Ovulation is the process in female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum intended for fertilization. The time immediately surrounding ovulation is referred to as the ovulatory phase or the periovulatory period. The initiation of ovulation marks the transition from puberty into reproductive maturity for women. From then on, throughout a woman’s reproductive years, ovulation occurs approximately once every 28 days. After ovulation, during the luteal phase, the egg will be available to be fertilized by sperm. In addition, the uterine lining (endometrium) is thickened to be able to receive a fertilized egg. By this time, the oocyte has completed meiosis I, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body. Meiosis II follows at once but will be arrested in the metaphase and will so remain until fertilization. The spindle apparatus of the second meiotic division appears at the time of ovulation. If no conception occurs, the uterine lining as well as blood will be shed during menstruation.

Hormonal regulation

The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones secreted in the anterior lobe of the pituitary gland, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In the pre-ovulatory phase of the menstrual cycle, the ovarian follicle will undergo cumulus expansion, which is stimulated by FSH (Pic. 1). Then, ovum will leave the follicle through the formed stigma. Estrogen levels peak towards the end of the follicular phase. This causes a surge in levels of LH and FSH. It lasts from 24 to 36 hours, and results in the rupture of the ovarian follicles, causing the oocyte to be released from the ovary via the oviduct. Several days after ovulation, the increasing amount of estrogen produced by the corpus luteum may cause one or two days of fertile cervical mucus, lower basal body temperatures, or both. This is known as a "secondary estrogen surge".

Induction and suppression

Ovulation induction is a promising assisted reproductive technology for patients with conditions such as polycystic ovary syndrome (PCOS) and oligomenorrhea. It is also used in in vitro fertilization to make the follicles mature before egg retrieval. Usually, ovarian stimulation is used in conjunction with ovulation induction to stimulate the formation of multiple oocytes.

On the other hand, contraception can be achieved by suppressing the ovulation. The majority of hormonal contraceptives and conception boosters focus on the ovulatory phase of the menstrual cycle because it is the most important determinant of fertility. Hormone therapy can positively or negatively interfere with ovulation and can give a sense of cycle control to the female.

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Anovulation ―sourced from Wikipedia licensed under CC BY-SA 3.0
Ovulation ―sourced from Wikipedia licensed under CC BY-SA 3.0
Ovarian cycle ―sourced from Boundless licensed under CC BY-SA 4.0
Hormonal Regulation of the Female Reproductive Cycle ―sourced from Boundless licensed under CC BY-SA 4.0
Menstrual cycle ―by Isometrik licensed under CC BY-SA 3.0
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