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Embryology of face
 

Embryology of face

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    Embryology of face Embryology of face Presentation Transcript

    • EMBRYOLOGY OF FACE PRESENTED BY SUKHJIT KAUR
    • INTRODUCTION BIRTH SPIRAL
    • Every individual spends the first 10 lunar months within the womb of its mother. During this period it develops from a small one-celled structure to an organism having billions of cells. Human face and jaws also develop through a dynamic series of tissue divisions, expansions, migrations, fusions and involutions.
    • Embryology Embryology is defined as the study of the formation and development of embryo from the moment of its inception up to the time when it is born as an infant. Subdivisions of embryology Descriptive embryology Comparative embryology Experimental embryology General embryology Systemic embryology
    • Development of embryo Prenatal Period of ovum (conception till 7th or 8th day) Embryonic period (2nd week to 8th week) Period of fetus (3rd to 10th lunar month) Postnatal Neonatal Infancy Childhood Adolescence Maturity
    • FORMATION OF GERM LAYERS 1- Fertilization Fertilization of ovum takes place in the ampulla of the uterine tube. The fertilized ovum is a large cell. At 2nd day, embryo is at 2-cell stage. (approx. 30 hrs after fertilization)
    • 2- Cleavage Cleavage is a series of mitotic divisions that results in a rapid increase in number of cells, blastomeres, which become smaller with each division. Compacted blastomeres divide to form a 16-cell morula on 3rd day of fertilization. As the morula enters the uterus on the fourth day after fertilization, a cavity begins to appear, and the blastocyst forms. The inner cell mass, which is formed at the time of compaction and will develop into the embryo proper, is at one pole of the blastocyst. The outer cell mass, which surrounds the inner cells and the blastocyst cavity, will form the trophoblast. The cells are still surrounded by Zona Pellucida that helps in prevention of its ectopic implantation.
    • 3- Blastocyst Formation & Implantation About the time the morula enters the uterine cavity, fluid begins to penetrate through the zona pellucida into the intercellular spaces of the inner cell mass. Gradually the intercellular spaces become confluent, and finally a single cavity, the blastocoele, forms. At this time, the embryo is a blastocyst. Cells of the inner cell mass, now called the embryoblast, are at one pole, and those of the outer cell mass, or trophoblast, flatten and form the epithelial wall of the blastocyst. The zona pellucida has disappeared, allowing implantation to begin (at the end of 1st week).
    • BLASTOCYST
    • 4- Formation of germ layers (4th-8th week) As the blastocyst develops further, it gives rise not only to tissues and organs of the embryo but also to a number of structures that support the embryo and help it to acquire nutrition. At a very early stage in development, the embryo proper acquires the form of three layered disc (also called embryonic disc, embryonic area, embryonic shield or germ disc).
    • Embryonic disc
    • The three layers that constitute this embryonic disc are : Endoderm (First germ layer to be formed) Ectoderm (Second germ layer to be formed) Mesoderm (Last germ layer to be formed) Some cells of inner cell mass (of blastocyst) differentiate into flattened cells that come to line its free surface. These constitute the endoderm. Remaining cells of inner cell mass become columnar & constitute the ectoderm. A space appears between ectoderm and trophoblast which forms amniotic cavity. It gets filled up with fluid called amniotic fluid.
    • Flattened endodermal cells spread and line through inside of blastocystic cavity to form primary yolk sac. Cells of trophoblast form mass of cells called Extra Embryonic Mesoderm (E.E.M.) or primary mesoderm. Cavities appear in E.E.M. called EXTRAEMBRYONIC COELUM Part inside of trophoblast and outside of amniotic cavity – PARIETAL OR SOMATOPLEURIC EXTRAEMBRYONIC MESODERM Part outside the yolk sac VISCERAL OR SPLANCHOPLEURIC EXTRAEMBRYONIC MESODERM Chorion- Parietal E.E.M and overlying trophoblast is called as chorion. Amnion- Amniogenic cells forming the wall of amniotic cavity excluding the ectodermal floor form the Amnion.
    • SECONDARY YOLK SAC Yolk sac becomes much smaller with the appearance of E.E coelom and is now called secondary yolk sac. Endodermal cells become cubical now. PROCHORDAL PLATE Near the margin of the disc cubical cells of endoderm become columnar. This area is called PROCHORDAL PLATE. It determines the central axis of the embryo and also helps to distinguish future head and tail ends.
