These include the brain, blood vessels, urogenital system, colon and rectum, gallbladder, skin, bone, and breast. The precise effects of estrogen on each of these organs will be described when the effect of a deficiency of estrogen is considered. Before menopause, the levels of estrogen rise and fall during each month as part of the process that causes monthly menstrual periods, as seen in the figure below. After menopause, estrogen levels fall to low levels as the ovaries stop making these female hormones. The remaining amounts of estrogen are then made in fat tissue or in the breast itself.
Progesterone is another female hormone that each month prepares the uterus or womb for a pregnancy.
During the second half of the month, progesterone levels increase for a few days and then fall to trigger a monthly period with bleeding. In birth control pills, synthetic forms of progesterone are added that are called progestins.