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Pregnancy
Begins with fertilization:
• The sperm enter the vagina, swim
through the cervix and the uterus and
into the two fallopian tubes.
• If an egg is present in the fallopian tube
fertilization could take place.
• Their speed averages one inch per hour.
• They swim a total of about six inches
Fertilization:
• Also known as conception
• Is the joining of an egg and a sperm.
• Sperm are capable of fertilization for 48
hours or longer after ejaculation
• Because of this the period during which
intercourse can result in fertilization
spans the two days before and the two
days after ovulation
Genetic determination
• Once inside the egg, the material that
makes up sperm joins with the egg.
• Inherited characteristics are determined
by units of information carried in the
egg & sperm.
Genetic material
• The units which carry the genetic
information are called genes
• Genes link together to form
chromosomes
• Chromosomes and genes are made up
of a chemical substance called
deoxyribonucleic acid (DNA)
DNA
• Every human cell
(except reproductive
cells) contain 46
chromosomes
arranged in 23 pairs
• Egg and sperm
contain only 23
chromosomes
Parenting
• Every gene on a
chromosome
contributed by one
parent has a
counterpart gene
contributed by the
other parent
Dominant and Recessive
genes:
• Often one gene in a
pair may be stronger
or dominant.
(curly hair, brown
eyes)
• One may be weaker
or recessive.
(straight hair, blue
eyes)
• Dominant gene is
expressed
Genetic disorders:
• Any abnormal condition that a person
inherits through the genes
• Examples of common genetic disorders:
hemophilia, cystic fibrosis, sickle cell
disease
• If a family member has a disorder it
could be something that you carry but
do not express.
The Zygote
• The fertilized egg (zygote) begins to
divide within hours of fertilization.
• While the cluster of cells are dividing
they move through the fallopian tube
toward the uterus.
• When they reach the uterus, the cells
have formed a blastocyst hollow ball
of cells called a
Implantation
• The blastocyst floats freely in the uterus
for a few days
• Then it will begin to attach itself to the
uterine wall this is called implantation
• Implantation usually occurs about one
week after fertilization.
• Once the blastocyst is attached to the
uterine wall it is called the embryo
Implantation
The Embryo
• The place of
attachment develops
into a structure called
the placenta
• The placenta allows
the exchange of
nutrients, oxygen and
waste between mother
and embryo.
Exchange of nutrients and
waste
• The embryo’s and
the mothers blood
do not mix.
• The two substances
are separated by
thin membranes in
the placenta that
allow these
substances to pass
through
The umbilical cord
• The embryo’s blood
travels to and from
the placenta through
blood vessels within
a cord called the
umbilical cord.
• The cord acts as the
baby’s lifeline until
birth
• After birth this cord
is cut and tied
The amniotic sac
• The baby is
enclosed in a bag of
thin tissue called the
amniotic sac
• The embryo floats
within the amniotic
sac in a liquid called
amniotic fluid
The Trimesters
• Pregnancy lasts for 40 weeks (approx..
9 months)
• This time is divided into three threemonth periods called trimesters
The First Trimester
• The fertilized egg develops into an
embryo
• Embryo grows to 3” long and has a
recognizable human form
• Facial features,limbs,hands, feet, fingers
& toes become apparent
• From this time until birth the embryo is
called a fetus.
The Second Trimester
• The fourth through sixth month of
pregnancy
• Fetus grows to 12”long and about 1 pound
• Hair and nails grow, the body facial
features and ears develop
• The fetus begins to move
• The skeleton, muscles and nervous systems
are developing
The Third Trimester
• The seventh through ninth months
• The fetus continues to grow and develop
until it is ready to be born
• Body size grows to be in proportion with
the head
• Eyelids open, the lungs and the digestive
system are developed
• By the end 18-22 inches long, 6-8 pounds.