At about day 13 to 15 in humans, the level of oestrogen increases rapidly. A slow rise in levels of oestrogen in follicular
phase inhibits GnRH production however, at a critcial high level, oestrogen stimulates the hypothalamus to secrete
more GnRH. GnRH secretion is also enhanced by a temporary increase in FSH and a suuden release of LH from the
pituitary gland. This massive outpouring of LH is called the ovulatory surge. The surge of LH and FSH brings about
ovulation, the release of a secondary oocyte from an ovarian follicle. These effects are a result of postive feedback.
Immediatly after ovulation, a women is fertile and can concieve if she has sexual intercourse, or if sperm is already present in her oviducts