The day of ovulation is when the ovary expels an egg. The ovum thus released is caught in the trunk of the uterus. This is where he can eventually join a sperm to form an egg.
A little girl is born with 500, 000 oocytes (future ovules) in her two ovaries, the majority of which will atrophy and disappear. Only about 450 will mature (one per cycle) and be expelled from the follicle that contains them: it is about ovulation. After 40 years, there are not many eggs left in the ovaries.
Inside the ovaries, the eggs are stored in structures called follicles.
The maturation of a follicle results in the production of an egg, it is ovulation.
The maturation of the follicles
Several follicles coexist in each ovary at different stages of maturation that takes place over several cycles. At the end of the process, a single follicle will be selected to become the mature follicle, called De Graff's follicle (named after the Dutch doctor who described it in the 17th century) and which will break during ovulation.
This pre-ovulatory follicle, or mature follicle, reached its maximum volume (2 cm). It can also be clearly seen on ultrasound. Under the effect of a sudden rise in the level of pituitary gonadotropin hormones, FSH and LH (hormones secreted by a small gland located at the base of the brain), the follicle bursts on the fourteenth day of the menstrual cycle, on average. It releases the mature oocyte become ovum, which leaves the ovary to be snapped up by the corresponding uterine horn.
If fertilized by a spermatozoon, the egg becomes an egg cell then a pre-embryo and migrates into the uterus. Once fixed in the uterus, the embryo sends hormonal signals to the exploded follicle that becomes a corpus luteum that, in turn, makes hormones to block the control of the ovaries. The pregnancy begins then.
If the egg is not fertilized, it will die and will disappear after a few hours. A next ovulation will be triggered at the next cycle.
Note: Birth control pills work at different levels of the genitals and the cycle of women. They intervene in particular on the ovulation by blocking it.
To better understand, here is a schematic presentation of ovulation:
To learn more about ovulation, read also our files:
> Ovulation: the luteal phase
> Ovulation: the follicular phase
> The duration of ovulation