DEVELOPMENTOFRESPIRATORYSYSTEM.docx

DEVELOPMENTOFRESPIRATORYSYSTEM.docx

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DEVELOPMENTOFRESPIRATORYSYSTEM

DEVELOPMENTOFRESPIRATORYSYSTEM

DEVELOPMENTOFRESPIRATORYSYSTEMANDITS

ANOMALIES

LEARNINGOBJECTIVES:

1.EnumeratethedifferentPartsofRespiratorySystem2.NametheDifferentPartsofForegut

3.Discusstheformationoflaryngo-trachealtube4.DiscusstheformationofLungBud

5.DescribetheBranchesofBronchi

6.DiscussthedifferentStagesofdevelopmentofLung7.DescribeMaturationofLung

8.Enumeratethecongenitalerrorsduringdevelopment

DIFFERENTIATION（ORGANOGENESIS）

•ORGanogenesisistheformationoftheorgans.Arisesfromthe

layeringofcellsthatoccursduringgastrulastage

•Thelayersaregermlayers;theyhavespecificfatesinthe

developingembryo:

–Endoderm

•Theinnermostlayer

•Goesontoformthegut

–Mesoderm

•Inthemiddle

•Goesontoformthemuscles,circulatorysystem,

bloodandmanydifferentorgans

–Ectoderm

•Theoutermost

•Goesontoformtheskinandnervoussystem

•

DifferentiationofPrimaryGermLayers（fromthegastrula）

EctodermMesodermEndoderm

NervoussystemSkeletonDigestivetract

EpidermisofskinMusclesRespiratory

system

CirculatorysystemLiver,pancreas

GonadsBladder

FUNCTIONALDIVISIONOFRESPIRATORYSYSTEMFunctionallytheRespiratorySystemisdividedintotwoparts:

ConductingPart

RespiratoryPart

CONDUCTINGPART:

NostrilsVestibule

NasalCavity

Nasopharynx

Oropharynx

Laryngopharynx

Larynx,

Trachea

PrincipalBronchi

SecondaryBronchi

SegmentalBronchiUptoTerminalBronchioles

RESPIRATORYPART

RespiratoryBronchioles

AlveolarDuct

AlveolarSac,

Alveoli

DevelopmentalDivisionofRespiratory

System

DevelopmentallytheRespiratorySystemisdividedintotwoparts:

1.UpperPartofRespiratorySystem2.LowerPartofRespiratorySystem

Upperpartofrespiratorysystem

Extendsfromnosetolarynx

DevelopsfromthePharyngealApparatuswhichisapartofHead

&Neck

LowerPartofRespiratorySystem

ExtendsbelowtheLarynxuptolungalveoli,ThispartdevelopsFromtheForegut

DEVELOPMENTOFTHENOSE

Relatedtoformationofface

Nasalplacodes-primordiaofnoseandnasalcavities,Proliferationofmesenchymeinmarginsofnasal

placodemedialandlateralnasalprominences,Nasalpit-primordiaofnaresandnasalcavities

Medialnasalprominencesformthetipofthe

nose,nasalseptum,andtheintermaxillary

segment

Lateralnasalprominencesformthesides（alae）ofthenose

Frontonasalprominenceformsthebridgeofthenose

LARYNX

GERMLAYERORIGIN

th,Mesoderm-cartilagesandmuscles（4th&6pharyngeal

arches,thyroid,cricoidand

Arytenoid）

Endoderm-internalliningofthe

epithelium

Transformationofmesenchymeto

cartilaginouscomponentsproducesT

shapedlaryngealorifice

Epithelium-endoderm

Thyroid,cricoid,arytenoidcartilagesandmusclesfrom4thand

6thbranchialarches

Transformationofmesenchymetocartilaginouscomponents

producesTshapedlaryngealorifice

DifferentPartsofForegut

Theforegutcanbedividedintothreeparts:

1.Thefirstpartliesventraltothedeveloping

brain,andformstheprimitivepharynx,

whichhasthebranchialarchesassociated

withit.

2.Thesecondpartliesdorsaltotheheart,

andformsthelungbudandthe

oesophagus.

3.Thethirdpartliesdorsaltotheseptumtransversumandforms

thestomachandotherrelatedgastro-intestinalstructures.

RespiratorySystemisderivedfromSecondPartofForeguta.Itbeginstodevelopinthebeginningofthefourthweek（day22）b.Itbeginsasalaryngo-trachealgrooveontheventralaspectoftheforegut,whichdeepensandformsarepiratorydiverticulum.c.Separatesfromtheoesophagus

DevelopmentofLungBud

Therespiratorydiverticulum'sbifurcatesintorightandleftbronchialbudsonday26-28.

DivisionofLungBud

Asymmetricbranchingoccursduringthefollowing2weekstoformsecondarybronchi:

3ontherightand2ontheleftformingthemaindivisionsofthebronchialtree.

Thelungbudanditssubsequentbranchesareofendodermal

origin.

Theygiverisetotheepitheliumliningalltherespiratory

passages,thealveoliandtheassociatedglands.

Thesurroundingmesoderm,thesplanchnopleure,givesriseto

allthesupportingstructures:

theconnectivetissue,cartilage,

muscleandbloodvessels.

BranchingofBronchi

Thepatternofbranchingisregulatedby

thesurroundingmesoderm.

Themesodermsurroundingthetrachea

inhibitsbranchingwhereasthe

mesodermsurroundingthebronchi

stimulatesbranching.

