Transcript Placenta

‫بسم هللا الرحمن الرحيم‬
Placenta
The placenta is the site
of nutrient and gas
exchange between the
fetus and mother.
Shape:
The full term placenta is
discoid in shape.
 Diameter = 15-25 cm,
 2-3 cm thick,
 Weight = 0.5 kg.
 Umbilical cord is attached
to its center.
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Surfaces:
- It has 2 surfaces:
1- fetal surface: which
is smooth and shinny
because it is covered by an
amniotic membrane. The
umbilical cord is attached
centrally to this surface.
2- maternal surface:
which is rough, reddish, and
has 15 – 20 elevated areas
called cotyledons with deep
grooves in between made by
the decidual septa.
Development:
Maternal part: decidua basalis.
Fetal part: chorion frondosum.
Villi:
-primary chorionic villi.
-secondary chorionic
villi.
-Tertiary chorionic villi.
A- Villi opposite decidua
basalis proliferate  chorion
frondosum.
Villi of chorion frundosum
are divided into:
1- Anchoring villi: reach
decidua basalis. They are used
for fixation of the fetus to the
uterus.
2- Free villi ( nourishing): do
not reach decidua basalis. They
are used for nutrition of the
fetus.
B- Villi opposite decidua
capsularis degenerate 
chorion laeve.
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Tertiary chorionic villi contain embryonic
blood vessels that develop in loose connective
tissue core. These blood vessels connect up with
vessels that develop in the chorion and
connecting stalk.
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Maternal blood is derived to the placenta by 80 – 100
spiral arteries in the uterus.
Erosion of these maternal vessels to release blood into
the intervillous spaces is done by trophoblast cells which
invade the terminal ends of spiral arteries.
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During the 4th and 5th month, the decidua forms a
number of decidual septa, which project into the
intervillous space.
As a result of this septum formation, the placenta is
divided into a number of compartments (cotyledons).
Sructure of placenta
Placental Circulation:
1. Fetal circulation.
2. Maternal circulation.
Maternal circulation
- Uterine artery → Spiral
artery → intervillous
space (where exchange
of oxygen and CO2
between mother and
fetus occurs through
the placental barrier)
- The venous blood will
collect in the marginal
vein → uterine vein.
Fetal circulation
- The CO2 and wast
products of the
embryo reaches to
the placenta through
2 umbilical arteries.
These 2 arteries end
by capillaries inside
the tertiary villi
where exchange of
CO2 and O2 will
occur through
placental barrier.
- The oxygen reaches
the embryo through
the umbilical vein.
Fetal Circulation
Placental (membranes)
barrier:
-These are layers separating the
fetal blood in the villi from
maternal blood in the intervillous
space.
-These layers prevent mixing of
the fetal and maternal blood but
they allow passage of certain
substances throw it.
-It is not a true barrier because
only few substances are unable
to cross it. Most drugs in the
maternal blood can pass through
it to the fetal circulation and
cause major fetal congenital
anomalies.
10 weeks
full term
(placental membrane)
- Early in pregnancy (till about 20 week gestation), it is formed of four
layers (Fig. 56):
a. The endothelial lining the fetal vessels.
b. The connective tissue (mesoderm) of the villus.
c. The cytotrophoblast layer.
d. The syncytiotrophoblast.
- After 20 weeks the cytotrophoblasts degenerate so increases the
permeability of the placenta.
- Towards the end of
pregnancy, a fibrinoid
material made of fibrin is
formed on the surface of
the villi to decrease the
permeability, so the
placental barrier is
formed of this fibrinoid
material, the
syncytiotrophoblasts, and
the endothelium of the
fetal blood vessels.
Functions Of The Placenta
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Exchange of gases (lung).
Exchange of Nutrients and Electrolytes
(GIT).
Excretion of waste products (kidney).
Transmission of Maternal antibodies
resulting in passive immunity of the fetus.
Hormone Production as Progesterone
(maintains the corpus luteum so prevents other
ovulations and prevents menses during
pregnancy), estrogenic hormones (estriol), HCG,
relaxin hormone to soften the uterine ligaments
to help delivery and Somatomammotropin.
Functions of placental barrier:
1.
2.
It prevents most organisms from passing to
the fetus, so it acts as a protective mechanism
against damaging factors, many viruses such
as Rubella, Coxackie virus, German measles
and poliomylitis virus traverse the placenta.
These viruses may result in congenital
malformations.
Most of the drugs in addition to cocaine,
heroin cross the placenta and cause serious
damage.
Abnormalities of placenta
1- According to site: Placenta Praevia
the placenta is attached to the lower uterine segment (due
to low level of implantation of the blastocyst). It causes
severe antepartum haemorrhage. There are three types:
2- Abnormal penetration into the
uterus:
1- Placenta accreta:
due to abnormal adhesion
between the chorionic
villi and the uterine wall.
2- Placenta percreta:
The chorionic villi
penetrate the
myometrium all the way
to the perimetrium.
- the placenta fails to
separate from the uterus
after birth and may cause
severe postpartum
hemorrhage.
3- Abnormal attachment of umbilical cord:
a- Velamentous attachment:
The cord does not reach the placenta itself but is attached
to amniotic membrane over the fetal surface of placenta.
The umbilical vessels pass in the membrane to reach the
placenta. It is easly torn.
B- Battle- dore placenta (marginal attachment of
the cord
4- Abnormalities according to
the number:
1- Double placenta
(bilobed or bidiscoid
placenta).
2- Triple placenta
(trilobed).
3- Accessory placenta (accessory one or more lobes). It may
cause severe postpartum hemorrhage if the accessory lobe is
retained in the uterus after labor.
5- Shape abnormalities: bi- or trilobed or horsehoe
placenta
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