Presentation on theme: "Embryology of the Head, Face and Oral Cavity Face and Oral Cavity Raj Gopalakrishnan B.D.S., Ph.D. Oral and Maxillofacial Pathology Dept. of Diagnostic."— Presentation transcript:
Embryology of the Head, Face and Oral Cavity Face and Oral Cavity Raj Gopalakrishnan B.D.S., Ph.D. Oral and Maxillofacial Pathology Dept. of Diagnostic and Biological Sciences University of Minnesota School of Dentistry
Prenatal Development Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Differentiation of the Morula into Blastocyst Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Formation of Two-Layered Embryo (2 nd week of gestation) Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”. Called bilaminar germ disk Ectoderm Endoderm Pre/prochordal plate Firm union between ectodermal and endodermal cells occur at prechordal plate
Formation of Three-Layered Embryo: Gastrulation (3 rd week) Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition Triploblastic embryo
Formation of Three-Layered Embryo: Gastrulation (3 rd week) Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
First 3 weeks: Leads to formation of triploblastic embryo Next 3-4 weeks: differentiation of major tissues and organs includes head and face and tissues responsible for teeth development differentiation of nervous tissue from ectoderm differentiation of neural crest cells (ectoderm) differentiation of mesoderm folding of the embryo (2 planes-rostrocaudal and lateral)
Neural tube undergoes massive expansion to form the forebrain, midbrain and hindbrain Formation of neural tube and neural groove Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”. Neural groove
Components of the mesoderm Along the trunk paraxial mesoderm breaks up into segmented blocks called somites Each somite has: sclerotome- 2 adjacent vertebrae and disks myotome-muscle dermatome-connective tissue of the skin over the somite In the head region the paraxial mesoderm only partially fragments to form a series of numbered somatomeres which contribute to head and neck musculature Intermediate mesoderm: urogenital system Lateral plate mesoderm: connective tissue of muscle annd viscera; serous membranes of the pleura; pericardium and peritoneum; blood and lymphatic cells; cardiovascular and lympahtic systems, spleen and adrenal cortex. Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
In the head, the neural tube undergoes massive expansion to form the forebrain, midbrain and hindbrain The hindbrain segments into series of eight bulges called rhombomeres which play an important role in development of the head
Folding of the Embryo Head fold forms a primitive stomatodeum or oral cavity; leading to ectoderm lining the stomatodeum and the stomatodeum separated from the gut by buccopharyngeal membrane Onset of folding is at 24 days and continues till the end of week 4 Embryo just before folding (21 days) Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Neural Crest Cells Group of cells separate from the neuroectoderm, migrate and differentiate extensively leading to formation of cranial sensory ganglia and most of the connective tissue of the head Embryonic connective tissue elsewhere is derived form mesoderm and is known as mesenchyme But in the head it is known as ectomesenchyme because of its origin from neuroectoderm Look up Fig 2-12 in text book for derivative of the germ layers and neural crest
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition Avian neural crest cells
Head Formation Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition Rhombomeres (one of the first are the occipital somites)
Neural Crest Cell Migration Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Pharyngeal arches expand by proliferation of neural crest cells Couly et al., 2002 Forebrain (prosencephalon) Midbrain (mesencephalon) Hindbrain (rhombencephalon) r3 r5
Migration of cranial neural crest cells Anterior midbrain Posterior midbrain Anterior hindbrain Imai et al., 1996 E E E FNM TG Md
Clinical Correlation Treacher Collins Syndrome is characterized by defects of structures that are derived form the 1 st and 2 nd branchial arches and is due to failure of neural crest cells to migrate properly to the facial region
Sagittal section through a 25-day embryo Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition Buccopharyngeal membrane ruptures at 24 to 26 days
26-day embryo Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
The Developing Human by Moore & Persaud groove/cleft pouch arch membrane esophagus The pharyngeal apparatus 1 2 3 4 Branchial arches form in the pharyngeal wall (which has lateral plate mesoderm sandwiched between ectoderm and endoderm) as a result of lateral plate mesoderm proliferation and subsequent migration by neural crest cells
Sagittal view of the branchial arches with corresponding grooves between each arch. Pharyngeal pouches are seen in the wall of the pharynx. The aortic arch vasculature leads from the heart dorsally through the arches to the face
