Download orofacial embryology lecture

Orofacial Embryology
Prenatal Development
Websites to check out
• http://www.bioscience.org/atlases/fert/htm/develhuman/f
etdev.htm
• http://embryology.med.unsw.edu.au/wwwhuman/stages/s
tage16.htm
• http://www.visembryo.com/
• http://www1.umn.edu/dental/course/dent_5725/
• http://www.fleshandbones.com/readingroom/pdf/101.pdf
• http://www.med.umich.edu/lrc/coursepages/M1/e
mbryology/embryo/05embryonicperiod.htm
Fertilization & Development in Utero
-fertilization in the upper third of the oviduct/fallopian tube
-fertilization = union of egg and sperm
-after fertilization = zygote
-first period of prenatal development = preimplantation period
-first week of development
-development of the unattached
zygote/embryo
-immediately prior to the union of
egg and sperm nuclei – the egg must
complete the final stages of meiosis
(meiosis I is completed as the egg
primordium then stops)
-fertilzation result in the combination
of the haploid egg and sperm =
diploid zygote
-called an embryo once it begins to
divide (within 24 hours)
-division = mitosis
Embryonic terms to consider
•
induction
– first process to occur during embryogenesis
– interaction between developing embryonic cells
•
morphogenesis
– may also be called morphodifferentiation
– development of form and specific tissues
– results from migration of embryonic cells and inductive interactions between
these cells
•
patterning
– specification of the embryo through segmentation
•
differentiation
– process of specialization of embryonic cells
•
proliferation
– controlled levels of mitosis
•
interstitial growth
– growth deep within a tissue of organ
– as opposed to appositional growth – growth at the periphery through the
addition of additional cell layers
Prenatal development
• 10 lunar months
• three phases (first two = embryonic stage)
– first – after fertilization and spans the first 4 weeks
• largely cellular proliferation and migration
• some differentiation
– next 4 weeks of development
• largely the differentiation of all major internal and external
organs = morphogenesis
• very vulnerable stage
– remaining phase – fetal stage
• largely a matter of growth and maturation
-preimplantation period –
first week
-embryonic stage week 2 to week 8
OVIDUCT:
-union of sperm and egg nuclei (zygote) -> first mitotic cell division (embryo) -> cell
division continues -> formation of the morula
UTERUS:
-morula forms a blastocyst or blastula (assymetrical ball of cells with a cavity) ->
implantation into the endometrium
-formation of the blastula marks the beginning of morphogenesis - shaping of the embryo,
migration of dividing cells to specific locations
-blastula = blastocyst - hollow ball of cells
-outer layer = trophoblast - forms extraembryonic tissues (e.g. placenta,
yolk sac)
-inner mass of cells at one end - totipotent embryonic stem cells
or embryoblasts
Second week of development
•
•
•
•
blastocyst increases in size by proliferation
a blastocoel or blastocyst cavity forms between the inner cell mass and the
trophoblast
differentiation of the inner cell mass ES cells begins
results in the formation of a bilaminar embryonic disc comprised of two cell
layers
– two layers are called an upper epiblast (ectoderm, mesoderm, endoderm) and a
lower hypoblast (extraembryonic endoderm)
– above this disk is an upper amniotic cavity and a lower yolk sac (primitive
hematopoietic organ for the embryo/fetus)
•
•
trophoblast also begins to differentiate to form a primitive placenta
the embryo connects to the developing placenta through a stalk
Third week of development
-the bilaminar embryonic disk converts into a trilaminar
disk of ectoderm, mesoderm, endoderm (gastrulation)
-formation of the primitive streak within the embryonic
disc critical to this formation
-migration of epiblast cells through the primitive streak
towards the hypoblast – eventually creates three tissue layers called the
germ layers
1. ectoderm
2. mesoderm
3. endoderm
humans are
deuterostomes
Fourth week of embryonic development
-portions of the mesoderm that
do not form the notochord
divide into sections called
somites -> specific body
regions and structures
-38 somite pairs
-give rise to most of the skeletal
structures of the head, neck and
trunk
-by the end of the third week: trilaminar embryonic disc has a definite orientation
-during the fourth week - embryo begins to form a tubular structure
-in front of the primitive streak is the primitive node – mesodermal cells that will form the
notochord
-also have differentiation of cells from the ectoderm forms the neuroectoderm
-a neural plate forms
-this plate thickens with proliferation – invaginates centrally and forms the neural groove
-this groove deepens and is surrounded by the two neural folds
