2. Introduction:
• A complex organ which originates from
trophoblastic layer of the fertilized ovum
• When fully developed it serves as the
interface between the mother and the
developing fetus carrying out functions that
the fetus is unable to perform during
intrauterine life
• The survival of the fetus depends on the
integrity and efficiency of the placenta
3. Development of the placenta:
• The placenta is completely formed and functional
10 weeks after fertilization
• Within a few days of fertilization, the trophoblast
begin to produce human chorionic gonadotrophin
(hCG), to ensure that the endometrium will be
receptive to the implanting embryo
• The endometrium undergoes a series of structural
changes referred to as decidualization in
preparation for implantation
4. • The endometrium in pregnancy is referred to as the
decidua
• The decidua has regions named according to its
relationship to the implantation site:
• The decidua basalis underlies the
developing embryo and forms the maternal
side of the placenta
5. • The decidua capsularis covers the developing
embryo and bulges into the uterine cavity as the
embryo and the fetus grows
• The decidua parietalis vera (otherwise known as
the decidua vera) lines the rest of the uterine
cavity
• By about 22 weeks of gestation, the desidua
capsularis fuses with the desidua parietalis ,
filling the uterine cavity
6. • Implantations involves two stages:
• Prelacunar
• Lacunar
Prelacunar stage:
• Seven days post conception the blastocyst makes
contact with the decidua and the process of
placentation begins
7. • The process of implantation is extremely
aggressive, involving chemical mediators,
prostaglandins and proteolytic enzymes, released
by both the decidua and the trophoblast
• Maternal connective tissue is invaded
• Nearby maternal blood vessels ensure there is
optimum blood flow to the placenta
• At this stage the cytotrophoblasts form a double
layer and further differentiate into various types of
syncytiotrophoblasts
8. Lacunar stage:
• Increasing numbers of syncytiotrophoblasts
surround the blastocyst and small lakes form within
these cells known as lacunae, which will become
the intervillous spaces between the villi
9. The chorionic villous tree:
• Chorionic villi are finger-like projections of chorion
surrounded by cytotrophoblastic and
syncytiotrophoblastic layers
• Villi become most profuse in the area where the
blood supply is richest (the decidua basalis which
eventually develops into the placenta)
• The villi erode the walls of maternal blood vessels
as they penetrate the decidua, opening them up to
form a lake of maternal blood in which they float
10. • The maternal blood circulates slowly enabling the
villi to absorb food and oxygen and excrete waste
• The centre of each chorionic villi consists of
mesoderm, fetal blood vessels and branches of the
umbilical artery and vein.
• These structures are covered by a single layer of
cytotrophoblast cells and the external layer of the
villus is the syncytiotrophoblast
11. • This means that four layers of tissue separate the
maternal blood and fetal blood making it
impossible for the two circulations to mix i.e
mesoderm, fetal blood vessels, cytotrophoblast
cells, and the syncytiotrophoblast.
12.
13.
14. Circulation through the placenta:
• Maternal blood is delivered to the placental bed in
the decidua basalis by spiral arteries and flows into
the blood spaces surrounding the villi, eventually
returning to the endometrial veins and maternal
circulation
• Fetal blood low in oxygen is pumped by the fetal
heart towards the placenta along the umbilical
arteries and transported along their branches to
the capillaries of the chorionic villi, where exchange
of nutrients takes place between the fetus and the
mother
15. • Having yielded up co2 and absorbed o2 the
blood is returned to the fetus via the
umbilical vein
16. THE PLACENTA AT TERM:
Appearance of the placenta at term:
• The placenta at term is discoid in shape , about
20cm in diameter and 2.5 cm thick at its centre
and weighs 470 grams, which is proportional to
the weight of the baby
• At term, the ratio of the placenta to that of the
baby is about 1 to 7 or a seventh of the baby’s
weight
17. • The weight of the placenta may be affected by
physiological or active management of the third
stage of labour owing to the varying amounts of
fetal blood retained in the vessels
• The placenta has a maternal surface and a fetal
surface
18. Maternal surface (basal plate):
• Dark red in colour due to maternal blood
• The surface is arranged in upto 40 lobes or
cotyledons which are separated by sulci (furrows)
The fetal surface (chorionic plate):
• Has a shinny appearance due to the amnion
covering it
• Branches of the umbilical vein and arteries are
visible , spreading out from the insertion of the
umbilical cord
19.
