2. Introduction
Introduction
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 3rd
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 3rd
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. DECIDUA
DECIDUA
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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
8. Placenta development
Placenta development
O Human placenta develops
from two sources
Fetal component- Chorion
frondosum
Maternal component- decidua
basalis
O Placental development begins
at 6 weeks and is completed
by 12th
week
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O Until the beginning
of the 8th
week, the
entire chorionic sac
is covered with villi.
O After that, as the sac
grows, only the part
that is associated
with Decidua basalis
retain its villi.
O Villi of Decidua
capsularis
compressed by the
developing sac.
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O Thus, two types of
chorion are formed:
O Chorion
frondosum
(villous chorion)
O Chorion laeve –
bare (smooth)
chorion
O About 18 weeks
old, it covers 15-
30% of the decidua
and weights about
1 6 of fetus
11. Cont
Cont..
O The villous chorion ( increase
in number, enlarge and
branch) will form the fetal
part of the placenta.
O The decidua basalis will form
the maternal part of the
placenta.
O The placenta will grow
rapidly.
O By the end of the 4th
month,
the decidua basalis is almost
entirely replaced by the fetal
part of the placenta
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12. Placenta at Term
O Is circular disc
O Diameter- 15-20 cm
O Weight-500gm
O Thickness-2.5 cm
O Spongy to feel
O Occupies 30% of the uterine wall
O Two surfaces- Maternal and fetal
O 4/5th
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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O Covered by smooth and
glistening amnion
overlying the chorion
O Umbilical cord is attached
near to its centre
O Branches 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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O Rough and spongy
O Maternal blood gives
it dull red colour
O Remanants of the
decidua basalis gives
it shaggy appearance
O Divided into 15-20
cotyledons by the
septa
15. O Cotyledons –about 15 to
20 slightly bulging villous
areas. Their surface is
covered by shreds of
decidua basalis from the
uterine wall.
O After 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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O Placenta consist of two
plates(layers)
Chorionic plate
The basal plate
chorionic plate
O It is lined by the amniotic
membrane on the fetal side
O The umbilical cord is
attached to it.
O Forms the roof of the
placenta
19. Cont
Cont..
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O From 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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O Layer of Nitabuch -
Is a fibrinous layer formed at the junction
of cytotrophoblastic shell with decidua due to
fibrinoid degeneration of syncytiotrophoblast
O It prevents excessive penetration of the decidua
by the trophoblast
O Nitabuch 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
O Endothelial lining of
fetal vessels
O Connective tissue
stroma of villus
O Basement membrane
O Cytotrophoblast
O Syncytiotrophoblast
24. Utero placental circulation
Utero placental circulation
O It is concerned with the circulation of the
maternal blood through the intervillous
space.
O A mature placenta has a volume of about
500 ml of blood.
O 350 ml of being occupied in the villi
system
O 150 ml lying in the intervillous space
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25. O Intervillous blood flow at
term is estimated to be 500-
600 ml per minute
O Blood in the inter villous
space Is replaced
completely replaced about
3-4 times per minute.
O The 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 circulation
Arterial circulation
O 120-200 spiral arteries open
in to the inter villous space
O Within 12 weeks of
pregnancy the
cytotrophoblast invade the
spiral arteries up to intra
decidual portion
O Within 12-16 weeks
secondary invasion of
trophobast extend up to
radial arteries within the
myometrium.
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27. O Thus spiral arteries
are converted to large
bore utero placental
arteries
O Trophoblast 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 drainage
Venous 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 circulation
Feto-placental circulation
O Two umbilical arteries carries
the impure blood from the fetus
O They enter the chorionic plate
underneath the amnion
O The arteries break up in to the
small branches which enters
the small chorionic villi
O Each in turn divide in to
primary ,secondary and
tertiary vessels of the
corresponding villi.
O The blood flows in to the
corresponding venous channel
through the terminal capillary
network.
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30. O Maternal and fetal blood flow
side by side but in opposite
direction
O This blood flow facilitate the
material exchange between
the mother and fetus
O The villous capillary pressure
is 20-40 mm of hg
O The fetal blood flow through
placenta is 400 ml /min
O This 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
O Simple diffusion-O2 and CO2
O Facilitated diffusion ( carrier mediated ) –
glucose ,vitamins
O Active transfer ( against concentration
gradient )-ions
O Endocytosis- invagination of cell membrane to
form intracellular vesicle
O Exocytosis-Release of substances in the
vesicles to extracellular space
eg IgG immunoglobulin
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33. Respiratory function
O Although fetal respiratory movement
occurs by 11 week, no active
exchange of gases takes place
O Intake of oxygen and output of carbon
dioxide take place by simple diffusion
across the fetal membrane
O O2 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 function
Excretory 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
O Glucose- transferred to the fetus by facilitated
diffusion
O Lipids for fetal growth and development has dual
origin. They are transferred across the fetal
membrane or synthesized in the fetus
O Amino acids are transferred by active transport
O Water and electrolytes- Na, K ,Cl cross by simple
diffusion, Ca , P, and Fe cross by active transport
O Water soluble vitamins are transferred by active
transport but the fat soluble vitamins are
transferred slowly
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36. Barrier Function
O Placental membrane is thought to be a protective
barrier for the fetus against harmful agents in the
maternal blood
O Substances with large molecular weight or size like
insulin or heparin are transferred minimally
O Only IgG ( not IgA or Ig M )antibodies and antigens
can cross the placental barrier
O Most drugs can cross the placental barrier and some
can be teratogenic
O Various viruses, bacteria, protozoa can cross the
placenta and affect the fetus in utero
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37. Immunological function
O Inspite 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
O Placenta 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
O Enzymes secreted are diamine oxidase-which
activates the circulatory pressor amines,
oxytocinase which neutralizes oxytocin,
phospholipase A2 which synthesizes
arachidonic acid
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