1. ALAQAH
• (Blood clot or Leech; something suspended or
attached to a surface.)
• This term is so important to remember that there
is a complete surah in Qur’an called Surah Al-
Alaq.
• The first five ayyat of Surah Al-Alaq is the first
revelation sent to Muhammad (SAS) in the cave
of Hira.
• Its importance is very much increased when we
see that in the very first revelation the
terminology of “alaq” is used.

3. • Read (O Prophet), in the name of your
RABB (Lord), Who ceated
• HE created insan from alaq (a clot of
congealed blood).
• Read: and your RABB is Most
Generous.
• Who taught knowledge by “qalam”
(pen).
• HE taught insan what he did not know.
• Al-Alaq. Surah 96, Ayat 1-5, Para 30

4. • This Qur’anic term refers to the presomite
embryo.
• It starts when the implantation begins and
ends when formation of somites begins.
• It extends for about 14 days.
• It starts on day 7 with the embedding of
blastocyst and is completed on day 20
when first pair of somites appears.

5. • We created man from a quintessence (gentle extraction) of
clay. We then placed him as Nutfah in a place of rest firmly
fixed. Then we made Nutfah into Alaqah and then we changed
Alaqah into Mudghah. Then we made Izam (bones) out of that
Mudghah. Then we clothed Izam with Lahm (muscles). Then
we developed out of him another creation. So blessed ALLAH
the best to create. Then after that you shall all die. Then most
surely you shall be raised up on the Day of Resurrection.
• (Surah 23, Al-Mu’minun, Ayat 12-16, Para 17)

6. • According to modern scientific
knowledge we can discuss
Alaqah in two stages:
1.Alaqah-1.
This is bilaminar germ disc.
2.Alaqah-2.
This is trilaminar germ disc.

7. •ALAQAH-1
•Bilaminar Germ Disc
•2nd week

9. IMPLANTATION
• Implantation of the blastocyst begins at
the end of the first week and ends by the
end of second week.
• At about 6th day after fertilization the
embryonic pole of the blastocyst becomes
attached to the endometrium and start
penetrating into it.

10. IMPLANTATION SITE
• The blastocyst usually implants in the midpoint
of the body of the uterus, more frequently on
the posterior than on the anterior wall.
• Implantation almost always occurs between the
openings of the glands and it is always close to
a maternal capillary suggesting some type of
tropism toward maternal blood.
• Implantation only occurs in stratum compactum and
never beyond that in normal cases.

12. EMBEDDING
The trophoblasts now start proliferating
rapidly and soon differentiate into two
layers:
1. An inner cytotrophoblast (cellular trophoblast)
consisting of mono-nucleated cells.
2. An outer syncytial trophoblast (syntrophoblast or
syncytiotrophoblast) consisting of a multinucleated
protoplasmic mass without individual cell
boundaries.

13. Day-8. Blastocyst is partly buried in
stratum compactum

14. • Mitotic figures are found in cytotrophoblast, but never
in syncytial trophoblast yet the thickness of the latter
increases considerably.
• The cells of the cytotrophoblast multiply and migrate
into the syncytial trophoblast, where they fuse
• The finger like processes of the syncytial trophoblast
grows into the endometrial epithelium and start
invading the endometrial stroma but they never go
beyond stratum compactum.
• The erosion of the endometrial stroma results from
proteolytic enzymes produced by syntrophoblast.

16. FORMATION OF BILAMINAR GERM DISC (DAY 8)
• Small spaces appear between the embryoblast and
trophoblast. By the 8th day, these spaces have
coalesced to form a small cavity between the
embryoblast and trophoblast called amniotic cavity.
• Concurrently, morphological changes occur in the
embryoblast resulting in the formation of a flattened,
essentially circular plate of cells called the embryonic
disc. The cells of the embryoblast also differentiate
into two layers:
1. A superior layer of high columnar cells adjacent to
the amniotic cavity, the epiblast.
2. An inferior layer of small cuboidal cells adjacent to
the blastocyst cavity the hypoblast.

17. Day-8. Blastocyst is partly buried in
stratum compactum

18. FORMATION OF AMNIOTIC CAVITY
• Small spaces appear between the embryoblast and
trophoblast. By the 8th day, these spaces have
coalesced to form a small cavity between the
embryoblast and trophoblast called amniotic cavity.
• As the amniotic cavity enlarges, it acquires a dome-
shaped thin epithelial roof of amnion, which is
continuous with the edges of epiblast layer of the
bilaminar germ disc.
• The amnion develops from epiblast on day 8. Flat cells
develop from epiblast and form a thin membrane
called amnion. The flat cells constituting the amnion
are called amnioblast. The amnion lines trophoblast
and surrounds the amniotic cavity. So amniotic cavity
has its own covering now called amnion.

