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18 April 2014
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You are here: BBC Science > Human Body & Mind > The Body > Puberty

Private parts

Girl sleeping
Puberty is triggered at night

On a night just like any other, a girl innocently sleeps. But this night will change her life forever.

In the very centre of her brain, a structure the size of a grape lights up. It sends out a pulse of hormone. By morning, the hormone pulse has stopped. The same thing happens again the following night, only this time the pulse is slightly stronger and lasts longer. This continues until eventually the hormone is being released at all times of day and night. By this time, the girl herself will have noticed her body starting to change. Puberty has begun.

The hormonal cascade

The trigger for puberty in both boys and girls is the production of 'gonadotrophin releasing hormone' (GnRH) from a part of the brain called the hypothalamus. This hormone stimulates the pituitary gland to release two hormones, Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). These hormones travel through the blood to the testicles and ovaries and switch on the development procedure which will lead to sexual maturity.

Interactive body See how puberty is triggered in girls.
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The sex hormone take-over

As puberty progresses, a girl's ovaries begin releasing oestrogen and progesterone. A boy's testicles will start secreting testosterone. Once these sex hormones are coursing through the body, all kinds of changes will take place. They will take a child on a rollercoaster ride to adulthood.

At the end of it they will have started their periods or had their first erection. They will have pubic hair, deeper voices and some spots. It is a time when a child will experience total loss of control over their body. They have no way of telling when puberty will happen, or how long it will last.

Interactive body See how puberty is triggered in boys.
You will need Flash Player, download it for free.

When will it all kick off?

Scientists still don't know what triggers the trigger. In other words - what causes the hypothalamus to start releasing the hormone that switches on puberty? It involves the nervous system and hormones. But social and psychological factors as well as eating habits are also likely to play a role. Puberty is starting earlier than it used to. In 1890, most girls had their first period at 15. Nowadays girls start their periods around the age of 13. But the age varies, puberty starts bewteen the ages of eight and 13 in girls and nine and 14 in boys.


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