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The Human Body Thursday, 25 June, 1998, 10:49 GMT 11:49 UK
The hormones take over
Beatrice Maude in different stages of adolescence
Beatrice Maude grows up
Parent problems, voice changes and, worst of all, spots - this is the daily nightmare of teenage life.

From the relatively calm port of childhood, young people sail out into uncertainty and danger. And their boat - or body - often feels out of their control.

Raging Teens - the fourth part of the BBC's landmark series The Human Body looks at a world of seething emotions and hormones.

Presenter Robert Winston says: "Usually it is our biology which controls us and this is particularly obvious during the great rollercoaster ride of puberty."

However much you are told what will happen in advance, you are never quite prepared for the full horrors of the biological revolution that leads to sexual, emotional and physical maturity.

Twelve-year-old Beatrice Maude is not looking forward to the inevitable. "I'm quite happy the way I am. I'm quite happy being a kid," she says.

Unique

Other animals mature very differently to humans and at a much faster rate. Humans are unique in having a long break between childhood and adulthood. This gives them the time they need to learn survival skills.

Brain cell
One of 100bn brain cells
The brain contains the hypothalamus gland which controls the hormones - the backbone of puberty.

At the beginning of puberty, they come out at night in 90-minute bursts. Testosterone in boys kick starts changes in the testes and in girls oestrogen does the same to the ovaries.

They can cause wild mood swings and turn an otherwise reasonable teenager into a raging monster.

Chests

Boys' and girls' chests are identical when they are children - until hormones come along. In girls, hormones cause the cells in the breast to divide for milk and the dark part of the nipple to grow. The breasts are not fully mature until after a woman has gone through pregnancy when they grow again.

Hormones in blood
Hormones rush through the bloodstream
Hormones are also behind the onset of periods. It takes three days for the egg to travel the 15 centimetres from the ovaries to the womb. The lining of the womb thickens to provide a cosy home for a fertilized egg. If the egg is not fertilized, the lining is shed. The average girl loses an eggcup full of blood with each period.

Testosterone causes boys' testes to grow. The skin of the scrotum expands and pubic hairs begin to sprout. The testes produce 1,000 sperm per second. The penis also enlarges and the skin darkens. The process takes four years. Because of their position, the testes are cooler than other parts of the body, which is better for the sperm.

Erections

And, as if expanding testes are not enough to cope with, teenage boys also face the terror of involuntary erections and wet dreams. The penis is packed with thousands of blood vessels. Blood flowing into the penis cannot get out and pressure builds up.

Boys' first wet dreams usually do not contain any sperm. Most of the fluid in semen is not sperm anyway - it is a liquid which protects the sperm from the acid walls of the vagina and gives the sperm energy.

It takes some time for teenage boys to learn how to control their bodies.

Hormones also cause changes in the hands which allow them to grow. Children's hands contain a lot of cartilage which blocks growth. Hormones help the cartilage turn to bone.

Faster

Girls grow faster than boys in early adolescence and it takes up to three years for boys to catch up. Girls' hip bones widen and flatten and the space in the middle opens enough for a baby's head to fit through it.

Muscle
Boys develop muscle power
Boys' heart and lungs expand. As more oxygen gets into their bodies, their muscles begin to grow.

Their voices drop an octave deeper than girls as their vocal chords expand. "It is like having to learn a new musical instrument," says Professor Winston.

Both boys and girls have to suffer extra hair growth in puberty - underarm hair, pubic hair and, for boys, chest hair. Pubic hair is short and curly because it grows sideways and its lifespan is only six months.

And if all that is not bad enough, puberty also brings emotional problems as teenagers learn to be more independent, discover that there are few black and white certainties in life and cope with having sex on the brain.

Hormones affect the centre of the brain which controls feelings and desires, but the body develops at a faster pace than the mind.

Reasoning

Teenagers are better able to reason than children because, during puberty, the nerves at the front part of their brain which control judgement become insulated, helping information to travel faster.

The worst aspect of adolescence for many is the curse of acne. Just as you are beginning to try to attract sexual attention, spots bombard your body. Hormones cause a rush of oil to the skin which blocks the skin ducts and traps bacteria.

All in all, growing up is hard to do and it is a relief to get off the rollercoaster and onto firmer ground. Beatrice Maude calls it "the curse of puberty" and wishes it could happen overnight. But that would spoil the hormones' fun.

The Human Body series is accompanied by a 19.99 book and a CD Rom, priced 29.99.

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