Placenta

1. THE PLACENTA
BY
SRIDEVI DEVARAJ
Sridevi Devaraj 1

2. IntroductionIntroduction
The placenta is a fetomaternal organ that
develops in uterus during pregnancy. This
structure provides oxygen and nutrients to
growing fetus and removes waste products
from fetus's blood. The placenta attaches to
the wall of uterus, and fetus's umbilical cord
arises from it. In most pregnancies, the
placenta attaches at the top or side of the
uterus.
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3. Further Development of
Chorionic Villi
Early in the 3
rd
week,
mesenchyme growth into
the primary villi forming a
core of mesenchymal
tissue. Thus the Secondary
Chorionic Villi are formed
over the entire surface of
the chorionic sac.
Some mesenchymal cells in
the secondary villi
differentiate into capillaries
and blood cells forming the
Tertiary Chorionic Villi.
The capillaries in the villi
fuse to form arteriocapillary
networks.
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4. Sridevi Devaraj 4
The previous formed
arteriocapillary
networks become
connected with the
embryonic heart
through vessels which
are formed in the
mesenchyme of the
chorion and
connecting stalk.
By the end of the 3
rd

week, embryonic blood
begins to flow through
the capillaries in the
chorionic villi.

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Oxygen & nutrients in
the maternal blood in the
intervillous space diffuse
through the walls of the
villi and enter the
embryo’s blood.
Carbon dioxide & waste
products diffuse from
blood in the fetal
capillaries through the
wall of the chorionic villi
into the maternal blood.

6. DECIDUADECIDUA
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This is the endometrium of
the gravid (pregnant)
uterus.
It has four parts:
1.Decidua basalis: it
forms the maternal
part of the placenta
2.Decidua capsularis:
it covers the
conceptus
3.Decidua parietalis:
the rest of the
endometrium
4.Decidua reflexa:
Junction between
capsularis &
parietalis

7. PlacentaPlacenta
Human placenta is

ODiscoid in shape
OHaemochorial
ODeciduate
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8. Placenta developmentPlacenta development
OHuman placenta develops
from two sources
Fetal component- Chorion
frondosum
Maternal component- decidua
basalis
OPlacental development begins
at 6 weeks and is completed
by 12
th
week
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9. Sridevi Devaraj 9
OUntil the beginning
of the 8
th
week, the
entire chorionic sac
is covered with villi.
OAfter that, as the sac
grows, only the part
that is associated
with Decidua basalis
retain its villi.
OVilli of Decidua
capsularis
compressed by the
developing sac.

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OThus, two types of
chorion are formed:
OChorion
frondosum
(villous chorion)
OChorion laeve –
bare (smooth)
chorion
OAbout 18 weeks
old, it covers 15-
30% of the decidua
and weights about
1\ 6 of fetus

11. ContCont..
OThe villous chorion ( increase
in number, enlarge and
branch) will form the fetal
part of the placenta.
OThe decidua basalis will form
the maternal part of the
placenta.
OThe placenta will grow
rapidly.
OBy the end of the 4
th
month,
the decidua basalis is almost
entirely replaced by the fetal
part of the placenta
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12. Placenta at Term
OIs circular disc
ODiameter- 15-20 cm
OWeight-500gm
OThickness-2.5 cm
OSpongy to feel
OOccupies 30% of the uterine wall
OTwo surfaces- Maternal and fetal
O4/5
th
of the placenta is of fetal origin and 1/5
is of maternal origin
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13. Fetal surface
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OCovered by smooth and
glistening amnion
overlying the chorion
OUmbilical cord is attached
near to its centre
OBranches of the umbilical
vessels are visible beneath
the amnion as they radiate
from the insertion of the
cord.

14. Maternal surface
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ORough and spongy
OMaternal blood gives
it dull red colour
ORemanants of the
decidua basalis gives
it shaggy appearance
ODivided into 15-20
cotyledons by the
septa

15. OCotyledons –about 15 to
20 slightly bulging villous
areas. Their surface is
covered by shreds of
decidua basalis from the
uterine wall.
OAfter birth, the placenta is
always inspected for
missing cotyledons.
Cotyledons remaining
attached to the uterine
wall after birth may cause
severe bleeding.
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16. Margins
Margin of the placenta are
formed by fused chorionic and
the basal plate
Attachment
Placenta is attached to
the upper part of the uterine
body encouraging to the fundus
either at the posterior or
anterior wall
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17. Separation
OAfter delivery ,placenta separates with the
line of separation being through decidua
spongiosum (intermediate spongy layer of
the decidua basalis)
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18. Structure of the
placenta
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OPlacenta consist of two
plates(layers)
Chorionic plate
The basal plate
chorionic plate
OIt is lined by the amniotic
membrane on the fetal side
OThe umbilical cord is
attached to it.
OForms the roof of the
placenta

19. ContCont..
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OFrom outside inwards consists of
Syncytiotrophoblast
Cytotrophoblast
Extra embryonic mesoderm with
branches of umbilical vessels

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The basal plate
OIt consist of the structures From
outside inwards
Compact and spongy layer of
decidua basalis
Layer of Nitabuch
Cytotrophoblastic shell
Syncytiotrophoblast
Basal plate is perforated by the
spiral arteries allowing entry of
maternal blood into intervillous
space

