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Home , Mandibular prominence, Pharyngeal arch

DEVELOPMENT OF PHARYNGEAL ARCHES

Dr. Sangeeta Kotrannavar Assistant Professor Dept. of 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 and Pharyngeal Arches – Early development

• Fourth week A.25 days, B.28days • Derived from Mesodermal tissue – give rise to musculature of & neck • cells • Most skeletal and connective tissue in H&N. • Series of surface elevations are seen caudal to stomatodeum (future mouth) & lateral to the developing  Pharyngeal Arches. • These grows ventrally & fuse with opposite arch in the floor of primitive pharynx.

Pharyngeal Apparatus Pharyngeal=branchial arches= Consists of : • Pharyngeal arches () • Pharyngeal pouches () • Pharyngeal grooves () • Pharyngeal membrane.

Pharyngeal arch

• Initially six pharyngeal (1-6) arches seen • Soon fifth arch disappears and is not visible on the surface of the • Five pharyngeal arches left • Derived from Mesoderm Structure of

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

• Derived - Mostly from 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 by intracartilaginous or intramembranous methods of . Derivatives of the pharyngeal arch cartilages 1.First arch- Mandibular / Meckel's Forms most of facial skeleton 1. First arch / / Meckel's cartilage

M - M

 Ventral  ventral end  (membranous ossification)  Dorsal end  and (middle )  Middle sphenomandibular lig. & ant. lig.of malleus.  Dorsal Maxillary Prominence  , zygomatic, & part of temporal . 2.Second arch - Hyoid arch / Reichert’s cartilage

S – S H

 Dorsal part  , styloid process of .  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

4.Fourth arch lamina of cartilage.

6.Sixth arch 4+5 A -  cricoid, arytenoid, corniculate & cuneiform cartilage of the larynx except . 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

Derivatives of pharyngeal arch nerves

 1st - maxillary &mandibular divisions of the fifth (trigeminal) V 5  2nd arch - VII 7  3rd arch - glossopharyngeal nerve IX 9  4th arch - superior laryngeal, branch of 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 . • Sixth – Summary Pharyngeal Nerve Muscles Skeleton Arch First V. Trigeminal: Mastication Maxilla, (mandibular) maxillary and (temporal; , 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 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 (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 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 dorsal part Pharyngeal Pouches derivatives Endoderm

Pouch Derivatives 1st Eustachian tube connects with pharynx. cavity and mastoid antrum. 2nd Palatine tonsils 3rd inferior /parathyroid III & 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 • -series of swellings arise on 1st & 2nd arches, joined with 1st cleft. • Remnants of 2nd,3rd & 4th cleft  () 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  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 ()  Descends into neck passing ventral to hyoid bone and thyroid cartilages • Ducts tip bifurcates  forms 2 lobes & isthamus. • 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 • Human embryology - I.B. Sing. • The developing human - K.L.Moore & T.V.N Persaud Terima kasih