In girls, the main hormone that starts to be highly expressed is estrogen and progesterone while in males, testosterone. This is triggered by the hypothalamus that releases gonadotrophic-releasing hormones (GnRH). GnRH then triggers the pituitary to release LH (Luteinizing Hormone ) and FSH (Follicle Stimulating Hormone) that act on the gonads (ovaries in females and testis in male)