The release of a mature, fertilizable egg from the dominant follicle is the culmination of a wonderfully integrated and synchronized succession of hormonal actions. The major players in this system are gonadotrophin releasing-hormone (GnRH), FSH (Follicle stimulating hormone), LH , oestrogen and progesterone but essential fine-tuning is provided by a large number of other factors. The steps involved in the process of ovulation, leaves one in awe of the ingenuity of the system and a little surprised that its breakdown, i.e. anovulation, does not occur much more frequently. Normal functioning is dependent on the correct synchronization of release and quantity of the hormones involved. These change dramatically throughout the cycle according to the stimulatory or suppressive signals received.
The ovary is a production line for a vast number of steroid hormones but also, arguably, the most dynamically, constantly changing organ in the female body during the reproductive life span. Of the millions of primordial follicles that started life in the ovary each containing an egg, only about 400 will actually achieve ovulation.
The key to being chosen as the month’s ovulatory follicle is sensitivity to FSH as only the most sensitive can survive, thrive and produce the most oestrogen and LH receptors. The others, starved of the possibility of FSH stimulation, simply fade away. The mid-cycle LH surge is the trigger for ovulation itself, activating a cascade of inflammatory responses in the dominant follicle leading to the breakdown of the follicular boundary wall and the escape of the oocyte with its surrounding cells, the cumulus oophorus