Foetal Membranes

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Foetal membranes

A/P Dr San San Thwin


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Foetal membranes

Placenta

Amnion

Connecting stalk withUmbilical cord, allantois

and umb: vess:

Yolk stalk ( vitelline duct)

Yolk sac


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Early developmental stage(1st Week)

After fertilization

Zygote Cleavage

( cell division)

Morula(16 cellstage)

-Blastocyst ( Outer

cell mass, inner cell

mass with

blastocyst cavity)


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Placenta

At the 8th day (2nd week)of intrauterine life,blastocyst is partiallyembedded in theendometrial stroma.

Blastocyst consists ofInner cell mass orEmbryoblast

Outer cell mass orTrophoblast

Trophoblast consists of -Cytotrophoblast- inner,mononucleated cells

-Syncytiotrophoblast-outer, multinucleated cells

without cell boundaries


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Placenta

As the blastocyst

penetrates deeper into

the endometrium in the

embryonic pole,

vacuoles appear in thesyncitium. These

vacuoles fuse to form

large lacunae. This

stage is known asLacunar stage


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Placenta

Subsequently maternal

sinusoids in the

endometrium are

eroded by

syncitiotrophoblast &as a result, maternal

blood enters the

lacunar spaces, thus

establishing utero-placental circulation.


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Placenta

By 3rd week, Trophoblast forms

A .Primary villus( 2 layers -cytotrophoblast &

syncitiotrophoblast), B. then 2ndary villus ( with mesoderm core) and

C. finally Tertiary villus( capp: formed in the core)

Chorionic Villi

CS

Formation of Chorionic Villi


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Placenta

Cappillaries in the tertiaryvilli make contact with themesoderm of chorionicplate & connecting stalk.

These vessels in turnestablish contact with theintra- embryoniccirculatory system, thereby connecting the placentaand the embryo( via theconnecting stalk)

Conn:

stalk


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Placenta

The cytotrophoblastic cellsin the villi penetrateprogressively into theoverlying syncitium untilthey reach theendometrium.

They establish contactswith the similar extensionsof the neighbouring villi,thus forming an Outertrophoblastic shell.

Villi that extend fromchorionic plate to decidualplate are called Anchoringvilli.


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Placenta

The chorionic cavity

becomes larger and the

embryo is attached to

the trophoblastic shell

by a narrow connecting

stalk, which later forms

the Umbilical cord.

Umb:

cord


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Placenta

During the following

months, smallextensions sprout from

the existing villous

stems into the

surrounding lacunar or

intervillous space.


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Placenta

Placental Membrane or

Placental Barrier

initially consists of

endothelial lining of

foetal vessels

the connective tissue

in the villous core

the cytotrophoblast

the syncitiotrophoblast


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Placenta

By 4th monthcytotrophoblastic cells &some connective tissuecells ( C& C) disappear.

The syncitium &endothelial wall of bloodvessel are the only layersthat separate the

maternal & foetalcirculation forming thePlacental Barrier.


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Placenta

Since the maternal blood in

the intervillous space is

separated from foetal bloodby a chorionic derivative,

the human placenta is

considered as Hemochorial

type.


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Chorion Frondosum and Decidua

Basalis

In the early week ofdevelopment, villi cover theentire surface of chorion.Villi on the embryonic polegrow & expand to form

Chorion Frondosum orBushy Chorion.

Villi on abembryonic poledegenerate & becomesmooth and is known asChorion Laevae or Smooth

Chorion. Decidua Basalis is derived

from maternalendometrium

D.

Basalis


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Chorion Frondosum and Decidua

Basalis

Decidual Reaction -Changes occur in thedecidua, which is thefunctional layer of

endometrium and it is shedduring parturition. Decidua that is in contact

with chorion frondosum isDecidua Basalis

Decidua over the

abembryonic pole- DeciduaCapsularis Decidua over the uterine

wall Decidua ParietalisD. Capsu

D. Bas

D. Pariet


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Placenta

With the increase in size

of the chorionic cavity,

the chorion laeve comes

into contact with the

decidua parietalis

Formation of placenta is

from 2 parts

1.Chorionic Plate or

Chorion Frondosum

2.Decidual Plate or

Decidua basalis


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Foetal Membranes

Similarly fusion of amnion

and chorion formAmniochorionic Membrane.

