placenta

2. PLACENTA
 The Placenta is an organ that connects the
developing fetus to the uterine wall of
mother.
 Placentas are defining characteristic of
placental mammals.
 The Placenta functions as a fetomaternal
organ with two components:
1. Fetal Placenta (Chorion Frondosum)
2. Maternal Placenta(Decidua Basalis)

3. STRUCTURE
1. In Humans, the placenta
averages 22cm in length and
2-2.5cm in thickness.
2. Weight = 500gms.
3. Colour = dark reddish blue
or crimson .
4. It connects to the fetus by an
umilical cord of approx. 55-
60cm which contains
2umbilical arteries and 1
umbilical vein.

4. PHYSIOLOGY
This Outer layer is divided into two further layers
The underlying Cytotrophoblast layer.
The overlying
Synctiotrophoblast layer.
The Outer layer of blastocyst becomes the trophoblast which
forms the outer layer of placenta.
The Placenta begins to develop upon implantation of the
blastocyst into the maternal endometrium.

5.  The syncytiotrophoblast is a multinucleated
continuous cell layer that covers the surface of
placenta.
 It forms as a result of differentiation & fusion of
underlying cytotrophoblast cells.
 The synctiotrophoblast thereby contribute to the
barrier function of placenta.
 The placenta grows throughout pregnancy.

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

7. Development Of Placenta
 The villous chorion ( increase in number, enlarge and
branch ) will form the fetal part of the placenta.
 The decidua basalis will form the maternal part of the
placenta.
 The placenta will grow rapidly.
 By the end of the 4th month, the decidua basalis is
almost entirely replaced by the fetal part of the
placenta.

8. DEVELOPMENT OF
PLACENTA
 Until the beginning of the 8th week,
the entire chorionic sac is covered
with villi.
 After that, as the sac grows, only the
part that is associated with Decidua
basalis retain its villi.
 Villi of Decidua capsularis
compressed by the developing sac.
 Thus, two types of chorion are formed:
Chorion frondosum (villous chorion)
Chorion laeve – bare (smooth) chorion
 About 18 weeks old, it covers
15-30% of the decidua and
weights about 1 6 of fetus

9. STRUCTURE OF STEM
CHORIONIC VILLUS

10. PLACENTAL MEMBRANE
 This is a composite structure
that consists of the extrafetal
tissues separating the fetal
blood from the maternal
blood.
 It has four layers:
 Syncytiotrophoblast
 Cytotrophoblast
 Connective tissue of villus
 Endothelium of fetal
capillaries
 After the 20th week, the
cytotrophoblastic cells
disappear and the placental
membrane consists only of
three layers.

11. FORMATION OF CHORIONIC VILLI
 The essential functional elements of placenta are small finger
like processes or villi.
 As the trophoblast along with underlying extra-embryonic
mesoderm, constitutes the chorion ,the villi, arising from it are
called chorionic villi.
 The chorionic villi are first formed all over the trophoblast and grow
into the surrounding decidua those related to the decidua capsularis
are transitory. After some time they degenerate. This part of the
chorion becomes smooth and is called the chorion laevae.
 In contrast, decidua undergo considerable development. Along with
the tissues of the decidua basalis these villi form a disc-shaped mass
which is called the placenta. The part of the chorion that helps form
the placenta is called the chorion frondosum.

12. • All elements (syncytium, cytotrophoblast and mesoderm) take part in
forming chorionic villi.Three stages in formation of chorionic villi are
seen:
 Primary villi : cytotrophoblast and is covered by the cells of
syncytiotrophoblast.
• Secondary villi : Outer syncytiotrophoblast, intermediate
cytotrophoblast & inner layer of extra embryonic mesoderm.
• Tertiary villi : like secondary villi except that there are blood
capillaries in the mesoderm.

13. 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

15. PLACENTAL CIRCULATION
PLACENTAL CIRCULATION
FETOPLACENTAL
CIRCULATION
MATERNAL PLACENTAL
CIRCULATION

16. PLACENTAL CIRCULATION

17. Functions Of Placenta
1.
•Transfer of nutrients & waste product.
2.
•Enzymatic function
3.
•Barrier function
4.
•Immunological function
5.
•Storage & Endocrinal function

18. FULL-TERM PLACENTA
 Cotyledons –about 15 to 20 slightly
bulging villous areas. Their surface
is covered by shreds of decidua
basalis from the uterine wall.
 After birth, the placenta is always
inspeced for missing cotyledons.
Cotyledons remaining attached to
the uterine wall after birth may
cause severe bleeding.
 Grooves – formerly occupied by
placental septa
 The fetal part of placenta; fetal
membranes called developmental
adnexa
 Placenta;fetal membranes which are
expelled are called afterbirth or
secundina

19. FULL-TERM PLACENTA
 Fetal surface:
 This side is smooth and shiny.
It is covered by amnion.
 The umbilical cord is attached
close to the center of the
placenta.
 The umbilical vessels radiate
from the umbilical cord.
 They branch on the fetal
surface to form chorionic
vessels.
 They enter the chorionic villi
to form arteriocapillary-
venous system.

20. PLACENTAL DISEASES
PLACENTA
PRAEVIA:-
 The attachment of
the placenta may
extend partially , or
completely into the
lower uterine
segment.

21. Various degrees of placenta praevia
 First degree:-the attachment of
placenta extends into the lower
uterine segment , but does not reach
the internal os.
 Second degree:- The margin of
placenta reaches the internal os but
does not cover it.
 Third degree:- The edge of placenta
reaches the internal os but when the
os dilates during childbirh the
placenta no longer occludes it.
 Fourth degree:- The placenta
completely covers the internal os ,
and occludes the os even after it has.

22. Other Anomalies Of
Placenta
•when it consists of two discs.
Bidiscoidal
•When it is divided into lobes.
Lobed
•When there is a hole in the
disc.Fenestrated

23. • When a small part of the placenta is
separated from the rest of it
Placenta
succenturiata
• When peripheral edge of placenta is
covered by a circular fold of decidua.Circumvallate
• When chorionic villi persist all round
the blastocyst; placenta is thin & does
not assume the shape of a disc.
Diffuse