begins its life when a sperm cell from its father meets an egg
cell - an ovum (more than one are ova) - from its mother
inside the mother's body. When the egg is fertilized by the sperm
cell, the two cells join together to form one new cell, which starts to grow
and divide. This is the beginning of the baby who will be ready to be born
about 9 months later.
come from the woman's ovaries. About once a month, from puberty
until the age of about 45, one egg is released from one of the two ovaries.
The egg then passes into one of the Fallopian tubes. Tiny 'hairs'
which line these tubes waft the egg down to the uterus (womb). The
uterus is a hollow organ with many blood vessels and strong, muscular
walls. Each month, the uterus lining thickens as it prepares to protect and
nourish a fertilized ovum. If it is not fertilized, an ovum dies after
about two days. The lining is now not needed, so along with the
unfertilized egg and some blood, it passes out of the woman's body through
the vagina. This loss of lining, blood and egg is called
menstruation, or a 'period'. Menstruation is controlled by the female
hormones progesterone and oestrogen. After menstruation, a
new uterus lining starts to form, ready to receive the next possible
made in a man's testes (one is a testis) from puberty
onwards. They are stored in a tightly coiled tube called the epididymus.
To pass to the woman's body, they travel to the penis through two
tubes called sperm ducts. Sperm swim in liquids made by glands
(including the prostate) around the urethra - a tube that runs
from the bottom of the bladder to the tip of the penis. The mixture of
sperm and liquids is called semen. Both semen and urine are carried
by the urethra, but muscles can close the exit from the bladder to prevent
the two fluids from meeting.
enter the woman’s body during sexual intercourse. The man's penis becomes
stiff and fits inside the woman's vagina. Semen, containing millions of
sperm, is then squirted from the penis into the woman's body. The sperm are
then helped towards the uterus by muscular contractions of the uterus and '
vagina walls, although the sperm themselves can 'swim' by thrashing their
tails. It takes them about 2 hours to reach the Fallopian tubes, where
fertilization usually occurs. As many as 300 million sperm may start the
journey, but only a few hundred reach the Fallopian tubes and only one sperm
fertilizes the egg. Fertilization, or conception can be prevented.
How a Baby Grows
single sperm cell has penetrated an egg cell, no more sperm can enter. The
nuclei of the two cells merge (fertilization) and the fertilized egg travels
down the Fallopian tube towards the uterus. On the way down, it divides
first into 2 cells, then into 4, then 8 and so on until a ball of at least
64 cells has been formed.
of cells embeds itself in the uterus lining, which has thickened in
preparation. The baby develops very quickly. After 4 weeks its heart
begins to beat. Some cells form the umbilical cord, which joins the
baby to its mother through a special organ in the uterus called the
cells form the amnion - a protective 'bag' filled with fluid. This
surrounds the baby and acts as a shock absorber to stop the baby - called an
embryo at this stage - from being jolted.
weeks, the embryo is about 2.5 cm (1 in) long and is called a foetus.
After about 12 weeks, it has all its organs. During the next 6 months,
it grows larger and develops 'details' such as fingernails and hair. At
about the fifth month of development, the foetus begins to move its limbs
and can be felt to kick. At this stage the baby can hear, distinguish light
and dark, swallow and suck its thumb. Some unborn babies even get
hiccoughs. At about 6 months, the baby turns itself around in the uterus so
that its head is pointing downwards - the position in which it is ready to
placenta develops at the place where the fertilized egg first embeds
itself. One side of the placenta is attached to the uterus wall. The
umbilical cord links the other side of the placenta to the baby. It is
through the umbilical cord that nourishment and oxygen pass to the baby from
the mother's bloodstream. Also waste products and carbon dioxide from the
developing baby pass back to be disposed of by the mother's body.
spending about 9 months developing inside its mother, the baby is fully
formed and ready to be born. The muscles of the uterus begin to contract.
These contractions get stronger and each one lasts longer, in order to push
the baby out of the mother's body. This is called labour. The
opening at the bottom of the uterus - the cervix widens so that the
baby's head is pushed into the vagina. Then the mother uses all her
strength to push downwards and the baby's head emerges into the outside
world. The umbilical cord is tied and cut by a doctor or midwife so that the
baby begins life on its own. It is the remains of the umbilical cord that
form your ‘belly button'.
The time a
baby takes to be born can be as short as 2 hours or longer than 24 hours.
After the baby has been born, the placenta is also pushed out of the body
through the vagina. The discarded placenta is often called the
afterbirth. Most babies are born head first, but sometimes babies do
not lie head first in the uterus just before birth and so doctors may decide
to open the mother's abdomen surgically and lift the baby out. This is
called a Caesarian section.
babies weigh about 3 kg (7 lb) when they are born and are about 500 mm (20
in) long. The first thing a new-born baby does is to fill its lungs with
air and cry. Its lungs need to start working immediately in order to supply
its body with oxygen.