2. Implantation
• The morula and blastocyst formed from the
fertilized egg is enclosed by Zona pellucida
• The ZP prevented the implantation of the
sticky blastomeres during the tubal passage to
the uterus
• As the blastocyst move toward the uterus, its
thin out and eventually disappears
3. Implantation
• Prior to the disappearance of the ZP, the
blastomeres had been arranged into
– The outer cell mass – which eventually become the
trophoblast
– The inner cell mass
• The outer cell mass make a direct contact with
the endometrium and attached to it with the
disappearance of the ZP
• This attachment is called Implantation which
occurred about 4 to 6 days after fertilization.
4. Implantation
• Implantation is a sequel of integrated
processes involving three principal
mechanisms which are
– Muscular
– Adhesive
– Invasive
• The implantation in man is interstitial with a
direct contact between the fetal membrane
and the maternal blood – Haemo-chorial
5. Implantation
• Prior to implantation the uterus is in the
secretory phase during which the uterine
glands and arteries become coiled and the
tissue becomes succulent.
• The endometrium is also arranged into three
layers namely
– Compact
– Spongy
– Basal
6. Implantation
• The human blastocyst normally implants in
the endometrium along the posterior or the
anterior wall of the body of the uterus, where
it becomes embedded between the openings
of the gland.
• More of the posterior than the anterior wall of
the uterus.
• Occationally, it can implant low in the uterusPlacenta previa
7. Implantation
• It adheres like a parasite to the uterine
mucous membrane and it destroys the
epithelium over the area of contact, and
excavates for itself a cavity in the mucous
membrane in which it becomes imbedded.
• The site of implantation is temporarily seal by
fibrin and blood clot but later the site is
replaced by the the mucous membrane
8.
9. Implantation
• The structure actively concerned in the
process of excavation is the trophoblast of the
ovum, which possesses the power of
dissolving and absorbing the uterine tissues.
• The trophoblast differentiate into two part
– Cytotrophoblast-Langhans layer (which is the
inner layer of mononucleated cells
– Syncytiotrophoblast- syncytium (an outer
multinucleated zone without cell boundaries
10. Implantation
• Two important process occurred at this stage
– In the syncytiotrophoblast, there is formation of
vacuoles which fuse together to form lacunae, this
stage of trophoblast development is called the
Lacunar stage
– The cell of the endometrium become polyhedral and
loaded with glycogen and lipids and the tissue are
highly edematous; this reaction is known as Decidual
reaction. This reaction is initially confined to the site
of implantation but later spread to other part of the
endometrium
11. Implantation
• As the syncytial cells penetrate deeper into the stroma
and erode the endothelial lining of the maternal
capillaries.
• These capillaries are congested and dilated and are
known as sinusoids
• The syncytial lacunae become continuous with the
sinusoids and the maternal blood enters the lacunar
system
• As the trophoblast continues to erode more and more
sinusoids, maternal blood begins to flow thru the
trophoblastic system, thus establishing the
uteroplacental circulation
12.
13. • At the beginning of the 3rd week, the
cytotrophoblast form columns which is
surrounded by the syncytium. This column is
called the primary villi
• During further development, the mesodermal
cells penetrate core of the primary villi and
grow in the direction of the decidual. This
newly formed columns is called the secondary
villi
14. • By the end of the 3rd week , the mesodermal core
differentiate into blood cells and blood small
vessels, thus, forming the villous capillary system.
The villus is now called tertiary villus or definitive
placental villus (Chorionic frondosum)
• The capillaries of the tertiary villi make contact
with the capillaries in the chorionic plate and in
the connecting stalk.
• These vessels in turn establish contact with the
intraembronic circulatory system, thus
connecting the placenta and the embroyo
15. • The cytotrophoblast in the villi continue to
grow until it makes contact with maternal
endometrium and it spread over the
endometrium. The portion is called the outer
cytotrophoblast shell. And this attached the
chorionic sac firmly to the maternal
endometrial tissue.
• This shell disappeared by the fouth month
when the placenta is fully developed
16. • The villi that extend from the chorionic plate
to the decidual plate is called the anchoring
villi, while the branching part is called the
free(terminal) villi. The free villi ensure the
exchange of nutrients, gases, drugs etc.
