Transcript
8/3/2019 3. Prenatal Growth
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Pre-natal Growth of
Craniofacial Complex
Dr. Munizeh Khan
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Embryology
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How much do you know about these??
Ectodermal Dysplasia Treacher-CollinsSyndrome
Cleft Lip & Palate
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Significance of Embryology
Weeks 4 through 8 are very important
Major tissues and organ systems are developing from theoriginal three germ layers during this time
Exposure of embryo to teratogens, such as viruses anddrugs, may result in congenital abnormalities
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Pre-natal Growth & Development
Dynamic phase in the development of a human being
During this period, the height increases by almost 5000times as compared to only a threefold increase during thepost-natal period.
The pre-natal life can be arbitrarily divided into threeperiods
1. Period of the Ovum2. Period of the Embryo
3. Period of the Fetus
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Pre-natal Stages
Period of ovum: from fertilization to 14th
day Cleavage & attachment of ovum to intra-uterine wall
Period of embryo: from 15th to 56th day
Major development of craniofacial region
Period of fetus: 57th day to birth
Accelerated growth of craniofacial structures resulting in
increase in size and change in proportions
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Week 1 of development
Fertilization = zygote
Zygote undergoes cleavage
Blastomeres form ball of cells called morula
Cells =
Trophoblast (outside) Embryoblast (inside)
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Week 2 of development
Two important events occur in the beginning of thesecond week after fertilization.
Implantation begins.
The inner cell mass forms bilaminar germ disk, and so called thebilaminar disk stage.
These two layers are called epiblast and hypoblast.
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Week 3 of development
Gastrulation The bilaminar disk is converted into a trilaminar disk.
Also called the trilaminar disk stage.
The three embryonic germ layers are formed: Ectoderm,
Endoderm
Mesoderm
All germ layers formed by Epiblast cells
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Derivatives of the 3 germ layers
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Neurulation
Process of development of neural plate,neuroectoderm and folding to produce neural tube
Neural tube is primordium of CNS
Anterior region enlarges to form: Forebrain
Midbrain
Hindbrain
Neural crest cells arise from neural folds and migratethroughout the body
Provide mesenchyme for craniofacial development
Express the Homeobox (HOX) genes
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Week 4 of development
A prominent bulge appears on ventral aspect of
embryo corresponding to the developing brain Below the bulge a shallow depression appears
called STOMODEUM = corresponds to the primitivemouth
The floor of the stomodeum is formed by thebuccopharyngeal membrane which separates thestomodeum from the foregut
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Week 4 of development
Trilaminar embryonic disk folds in two planes to forma cylindric, C-shaped embryo
The buccopharyngeal membrane separates the
foregut and the primitive oral cavity (stomodeum)
Rupture of buccopharyngeal membrane occurs
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Clinical Scenario
An 8 year old child is brought to you at theOrthodontic Clinic. His medical reports reveal a
diagnosis of ECTODERMAL DYSPLASIA.
What structures would you expect to be abnormallydeveloped in this child?
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Pharyngeal Arches
Begin to develop during 4th
week
Consists of a series of bilaterally paired arches,pouches (clefts), grooves and membranes
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Pharyngeal arches develop as a result of migrationof neural crest cells into the head and neck region
At end of 4th week, 4 distinct pairs of pharyngealarches seen.
Arches V and VI are poorly developed in humans.The 5th arch completely regresses. Arch VI results
due to fusion of arches IV and VI
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Each pharyngeal arch is externally covered by the
ectoderm and internally by the endoderm
The pharyngeal arches are separated externally bydeep ectodermal clefts called pharyngeal clefts(grooves)
Pharyngeal pouches partially separate the arches onthe internal aspect
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Significance of Pharyngeal Arches
Each of these arches gives rise to followingstructures of the future face and neck regions:
skeletal components
muscles
connective tissue
vasculature
neural components
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Derivatives of the Pharyngeal Arches
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Derivatives of the Pharyngeal Arches
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Derivatives of Pharyngeal Pouches, Grooves
and Membranes
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Derivatives of Pharyngeal Pouches, Grooves
and Membranes
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Development of the Face
Development of face occurs primarily betweenweeks 4-8 IUL
Five facial swellings (processes) appear at 4th to 8th
week around stomodeum:
Fronto-nasalprominence
A pair ofmaxillary swellings pharyngeal
A pair ofmandibular swellings arch 1
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Facial Development
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Development of the Nose
On infero-lateral portion of the frontonasal process, bilateral areas ofsurface ectoderm thicken to form nasal placodes
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Development of the Nose
The mesenchyme around placodes proliferate to form horseshoeshaped ridges called Medial & Lateral nasal processes
Nasal placodes eventually become nasal pits (nostrils & nasal
cavities)
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Development of the Maxilla
Maxillary swellings proliferate & migrate medially
MNP fuse in the midline and form the intermaxillary segment,
This intermaxillary segment gives rise to:
Philtrum of upper lip
Four incisor teeth
Alveolar bone & gingivae
Primary palate
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Development of the Palate
Development extends from weeks 6-12 IUL
Palate develops from 2 structures:
1) Primary palate:
Triangular-shaped, anterior to incisive foramen
Originates from intermaxillary segment (MNP)
2) Secondary palate: Gives rise to hard and soft palate
Arises from paired lateral palatine shelves of maxilla
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Development of the Palate
Lateral palatine shelves orient horizontally
Shelves fuse with each other
Lateral palatine shelves fuse with primary palate andnasal septum (9th week)
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Fusion of processes
Fusion of prominences/processes involves:
Breakdown of surface epithelium at area of contact
Underlying mesenchymal cells merge with one another
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Fusion
Facial prominences fuse between weeks 7-10 IUL
Maxillary prominences fuse laterally with Mandibular
prominences
MNP fuse with Maxillary prominences
MNP fuse with LNP
LNP fuse with Maxillary prominences
Lateral palatine shelves fuse with each other
Lateral palatine shelves fuse with primary palate andnasal septum
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Disturbances of Fusion
Defective or incomplete fusion between various processesresult in clefts
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Questions?
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