Ovulation – How Does It Happen?
A woman increases her chances of conception when she has sex during the ovulatory phase of her monthly cycle. However, learning how your body actually functions can help you in better pin pointing this phase.
Biological Effects of Ovulation
For women who have a 28 to 32 day menstrual cycle, ovulation will typically occur between days 11 and 21, according to the American Pregnancy Association. It is during this time that a preovulatory follicle will release a mature ovum to be fertilized in the oviduct. In order for ovulation to happen correctly, there needs to be surges of both FSH and LH. The ovum matures during ovulation with the help of the LH surge.
Following a latent period and during ovulation, the oocyte in the preovulatory follicle resumes meiosis. The germinal vesicle, or oocyte nucleus, transitions through varies changes that entail germinal vesicle breakdown (GVBD), as well as the advancement of meiosis to the second meiotic metaphase or first polar body stage. Meiosis is detained at this stage and will not progress any further unless fertilized of the ovulated egg occurs. Meiotic maturation is an important element in ovulation since it is necessary for normal fertilization. The surge in both LH and FSH triggers meiotic maturation through desensitization and down regulation of both the LH and FSH receptors.
One of the most extraordinary changes that happen in the course of ovulation involves the creation of a hole in the surface of the ovary. Known as the stigma, this is the location where the ovum is implanted after being fertilized. The follicle produces proteases that degrade the ovarian tissues during this progression. LH aids the formation of the stigma and in response to the surge of LH, the preovulatory follicle creates progesterone and prostaglandin, with are both equally necessary for the stigma to develop properly. Therefore, anovulation happens when the dominant follicles failure to ovulate because the formation of the stigma is compromised. It is still unknown as to how the LH-induced progesterone and prostaglandin production come together to form the stigma.
Hormones at Play in Ovulation
Throughout ovulation, many different hormones become synchronized to prepare the body for ovulation, fertilization, and implantation. Ovulation then happens more or less 10-12 hours after the peak of LH. Those hormones at play during ovulation include:
Approximately 2 weeks after ovulation, the ovaries produce large amounts of progesterone. The progesterone helps to increase the thickness of the nutrient-rich endometrium so that it can better house the fertilized egg. Progesterone also helps in milk production during lactation.
Prior to ovulation, the amount of estrogen production is increased to help build up the endometrium lining after menstruation. Estrogen and progesterone work together to control the increase or decrease of the hormones LH and FSH to regulate the menstrual cycle.
Estrogen and progesterone are both created from cholesterol in the ovaries. At first, cholesterol is used by the ovaries to develop progesterone and testosterone, then they convert a certain quota of progesterone and testosterone into estrogen. Once ovulation is completed and during the last half of the menstrual cycle, more progesterone is created specifically to be converted.
The preovulatory follicle produces estrogen, which rises significantly and triggers a surge in LH. This surge happens approximately 34 to 36 hours before actual ovulation occurs and, once recognized, can be used to time ovulation. The LH surge motivates luteinization, as well as the fusion of progesterone that is accountable for the mid cycle FSH surge. In addition, the recommencement of meiosis and the release of the ovum are stimulated by the LH surge.
Right before the LH peak, estradiol levels fall significantly. It is believed that during this time, elevated FSH levels free the ovum from the follicular attachments. This mid cycle rise in FSH is stimulated by Progesterone; however, it is unknown what causes the postovulatory fall in LH. It is thought that this LH decrease may be a result of the loss of the positive feedback effect of estrogen, or because of the increasing inhibitory feedback effect of progesterone, or attributable to a reduction of LH content of the pituitary from down regulation of the GnRH receptors.