    • PRIMITIVE STREAK Ectodermal cells lying along the central axis, near the tail end begin to proliferate to form an elevation that bulges into the amniotic cavity. It is called as primitive streak. Cells in this area pass sideways and push themselves between ectoderm and endoderm to form 3rd layer called as intra- embryonic mesoderm. It spreads throughout the disc except in the region of prochordal plate. Here ectoderm and endoderm remain in contact and will form buccopharyngeal membrane. The process of formation of primitive streak & of intra embryonic mesoderm by the streak is termed gastrulation.
    • GASTRULATION
    • GASTRULATION FORMATION OF NOTOCHORD Cranial end of primitive streak becomes thickened. This thickened part of streak is called Primitive Knot, Primitive Node or Henson’s node. A depression appears in its centre which is known as blastopore.
    • Cells in the primitive knot multiply & pass between ectoderm and endoderm reaching up to caudal margin of prochordal plate. These cells form notochordal process and undergo several rearrangements to form solid rod called as notochord. As embryo enlarges notochord elongates and comes to lie in the midline, in a position to be later occupied by the vertebral column. Most of it disappears but part persists in the region of each intervertebral disc as nucleus pulposus.
    • FORMATION OF NEURAL TUBE Ectoderm above the notochord proliferates and forms Neural plate. Neural plate becomes depressed along the midline as a result of which neural groove is formed. This groove then becomes deeper. At the same time, 2 edges of neural plate come nearer each other and fuse, thus converting groove into tube. It will give rise to brain and spinal cord. It is soon divisible into cranial enlarged part, that forms brain and caudal tubular part which forms spinal cord. This process of neural tube formation is called as neurulation.
    • FORMATION OF HEAD AND TAIL FOLDS Embryonic disc develops lateral and head and tail folds to form FOREGUT, MIDGUT AND HINDGUT. Part of yolk sac endoderm is incorporated into the cranial end of embryo forming foregut. Part of yolk sac endoderm incorporated into caudal end forms the hindgut. Intervening portion is the midgut which communicates with yolk sac through yolk stalk.
    • FOLDING OF EMBRYO
    • DERIVATIVES OF VARIOUS GERM LAYERS Derivatives of Ectoderm Skin, including its pigments cells (from neural crest). Mucous membrane of lips; cheeks, gums, part of the floor of the mouth, part of the palate, nasal cavities and paranasal sinuses. Anterior epithelium of cornea, epithelium of conjunctiva, epithelial layers of ciliary body and iris. Outer layer of tympanic membrane, epithelial lining of membranous labyrinth including the special end organs. Exocrine: Sweat glands, sebaceous glands, parotid, mammary gland, lacrimal gland. Endocrine: Hypophysis cerebri, adrenal medulla. Hair, Nails. Enamel of teeth. Lens of eye; musculature of iris; vitreous humor. Nervous system including all neurons, neuroglia and Schwann cells. Pia-arachnoid. Branchial cartilage.
    • Derivatives of Endoderm Epithelium of part of the mouth, part of the palate, tongue, tonsil, pharynx, oesophagus, stomach, small and large intestines, and upper part of anal canal. Epithelium of pharyngo-tympanic tube, middle ear, inner layer of tympanic membrane, mastoid antrum and air cells. Epithelium of respiratory tract. Epithelium of gall bladder and extrahepatic duct system, epithelium of pancreatic ducts. Endocrine: Thyroid, parathyroid, thymus, islets of Langerhans. Exocrine: Liver, pancreas, glands in wall of gastrointestinal tract, greater part of prostate (except inner glandular zone) and its female homologous.
    • Derivatives of Mesoderm All connective tissues including loose areolar tissue filling the interstices between other tissues, superficial and deep fascia, ligaments, tendons, aponeuroses, and the dermis of skin. Specialized connective tissues like adipose tissue, reticular tissue, cartilage and bone. Dentine of teeth. All muscle – smooth, striated and cardiac- except the musculature of the iris (ectoderm). Heart, all blood vessels and lymphatics, and blood cells. Substance of cornea; sclera, choroids, ciliary body and iris. Dura mater, pia-arachnoid, microglia, etc. Tympanic membrane is derived from both Ectoderm and Endoderm.