19. On eighth day
three events occur:
1. Trophoblast forms two layers,
cytotrophoblast and syncytial
trophoblast.
2. Embryoblast gives rise to two layers
epiblast and hypoblast.
3. Amniotic cavity develops

20. Lacunar stage (Days 9 to 11)
• The naughty trophoblast shows considerable progress
in the development particularly at the embryonic pole.
• The growth is so rapid that isolated spaces or
vacuoles appear in the syncytiotrophoblast.
• These vacuoles fuse to form large lacunae. The
adjacent lacunae by fusion form a lacunar network
throughout the syncytial trophoblast.
• By the 9th day the conceptus is more deeply
embedded and the penetration defect in the surface
epithelium is closed by a fibrin coagulum.

22. FORMATION OF PRIMARY YOLK SAC
• By the 9th day, a crop of flattened cells develops
inside the cytotrophoblasts.
• These cells either originate from the cytotrophoblasts
or from the hypoblast. ALLAH The Creator knows
better.
• These cells form a thin membrane, known as the
exocoelomic (Heuser’s) membrane, which lines the
blastocyst cavity.
• Exocoelomic (Heuser’s) membrane is continuous
superiorly with the hypoblast of the embryonic
bilaminar germ disc and circumscribes a large cavity
called exocoelomic cavity or primary (primitive) yolk
sac.

23. Establishment of utero-placental
circulation (Days 11 to 12)
As the conceptus penetrates the endometrial
stroma, the endometrial capillaries become
more and more congested and dilated and
become sinusoids.
As the syncytial cells penetrate deeper in the
stroma, they finally erode endothelial lining
of maternal capillaries.
The syncytial lacunae then become
continuous with the sinusoids and maternal
blood enters the lacunar system.

25. As trophoblast continues to erode
more and more sinusoids, maternal
blood begins to flow through lacunar
system, thus establishing the primitive
utero-placental circulation.
By the 12th or 13th day of development the
blastocyst is completely embedded in the
endometrial stroma the surface defect in the
endometrium has usually healed and the
surface epithelium covers entirely the original
defect.

26. FORMATION OF
EXTRA-EMBRYONIC MESODERM
• A new population of cells develops between the inner
surface of the cytotrophoblast externally and the outer
surface of the amnion and exocoelomic cavity
internally.
• These cells form a fine loose connective tissue
(mesenchymal tissue) called extra-embryonic
mesoderm. It is derived from cytotrophoblast probably
(ALLAH knows better).
• On the 11th day a thick zone of extra-embryonic
mesoderm is formed.

29. • Now isolated coelomic spaces appear in it.
These spaces rapidly fuse to form large
isolated cavities of extra-embryonic coelom.
Soon these become confluent and a continuous
crescent shaped extra-embryonic coelomic
cavity is established
• This cavity surrounds the primitive yolk sac and
amniotic cavity except on the caudal end of the
developing germ disc, where extra-embryonic
mesoderm remains solid and is given the name
connecting stalk.

30. • The formation of extra-embryonic
coelomic cavity divides the extra-
embryonic mesoderm into two layers.
1. The outer layer lines the cytotrophoblast
and is called somatic mesoderm.
2. The inner layer covers the amniotic cavity
and yolk sac.
The part covering the amniotic cavity is also
called somatic mesoderm and the part
covering the yolk sac is called splanchnic
mesoderm.

32. CONNECTING STALK
• Connecting stalk determines the side of the
embryo because it develops on the caudal
aspect of bilaminar germ disc.
• The connecting stalk is the pathway along
which the blood vessels of the embryo later
establish communication with those of the
chorion.
• Subsequently the connecting stalk is converted
into part of the umbilical cord and establish
communication between embryo and placenta.
•

33. FORMATION OF
SECONDARY YOLK SAC
• As the extra embryonic coelom increases in size
primary yolk sac decreases in size. Part of primary
yolk sac is drawn out and pinched off into the
mesodermal strands.
• The hypoblast cells produce additional cells that
migrate along the exocoelomic or Heuser’s
membrane. These cells proliferate and gradually
replace the primitive yolk sac or exocoelomic cavity.
• This new cavity is known as secondary or definitive
yolk sac.

35. FORMATION OF
CHORIONIC CAVITY
• As primary yolk sac is replaced by a smaller
secondary yolk sac, the extraembryonic coelom
increases in size, and now it is usually called chorionic
cavity. But still we can call it extraembryonic coelom, a
better and explanatory name.
• The trophoblast (both cytotrophoblast and syncytial
trophoblast) and the extraembryonic somatic
mesoderm lining the trophoblast together constitute
chorionic plate.

36. DECIDUA REACTION
• As the conceptus erodes and sinks into the
endometrium, the endometrial stroma around
the implantation site becomes edematous and
highly vascular.
• Adjacent large tortuous glands start secreting
abundant glycogen and mucus.
• The endometrial stromal cells enlarge and
become laden with glycogen and lipids and they
become polyhedral in appearance, now called
decidual cells.
• All these cellular, vascular and glandular
changes are collectively called decidua reaction.

37. • This decidua reaction is first confined to the
area immediately surrounding the implantation
site, but soon spreads throughout the
endometrium and by the days 13 to 14 there is
marked decidua reaction throughout the
endometrium.
• Some of the decidual cells degenerate in the
region of the penetrating syncytiotrophoblast
and provide a rich source of material for
embryonic nutrition.
• Later on the conceptus receives nutrients
directly from the maternal blood.