-development of the neural crest cells from these neural folds
Fourth week of embryonic
development
• the neural folds meet superior to the neural
groove and forms the neural tube
• neural folds also form the cells of the neural
crest
– migratory population of cells
– multipotent
– gives rise to ectodermal tissues and
mesenchyme in specific areas of the head/face
• embryo folds along this tube – results from
extensive proliferation of the ectoderm and the
differentiation of specific tissues at the
cephalic end
• the anterior end of the neural tube rapidly
expands to form the beginnings of the
forebrain, midbrain and hindbrain
• also folds along the rostrocaudal axis
• continued development of the somites
• development of a head fold
• is critical to the formation of the
primitive oral cavity
– folding results in the formation of
the primitive oral cavity =
stomatodeum
– separated from the developing
and expanding gut by a
buccopharyngeal membrane
(or oropharyngeal
membrane)
• the mesoderm can be divided
into three distinct types
– paraxial mesoderm
– intermediate mesoderm
– lateral plate mesoderm
• the lateral folding determines
the disposition of the germ
layers
– with lateral folding the
amniotic cavity encompasses
the entire embryo
– the paraxial mesoderm
remains adjacent to the
developing neural tissue
(induction)
– the lateral plate mesoderm
drops down and cavitates the resulting cavity forms the
coelom
Check out this site
• http://php.med.unsw.edu.au/embryology/in
dex.php?title=2010_Lecture_11#Animation
_of_Face_Development
Head
formation
• rostral or head fold
• anterior portion of the neural tube
expands as the forebrain, midbrain
and hindbrain
• the neuroectoderm in this region will
form the olfactory, orbital and
otic placodes
• the hindbrain forms 8 bulges =
rhombomeres
• the paraxial mesoderm in this region
also segments into somites
• migration of neural crest cells into
this region provides the embryonic
connective tissue (mesenchyme)
required for development of the
craniofacial structures
• these neural crest cells arise from the
midbrain and the first two
rhombomeres as two streams
Branchial arches
•
•
•
•
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also called pharyngeal arches
figure 4-11
fourth week: development of a
frontal prominence forms the
stomatodeum
below this is the formation of the
first branchial arch
(mandibular arch)
6 pairs – U shaped
– core of mesenchymal tissue
formed from neural crest cells that
migrate in to form the arches
– covered externally by ectoderm
and lined internally by endoderm
– each has its own developing
cartilage, nerve, vascular and
muscular components
•
these arches separate the
stomatodeum from the developing
heart
Branchial arches
• separated laterally by branchial grooves/clefts
• medially they are separated by pharyngeal pouches
• first arch (mandibular arch) – maxillary and mandibular
processes
• second arch (hyoid arch) - hyoid bone, part of the temporal bone
(VII nerve)
• cartilage = Reichert’s cartilage
• the mesoderm of this arch will form the muscles of facial expression, the
middle ear muscles
• third arch –tongue (IX nerve)
• fourth arch –tongue, most of the laryngeal cartilages (IX and X
nerves)
• fifth arch – becomes incorporated into the fourth
• sixth arch – most of the laryngeal cartilages (IX and X nerves)
Pharyngeal Pouches
– four well-defined pairs of pharyngeal pouches develop from
the lateral walls of the pharynx
– first pouch (betwen the 1st and 2nd arches) - external acoustic
meatus, tympanic membrane, and eustachian tube
– second pouch – palatine tonsils
– third pouch - thyroid and parathyroid glands,
– fourth pouch – parathryoid gland
– fifth pouch -becomes incorporated into the fourth
Development of the Face
• forms from the fusion of 5 face primordia
which develop during week 4 and fuse
during weeks 5 through 8
– primordia = ectodermal swellings or
prominences that are filled with mesodermal
and neural crest cells
• frontonasal prominence
• mandibular prominences (2) – from branchial
arch #1
• maxillary prominences (2) – from branchial arch
#1
Development of
the Face
MOVIE
http://www.indiana.edu/~anat550/hnanim/face/face.html
Stomatodeum
• primitive
stomatodeum forms
a wide shallow
depression in the
face – limited in its
depth by the
buccopharyngeal
membrane
Development of the Upper Face
•
•
•
•
within the fourth week (weeks 5 –
8)
the frontonasal prominence
develops two sets of placodes
(nasal and lens)
formation is dominated by the
proliferation and migration of
ectomesenchyme cells
MAJOR EVENTS
– development of medial and lateral
nasal processes or swellings which
encircle the nasal pits
– fusion of the medial nasal
processes at the midline =
intermaxillary/premaxillary