    • FORMATION OF BRANCHIAL ARCHES After the establishment of head folds, the foregut is bounded ventrally by the pericardium, and dorsally by the developing brain. Cranially, it is at first separated from the stomatodaeum by buccopharyngeal membrane. When the membrane breaks down, the foregut opens to the exterior through the stomatodaeum. At this stage, the head is represented by the bulging caused by developing brain, while pericardium may be considered as occupying the region of future thorax. The two are separated by the stomatodaeum which is the future mouth. It is apparent that neck is not present yet.
    • Pharyngeal arches
    • The neck is formed by the elongation of the region between the stomatodaeum and the pericardium. This is achieved partly, by a ‘descent’ of the developing heart. However, this elongation is due mainly to the appearance of a series of mesodermal thickenings in the wall of the cranial most part of the foregut. These are called as pharyngeal, or branchial arches.
    • At this stage, the endodermal wall of the foregut is separated from the surface ectoderm by a layer of mesoderm. Soon, thereafter, the mesoderm comes to be arranged in the form of six bars that run dorso-ventrally in the side wall of the foregut. Each of these bars grows ventrally in the floor of the developing pharynx and fuses with the corresponding bar of opposite side to form a pharyngeal or branchial arch. In the interval between any two adjoining arches, the endoderm extends outwards in the form of a pouch (endodermal or pharyngeal pouch) to meet the ectoderm which dips into this interval as an ectodermal cleft. At first there are six arches. The fifth arch disappears and only five remain. Each pharyngeal arch contains a skeletal element (cartilage that may later form bone), striated muscle supplied by nerve of the arch, and an arterial arch
    • STRUCTURES FORMED IN MESODERM OF EACH ARCH
    • NERVE SUPPLY OF PHARYNGEAL ARCHES
    • STRUCTURES & DERIVATIVES OF VARIOUS ARCHES
    • FATE OF ECTODERMAL CLEFTS After the formation of the pharyngeal arches, the region of the neck is marked on the outside by a series of grooves, or ectodermal clefts. The dorsal part of the first cleft (between the first and second arches) develops into the epithelial lining of the external acoustic meatus. The pinna (or auricle) is formed from a series of swellings that arise on the first and second arches, where they adjoin the first cleft. The ventral part of this cleft is obliterated.
    • FATE OF ENDODERMAL POUCHES First Pouch: Its ventral part is obliterated by formation of tongue. Its dorsal part receives a contribution from the dorsal part of the second pouch, and these two together form a diverticulum that grows towards the region of the developing ear. This diverticulum is called the tubotympanic recess. The proximal part of this recess gives rise to the auditory (pharyngotympanic) tube, and the distal part to the middle ear cavity, including the tympanic antrum.
    • Endodermal pouches
    • Second Pouch The epithelium of the ventral part of this pouch contributes to the formation of tonsil. The dorsal part takes part in the formation of the tubotympanic recess. Third Pouch This gives rise to the inferior parathyroid glands, and the thymus. Fourth Pouch This gives origin to the superior parathyroid glands, and may contribute to the thyroid gland.
    • Fifth Or Ultimobranchial Pouch A fifth pouch is seen for a brief period during development. In some species it gives rise to the ultimobranchial body. Its fate in man is controversial. It is generally believed to be incorporated into the fourth pouch, the two together forming the caudal pharyngeal complex. The superior parathyroid gland arises from this complex. The complex probably also gives origin to the parafollicular cells of the thyroid gland.
    • DEVELOPMENT OF FACE Developing brain and pericardium form two bulgings on the ventral aspect of embryo which is separated by stomatodaeum. The floor of stomatodaeum is formed by buccopharyngeal membrane which separates it from foregut. Mesoderm covering developing forebrain proliferates and forms a downward projection called frontonasal process. So finally face has to develop from: Frontonasal process. Mandibular arch which gives a bud from dorsal end. This is maxillary process which grows ventromedially cranial to the main part of the arch; now called mandibular process.
