fetal membranes , placenta and twins

Fetalmembranes,placenta&twins

Dr.MohamedElfikyProfessorofanatomyandembryology

Early Human Development

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Early Human Development

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Early Human Development

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Early Human Development

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Embryo after foldingHead swelling

Cardiac swelling

Umbilical cord

Y.S

GUT

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• Thetermfetalmembraneisappliedtothosestructuresderivedfrom

theblastocystwhichdonotcontributetotheembryo.

ØTheamnion,

Øthechorion,

Øtheyolksac

ØAllantois

ØUmbilicalcord

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Amnion•Amniotic membrane : amniotic epi. + extraembryonic mesoderm

•Amniotic fluid:Produce:1)amniotic cells

2) infusion of fluid from maternal blood

3) urine output from the fetus4) pulmonary secretions

Output: 1) absorbed by amniotic cells2) fetus swallow

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AmnioticFluid

• Playsamajorroleinfetalgrowthanddevelopment.

• Dailycontributionoffluidfromrespiratorytractis300-400ml.

• 500mlofurineisaddeddailyduringthelatepregnancy.

• Amnioticfluidvolumeis30mlat10weeks,350mlat20weeks,

700-1000mlat37weeks.

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CompositionofAmnioticFluid• 99%iswater• Desquamatedfetalepithelialcells• Organic&inorganicsalts• Protein,carbohydrates,fats,enzymes,hormones• Meconium&urineinthelatestage

Abnormalitiesofamnioticfluid• Oligo-hydramnios: thevolumeoftheamnioticfluidislessthan½litre.Thismayleadtoadhesionsbetweentheembryoandtheamnion.

• Poly-hydramnios: thevolumeoftheamnioticfluidismorethan2litres.Thismayleadtoprematureruptureoftheamnion.

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Significance of Amniotic Fluid• Permitssymmetricalexternalgrowthoftheembryoandfetus

• Actsasabarriertoinfection

• DuringlaborithelpdilatationofthecervixoftheuterusandItwashbirthcanaland

protectthefetusagainstinfections

• Preventsadherenceofamniontofetus

• Cushions&protectstheembryoandfetus

• Helpsmaintainthebodytemperature

• EnablesthefetustomovefreelyMohamed el fiky

Yolk Sac• Itislargeat32days

• Shrinksto5mmpearshaped

remnantby10th week&

connectedtothemidgutbya

narrowyolkstalk

• Becomesverysmallat20

weeks

• Usuallynotvisiblethereafter

Primaryyolksac

secondaryyolksacMohamed el fiky

Significance of Yolk Sac

• Hasaroleintransferofnutrients duringthe2nd and3rd weeks

• Blooddevelopmentfirstoccurshere• Incorporateintotheendodermofembryoasaprimordialgut

• Primordialgermcellsappearintheendodermalliningofthewalloftheyolksacinthe3rd week

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Fate of Yolk Sac• At10weeksliesinthechorioniccavitybetweenchorionicandamnioticsac• Atrophiesaspregnancyadvances• Sometimesitpersiststhroughoutthepregnancybutofnosignificance• Inabout2%ofadultstheproximalintra-abdominalpartofyolkstalkpersistsasanileal diverticulumorMeckeldiverticulum

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Allantois• Inthe3rd weekitappearsasa

sausagelike diverticulumfromthe

caudalwallofyolksacthatextends

intotheconnectingstalk

•Duringthe2nd month,the

extraembryonicpartoftheallantois

degenerates Mohamed el fiky

Functions of Allantois• Bloodformationoccursinthewallduringthe3rd to5th

week

• Itsbloodvesselspersistastheumbilicalveinand

arteries

• BecomesUrachus andafterbirthistransformedinto

medianumbilicalligamentextendsfromtheapexof

thebladdertotheumbilicus

Anomaliesofallantois:• Urachalfistula:Theurachus remainspatent,urinedischargesfromtheumbilicus.

• Urachalsinus:Theupperendoftheurachus remainspatent.

• Urachalcyst:Themiddlepartoftheurachus remainspatent.

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TheUmbilicalCordAnatomy

•Origin: Itdevelopsfromtheconnectingstalk.•Length:

Atterm,itmeasuresabout50cm.•Diameter: 2cm.

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Structure: It consists of mesodermalconnective tissue called Wharton's jelly, covered by amnion.

It contains:1. One umbilical vein carries

oxygenated blood from the placenta to the foetus

2. Two umbilical arteries carry deoxygenated blood from the foetusto the placenta,

3. Remnants of the yolk sac and allantois.

TheUmbilicalCord

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Insertion:•The cord is inserted in the foetal surface of the placenta near the center "eccentric insertion" (70%)

• Or at the center "central insertion" (30%).

