Chemicals can alter many functions of the reproductive system; many different systems, many targets. Prdocution of sex hormones necessary for sexual maturation and successful reproduction: responsible for gametogenesis, reproductive organ function, reproductive cycles. Throughout these events both timing and doeses/concentrations of formones (or toxicants) affect the outcome dramatically) Estradiol, synthetic enzyme, p-450 aromatase frome testosterone and estrogen trecptors at their highest levels in the brain prenatually or first few days of life. Y chromosome gene sry expresses protein to determine sex in first weeks of embryonic development (bipotential gonad male) Altered gonadotropin (fsh and lh) production or release (cns) Impaired or altered steroidogenesis (estrogen, progesterone), in ovary/placenta. Toxins can bind to receptors that inhibit or induce theses enzymes. Ex keyoconazole (oral fungicide androgen receptor antagonist, interferes with steroidogenesis) Central dna- binding domain that targets the receptor to a hormone responsive element (hre:ere for er) Unified nomenclature parallel to p-450 gene system. Steroid hormone and hormonelike receptors designated as nr3.