Embryology - II: Branchial Arches, Face & Palate Development PDF

WHAT IS GROWTH? WHAT IS DEVELOPMENT?...

WHAT IS GROWTH? WHAT IS DEVELOPMENT?  “Developmental increase in mass.’’- Stewart.(1982) Development of EMBRYOLOGY – II “Development is a progress towards maturity” Pharyngeal Arches, BRANCHIAL ARCHES,  “An increase in size or number.” - Profitt. (1986) – Todd(1931) Clefts & Pouches DEVELOPMENT OF  “Normal changes in amount of living substance.’’ “Development is a maturational process FACE & PALATE - Moyers(1988) involving progressive differentiation at the CONTENT Taibah University I- What is Pharyngeal Arch? cellular and tissue levels” – Enlow College of Dentistry II. Anatomy of Pharyngeal Arch, Cleft & Pouches.  “Growth signifies an increase, expansion or extension Division of Oral Biology, OBC 310 III. Derivatives of Pharyngeal Arch, Cleft & Pouches Department of Oral Basic and Clinical Sciences of any given tissue.” - Pinkham.(1994) i When the stomatodeum first PHARYNGEAL (BRANCHEAL) PHARYNGEAL (BRANCHEAL) 4 Weeks Embryo ARCHES ARCHES, CLEFTS AND POUCHES Pharyngeal pouches are the out pocketing those appear forms, it is limited by frontal along the inner aspect of lateral walls of the pharynx. prominence rostrally and by The most distinctive feature in developing cardiac bulge, caudally. the development of head and Pharyngeal arches appear in the 4th and outer The buccopharyngeal membrane neck is the presence of 5th week of development. is a bi-laminar structure consisting of Pharyngeal Arches [the old Initially six (6) cylindrical thickening apposed ectoderm and endoderm. www.rnge term was Branchial Arch because they sometimes forms bilaterally but the 5th and the 6th It separates the stomatodeum from are transient structures in human. resemble the gills (brancia) of a the foregut, but soon it breaks down fish.] so that the stomatodeum communicates directly with the foregut. a in atiiIin Iiiii fhppar intheendit.si  4 5 ANATOMY OF PHARYNGEAL ARCHES A N ATO M Y O F P H A RY N G E A L A R C H E S A N ATO M Y O F P H A RY N G E A L A R C H E S Pharyngeal arches are cylindrical The muscular thickening those are formed in the  Each Pharyngeal arch components of each pharyngeal walls as a proliferation consists of a core of Core of each arch arch have their own of mesoderm infiltrated by mesenchymal tissue.  On the outside, it is receives substantial cranial nerve and migrating Neural crest cells. covered by surface numbers of Neural crest wherever the muscle Initially, they consists of bars of ectoderm. cells migrate, they mesenchymal tissue separated by cells, which migrates  On the inside, it is carry their nerve deep clefts. into the arches to component with them covered by epithelium of contribute to skeletal (also arterial endothermal origin. components of the face. components). arch Pharyngeal tissue mesenchymal core cells crest haveneural face c.fif cellmarginattheycarry outside ectoderm inside endoderm itsowncranialnerve everyarchhave Development of the pharyngeal arches and pouches 1 ST PHARYNGEAL ARCH 3 RD , 4 TH & 6 TH PHARYNGEAL ARCH 2 ND PHARYNGEAL ARCH The First pharyngeal arch consists of a The Second pharyngeal arch (or hyoid The cartilage of the Third Pharyngeal dorsal portion, the maxillary process arch) or Reichat’s Cartilage. and This cartilage ossify during dvpt to form arch produces the lower part of the body the stapes of the middle ear while the A ventral portion, the mandibular ventral portion ossifies to form the and greater horn of the hyoid bone. process which contains Meckel’s cartilage. lesser cornu and upper part of the body of the hyoid bone. Cartilaginous components of the Fourth Mesenchyme of the Maxillary process gives rise to Pre-maxilla, Maxilla, and Sixth pharyngeal arches fuse to form Zygomatic bone and part of the the thyroid & part of the larynx. Temporal bone. Meckel’s cartilage leaves two portions incus & malleus and the rest disappears. hyoid bone  5 Adult Derivatives of Pharyngeal Pouches Pouch Adult derivatives 1st External auditory meatus, Derivatives of the 1st branchial arch arch Tympanic membrane, Tympanic  The mandible and maxilla antrum, Mastoid antrum and Eustachian tube.  All the teeth 2nd Tonsilar fossa and the epithelial  All musles of mastication arch covering the palatine tonsils and Only the tonsillar crypts (which is later  Anterior 2/3 of the tongue one cleft invaded by the lymphocytes to  All salivary glands form the lymphoid tissue of the tonsil.).  Lower lip part of upper lip and cheek (except 3rd Inferior parathyroid glands, philtrum) arch Thymus gland. 