20. The membranes:
• There are two membranes:
• Amnion
• Chorion
The Amnion
• The amnion is the inner membrane derived from
the inner cell mass and consists of a single layer of
epithelium with a connective tissue base
• It is a tough, smooth and translucent membrane
• Can be peeled off upto the insertion of the
umbilical cord
21. • It contains amniotic fluid which it produces in
small quantities as well as prostaglandin E2
which plays a role in initiation of labour
The chorion:
• Is the outer membrane that is continuous with
the edge of the placenta
• Rough, thick, opaque, friable membrane
derived from the trophoblast
22. • Its continuous with the edge of the placenta
and cannot be separated from it
• Produces enzymes that can reduce
progesterone levels and also produces
prostaglandin and oxytocin which stimulate
uterine activity
NOTE:As long as the membranes remain intact
, they protect the fetus against ascending
bacterial infections
23. FUNCTIONS:
• Functions of the placenta can easily be summarised
by using the MNEMONIC SERPENT:
1. Storage:
• The placenta metabolises glucose and stores it in
the form of glycogen and reconverts it to glucose
as required
• Also stores iron and fat soluble vitamins
24. 2. Endocrine:
• Human chorionic gonadotrophin (HCG) is
produced by the cytotrophoblastic layer of the
chorionic villi
• Its function is to stimulate the growth and
activity of the copus luteum
• Oestrogen is secreted in large amounts throughout
pregnancy
• The amount of oestrogen produced is a
measure of feto-placental well being
25. • Progesterone is produced in increasing
quantities until immediately before the onset of
labour when its levels fall
• Its main function is to act on tissues that
have already been receptive to oestrogen
• Human placental lactogen (hPL) (human
chorionic somatomammotropin hormone
(hCS)) has a role in metabolism of glucose in
pregnancy.
• Stimulates proliferation of breast tissue in
preparation for lactation
26. • Human placental growth hormone (hPGH) levels
rise throughout pregnancy
• It’s involved with hPL as a determinant of insulin
resistance in late pregnancy
• It mobilizes maternal glucose for transfer to the
fetus and contributes to lipolysis, lactogenesis and
fetal growth
27. 3. Respiration:
• The fetus obtains oxygen and excrete carbon
dioxide through the placenta
• Oxygen from the maternal haemoglobin
passes into the fetal blood by simple
diffusion, also, the fetus gives off carbon
dioxide into the maternal blood
28. 4. Protection:
• Provides limited barrier to infections
• Few bacteria can penetrate with the exception of
treponema of syphilis and the tubercle bacillus
• Substances including alcohol, some chemicals
associated with cigarrete smoking and several
types of viruses including HIV and rubella can cross
the placental barrier and this may cause congenital
abnormalities
29. • Some parasitic and protozoal diseases, such as
malaria and toxoplasmosis, will cross the placenta
• Immunoglobulins will be passed from mother to
fetus transplacentally in late pregnancy, providing
about 6–12 weeks’ naturally acquired passive
immunity to the baby.
30. 5.Excretion:
• Main substance excreted from the fetus is
carbon dioxide
• Bilirubin is also excreted as red blood cells are
replaced relatively frequently
• Small amounts of urea and uric acid are also
excreted
31. 6. Nutrition:
• Nutrients are transferred from the maternal
to fetal blood through the walls of the villi.
• These nutrients include amino acids required
for body building, large quantities of glucose
for growth and development, calcium and
phosphorus for bones and teeth, iron and
other minerals for blood formation
32. 7. Transfer of substances:
• Substances transfer to and from the fetus by
a variety of transport mechanisms:
• Simple diffusion of gases and lipid soluble
substances
• Water soluble substances are transferred
through water pores as a result of osmotic
and potentially hydrostatic forces
33. • Facilitated diffusion of glucose using
carrier proteins
• Active transport against concentration
gradients of ion, calcium, and phosphorus
• Endocytosis (pinocytosis) of
macromolecules
34. AMNIOTIC FLUID (LIQUOR
AMNII):
• Amniotic fluid is a clear , alkaline, and slightly
yellowish liquid contained within the amniotic sac.
