PLACENTA
Placenta
-?
Placenta
Placenta
Maternal component: Uterine Endometrium
(decidua)
Fetal component : Trophoblast and
Extraembryonic mesoderm.
Measurement : Discoid – 15-25 cm in diameter.
3 cm thick in the centre.
500-600gm in weight
Full-term placenta
A. Fetal surface is smooth
1. Covered by amnion & Chorionic plate
2. The umbilical cord is attached close
to the center of
this surface.
3. Beneath the amnion, the chorionic
( umbilical) radiate from the cord.
B. Maternal surface is rough
and irregular
4. Shows polygonal areas(15-30) the
cotyledons,
limited by fissures.
5. Each fissure is occupied by placental
(decidual)
septum.
In one area, the decidua has been
removed to show the cotyledons.
Villous
Basal
placenta
plate
Amni
on
Chori
on
laeve Uteri
ne
Decidua
wall
parietalis
Cerv
ix
The PLACENTA and FETAL MEMBRANES separate the fetus
from the ENDOMETRIUM, mucous membrane of the uterine
wall.
interchange of substances, such as nutrients between the
maternal and fetal blood streams through the placenta.
VESSELS in UMBILICAL CORD connect placental
circulation and fetal circulation.
After birth, PLACENTA and FETAL MEMBRANES -
AFTERBIRTH.
Functions
1. Nutrition -Transfer of water , nutrients and electrolytes
such as glucose, amino acids, free fatty acids,
carbohydrates , lipids and vitamins.
2. Respiration Gas Exchange
3.
3. Excretion Excretion of waste products
4. Hormones- Progesterone , Estrogen , Human
chorionic gonadotrophin and Somatomammotrophin
5. Maternal Transfer - immunoglobulins antibodies
Provide passive immunity against diseases
Transfer is by micropinocytosis
Formation: placenta
The fetal part of the placenta is formed by
the chorionic villi at the embryonic pole,
called as chorion frondosum.
The chorionic villi at the abembryonic pole,
degenerate and known as chorion laeve.
The maternal part of the placenta is
formed by the decidua basalis.
Thus the placenta is formed by Chorion
frondosum & Decidua basalis.
Formation:Foetal Part
Early placental
development is
characterized by:
1. The rapid
proliferation of
the trophoblast
and
2. Development of
the chorionic sac
and chorionic
villi.
Formation:Foetal Part
Trophoblast –
1. Forms outer wall of blastocyst.
2. Proliferate and forms two layers:-
Inner - cytotrophoblast
Outer - syncytiotrophoblast
Chorion -
Trophoblast lined by extraembryonic
somatopleuric mesoderm
Chorionic villi -
Projections of syncytiotrophoblast and then
cytotrophoblast
Then its lining mesoderm into the decidua
basalis.
Chorion
At 32-33
days
(Trophoblast lined by extraembryonic
somatopleuric mesoderm)
Embryonic pole
shows extensive
villous formation
at the chorion
frondosum.
Abembryonic
pole smooth
and villous
free at the
chorion
Chorionic villi
Primary chorionic villi - inner
cytotrophoblast and outer
syncytiotrophoblast
Secondary chorionic villi -
extraembryonic mesoderm
penetrates in the core of primary
villi
Tertiary / definitive chorionic
villi mesoderm differentiate to
form capillaries
Villi
STEM or ANCHORING VILLI :
The cytotrophoblast within the villi
continues to grow through the invading
syncytiotrophoblast and makes direct contact
with the decidua basalis
CYTOTROPHOBLASTIC SHELL
Further cytotrophoblast proliferation occurs
laterally so that neighbouring outgrowths
meet to form a spherical CYTOTROPHOBLASTIC
SHELL around the conceptus.
Lateral projections from the main stem villus
form TRUE and TERMINAL VILLI .
Development of placenta
Cotyledonary
septum
Cytotrophbla Basal
stic plate
Lacunae
cell
Lacuna column
Lacunae in enlarging
r as intervillus
syncytyium
circulat spaces
Maternal ion
vessels
In decidua
Intervill
us
space
Cytotroph
blast
Fetal In growth of
vessels cytotrophoblas Chorio
Maternal t True nic
1. Primary blood and mesoblast villus Secondar
y plate
bearing fetal
villus vessels
syncytial
3. Tertiary fusion
2. villus
Secondary 4. Stem or 5. True or Terminal
villus Anchoring villus
villus
1. Projections of 4 . Cytotrophoblast within the villi continues
syncytiotrophoblast to
2. Invaded first with cytotrophoblast grow through the invading syncytiotrophoblast
and then with
and makes direct contact with the
mesenchyme 5. Lateral projections from the main stem
3. Fetal capillaries develop in thedecidua
villus
basalis
mesenchymal core
Maternal part of placenta
DECIDUAL REACTION
At implantation endometrium in
secretary phase stromal cells
enlarged, vacuolated, contain
glycogen and lipids.