4th Superior parathyroid glands, arch Parafollicular cells of thyroid gland. Dorsal face frontalPronanse DEVELOPMENTAL DEFECT RELATED TO BRANCHIAL ARCHES Development of the Face At the end of the 4th week, the centre of the face is formed by the stomodeum, surrounded by the first pair of Pharyngeal arch. First Arch Defect : The face develops iii When the embryo is 42 days (after 6th week) old, 5 (Five) mesenchymal Treacher Collin’s Syndrome : Hypoplasia of Maxilla, Mandible and II-DEVELOPMENT between the 24th prominences are recognised : Zygomatic arch due to insufficient migration of Neural Crest cells OF THE FACE and 38th days of 1. Frontonasal Prminence : A slightly rounded elevation cranial to the gestation. in the First branchial Arch. AND stomodeum. o_0 ORAL CAVITY a Cleft Palate On 24th day, the 2. Maxillary Prominences : Dorsal portion of the First Pharyngeal arch, lateral to 1st branchial arch the stomodeum. External Ear, Auditory Canal or Middle ear defect Robin Sequence : Micrognathia (mal development of Mandible), divides into 3. Mandibular Prominences : First pharyngeal arch, caudal to the stomodeum. Branchial Fistula : When the 2nd pharyngeal arch fails to grow maxillary and g associated with Cleft palate and Glossoptosis (Posteriorly caudally over the third and Fourth arches.  Developmental prominences are later complemented by formation of Nasal mandibular arches placed Tongue). Prominences. Ectopic Thyroid and Parathyroid Tissue (3rd & 4th arch defect) freacher collin's hypoplasiamaxilla L it i iI m andible zygmatica fi areanaitorycanai.middleeardetect Robin s equencesmicroganatni.es Development of the Face and Oral Cavity ** As a result of this Development of the Face and Oral Cavity **Rapid proliferation of the At about day 28 of gestation, elevation the nasal At the 4th to 5th week of IUL, the face develops from five facial primordia bi-lateral (oval shaped) underlying mesenchyme around placode is converted into 3 - Two mandibular processes (one surrounding the stomodeum: from each side) form the caudal the nasal placodes will result in nasal pit. thickening develop within the 1-The frontonasal process is formed boundary of the stomodeum (the formation of two horse-shoe by the proliferation of the mesoderm mandibular processes is the ventral part ectoderm of the frontal Lateral nasal process gives covering the forebrain ventrally (i.e. in a of the mandibular arch). shaped elevations on each side. rise the alae of the nose. caudal direction), pushing the ectoderm prominence, just above the ** The lower jaw is the first part of the The lateral and medial edges of at this region to form the cranial face to be developed by the fusion of the opening of the stomatodeum. boundary of the stomodeum. each elevation are called lateral medial ends of the two mandibular 2- Two maxillary processes (one processes. These thickenings are and medial nasal processes from each side) form the lateral (Then develop the lower lip, the chin Olfactory Placodes or Nasal respectively. boundaries of the stomodeum (the maxillary processes is an extension from and the lower portion of the Placodes. the dorsal end of the mandibular arch and cheeck). is innervated by the maxillary nerve). e intermaxillarysegments The maxillary process grows medially and approaches the lateral and medial nasal processes but remains separated from them by ** Further rapid growth of the At the same time the two **The intermaxillary segment or distinct grooves: maxillary process, push the medial maxillary processes fuse with the Frontonasal Prominence gives rise **The maxillary 1. The Naso-lacrimal groove 2. The Buco-nasal groove nasal processes from both sides till they unite to become one medial inter-maxillary segment. This fusion obliterate the bucco- to: 1-Middle portion of the upper lip ma processes give rise to: a) Lateral portion of nasal prominence called nasal groove and result in the (philtrum of the lip). the upper lip. formation of the lateral aspects of 2-The anterior portion of the b)Most of the maxilla Intermaxillary segment or Fronto- the upper lip. maxilla carrying the incisor teeth with its associated a nasal Prominence. **In this way the middle portion of The lower lip, Chin and lower (pre-maxilla). 3-The anterior portion of the portion of the cheek. c)The secondary palate. the upper lip or philtrum is formed. portion of the cheek are formed by merging of two mandibular palate called primary palate. 4- The middle portion of the nose. process.  