DEVELOPMENT OF PHARYNGEAL ARCHES Dr. Sangeeta Kotrannavar Assistant Professor Dept. of Anatomy USM-KLE IMP Belagavi Objectives • Describe the development of the Pharyngeal Arches and its derivatives Pharyngeal Arches - Early development • By the end of the fourth week, 4 pairs of pharyngeal arches are visible externally • These embryonic structures contribute to the formation of the lateral and ventral regions of the head and neck Pharyngeal Arches – Early development • Fourth week A.25 days, B.28days • Derived from Mesodermal tissue – give rise to musculature of face & neck • Neural crest cells • Most skeletal and connective tissue in H&N. • Series of surface elevations are seen caudal to stomatodeum (future mouth) & lateral to the developing pharynx Pharyngeal Arches. • These grows ventrally & fuse with opposite arch in the floor of primitive pharynx. Pharyngeal Apparatus Pharyngeal=branchial arches=Gill Consists of : • Pharyngeal arches (Mesoderm) • Pharyngeal pouches (Endoderm) • Pharyngeal grooves (Ectoderm) • Pharyngeal membrane. Pharyngeal arch • Initially six pharyngeal (1-6) arches seen • Soon fifth arch disappears and is not visible on the surface of the embryo • Five pharyngeal arches left • Derived from Mesoderm Structure of Pharyngeal arch Each pharyngeal arch consists of Mesenchymal core centrally Ectoderm externally Endoderm internally Pharyngeal arch components A. A cartilaginous rod that forms the skeleton of the arch. B. A muscular component that differentiates into muscles of head & neck. C. A nerve that supplies the mucosa & muscles derived from the arch D. An aortic arch artery that arises from truncus arteriosus of primordial heart. Derivatives of the pharyngeal arch cartilages • Derived - Mostly from mesenchyme of neural crest cells. • Cartilaginous bar is enveloped by perichondrium. • During development • Some remain as cartilages. • some degenerates & its perichondrium persists as ligaments. • some are converted into bones by intracartilaginous or intramembranous methods of ossification. Derivatives of the pharyngeal arch cartilages 1.First arch- Mandibular / Meckel's cartilage Forms most of facial skeleton 1. First arch / Mandibular Prominence / Meckel's cartilage M - M Ventral ventral end Mandible (membranous ossification) Dorsal end Incus and malleus (middle ear) Middle sphenomandibular lig. & ant. lig.of malleus. Dorsal Maxillary Prominence Maxilla, zygomatic, palate & part of temporal bone. 2.Second arch - Hyoid arch / Reichert’s cartilage S – S H Dorsal part stapes, styloid process of temporal bone. Middle Stylohyoid lig. Ventral part Lesser (smaller) horn and upper (superior) part of the body of hyoid 3. Third arch Greater horn & lower part of body of hyoid bone 4.Fourth arch lamina of thyroid cartilage. 6.Sixth arch 4+5 A -Larynx cricoid, arytenoid, corniculate & cuneiform cartilage of the larynx except epiglottis. Derivatives of the pharyngeal arch muscles First (mandibular) M - Mast Derivatives of the pharyngeal arch muscles Second arch S – Fac Derivatives of pharyngeal arch muscles Third arch • forms stylopharyngeus Fourth arch • forms muscles of palate (except-tensor veli palatini), • constrictors muscles of pharynx & • cricothyroid(Larynx) Sixth arch • forms all intrinsic muscles of the larynx except cricothyroid. Derivatives of the pharyngeal arch nerves • Each nerve innervates - corresponding arch • In lower animals each arch nerve divides into post and pre trematic nerve. • In human embryo –seen only in 1st arch. • Motor branches to the muscles • Sensory branches to skin and mucous membrane Derivatives of pharyngeal arch nerves 1st - maxillary &mandibular divisions of the fifth (trigeminal) V 5 2nd arch - facial nerve VII 7 3rd arch - glossopharyngeal nerve IX 9 4th arch - superior laryngeal, branch of vagus nerve X 10 6th arch -recurrent laryngeal nerve branch of the vagus X Derivatives of the Aortic arch arteries An aortic arch artery that arises from the truncus arteriosus of the primordial heart Derivatives of the Aortic arch arteries 3rd 4th 4th • First – Maxillary 6th • Second – Stepedial • Third – Common, internal & external carotid arteries. • Fourth – Left-part of arch of aorta, Right – part of subclavian artery. • Sixth – pulmonary artery Summary Pharyngeal Nerve Muscles Skeleton Arch First V. Trigeminal: Mastication Maxilla, (mandibular) maxillary and (temporal; zygomatic