Female reproductive cycle typically follows a 28-day pattern. However, some women may experience shorter or longer cycles. A woman’s menstrual cycle is normally controlled by four hormones:
DAY 1-5 ESTROGEN FALLS, FSH RISES Normal menstrual cycle starts on DAY 1. The cycle usually lasts approximately 5 days. A few days before DAY 1, a sharp fall of estrogen and progesterone occurs. It tells the uterus that pregnancy has not occurred during this cycle. This signal results in a shredding of the endometrial lining of the uterus.
Estrogen is responsible for FSH suppression. Therefore, the drop of estrogen allows the level of FSH to rise. The role of FSH is to stimulate follicle development. By day 5 to 7 of the menstrual cycle, one of these follicles responds to FSH stimulation more than the other, and becomes dominant. The dominant follicle then begins to secret large amounts of estrogen.
DAY 7-14 OVULATION PERIOD THE DOMINANT FOLLICLE SECRETES A LARGE AMOUNT OF ESTROGEN Estrogen plays important roles in: 1. Stimulates the endometrial lining of the uterus. The uterus then becomes thicker and enriched so that it can receive and support a fertilized egg if necessary. 2. Suppresses further secretion of FSH 3. Assists stimulation of a large amount and sudden release of LH. This LH surge is normally accompanied by a rise in body temperature, which is a sign of ovulation. 4. LH surge causes the follicle to rupture and expel the egg into the fallopian tube. DAY 14-28 ESTROGEN & PROGESTERONE SECRETION FIRST RISES and then FALLS After the follicle rips open, its walls collapse. We now refer to this ‘ripped-open’ follicle as the corpus luteum. The corpus luteum begins to secrete large amounts of progesterone immediately after ovulation. This process helps to prepare the endometrial lining for implantation of the fertilized egg. If the egg is fertilized, a small amount of the hormone called human chorionic gonadotrophin (HCG) is released. This HCG hormone can be detected as early as seven days after fertilization. Pregnancy tests often use this hormone to detect conception.
In addition, HCG also helps to keep the corpus luteum viable, so it can keep producing estrogen and progesterone, which keeps endometrial lining in place. Normally, by about week 6 to week 8 of gestation, the newly formed placenta takes over the progesterone secretion.
If the egg is not fertilized, the corpus luteum starts to fade away, causing the levels of estrogen and progesterone to drop. Without these hormones to support it, the uterus then sheds the lining. This is when menstruation begins. Additionally, with no estrogen to suppress it, FSH levels again start to rise. This process ends one cycle and another begins.
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Menopause Overview 
