Embryology & Anatomy of The upper lip & palate Embryology & Anatomy of The upper lip & palate
References
Scoot-Brown’s Otolaryngology , Sixth Edition 1997 ,vol.1 basic sciences (edited by Micheal Gleeson) & vol.6 Paediatric otolaryngology (edited by David A. Adams Micheal J. Cinnamond)
Cunningham s manual of practical anatomy ,vol.3,14th edition 1979 by G. J. Romanes.
CD product based on Grabb & Smith s Plastic Surgery and is copyrighted (c) 1997 by Lippincott - Raven Publishers.
Embryology
Facial development largely occurs between the fourth and eighth weeks, and the face has a clearly human appearance by age 10 weeks.
Five facial prominences (two paired and one unpaired) bordering the stomodeum are responsible for the development of adult facial features.
The Frontonasal prominence, a central process formed by the proliferation of the mesenchyme ventral to the forebrain, forms the cranial boundary of the stomodeum.
The paired maxillary and mandibular prominences derived from the first arch form the lateral and caudal borders of the stomodeum (primitive mouth), respectively .
Bilateral thickenings of the surface ectoderm, called nasal placodes, develop at the inferior, lateral aspect of the frontonasal prominence by the end of the fourth week .
With further elevation of the margins of the nasal placodes the sides develop into the medial and lateral nasal prominences, respectively, while the depressed central region of the placodes develops into the nasal pit (precursors of the nares ).
The paired maxillary prominences continue to migrate medially .
Fusion of the medial nasal and maxillary prominences results in separation of the nasal pits from the stomodeum and subsequent separation of the oral and nasal cavities.
Merging of the medial nasal prominences forms the philtrum and Cupid’s bow region of the upper lip, the nasal tip, the premaxilla and primary palate, and the nasal septum.
The lateral nasal prominences form the nasal alae
The nasolacrimal groove develops as a furrow separating the lateral nasal prominence from the maxillary prominence.
The maxillary prominence accounts for the major portion of the upper lip (excluding the philtrum) and the upper cheek regions
Development of the palate
The palate represents both the frontonasal and maxillary prominences, with the interface between the two becoming the junction between the primary and secondary palates.
The median palatine process is derived from the frontonasal prominence and is formed from the merging of the medial nasal prominences
The lateral palatine processes are derived from the maxillary prominences.
During the eighth week the orientation of the lateral palatine processes alters from vertical to horizontal to initiate their fusion.
During this process the mandible becomes more prognathic, thereby allowing more room for partitioning of the oronasal chambers without interference by the tongue
The median palatine process subsequently gives rise to the premaxillary portion of the maxilla and forms the primary palate.
The lateral palatine processes give rise to the secondary palate. Ossification occurs in the primary palate and the anterior portion of the secondary palate to form the hard palate, while the posterior portion of the secondary palate does not undergo ossification and remains the soft palate
Ossification occurs in the primary palate and the anterior portion of the secondary palate to form the hard palate, while the posterior portion of the secondary palate does not undergo ossification and remains the soft palate
Cleft lip result from failure of fusion of the medial nasal ,lateral nasal and maxillary processes on either or both sides.
It has been suggested that several interactive processes can lead to this failure :-
1-Hypoplasia of the facial processes
2-Alterd facial geometry
3-Defective ability of the surface epithelia to participate in the fusion process.
4- Excessive cell death in the fusing epithelial seams , mesenchymal deficiency and post fusion rupture
Isolated cleft palate may be a result of disruption of one or more of a number of mechanisms:-
1-Palatel shelves too small to meet – hypoplasia.
2- Failure of palatal shelf elevation at the correct time either due to diminished intrinsic force , or due to increased resistance , principally by the tongue position remaining high and between the palate shelves.
3- Excessive head width causing failure of normal sized palatal shelves to meet.
4-Failure of shelf fusion due to defective epthelio mesnchymal interaction
Anatomy of the Upper Lip
The vermilion border of the lips is characteristic of the human species , and the red zone in the upper lip protrudes in the midline to form the tubercle
In the midline of the upper lip is the philtrum and the corners of the lip , known as the commissures
The reflection of the mucosa from the alveolus to the lips & cheeks is the fornix of the vestibule.
The upper & lower labial frenula are consistent folds of mucosa running from lip to the alveolus.
The muscles of the lip is orbicularis oris .
Tow muscles extend to the corners of the mouth , the risorius & the buccinater muscles.
Blood supply is derived from facial artery & the venous drainage through facial vein .
Motor nerve supply through the facial cranial nerve & the sensory through the branches of the trigeminal nerve
Anatomy of the palate
The palate is divided into the bony anterior hard palate & the mobile posterior soft palate .
Immediately behind the anterior teeth the mucosa of the hard palate shows distinct prominence of the incisive papillae.
In the midline of the of the free edge of the soft palate is the uvula.
The bony hard palate is formed anteriorlly by the alveolar and palatine processes of the maxilla & posteriorlly by the horizontal plates of the palatine bones.
The soft palate is a fibrous aponeurosis , the shape and position of which is altered by the tenser palati muscles , the levator palati muscles , the palatogossus & the palatopharyngeus muscles.
The blood supply of the palate is derived form greater & lesser palatine branches of the maxillary artery & the venous drainage follow facial vein
The motor nerve supply of the muscles of the soft palate is derived from cranial accessory & mandipular division of the trigeminal nerves.
The sensory nerves of the palate are nasopalatine nerve (anteriorlly ) & posterior palatine nerves (posteriorlly).
The lymphatic drainage from the anterior part of the face into submental & submandipualr nodes on ipsilateral side & then into deeper jugulodiagastric nodes , whereas lymph from the posterior part drains directly into the jugulodiagastric nodes.