The trigger for puberty is the production of sex hormone releasing factors from the pituitary gland at the base of the brain, which cause sex hormones to be manufactured in the gonads – oestrogen from the ovaries of females, and testosterone from the testes of males.
Both sexes show a marked increase in weight and height, while boys develop more muscle and girls acquire the fatty deposits, which give their rounded feminine shape. There are also gender-based differences in the way the skeleton grows – boys develop wider shoulders leading to greater physical strength and girls develop wider hips to facilitate childbearing. As a general rule, the bones stop growing in girls by the age of about 16 and in boys by the age of about 18, although sometimes growth continues until the early twenties.
Some parts of the body are affected by the adolescent growth spurt more than others. The hands and feet mature first, then the legs, then the trunk, so children stop growing out of their jeans a year or so before they stop growing out of their jumpers.
On average puberty starts in girls a year or two earlier than in boys – usually about 10 or 11 years of age in girls, and 12 or 13 years of age in boys. Girls have been known to reach puberty as early as 8 and as late as 15 or 16. Boys vary similarly. Heredity is an important factor in the age of maturity. A girl whose mother started her periods late is likely also to be somewhat later than average in developing.
Puberty is also affected by general health. A child who has been undernourished or experienced a lot of illness may have the onset of maturity delayed. Children who are much smaller than the norm may also not mature as early as usual. Generally speaking there is no cause for concern unless a child shows no signs of development by the age of about 15 or 16.
The physical changes of puberty are accompanied by psychological and emotional changes, also due to the production of sex hormones. In both boys and girls, there is an increased interest in sexuality as well as greater natural assertiveness, which helps to explain why teenagers are rebellious and often seen by their despairing parents as turning life into a never-ending argument. Rising levels of the male hormone testosterone are thought to be the reason adolescent boys are so often adventurous and aggressive.
In girls the physical changes include the development of the breasts, including an increase in the size of the nipples and possibly a darkening of the pigmentation. As well as the widening of the hips, the vagina and uterus develop further. Glands that will supply lubrication during sexual intercourse develop in and around the vagina. Hair grows in the armpits and the pubic region. In girls the pubic hair triangle has the base of the triangle closest to the navel and the apex points to the genitals. Fine hair may develop on the forearms, parts of the legs and the upper lip.
The major change in any girl’s life is the start of menstruation or the onset of her periods (the menarche). From this time on, every month the uterus prepares itself for a possible pregnancy by increasing the thickness of its lining to nourish a fertilised egg. If a fertilised egg does not arrive, the thickened lining is not needed and breaks down to be discarded from the body. It is this lining, together with some blood, that flows out through the vagina as the monthly menstrual flow. The first time a girl has a period, it reveals that her body has started releasing its eggs (all of which are present from birth) and is capable of becoming pregnant. An entire cycle normally takes 28 days, with menstruation lasting four or five days. A girl’s periods are usually irregular for the first few months, since it takes a while for a pattern to be established. Some women continue to have irregular periods for their entire reproductive lives, while other women are as regular as clockwork.
In boys the main physical signs of maturity are an enlargement of the penis and testicles and the ability to produce sperm to fertilise a female egg. Most boys will experience wet dreams or the involuntary emission of semen (the fluid in which sperm is contained) while they are asleep. These are completely normal and no reason for concern.
The boy will also grow a triangular patch of body hair in the pubic region and under the arms. In boys, the pubic hair triangle is widest near the genitals and has its apex pointing towards the navel. Hair also appears on the face, and he will need to shave. Generally the hair is soft and downy to start with and becomes thicker and coarser as the maturing process progresses. Finally a boy’s voice breaks and the pitch becomes lower due to the thickening of the vocal cords.