This membrane ruptures

during delivery of the baby

known as Breaking of

Water.


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Placenta

Structure of placenta By the beginning of 4th month,

placenta has 2 components Maternal portion- decidua

basalis or decidualplate Foetal portion chorionic plate

or chorion frondosum In the junctional zone decidual

and syncitial cells intermingle. During 4th and 5th month,

decidua forms a number ofsepta, the decidual septa

project into intervillous spacesbut do not reach the chorionicplate. As a result, the placentais divided into a number ofcompartments or cotyledons.

Cotyledons


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Placenta

Functions Exchange of gases- like

O2, Co2, Co Exchange of nutrients and

electrolytes like aminoacid, fatty acid,carbohydrate, vitamins

Transmission of maternalantibodies- likeimmunoglobulin G

Hormones production- likeprogesteron, oestrogen,human chorionicgonadotropin ( HCG),somato-mammotropin


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Placenta

Full term placenta

Discoid shape, diameter of 15-

25 cm, 3 cm thick, and weight

is 500-600 gm.

It comes out 30 minutes afterthe birth of the child.

On the maternal side, it has 15-

20 cotyledons covered by a

thin layer of decidua basalis

and grooves between thecotyledons are formed by

decidual septa ..

Cotyle

:


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Placenta

. The fetal surface of placentais covered by chorionic

plate with chorionic

vessels & umbilical cord,

chorion and amnion

Attachment of umbilical

cord is usually eccentric

and occasionally marginal

Placenta with a marginalattachment of umbilical

cord is called a battledore

placenta


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Placenta

Velamentous

type whereumbilical cord is

attached to the

chorionic

membranes andnot to the

placenta


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Placental abnomalities

Placenta accreta-chorionic villipenentrate themyometrium

Placenta percreta-

chorionic villipenentrate myometriumand perimetrium

( peritoneal lining) Placenta previa-

blastocyst implantsclose to or overlying theinternal os ( openingnear cervix)


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Foetal Membranes

Other foetal membranes are:-

1.The connectingstalk( umbilical cord)-containing the allantoisand umbilical vessels (2arteries and 1 vein)

Wharton jelly a looseconnective tissue in theumbilical cord forms aprotective layer for theumbilical vessels.


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Foetal Membranes

2.Yolk stalk or vitelline ductor vitello-intestinal duct

Canal connecting the

intraembryonic and

extraembryonic cavities

Yolk Sac- is present in the

chorionic cavity. Later with

the enlargement of

amniontic cavity, the

amnion comes in contact

with chorion there by

obliterating the chorionic

cavity. Yolk sac shrink and

is later obliterated.


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Foetal Membranes

3.Allantois is an

endodermal diverticulum

from the hind gut

It extends from urinarybladder to umbilicus and

involutes to form urachus

and after birth becomes

median umbilical ligament

birth


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Foetal Membranes

4.Amnion, Amniotic fluid clear, watery fluidproduced by amniotic cellsand primarily frommaternal blood. It is about800-1000 ml at 37th week.

Functions protective cushion,absorbs shock

prevent adherence ofembryo to the amnion

allow foetal movements

exchange of metabolicwastes during child birth, it forms

a hydrostatic wedge thathelps to dilate the cervicalcanal.


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Foetal Membranes

Clinical correlations

Hydramnios or polyhydramnios where there is

excess of amniotic fluid( 1500 2000ml)

Oligohydramnios refers to a decreased amount of

amn: fluid ( 400 ml)

Premature rupture of amnion is the most common

cause of preterm labor and occurs in 10% of

pregnancies


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An extremely long

umbilical cord may

encircle the neck or

any part of the body

or a short cord may

cause difficulty indelivery by pulling

the placenta.


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Ocassionallytear in amnionresult inamniotic bandsthat mayencircle part of

foetus formingringconstrictions,amputations orotherabnomalities.


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Foetal Membranes

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