In girls, the change towards womanhood starts at about the age of 10 years or even earlier. The pelvis starts to grow, and fat is deposited around the thighs and buttocks. There is noticeable development of the breasts and the nipples increase in size; pubic hair also starts to appear. Between the ages of 11 and 13 years the area around the nipples and the internal and external genitalia grow and develop; the vaginal walls thicken and may secrete fluid. From 12 to 14 years the breasts develop to adult size. The most important part of adolescence as far as most girls are concerned is the onset of menstruation, the monthly loss offrom the uterus. The first menstruation, or period, is known as the menarche and is a highly emotional time for most young girls.
Before menstruation can occur the girl has to reach puberty, which can be regarded as the age at which the internal reproductive organs reach maturity. Some time before the menarche, the pituitary gland starts to release. One of these is the growth hormone responsible for the pre-menarche growth spurt.
Another is the follicle-stimulating hormone (FSH), which stimulates the growth of the eggin the girl’s ovaries. These start to secrete a hormone called oestrogen. Each month, an increasing number of are developed causing an ever-increasing amount of oestrogen to be produced. This hormone is responsible for stimulating nipple and breast growth, ers the changes in vaginal structure. Oestrogen also causes fat to be deposited on the hips and slows down the growth spurt triggered off by the growth hormone. This is the point when boys start to get taller than girls.