TheUmbilicalCord

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AbnormalitiesOfTheUmbilicalCord

(A)Abnormalcordinsertion1. Marginal insertion : in the placenta ( battledore insertion).2. Velamentous insertion: in the membranes and vessels

connect the cord to the edge of the placenta. • If these vessels pass at the region of the internal os , the

condition is called " Vasa praevia".

1. Short cord which may lead to :i-Intrapartum haemorrhage due to premature separation of the

placenta,ii-Delayed descent of the foetus druing labour,iii-Inversion of the uterus.2. Long cord which may lead toi-Cord presentation and cord prolapse,ii-Coiling of the cord around the neck,iii-True knots of the cord. Mohamed el fiky

Velamentous insertion(B)Abnormalcordlength

Chorion

Chorion1- extraembryonicmesoderm2- cytotrophoblast3- Syncytiotrophoblast

Chorion• Definition: Chorionisthenamegiventothetrophoblastaftertheformationoftheextraembryonicmesodermfromitsinnersurface.

• Thechorioniscomposedof:• Syncito-trophoblast (outer layer).• Cytotrophoblast (middlelayer).• Extra-embryonicmesoderm(innerlayer).

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CHORIONFRONDOSUMANDDECIDUABASALIS

• Intheearlyweeksofdevelopment,villi

covertheentiresurfaceofthechorion.

Aspregnancyadvances,villionthe

embryonicpolecontinuetogrowand

expand,givingrisetothechorion

frondosum(bushychorion).Villionthe

abembryonic poledegenerateandbythe

thirdmonththissideofthechorion,now

knownasthechorionlaeve,issmoothMohamed el fiky

Chorion• Chorionicvillicovertheentirechorionicsacuntilthebeginningof8th week

• Asthissacgrows,thevilliassociatedwithdeciduacapsularis arecompressed,reducingthe

bloodsupplytothem

• Thesevillisoondegeneratesproducinganavascularbareareasmoothchorion(chorion

laeve)

• Asthevillidisappear,thoseassociatedwiththedeciduabasalisrapidlyincreaseinnumber

• Branchprofuselyandenlarge

• Thisbushypartofthechorionicsacisvillouschorion

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CHORIONICVELLI• Bythebeginningofthethirdweek, thetrophoblastischaracterizedby

primaryvillithatconsistofacytotrophoblastic corecoveredbyasyncytial

layer.Duringfurtherdevelopment,mesodermalcellspenetratethecoreof

primaryvilliandgrowtowardthedecidua.Thenewlyformedstructureis

knownasasecondaryvillus.

• Bytheendofthethirdweek,mesodermalcellsinthecoreofthevillusbegin

todifferentiateintobloodcellsandsmallbloodvessels,formingthevillous

capillarysystem.Thevillusisnowknownasatertiaryvillusordefinitive

placentalvillus. Mohamed el fiky

PRIMARY villous

•Growthoftheseextensionsarecausedbyunderlyingextraembryonicsomaticmesoderm

• Thecellularprojectionsformprimarychorionicvilli Mohamed el fiky

SECONDARY CHORIONIC VILLI

Earlyin3rdweek,extraembryonicmesodermextendsinsidethevilli

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Tertiary villus

During3rd week,arterioles,venules &capillariesdevelopinthemesenchymeofvilli&joinumbilicalvesselsBytheendof3rd week,

embryonicbloodbeginsto

flowslowlythrough

capillariesinchorionicvilliMohamed el fiky

Decidua• Thegravidendometriumisknownas

decidua

• Itisthefunctionallayerofendometriumin

apregnantwoman

• Thispartoftheendometriumseparates

fromtherestoftheuterusafter

parturition

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Parts of decidua• Deciduabasalis: Itisthepartofdecidua

betweenblastocystandmyometrium.It

formsthefetalpartofplacenta.

• Deciduacapsularis: Itcoversthe

blastocystexceptembryonicpoleand

separatesitfromuterinecavity.

• Deciduaparietalis: Itistherestof

endometriumthatlinestherestof

uterinecavity.Mohamed el fiky

Fateofdecidua• Deciduabasalissharesinthe

formationofplacenta.

• Deciduacapsularisand

parietalisfusetogetherand

sheddedwithplacentaafter

delivery.

Deciduabasalis

Amnioticcavity

Fuseddeciduaparitalis,chorionlaeveandamnion

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PLACENTA

• Thisisafetomaternal organ.

• Ithastwocomponents:

• Fetalpart – developsfromthechorion

frondosum)

• Maternalpart – derivedfromthedecidua

basalis)

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• Duringthe4th and5th month,thedeciduaformsanumberofdecidual septa,whichprojectintotheintervillous space.