    • DEVELOPMENT OF FACE
    • NASAL PLACODES The ectoderm overlying the frontonasal process shows bilateral thickenings above the stomatodaeum called nasal placodes. They soon sink to form nasal pits. The edges of the pits get raised above the surface. Medial raised edge- median nasal process Lateral raised edge- lateral nasal process
    • LOWER LIP The mandibular processes of two sides grow towards each other and fuse in the midline to form the lower margin of stomatodaeum. The fused mandibular processes give rise to lower lip and lower jaw.
    • UPPER LIP Each maxillary process now grows medially and fuses, first with lateral nasal process and then with median nasal process. The two fuse with each other. In this way nasal processes are cut off from the stomatodaeum. Maxillary process grows and frontonasal process becomes much narrower and the two nares come closer. Mesodermal bases of lateral part of the lip are formed from maxillary process. Overlying skin of lateral part of lip develops from ectoderm covering this process A mesodermal base of median part of the lip called philtrum, is formed from frontonasal process. The ectoderm of the maxillary process overgrows this mesoderm to meet that of opposite side in the midline.
    • NOSE Anterior nares are formed when nasal pits are cut off from stomatodaeum by the fusion of maxillary process with median nasal process. Anterior nares approach each other because of the frontonasal process becoming narrower. Mesoderm becomes heaped up in the median plane to form prominence of the nose. As the nose becomes prominent, anterior nares come to open downwards instead of forwards.
    • NASAL CAVITIES The intervening tissue between the two nasal processes becomes much thinned to form the nasal septum. The nasal cavities are separated from the mouth by the development of the palate The lateral wall of the nose is derived on each side from the lateral nasal process The nasal conchae appear as elevations on the lateral wall of each nasal cavity Extension of the nasal pits lead to formation of the nasal cavity. Nasal pits deepen to form nasal sac which expand both dorsally and caudally. Dorsal part of this sac is separated from stomatodaeum by a thin bucconasal membrane which soon breaks down. The nasal sac has a ventral orifice that opens onto the face forming anterior nares. The dorsal orifice opens into stomatodaeum forming posterior nares.
    • CHEEKS After the formation of the upper & lower lips, the stomatodaeum is very broad. In its lateral part, it is bounded above by the maxillary process & below by the mandibular process. These processes undergo progressive fusion to form the cheeks. NASOLACRIMAL DUCT The fusion of the maxillary process not only occurs in the region of lip but also extends up to medial angle of eye. This line of fusion is marked by a groove called naso-optic furrow. A strip of ectoderm gets buried along this furrow and gives rise to nasolacrimal duct.
    • EYE On the ventral side of developing forebrain lateral and cranial to nasal placodes develops an ectodermal thickening called lens placode. It sinks below the surface and is cut off from surface ectoderm. The developing eyeball produces a bulging which are first directed laterally and then lie in angle between maxillary process and lateral nasal process. Eyelids are derived from folds of ectoderm and by mesoderm enclosed within the folds.
    • EXTERNAL EAR It is formed from the dorsal part of the first ectodermal cleft and mesodermal thickenings (called tubercles or hillocks) which appear on the mandibular and hyoid arches where they adjoin this cleft. Pinna is formed by fusion of these thickenings. When first formed, pinna lies caudal to the developing jaws. It is pushed upward and backward to its definitive position due to great enlargement of the mandibular processes.
    • DEVELOPMENT OF FACIAL SKELETON The skeletal system develops from the mesodermal germ layers during 3rd week of development. Somites form on each side of neural tube. It becomes differentiated into sclerotome, dermatome, myotome. At the end of 4th week, the sclerotome cells become polymorphous and form loosely woven tissue known as MESENCHYME or embryonic connective tissue. The characteristic feature of mesenchymal cells is that, it can migrate and differentiate into many type of cells. Such as fibroblasts, chondroblasts, osteoblasts. Neural crest cells in the head region differentiate into mesenchyme and participate in the formation of bones of the face.
    • MEMBRANOUS NEUROCRANIUM (DESMOCRANIUM) The sides of roof of skull develop from mesenchyme investing the brain and undergo membranous ossification. As a result a number of flat membranous bone are formed which are characterized by the presence of needle like bone spicules. The membranous bones enlarges by apposition of new layers on the outer surface and by simultaneous osteoclastic resorption from the inside.
