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A
Woman's Reproductive System
Every
month, during the childbearing years, a woman's body prepares an
egg for possible fertilization. A woman's entire supply of eggs
actually develops when she is a fetus. A newborn girl has approximately
2 million immature eggs at birth. By the time puberty arrives, the
number has been reduced to about 300,000 to 400,000 eggs.
Each
month the hypothalamus of the brain tells the pituitary gland to
secrete follicle-stimulating hormone (FSH) which causes the ovaries
to produce a mature egg. When the egg is at the proper stage, the
pituitary gland secretes the next hormone, lutenizing hormone (LH),
which causes the ovary to release the egg. In the mean time, the
hormones estrogen and progesterone are causing the lining of the
uterus to thicken and prepare for a possible pregnancy.
The
egg travels down into the fallopian tube. Sperm must reach the mature
egg while it is in the fallopian tube in order for fertilization
to occur. Once an egg is released from the ovary it only lives about
one day, making timing crucial. If the egg and the sperm are united,
the fertilized egg (zygote) must continue down the fallopian tube
and into the uterus, finally implanting itself into the uterine
lining. The fertilized egg must then divide and develop normally
to become a healthy fetus.
If
fertilization does not occur, the uterine lining is sloughed off
in the monthly menstrual cycle. The complete cycle repeats itself
roughly every 28-32 days.
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