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Reproduction - a guide to eggs, sperm, & conception
Women's bodies
You have two ovaries, one on each side of your uterus. Ovaries are the
size and shape of almonds and they contain your ova, or eggs. The funnel-like
ends of your fallopian tubes are near the ovaries. These are tiny tubes
- only as wide inside as a thick human hair and just 10cm long! They carry
the egg from the ovary 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 (or womb) is made of muscle. It's about the size and shape of an upside down pear, hollow and very stretchy. If pregnancy does occur; it is here that the baby develops. The womb can stretch to hold a baby and shrink more or less back to its pre-pregnancy size after the baby is born
The lower part of the uterus which connects to the vagina is called the cervix. A man's sperm swim from the vagina through here to reach an egg. The cervix contains small glands which produce secretions called mucus. The mucus alters in texture and amount during your menstrual cycle. In your fertile phase (the time around ovulation or egg release) it changes from being thick and sticky to being wetter thinner and more stretchy - like raw egg white. This helps sperm reach an egg more easily When a woman is pregnant, the cervix is plugged with mucus to protect the developing baby from infection. Your vagina is a muscular tube 7-1Ocm long which leads from your cervix to your vaginal entrance (vulva)
The vagina opens between your legs, between the urethra (the tube through which you pee) at the front and anus at the back. The vagina tilts towards your back. It has glands which produce secretions when you are sexually aroused to help the penis enter the vagina (penetration). Like the womb, the vaginal walls are stretchy allowing it to hold a tampon and stretch around a penis during sex or a baby during delivery. The vulva includes the opening to the vagina which is surrounded by inner and outer lips called labia and the clitoris. The clitoris is found towards the front of the vulva and when stimulated can result in sexual arousal and orgasm
The menstrual cycle
The menstrual cycle is the process in which an egg develops and is released,
and the lining of the womb is prepared for a possible pregnancy. The lining
of the womb is then shed, as your period, if you don't get pregnant. These
events are caused by hormones - chemical messengers which travel around
your body in the blood stream. The menstrual cycle begins with the first
day of your period. This is counted as day I of the cycle. While the period
is happening, about 20 eggs start to ripen in the ovary, although only
one of these will finally be released at ovulation. A short time after
this the hormone oestrogen causes a new womb lining to start to thicken
in preparation for a fertilised egg. It also causes the mucus in the cervix
to become thinner and more stretchy allowing sperm to pass through the
cervix more easily and swim to the egg
Ovulation is when an egg is released from an ovary This occurs in most, but not all cycles. Occasionally more than one egg is released (within 24 hours of the first ovulation) which, if fertilised, can lead to a multiple pregnancy such as twins. Once the egg has been released, it travels down the fallopian tube to the womb. Ovulation triggers the production of a second hormone, progesterone. This prepares the womb lining even further; ensuring that it is spongy and thick and full of nutrients so that a fertilised egg can settle or implant into it. After ovulation the mucus in the cervix goes back to being thick and sticky. If the egg is not fertilised it will be reabsorbed naturally, the level of hormones falls, and this menstrual cycle comes to an end. The cycle then begins again with the womb lining breaking down and being shed through the vagina as a period, also called menstruation
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. On average
it takes around 28 days, although this is rarely exact and regular cycles
of longer and shorter lengths are common. In all cycles, regardless of
how long or short they are, ovulation will always happen around 12-16
days before the start of the next period. It is the time from the first
day of the period to ovulation that can be variable
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The female sex hormones oestrogen and progesterone,
are responsible for female characteristics such as body shape, developing
breasts and periods |
At birth you will have 1-2 million eggs in your
ovaries but by the time you reach puberty you have less than half
that amount |
During your reproductive life only about 400 eggs
will actually be released at ovulation |
An egg is less than 1/10 of the size of a full
stop - invisible to the naked eye |
Men's bodies
Your 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 the size of small plums which lie outside your
body behind the penis in a soft pouch of skin called the scrotum. They
hang outside the body because 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 they drop down to cool off and when they are cold
they shrink closer to your body to keep warm. Hormones are just as important
for reproduction in men as they are in women. The male hormone testosterone
is produced by the testicles. It helps sperm mature, is important for
male sex drive and controls male characteristics such as hair growth and
the deepening of the voice. Inside each testicle are about 1,000 tightly
coiled tubes. It is within these tubes that individual sperm are continuously
made. 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. As you reach
orgasm, sperm or semen as it is now called, passes along the vas deferens
(sperm ducts) to the penis and out of the body through the urethra. On
the way several glands add fluid to the semen which nourishes and transports
the sperm and gives the semen its white creamy appearance. The average
ejaculation contains up to 300 million sperm and will fill a small teaspoon
The penis contains erectile tissue which fills with blood when you are 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 gland. This fluid leaks out of the penis before ejaculation and can 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 to release the sperm
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You start to produce sperm at puberty, the time
when your body goes through changes from a boy to a man |
It takes about 70 days for a sperm to be produced
but there is always plenty of fully grown sperm at any one time |
Sperm are minute - only 0.04mm long and 0.004mm
wide, which is about a hundred times smaller than the female egg |
They are made up of 3 parts, a head containing
the sex genes, a middle which gives them energy, and a tail for
swimming |
On average you produce around 150-1000 million
sperm everyday |
Sperm are excellent swimmers. With the right conditions
the best swimmers are able to swim through the cervix into the womb
in about 2 minutes |
Sperm are also survivors being able to live for 3-5 days on average inside the woman's body, but up to 7 days if the conditions are right |
Conception
Conception is a process that begins with fertilisation. For fertilisation
to take place an egg needs to meet a sperm - usually through a man and
woman having intercourse. When the ovary releases the egg, it is picked
up by the fallopian tube and it is here that it will be fertilised by
the sperm. Sperm are able to wait around in the womb and fallopian tube
until the egg is released. Small beating hairs and tiny wavelike contractions
help the egg travel along the fallopian tube where it may meet a sperm
within minutes or within hours. The egg only lives between 12-24 hours
so it increases the chance of pregnancy if the sperm are ready and waiting.
Out of all the millions of sperm that are ejaculated into the vagina only
a smaller number 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 by producing a special substance it dissolves the
outer coat of the egg and enters. 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 time from ovulation to implantation is around 10 days, during which time the egg is fertilised and is wafted down the fallopian tube to the ready-prepared womb. Here it settles and attaches itself to the thick, nutritious lining. Implantation has now taken place, conception is complete and the pregnancy begins. Very rarely a pregnancy develops outside the womb, usually in the fallopian tube. This is called an ectopic pregnancy
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. To date, there is no reliable scientific evidence
to support claims made for choosing the sex of the baby, such as timing
of intercourse, intercourse positions and diet
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It takes about 3 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 to 6 months
to conceive, if they are having sex regularly |
An average pregnancy lasts 280 days |
Making sense of contraception
Understanding how your bodies work can help you and your partner to plan
a pregnancy or to avoid one. There are I 3 methods of contraception and
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: Emergency pills
- must be started up to 3 days (72 hours) after sex. They are more effective
the earlier they are started after sex. An IUD - must be fitted up to
5 days after sex. If you cannot visit a doctor or a clinic, then a sexual
health clinic or hospital accident and emergency department may be able
to help you (phone first to check)
Source: Family Planning Association
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