3. Prenatal Growth

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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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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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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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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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?

3. Prenatal Growth

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