillae appear by the end of 8th week
Vallate and foliate papillae appear first, fungiform and
filiform (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 invading
gustatory nerve cells from chorda tympani, glossopharyngeal
and vagus nerves
Thyroid gland development (4 to 7 weeks)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Lingual thyroid
Thyroglossal duct cyst
Development of Jaw Bones
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Development of Mandible
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Fate of Meckel’s Cartilage
Posterior – malleus of the inner ear
Sphenomandibular ligament
Anteriorly, may contribute to mandible
by endochondral ossification (some evidence)
Rest are resorbed completely
Secondary Cartilages
Three secondary (growth) cartilages govern further growth of
mandible until birth
1. Condylar cartilage (most important)
2. Coronoid cartilage
3. Symphysial cartilage
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
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
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