The placenta develops from trophoblast cells of the embryo. It forms chorionic villi which branch into tertiary villi containing fetal blood vessels. The placenta supports fetal growth through nutrient and gas exchange between maternal and fetal blood across the thin placental membrane. It also produces hormones like HCG, progesterone and estrogen essential for maintaining pregnancy. The mature placenta has a fetal side and a maternal side with cotyledons and septa. It transfers nutrients, gases, antibodies and metabolites while acting as a barrier and producing hormones throughout gestation. Exposure to certain chemicals, drugs or infections during pregnancy can potentially cause fetal abnormalities known as teratogenesis.

1. Placental structure and
Function.

2. Competency
• OG4.1:Describe and discuss the basic
embryology of fetus, factors influencing
fetal growth and development, anatomy
and physiology of placenta, and
teratogenesis

3. Competency
• OG4.1 (part 2): Development of Placenta,
anatomy and physiology of placenta and
teratogenesis.

4. Objectives
• At the end of this session you will
understand
• 1.Development of placenta,
• 2. Anatomy and physiology of Placenta,
• 3. Teratogenesis.

5. Introduction
• The placenta is the highly specialized organ of pregnancy
that supports the normal growth and development of the
fetus.
• Term placenta means a circular cake, was first used by
Realdus Columbus in 1559.
• Also known as the after birth, placenta has varied
functions in fetuses’ intrauterine life.
• It serves as the conduit between the mother and fetus
transferring nutrients , gases and immunity from mother.
• It also secretes hormones to support the pregnancy.

6. Early development of embryo.
• Ovulation
• Fertilization.
• Mitotic cell division - morula.
• Blastula/ blastocyst.
• Hatching of blastocyst.
• Development of trophoblast.
• Division into cyto/ syncitiotrophoblast.
• Implantation.

7. Early development

9. Implantation.
• Zona pellucida disappears,7 ½ days after
fertilization.
• Adherence of blastocyst to endometrial
surface.
• Erosion of endometrium-> blastocyst sinks
into endometrium.
• The crater thus created sealed by decidua
parietalis.

10. Placenta and Embryo at 8
Weeks
At 8 weeks of pregnancy,
the placenta and fetus have
been developing for 6
weeks. The placenta forms
tiny hairlike projections
(villi) that extend into the
wall of the uterus. Blood
vessels from the embryo,
which pass through the
umbilical cord to the
placenta, develop in the
villi. A thin membrane
separates the embryo's
blood in the villi from the
mother's blood that flows
through the space
surrounding the villi
(intervillous space). This
arrangement allows
materials to be exchanged
between the blood of the
mother and that of the
embryo. It also prevents the
mother's immune system
from attacking the embryo
because the mother's
antibodies are too large to
pass through the
membrane.
The embryo floats in fluid
(amniotic fluid), which is
contained in a sac (amniotic
sac). The amniotic fluid
provides a space in which
the embryo can grow freely.
The fluid also helps protect
the embryo from injury. The
amniotic sac is strong and
resilient.

11. Formation of placenta.
• As early as 72 hours after fertilization the 58 cell
blastula has 5 embryo producing cells and 53
trophoblast producing cells.
• Outer layer of embryo ->trophoblast.
• Divides into outer - syncytiotrophoblast.
• inner  cytotrophoblast.
• It invades maternal decidua,maternal blood
vessels are invaded.
• Large vacuolated spaces form in
syncytiotrophoblast called lacunae, soon get
filled with maternal blood,

12. Placental development.
• Placenta develops from trophoblast.
• The basic unit of placenta is the chorionic
villous.
• The outgrowth of trophoblast in finger like
projections gives rise to a primary villous.
• It branches several times to form
secondary villous.
• A core of mesodermal tissue invades the
chorion to form blood vessels.

14. Chorionic villous.
• Villi are formed as early as12th day after
fertilization.
• They are the main structure which forms
placenta.
• Solid columns of cyto+ syncytio trophoblast are
formed all around the embryo.primary
villous.
• A core of mesenchyme invades into the finger
like villi, secondary villous.
• The villi branch into tertiary villous.

15. Chorionic villi

16. Tertiary villous.
• Is covered by two layers of trophoblast, with a
mesenchymal core which differentiates into
blood vessels.
• The intervillous space develops big lacunae
which get filled with maternal blood.
• By 17th day maternal and fetal blood vessels are
functional.
• Fetal circulation is completed when vessels of
embryo are connected to the chorionic blood
vessels.

17. Chorionic villous
• The blastocyst buries into decidua is covered by
decidua parietalis.
• Decidua below it is called decidua basalis, the
decidua of the rest of the uterine cavity is
decidua capsularis.
• The chorion in contact with decidua is called
chorion frondosum,and the rest of the chorion is
called chorion leavae, which thins down to form
chorionic membrane..

18. Placental cotyledons
• Chorionic villi extend from the chrionic plate to
the decidua and serve as anchoring villi.
• Most villi end free in the intervillous space
bathed by maternal blood, without reaching
decidua.
• As placenta matures these villi branch
repeatedly ,each of the main stem villous forms
the cotyledons.
• Multiple such cotyledons make circular cake like
structure of the mature placenta.

20. Placenta –gross appearance

21. Placental septa.
• Origin of the septa which separate the
cotyledons is not clear,
• They might have maternal as well as fetal
components.
• These are absent in the early gestation ,
but as fetus grows and placenta matures
these get more pronounced, in a mature
grade 3 placenta these reach the basal
plate.

