Puberty, the menstrual cycle and contraception – GCSE Combined Science Biology

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Hormones are chemical messengers. A gland makes them and sends them in the blood to another part of the body. Reproductive hormones control how the body changes in puberty and how the menstrual cycle works.

This matters because it is part of how every human body develops. Understanding it also helps people make informed choices about contraception and fertility.

By the end you will be able to name the main reproductive hormones and what they do. You will describe the stages of the menstrual cycle. You will also compare contraception methods and explain how fertility can be treated.

Puberty

Puberty is the stage when the body becomes able to reproduce. It starts because hormones rise. The pituitary gland, a small gland in the brain, helps to control them.

In males the testes make testosterone, the main male reproductive hormone. It causes secondary sexual characteristics, such as a deeper voice and body hair. It also stimulates sperm production.

In females the ovaries make oestrogen, the main female reproductive hormone. It causes breast development and starts the menstrual cycle. The cycle includes the release of eggs from the ovaries.

The menstrual cycle

The menstrual cycle lasts about 28 days. It prepares the body for a possible pregnancy. The uterus is the womb, where a baby grows. Its lining is like a bed made up for a guest.

On days 1 to 5 the lining breaks down and leaves the body. This is menstruation. The lining then builds up again.

Around day 14 an egg is released from an ovary. This is ovulation. The lining stays thick until about day 28. If no egg is fertilised, the lining breaks down and a new cycle starts.

The four hormones

Four hormones control the cycle. They pass messages like runners in a relay. FSH comes from the pituitary gland. It matures an egg in an ovary and makes the ovary release oestrogen.

Oestrogen builds up the lining of the uterus. It also tells the pituitary to release LH. LH causes ovulation. Progesterone is made by the empty follicle in the ovary after ovulation. It maintains the lining.

High oestrogen and progesterone stop FSH being released. So no more eggs mature.

Hormonal contraception

Contraception prevents pregnancy. Some methods use hormones, which are chemical messengers.

The contraceptive pill contains oestrogen and progesterone. They stop FSH being released, so no eggs mature. If there is no egg, there is nothing to fertilise. Think of it as keeping the starting signal for egg growth switched off. The implant, the patch and the injection also use hormones. The implant sits under the skin, and the patch sticks onto it.

Hormonal methods are very effective. But they can cause side effects, and they do not protect against infections.

Other types of contraception

Barrier methods stop sperm reaching the egg. Condoms and diaphragms are examples. Condoms also reduce the risk of sexually transmitted infections. A diaphragm is a soft cap that covers the cervix, which is the entrance to the uterus.

An intrauterine device, or coil, stops an embryo implanting in the uterus. Spermicides are chemicals that kill sperm.

Surgical methods, such as sterilisation, are permanent. Abstinence means not having sex near ovulation. Each method has good and bad points.

Fertility treatments

Some women do not release eggs. They can take FSH and LH, which help eggs mature and be released.

In vitro fertilisation, or IVF, is another treatment. Eggs are collected after the woman takes FSH and LH. They are fertilised with sperm in a laboratory. The embryos grow for a few days, and one or two are put into the uterus.

IVF can give a baby to couples who cannot conceive. But it has a low success rate. It is stressful and expensive. It can also cause multiple births, which are risky for the mother and babies.

Clomifene therapy is another treatment. Clomifene is a drug that is taken as a tablet. It stimulates the body to release more FSH and LH, so that eggs mature and are released. It is used for women whose eggs do not mature or are not released.

Recap

Testosterone comes from the testes. Oestrogen comes from the ovaries.

Menstruation is days 1 to 5. Ovulation is about day 14. The cycle is about 28 days.

FSH matures the egg. Oestrogen builds the lining. LH causes ovulation. Progesterone maintains the lining.

Contraception can be hormonal, barrier, a coil, spermicide, surgical or abstinence. IVF can help couples who cannot conceive.