Fertilization & Fetal Development.pdf

PRESENTED BY:
Mrs. Vruti Patel
Assistant Professor
S.N.C.

TERMINOLOGIES
 GAMATOGENESIS : the process involved in
the maturation of the two highly specialised
cells, spermatozoon in male and ovum in
female before they unite to form zygote, is
called gamatogenesis.

 OOGENESIS : the process involved in the
development of a mature ovum.

 SPERMATOGENESIS : the process involved
in the development of spermatids from the
perimordial male germ cells and their
differentiation into spermatozoa.

 Following ovulation the ovum(0.15 mm
in diameter), passes into the uterine
tube and move towards the uterus.
 At intercourse about 300 million
sperms are deposited in the posterior
fornix of the vagina.
 More will die on the journey, and only
thousands will reaches the uterine
tube.
 The sperms meet the ovum usually in

 The nuclei of two cells fuse and each
contribute half the complement of
chromosomes to make a total of 46.
 The fertilized ovum is known as
Zygote.
 Neither sperm or ovum can survive for
longer than two-three days.
 Fertilization occurs when intercourse
takes place not more than 48 hours
before or 24 hours after ovulation.
 Conception will take place about 14
days before the next period is due.

 After fertilization the ovum reaches the
uterus 3-4 days later.
 During this time cell devision takes place
and fertilized ovum divides into 2, 4, 8, 16
cells and so on until a cluster of cells is
formed, known as morulla.
 This occurs once every 12 hours.

 A fluid filled cavity (blastocele)appears
in the morulla and which is now known
as blastocyst.
 A single layer of cell sorround the
blastocyst-known as trophoblast which
will form the placenta and chorion

 The remaining cells are clumped
together at one end forming the inner cell
mass which will become the fetus,
amnion and the umbilical cord.
 After 2-3 days the trophoblast becomes
quite sticky and adhere to the
endometrium.
 Embedding sometimes known as
nidation (nesting) is normally complete
by 11th day after ovulation and the
endometrium closed over it completely.

♣ The endometrium is known as decidua during
pregnancy.
♣ It grows four times in thickness than the non
pregnant state.
♣ This accounts for soft, vascular, spongy bed in
which the fertilized ovum implants.
♣ Three layers are found: Basal layer, Functional
layer and the Compact layer.

 This layer lies immediately above the
myometrium.
 Remains unchanged but regenerate
during puerperium.

 This consist of tortuous gland which is rich in secretion.
 The stroma cells are enlarged and known as decidual reaction.
 This is a defense against the excessive invasion by the
syncytiotrophoblast and limits its advance to this spongy layer.
 It provides a secure anchorage for the placenta and allows its access
to nutrition and O2.
 as soon as the baby is born separation takes place.

 This forms the surface of the decidua and is
composed of closely packed stroma cells
and neck of the gland.
 The decidua underneath the blastocyst
known as basal dacidua.
 Capsular decidua covers the basal decidua.
 Remainder is called as true dacidua.
 As embryo grows and fill the uterine cavity
the capsular decidua meets and fuses with
parietal (true) decidua.

SYNCYTIO
TROPHOBLAST
CYTO
TROPHOBLAST

 Composed of nucleated protoplasm ,
capable of breaking down tissue as in the
process of embedding.
 It erodes the walls of the blood vessels of
the decidua, making the nutrients in the
maternal blood accessible to the
developing organism.

 It produces the hormone known as HCG.
 Corpus luteum is responsible for
producing the hormone eastrogen and
progesterone which maintains the
integrity of the decidua so that shedding
does not take place.

 The inner cell mass forming the fetus itself
 It differentiate into three layers
Ectoderm Mesoderm
Endoderm
Form the skin and
other system
Forms the mucus membranes
and glands
Forms bones and muscles,heart ,
blood vessels.certain internal
Organs also originate here.

