The begin the reproductive cycle, a hormone, called follicle-stimulating hormone, (FSH) is produced by the pituitary gland in the brain. FSH travels through the bloodstream to the ovaries, causing a few of the many tiny follicles there to begin ripening, or maturing. Each follicle is a tiny ring of cells with a tiny ovum, or egg, inside. As the follicles ripen, they produce another hormone, called estrogen. Estrogen causes the cervix, the opening of the uterus, to begin making moisture and mucus. This is when a woman notices wetness or mucus outside the vagina. This mucus is not a sign of disease. It is a natural part of the cycle and indicates that the ova are maturing in the ovaries. If intercourse occurs at this time, the mucus will protect the sperm from the acidity of the vagina, assuring that the sperm will still be alive at ovulation.

Estrogen also causes the endometrium, the lining of the uterus, to grow soft and spongy, forming a kind of bed that can, in the event of pregnancy, hold and nourish a baby. Finally, estrogen signals the pituitary gland in the brain that some follicles have matured in the ovaries.

When the pituitary gland receives the message that some follicles have matured, it produces another hormone, leutenizing hormone, or LH. LH causes one of the ripening follicles to release its ovum into a fallopian tube. This is called ovulation. The ovum travels along the fallopian tube for 12 to 24 hours. If pregnancy does not occur during that time, it disintegrates and is reabsorbed by the body. The empty follicle, which is called the corpus luteum, lives for another two weeks, all the while making progesterone, another hormone.

Progesterone causes the endometrium to grow soft and spongy, in case of a pregnancy. And progesterone stops the pituitary in the brain from sending any more hormonal messages to begin another cycle. Progesterone continues to delay the beginning of another cycle for about two weeks, when the empty follicle dies. When the empty follicle dies and pregnancy has not occurred, the lining of the uterus is shed with menstruation. The bloody menstrual flow is actually the bed that would have held and nourished a baby if pregnancy had occurred.

As soon as menstruation begins, FSH may again be sent from the brain to the ovaries, beginning another cycle.