PharyngealPharyngeal archesarches andand pouchespouches

L.MossL.Moss--SalentijnSalentijn PharyngealPharyngeal arches:arches: aa definitiondefinition

A segmental series of five paired swellings that surround the foregut between days 20 to 35 of embryonic development. These segments, which are unique to vertebrates, are “wedged” between the developing forebrain and heart. PharyngealPharyngeal archesarches

„ a.k.a.a.k.a. visceralvisceral oror branchialbranchial archesarches „ DevelopDevelop (and(and disappeardisappear asas distinctivelydistinctively visiblevisible structures)structures) inin aa rostrorostro--caudalcaudal sequencesequence „ RequireRequire neuralneural crestcrest cellscells forfor theirtheir developmentdevelopment „ EvenEven afterafter theythey areare nono longerlonger visiblevisible externally,externally, theythey havehave aa lastinglasting impactimpact onon thethe anatomyanatomy ofof thethe headhead andand neckneck andand ofof thethe greatgreat vesselsvessels 55 PharyngealPharyngeal archesarches 55 AorticAortic archesarches ArchesArches numberednumbered 11--66 Arches,Arches, grooves,grooves, pouches,pouches, andand membranesmembranes

Pharyngeal groove Pharyngeal pouch Pharyngeal arch Foregut Pharyngeal membrane PharyngealPharyngeal cleftcleft transienttransient “gill“gill--slit”slit” photograph by Purcell R,National Geographic November 2006 Dell H (2006) BasicBasic bodybody planplan ofof allall chordateschordates (incl.(incl. vertebrates)vertebrates)

Dorsal hollow neural tube Segmented lateral mesoderm Central notochord Ventral digestive tube (Pharyngeal gill slits)

EvolutionEvolution ofof vertebratesvertebrates involved:involved: „ DevelopmentDevelopment ofof organsorgans ofof specialspecial sensesense inin headhead regionregion toto detectdetect preyprey „ DevelopmentDevelopment ofof aa largelarge neuralneural circuitrycircuitry (the(the brain)brain) toto integrateintegrate inputinput andand responsesresponses „ DevelopmentDevelopment ofof anan effectiveeffective feedingfeeding apparatusapparatus (jaws:(jaws: pharyngealpharyngeal archarch derivatives)derivatives) „ DevelopmentDevelopment ofof anan improvedimproved respiratoryrespiratory apparatusapparatus (gills:(gills: pharyngealpharyngeal archarch derivatives).derivatives). ThisThis requiredrequired thethe recruitmentrecruitment ofof anan existingexisting groupgroup ofof cells:cells: neuralneural crestcrest cells,cells, forfor aa newnew role.role. MesenchymeMesenchyme inin cephaliccephalic regionregion isis derivedderived from:from:

„„MesodermMesoderm „„NeuralNeural crestcrest NeuralNeural crestcrest andand mesodermmesoderm inin H&NH&N areaarea Chai Y, Ito Y, Han J (2003)

ExtentExtent ofof cephaliccephalic (cranial)(cranial) neuralneural crestcrest NeuralNeural crestcrest involvementinvolvement inin thethe developmentdevelopment ofof thethe heartheart Somite segmentation clock and wavefront (chick embryo)

Kiefer, JC (2005)

Creuzet S, Couly G, Le Douarin NM (2005) SegmentalSegmental componentscomponents ofof archesarches

Connective tissues - nc

Muscle – mesoderm Branchiomeric nerve – nc,ectoderm,neurectoderm Skeletal bar- nc - (cartilage) last to form Artery – mesoderm- first to appear

Muscles

Arch 1: Muscles of mastication (V) Arch 2: Muscles of facial expression (VII) Arch 3: Stylopharyngeus muscle (IX) Arch 4-6: Laryngeal muscles (X-XI) Arey’s Embryology

TheThe cartilagecartilage elementselements ofof thethe pharyngealpharyngeal archesarches (cartilaginous(cartilaginous viscerocraniumviscerocranium,, purple)purple) atat 77 weeks.weeks. SkeletalSkeletal elementselements SkeletalSkeletal derivativesderivatives ExternalExternal earear receivesreceives contributionscontributions fromfrom archesarches 11 andand 22 ExternalExternal earear developmentdevelopment byby mergingmerging ofof 66 auricularauricular hillockshillocks EndodermalEndodermal swellingsswellings onon archesarches 11--44 contributecontribute toto thethe tonguetongue

1. Paired lingual swellings and single median tuberculum impar

2. Single median copula

3-4. Combined median hypobranchial eminence MergingMerging ofof linguallingual swellingsswellings ThyroidThyroid glandgland developmentdevelopment ThyroglossalThyroglossal ductduct

FateFate ofof pharyngealpharyngeal groovesgrooves 22--44

CoveredCovered byby rapidrapid outgrowthoutgrowth ofof 22nd archarch “operculum.”“operculum.”

EndodermEndoderm playsplays keykey rolerole inin morphomorpho-- genesisgenesis ofof pharyngealpharyngeal regionregion DerivativesDerivatives ofof dorsaldorsal andand ventralventral partsparts ofof pharyngealpharyngeal pouchespouches

SuperiorSuperior andand inferiorinferior parathyroidparathyroid glandsglands