THE AMNIOTIC CAVITY
 It lies on the side of the ectoderm
 Filled with fluid and gradually enlarges and
folds around the embryo to enclose it.
 The amnion forms from its lining .
 It swells out into chorionic cavity

 It lies on the side of the endoderm
 Provides nourishment for the
embryo
 Part of it contributes to the
formation of the primitive gut
THE YOLK SAC

 The normal fetus swallows the amniotic
fluid.
 If anything interferes with swallowing
then volume remains excessive.
 If the fetus is unable to pass urine then the
amount reduces.
AMNIOTIC FLUID

 It is secreted by the amnion specially the
part covering the placenta and the
umbilical cord
 Some fluid is exuded from maternal
vessels in the decidua and some from fetal
vessels in the placenta
 Fetal urine is also contribute to the
volume from tenth weeks onwards
 The water in the amniotic fluid is
exchange as often as every three hours
AMNIOTIC FLUID

 It is clear, pale straw colored consisting
of 99% water.
 The remaining 1% is dissolved solid
matter including food substances and
waste products.
 Fetus sheds skin cells, vernix caseosa,
lanugo into the fluid.
 Aspiration of amniotic fluid for
examination is termed as amniocentesis.
AMNIOTIC FLUID

 The total amount till 38th weeks is
1000 ml.
 After that it slightly decreases till
term and remains 800 ml.
 If total amount crosses 2000 ml –
polyhydramnios.
 If volume is less than 200 ml-
oligohydramnios.
AMNIOTIC FLUID

 The fluid distends the amniotic sac and
allows for the growth and free movement of
the fetus.
 It equalizes the pressure and protects the
fetus from jarring and injury.
 It maintains a constant temperature for the
fetus and provides small amount of
nutrients.
AMNIOTIC FLUID

 During labour it protects the placenta and the
umbilical cord from the pressure of uterine
contractions.
 It aids effacement of the cervix and dilatation
of the uterine Os.
AMNIOTIC FLUID

 It extends from the fetus to the placenta and
transmits the umbilical blood vessels: two
arteries and one vein.
 It is protected by Whartson’s Jelly (gelatinous
substance) formed from mesoderm.
 The whole cord is covered in a layer of amnion
continuous with that covering the placenta.
 The average length of the cord is about 50 cm.
UMBILICAL CORD

Umbilical cord
 Cord contains one vein and two arteries.
 Vein carry oxygenated blood from placenta to
fetus
 Arteries carry deoxygenated blood from fetus
towards the placenta.

 If it is < 40 cm- short cord
 The lumps of Whartson’s jelly on the side of
the cord is known as false knot.
 The disadvantage of long cord is it may
become wrap around the neck of the fetus and
becomes knotted- known as true not.
 True knot has to be differentiated properly
from the false knot during examination.
UMBILICAL CORD

 Preembryonic Stage: Fertilization to 2 to 3
Weeks
 Rapid cell division and differentiation
 Develop embryonic membranes and germ layers
 Embryonic Stage: 4 to 8 Weeks' Gestation
 Most critical stage of physical development
 Organogenesis
 Fetal Stage: 9 Weeks to Birth
 Every organ system and external structure present.
 Refinement of fetus and organ function occurs.
FETAL DEVELOPMENT

Day 15
The
primitive
streak
can be
seen on
Day 17
The primitive streak can still
be seen, and the opposite end
of the embryo is starting to
fold up.
The Blastocyst begins
to
collapse

Day 19
The neural tube is seen along with somites
on either side of it.
Somites - zipper-like motion of the neural tube closing together,
three pairs of small bumps form on either side of the closure.
they will form the skeleton and the major muscles of the body.
Thirty-eight pairs of somites will line the neural tube within 2
weeks.

5 Week
Embryo
5 Week, 4 day Embryo

Four Weeks
Embryo
After the cluster of cells attaches to
the womb it is called an embryo.
The embryo is between 1/100 and
4/100 inch long at this time.
The embryo continues rapid
growth.

* 8 Weeks
•The embryo is about ½ inch
long.
•The heart now has four
chambers.
•Fingers and toes begin to
form.
•Reflex activities begin as the
brain and nervous system
develop.
•Cells begin to form the eyes,
ears, jaws, lungs, stomach,
intestines and liver.

10
Weeks
The embryo, is about 1 to 1¼
inches long (the head is about
half the length) and weighs less
than ½ ounce.
The beginnings of all key body
parts are present, but they are
not completed.
Structures that will form eyes,
ears, arms and legs can be seen.
Muscles and skeleton are
developing and the nervous
system becomes more
responsive.

12
Weeks
The fetus is about 2½ inches long and weighs about ½
ounce.
Fingers and toes are distinct and have nails.
Hair begins to develop, but won't be seen until later in
the pregnancy.
The fetus begins small, random movements, too slight
to be felt.
The fetal heartbeat can be detected with a heart monitor.
All major external body features have appeared.
Muscles continue to develop.

14
Weeks
The fetus is about 3½ inches long
and weighs about 1½ ounces.
The fetus begins to swallow, the
kidneys make urine, and blood
begins to form in the bone marrow.
Joints and muscles allow full body
movement.
There are eyelids and the nose is
developing a bridge.
External genitals are developing.

