Menstrual Cycle

The sexual reproductive organs are the parts of the body that make it possible for us to reproduce (have a baby) when we choose to be parents. The sex organs inside the body are called the internal reproductive organs. Those on the outside are called genitals. When our internal reproductive organs have developed enough for us to eventually get pregnant, we will get our first period. This section explains how menstruation happens as part of the menstrual cycle.


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The Genitals

The Genitals protect our female reproductive organs on the outside. They are collectively called the Vulva and are found between the legs in the area covered by pubic hair. The Vulva consists of the mons pubis (Latin name for pubic mound), labia majora (outer lips), labia minora(inner lips), clitoris and the outside openings of the urethra and vagina. See our handy Vagina Diagram!


The Vagina is the passageway into and out of our internal reproductive organs. Menstrual blood flows out of the vagina. Babies are also usually born through the vagina.

The opening of our vagina is surrounded and protected by the labia minora, shaped like two lips. The labia minora is covered by the labia majora, which is also shaped like to lips and is covered by skin. The labia minora and majora also protect the opening of the urethra. The urethra is connected to the bladder and is the hole through which urine leaves the body. It is protected by the tip of the clitoris, which is found at the point where the different sides of the labia minora join together. Pubic hair grows on the labia majora but does not grow on the labia minora.


We are born with a hymen, a thin strip of membrane (biological material) covering part of the vagina’s opening. It’s normal for the membrane to have one or more holes. The hymen can be broken in many different ways, like sports, sex and menstrual hygiene products inserted into the body through the vagina.

diagram of female genitalia

diagram of the female internal reproductive system

Internal Reproductive System

The Ovaries are two roundish organs on either side of our pelvis. The ovaries contain eggs (or ova) that combine with sperm to make a baby. We are born with all the eggs that we will release through our lives, but only begin to release eggs during puberty. At around the same age when we start to release ova, boys begin to produce sperm that can fertilise the egg.

The Uterus is the space that our body prepares each month to possibly carry a baby. The walls of the uterus are made up a layer of connective biological material called the endometrium.

Our Fallopian Tubes look like two arms with fingers reaching out towards the ovaries. The egg travels down the fallopian tube towards the uterus. By waving back and forth, the “fingers” guide a ripe egg through the fallopian tube into the uterus.


The Cervix is the opening separating the uterus and the vagina. It is made up of a layer or muscles that can open and close the entrance to the uterus. The position of our uterus tends to change depending on the stage of the menstrual cycle. Sometimes it’s closer to the opening of the uterus. Other times it’s closer to the vagina.

The Menstrual Cycle

During the menstrual cycle, an egg ripens and leaves one of the ovaries, in a process called ovulation. Usually only one egg is released from one ovary during each menstrual cycle. While the egg is getting ready to be released, the endometrium (lining) of the uterus becomes thicker and increases the amount of blood and nutrients that come to the uterus from other parts of the body.


As part of sexual reproduction, sperm from a man’s penis can travel through the vagina (see our vagina diagram) and then through the cervix into the uterus. From there sperm can travel into the fallopian tubes. If there is a ripe egg in a fallopian tube when sperm arrives, the egg may become fertilised and could develop into a baby. If an egg is fertilised by sperm on its ways to the uterus, the embryo will then attach to the endometrium and grow into a baby that can be born about 9 months after it attaches to the uterus. When there is a baby in it the uterus is called a womb.

Once an egg is released from an ovary, it can only be fertilised by sperm for 24 to 36 hours. An egg that is not fertilised does not attach to the lining of the uterus. Without a developing baby to nourish there is no need for the endometrium to remain thick. The body then releases the extra layer of endometrium, which dribbles out of the vagina during what is called menstruation or a period. Women who are pregnant do not get a period because the thick endometrium is needed to support a developing baby, so it is not released.


After menstruation, the ovaries prepare to release another egg. The endometrium becomes thick again and prepares itself to receive another embryo. This cycle of ovulation and menstruation repeats itself about every 28 days. That is why periods usually occur once a month. The first day of menstruation marks the beginning of a new menstrual cycle.

diagram of the menstrual cycle

Calendar showing the various stages of the menstrual cycle

During the first few years after we start getting our period, we may not experience menstruation every month. It can take several months for the body to adjust to the menstrual cycle. Once the body adjusts, menstruation can then occur every 25 to 32 days. Most women have periods until they are around 50 years old.


During the menstrual cycle, which includes ovulation, the building of the uterine lining and menstruation, it is possible to experience physical and emotional changes in the body at around the same time every month. For example, changes in body temperature, bigger or sore breasts, headaches, pain in the pelvic area, tiredness, and even a faster or slower heart rate. On the days before and during a period, girls can also sometimes feel more emotionally sensitive than usual. This is normal.