22. Mature placenta
• Shape circular
• Weight -500-600 gms[1/6th of fetus]
• Diameter 15 to 20 cms
• Thickness -2 to 3 cms
• Surfaces –
– fetal surface
– Maternal surface

23. Mature placenta.
• Mature placenta is circular discoid structure.
• It has a maternal surface and a fetal surface
• Maternal surface is in close opposition to the
uterine decidua,
• it is broken down into lobes or cotyledons
separated by septae.
• Giving it a cauliflower like appearance.

24. Mature placenta
• The fetal surface is facing toward the
amniotic cavity,
• is covered by amniotic membrane,
• the umbilical cord is attached in the
centre,
• the placental vessels radiate from the
central cord insertion

25. Term placenta

26. Abnormal placenta.
• Battledore placenta.
• Succenturate lobe.
• Velamentous attachment of cord.
• Morbidly adherent placenta.

27. Placental aging.
• As the villi branch the volume and prominence of
cytotrophoblast decreases, and syncytial knots
appear.
• Vessels become more prominent and lie closer
to the surface.
• The connective tissue interposing the villi
becomes more prominent.
• Hofbauer cell (fetal macrophages)decrease in
the stroma,
• Syncitial layer thins and cells of Langerhans
disappear.

28. Functions of placenta.
• Transfer of nutrients.
• Respiration.[Oxygen and CO2 exchange]
• Transfer of antibodies.
• Production of hormones.
– HCG, HPL, estradiol, progesterone, Human chorionic
thyrotropin.
– Chorionic ACTH,
• Production of non specific pregnancy associated
proteins and hormones.

29. Transfer of nutrients
• Glucose is the main nutrient that reaches foetus by
facilitated diffusion
• Fats and phospholipids are picked up by placenta and
converted to simpler fats in the membrane
• Amino acid are in greater concentration than maternal
serum ,transferred across a gradient
• Most of the foetal fats come from carbohydrates.
• Water is transferred by both transfusion and osmotic
transfer
• About 3-4 litres of water is exchanged between mother
and foetus/day

30. Gaseous exchange
• Gases oxygen and Carbon dioxide cross
placenta by simple diffusion
• The red cells of foetus have a greater
affinity for oxygen.

31. Metabolic function
• It metabolizes a number of substances
and can release metabolic products into
maternal and/or fetal circulations
• The placenta can help to protect the fetus
against certain infections and maternal
diseases.

32. Hormonal function
• Progesterone is formed in placenta from
maternal cholesterol
• Most of this is transferred to mother but some of
it goes to foetus for conversion to gluco-
corticoids and minerelo-corticoids by foetal
adrenal gland
• Oestrogen is produced by placenta from 19-
carbon androgen(androstenedione and dehydro-
epiandrosteinidione)by action of aromatase
enzyme.
• Placenta gets the substrate from mother

33. Function of oestrogen and
progesterone
• Maintenance of pregnancy
• Growth ,vascularity and decidualization of
uterus, uterine quiescence
• Onset of labour –by fall of progesterone
near term, increases uterine excitability
• Development of breasts (Ducts 
progesterone , Glands ,oestrogen )
• Initiation and maintenance of Lactation

34. HCG
• Secreted by syncytiotrophoblast soon after implantation
detected in maternal serum by 8 day post conception
• Actions –
– sustains corpus leuteum
– Stimulates Leydig cells of male foetus to secrete testosterone 
development of male genatalia
– Stimulates maternal thyroid gland
– Immunosupressive action helps in maintaining pregnancy
– Promotes relaxin secretion by corpus leuteum

35. HPL
• Polypeptide hormone
• Levels of HPL correspond with foetal and placental
growth
• Responsible for diabetogenic state of pregnancy along
with other placental hormones
• A potent angiogenic hormone promotes foetal
vasculature formation

36. PAPP-A
• Produced by developing placenta ,increases
after 7 weeks of pregnancy
• Clinical application in first trimester is for
screening for aneuploidies
• Useful in predicting preeclampsia along with
uterine artery Doppler studies.
• Other hormones produced by placenta are
relaxin, pregnancy specific beta1 glycoprotein,
placental protein 13,and growth hormone

37. Immunologic and barrier function
• Foetus gets passive immunity against infectious
diseases from mother through placenta
• Placenta transfers some drugs given to mother
which used to treat foetus eg steroids
• Placenta also acts as a barrier against some
drugs consumed by mother

38. Teratogenesis
Any chemical/drug,
infection,physical condition or
deficiency that on foetal exposure
can alter foetal morphology or
subsequent function.

39. Causes :
-Multifactorial (70%),
-Genetic(20%),
-Enviornmental(10%)
intrauterine inf 2 %,
maternal metabolic disorders (2%)
drugs and chemicals ( 5%)
ionizing radiations (1%)

40. Factors determining the effect of
teratogenesis :
Fetal factors:
-Developmental stage:
-Prodifferentiation stage (0-7 days
of gest):
death or no effect.
-Differentiation stage(7- 57 days of
gest.):
malformation

41. Post differentiation stage(after
57days of gest.):
-functional defects,
-growth retard.

42. Ques./Ans.
Q1. Maternal component in
development of placenta is:
a. decidua parietalis
b. decidua basalis,
c. decidua capsularis

43. Q.2. Functions of placenta is
/are:
a. nutritive,
b. respiratory,
c. excretory,
d. all of above

44. Q.3.Which blood is in intervillous
space?
a. mixed maternal and fetal
b. maternal blood
c. fetal blood
d. there is no blood here

45. Thank you.