Physiology of Fertilization, Implantation, Placental & Fetal Development

THE PHYSIOLOGY OF FERTILISATION, IMPLANTATION,
PLACENTAL AND FETAL DEVELOPMENT.
The eggs, sperm and embryos are the stuff of new life.
Oogenesis – is the series of cellular transformations, that change
the premorbial germs to oogonia and finaly to oocytes.
The primary oocyte comletes the first, the second meiotic
division, the egg contains a haploid number of chromosoms.
Sperm gametogenesis include:
-prolifiration of spermatogonia;
-transit;
-ejaculation;
-capacitation;
-movement of sperm.
Indeed , most of the sperm found in the ampullary portion of the fallopian tube.

FERTILISATION (Gamete and Zygote Passage)
-Spermatozoa must transverse the cervix, uterus, uterotubal
junction, the ampullary region of the fallopian tubes.
-The ovulated ovum in the metaphase stage II of the second
meiotic division must be picked up by the4 fimbria and
transported into the ampulla for fertilisation.
-In the human, semen is deposited at ejaculation in the vagina
close to the external cervical os. Spermatozoa penetrate the
cervical mucus and are transpirted by ciliary action through the
uterus and uterotubal junction and into the fallopian tube (2-3
mm/min).
-Cervical mucus select the normal superior sperm. Less than 1%
of sperm arrive at the site of fertilisation

Stages of development from fertilization to
implantation

IMPLANTATION PROCESS
After ovulation the luteal- phase supply of progesterone
with estrogens generates a progressive secretory endometrium,
which can nurture the free embryo as well as nidation process:
-by day 7, the trophoblast has begun to invade the endometrium,
and the blastocyst slowly sinks into the endometrium.
-by day 8 , the inviding trophoblast forming the amniotic cavity
and soon become filled with maternal blood and endometrial
gland secretion.
-differentiation of trophectoderm is complete before invasion of the
endometrium at implantation .
Succesful implantation and normal development are determined
by:

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Embrionic development.
- As progesterone levels rise in the luteal phase after ovulation.
The zygote is transported towards the uterine cavity, usually
arriving about three days after fertilisation.
-Hormone-mediated changes in oviductal fluid affect tubal
capacity to support embrionic development.
-Fertilized oocyte is moved along with the tubal fluid, which is
rich in muco-proteins, electrolytes, enzymes, which provide
support and a nutritive environment for the sperm, oocyte,
embryo.
-After ovum pick up by the fimbria, sperm/egg interaction
typically occurs in the ampulla of the oviduct. Passage of the
sperm through the zona takes approximately 30 min. The sperm
plasma membrane fuses with the egg plasma membrane. The
mingling of chromosomes signifiels the transition from
fertilization to the beginning of embrionic development.

-the developmental stage of the embryo at the time of transfer
to the uterus;
-the time in the cycle during which implantation can be initiated
(the “window of implantation”),
-the synchronization between the postovulation state of the
embryo and the endometrium,
-the capacity of the embryo for delayed implantation.

PLACENTATION
The placenta is an anatomic barrier to immune response. Other
substances normally found in the sera of pregnant women:
corticosteroids, ovarian steroid hormones, prostaglandins,
pregnancy-specific B globulin, hCG, human placental lactogen,
pregnancy-associated plasma protein (PAPP-A) and other
placental proteins.
HCG is first detected in serum at approximately the time that
implantation is initiated. “maternal recognition of pregnancy.”
The trophoblast secretes hCG at leas from the time of attachment.
hCG is first detected in serum at approximately the time of
implantation, it is present at the maximal levels near the end of
the first trimester and then declines.

Implantation of the blastocyst.
Development of early placentation

GROSS PLACENTAL DEVELOPMENT
The early stages of fetal and placental development are;
Villi cover the entire surface of the chorion early in pregnancy,
decidua basalis continue to grow:
 by the end of the third month, this side of the chorion is
smooth, and the chorion frondosum goes on the form of normal
placenta:
By 12 weeks, the location and texture of placenta can be
established by US.
Fetal and maternal placental circulation
•The umbilical cord runs from the fetus umbillicus to the point
of it s insertion in the placenta
•The single umbilical vein in the cord carries oxygenated and
nutrient-containing blood

Vascular structure of the umbilical cord:
transverse section (left) shows two arteries
carrying de-oxygenated blood
blood and one vein carrying oxygenated blood

-The single umbilical vein enters the fetus, runs along the
anterior abdominal wall to the liver
-blood is returned to the placenta through to the two umbilical
arteries, which are distal branches of the hypogastric
arteries
- A small amount of connective tissue, within which is
distributed a gelatinous material known as WARTON S
JELLY, supports these structures
- On the maternal side, the uterus derives its blood supply
from the uterine arteries (branches of the internal iliac
artery) and the ovarian arteries (branches of the abdominal
aorta). Uteroplacental arteries at the distal end of the spiral
arteries.

THE FETAL MEMBRAINES
THE FETAL MEMBRANES LINE THE UTERINE CAVITY AND
COMPLETELY SURROUND THE FETUS (the chorion, the
amnion).
THE MEMBRANES PLAY A CRITICAL ROLE IN THE DEVELOPMENT
AND PROTECTION THROUGHOUT PREGNANCY

Amniotic fluid secreted in the amnion is
swallowed by the fetus, absorbed through the
gut and excreted in fetal urine

AMNIOCENTESIS- is the aspiration of amniotic fluid for
genetic purposes at 14-17 weeks of gestation
Amniotic fluid is obtained by amniocentesis
under ultrasound control

Fetal circulation showing the distribution of
arterial, venous and mixed blood

ROMOSOMAL ABNORMALITIESСН
Phenotypic variation – normal or abnormal – may be
considered in terms of several etiologies:
•Chromosomal abnormalities, numeral or structural;
•Single-gene disoders;
•Polygenic and multifactorial mechanisms;
•Environmental factors (teratogens)

Screening for neural tube defects

Two common abnormalities of the central
nervous system

PATHOLOGY OF PLACENTA
LOW-LOWING PLACENTA
PLACENTA PREVIA – CENTRALIS
LATERALIS
MARGINALIS
PLACENTA ADHERENT
INCRETA
PERCRETA
PREMATURE SEPARATION OF THE NORMALLY IMPLANTED
PLACENTA
HYPERTROPHY OF PLACENTA –diabetes, macrosomia of
fetus, lues, placental tumor - FPK more than 0,2
HYPOPLASY OF PLACENTA - infection, death one of the
fetus from twins, FPK less 0,1
UMBILICAL CORD PATHOLOGY – knots (true, false),
Fall of the loops of UC
Absolutely short UC, entwine of UC around the neck

AMNIOTIC FLUID VOLUME 0,5-1,5 LITER
(38-40 w.)
POLYGYDRAMNION
Frequency – 2-4,25%
Reasons: diabetes, infection,
amnionitis, placentitis
Clinic: acute, chronic
shortness of breath,
violations of CVS
Diagnosis: disparity of sizes of
uterus to the term of pregnancy:
Tension of walls of uterus,
impossible to define parts of the
fetus, US, tension of AF(vag.
Exam.)
OLYGOGYDRAMNION
Frequency – 0,2-1,25%
Reasons: defects of the urinary
system of the fetus,
FPInsuf.
Clinic: physiological,
pains with moving of the
fetus
Diagnosis: US

Physiology of Fertilization, Implantation, Placental & Fetal Development

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Physiology of Fertilization, Implantation, Placental & Fetal Development