How the Body Works: Hormones at puberty

A boy reaches puberty when the hypothalamus directs the pituitary gland to increase the secretion of the trophic hormones--luteinizing hormone, follicle-stimulating hormone and adrenocorticotrophic hormones. These act on the testes to start the production of sperm and on the adrenal cortex and testes to produce male hormones, or androgens. Testosterone, the most important androgen, promotes and controls the devlopment of the sex organs and such secondary sexual characteristics as pubic and facial hair. In a girl, the trophic hormones stimulate the ovaries and adrenal glands to secrete androgens that control the shape of the female body. The ovarian hormones, progesterone and estrogen, initiate menstruation.