• Asaresultofthisseptumformation,theplacentaisdividedintoanumberofcompartments(cotyledons).

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PLACENTALMEMBRANE(placentalbarrier)

• Thisisacompositestructurethat separatingthefetalbloodfromthe

maternalblood.

• Earlyplacentalbarrier:(Ithasfourlayers):

• Syncytiotrophoblast

• Cytotrophoblast

• Connectivetissueofvillus

• Endotheliumoffetalcapillaries

• Lateplacentalbarrier:Afterthe20th week,thecytotrophoblastic cells

disappearandtheplacentalmembraneconsistsonlyof 2layer:• Syncytiotrophoblast

• Endotheliumoffetalcapillaries 35Mohamed el fiky

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It separates fetal from maternal blood.It prevents mixing of them.

It is an incomplete barrier as it only prevents large molecules to pass ( heparin & bacteria)

But cannot prevents passage of viruses(e.g. rubella), micro-organisms(toxoplama, treponemapallidum) drugs and hormones.

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isdiscoidinshape.

n Diameter=15-25cm,

n 2-3cmthick,

nWeight=0.5kg.

n Umbilicalcordisattachedtoitscenter.

nPosition : in the upper uterine

segment (99.5%), either in the posterior

surface (2/3) or the anterior surface (1/3).

Thefulltermplacenta

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1- Fetalsurface:whichissmoothandshinnybecauseitiscoveredbyanamnioticmembrane.Theumbilicalcordisattachedcentrallytothissurface.

2- Maternalsurface:whichisrough,reddish,andhas15– 20elevatedareascalledcotyledonswithdeepgroovesinbetweenmadebythedecidual septa.

Surfaces

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Functionofplacenta:-1. Respiratoryfunction2. Excretoryfunction3. Nutritionalfunction4. Endocrinefunction:- placentaactsasendocrine

gland5. Barrierfunction:- preventstransferofmaternal

infection.6. Enzymaticaction-7. Immunologicalfunction:- igG.

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AbnormalitiesOfThePlacenta

(A) Abnormal Shape

(B) Abnormal Diameter

(C) Abnormal Weight

(D) Abnormal Position

(E) Abnormal AdhesionMohamed el fiky

Abnormalitiesofplacenta1- Abnormalposition:PlacentaPreviatheplacentaisattachedtotheloweruterinesegment(duetolowlevelofimplantationoftheblastocyst).Itcausessevereantepartumhaemorrhage.Therearethreetypes:

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MarginalisLateralis(parietalis)

Centralis

the placenta does not reach the

internal os of the cervix.

the margin of the placenta overlies the internal os of the cervix.

the center of the placenta overlies the internal os

of the cervix .

2- Abnormaladhesion:1- Placentaaccreta:duetoabnormal

adhesionbetweenthechorionicvilliand

theuterinewall.

2- Placentapercreta:Thechorionicvilli

penetratethemyometriumallthewayto

theperimetrium.

- theplacentafailstoseparatefromthe

uterusafterbirthandmaycausesevere

postpartumhemorrhage.Mohamed el fiky

3- Abnormalattachmentofumbilicalcord:a- Velamentous attachment:Thecorddoesnotreachtheplacentaitselfbutisattachedtoamnioticmembraneoverthefetalsurfaceofplacenta.Theumbilicalvesselspassinthemembranetoreachtheplacenta.Itiseasly torn.

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(4)AbnormalShapeA- Accessoryplacenta: oneortwolobesarecompletelyseparatedfromthemain

placenta.Bilobate , Bipartite B- Placenta Fenestrate

(5)AbnormalDiameter:Placentamembranacea :Theplacentaislarge,thinandmaymeasure30-40cmindiameter.mayencroachontheloweruterinesegment

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Twins

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Twins• Di-zygotictwins

• Incidece :morecommon(70%).

• Mechanismofdevelopment: resultsfromfertilizationof2ova(from2

ovaries)duringanoverian cycleby2separatesperms.

• Placenta: 2separateplacentae.

• Chorion: 2separatechorionicsacs.

• Sex:maybeofthesameordifferentsex.

• Features:differentfetures. Mohamed el fiky

Twins•zygotic-Mono

• Incidece :lesscommon. resultsfromfertilizationofoneovabyonesperms.• Mechanismofdevelopment:resultsfromdivisionofasinglefertilizedovumduringoneofthefollowingstagesofdevelopment:

• Twocellstage.• Stageofblastocyst,wheretheinnercellmassdividesinto2masses.• Placenta:singlecommonplacenta.• Chorion:singlecommonchorionicsac.• Sex:alwaysofthesamesex.• Features:exactlyidentical.

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