Fate of the Pharyngeal Grooves and Pouches First groove and pouch: external auditory meatus tympanic membrane tympanic antrum mastoid antrum pharyngotympanic or eustachian tube 2 nd, 3 rd and 4 th grooves are obliterated by overgrowth of the second arch forming a cervical sinus – if persists forms the branchial fistula that opens into the side of the neck extending form the tonsillar sinus 2 nd pouch is obliterated by development of palatine tonsil 3 rd pouch: dorsally forms inferior parathyroid gland ventrally forms the thymus gland by fusing with the counterpart from opposite side
4 th pouch: dorsal gives rise to the superior parathyroid gland ventral gives rise to the ultimobranchial body (which gives rise to the parafollicular cells of the thyroid gland) 5 th pouch in humans is incorporated with the 4 th pouch
(A) Tissue from arch II and V growing towards each other (arrows) to make branchial arches and grooves disappear (B) Resulting appearance following overgrowth (C) Contribution of each pharyngeal pouch
Anatomy of the Branchial Arches Cartilage of 1 st arch: Meckel’s Cartilage of 2 nd arch: Reichert’s Other arches not named Some mesenchyme around cartilage gives rise to striated muscle Each arch also has an artery and nerve Nerve: two components (motor and sensory) Sensory nerve divides into 2 branches: 1.Posttrematic branch: covers the anterior half of the arch epithelium 2.Prettrematic: covers the posterior half of the arch epithelium Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Meckel’s cartilage: Has a close relationship with the developing mandible BUT DOES NOT CONTRIBUTE TO IT Indicates the position of the future mandible. The mandible develops by intramembranous ossification. The malleus and the incus develop by endochondral ossification of the dorsal aspect of this cartilage. Innervation: V cranial nerve Reichert’s: Dorsal end: stapes and styloid process Ventral end: lesser horns of hyoid bone and superior part of the body of the hyoid bone Innervation: VII cranial nerve Cartilage of the 3 rd arch: inferior part of the body and greater horns of the hyoid bone Cartilage of 4 th and 6 th arches: fuse to form the laryngeal cartilage
Table obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Aortic Vasculature Development (A)At 4 weeks the anterior vessels have passed through each branchial arch tissue and have disappeared. The pouches project laterally between each arch. (B)At 5 weeks the 3 rd branchial arch vessel becomes the common carotid, which supplies the face by means of the internal carotid and stapedial arteries. Face, Neck and Brain are supplied by the common carotid through internal carotid. But by 7 weeks the circulation of face and neck shifts from the internal carotid to external carotid. The internal carotid continues to supply the brain.
Details of the aortic arch changes during early development. Aortic arch vessels numbers 1,2 and 5 disappear. Arch 3 becomes the common carotid artery. Arch 4 becomes the dorsal aorta and enlarges so that the common carotid arises from the aorta. Arch 6 becomes the right and left pulmonary arteries
Shift in the vascular supply to the face (A)Face and brain are supplied first by the internal carotid artery (B)Facial vessels detach from the internal carotid and attach to the external carotid
Muscle cells in the first arch become apparent during the 5 th week and begin to spread within the mandibular arch into each muscle site’s origin in the 6 th and 7 th week. These form the muscles of mastication – masseter, medial pterygoid, lateral pterygoid and temporalis muscle. They all relate to the developing mandible By 7 weeks the muscles of 2 nd arch grow upward to form the muscles of face. As these muscles grow and expand they forms sheet over the face and forms the muscles of facial expression
Facial muscles grow from the 2 nd branchial arch to cover the face, scalp and posterior to the ear Masticatory muscles of the mandibular arch
Cartilages derived from the branchial arches Arch 1: Meckel’s cartilage and incus Arch 2: Stapes, stylohyoid and lesser hyoid Arch 3: Greater hyoid Arch 4 and 6 thyroid and laryngeal cartilage
Congenital auricular sinuses and cysts Branchial cysts Branchial sinuses Branchial fistula Branchial vestiges (cartilaginous or bony remnants) Branchial cysts Anomalies of the head and neck Dermatlas
Apparent fusion of facial processes by elimination of furrows True fusion of facial processes by breakdown of surface epithelium Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Development of the Face The face develops between the 24th and 38th days of gestation On 24 th day, the 1 st branchial arch divides into maxillary and mandibular arches Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Frontonasal process Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Middle portion of the upper lip: Formed by the fusion of the medial nasal process of both sides along with the frontonasal process Lateral portion of the upper lip: Fusion of the maxillary processes of each side and medial nasal process Lower lip: Formed by the fusion of the two mandibular processes Formation of the Lips Unusual fusion between maxillary process and lateral nasal process leading to canalization and formation of the nasolacrimal duct
