Download Implantation

Conception, Implantation & Embryology
Dr. Dina Nawfal
Conception:
Is the union of male and female pronuclear elements
Conception normally takes place in the fallopian tube
after which the fertilized ovum continues to the
uterus and implantation will takes place
Spermatogenesis takes about 74 days together
with transportation, a total of about 3 months
elapses before sperm are ejaculated
The sperm achieve motility during their passage
through the epididymis
sperm capacitation which render them capable of
fertilization in vivo does not occur until they are
removed from the seminal plasma after ejaculation.
Those sperm that do penetrate the cervical os are
directed along channels of lower viscosity mucus into
the cervical crypts where they are stored for later
ascent
Uterine contractions probably facilitated by PG in the
seminal plasma propel the sperm to the tubes within
5 minutes.
Capacitation is the physiological change that sperm
must undergo in the female reproductive tract before
fertilization
The acrosome reaction is the principal components
of capacitation,
the acrosome is a modified lysosome lies over the
sperm head( as a kind of chemical drill-bit)
It is designed to enable the sperm to burrow its way
into the oocyte
Following penetration of the oocyte, the male
pronucleus which approaches and finally fuses with the
female pronucleus to form the zygot
Fertilization restore the diploid number of chromosomes
and determine the sex of the zygot.
Cleavage, Morula& blastocyst
Following fertilization, cleavage occurs, this consist of
rapid succession of mitotic divisions that produce a
mulberry like mass known as morula.
Fluid is secreted by the outer cells of the morula &
a single fluid filled cavity develops, known as the
blastocyst cavity.
An inner cell mass can be identified attached
eccentrically to the outer layer of flattened cells; the
latter become the trophoblast
.
The embryo at this stage of development is called the
blastocyst.
Implantation:
The fertilized ovum reaches the endometrial cavity about
3 days after ovulation
this occurs under the hormonal (estrogen and
progesterone) and the ciliary motility of the fallopian
tube.
Initial embryonic development primarily occurs in the
ampullary portion of the fallopian tube, with subsequent
rapid transit through the isthmus this process takes
about 3 days
On reaching the uterine cavity, the embryo undergo
further development for 2-3 days before implanting
The blastocyst adheres to the endometrium & a variety
of proteolytic enzymes may play a role in separating the
endometrial cells and digesting the intercellular matrix.
The wall of the blastocyst facing the uterine lumen
consist of a single layer of flattened cells.
The thicker opposite wall has two zones;
The trophoblast & inner cell mass (embryonic disk) the
latter then differentiate into a thick plate of primitive
(dorsal) ectoderm and the underlying layer of (ventral)
endoderm.
A small cells appear between the embryonic disk and
trophoblast and the space develop within them, which
become the amniotic cavity
Under the effect of progesterone decidual changes occu
in the endometrium of the pregnant uterus. Which is
thickened to a depth of 5 to 10 mm
The decidua basalis directly beneath the site of
implantation
The decidua capsularis overlying the developing ovum
The decidua vera (parietalis) the remaining lining of the
uterine cavity
The space between the decidua capsularis and decidua
vera is obliterated by 4th month with fusion of capsularis
and vera
The decidua basalis is invaded extensively by
trophoblastic giant cells which appears as early as the
time of implantation
At about 9th days, lacunae, irregular fluid filled spaces
appears within a thickened trophoblastic syncytium
this is soon followed by the appearance of the
maternal blood within the lacunae as maternal tissue
is destroyed and the wall of the maternal capillaries
are eroded