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OLayer of Nitabuch -
Is a fibrinous layer formed at the junction
of cytotrophoblastic shell with decidua due to
fibrinoid degeneration of syncytiotrophoblast
OIt prevents excessive penetration of the decidua
by the trophoblast
ONitabuch membrane is absent in placenta
accreta and other morbidly adherent placentas

22. Placental barrier or membrane
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Maternal and fetal blood
are separated by
placental membrane or
barrier(0.025mm thick)
It consist of
OEndothelial lining of
fetal vessels
OConnective tissue
stroma of villus
OBasement membrane
OCytotrophoblast
OSyncytiotrophoblast

23. Placental CirculationPlacental Circulation
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Placental CirculationPlacental Circulation

24. Utero placental circulationUtero placental circulation
OIt is concerned with the circulation of the
maternal blood through the intervillous
space.
OA mature placenta has a volume of about
500 ml of blood.
O350 ml of being occupied in the villi
system
O150 ml lying in the intervillous space
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25. OIntervillous blood flow at
term is estimated to be 500-
600 ml per minute
OBlood in the inter villous
space Is replaced
completely replaced about
3-4 times per minute.
OThe pressure within the
intervillous space
- During uterine
relaxation is about 10-15
mm of hg
-During uterine
contraction is about 30-50
mm of hg
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26. Arterial circulationArterial circulation
O120-200 spiral arteries open
in to the inter villous space
OWithin 12 weeks of
pregnancy the
cytotrophoblast invade the
spiral arteries up to intra
decidual portion
OWithin 12-16 weeks
secondary invasion of
trophobast extend up to
radial arteries within the
myometrium.
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27. OThus spiral arteries
are converted to large
bore utero placental
arteries
OTrophoblast cells that
do not take part in
villous structure
extravillous
trophoblast
these are two tyes
-endovascular
extravillous
trophoblast
-Interstitial
extravillous
trophoblast
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28. Venous drainageVenous drainage
O the venous blood of the inter villous space drains
through the uterine veins which pierce the basal plate

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29. Feto-placental circulationFeto-placental circulation
OTwo umbilical arteries carries
the impure blood from the fetus
OThey enter the chorionic plate
underneath the amnion
OThe arteries break up in to the
small branches which enters
the small chorionic villi
OEach in turn divide in to
primary ,secondary and
tertiary vessels of the
corresponding villi.
OThe blood flows in to the
corresponding venous channel
through the terminal capillary
network.
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30. OMaternal and fetal blood flow
side by side but in opposite
direction
OThis blood flow facilitate the
material exchange between
the mother and fetus
OThe villous capillary pressure
is 20-40 mm of hg
OThe fetal blood flow through
placenta is 400 ml /min
OThis is mainly facilitated by
pumping action of heart
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31. Placental Function
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Transfer of gases ,nutrients and waste
products , namely
Respiratory function
Nutritive function
Excretory function
Endocrine and enzymatic function
Barrier function
Immunological function

32. Mechanism involved in the transfer of
substances
OSimple diffusion-O2 and CO2
OFacilitated diffusion ( carrier mediated ) –
glucose ,vitamins
OActive transfer ( against concentration
gradient )-ions
OEndocytosis- invagination of cell membrane to
form intracellular vesicle
OExocytosis-Release of substances in the
vesicles to extracellular space
eg IgG immunoglobulin
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33. Respiratory function
OAlthough fetal respiratory movement
occurs by 11 week, no active
exchange of gases takes place
OIntake of oxygen and output of carbon
dioxide take place by simple diffusion
across the fetal membrane
OO2 delivery to the fetus is at the rate
of 8 ml/kg which is achieved by cord
blood flow of 160-320ml/min
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34. Excretory functionExcretory function
OWaste products from the fetus
such as urea, uric acid,
cretinine are excreted to the
maternal blood by simple
diffusion.
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35. Nutritive function
Fetus obtains its nutrients from the maternal blood
OGlucose- transferred to the fetus by facilitated
diffusion
OLipids for fetal growth and development has dual
origin. They are transferred across the fetal
membrane or synthesized in the fetus
OAmino acids are transferred by active transport
OWater and electrolytes- Na, K ,Cl cross by simple
diffusion, Ca , P, and Fe cross by active transport
OWater soluble vitamins are transferred by active
transport but the fat soluble vitamins are
transferred slowlySridevi Devaraj 35

36. Barrier Function
OPlacental membrane is thought to be a protective
barrier for the fetus against harmful agents in the
maternal blood
OSubstances with large molecular weight or size like
insulin or heparin are transferred minimally
OOnly IgG ( not IgA or Ig M )antibodies and antigens
can cross the placental barrier
OMost drugs can cross the placental barrier and some
can be teratogenic
OVarious viruses, bacteria, protozoa can cross the
placenta and affect the fetus in utero
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37. Immunological function
OInspite of foreign paternally
inherited antigens in the fetus and
placenta, there is no graft rejection
due to immunological protection
provided by the placenta
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38. Endocrine and Enzymatic
function
OPlacenta secretes various hormones – Protein
hormones like HCG, human placental
lactogen,pregnancy specific beta 1
glycoprotein,,pregnancy associated plasma
protein, steroidal hormones like estrogen and
progestrone
OEnzymes secreted are diamine oxidase-which
activates the circulatory pressor amines,
oxytocinase which neutralizes oxytocin,
phospholipase A2 which synthesizes
arachidonic acidSridevi Devaraj 38

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OThank you