Transplantationofpartofthebronchial

mesodermtoreplacepartofthe

trachealmesodermformsanectopic

lobeofthelungarisingdirectlyfromthe

trachea.Transplantationofpartofthetracheal

mesodermtoreplacepartofthebronchial

mesodermsuppressestheformationofalobe.

Duringweeks7to16branchingoccursabout14timestothelevelofterminalbronchioles.Atthisstagetherearenoalveoli.Thefoetallungduringthisperiodisdescribedastheglandularstagebecausetheterminalbronchiolesresembleglandularacini.Thebronchi,containingcartilageintheirwalls,identifythesectionsasfoetallung.

StagesofDevelopmentoftheLungs

1.ThePseudo-glandularstage–weeks6to16–thereis

repeatedbranchingabout14times）totheleveloftheterminal

bronchioles.

2.Thecanalicularstage–weeks16to26–therespiratory

bronchiolesdevelop

3.Thesaccularstage–weeks26to36Development（the

primaryalveolidevelop）.

4.Thealveolarstage–weeks36to40–thealveolimature:

Pseudoglandularphase（6to16Weeks）

AtthisstagethelungsresemblethedevelopmentofaExocrineGland.

Bytheendof16weeksallthemajorelementsofthelungdevelopmenthaveformedexceptthoseinvolved

withgasexchange.Respirationisnotpossible,hencefetusesbornduringthisperiodareunabletosurviveCANALICULARPHASE

Intheclassicaldescriptionoflungdevelopment,inthisphasethecanaliculibranchoutoftheterminalbronchioli.Thecanaliculicomposetheproperrespiratorypartofthelungs,thepulmonaryparenchyma.Alloftheairspacesthat

derivefromaterminalbronchiolusformanacinus.

Eachonecomprisesrespiratorybronchioliandthe

alveolarductsandlaterthealveolarsacculi.

Thechiefcharacteristicofthiscanalicularphaseisthealterationoftheepitheliumandthesurroundingmesenchyma.

Alongtheacinus,whichdevelopsfromtheterminal

bronchiolus,aninvasionofcapillariesintothemesenchymaoccurs.Thecapillariessurroundtheaciniandthusformthefoundationforthelaterexchangeofgases.Thelumenofthetubulesbecomeswiderandapartoftheepithelialcellsgettobeflatter.FromthecubictypeIIpneumocytesdeveloptheflattenedtypeIpneumocytes.

Saccularphase

Fromthelasttrimesterwholeclustersofsacsformontheterminalbronchioli,whichrepresentthelastsubdivisionof

thepassagesthatsupplyair.Inthesaccularphase

thelastgenerationofairspacesintherespiratory

partofthebronchialtreeisborn.Attheendof

eachrespiratorytractpassagesmooth-walled

sacculiform,coatedwithtypeIandtypeII

pneumocytes.

Saccularphase

Thesepta（primarysepta）betweenthesacculiare

stillthickandcontaintwonetworksofcapillaries

thatcomefromtheneighboringsacculi.

Theinterstitialspaceisrichwithcellsandtheproportionofcollagenandelasticfibersisstillsmall.Thismatrix,though,playsanimportantroleforthegrowthanddifferentiationoftheepitheliumthatliesaboveit

Alveolarphase

Dependingontheauthor,thealveolarphasebegins

atvaryingtimes.Probablyinthelastfewweeksof

thepregnancy,newsacculiand,fromthem,thefirst

alveoliform.Thus,atbirth,1/3oftheroughly300

millionalveolishouldbefullydeveloped.Thealveoli,though,areonlypresentintheirbeginningforms.

Betweenthemliestheparenchyma,composedofadoublelayerofcapillaries,thatformstheprimaryseptabetweenthealveolarsacculi.

MaturationofLung

Characteristicmaturealveolidonotformuntilafterbirth,about95%ofalveolideveloppostnatally.Beforebirththeprimordialalveoliappearassmallbulgesonthewallofrespiratorybronchiolesandterminalsaccules.From3rdto8ththenumberofimmaturealveolicontinuestoincrease.Themajormechanismforincreasingnumberofalveoliistheformationofconnectivetissueseptathatsubdivideexistingprimordialalveoli.About50millionalveoli,onesixthoftheadultnumberarepresentinthelungsoffulltermnewborninfant.Byabouttheeightyear300millionalveolipresentinlungsBreathingmovementsoccurbeforebirth,exertingsufficientforcetocauseaspirationofsomeofamnioticfluidintolung.Thesemovementareessentialfornormaldevelopmentoflung.Fetalbreathingmovement,whichincreaseasthetimedeliveryapproaches,probablyconditiontherespiratorymuscles.Thesemovementsstimulatelungdevelopment,possiblybycreatingapressuregradientbetweenlungsandamnioticfluid.

LungExpansionatBirth

Atbirthabouthalfthelungsarefilledwithfluid,derivedfromtheamnioticcavity,lungandtrachealglands.Aerationoflungsatbirthoccurduerapidreplacementofintra-alveolarfluidbyair.Thefluidinthelungsisclearedatbirthbythreeroutes:

•Throughmouthandnosebypressureonthoraxduringdelivery

•Intopulmonarycapillaries

•IntolymphaticandpulmonaryArteriesandVeins

FactorsImportantfornormalLungDevelopment

•Adequatethoracicspaceforlunggrowth

•Feta