Development of Pharyngeal Arches PDF

Subject: Histology and embryology Lecture: Development of the pharyngeal arches and pouches dr Kamila Misiakiewicz-Has First year, Faculty of Medicine, 2020/2021 Department of Histology and Embryology Pomeranian Medical University i...

Subject: Histology and embryology Lecture: Development of the pharyngeal arches and pouches dr Kamila Misiakiewicz-Has First year, Faculty of Medicine, 2020/2021 Department of Histology and Embryology Pomeranian Medical University in Szczecin  Head freck The most typical feature in development of the head and neck is formed by pharyngeal or branchial arches. They appear in the 4th 5th 4th and 5th week and 5th weeks of development. 25th day 28th day 5th week Initially, they consist of bars of mesenchymal tissue separated by clefts (pharyngeal clefts). With development of arches and clefts, a number of outpocketings, the pharyngeal pouches, appear along the lateral walls of the pharyngeal gut (the most cranial part of the foregut) and penetrate the surrounding mesenchyme.  Pharyngeal arches Each arch consists of a core of mesenchyme covered on the outside by surface ectoderm and on the inside by epithelium of endodermal origin. The core contains mesenchyme derived from paraxial and lateral plate mesoderm and neural crest cells which migrate into the arches. Each arch is characterized by its own muscular components. The muscular components of each arch have their own cranial nerve. Each arch has its own arterial component.  First pharyngeal arch  dorsal portion – maxillary process  Ventral portion – the mandibular process which contains Meckel’s cartilage. Maxillary process Meckel’s cartilage Meckel’s cartilage disappear except for two portions at its dorsal end and form the Pharyngeal incus and malleus. cleft Mesenchyme of the maxillary process gives rise to the premaxilla, maxilla, zygomatic bone Mandibular arch Hyoid arch The mandible is also formed by membranous ossification of Cardiac mesenchymal tissue bulge  & -Mandibuleu Arch 2nd (hyoid arch) – (Reichert’s cartilage) arch The cartilage gives rise to: Maxillary  stapes  styloid process of the temporal bone  stylohyoid ligament  lesser horn of the hyoid bone leser 3rd pharyngeal arch the cartilage gives rise to:  lower part of the body of the hyoid bone  greater horn of the hyoid bone Grab 4th and 6th pharyngeal arch Cartilaginous components fuse to form:  cartilages of theClarynx  thyroid  cricoid  arytenoid, corniculate and cuneiform  Pharyngeal pouches The human embryo has 4 pairs of pharyngeal pouches. The 5th pair is absent or rudimentary. Epithelial endodermal lining of the pouches Pharyngeal pouches gives rise to a number of organs. Pharyngeal clefts First pharyngeal pouch  Forms a stalk-like diverticulum, the tubotympanic recess that comes in contact with the epithelial lining of the 1st pharyngeal cleft (future external auditory meatus)  The distal portion widens – middle ear cavity  The proximal portion remains narrow forming the auditory (eustachian) tube. Second pharyngeal pouch The epithelial cells proliferate and form buds that penetrate into the surrounding mesenchyme.  during the 3rd and 5th months the palatine tonsil is infiltrated by lymphatic tissue. End and 5th  3rd pouch Third pharyngeal pouch Contains dorsal and ventral wing parathyroid gland  epithelium of the dorsal wing – inferior parathyroid gland (5th week)  ventral wing – part of the thymus lesser Primitive tympanic cavity Great Gresste - External Auditory Fourth pharyngeal pouch auditory tube canal  epithelium of the dorsal wing forms Palatine tonsil superior parathyroid gland Parathyroid gland (inferior)  the ventral part develops into the ultimobranchial body which is later thymus incorporated into the thyroid gland. Parathyroid Cervical sinus gland (superior) Cells of the ultimobranchial body give rise Ultimobranchial to the parafollicular (C cells). They body differentiate from the neural crest cells.  Pharyngeal clefts week 5 Pharyngol 5 The 5-week embryo is characterized by the continuation ofpouches presence of four pharyngeal clefts.  the dorsal part of the 1st cleft penetrates the underlying mesenchyme and gives rise to external auditory meatus The epithelial lining - eardrum The 2nd, 3rd and 4th clefts loose contact with the outside Temporarily, the clefts form a cavity – cervical sinus, which disappears with further development  Clinical correlations Branchial fistula When the 2nd pharyngeal arch fails to grow caudally over 3rd and 4th arches, leaving remnants of the 2nd and 3rd and 4th clefts in contact with the surface by a narrow canal. Such a fistula found on the lateral aspect of the neck, usually provides drainage for a lateral cervical cyst. External auditory meatus Cysts are remnants of the cervical sinus and are located just below the angle of the jaw. Palatine tonsil Frequently, a lateral cervical cyst is not visible at birth but becomes evident as the Lateral result of enlargement during childhood. cervical cyst External branchial fistula A lateral cervical cyst opening at the side of the neck by way of fistula. Internal branchial fistula Results from a rapture of the membrane between the 2nd pharyngeal cleft and pouch at some time during development Occur when the cervical sinus is connected to the lumen of the pharynx by a small canal, which usually opens in the tonsillar region.  Neural crest cells are essential for formation of much of craniofacial region. Disruption of crest cell development results in severe craniofacial malformations. Crest cells are easily killed by compounds such as alcohol and retinoic acid. Crest cells also contribute to the conotruncal endocardial cushions, which septate the outlow tract of the heart into pulmonary and aortic channels. Robin Seque Treacher Collins syndrome (mandibulofacial dysostosis) Robin sequence Autosomal dominant trait.  