"[These webpages] give a clear explanation on how the polymerase chain reaction works and why it is useful."
Sex hormones are responsible for some of the most dramatic changes that occur in the body. They control puberty, egg and sperm production, pregnancy, birth and lactation (breastfeeding).
In girls, between the ages of about 10 and14, the pituitary gland produces Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH) which together stimulate the production of the sex hormones by the ovaries.
The ovaries start to produce oestrogen and progesterone which begin the bodily changes that happen during puberty. The changes, known as secondary sexual characteristics, are: