The male and female parts of the human reproductive system
can bring together an egg and a sperm so that they join and begin the
development of a new human being. The female system also protects and nourishes
the developing foetus during the nine months of pregnancy. About 150,000 eggs
are present in a girl’s ovaries at birth; however, sperm production in
boys begins only at the start of puberty.
Sperm are made in the testes and mature in a coiled tube, the
epididymis. At the end of sexual intercourse, they travel along the vas
deferens and mix with fluids made by the prostate gland and seminal vesicle.
The sperm then pass along the urethra to the tip of the penis and into the
female vagina. From there they begin their journey up the female reproductive
tract.
FEMALE REPRODUCTIVE SYSTEM
From puberty, an egg is released monthly from one of the ovaries
and passes along the adjoining fallopian tube towards the uterus. The ovaries
also produce female sex hormones. The uterus is the home for the foetus during
pregnancy. The outlet of the uterus is called the cervix. It stretches wide
open during childbirth to allow the baby to pass through.
Millions of sperm leave the penis during sexual intercourse and are
deposited in the vagina. From there they travel through the cervical canal into
the uterine cavity and then into the fallopian tubes. About 500 sperm reach the
tubes. If one fertilizes an egg, the tiny fertilized egg begins to grow by
dividing – into two cells, then four, and so on. As it divides, it
travels along the fallopian tube to the uterus. There, it embeds in the uterine
lining as an embryo.
Fertilization occurs in the outer part of the fallopian tube. Once
they reach the egg, the sperm release substances that allow them to break
through the egg’s outer layers. Only one sperm penetrates the egg. The
egg, and the sperm that successfully penetrates it, each provide half the
genetic information needed to form a new individual.
During birth, the opening
or canal in the mother’s cervix widens, and the uterus contracts. As the
baby moves down, first its head and then the rest of the body passes through
the mother’s cervical canal and vagina to the outside world.
FROM FERTILIZED EGG TO NEWBORN BABY
A fertilized egg divides to form a ball of cells called a morula.
This reaches the uterus a few days after fertilization, moved along by wafting
cilia, hairlike structures in the lining of the fallopian tube. The early
embryo then embeds itself in the uterine lining.
By this time, the embryo’s cells have developed and grouped
together to form tissues and organs. Most organs are formed by eight weeks, and
the embryo is now called a foetus. At 10 weeks, the foetus is 5 cm (2 in) long
and has facial features and limbs.
At about this time the mother may start to feel the baby move. The
umbilical cord connects the foetus to the
placenta. This pad of tissue attached to the wall of the uterus supplies
nutrients to the foetus and removes waste.
The baby is growing fast now and maturing in preparation for its
journey into the outside world.
Once delivered, the baby starts breathing. The umbilical cord is
clamped shut and cut, and the baby is then immediately given to the mother to
suckle. The remaining stump of umbilical cord falls off a few days later,
leaving the umbilicus (tummy button).
