In general, a woman's reproductive health involves her:
- Hypothalamus (pronounced high-poe-THAL-amus)—part of the brain that functions as the main control for the body's reproductive system. The hypothalamus works like a thermostat in a furnace, in that it controls the levels of different hormones and other chemicals in the body. If the hypothalamus detects that there is too little of a hormone in the body, it orders the body to make more.
- Pituitary (pronounced pitt-OO-ih-terry) gland—the body's master gland. The pituitary sends out hormones, or chemical signals to control the other glands in the body. The pituitary gets orders from the hypothalamus about what the body needs.
- Ovaries—the source of eggs in a woman's body. The ovaries have follicles, which are tiny, fluid-filled sacs that hold the eggs. The ovaries also make hormones that help to maintain a woman's health, such as estrogen, progesterone, and testosterone. The ovaries receive the chemical signals from the pituitary and respond by making certain hormones. In POF, the ovaries stop working correctly in both their egg production role, and in their hormone production role.
- Uterus—where a woman carries a baby, also called the ?omb.?The uterus has different layers; its innermost layer or lining is called the endometrium—endo means ?nside?and metrium (pronounced MEE-tree-um) means ?omb.?The endometrium functions as a bed for an embryo when a woman is pregnant. If no pregnancy occurs during the cycle, then the endometrium is shed as a menstrual flow, or a period, and the cycle starts all over again.
These parts interact with one another to coordinate a woman's monthly menstrual cycle.
- The hypothalamus keeps track of the level of estradiol (pronounced ess-trah-DYE-awl) in the body. Estradiol is the natural estrogen that a woman's body makes, so we'll call it estrogen from now on.
- When the level gets low, the hypothalamus sends an order to the pituitary gland telling it that the body needs more estrogen.
- The pituitary gets the order and responds by sending out follicle stimulating hormone (FSH), a hormone that causes the follicles on the ovary to grow and mature. Mature follicles make estrogen and other substances, such as inhibin. The pituitary continues to make FSH until the mature ovarian follicles make enough estrogen. If the follicles don't make enough estrogen, the level of FSH goes even higher.
- When the level of estrogen gets high enough, the hypothalamus and pituitary know that there is a mature egg in one of the follicles. To get this egg to the uterus so that it can be fertilized, the pituitary sends out a large burst of luteinizing hormone (LH). LH breaks open the mature follicle to release the egg, which allows it to move toward the uterus. The level of LH is only high during the time an egg is being released. This LH burst is the basis for home ovulation detection kits. Because LH may be high throughout much of the menstrual cycle in women who have POF, home ovulation detection kits are unreliable in these women.
- The empty follicle is then transformed into a yellowish, corpus luteum (pronounced CORE-puss loo-tee-um). Corpus means 'body' and luteum means 'yellow.' The corpus luteum makes progesterone, the hormone that prepares the uterus for pregnancy.
- Increased levels of progesterone cause the endometrium to change in preparation for pregnancy, should it occur. Once the endometrium is properly prepared, it can support an embryo and allow the embryo to grow.
- If the egg is fertilized, it sends out a hormone called HCG to let the body know that it's there. HCG causes the corpus luteum to continue to make progesterone, the hormone needed for pregnancy. Pregnancy tests measure the level of HCG. If HCG is present, then it's likely that a woman is pregnant.
- If there is no signal, that is, no HCG is present because the egg wasn't fertilized, the corpus luteum stops making progesterone. Without progesterone, the endometrium starts to break down, and the woman's body sheds it as her period.
