Embryonic and Fetal Growth and Development 11-10-10

8/6/2019 Embryonic and Fetal Growth and Development 11-10-10

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Embryonic and Fetal growth andEmbryonic and Fetal growth anddevelopment development

A/P Dr A/P Dr SanSan SanSan ThwinThwin


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Continuation of GERM LAYERSContinuation of GERM LAYERSThird to Eighth Week: The Embryonic PeriodThird to Eighth Week: The Embryonic Period

Embryonic period-It is theperiod of Organogenesis(formation of organs)

Derivatives of Ectoderm-

During 3rd week, notochordand precordal mesoderminduces( induction) the

overlying ectoderm tothicken and form NeuralPlate formingNeuroectoderm, this processbeing known as Neurulation

induction


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NeurulationNeurulationSlipper shapedSlipper shaped

Neural plate becomeNeural plate becomeNeural folds at theNeural folds at the

end of 3rd week.end of 3rd week.

Neural folds laterNeural folds laterbecome Neuralbecome Neuralgroove and thengroove and thenNeural Tube.Neural Tube.


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NeurulationNeurulation

Cephalic and caudalCephalic and caudalends of Neural tubeends of Neural tubeform cranial andform cranial andcaudal neuroporescaudal neuroporesClosure of cranialClosure of cranialneuropore occurs atneuropore occurs atapproximately dayapproximately day2525

Closure of posteriorClosure of posteriorneuropore occurs atneuropore occurs atday 27day 27


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NeurulationNeurulationNeural foldsNeural folds becomebecomeNeural grooveNeural groove thenthenNeural TubeNeural Tube ..Lateral border or crestLateral border or crestofof neuroectodermneuroectodermbecome separated andbecome separated andformform Neural crestNeural crestcellscells , which migrate, which migrateand enter theand enter theunderlying mesodermunderlying mesodermNeural tube gives riseNeural tube gives riseto brain vesiclesto brain vesicles(( brain) and spinalbrain) and spinalcordcord

induction


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Derivatives of Neural Crest cellsDerivatives of Neural Crest cells

( Neural Ectoderm)( Neural Ectoderm)

are Connective tissue and bones of face andare Connective tissue and bones of face andskull, Dermis of face & neckskull, Dermis of face & neckSpinal rootSpinal root gangliaganglia , Cranial nerve, Cranial nerve gangliaganglia ,,ParasympatheicParasympatheic gangliaganglia of GI sys:, Sympatheticof GI sys:, Sympatheticchain &chain & gangliagangliaC cells of thyroid gland,C cells of thyroid gland, OdontoblastsOdontoblasts, ,MelanocyteMelanocytes s,, Adrenal Adrenal medullamedulla

ShwannShwann cells,cells, glialglial cellscells, , Arachnoid Arachnoid andand PiamaterPiamater((MeningesMeninges) )ConotruncalConotruncal septumseptum


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Derivatives of Ectoderm

During 5During 5 thth week,week,EctodermalEctodermalthickenings, otic (OP)thickenings, otic (OP)and lens placodes (LP)and lens placodes (LP)occuroccur

These placodesThese placodes

invaginate to form oticinvaginate to form oticvesicle and lensvesicle and lensvesicle which developvesicle which developinto inner ear and lensinto inner ear and lens

OPLP


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Summary of derivatives of Ectoderm

Epidermis ,hair,Epidermis ,hair,nails,nails,subcutaneoussubcutaneousglands,glands,mammarymammaryglands,glands,

sensorysensoryepithelium ofepithelium ofear, nose andear, nose andeye,eye,

CNS, PNS,CNS, PNS,pituitary glandpituitary glandand enamel ofand enamel ofteethteeth


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Derivatives ofDerivatives ofMesoderm GermMesoderm Germ

LayerLayer

Mesodermal germ layerMesodermal germ layerdivides into 3 zones,divides into 3 zones,paraxial, intermediateparaxial, intermediateand lateral plateand lateral platemesodermmesoderm

Intraembryonic cavityIntraembryonic cavityappears in the lateralappears in the lateralplate mesoderm, dividingplate mesoderm, dividingit into somatic or parietalit into somatic or parietalmesoderm andmesoderm andsplanchnic or visceralsplanchnic or visceralmesodermmesoderm

This cavity is continuousThis cavity is continuouswith the extraembryonicwith the extraembryoniccavitycavity


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Derivatives ofDerivatives ofMesoderm GermMesoderm Germ

LayerLayerParaxial mesodermParaxial mesoderm- -At At33 rdrd week it formsweek it formsSomatomeres in theSomatomeres in thehead region becomehead region becomeassociated withassociated withneuromeres of the neuralneuromeres of the neuraltubetubeIn the cervical regionIn the cervical region

and lower down, it formsand lower down, it formsSomites( SoSomites( So ))

