3 - EMBRTongue.pdf

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ Taibah University College of Dentistry Division of Oral Biology, OBC 310 Department of Oral Basic and Clinical Sciences Embryology – III Development of Palate & Tongue I - Development of Palate CONTENT I – Development...

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ Taibah University College of Dentistry Division of Oral Biology, OBC 310 Department of Oral Basic and Clinical Sciences Embryology – III Development of Palate & Tongue I - Development of Palate CONTENT I – Development of Palate I I. How Cleft Palate develops?  Abnormalities in Development of Face & Palate  CONGENITAL DEFFECTS After 8th week of IUL, development is essentially a matter of growth. Embryogenesis being a complicated and delicately balanced process, any malfunction occurred in this time scale (1st to 8th week of IUL) may produce congenital defects. Environmental factors and Teratogens (agents that may cause congenital defects) are responsible for malformation of embryo.  CONGENITAL DEFFECTS ❑ Timing of environmental factors are very critical. ❑ If a Teratogen exerts its effect during the first four (4) weeks of IUL (when the embryo is developing rapidly), the teratogen usually damages so many cells that death of the embryo occurs. ❑ But if a few cells are damaged, normal proliferation is great enough to eliminate that minor damage. ❑ During the next stage of development (between 5th -8th week), when histo-differentiation and organ differentiation take place, teratogenic agents are most likely to produce malformation. ❑Environmental factors affecting the embryo: 1. Infectious Agent : Rubella Virus causing German Measles; infection of the pregnant mother may results into Cleft Palate and deformities of Tooth 2. X-ray Radiation : Direct irradiation of Gamma ray to Pregnant women may lead to genetic mutation resulting into many developmental defects including cleft palate. 3. Drugs & Hormones : Thalido-amides, Cortison 4. Nutritional Deficiency : Vitamin deficiency 5. Smoking, drinking Alcohol and Caffeine increase the incidence of cleft lip and palate.  The extent of clefting reflects the time when the process involved in closure of the secondary palate, have been affected.  Full clefting results from interference at the start of the closure.  Partial clefting results from interference at a later stage. Facial clefts and Cleft lip may be associated with or without Palatal clefts.  Various types of Facial Clefts : Oblique Facial Cleft Unilateral Cleft Lip Bilateral Cleft Lip Median Cleft Lip Mandibular Cleft Unilateral Macrostomia  1. Oblique Facial Cleft : Results from lack of fusion between the maxillary process and lateral nasal process. Unilateral incomplete cleft lip  Bilateral complete cleft lip Clefts of the Lip and Palate 2. Cleft lip: a. Unilateral cleft lip with palate: results from failure of the maxillary prominence to merge with medial nasal prominence on the affected side. Unilateral complete cleft lip with Palate b. Bilateral cleft lip with Palate : Results from failure the maxillary prominences to merge with the medial nasal prominence on both sides c. Median cleft lip: Hare Lip : Results from failure of the medial nasal prominences to merge and form the inter- maxillary segments. Cleft of the Secondary PalatePalate with / without Primary Palate 4. Macrostomia or Transverse facial cleft:  Failure of fusion of the mandibular and maxillary processes for proper distance.  Extend from angle of mouth for varying distance toward ear.  Unilateral or bilateral.  Very large mouth opening. 5. Microstomia:  Over fusion of the mandibular and maxillary processes.  Very small mouth opening. 6. Mandibular cleft :  Due to lack of fusion between the mandibular processes.  Very rare.  Cleft of Secondary Palate:  Due to failure of fusion of two palatine shelves with each other and with the nasal septum on the median line.  Shows cleft of the secondary palate with cleft of uvula.  When clefts of the palate occurs with no corresponding facial cleft, the cause is different. Such palatal clefts may result from : 1. Failure of palatal shelves and septum to contact each other because of a lack of growth or due to disturbance in the mechanism of shelf elevation. 2. Failure of the shelves and septum to fuse after contact has been made because the epithelium covering the shelves does not break down or is not resorbed. 3. Rapture after fusion of the shelves has occurred. 4. Defective merging and consolidation of the mesenchyme of the shelves.  **The motive force for shelf elevation is not clearly elucidated** 1 - Contractile fibroblast in the palatine processes may be involved. 2 - Differential growth may be the cause by the mesodermal cells proliferation in the lateral surface of the vertical palatine processes especially at the angle between the process itself and the lateral part of the oral roof. 3 - The oral surface of the folds grows more rapidly than the nasal surface, thus leading to a rapid change in the position of the fold away from the faster growing side. 4 - The displacement of the tongue downward helps in the elevation of the two palatine processes. II-Development of Tongue Tongue  Development of the Tongue The tongue is a sac of mucous membrane on the floor of the mouth filled with mass of muscles. It begins to develop at the end of 4th week of IUL. It is formed in two parts : Anterior 2/3rd. & Posterior 1/3rd. Both differ in origin, structure, function and nerve supply.  