decreasing growth of the  malformed external ears mandible (micrognathia)  mandibular hypoplasia  cleft palate  lower eyelid colobomas  posteriorly placed  underdevelopment of the zygomatic tongue (glossoptosis) bones of the face – malar hypoplasia Mandlacht ele Robin-stongu mandbilln DiGeorge sequence (3rd and 4th pharyngeal pouch syndrome) – 22q Zyqumestic deletion syndrome  absence of the thymus and parathyroid gland  Cardiovascular defects  Abnormal external ears, eyes  Widely spaced eyes (hypertelorism)  Cleft palate  Small mandibule (micrognathia)  Tongue The tongue appears in embryos of approximately 4 weeks in the form of two lateral lingual swellings and one medial swelling (the tuberculum impair) (originate from the 1st pharyngeal arch). A second median swelling (the copula) (hypobranchial eminence) is formed by the 2nd, 3rd and part of the 4th arch. A third median swelling, formed by the posterior part of the 4th arch, marks development of the epiglottis. 1st arch-literal and medial swelling 2 arch Medic ↳  As the lateral lingual swellings increase in size, they overgrow the tuberculum impair and merge with each other, thus forming the anterior two-thirds (body) of the tongue.  The anterior two-thirds is separated from the posterior third by V-shaped groove, the terminal sulcus.  The posterior part (root) of the tongue originates from the 2nd, 3rd and part of the 4th pharyngeal arch. Clinical correlates Ankyloglossia (tongue-tie) - O Anky glassic artung Ans Reffers to the case where the tongue is not freed from the floor of the mounth. Normally, extensive cell degeneration occurs and the frenulum is the only tissue persisting, tying the tongue to the floor of the mouth. In the most common form of ankyloglossia, the frenulum extends to the tip of the tongue.  Face development At the end of the 4th week, facial prominences consisting primarily of neural crest-derived mesenchyme appear (I pair of pharyngeal arches).  Maxillary prominences – lateral to the stomodeum  Mandibular prominences – caudaly  The frontonasal prominence – formed by the proliferation of mesenchyme ventral to the brain vesicles Nasal (olfactory) placodes – local thickening of the surface ectoderm (on both sides of the frontonasal prominences) During the 5th week, the nasal placodes invaginate to form nasal pits and they create a ridge of tissue that surrounds each pit and forms the nasal prominences: lateral nasal prominences (on the outer edge of the pits); medial nasal prominences (on the inner edge). 6-7 week: the maxillary prominences continue to increase in size in median direction, compressing the medial nasal prominences toward the midline. The medial nasal and maxillary prominescence fuse. The upper lip is formed by the two medial nasal prominences and the two maxillary prominences. The lower lip and the jaw are formed from the mandibular prominences that merge across the midline.  Face development Prominences Structures Formed _______________________________________________________________________________ Frontonasal Forehead, bridge of nose, medial and lateral nasal promiences Maxillary Cheeks, lateral portion of upper lip Medial nasal Philtrum of upper lip, crest and tip of nose Lateral nasal Alae of nose Mandibular Lower lip  Intermaxillary segment As a result of medial growth of the maxillary prominescences, the two medial nasal prominences merge not only at the surface but also at a deeper level. The structure formed – intermaxillary segment. It is composed of:  a labial component, which forms the philtrum of the upper lip  an upper jaw component, which carries the four incisor teeth  a palatal component, which forms the triangular primary palate  Secondary palate The primary palate is derived from the intermaxillary segment. The main part of the definitive palate is formed by two shelf-like outgrows (palatine shelves) from maxillary prominences. The palatine shelves appear in the 6th week of development and are directed oblique downward on each side of the tongue. In the 7th week, the palatine shelves ascend to attain a horizontal position above the tongue and fuse with each other forming the secondary palate. Anteriorly, the shelves fuse with the triangular primary palate. 7,5 week 6,5 week 10th week  Cleft lip and cleft palate The incisive foramen is considered the dividing landmark between the anterior and posterior cleft deformatives. Those anterior to the incisive foramen include:  lateral cleft lip  cleft upper jaw  cleft between the primary and the secondary palate. Such defects are due to a partial or complete lack of fusion of the maxillary prominence with the nasal prominence on one or both sides. Those that lie posterior to the incisive foramen include cleft secondary palate and cleft uvula. Cleft palate results from a lack of fusion of the palatine shelves the third cathegory is formed by a combination of clefts lying anterior as well as posterior to the incisive foramen.  Cleft lip Normal Unilateral cleft lip Bilateral cleft involving the lip and jaw extending into the nose Caused by failure of the maxillary prominences to merge with its corresponding nasal prominences 1:1000 births 60-80% ♂  Median cleft lip Rare abnormality, caused by incomplete merging of the two medial nasal prominences in the midline  Cleft palate Palatine shelves Isolated cleft palate 1:2500 births Genetic factors contribute to cleft lip and cleft palate formation. Environmental influences may also cause orofacial clefting: - maternal hypoxia, as caused by e.g. maternal smoking, maternal alcohol abuse or some forms of maternal hypertension treatment. - seasonal causes (such as pesticide exposure) - maternal diet and vitamin intake; retinoids — which are members of the vitamin A family; - anticonvulsant drugs; - alcohol; cigarette use; nitrate compounds; organic solvents; parental exposure to lead; and illegal drugs (cocaine, crack cocaine, heroin, etc.). Folic acid can reduce the incidence of clefting !!!  Literature Sadler T.W. Langman’s Medical Embryology 2018