ENDOMETRIUM is now called
DECIDUA .
DECIDUA BASALIS - At the site of
implantation.
DECIDUA CAPSULARIS - The part
that separate the embryo from the
uterine cavity.
DECIDUA PARIETALIS - The
part lining the rest of uterine cavity.
At the termination of pregnancy, the
decidua is shed off, along with
placenta and Membranes.
DECIDUA
(
1
1. BASALIS )
2. CAPSULARIS
3. PARIETALIS
(
3
)
(2)
Cotyledons in the basal plate
3rd month onwards:
The basal plate --- PLACENTAL OR COTYLEDONARY
SEPTA (ingrowths of the cytotrophoblast covered with syncytium)
that grow toward but do not fuse with the chorionic plate.
TheSEPTA divide the maternal surface of the placenta into
15–30 LOBES, termed COTYLEDONS.
Each cotyledon surrounds a limited portion of the intervillous
space associated with a villous trunk from the chorionic plate.
4th month onwards
These septa are supported by tissue from
the DECIDUA BASALIS.
Throughout the second half of pregnancy :
1. The basal plate becomes thinned
2. Diminution of the decidual elements
3. Increasing deposition of fibrinoid
4. Admixture of fetal and maternal derivatives.
TS: full-term placenta
Fetal
circulation
(1) The villous chorion (fetal part of
placenta)
The decidua basalis (maternal
part of placenta).
(2) The fetal placental circulation.
The umbilical arteries (poorly
oxygenated fetal blood) .
The umbilical vein (oxygenated blood)
(3) The maternal placental circulation.
Maternal blood flows into the
intervillous space from the
spiral endometrial arteries.
The inflowing arterial blood pushes into the
endometrial veins of the decidua
basalis. Maternal
(4) The cotyledons are separated from each circulation
other by placental septa.
Each cotyledon consists of two or more main
stem villi and many branch villi.
Placental Barrier
Placenta consists of ?
Transfer Through ?
Layers of ?
Placental Barrier - ?
Layers of barrier- ?
Formation placental barrier 4th
week
A
B
A.
A. During the fourth week. B C. T.S. of the villus showing
The . Placental barrier
extraembryonic
mesoderm
penetrates the
Formation placental barrier 4th
month
Deci
dua
A. In many small villi, the wall of A. T.S. of the villus
the showing
capillaries is in direct Placental
contact barrier
with the syncytium.
A full-term human fetus in the
uterus
Sectional view of the placenta:
Amnion (mauve)
Chorion (green)
Uterine wall and cervix (yellow)
The cervix with a mucus plug in the cervical
canal
The umbilical cord and its contained vessels
The characteristic flexed posture of the
fetus
Relation of fetal membranes to the wall of
the uterus.
Chorionic
and
Uterine
cavities
are
obliterated
End of the 2nd month. End of the 3rd month.
The yolk sac is in the chorionic cavity The amnion and chorion have fused.
between the amnion and chorion. The uterine cavity is obliterated by
At the abembryonic pole, villi have fusion
disappeared (chorion laeve). of the chorion leave , and the
decidua parietalis.
Relation of the placenta to the uterine
segments
The uterus is divided into two main
regions: (Normal attachment of
body forms the upper two-thirds,
placenta)
cervix forms the lower third.
The upper uterine segment
Fundus
Greater part of the body
The lower uterine segment
Lower part of the body
Upper 1/3rd of Cervix
Placenta praevia and its types
Attachment of placenta into
lower uterine Segment is called
PLACENTA PRAEVIA
Difficulty during child birth
Can cause severe bleeding.
A B
Firs Seco
t nd
deg degr
ree ee
C D
Thir Fou
d rth
deg deg
ree ree
Placenta Praevia
It is of four types:-
A. First degree
Extend into L.U.S. ,but
does not reach the
internal os
B. Second degree A B
Reach the I.O. , but does
not cover it. Firs Seco
C. Third degree t nd
Covers the Internal os , deg degr
but does not occlude the ree ee
os when it is dilated
during child birth.
D. Fourth degree
Completely covers the C D
internal os and occludes
the os even when Fou
it is dilated. Thir
d rth
deg deg
ree ree
Anomalies of placenta
Bidiscoidal Two discs
Lobed Divided into lobes
Diffuse Chorionic villi
persist
all over the
blastocyst
Placenta succenturiata
When a small
part of it is
separated from
rest of it
Fenestrated placenta Fold of
decidua
Presence of hole
in the disc
Circumvallate placenta
Periphery is covered
by decidua
attachment of umbilical cord to placenta
(A) Normal
Near the centre
(B) Battledore
(Marginal ) At the
margin
(C) Furcate
Blood vessels divide
before reaching the placenta
D) Velamentous Insertion of
cord: cord fails to reach placenta
attached to the foetal membrane
close to periphery of the organ
Vessels are attached to the
amnion , where they ramify before
reaching the placenta
?