So

oS


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SomitesSomites

Somites appear inSomites appear incraniocaudal sequencecraniocaudal sequence

Altogether 44 pairs of Altogether 44 pairs ofsomites appear betweensomites appear between20th day to 30th day of20th day to 30th day of

developmentdevelopment


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SomitesSomitesSomitesSomites - -Are blocks of paraxial Are blocks of paraxial

mesoderm, having its ownmesoderm, having its ownsegmental componentssegmental components

At 4 At 4 thth week, Eachweek, Each somitesomite formsformsSclerotomeSclerotome, , MyotomeMyotome andandDermatomeDermatome

SclerotomeSclerotome form the vertebralform the vertebralcolumncolumn

MyotomeMyotome form limb and bodyform limb and body

wall musculaturewall musculature

Dermatome forms dermis andDermatome forms dermis andsubcutaneous tissuesubcutaneous tissue


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SomitesSomites


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Somites ( 44 Pairs)Somites ( 44 Pairs)

They areThey are- -4 Occipital4 Occipital8 Cervical8 Cervical12 Thoracic12 Thoracic5 Lumbar5 Lumbar

5 Sacral5 SacralCoccygeal 8Coccygeal 8- -1010

Later 1Later 1 st st Occipital andOccipital andlast 5last 5 --7 Coccygeal7 Coccygeal

disappeardisappear


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B lood and B loodB lood and B loodvesselsvessels

Hemangioblasts areHemangioblasts arederived fromderived frommesenchymal cells ofmesenchymal cells ofvisceral mesoderm ofvisceral mesoderm ofyolk sac. They formyolk sac. They formextraembryonic bloodextraembryonic blood

and blood vesselsand blood vessels

Intra embryonic bloodIntra embryonic bloodcells and blood vesselscells and blood vessels

are also form similarly,are also form similarly,in liver and bonein liver and bonemarrowmarrow


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Blood and Blood vesselsBlood and Blood vessels

HemangioblastsHemangioblasts- -are derived fromare derived frommesenchymal cellsmesenchymal cellsCentral cellsCentral cellsbecome primitivebecome primitiveblood cells andblood cells and

peripheral cellsperipheral cellsform endothelialform endothelialcells of bloodcells of bloodvesselsvessels


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Lateral PlateLateral PlateMesodermMesoderm

Lateral plate mesodermLateral plate mesodermsplits into parietal andsplits into parietal and

visceral layers whichvisceral layers whichline theline the intraembryonicintraembryoniccavitycavity

Parietal or somaticParietal or somaticmesoderm (SM) andmesoderm (SM) andoverlying ectoderm willoverlying ectoderm willform the lateral andform the lateral andventral body wallventral body wall

Visceral or Visceral or splanchnicsplanchnicmesoderm(mesoderm( SplSpl M )M ) --form serous membraneform serous membraneof pericardial, pleuralof pericardial, pleuraland peritoneal cavitiesand peritoneal cavities

SM

Spl M


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IntermediateIntermediate

MesodermMesodermIn cervical andIn cervical andthoracic region, itthoracic region, itforms segmental cellsforms segmental cellsclustersclusters

And caudally And caudallyunsegmented mass ofunsegmented mass oftissue, thetissue, thenephrogenic cordnephrogenic cordThis cord give rise toThis cord give rise tourinary system andurinary system andgonadsgonads

(Int :Me )


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Summary of derivatives of MesodermSummary of derivatives of Mesoderm

SupportingSupporting tissuetissuesuch as conn: tiss:such as conn: tiss:

cartilage and bonecartilage and boneStriated andStriated andsmoothsmoothmusculaturemusculatureB lood and lymphB lood and lymphcells and vessels,cells and vessels,heartheart

Kidneys, gonads andKidneys, gonads andtheir ductstheir ductsSuprarenaSuprarenal cortexl cortexSpleenSpleen


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Summary of derivatives of Ectoderm,Summary of derivatives of Ectoderm,Mesoderm & EndodermMesoderm & Endoderm


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Derivatives ofDerivatives of

Endoderm (E)Endoderm (E)With the formation ofWith the formation ofcephalocaudal foldingcephalocaudal foldingand lateral foldings,and lateral foldings,Part of thePart of theendodermal lining ofendodermal lining ofthe yolk sac (Y S) isthe yolk sac (Y S) isincorporated into theincorporated into theembryo proper withembryo proper withthe formation ofthe formation offoregut, midgut andforegut, midgut andhind guthind gut

(E)

Y S


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Primitive GutPrimitive Gut At the cephalic end of At the cephalic end ofprimitive gut is theprimitive gut is theB uccopharyngealB uccopharyngealmembrane( ectodermmembrane( ectoderm

and endoderm fused)and endoderm fused)

At the caudal end is the At the caudal end is theCloacal membraneCloacal membrane( ectoderm and( ectoderm andendoderm fused)endoderm fused)

Partial incorporation ofPartial incorporation ofallantois in theallantois in theformation of cloacaformation of cloaca


