• You can also view Bodyworks: Your guide to understanding reproduction as a PDF.
• Our contraception booklets can be purchased in the publications and resources section.

Introduction

This information will tell you all about the reproductive system in men and women. It’s particularly useful if you want to understand:

• how the reproductive organs work
• the menstrual cycle (ovulation and periods)
• what’s involved in conception (getting pregnant)
• how contraception works to prevent pregnancy.

Women’s bodies

The reproductive system in women is made up of external and internal organs. These are found in the lower abdomen, the part of the body below the umbilicus (tummy button). This area is often referred to as the pelvic area. They include:

The external organs

• vaginal entrance (opening)
• labia (vaginal lips)
• clitoris.

The external organs are known as the vulva.

The internal organs

• uterus (womb)
• fallopian tubes
• ovaries
• vagina
• cervix.

The female reproductive organs outside the body

The vulva includes the opening to the vagina, the inner and outer lips (called labia) and the clitoris. The external part of the clitoris is found towards the front of the vulva, it is highly sensitive and when stimulated can make women feel sexually aroused and lead to orgasm.

Hormones and eggs – did you know?

Did you know?

• The female sex hormones, estrogen and progesterone, are responsible for female characteristics such as body shape, developing breasts, periods and controlling the menstrual cycle.
• When a woman reaches puberty she will have up to one million eggs in her ovaries.
• During a woman’s reproductive life only about 400–500 eggs will actually be released at ovulation.
• As a woman gets older (over 30 years) the number and quality of her eggs declines making conception more difficult.
• An egg is less than 1/8 of the size of a grain of sand – invisible to the naked eye.

The female reproductive organs inside the body

Ovaries

Women have two ovaries, one on each side of the uterus. Ovaries are the size and shape of almonds and they contain ova (eggs) in structures called follicles. The ovaries also produce the two female sex hormones – estrogen and progesterone.

The fallopian tubes

The two fallopian tubes are found on each side of the uterus, near the ovaries. These are tiny tubes – only as wide inside as a thick human hair and just 10cm long! The funnel-like ends of the fallopian tubes pick up the egg released by the ovary and carry it to the uterus. Tiny, microscopic hairs line the inside of the fallopian tubes and help move the egg along. The inside of the tube is very delicate and can very easily be damaged or blocked by infection.

The uterus

The uterus is made of muscle. It’s about the size and shape of an upside down pear, hollow and very stretchy. This is where the baby develops if a woman becomes pregnant. The uterus can stretch to hold a baby and shrink more or less back to its pre-pregnancy size after the baby is born.

The cervix

The lower part of the uterus which connects to the vagina is called the cervix. Sperm released by the man during sex swim from the vagina through the cervix to reach an egg.

The cervix contains small glands which produce secretions called mucus. This alters in texture and amount during a woman’s menstrual cycle. In her fertile phase (the time around ovulation – when an ovary releases an egg) it changes from being thick, sticky and creamy in colour to being clearer, wetter, and more stretchy – like raw egg white. These changes allow sperm to pass through the cervix and reach the egg more easily. When a woman is pregnant, the cervix becomes plugged with very thick mucus to protect the developing baby from infection.

Vagina

The vagina is a muscular tube 7–10cm long which leads from the cervix to the vaginal opening (vulva).The vaginal opening is between the legs, between the urethra (the tube women pee through) at the front and the anus at the back. The vagina tilts upward and towards the small of the back. It has glands which produce lubricating secretions when women are sexually aroused to help the penis enter the vagina (penetration). Like the uterus, the vaginal walls are stretchy, allowing it to hold a tampon and stretch around a penis during sex, or a baby during delivery.

The menstrual cycle

The menstrual cycle is the process during which an egg develops and is released from the ovaries, and the lining of the uterus prepares for a possible pregnancy. If a woman does not become pregnant the lining of the uterus is shed, as her period.

These events are caused by hormones – chemical messengers which travel around the body in the blood stream.

How long does the cycle take?

• The number of days in the menstrual cycle is calculated from the first day of the period to the day before the start of the next period.
• The average length of the menstrual cycle is around 28 days, although many women have longer or shorter cycles and this is normal.

What happens during the menstrual cycle?

