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Page 11
| FSH secretion is increased. This hormone does exactly as its name indicates: it stimulates the development of follicles, a structure containing an egg and other cells in the ovary. Only one of these follicles will ovulate while the others will degenerate. During this time LH begins to rise slowly as well, and estrogen and progesterone are produced by the ovaries in constant low levels. |
| The ovulatory phase is a complex mechanism resulting in a surge of LH release by the pituitary. The egg is released from the follicle due to this LH surge. While estrogen production begins to increase slowly several days before the surge, it increases much more rapidly and peaks about a day before the LH surge. The FSH level begins to fall once the follicle has been developed. Also just before the LH surge, progesterone levels begin to increase significantly. Unlike estrogen, which peaks at the LH surge, progesterone continues to rise after the surge. |
| The postovulatory phase, also known as the luteal phase, is so named because of the corpus luteum, the supportive structure of the released egg. The production of progesterone becomes the task of the corpus luteum during this phase. Progesterone peaks on about the eighth day after the LH surge. At this time LH and FSH levels remain low only to begin the cycle over again by increased secretion when bleeding occurs. Hormones that mark the beginning or cessation of phases of the cycle have effects on other parts of the body besides the ovaries. Certainly the uterus responds dramatically to changes in hormone levels. Estrogen causes the lining of the uterus to thicken, engorging itself with a rich blood supply so that a fertilized egg can be implanted and nourished. Under the influence of progesterone, the lining of the |
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