Functions:
• Distends the amniotic sac and allows for the
growth and free movement of the fetus
• Acts as a shock absorber and protects the fetus
from jarring and injury
• The fluid maintains intrauterine temperature for
the fetus
35. • Provides small amounts of nutrients
• Protects the placenta and umbilical cord
from the pressure of uterine contractions
• Aids effacement of the cervix and dilatation
of the uterine os, particularly where the
presenting part is poorly applied
36. Origin:
• The source is thought to be both maternal and
fetal
• Its secreted by the amnion especially that which
covers the placenta and umbilical cord
• Some fluid is exuded from maternal vessels in
the decidua and some from fetal vessels in the
placenta
• Fetal urine also contributes to the volume from
the 10th week gestation onwards
37. Volume:
• Amniotic fluid increases in volume as the
fetus grows
• The volume is greatest at approximately 38
weeks gestation when there is about 1 litre,
it then diminishes slightly until term, when
approximately 800mls remains
38. • If the total amount of fluids exceeds
1500mls, the condition is known as
polyhydramnios(hydramnios)
• If less than 300 mls, the condition is known
as oligohydramnios
• Such abnormalities are often associated with
congenital malformations of the fetus
39. • The normal fetus swallows amniotic fluid but if
anything interferes with swallowing, an excessive
amount of fluid will accumulate
• Similarly if the fetus is unable to pass urine, the
amount of fluid will be reduced
40. Constituents of amniotic fluid:
• Consist of 99% water
• The remaining 1% is dissolved solid matter
including food substances and waste products
• The fetus also sheds skin cells, vernix caseosa and
lanugo into the fluid
• In the case of fetal compromise, meconium may
give valuable diagnostic information about the
condition of the fetus
41. THE UMBILICAL CORD (funis):
• Extends from the fetal surface of the placenta to
the umbilical area of the fetus, and is formed by
the 5th week of pregnancy
• It originates from the duct that forms between the
amniotic sac and the yolk sac and transmits the
umbilical blood vessels
43. Structure:
• The umbilical cord contains 2 arteries and one vein
which are continuous with the blood vessels in the
chorionic villi of the placenta
• The blood vessels are enclosed and protected by
wharton’s jelly, a gelatinous substance formed
from mesoderm
• The whole cord is covered by a layer of amnion
which is continuous with that covering the placenta
• A missing blood vessel in the cord may indicate
renal malformations in the fetus
44.
45. Measurements:
• Approximately 1-2 cm in diameter and 50 cm in
length
• A cord is considered short when it measures less
than 40cm
• Disadvantages of a long cord are that it may
become wrapped round the neck or body of the
fetus, or may become knotted
46. • Any of these events may result to occlusion of the
blood vessels especially during labour
• True knots should be noted on examination of the
cord and should be distinguished from false knots
which are lumps of wharton’s jelly on the side of
the cord and are not significant
47. ANATOMICAL VARIATIONS OF
THE PLACENTA AND THE CORD:
Succenturiate lobe of placenta:
• A small extra lobe is present , separate from the
main placenta and joined to it by blood vessels
which run through the membranes to reach it
• If retained in utero after the placenta is delivered ,
and not removed , may lead to infection and
haemorrhage
• Every placenta must be examined for evidence of a
retained succenturiate lobe which can be identified
by a hole in the membranes with blood vessels
running to it
48.
49. Circumvallate placenta:
• An opaque ring is seen on the fetal surface of the
placenta
• Formed by a doubling back of the chorion and
amnion and may result in the membranes leaving
the placenta nearer the centre instead of at the
edge
• It’s associated with placental abruptio and
intrauterine growth restriction (IUGR)
50.
51. Battledore insertion of the cord:
• The cord is attached at the very edge of the
placenta in the manner of a table tennis bat
• It is not important unless the attachment is fragile
52.
53. Velamentous insertion of the cord:
• The cord is inserted into the membranes some
distance from the edge of the placenta
• The umbilical vessels run through the membranes
from the cord to the placenta
• The cord may be detached upon applying traction
during delivery
54. • If the placenta is low lying , the blood vessels may
pass across the uterine os (vasa praevia) and may
be ruptured during ARM leading to fetal
haemorrhage
55.
56. Bipartite placenta:
• Two complete and separate parts are present each
with a cord leaving from it
• The bipartite cord joins a short distance from the
two parts of the placenta
• A tripartite placenta is similar to a bipartite but it
has 3 distinct parts.