• The first day of the period is known as day one of the cycle. When a woman has her period about 20 eggs start to develop in the ovary.
• The hormone estrogen causes the lining of the uterus (endometrium) to start to thicken in preparation for a fertilised egg. It also causes the mucus in the cervix to become thinner, wetter and more stretchy, allowing sperm to reach an egg more easily.
• Regardless of how long or short a woman’s cycle is, ovulation (egg release from an ovary) will usually happen around 10–16 days before the start of her next period. However, the time from the first day of the period to ovulation can vary between women.
• Occasionally, more than one egg is released (if this happens it will occur within 24 hours of the first egg being released). If more than one egg is fertilised it can lead to a multiple pregnancy such as twins.
• Ovulation triggers the production of a second hormone, progesterone. This prepares the lining of the uterus even further, ensuring that it is spongy, thick and full of nutrients so that a fertilised egg can settle or implant into it.
• After ovulation the cervical mucus goes back to being thick and sticky. If the egg is not fertilised it will be reabsorbed naturally by the body, the level of hormones falls, and this menstrual cycle comes to an end.
• The cycle then begins again. The lining of the uterus breaks down and is shed through the vagina as a period, also called menstruation.

Periods – did you know?

About periods:

• Some menstrual cycles can be as short as 21 days and some as long as 40 days.
• Some women have menstrual cycles that vary in length from month to month.
• The amount and quality of cervical secretions will vary from woman to woman and also from one cycle to the next.
• The average amount of menstrual blood lost in a period is three–five tablespoons.
• A period usually lasts between 3–7 days.
• Women living together often find that they have their periods at the same time.
• Some women have pain around ovulation – Mittelschmerz – this means ‘middle pain’.

Men’s bodies

Unlike women’s reproductive organs, men’s reproductive organs are found entirely outside the body.

The male reproductive organs

Testicles and scrotum

The testicles (balls) are the male equivalent of a woman’s ovaries. It is inside these that sperm are made and important male hormones produced. There are two testicles, roughly the size of small plums, and they are protected in a soft pouch of skin called the scrotum.

The scrotum hangs outside the body just behind the penis and between the legs. This helps the testicles keep cool – the average body temperature (37°C) is too hot to produce healthy sperm. They are very sensitive to heat and if they get too hot the scrotum drops down to cool off and when they are cold it shrinks closer to the body to keep warm.

Male hormones

Hormones are just as important for reproduction in men as they are in women. The testicles produce the male hormone testosterone. It is responsible for sperm production and growth and is important for male sex drive. It also controls male characteristics such as hair growth and the deepening of the voice.

Sperm

Inside each testicle are about 1,000 tightly coiled tubes. Individual sperm are continuously made in these tubes. The growing sperm travel along the tiny tubes to a larger coiled tube called the epididymis, which is at the top of the testicle. Here they stay until they are fully mature and ready to be ejaculated.

Ejaculation

At ejaculation sperm passes along the vas deferens (sperm ducts) to the penis and out of the body through the urethra. On the way, fluid from the seminal vesicles and prostate gland is added to the sperm. This helps nourish and transport them and gives semen (as it is now called) its white creamy appearance. The average ejaculation contains up to 300 million sperm and will fill a small teaspoon.

Sperm – did you know?

Did you know?

• Boys start to produce sperm at puberty, the time when their body goes through changes from a boy to a man.
• It takes about 70 days for a sperm to be produced, but as production is a continuous process there is always plenty of fully mature sperm at any one time.
• Sperm are minute – only 1/25mm long and 1/250mm wide, which is about a hundred times smaller than the female egg. Sperm are made up of three parts, a head containing the sex chromosomes, a middle which gives them the energy, and a tail for swimming.
• On average men produce around 150–1,000 million sperm everyday, so they are unlikely to run out.
• Sperm are excellent swimmers. With the right type of conditions the best swimmers are able to swim through the cervix into the uterus in about two minutes.
• Sperm are also survivors and can live for up to five days on average inside the woman’s body but up to seven days if the conditions are right.
• Sperm production can be damaged by untreated sexually transmitted infections, excessive heat, alcohol, smoking or recreational drugs.

The penis contains erectile tissue which fills with blood when a man is sexually aroused and causes an erection, making the penis longer and thicker.

To prepare for ejaculation a small amount of lubricating fluid, known as pre-ejaculation fluid is produced from the Cowper’s glands. This fluid leaks out of the penis before ejaculation and may contain sperm. When a man ejaculates, the muscles of the penis contract forcing the semen out of the penis in spurts. Straight after ejaculation the fluid is thick but it becomes more liquid after a few minutes – this helps to release the sperm.

Conception – getting pregnant

Conception is a process that begins with fertilisation and ends with implantation. For fertilisation to take place an egg needs to meet a sperm – usually through a man and woman having sex.

