Module 3 Lesson 5 - 5

Lesson Summary

The proper control of the sexual hormones leads to a healthy reproductive system and a greater chance of having offspring.  For women, puberty begins with the increase in GnRH, which causes the pituitary to release FSH and LH hormones. These hormones help with sexual development, successful formation of functioning gametes, and continual movement through the menstrual cycle.

The menstrual cycle is said to begin on the first day of bleeding and is usually a 28-day cycle. It is is divided into the follicular stage and the luteal stage. During the follicular stage, high levels of FSH  stimulate normally one follicle to mature. The maturing follicle releases the ovarian hormones estrogen (mainly) and progesterone (some). Estrogen feeds back negatively to the hypothalamus and pituitary to cause a reduction in the release of FSH. When the amount of estrogen reaches a certain level (around day 12) it exerts positive feedback on the anterior pituitary to release a surge of LH.  This LH surge stimulates ovulation of the primary oocyte from the follicle (around day 14).

The end of ovulation is considered the end of the follicular stage and the beginning of the luteal stage. With the release of the egg, the follicle develops into the corpus luteum under the influence of LH. The corpus luteum secretes mainly progesterone and some estrogen, and the increased levels of these ovarian hormones feed back negatively to the hypothalamus and anterior pituitary to inhibit production of FSH and LH. As the corpus luteum disintegrates, the ovarian hormone levels in the blood decrease. The low blood levels of progesterone and estrogen are detected by the anterior pituitary which causes an increase in FSH and LH - and the cycle starts again.