Fetal membranes and placenta

Any membrane that functions for the protection

or nourishment or respiration or excretion

of a developing fetusis called a fetal membrane.

AMNION

Derived from Derived from ectodermectoderm

Completely covers the Completely covers the embryo and lines the embryo and lines the fetal aspect of placentafetal aspect of placenta

Secretes amniotic fluid Secretes amniotic fluid to protect the fetusto protect the fetus

The amniotic fluid is derived from the amniochorionic membrane, through the fetal skin, from the respiratory tract and urinary tract.

The fetus swallows about 400ml of amniotic fluid a day in the

final stages of pregnancy.

Amniotic fluid(liquor amnii)

increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter.

Amniotic fluid

It allows of the free movements of the fetus during the later stages of

pregnancy,

and also protects it by diminishing the risk of injury from without.

An abnormally High levels of amniotic fluid, is called polyhydramnios (>2000ml). Low levels of amniotic fluid (<1000ml at term) is called oligohydramnios.

Both conditions are associated with

congenital anomalies(birth defects)

amniocentesis

chorion

chorion

The outer membrane The outer membrane derived from the wall of derived from the wall of the blastocystthe blastocyst

Made up of Made up of syncitiotrophoblast,syncitiotrophoblast,

Cytotrophoblast,Cytotrophoblast, andand Extra embryonic Extra embryonic

mesoderm(from outside to mesoderm(from outside to inside)inside)

Chorion forms fingerlike projections called villiWhere the villi are present,it is

Chorion frondosum(fetal part of the placenta).where the villi disappear and is smooth

is called chorion laeve.

Rough,maternal part

Smooth,fetal part

Placenta and fetal membranes

(cotyledons)

Chorionic villi are the functional units of placenta.Fragments of these villi can be studied for

congenital anomalies of the fetus.

This procedure is called

Chorion villus sampling(CVS)

or chorion villus biopsy

Allantois(allantoic diverticulum)

Allantoic divericulum

A projection from the A projection from the yolk sac in to the yolk sac in to the connecting stalk.(body connecting stalk.(body stalk)stalk)

After the tail folding After the tail folding of the embryo, it is of the embryo, it is incorporated into the incorporated into the hindgut.hindgut.

In adults, it remains asIn adults, it remains as median umbilical ligamentmedian umbilical ligament

connecting the apex of the urinary bladderconnecting the apex of the urinary bladder to the umbilicusto the umbilicus..

allantois

allantois

It collects waste materials from the embryo,

and can be a site of gas exchange.

Urachus and anomalies

A partially obliterated A partially obliterated allantois in fetal life is allantois in fetal life is called Urachus.called Urachus.

This will obliterate This will obliterate postnatal and becomes the postnatal and becomes the median umbilical median umbilical ligament.ligament.

Any failure to do so Any failure to do so results inresults in

patent Urachus(weeping patent Urachus(weeping umbilicus)umbilicus)

allantois(1)urinary bladder(2)

yolk sac

Yolk sac Yolk sac:Yolk sac: Not all yolk Not all yolk has to do with birds' has to do with birds' eggs. eggs.

human beings have a human beings have a yolk sac, too.yolk sac, too.

The human yolk sac is a The human yolk sac is a membrane outside the membrane outside the embryo that is connected embryo that is connected by a tube (the yolk stalk) by a tube (the yolk stalk)

through the umbilical through the umbilical opening to the embryo's opening to the embryo's midgut.midgut.

yolk sac

The yolk sac serves as an early site for The yolk sac serves as an early site for the formation of blood and in time is the formation of blood and in time is

incorporated into the primitive gut of the incorporated into the primitive gut of the embryo.embryo.

Primordial germ cells are formed in the Primordial germ cells are formed in the yolk sacyolk sac

Yolk sac

Human placenta

placenta: an organ that develops from fetal membranes and functions to pass oxygen,

nutrients, and other substances to and waste material from the fetus.

Decidua

After implantation the endometrium is After implantation the endometrium is called ‘Decidua’called ‘Decidua’

Divided into D.basalisDivided into D.basalis D.capsularisD.capsularis D.parietalisD.parietalis

Maternal part from Decidua basalisFetal part from chorion frondosum

Parts of placenta

1.primary villus--- has an outer syncitio trophoblast and inner cyto trophoblast2. Secondary villus--- syncitio trphoblast+ cyto trophoblast+Extra embryonic mesoderm3. Tertiary villus--- above structures+fetal blood vessels

Stages in the formation of Chorionic villi

                                                

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Placentation

Figure 28.7a-c

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Placentation

Figure 28.7d

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Placentation

Figure 28.7f

Chorion laeve

After birth

The placenta,chorion,and amnion are The placenta,chorion,and amnion are expelled approx. after 30 minutes after the expelled approx. after 30 minutes after the child delivery by uterine contractions.child delivery by uterine contractions.

This process is called afterbirthThis process is called afterbirth

First stage of labor:Cervical dilation

Second stage of labor:Delivery of the baby

Third stage of labor:Delivery of the placenta

Partially dilated cervix

Placenta

Uterus

Umbilical cord

(the shedding of placenta)After birth

Gross features of placenta

The human placenta is defined as

Discoidal Deciduate

Hemochorial Chorioallntoic

Villus type

Placenta at termAbout 500g in weight

Has rough maternal surface showing cotyledonsAnd a fetal surface which is smooth andTo which the umbilical cord is attached.

Abnormalities of placenta (variations)

Bi lobate placenta

Placenta succenturiata

A small part of the A small part of the placenta is separate from placenta is separate from the main massthe main mass

Battledore placenta

The umbilical cord is The umbilical cord is attached to the attached to the periphery.periphery.

Velamentous placenta

The umbilical vessels The umbilical vessels divide into many divide into many branches before branches before entering placentaentering placenta

Diffuse placenta

Chorionic villi persist at the abemembryonic pole alsoresulting in diffuse placenta

Circumvallate placenta

Abnormalities of the placenta

• Placenta previa– placenta implantation at the lower segment of

the uterus

– obstructing the descent of the baby’s head

– presented with antepartum hemorrhage

Placenta previa