• When the ovary releases the egg, it is picked up by the fallopian tube where it can be fertilised by the sperm. Sperm are able to wait around in the uterus and fallopian tube until the egg is released.
• Small beating hairs and tiny wave-like contractions help the egg travel along the fallopian tube where it may meet a sperm within minutes or hours of being released from one of the ovaries. The egg only lives for up to 24 hours so it increases the chance of pregnancy if the sperm are ready and waiting. If you have sex 2–3 times a week you will help ensure there is always sperm waiting.
• Only a smaller number of sperm will actually survive the trip to the fallopian tubes and finally only one sperm will actually enter the egg.
• The sperm attaches itself to the egg and produces a special substance which dissolves the outer coat of the egg. Once it has entered, a quick repair of the egg coating means that no other sperm can get in.
• Once the sperm is fully inside the egg, fertilisation has taken place.
• The fertilised egg is wafted down the fallopian tube to the ready-prepared uterus. Here, it settles and over a few days attaches itself to the thick, nutritious lining. Implantation has now taken place, conception is complete and the pregnancy begins. The time from ovulation to implantation is around ten days.
• Once the pregnancy has begun, the pregnancy hormone human chorionic gonadotrophin (hCG) begins to be produced.

Sometimes a pregnancy develops outside the uterus, usually in the fallopian tube. This is called an ectopic pregnancy.

Conception – did you know?

Conception is a process that starts with fertilisation and ends with implantation.

• It takes about three hours for the sperm to fully enter the egg.
• The egg can be fertilised by sperm that have been ejaculated up to seven days before.
• The egg has special places on the outside coat that attract the sperm. It takes a couple an average of 3–6 months to conceive, if they are having sex frequently (2–3 times per week) during their fertile time.
• Women over 30 years old may take longer to conceive.
• Women who are either very underweight or very overweight may have more difficulties conceiving.
• An average pregnancy lasts 280 days.

Pregnancy - the pregnancy test

The earliest and most reliable sign of pregnancy for women with a regular menstrual cycle is a missed period. Sometimes women who are pregnant have a shorter or lighter period than normal.

A woman can carry out a pregnancy test from the first day of a missed period. Some tests suggest that pregnancy tests can be carried out earlier than this, but the effectiveness of this varies. For women who don’t have regular periods, the earliest time to do a test is 21 days from the last time that they had unprotected sex. For some women the test does not show positive until their period is at least a week late.

Pregnancy tests look for the pregnancy hormone hCG, which is found in the urine of pregnant women. A positive test is almost always correct. But women can sometimes get a negative result if the test is carried out too early or not correctly, even though they may be pregnant.

It’s all in the genes

How a baby looks is determined by the genes it inherits from its parents. Genes are contained in chromosomes – tiny thread like structures – and each chromosome contains thousands of genes. It is these genes that determine your height, build, blood group, and eye and hair colour. Some characteristics will be inherited from the mother and some from the father.

So how is the sex of the baby decided?

An egg has 22 chromosomes and one sex chromosome known as the X chromosome. A sperm also has 22 chromosomes and one sex chromosome which can either be an X or a Y chromosome. It is the sperm’s chromosome that determines the sex of the baby. A simple way to look at it is like this:

• If the egg is fertilised by a sperm containing an X chromosome the baby will be female. Mother X + Father X = XX = Female.
• If the sperm contains a Y chromosome the baby will be male. Mother X + Father Y = XY = Male.

To date, there is no reliable scientific evidence to support claims made for choosing the sex of the baby, such as when you have sex, sexual positions or diet.

Making sense of contraception and sexual health

Understanding how your body works can help you and your partner to plan a pregnancy or to avoid one. There are many different methods of contraception which suit people at different times of their lives. They all work in different ways, either by preventing or affecting ovulation, stopping fertilisation by preventing the sperm from meeting the egg, or by identifying the fertile and infertile times of the menstrual cycle.

Emergency contraception

If you have had sex without using contraception or think your method might have failed there are two emergency methods you can use.

• The emergency hormonal pill – must be taken up to three days (72 hours) after sex. It is more effective the earlier it is taken after sex.
• An IUD – must be fitted up to five days after sex, or up to five days after the earliest time you could have released an egg (ovulation).

Ask your doctor or nurse about getting emergency pills in advance, just in case you need them.

Sexually transmitted infections

Most methods of contraception do not protect you from sexually transmitted infections.

Male and female condoms, when used correctly and consistently, can help protect against sexually transmitted infections. Diaphragms and caps may also protect against some sexually transmitted infections. If you can, avoid using condoms containing Nonoxinol 9 (spermicidally lubricated), as this does not protect against HIV and may even increase the risk of infection.

Where can I get more information and advice?

Find out how to get help with your sexual health.