    • CARTILAGENOUS NEUROCRANIUM This part of the skull consists initially of number of separate cartilages which fuse and ossify by endochondral ossification, Example- the base of the skull. CARTILAGE FORMING STRUCTURE Parachondral Cartilage & Occipital Sclerotomes Occipital Bone Hypophyseal Cartilage Body of Sphenoid Trabeculae Cranii Ethmoid bone
    • MESENCHYMAL CONDENSATION FORMING STRUCTURE Ala Orbitalis Lesser Wing of Sphenoid Ala Temporalis Greater Wing of Sphenoid Periotic Capsule Peterous & Mastoid Part of Temporal Bone
    • VISCEROCRANIUM It consists of bone of face and is formed mainly by cartilages of first two pharyngeal arches. Dorsal portion of the first arch (maxillary process) gives rise to maxilla, zygomatic bone and part of temporal bone. The ventral portion is known as Meckel’s cartilage or mandibular process. The mesenchyme around Meckel’s cartilage condenses and ossifies by intramembranous ossification, to give rise to mandible. Meckel’s cartilage disappears except in sphenomandibular ligament. The dorsal tip of mandibular process along with that of the second arch give rise to incus, malleus and stapes. At first face is small in comparison with neurocranium. This is caused by virtual absence of paranasal sinuses and small size of the bones.
    • VISCEROCRANIUM
    • ORIGIN OF BONES OF HEAD & NECK Endochondral Conversion of mesenchymal connective tissue first into a cartilage and then bone is called as endochondral ossification. Examples of bones formed by endochondral ossification are- Squamous & basilar part of Occipital bone except supranuchal squamous part. Occipital condyle Sphenoid (Medial pterygoid plate, lesser wing of sphenoid, portion of greater wing of sphenoid- alisphenoid cartilage, anterior & posterior part of sphenoid body. Ethmoid Temporal (Petrous and Styloid). Condyle of mandible. Ear ossicles. Hyoid
    • Intra-membranous Conversion of mesenchymal connective tissue, usually in membranous sheaths, directly into osseous tissue is known as intramembranous ossification. Examples of bones formed by intramembranous ossification are- Supranuchal squamous part of occipital bone. Sphenoid- Greater wing, lateral pterygoid plate. Temporal- squamous & tympanic. Body of mandible. Nasal, Lacrimal, Vomer, Frontal, Parietal. Maxilla, Palatine, Zygomatic Bones
    • CENTRES OF OSSIFICATION In both types of bone formation, ossification begins at definite points known as Centres of Ossification. A primary centre of ossification is first to appear mostly before birth, which may be followed by one or more secondary centres, generally postnatally, all of which coalesce into a single bone.
    • MAXILLA A primary intramembranous ossification centre appears for each maxilla in 8th week at the termination of infraorbital nerve just above canine tooth. Secondary cartilages appear in the end of 8th week in the region of zygomatic and alveolar process that ossify and fuse with primary intramembranous centre. 2 intramembranous premaxillary centers appear anteriorly on each side and fuse with primary maxillary centre Maxilla has different units on which its growth depends Alveolar unit –teeth Nasal unit- septal cartilage Orbital unit –eyeball Pneumatic unit-maxillary sinus expansion
    • MANDIBLE First structure to develop in the primordium of the lower jaw is the mandibular division of trigeminal nerve. Mandible is derived from ossification of an osteogenic membrane formed from ectomesenchymal condensation at 5-6th weeks of development. Cartilage of first arch is Meckel’s cartilage. A single ossification centre for each half of mandible arises in 6th week at the bifurcation of inferior alveolar nerve and artery into mental and incisive branches. Ossifying membrane which is located lateral to Meckel’s cartilage ossifies dorsally and ventrally to form body and ramus of the mandible. Ossification stops dorsally at site that will later become lingula.
    • Core of Meckel’s cartilage diverges dorsally to end in tympanic cavity of middle ear where it ends as ear ossicles- malleus and incus. Major portion of Meckel’s cartilage disappears. A part transforms into sphenomandibular ligament and anterior malleolar ligament. Secondary cartilages appear between 10 and 14 week of intra uterine life to form head of condyle, part of coronoid and mental protuberence. Coronoid cartilage later becomes incorporated into ramus and disappears before birth. Condylar cartilages appear during 10th week of development as primordia of future condyle.