Anterior 2/3rd of the tongue is known as the body of the tongue. It is covered by numorous papillae. The posterior 1/3rd of the tongue is known as the base of the tongue. It contains the lymphoid tissue. In the fourth week, the tongue develops from mesenchymal swellings covered with ectoderm and endoderm on the floor of the pharynx. ❑One small median elevation named tuberculum impar develops from the endodermal floor of the pharynx at the region just posterior to the lateral lingual swellings. ❑Two lateral mesenchymal swellings develop from the internal surface of the two mandibular processes on each sides of their median line and are called the lateral lingual swellings. By the rapid growth, the two lateral lingual swellings quickly enlarge and merge with each other and also grow backward to fuse with the tuberculum impar and give rise to the anterior 2/3 of the tongue.  Growth of the body of the tongue is accomplished by a great expansion of the lateral lingual swellings, with a minor contribution by the tuberculum impar.  Development of the posterior 1/3 of the tongue: The posterior 1/3 of the tongue begins development by appearance of a median swelling on the floor of the pharynx caudal to the tuberculum impar which is called the hypo- branchial eminence or (copula of His  4 ). DEVELOPMENT OF TONGUE The posterior one-third of the tongue comes from a single swelling, the hypobranchial eminence, derived from the third and fourth pharyngeal arches. The second pharyngeal arch makes no contribution to the tongue. Thus, the mucous membrane of the posterior one-third of the tongue comes from a single swelling, the hypobranchial eminence, derived from the third and fourth pharyngeal arches  Development of the posterior 1/3 of the tongue: ❑ The mucosa of the posterior 1/3rd of the tongue is innervated by the glossopharyngeal nerve (the nerve of the third arch). ❑ This suggests that the 3rd arch grow over the second arch swelling and bury its elements.  The anterior and posterior portions of the tongue develop at the same time and fuse in a v shaped groove called sulcus terminalis. A midline depression at the apex of the sulcus terminalis, the foramen caecum, marks the origin of the thyroid gland  The most posterior part of the tongue and the epiglottis are innervated by superior laryngeal nerve, a branch from the vegus nerve (nerve of the 4th branchial arch) which suggests that this area may be derived from the 4th arch. So development of the tongue from the branchial arches explains its nerve supply. Development of the Anterior 2/3 of the Tongue: Foramen Cicum Anterior 2/3rd of the Tongue develops from two swelling: 1. Tuberculum Impar : arising in the Midline 2. Lateral swelling arising anteriorly on the both side of the midline. ❑The thyroid gland is formed during the early stage of tongue development. ❑It develops just posterior to the tuberculum impar on the floor of the pharynx as a pit from which the thyroid gland migrates to the neck through a canal called Thyro-glossal duct. ❑This duct soon atrophies and disappears leaving its opening in the tongue as the foramen If Remnants from the caecum. thyroglossal duct persists, it gives rise to cysts in the middle of the neck. Development of the tongue muscles: During the 2nd month (8th week) of IUL, both intrinsic and extrinsic muscles of tongue develops from the occipital myotomes migrating from the occipital areas to the tongue carrying with them the hypoglossal nerve.  Development of the tongue papillae  At the 9th week of IUL, the epithelium of the tongue proliferates to give rise to papillae, and the taste buds appear as a result of interaction between the lingual epithelium and the nerve fibres of the facial, glossopharyngeal and vegus nerves.  At that time the Circumvalate, Foliate and Fungiform papillae begin to develop. Then the Filiform papillae make their appearance later on at 10th week of IUL. Innervations of the Tongue The nerve supply of the tongue indicates its origin. A) Sensory innervation of the anterior 2/3 of the tongue: 1 - General sensation : Lingual nerve It is derived from the first arch (mandibular division of Trigeminal Nerve, V) 2 - Special Sensation : Taste sensation (excluding circumvallat papillae): Chorda tympani. It is derived from the first arch (Facial Nerve, VII).  2. Sensory innervation for Posterior 1/3rd including Circumvallat papillae: General and taste sensation: Glossopharngeal nerve (XII). 3. Root of the Tongue (most posterior part) including epiglottis: Superior Laryngeal branches of Vagus (X). MOTOR NERVE SUPPLY: All Extrinsic and Intrinsic muscles are supplied by the Hypoglossal Nerve (XII) except Palatoglossus muscle which is supplied by Vegus nerve (via Pharyngeal Plexus)  Abnormalities in the Development of Tongue Tongue Tie (Ankyloglossia) An unusually short, thick or tight band of tissue (lingual frenulum) tethers the bottom of the tongue's tip to the floor of the mouth. It may interfere with breast-feeding. Median Rhomboid Glossitis Failure of complete coverage of the tuberculum impar results in appearance of a median shiny area at the middle of the anterior two thirds of the tongue called median rhomboid glossitis (devoid of lingual papilla). Bi-fid Tongue (Glosso-schissis)  Bifid or Cleft Tongue is a tongue with a groove or split running lengthwise along the tip of the tongue.  It is the result of incomplete fusion of the lateral tongue swellings.