Estrogens are female sex hormone produced by the ovary. It acts on the stimulation of growth, activities of female secondary sex organs, development of growing ovarian follicles, the appearance of female secondary sex characters (e.g., high pitch of voice, etc.) and mammary gland development. Estrogens also regulate female sexual behaviour. Androgens are male sex hormones which are responsible for the secondary sexual characteristics in male. Melatonin is a hormone released by the pineal gland. It regulates the circadian rhythms (variations following a 24 -hour cycle) of our body. Progesterone is a hormone released by the corpus luteum which is responsible for maintaining the pregnancy in human females.