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 THE PRODUCTION OF HORMONES DURING THE FEMALE CYCLE In the normal female
cycle, during the reproductive years, the ovaries produce estrogen and
progesterone in a cyclic and balanced fashion.  In the first half of the
cycle, estrogen is the dominant hormone.  It stimulates the build up of
tissue and blood in the uterus. About 14 days after the previous
menstruation ovulation occurs.  The egg is released from the follicle on
the ovary and begins its journey down the fallopian tube.  The now empty
follicle becomes the corpus luteum, the yellow body.  This is the site for
the production of progesterone.  Progesterone is the dominent hormone of
the second half of the menstrual cycle.  It has the action of refining the
tissue and blood of the uterus that has already been influenced by the
estrogen hormone.  If pregnancy does not occur 10 to 12 days after
ovulation, estrogen and progesterone levels fall rapidly.  This hormonal
decline triggers mensturation, and the cycle begins again.