process or process
•
formation of the upper portion of
the face is faster than the lower
portion (finally cease to grow at
puberty)
MOVIE
http://www.indiana.edu/~anat550/hnanim/face/face.html
Development of the Upper Face
– rapid proliferation of the underlying
mesenchyme around the placodes
results in bulges in the frontal
eminence and produces a horseshoeshaped ridge in each olfactory placode
• medial and lateral nasal processes
– in between the medial nasal processes
is where the nose develops = called
the frontonasal prominence
– the medial nasal processes of both
sides + the frontonasal prominence
give rise to the middle portion of the
nose, upper lip, anterior portion of
the maxilla and the primary palate
– the medial nasal processes also fuse
internally and form the
premaxillary segment
– the frontonasal prominence will also
form part of the forehead
Development of the Upper Face
• day 24: development of the
frontal prominence (covers the
rapidly expanding forebrain)
– beginnings of the mandibular
and maxillary processes from the
1st branchial arch
– well-defined boundaries of the
stomatodeum results
• day 26: well-formed maxillary
and mandibular processes
• day 27: appearance of the
nasal placode and the
odontogenic epithelium
• day 28: localized thickenings
develop within the frontal
prominence = olfactory
placodes
Upper lip formation
• during the fourth week
• fusion of the maxillary processes with
each medial nasal process
• this contributes to the lateral sides of
the upper lip – together with the
medial nasal processes which
contribute to the medial aspect of the
upper lip
• the maxillary processes also fuse with
the lateral nasal processes – results in
a nasolacrimal groove which
extends from the medial corner of the
eye to the nasal cavity
Development of the Palate
• involves the formation of a
primary palate, a secondary palate
and fusion of their processes
• Primary palate
– forms from an internal swelling of the
intermaxillary/premaxillary process
(fusion of medial nasal processes)
• Secondary palate
– forms from the two lateral palatine
shelves or processes
– develop as internal projections of the
maxillary prominences
• fusion of the
median nasal
processes gives rise
to the median
palatine process –
fuses to form the
primary palate
Primary palate
MOVIES
http://www.indiana.edu/~anat550/hnanim/face/face.html
Secondary Palate
• the common oronasal cavity is bounded
anteriorly by the primary palate and
occupied by the developing tongue
• only after the development of the
secondary palate can oral and nasal
cavities by distinguished
• three outgrowth appear in the oral cavity
– nasal septum:
• grows downward through the oral cavity
• it encounters the primary and secondary
palates
– two palatine shelves
• closure of the secondary palate is likely
to involve the hardening of the palatine
shelves – mechanism remains unknown
+ the withdrawl of the tongue
Palatine shelves
Cleft lip and
palate
Nose
• complex combination of contributions of the frontal prominence
(forms the bridge), the merged medial nasal prominences (form the
median ridge and tip of nose), the lateral nasal prominences (form
the alae) and the cartilage nasal capsule (forms the septum and the
nasal conchae)
• the external nasal region develops from the superficial alar field –
gives rise to the alae
• Nasal pits and cavities
– separate anteriorly from the stomatodeum by fusion of the medial nasal,
lateral nasal and maxillary prominences – form the nostrils
– separate posteriorly from the stomatodeum by the oronasal membrane
– the developing nasal cavities are separated from the oral cavity by the
intermaxillary process (forms the floor of the nasal cavity)
• Nasal capsule and nasal septum
– condensation of the mesenchyme within the frontonasal prominence –
forms the precartilagenous nasal capsule
– the capsule develops as two masses around the nasal cavities
– the median mass becomes the progenitor of the nasal septum
– the lateral masses will form the conchae and nasal alar cartilages
• nasal cavity
– early development of the face is
dominated by the proliferation and
migration of tissue involved in the
formation of the primitive nasal cavities
– about 28 days localized thickenings
develop within the primitive ectoderm of
the embryo – olfactory placodes
– rapid proliferation of the underlying
mesenchyme around the placodes bulges
the frontal eminence forward and
produces the nasal pit
– the lateral arm of this pit = lateral nasal
process
– the media arm = medial nasal process
– in between these nasal pits is the
frontonasal process – where the nose
develops
– the two medial processes + the
frontonasal give rise to the medial portion
of the nose and upper lip, the anterior
portion of the maxilla and palate
