Transcript Pregnancy PPT

Pregnancy
Passing on your DNA
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ogram_adv.html#
Pregnancy
• You have learned what happens in the
female body if a mature egg is not
fertilized (MENSTRUATION) – now it is
time to learn what happens if an egg IS
fertilized
The Egg’s Journey
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Pregnancy
• Once sperm are deposited in the vagina,
they move through the uterus and into the
oviducts where fertilization occurs – only
one sperm will fertilize the egg
• If the nucleus of a sperm cell fuses with
the nucleus of the egg cell, a zygote is
created.
The Sperm’s Journey
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Pregnancy
• The zygote continues down the oviduct toward
the uterus and after 24 to 36 hours, it begins
the process of mitosis, undergoing a series of
rapid cell divisions
• By the time it reaches the uterus, it has become
a mass of cells arranged to form an almost
hollow ball of cells called a blastocyst
Blastocyst
• The blastocyst contains a group of cells
called the inner cell mass which forms the
embryo
• The outer cells of the blastocyst will
eventually help form the placenta, a
blood-vessel rich organ that is present
only during pregnancy.
Implantation
• The embryo now attaches itself to the
thickened lining of the uterus – this is
called implantation and occurs six to ten
days after fertilization
• The attached embryo produces a
hormonal signal that prevents the woman
from menstruating.
The First Two Weeks
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Embryo Development
• During the second week of embryo
development, cells begin to specialize to form a
gastrula, in a process called gastrulation.
• In gastrulation, the cells of the growing embryo
become arranged into three distinct layers called
germ layers – the endoderm, the mesoderm,
and the ectoderm
Embryo Development
• Cells in each layer develop into different
parts of the body
• The ectoderm for the skin and nervous
system
• The mesoderm forms the kidneys,
skeleton, muscles, blood vessels, and
gonads
• The endoderm forms the lungs and lining
of the digestive tract
The Embryo Take Shape
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Messages in the Genes
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Supporting Tissues
• Between the tenth and fourteenth days of
development, the outer portions of the
embryo develop important tissues, the
yolk sac, placenta and the amnion.
• The yolk sac supplies nutrients to the
embryo for about the first two months of
development
Supporting Tissues
• The amnion forms a fluid-filled sac around the
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embryo which serves as a kind of shock
absorber to help protect the embryo
The placenta is the embryo’s supply line for
survival inside its enclosed world. It ensures
delivery of nutrients and oxygen to the
developing organism and makes sure wastes are
removed. The embryo is attached to the
placenta by the umbilical cord
Differentiation
• Different cells become specialized to perform the
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different tasks of various tissues and organs in
the body
By the end of the forth week, the embryo is 500
times its original size
The human gestation period is about 38 weeks
and can be divided into three block of time
based on the formation of different tissues and
organs. Each block of time (approx. three
months in length) is called a trimester
Feeding the Growing Fetus
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First Trimester (weeks 1-12)
• At four weeks the limbs, eyes, and spine begin
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to form
At eight-nine weeks the embryo forms its first
bone cells – the embryo is now called a FETUS
By the end of 12 weeks, all the major organs
have begun their development – liver, stomach,
brain, and heart
The fetus has a length of 100mm
The sex can be identified using ultrasound
Second Trimester (weeks 12-24)
• The skeleton begins to form, the brain
grows rapidly, and the nervous system
begins to function
• The mother begins to feel movement
• By 24 weeks the fetus is about 300mm
long
• Most organs are formed but are not yet
fully developed – little chance of survival if
born prematurely
Third Trimester (weeks 24-38)
• The fetus rapidly increases in overall size and
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begins to move around in its amniotic sac,
stretching and kicking.
Proper nutrition is more important than ever
before, mainly for the building of vital brain
tissue.
By the eighth month the fetus opens its eyes
By the end of the third trimester, the fetus has
grown to an average length of 500mm and an
average weight between 2700 and 4100 grams
Risk Factors
• Cigarette smoke may constrict the fetus’s
blood vessels, which can prevent it from
getting enough oxygen.
• Alcohol can affect the function of the
fetus’s brain, central nervous system, and
physical development. (FAS) Alcohol can
remain in the bloodstream of the fetus for
a longer time than in the mother – liver
can’t process the alcohol
Risk Factors Cont…
• Radiation and certain pollutants can lead
to cancer or genetic defects
• Certain drugs may cause deformities in
new-borns (thalidomide 1950’s)
• The risk of genetic disorders increases
with the age of the mother (1 in
thousands for young adults – 1 in 20 for
women over 45)
Birth
• During pregnancy, high hormone levels
help maintain the pregnancy – a sharp
drop in these hormones cause the muscles
of the uterus to begin to contract
• This process where by the uterus
contracts and the birth canal opens is
called labour
Birth – Dilation Stage
• Uterine contractions cause the cervix to
open, or dilate
• The amnion breaks and the amniotic fluid
is released through the vagina
• The dilation stage lasts an average of 2 to
20 hours
Birth – Expulsion Stage
• Contractions in the uterus become so
forceful that the baby is pushed through
the cervix to the birth canal.
• Duration lasts 0.5 to 2 hours
• As the baby move through the canal its
head rotates, making it easier for its body
to pass through the birth canal
Birth – Placental Stage
• The placenta and umbillica cord are
expelled from the uterus
• Occurs 10 to 15 minutes after the baby is
born
• The expelled placenta is called the after
birth
Birth
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