developmentoffaceandoralcavity-121122020529-phpapp02

8/13/2019 developmentoffaceandoralcavity-121122020529-phpapp02

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DEVELOPMENT OF FACE AND

ORAL CAVITY


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Origin of Facial Tissues

fertilization ovum egg cell mass (morula)

epiblast, hypoblast inner cell mass

the anterior end of the primitive streak formendoderm which embedded the midlinenotochondral, prospective mesodermal cellmigrate from the epiblast through the

primitive streak to form mesoderm, cellremaining in the epiblast form ectoderm,completing formation of the three germ layer


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HUMAN EMBRYOGENESIS


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Figure 2-11 A,The mesoderm, situated betweenthe ectoderm and endoderm in the trilaminar

disk. B,Differentiation of the mesoderm intothree masses: the paraxial, intermediate, andlateral plate mesoderm. Cthrough E,With lateralfolding of the embryo, the amniotic cavityencompasses the embryo, and the ectoderm

constituting its floor forms the surfaceepithelium. Paraxial mesoderm remains adjacentto the neural tube. Intermediate mesoderm isrelocated and forms urogenital tissue. Lateral

plate mesoderm cavitates, the cavity forming thecoelom and its lining the serous membranes ofthe gut and abdominal cavity.


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Development of Facial Prominences

Development of nasal placodes, frontonasal

region, primary palate, and nose

Development of maxillary prominences and

secondary palate

Development of visceral arches and tongue


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Development of nasal placodes, frontonasal

region, primary palate, and nose

Thickening of the surface ectoderm on either

side of the frontal prominence just above the

stomodeum is the first indication of the nasal

cavity called the nasal (olfactory) placodes

Nasal placodes are ectoderm induced by

ventral forebrain

At this time there are 5 prominence and 2

nasal placodes


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Nasal (olfactory) pits are located on either side ofthe frontonasal prominence and are surroundedby horseshoe-shaped eminences. The medial

portion of these eminences is called the medialnasal process (MNP). The lateral portion of whichis called the lateral nasal process (LNP). Thelateral nasal process is separated from the

maxillary process (the more rostral portion of thefirst branchial arch) by a furrow which reachesthe medial aspect of the developing eye.


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Figure 3-17 Human facial development from 24days through 38 days. Left-column photographsshows actual embryos; the middle and rightcolumns are diagrams of frontal and lateral views.A,Boundaries of the stomatodeum in a 26-dayembryo. B,A 27-day embryo. The nasal placode isabout to develop, and the odontogenicepithelium (white bars)can be identified. C,A 34-day embryo. The nasal pit, surrounded by lateraland medial nasal processes, is easily

recognizable. D,A 36-day embryo shows thefusion of various facial processes that arecompleted by 38 days (E)


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The anterior aspect of this partition is derived

from the area of the upper jaw formed by the

medial nasal processes (intermaxillary

segment) and is called theprimary palate

(median palatine process).


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Development of maxillary prominencesand secondary palate

Most of the palatine partition, is derived fromthe medial growth of shelf-like processesoriginating from the maxillary process called

the palatine shelves(lateral palatineprocesses). This segment of the palate iscalled the secondary palate. As the secondarypalate is formed, the nasal septumgrows

inferiorly toward it. The nasal septum and thetwo palatine shelves unite to form separateright and left nasal chambers


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Most of the hard palate and all of the soft

palate form from the secondary palate


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Development of visceral arches

and tongue

In humans there are six visceral arches, whichthe fifth is rudimentary.

The proximal portion of the first arch becomes

maxillary prominence, the mandibular andhyoid arches develop at their distal portion tobecome consolidated in the ventral midline

Nerve fibers from 5, 7, 9, and 10 cranial nervesextend to the mesoderm of the first fourvisceral arches.


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Figure 3-22 Development of the tongue. A,The floor ofthe primitive stomatodeum, viewed from above, isformed by the branchial arches. Three swellings, thetuberculum impar and the paired lingual swellings,appear in the mesenchyme of the first arch beneaththe epithelium. A midline swelling (the hypobranchialeminence) appears in the third arch; the sagittalsection through the arches is shown in the lowerdrawing. B,The increased swelling of the lingualswellings, together with the tuberculum impar, willform the anterior two thirds of the tongue. Thehypobranchial eminence overgrows the second arch(depicted in the sagittal section in the lower drawing).

C,Final disposition of the tongue and the relativecontributions of the first and third arches. The sagittalsection is shown in the lower drawing. The arrowdepicts the route of incoming occipital myotomes thatform the tongue muscle.


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Know that the anterior two thirds of the

tongue is covered by ectoderm and derived

from first arch mesenchyme

And posterior one third of tongue is covered

by endoderm and be primarily derived from

the third arch mesenchyme

developmentoffaceandoralcavity-121122020529-phpapp02

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