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Primitive GutPrimitive Gut

Midgut isMidgut istemporarilytemporarily

connected toconnected toyolk sac byyolk sac byvitelline ductvitelline duct

Yolksac


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Summary of derivatives of EndodermSummary of derivatives of Endoderm

Epithelial lining ofEpithelial lining ofrespiratory tract , GIrespiratory tract , GItracttract

Parenchyma ofParenchyma ofthyroid, parathyroids,thyroid, parathyroids,liver and pancreasliver and pancreas

Tonsils and thymusTonsils and thymus

Epithelial liningEpithelial lining of ofurinary bladder andurinary bladder andurethraurethra

Epithelial liningEpithelial lining of oftympanic cavity andtympanic cavity andauditory tubeauditory tube


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External appearanceExternal appearance

As the main external As the main externalfeatures are somitesfeatures are somitesand pharyngeal archesand pharyngeal archesduring 20th to 30during 20th to 30 ththdays of developmentdays of development

Age of embryo during Age of embryo duringthat peroid isthat peroid isexpressed in no: ofexpressed in no: ofsomitessomites

SoPh

Ar


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Human Embryo in 5th weekHuman Embryo in 5th week

Formation of hand platesFormation of hand plates(HP) and foot plates (FP)(HP) and foot plates (FP)PericardialPericardial- -Liver bulge (P)Liver bulge (P)can be seencan be seen

Age of embryo in 2 Age of embryo in 2 ndndmonth is expressed asmonth is expressed ascrowncrown- -rump length (CRL)rump length (CRL)

P

UC

Ph Ar

HP

FP

So


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Fetal Period (from third month to birth )Fetal Period (from third month to birth )

Growth inGrowth inheight isheight isstriking duringstriking during33 rdrd , 4, 4 thth and 5and 5 ththmonthmonth

Increase inIncrease inweight is mostweight is moststriking duringstriking duringlast 2 last 2 monthsmonths


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Fetal Period from 3Fetal Period from 3 rdrd month tomonth toBirthBirth


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Fetal periodFetal period

At 3 At 3 rdrd month themonth thehead constituteshead constitutes of the CRL, of the CRL,

B y 5B y 5 thth month themonth thesize of head is 1/3size of head is 1/3of CHL (Crownof CHL (CrownHeel Length)Heel Length)

At birth it is about At birth it is about of CHL of CHL


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Fetal Period, Third MonthFetal Period, Third Month

Face becomesFace becomesmore humanmore human

lookinglookingLower limb lessLower limb lessdeveloped thendeveloped thenupper limbupper limbIntestinal loop isIntestinal loop iswithdrawn intowithdrawn intoabdominal cavityabdominal cavity


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Fourth and fifth monthFourth and fifth month

Fetus is covered byFetus is covered byfine hair known asfine hair known as

lanugo hairlanugo hair

Movements of theMovements of thefetus clearlyfetus clearly

recognized by therecognized by themothermother( quickenings)( quickenings)


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Second half of intrauterine lifeSecond half of intrauterine life

At 6 At 6thth

month skin ismonth skin iswrinkled due towrinkled due tolack of conn: tissuelack of conn: tissueand fatand fat

Fetus born beforeFetus born before77 thth month cannotmonth cannotsurvive becausesurvive becauserespiratory andrespiratory andCNS are not fullyCNS are not fullydeveloped yetdeveloped yet


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88 thth and 9and 9 thth monthmonth. At the last 2 months there. At the last 2 months thereis deposition ofis deposition ofsubcutaneous fat andsubcutaneous fat andhence the embryo has wellhence the embryo has well

rounded contourrounded contourSkin is covered by whitishSkin is covered by whitishfatty tiss: (vernix caseosa)fatty tiss: (vernix caseosa)

At 9 At 9 thth month the skull hasmonth the skull hasthe largest circumference,the largest circumference,an important fact withan important fact withregard to its passageregard to its passagethrough the birth canal,through the birth canal,sexual characteristics aresexual characteristics arepronounced.pronounced.


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Date of Birth (EDDDate of Birth (EDD--expected dateexpected date

of delivery )of delivery )Date of birth is most accuratelyDate of birth is most accuratelyindicated as 266 days, or 38indicated as 266 days, or 38 thth weeksweeks

after fertilizationafter fertilization

Or 40 weeks after the first day of theOr 40 weeks after the first day of thelast menstrual periodlast menstrual period


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DiagnosticDiagnosticInvestigationsInvestigations

Ultrasound can alsoUltrasound can alsohelp in determining thehelp in determining theage of the embryo.age of the embryo.

Amniocentesis and Amniocentesis andassessment of alphaassessment of alphafeto protein ( in thefeto protein ( in theamnionic fluid)amnionic fluid)in diagnosing fetalin diagnosing fetal

abnormalitiesabnormalitiesB iopsies of chorionicB iopsies of chorionicvilli used for detectingvilli used for detectingchromosomal disorderschromosomal disorders


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Embryonic and Fetal Growth and Development 11-10-10

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