At puberty the reproductive hormones cause the body to change. In males the testes make testosterone. It stimulates sperm production and causes the male secondary sexual characteristics, such as a deeper voice, facial hair and more muscle.
In females the ovaries make oestrogen. It causes the female secondary sexual characteristics, such as breast development and wider hips. Oestrogen also repairs and thickens the lining of the uterus during the menstrual cycle.
The menstrual cycle lasts about 28 days and is controlled by hormones. FSH is released by the pituitary gland. It makes an egg mature in one of the ovaries and stimulates the ovaries to release oestrogen. After an egg is released, the ovary makes progesterone, which keeps the lining of the uterus thick and ready for a pregnancy.