    • PARANASAL SINUSES Sinuses appear as diverticula’s from the nasal cavity. The diverticula’s invade the bone after which they are named.
    • PALATE The palate is formed by the contributions of the : Maxillary process Palatal shelves given off by the maxillary process Frontonasal process which gives rise to the premaxillary region while the palatal shelves form the rest of the palate From each maxillary process a plate like shelf grows medially called as palatal process. Each palatal process fuses with each other in the midline and also with the posterior margin of primitive palate (which is formed from the frontonasal process). The medial edges of palatal processes fuse with the lower edge of the nasal septum thus separating two nasal cavities from each other and from the mouth. Medial growth of the palatal shelves & their union is prevented by the presence of the tongue, thus the palatal shelves grow vertically downwards initially. During the 7th week of intrauterine life, a transformation in the position of the palatal shelves occurs i.e from a vertical to a horizontal position.
    • Palate
    • The connective tissue of the palatal shelves intermingle with each other resulting in their fusion around the 8 ½ weeks of intra-uterine life Mesoderm in the palate undergoes intramembranous ossification to form the hard palate. Ossification does not extend into posterior most portion which remains as the soft palate.
    • TEMPOROMANDIBULAR JOINT TMJ develops initially from widely separated temporal and condylar blastema that grows towards each other. TMJ has a fibrous tissue rather than hyaline cartilage on the articular facets of temporal fossa and condyle. Between 10th to 12th week, mesenchyme between growing secondary cartilage of condyle and temporal bone differentiate into fibrous tissue. During 12th week 2 clefts develops in the interposed vascular fibrous connective tissue forming two joint cavities and thereby defining intervening articular disc.
    • Primary and secondary joint
    • Compression of central portion of articular disc occurs as it takes biconcave shape. Tissue of disc becomes continuous with tendon of lateral pterygoid anteriorly. Posteriorly it gets attached to portion of Meckel’s cartilage which differentiates into malleus. A condensation of mesenchyme forms the analogue of the joint capsule thereby isolating the joint with its synovial membrane from its surrounding tissues.
    • TONGUE Tongue develops in relation to the pharyngeal arches in the floor of developing mouth. Medial most part of mandibular arches proliferates to form 2 lingual swellings. Two lingual swellings are separated by a median swelling called tuberculum impar. Anterior 2/3rd of tongue is formed by fusion of: Two lingual swellings Tuberculum impar Midline swelling seen in relation to medial ends of 2nd, 3rd, and 4rth arches form hypobranchial eminence. This shows subdivision into a cranial part (related to 2nd and 3rd arches) called copula, and a caudal part which forms epiglottis.
    • Posterior 1/3rd is formed from cranial part of hypobranchial eminence. Posterior most part is derived from fourth arch. Musculature of the tongue develops from occipital myotomes. Initially epithelium is single layered but later becomes stratified and papillae become evident. Taste buds are formed in relation to terminal branches of innervating nerve fibers.
    • NERVE SUPPLY OF TONGUE Sensory Lingual nerve for anterior two –third Glossopharyngeal nerve for posterior one –third Motor All the muscle except palatoglossus are supplied by hypoglossal nerve Palatoglossus is supplied by cranial part of accessory nerve Taste Chorda tympani nerve for anterior two –third Glossopharyngeal nerve for posterior one –third
    • Anterior two–third part of tongue Develops from two lingual swellings & tuberculum impar of first branchial arch. Supplied by lingual nerve and Chorda tympani nerve Posterior one–third part of tongue Develops from hypobranchial eminence of third branchial arch. Supplied by glossopharyngeal nerve. Posterior most part Develops from fourth branchial arch. Supplied by vagus nerve
    • SALIVARY GLANDS Oral epithelium buds invade the underlying mesenchyme. All parenchymal tissue of the glands arises from proliferation of oral epithelium that may be either ectodermal or endodermal in origin. Stroma of glands originates from mesenchyme that may be either mesodermal or neural crestal in origin. Following the initial bud formation, there is elongation of epithelial cell cords to form the main duct primordia, branching produces arborization and terminal bulbs. It is first solid and later canalises It branches repeatedly to form duct system. Terminal parts of the duct system develop into secretory acini Parotid arises in relation to line along which maxillary and mandibular processes fuse to form cheeks and is considered ectodermal Submandibular and sublingual glands arise in relation to linguogingival sulcus and are considered endodermal in origin.