18
Weeks
and weighs about 7 ounces.
The skin is pink and
transparent and the ears are
clearly visible.
All the body and facial features are
now recognizable.
The fetus can grasp and
move its mouth.
Nails begin to grow.
The fetus has begun to kick. Some
women feel this movement.

20
Weeks
The fetus is about 6¼
inches long and weighs about 11½ ounces.
All organs and structures
are formed
Skin is wrinkled and pink to reddish in color - thin and close to
the blood vessels.
Protective skin coating, (vernix) begins to develop.
Respiratory movements occur - lungs have not developed
enough to permit survival outside the uterus.
By this time, mothers usually feel the fetus moving.
At this time an ultrasound can often identify the sex of the fetus.

22
Weeks
The fetus is about 7½ inches
long weighs about one
pound.
.
It has fingerprints and some
head and body hair. It may
suck its thumb and is more
active. The brain is growing
very rapidly.
The fetal heartbeat can be
easily heard.
The kidneys start to work. At
23 weeks, approximately
31% of babies born survive.

24
Weeks
The fetus is about 8¼ inches long and
weighs about 1¼ pounds.
Bones of the ears harden making
sound conduction possible. The fetus
hears mother’s sounds such as
breathing, heartbeat and voice.
The first layers of fat are beginning to
form.
This is the beginning of substantial
weight gain for the fetus.
Lungs continue developing
At 25 weeks, approximately 68% of
babies born survive. Babies born at
this age require intensive care and
usually have life-long disabilities and
chronic health conditions.

26
Weeks
The fetus is about 9 inches long and
weighs about 2 pounds.
The fetus can respond to sound
from
both inside and outside the womb.
Reflex movements continue to
develop and body movements are
stronger.
Lungs continue to develop.
The fetus now wakes and sleeps.
The skin is slightly wrinkled.
At 27 weeks, approximately 87% of
babies born survive. Babies born at
this age require intensive care and
have an increased risk of
developmental delays and chronic

28
Weeks
The fetus is about 10 inches
long and weighs about 2
pounds, 3 ounces.
Mouth and lips show more
sensitivity.
The eyes are partially open
and can perceive light.
More than 90% of babies
born at this age will survive.
Some survivors have
developmental delays and
chronic health conditions.

30
Weeks
and weighs about 3 pounds.
The lungs that are capable of
breathing air, although medical
help may be needed.
The fetus can open and close its
eyes, suck its thumb, cry and
respond to sound.
The skin is smooth.
Rhythmic breathing and body
temperature are now controlled by
the brain.
Most babies born at this age will
survive.

32
Weeks
The fetus is about 11
inches long and weighs
about 3 pounds, 12
ounces.
The connections
between the nerve cells
in the brain increase.
Fetal development now
centers on growth.
Almost all babies born
at this age will survive.

34
Weeks
The fetus is about
12 inches long and
weighs about 4½
pounds.
Ears begin to hold
shape.
Eyes open during
alert times and
close during sleep.
Almost all babies
born at this age
will survive.

36
Weeks
 The fetus is about 12 to 13 inches long and
weighs about 5½ to 6 pounds.
 Scalp hair is silky and lies against the head.
 Muscle tone has developed and the fetus can
turn and lift its head.
 Almost all babies born at this age will survive.

38
Weeks
The fetus is about 13½
to 14 inches long and
weighs about 6½
pounds.
Lungs are usually
mature.
The fetus can grasp
firmly.
The fetus turns toward
light sources.
Almost all babies born
at this age will

40 Weeks
The fetus is about 18
to 20 inches long
and may weigh
about 7½ pounds.
At the time of birth,
a baby has more
than 70 reflex
behaviors, which are
automatic behaviors
necessary for
survival.
The baby is full-term
and ready to be born.
Photo and Text Courtesy of
Georgia Department of
Human Resources,
Division of Public Health

 Rapid growth
 Formation of the embryonic plate.
 Primitive central nervous system forms.
 Heart develops and begins to beat.
 Limbs buds form.
FETAL DEVELOPMENT

• The embryo is about ½ inch long.
 Very rapid cell division.
 Head and facial features develop.
 All major organs laid down in primitive form.
 External genitalia present but sex not distinguishable.
 Early movements.
 Visible on ultrasound from 6 weeks.