17. The Placenta
• The placenta connects the fetus to the uterine
wall, and is the organ by means of which the
nutritive, respiratory, and excretory functions
of the fetus are carried on. It is composed of
fetal and maternal portions. The fetal part is
formed by the chorion frondosum while the
maternal part is formed by the stratum
compactum and the intervillous spaces of the
decidua basalis
18.
19. The Placenta
• The fetal portion of the placenta consists of
the villi of the chorion frondosum; these
branch repeatedly, and increase enormously
in size.
• These greatly ramified villi are suspended in
the intervillous space, and are bathed in
maternal blood, which is conveyed to the
space by the uterine arteries and carried away
by the uterine veins.cells.
20. The Placenta
• A branch of an umbilical artery enters each villus and
ends in a capillary plexus from which the blood is
drained by a tributary of the umbilical vein.
• The vessels of the villus are surrounded by a thin layer
of mesoderm consisting of gelatinous connective
tissue, which is covered by two strata of ectodermal
cells derived from the trophoblast: the deeper stratum,
next the mesodermic tissue, represents the
cytotrophoblast or layer of Langhans; the superficial, in
contact with the maternal blood, the
syncytiotrophoblast. After the fifth month the two
strata of cells are replaced by a single layer of
somewhat flattened cells
21. The Placenta
• The maternal portion of the placenta is
formed by the decidua basalis containing the
intervillous space which contain blood
22.
23. The Placenta
• The fetal and maternal blood currents traverse
the placenta, the former passing through the
blood vessels of the placental villi and the latter
through the intervillous space. The two currents
do not intermingle, being separated from each
other by the delicate walls of the villi.
Nevertheless, the fetal blood is able to absorb,
through the walls of the villi, oxygen and nutritive
materials from the maternal blood, and give up to
the latter its waste products.
24. The Placenta
• The blood, so purified, is carried back to the fetus
by the umbilical vein. It will thus be seen that the
placenta not only establishes a mechanical
connection between the mother and the fetus,
but subserves for the latter the purposes of
nutrition, respiration, and excretion. In favor of
the view that the placenta possesses certain
selective powers may be mentioned the fact that
glucose is more plentiful in the maternal than in
the fetal blood.
25. Separation of the Placenta
• After the child is born, the placenta and
membranes are expelled from the uterus as
the after-birth.
• The separation of the placenta from the
uterine wall takes place through the stratum
spongiosum, and necessarily causes rupture of
the uterine vessels.
26. Separation of the Placenta
• The orifices of the torn vessels are, however,
closed by the firm contraction of the uterine
muscular fibers, and thus postpartum
hemorrhage is controlled.
• The epithelial lining of the uterus is
regenerated by the proliferation and extension
of the epithelium which lines the persistent
portions of the uterine glands in the unaltered
layer of the decidua.
27. The Placenta
• The expelled placenta appears as a discoid
mass which weighs about 450 gm. and has a
diameter of from 15 to 20 cm.
• Its average thickness is about 3 cm., but this
diminishes rapidly toward the circumference
of the disk, which is continuous with the
membranes.
28. The Placenta
• Its uterine surface is divided by a series of
fissures into Iobules or cotyledons, the
fissures containing the remains of the septa
which extended between the maternal and
fetal portions.
• Overall there are about 15-30 cotyledon
29. Nutrition of the ovum and the
embroyo
• Oocyte
blood vessel of the ovary via the
theca interna, granulosa cell and Zona
pellucida
• After ovulation
secretion by the lining of
the tube
30. Nutrition of the ovum and the
embroyo
• In the uterus
Uterine secretion (uterine
milk which is rich in glycogen,
mucopolysaccharides, and the lipid
• During implantation
cytolytic products
from the breakdown of stroma cells, blood
cells, grandular epithelium, capillary walls and
glandular secretions
• From the placenta which is fully developed by
the 4th month
31. The Placenta
• Function of the placenta
– Respiration
– Nutrition – Water, inorganic salts, carbohydrates,
fats, protein and vitamin
– Excretion- metabolic waste (kidneys)
– Protection- barrier to injurious substances
– Endocrine
32. Placental circulation
• The total capacity of the intervillous space is
175ml of maternal blood
• About 500ml of maternal blood flow thru the
placenta per min
• About 400ml of fetal blood flow thru the
placenta/ min