    • TONSILS 2nd pharyngeal pouch gives rise to palatine tonsil. Pharyngeal and lingual tonsils develop in the mucosa of posterior wall of the pharynx and root of tongue. Lateral extension of lymphoid tissue posterior to the opening of auditory tube forms tubal tonsil. Invasion of lymphoid tissue into the palatine, posterior pharyngeal and lingual tonsillar region takes place during 5th month I.U.L.
    • DEVELOPMENTAL ANOMALIES OF FACE
    • DEVELOPMENTAL ANOMALIES OF FACE Formation of face involves fusion of diverse components. This fusion is often incomplete and gives rise to various abnormalities. 1. HARE LIP Upper lip of hare has normally a cleft hence the term hare lip is used for such defects. When one or both the maxillary processes do not fuse with medial nasal process, this gives rise to defects in upper lip. Defective development of frontonasal process give rise to midline cleft of upper lip When two mandibular processes do not fuse with each other lower lip shows defect in midline. 2. OBLIQUE FACIAL CLEFT Nonfusion of maxillary and lateral nasal processes give rise to cleft running from medial angle of eye to the mouth. Thus nasolacrimal duct is not formed. (Various genes and loci have been identified as responsible for orofacial clefts. These include 1q, 2p, 4q, 6p, 14q, 17q, and 19q)
    • FACIAL CLEFTS unilateral bilateral oblique
    • 3. MACROSTOMIA Inadequate fusion of maxillary and mandibular process leads to macrostomia 4 MICROSTOMIA Too much fusion may lead to microstomia
    • 5. NOSE Nose may be bifid or one half may be absent. Rarely nose forms a cylindrical projection or proboscis. 6. MANDIBULOFACIAL DYSOSTOSIS Entire first arches may remain underdeveloped on one or both sides, affecting the lower eyelid, maxilla, mandible or external ear. The prominence of cheek is absent and ear may be displaced caudally and ventrally. This condition is MANDIBULOFACIAL DYSOSTOSIS.
    • 7. FACIAL HEMI HYPERTROPHY One half of the face may be underdeveloped leading to facial hemi atrophy or overdeveloped leading to facial hemi hypertrophy. 8. RETROGNATHIA Mandible may be small as compared to rest of face resulting in a receding chin (retrognathia). 9. CONGENITAL TUMORS These may be present in face. They may represent attempt at duplication of some parts.
    • 10. HYPERTELORISM Eyes may be widely separated (hypertelorism) 11. DOUBLE LIP Lips may show congenital pits or fistulae. Lips may be double
    • ANOMALIES OF NASAL CAVITY There may be atresia of cavity at the anterior nares or at the posterior nares or in the cavity proper. This may be unilateral or bilateral. There may be absence of nasal passages. Congenital defects in the cribriform plate of the ethmoid bone may lead to a communication between cranial cavity and nose. Nasal septum may be absent or may be deviated. Nasal cavity may communicate with the mouth.
    • ANOMALIES OF TONGUE Tongue may be too large (macroglossia) or too small (microglossia). Very rarely tongue may be absent (aglossia). Apical part of tongue may be attached to floor of mouth by an overdeveloped frenulum.condition is ankyloglossia or tongue tie. Occasionally tongue may be attached to palate (ankyloglossia superior). A red, rhomboid shaped smooth zone may be present on tongue in front of foramen caecum because of persistence of tuberculum impar (median rhomboid glossitis). Thyroid tissue may be present in the tongue either under mucosa or within the muscles. Remnants of thyroglossal duct may form cysts at the base of tongue (Thyroglossal tract cyst). Surface of tongue may show fissures (fissured tongue).
    • ANOMALIES OF LIPS Congenial lip and commissural pits and fistulae Double lip Cleft lip and palate Chelitis glandularis Chelitis granulomatosa or meischer’s syndrome Hereditary intestinal polyposis or peutz jeghers syndrome
    • DEVELOPMENTAL DISTURBANCES OF SALIVARY GLANDS Aplasia Xerostomia Hyperplasia of palatal glands Artesia Aberrancy Developmental lingual mandibular salivary gland depression (static cavity or Stafne cyst)