|
As I understand it, the actual beginning proper is the beginning of the follicular phase, when FSH* and LH** levels are increased relative to the baseline.
*folicle stimulating hormone: secreted by the anterior pituitary gland and is essential for follicular growth until the antrum developes. It induces estrogen and progesterone secretion at the level of the ovary by activating aromatase and p450 enzymes and exerts negative feedback onGnRH secretion. FSH further induces the proliferation of granulosa cells and expression of LH receptors on granulosa cells.
**luteinizing hormone: secreted by the anterior pituitary gland and is required for both growth of preovulatory follicles and luteinization and ovulation of the dominant follicle. During the follicular phase of the menstrual cycle, LH induces androgen synthesis by theca cells; stimulates proliferation, differentiation, and secretion of follicular thecal cells; and increases LH receptors on granulosa cells. The preovulatory LH surge drives the oocyte into the first meiotic division and initiates luteinization of thecal and granulosa cells. The resulting corpus luteum produces high levels of progesterone and some estrogen.
|