Nasal and Paranasal tissues
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•
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nasal cavity lined with a respiratory mucosa like the rest of the respiratory
system
pseudostratified columnar epithelium with cilia
interspersed are goblet cells which rest on the basement membrane
•
very vascular lamina propria – warms the air
roof of the nasal cavity is a specialized area that contains the olfactory
epithelium
on the medial wall are the three nasal conchae
•
paranasal sinuses
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–
–
–
–
frontal, sphenoid, maxillary and ethmoid sinuses
provide mucus for the nasal cavity
respiratory mucosa of ciliated pseudostratified columnar epithelium
but is thinner than the nasal mucosa – also has fewer goblet cells
no erectile tissue
Development of Sinuses and Nasal
cavity
• paranasal sinuses
– some develop during late fetal life
• frontal and sphenoid not present at birth
• at 2 years the two most anterior ethmoid sinuses grow into
the frontal bone – visible on X-rays by age 7
• two most posterior ethmoid sinuses grow into the sphenoid
bone
• sinuses are important in the size and shape of the face
during infancy and the resonance of the voice
–
–
–
–
the rest develop after birth
form as outgrowths of the wall of the nasal cavity
become air-filled extensions in the adjacent bones
the original openings of these outgrowths persist as
the orifices of the adult sinuses
Maxilla formation
•
centers of ossification develop in the mesenchyme of the maxillary
processes of the first branchial arch
•
spreads posteriorly below the orbit towards the developing zygoma and
anteriorly toward the future incisor region and superiorly to form the
frontal process
•
ossification also spreads into the palatine process to form the hard palate
•
at the union between the palatal process and the main body of the
developing maxilla is the medial alveolar plate – together with the
lateral plates – development of the maxillary teeth
•
a zygomatic or malar cartilage appears in the developing zygomatic
processes and contributes to the development of the maxilla
Development of the Lower Face
• within the fourth week
• two bulges form inferior to the
stomatodeum
Mandible formation
•
the cartilage of the first branchial arch
associated with the formation of the
mandible = Meckel’s cartilage
•
6 weeks: Meckel’s cartilage forms a rod
surrounded by a fibrocellular capsule
•
the two cartilages do not meet at the midline
but are separated by a thin line of cartilage =
symphysis
on the lateral aspect of this symphysis – a
condensation of mesenchyme forms
•
•
•
at 7 weeks intramembranous ossification
begins in this mesenchyme and spreads
anteriorly and posteriorly to form the bone
of the mandible
the bone spreads anteriorly to the midline of
the developing lower jaw – the bones do not
fuse at the midline – mandibular symphysis
forms (from meckel’s cartilage)
–
•
which fuses shortly after birth
the ramus develops from rapid ossification
posteriorly into the mesenchyme of the first
arch
Mandible formation
-Meckel’s cartilage does NOT contribute directly to the ossification of
the mandible
-posterior extremity – malleolus of the inner ear
-portion persists as the sphenomandibular ligament
-significant portion is resorbed entirely
-most anterior portion near the midline may contribute to the jaw
through endochondral ossification
-growth of the mandible until birth is influences by the appearance of
three secondary (growth) cartilages
1. condylar – 12th week, developing ramus by endochondral
ossification, a thick layer persists at birth at the condylar head
(mechanism for post-natal growth of the ramus = endochondral)
2. coronoid – 4 months, disappears before birth
3. symphyseal – appears in the connective tissue at the ends of the
Meckel’s cartilage, gone after 1 year after birth
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•
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Development of the Tongue
begins to develop about 4 weeks
localized proliferation of the
mesenchyme results in formation of
several swellings in the floor of the oral
cavity
the oral part (anterior two-thirds)
develops from the fusion of two distal
tongue buds or lateral lingual
swellings and a median tongue
bud (tuberculum impar)
the pharyngeal part or root of the
tongue (posterior one-third) develops
from the copula and the
hypobranchial eminence (forms
from the 2nd, 3rd and 4th branchial
arches)
B.As #1,2 and 3
hypobranchial arch
overgrows the 2nd arch
these parts fuse (adult = terminal
sulcus)
muscles of the tongue arise from
occipital somites which migrate into
the tongue area
MOVIE: http://php.med.unsw.edu.au/embryology/images/8/88/Tongue.gif