Fertilisation
• Refers to the sperm and ovum meeting
• It takes place in the upper part of the fallopian
tube.
• Ovulation refers to the release of an ovum from the
ovaries.
• For approximately 15 hours after ovulation, the
ovum is susceptible to fertilisation
• Sperm have to be present in the female
reproductive tract during the 72 hours before or 15
hours after ovulation
• http://bcove.me/msejck9u
Fertilisation continued
• Billions of sperm are deposited in
the vagina during intercourse
• Sperm are capable of surviving
for 4 to 7 days in the female
reproductive tract
• The nucleus of the sperm fuses
with the nucleus of the ovum,
mixing the DNA of each cell
• An fertilised ovum is referred to as
a Zygote.
The conception process
Twins
We have two types:
• Identical twins occurs when
one sperm fertilises one ovum
and thus resulting in the zygote
splitting in half resulting in the
same genetic information for
each.
Videos\How a baby develops
during pregnancy.mp4
• Fraternal twins,
triplets or
quadruplets results
form two separate
sperm fertilising two
ova.
Germinal Stage
• Starts at fertilisation and ends with implantation
• Implantation starts at day 5 and ends around days
10 -12.
• This stage is characterised by rapid cell division
through mitosis
When the
blastocyst
reaches the
uterus, it implants
itself in the
endometrium
The blastocyst at around 5
days after fertilisation
Germinal Stage in action
o Zygote begins dividing about 30 hours after
fertilisation
o The blastocyst is swept along the fallopian tube
through the action of cilia (tiny hairs) and muscular
contractions
o This occurs while fertilised ovum is being
transported through the uterine tube over 3 to 5
days
o In the uterus, cell division continues for an
additional 2 to 4 days before becoming implanted
in the endometrium
o After approximately 7 days, the blastocyst enters
the uterus and a few days after that it will begin to
attach to the uterine wall
Germinal Stage in action
o The blastocyst secretes enzymes that dissolve part of the
lining of the uterus
o The outer cells of the blastocyst multiply and invade the
lining until they reach the blood vessels underneath
o Within approximately 14 days the blastocyst has
completely disappeared beneath the surface of the
uterine lining
o This is known as implantation
o When the blastocyst has fully implanted it is called an
embryo
o Progesterone is vital in allowing the endometrium to
receive and nourish the blastocyst.
Amniotic Sac
• The amniotic sac is a
bag of fluid in which the
embryo floats
• The fluid:
o Acts as a shock absorber
to protect the embryo
o Helps to regulate the
temperature of the
embryo
o The volume of fluid
increases throughout the
pregnancy
Umbilical cord
• The umbilical cord links the embryo to the placenta
• It consists of 2 arteries and 1 vein
• Blood flow through these vessels transports nutrients
and waste products between the embryo and the
maternal blood supply
• Unfortunately, the umbilical cord can transport
potentially harmful substances
Yolk Sac
o The yolk sac is a temporary structure that
produces blood cells until the heart and
circulatory system are established
o The liver starts to take over this function at
around week 7
Embryonic stage
• Starts at implantation and ends at eighth week.
• The child is referred to as an embryo during this
stage
• Cells in the inner layer of the embryo differentiate to
form organs such as skin cells
• Cells in the outer layer of the embryo differentiate
to form the life support system for the embryo such
as heart cells.
Embryonic Stage
• The nervous system and the circulatory system
develop early in this stage
• Other organs, like the kidneys, stomach and ear
canal, develop later
• Internal sex organs develop
• Limbs start forming as buds and continue to grow
and develop – which principle of development?
• Head and neck account for half the length of
embryo – which principle of development?
• Major organs and systems are formed, embryo is
sensitive to environmental influences – Teratogens.
What are some influences that may effect an
embryo developing?
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter3/
animation__fetal_development_and_risk.html
Foetal Stage
• Starts at the ninth week of pregnancy and
continues until birth at around 40 weeks.
• Unborn baby referred to as “foetus”
• Characterised by rapid growth
• Placenta is fully developed and functioning
Placenta
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The placenta is a large, flat organ about
the size and shape of a small dinner
plate
It is connected to the uterus on one side
and the embryo, via the umbilical cord,
on the other
It consists of a very rich supply of blood
vessels
Blood from the embryo flows through the
umbilical cord into the blood vessels of
the placenta
The placenta blood vessels pass through
pools of maternal blood
The maternal blood and the embryo’s
blood never mix
Substances, such as oxygen and carbon
dioxide, pass through from mother to
child and from child to mother through
diffusion
Unfortunately, potentially harmful
substances can pass through the
placental barrier
Videos\Structures and Functions of
Placenta.mp4
Foetal Stage
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Sex organs are fully developed
Movement occurs
Sucking and grasping reflexes are highly responsive
Lungs are filled with amniotic fluid, not air
Fat is deposited under the skin to assist with
temperature regulation after birth.