Reproduction In A Woman

Five important hormones stimulate the reproductive system of a woman:

• gonadotropin-releasing hormone

• luteinizing hormone

• follicle stimulating hormone

• estrogen

• progesterone

Here is how the hormones work:

• The hypothalmus, a region in the brain, first releases a hormone called gonadotropin-releasing hormone (GnRH).

• GnRH causes the pituitary gland to produce two more hormones--luteinizing hormone and follicle stimulating hormone.

• These hormones, in turn, tell the ovaries to release estrogen and progesterone.

How hormones regulate a woman's fertility

A woman's ovaries contain 200,000 to 400,000 egg follicles--small sacs that contain the ingredients needed to form ripened eggs.

• Over a two-week period in a woman's monthly cycle, FSH causes several follicles in the ovaries to ripen and mature.

• FSH also orders the ovaries to produce estrogen, which in turn, launches the manufacture of large amounts of LH hormone.

• LH hormone stimulates the release of an egg from the largest follicle into the fallopian tubes - a process called ovulation.

• LH hormone also stimulates the follicle to produce corpeus luteum - a collection of yellow tissue that manufactures progesterone.

• Progesterone and estrogen work together to thicken and prepare the lining of the uterus for a fertilized egg.

• Together, these hormones swell the lining of the uterus with blood, making it easier for a fertilized egg to implant itself there.

How the egg is fertilized

An egg is usually fertilized by sperm within the fallopian tubes - but only if the woman has sex with a man around the time the egg is released. The sperm must penetrate the egg to fertilize it.

Sperm can survive for six days after entering a woman's vagina and can fertilize the egg at any time during this period. However, research shows that fertilization is most likely to occur two days before or on the day the egg is released. The fertilized egg then moves on to the uterus, where it implants and grows into an embryo, and pregnancy results.

The Unfertilized Egg

If the egg is not penetrated by sperm, it lives for 12 to 24 hours. The egg and the bloody lining of the uterus then slough off, traveling out of the uterus, the cervix and vagina - a process called the woman's menstrual period.