Human embryo at 7 weeks Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Pituitary Gland Development Ectodermal in origin and develops from 2 sources: 1.An upgrowth from the ectodermal roof of the stomatodeum called hypophysial diverticulum (Rathke’s Pouch) - adenohypophysis 2.A downgrowth from the neuroectoderm of the diencephalon called the neurohypophysial diverticulum – neurohypophysis During the 4 th week of development, a hypophysial diverticulum (Rathke’s pouch) projects from the roof of the stomatodeum and lies adjacent to the floor (ventral wall) of the diencephalon. By the 5 th week, this pouch has elongated and has become constricted at its attachment to the oral epithelium and is in contact with the infundibulum (derived from the neurohypophysis)
Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Derivation and Terminology of the Pituitary Gland Oral Ectoderm AdenohypophysisPars distalis ( hypophysial diverticulum (glandular portion) Pars tuberalis from roof of stomodeum) Pars intermedia NeuroectodermNeurohypophysisPars nervosa (neurohypophysial (nervous portion)Infundibular stem diverticulum fromMedian eminence floor of diencephalon ) Clinical Significance: Craniopharyngiomas develop from remnants of stalk of hypophysial diverticulum (in pharynx of sphenoid bone)
Formation of the palate (weeks 7 to 9) Palate develops from the primary palate and the secondary palate The primary palate develops at about 28 days of gestation Primary palate develops from the frontonasal and medial nasal processes and eventually forms the premaxillary portion of the maxilla The secondary palate develops between 7 th and 8 th week of gestation and completes in the 3 rd month The critical period of palate development is from the end of 6 th week till the beginning of 9 th week
Formation of the secondary palate (starts between 7 to 8 weeks and completed around 3 months) Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Formation of the Tongue The tongue begins to develop at about 4 weeks. The oral part (anterior two-thirds) develops from two distal tongue buds (lateral lingual swellings) and a median tongue bud (tuberculum impar) [1st branchial arch]. Innervation: V nerve The pharyngeal part develops from the copula and the hypobranchial eminence [2nd, 3rd and 4th branchial arches]. Innervation: IX cranial nerve The line of fusion of the oral and pharyngeal parts of the tongue is roughly indicated in the adult by a V-shaped line called the terminal sulcus. At the apex of the terminal sulcus is the foramen cecum. Muscles of the tongue develop form the occipital somites and innervated by hypoglossal nerve
Lingual swelling Tuberculum impar Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
The lingual papillae appear by the end of 8 th week Vallate and foliate papillae appear first, fungiform and filiform (10-11 weeks) papillae appear later Taste buds develop during the 11 to 13 weeks by inductive interaction between epithelial cells of the tongue and invading gustatory nerve cells from chorda tympani, glossopharyngeal and vagus nerves
Thyroid gland development (4 to 7 weeks) Figures obtained from “Before We Were Born; Moore and Persaud, 6 th edition, 2003”.
Fate of Meckel’s Cartilage Posterior – malleus of the inner ear Sphenomandibular ligament Anteriorly, may contribute to mandible by endochondral ossification (some evidence) Rest are resorbed completely
Three secondary (growth) cartilages govern further growth of mandible until birth 1.Condylar cartilage (most important) 2.Coronoid cartilage 3.Symphysial cartilage Secondary Cartilages
Appears during 12 th week and occupies most of the ramus and is quickly ossified by endochondral ossification, with a very thin layer of cartilage present in the condylar head. This remnant persists until 2 nd decade of life and is important for growth of mandible Appears at 4 months and disappears immediately Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 th edition
Development of Maxilla Develops from one center of ossification in maxillary process of the 1 st branchial arch Center of ossification is angle between the divisions where the anterosuperior dental nerve is given off from inferior orbital nerve from where it spreads posteriorly, anteriorly and superiorly No arch cartilage is present, so maxilla develops in close association with the nasal cartilage One secondary cartilage also contributes to maxilla development: zygomatic cartilage