The ovary and the brain are the main structures involved in reproductive functions. Communication among them is mainly by hormones released into the blood stream. The hypothalamus and the hypophysis or pituitary gland, located in the base of the brain, are involved in the synthesis and release of the Follicle Stimulating Hormone (FSH) and the Luteinizing Hormone (LH) respectively. These two hormones stimulate the ovary to develop the follicles containing the eggs or oocytes and are the ones utilized clinically by your physician to achieve the same goal. Daily production and release of FSH and LH are under inhibitory control by low levels of estrogen produced by the ovary. This means that when estrogen is present, there is minimal FSH and LH being released. The Gonadotropic Releasing Hormone (GnRH or commercially known as Factrel or Lupron), secreted by the hypothalamus upon the influence of increasing estrogen levels is in charge of inducing the LH surge prior to ovulation. On the other hand, the ovaries and more precisely the ovarian follicle, a blister like structure housing the egg or oocyte, produce estrogen and testosterone in response to FSH and LH respectively. Testosterone, produced upon the influence of LH, is converted into estrogen by the action of FSH in the follicle. As the follicle grows, it becomes more sensitive to FSH and LH and slowly the levels of estrogen start to rise prior to the LH peak preceding ovulation. Upon the influence of estrogen, the uterus starts to get ready for an eventual implantation by developing the endometrium or lining of the uterus. The LH surge shuts down estrogen production and marks the onset of progesterone production, which will induce the final preparatory endometrial changes prior to embryo implantation. The same follicular cells, which were producing estrogen, now are in charge of progesterone synthesis and release under a different histologic structure known as the corpus luteum. In the absence of implantation, the corpus luteum is destroyed, progesterone levels decrease and the endometrium is shed leading to menstrual bleeding.