bone, part of mandibular masseter; medial & temporal bone, divisions Lateral pterygoids); Meckel’s cartilage, mylohyoid; mandible malleus, anterior belly of incus, anterior ligament digastric; tensor of malleus, palatine, tensor sphenomandibular Tympani ligament Second VII. Facial Facial expression Stapes (hyoid) (buccinator; Styloid process auricularis; Lesser cornu of hyoid bone frontalis; Upper part of body of hyoid platysma; bone orbicularis oris; orbicularis oculi); posterior belly of digastric; stylohyoid; stapedius Pharyn Nerve Muscles Skeleton geal Arch Third IX. Greater cornu of hyoid bone Glossophar Stylopharyngeus Lower part of body of hyoid bone yngeal Fourth & Superior Cricothyroid Laryngeal cartilages sixth laryngeal Levator veli palatini (thyroid, cricoid, branch of Constrictors of arytenoid, corniculate, vagus (CN pharynx cuneiform) X) Intrinsic muscles of Recurrent larynx laryngeal branch of vagus (CN X) Summary MTF A Maxilla develops from 1st arch B Facial muscles derived from 1st arch C Hyoid bone develops from 2& 3rd arch D Laryngeal muscles supplied by recurrent laryngeal nerve E Arch is endodermal in origin SEQ • State pharyngeal arch muscles / cartilage / nerves Pharyngeal Pouches 5 Pharyngeal Pouches, 4 well developed & 5th is rudimentary/absent. Divides into ventral part obliterated by developing tongue dorsal part Pharyngeal Pouches derivatives Endoderm Pouch Derivatives 1st Eustachian tube connects with pharynx. middle ear cavity and mastoid antrum. 2nd Palatine tonsils 3rd inferior parathyroid gland/parathyroid III &Thymus 4th Superior parathyroid gland/parathyroid IV. 5th ultimobranchial body fuses with thyroid & forms parafollicular C cells calcitonin. Pharyngeal Grooves / clefts Ectoderm • Four on each side • Ectodermal clefts • First External acoustic meatus • Auricle -series of swellings arise on 1st & 2nd arches, joined with 1st cleft. • Remnants of 2nd,3rd & 4th cleft (cervical sinus) which obliterates Pharyngeal clefts anomalies Lateral cervical cysts and fistulas • Develop along anterior border of SCM, inferior to angle of mandible • Remnants of cervical sinus and/or second groove Pharyngeal Anomalies of First Arch Treacher Collins syndrome (mandibulofacial dysostosis) Characterized by mandibular hypoplasia, underdevelopment of the zygomatic bones, down-slanting palpebral fissures, lower eyelid colobomas, and malformed external ears Inherited as an autosomal dominant trait, Pierre Robin syndrome Micrognathia (small mandible), cleft palate, glossoptosis (posteriorly placed tongue) and defects of the eye and ear Genetic and/or environmental factors Pharyngeal Anomalies • DiGeorge Syndrome (Congenital Thymic and Parathyroid Aplasia) • Failure of third and fourth pouches to differentiate into thymus and parathyroid glands • Hypoparathyroidism • Increased incidence of infections • Shortened philtrum • Low-set notched ears • Nasal clefts • Thyroid hypoplasia • Cardiac anomalies Development of Tongue Mesodermal thickening Time – end of 4th week. Fusion of tuberculum impar & 2 lingual swellings(1starch) ant. 2/3rd part Crainial part of hypobranchial eminence & Copula(2nd&3rd arch) post.1/3rdpart Terminal sulcus divides anterior and posterior part Caudal part of hypobranchial eminence (4th arch)posterior most part. Muscles Derived from occipital myotomes. Tongue – nerve supply • 1st arch anterior 2/3rd part • 2nd & 3rd arch posterior 1/3rd part • 4th arch posterior most part Histo genesis -- Endoderm – surface epithelium. -- Mesoderm -- connective tissue, blood vessels & lymphatics Thyroid Gland Endodermal thickening in the floor of the pharynx Forms an out pouching (thyroid diverticulum) Descends into neck passing ventral to hyoid bone and thyroid cartilages • Ducts tip bifurcates forms 2 lobes & isthamus. • Thyroglossal duct degenerates Blind pit marks the foramen cecum Thyroid Anomalies • Thyroglossal Duct Cysts and Sinuses • May form anywhere along the course followed by the thyroglossal duct • Asymptomatic unless infected • Midline, painless, moveable neck mass • Sinuses are open, cysts are closed Pharyngeal Membranes • Only one pair contribute to adult structures • First tympanic membrane Watch video • https://www.youtube.com/watch?v=fp3Z_Y--0jo&t=46s References : • Langmans medical embryology • Human embryology - I.B. Sing. • The developing human - K.L.Moore & T.V.N Persaud Terima kasih .