Menstrual cycle: animation
A woman's reproductive system consists of an arrangement of organs
that each month prepares itself for the possibility of creating a baby.
It is made up of the ovaries, the Fallopian or uterine tubes,
the uterus or womb and the vagina.
These all play a part in the menstrual cycle,
which is centred around the release of an egg from the ovaries
approximately every 28 days.
Let's have a look inside the body to see what happens during this cycle.
The ovaries are a pair of almond-shaped glands
that are positioned either side of the uterus.
They are enclosed by the finger-like ends of the Fallopian tubes,
which are hollow passageways connecting the ovaries to the uterus.
The uterus is a hollow, pear-shaped organ
that has thick muscular walls
and is where the embryo grows to become a baby.
It is attached to the upper end of the vagina.
The eggs develop and mature inside the ovaries.
This process is controlled by the pituitary gland
at the base of the brain,
which releases hormones into the bloodstream,
causing the ovary to release a mature egg.
This is known as ovulation,
a process which usually occurs sometime between day 13 and day 15 of each cycle,
day one being the first day of your menstrual bleed or period.
The ovaries also release the female hormone oestrogen,
which causes the lining of the uterus to thicken
in preparation to receive a fertilised egg.
Once released from the ovaries,
the egg makes its way along the Fallopian tube,
where it might meet a sperm, if sexual intercourse has occurred,
and fuse with it in a process known as fertilisation.
The fertilised egg moves through the Fallopian tube to the uterus,
where it embeds itself in the thickened lining
and continues to grow.
If the egg is not fertilised, it breaks down,
and the level of hormones produced by the ovary begins to fall.
This causes the lining of the uterus to also break down.
Both the unfertilised egg and the lining of the uterus
are then shed from the body via the vagina during menstruation,
known as a period,
and the cycle starts all over again.