The primitive lip and cheeks are invaded by the mesenchymal tissues of the second branchial arch which give rise to the muscles of facial expression. F III-DEVELOPMENT OF PALATE PALATE The roof of the mouth in vertebrates having a complete or partial separation of the oral and nasal cavities and consisting of the hard palate (primary palate, secondary palate) and the soft palate. Concomitant growth of the Face and Oral cavity They are supplied by the facial nerve (the nerve of the second arch), while the mesenchyme of the mandibular arch (1st arch) differentiated into the masticatory muscles and are innervated by the mandibular nerve. Palate proper develops from primary and secondary components of palate. The final development of the face occurs slowly and results from changes in the proportion and relative position of the facial processes at the third month of IUL. Development of Primary Palate Development of Secondary Palate Three outgrowths appear in the oral cavity: The tongue is narrow and high Formation of secondary palate commences between 7 & 8 weeks of and reaches up to the nasal The nasal septum grows downwards septum. IUL and completes around the 3rd month (12th week) of IUL. Merging of the two from the frontonasal process along the Each maxillary process sends The oral cavity has an incomplete horseshoe shaped roof formed midline. vertically downwards a palatine medial nasal processes anteriorly by the primary palate and laterally by the horizontal process (Palatine shelves) on results in the formation surfaces of the two maxillary processes. Two palatine shelf or processes, one either side of the high narrow of that part of maxilla from each side extend from the tongue. maxillary processes toward the At this stage the stomodeum carrying the incisor increases in height and the nasal teeth and the Primary midline. septum grows backwards, Palate. The shelves are directed first down- The oral cavity communicates freely with the nasal cavity. ward on each side of the tongue. 42 4 stomodume t.tn fffcess nedi premitiveoraian.gr  istheProcess diffronation g rowth lefttheverticleshey that tobehooantlyplaced The two palatine processes grow Fusion of palatine shelves Development of Primary Nasal Cavity After 7th week of development, the towards each other, unite together and The shelves now elevates and fuse with with the primary palate anteriorly with each other tongue is withdrawn from between the each other and with the primary palate forming Y shaped appearance and with At the 6th week of development, the nasal pits deepens during the shelves. with nasal septum growth of surrounding nasal swellings and penetrate into the above the tongue. the nasal septum, but still separated from each other by a median cleft. underlying mesenchyme. The developed tongue has now The vertical palatine processes are elevated This cleft closes gradually in an evacuated the nasal cavity. and become horizontal in position now. anteroposterior direction at the 9th week Initially, the nasal pits are separated from the oral cavity by Oro- This is achieved by a rapid growth of of IUL. nasal membrane. the mandible and thus leaves a space Fusion of the two palatine processes occurs from the center of Y shape. for the tongue to be withdrawn from iw By this way, the secondary palate now between the palatine processes and separates the oral cavity from the nasal move downwards into the wide space cavity. within the mandible. More posteriorly the soft palate and uvula develop. iiiiiiiiiiiiiiiiiiiiiii iiii.si iiiiii i e  Soon this membrane breakdown  The lateral nasal processes of and allows the nasal and oral both sides are separated from the cavities to communicate each other maxillary processes by a deep furrow named naso-lacrimal until the secondary palate develops. groove.  The ectoderm at the roof of the  The epithelium at the depth of primary nasal cavity becomes the groove canalizes to form the specialized epithelium. as the olfactory s naso-lacrimal duct.  When the duct is separated, the two processes merge by infilling of mesenchyme.  dvpt of the mouth orifice is determined by the degree of fusion between the maxillary and mandibular processes of both sides. the epithium or timeoral than cavitydisserent nasa facedevelopsbetween 24 and 38 daysofgastation 24dad 1stbarnchealarch willbelateraltostomodeum i.IT i 4.5week facewillbedevelopedinto5Primordiazmaxzmanfrontal Mandibulardevelopmentand fffffe 28 9 from the EctodermoffrontalProminance there willbebiLateralovalshaped thisisolfactorynasalPlasodes underlyingmesechymearoundnose willmaktwohorseshoe at LateralandmedialnasalrespiratoryProcess nasalpit lateral alarofnose Nasolacrimalgroovelnas.io Maxillary development butremainnagged dystoniagroove by Naso buccalgroovemaxonasal PushmadialnasalProcesse tobecome 1madialnasalPronance called intermaxillarysegmentsORfrontonasalProminanse maxillary fusion I 6 aug theNaso buccalgroove cheekoriginismesenchymal of2ndbranchialarch tissue o.SI ii is 1starchbymandibularnerve Thesetwoareslowly 2nd Part of lecture