•Fertilization is the process whereby the sperm
fuses with the ovum to form the zygote. It
occurs in the upper part of the Fallopian tube.
•Only one sperm is needed to fertilize the
Fertilization and pregnancy
The journey of the sperms to the
1. Sperms enter the
2. Sperms swim up the
3. Sperms swim along
the Fallopian tube
4. Sperms swim around
the egg if it is
•The rapid growth and development of the baby
between the zygote stage and birth is called
•The zygote undergoes cell division as it travels
down the Fallopian tube towards the uterus.
•The zygote forms a ball of cells and is referred to
as an embryo.
•About the seven days after fertilization, the
embryo embeds in the tissues of the uterus lining.
This process is called implantation.
Stages leading to implantation
1. Ovum fertilized
by a sperm.
the uterine wall.
•During this early stage of pregnancy, the embryo
obtains its nourishment from nutrients in the ovum
and the uterus lining.
•The surfaces of the embryo and the uterus lining
bind firmly to form a large disc called the placenta.
•The job of nourishing the embryo is taken over by
•By eight weeks after fertilization, the developing
embryo becomes clearly human and is called the
Growth and development of the
foetus in the uterus.
•At the placenta, the foetal and the maternal
blood vessels flow very close to each other but
do not mix.
•The foetus is attached to the placenta by the
•The umbilical cord has two blood vessels.
a.An umbilical artery which carries carbon dioxide
and other wastes from the foetus to the placenta
b.An umbilical vein which carries blood containing
oxygen and food from the placenta to the foetus.
•Oxygen, soluble food, water and salts pass from
the mother’s blood into the foetal blood.
•Carbon dioxide and nitrogeneous waste pass from
the foetal blood into the mother’s blood.
•The foetus is completely surrounded by a
membrane called amnion. The amnion is filled with
•The amniotic fluid protects the embryo and the later
the foetus by cushioning it from physical damage.
•The time for the full development of a foetus is forty
weeks. This is oftern reffered to as the gestation
•In humans, birth occurs in three main stages:
a.The expansion of the cervix so that the baby’s
head can pass into the vagina.
b.The strong contractions of the uterus which
push the baby out of the mother’s body.
c.Further contractions of the uterus to expel the
umbilical cord and placenta from the mother’s
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