 Eyelids fuse
 Kidneys begin to function and the fetus passes
urine from 10th weeks.
 Fetal circulation functioning properly.
 Sucking and swallowing begin
 Sex apparent
 Moves freely but not felt by mother.
 Some primitive reflexes present.

 Rapid skeleton development- visible on x-ray
 Meconium present in gut
 Lanugo appears.
 Nasal septum and palate fuse.

 “Quickening”
 FHS heard on auscultation.
 Vernix caseosa appears.
 Fingernails can be seen.
 Skin cells begin to be renewed.

 Most organs become capable of
functioning.
 Periods of sleep and activity
 Responds to sound
 Skin red and wrinkled.

 Survival may be expected if born.
 Eyelids reopen.
 Respiratory movements.

 Begins to store fat and iron.
 Testes descends into scrotum.
 Lanugo disappears from face.
 Skin becomes paler and less wrinkled.

 Increased fats make the body
more rounded.
 Lanugo disappears from body.
 Head hair lengthens.
 Nails reach tip of fingers.
 Ear cartilages soft.
 Plantar creases visible.

 Term is reached and birth
is due.
 Skull firm.

UMBILICAL VEIN TO
PORTAL CIRCULATION
 The umbilical vein carry 80% saturated
oxygenated blood from the placenta enter fetus at
the umbilicus and run at the falciform ligament of
liver.
 Some blood from the umbilical vein enters the
portal circulation allowing the liver to process
nutrients.
 The majority of the blood enters the ductus
venosus, a shunt which bypasses the liver and puts
blood into the inferior vena cava.

 Deoxygenated blood returning from lower
regions mingles with oxygenated blood from
Ductus Venosus in IVC.
 This mixed blood enters in to the right atrium.
 Deoxygenated blood returning from the upper
regions of fetus enters the SVC and passes into
right atrium.
UMBILICAL VEIN TO
PORTAL CIRCULATION

FORAMEN OVALE
 It is the opening in the
septum between left and
right atrium.
 Is a valve with two flaps that
prevent back-flow.
 More than one-third
(75%)of blood takes this
route and guided towards
left atrium.
 Other 25% of the blood
move to the right ventricle
from the right atrium
through tricuspid valve.

 The blood from the right ventricle is pumped into the
pulmonary trunk during vetricular contraction but
little reaches to the lungs.
 Most of these blood is shunted into the aortic arch
through the Ductus Arteriosus to all parts of the body.
 This shunting takes place due to high resistance in
pulmonary artery because of non- functional lungs.
DUCTUS ARTERIOUSUS

FETAL CIRCULATION
 The blood in the left atrium is guided towards the left
ventricle via bi-cuspid valve.
 During ventricular contraction this blood is pumped
into the ascending aorta- aortic arch and circulating
the head, neck, brain and upper part of the body.
 Then it mixes with the blood from the ductus
arteriosus in the descending aorta and carrying blood
to all parts of the body.

 The deoxygenated blood from all parts of the body
moves towards the common iliac arteries-hypogastric
arteries and then reaches to the umbilical arteries.
 The umbilical artery reaches to the placenta – gets
ready for another exchange of material.
 The mean cardiac output is high in fetus i.e 255
ml/kg/min.
FETAL CIRCULATION

NORMAL CIRCULATORY
CHANGES AT BIRTH
 When the umbilical cord is clamped, the blood
supply from the placenta is cut off and
oxygenation must then take place in the
newborn’s lungs.
 As the lungs expand with air, the pulmonary
artery pressure decreases and circulation to
lungs increases.
 This leads to some structural changes to occur in
the vascular changes.

Foramen ovale Closes shortly after birth as the LA
pressure increases and RA pressure
decreases when lungs starts
functioning, fuses completely in first
year. It becomes fossa ovalis.
Umbilical arteries functional closure is instant. Actual
obliteration takes about 2-3 months
and become Medial umbilical
ligaments.
Umbilical vein Obliteration occur a little later than
arteries so that few extra volume of
blood (80-100 ml) reaches fetus
from placenta. Ultimately it becomes
Ligamentum teres.

Ductus
Arteriousus
Within few hours of respiration
the muscle wall of ductus
arteriosus contracts in response
to rising O2 tension of blood.
Anatomical obliteration takes
about 1- 3 months and becomes
ligamentum arteriousum.
Ductus Venosus It collapses and the venous
pressure in the IVC falls as well
as of RA. After obliteration it
becomes Ligamentum venosum.

Fertilization & Fetal Development.pdf

Fertilization & Fetal Development.pdf

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