Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg). Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle. The time immediately surrounding ovulation is referred to as the ovulatory phase or the periovulatory period.
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 follicular (pre-ovulatory)
phase of the menstrual cycle, the ovarian follicle will undergo a
series of transformations called cumulus expansion, this is stimulated
by the secretion of FSH. After this is done, a hole called the stigma
will form in the follicle, and the ovum will leave the follicle through
this hole. Ovulation is triggered by a spike in the amount of FSH and
LH released from the pituitary gland. During the luteal
(post-ovulatory) phase, the ovum will travel through the fallopian
tubes toward the uterus. If fertilized by a sperm, it may perform
implantation there 6–12 days later.
In humans, the few days near ovulation constitute the
fertile phase. The average time of ovulation is the fourteenth day of
an average length (twenty-eight day) menstrual cycle. It is normal for
the day of ovulation to vary from the average, with ovulation anywhere
between the tenth and nineteenth day being common.
Cycle length alone is not a reliable indicator of the day
of ovulation. While in general an earlier ovulation will result in a
shorter menstrual cycle, and vice versa, the luteal (post-ovulatory)
phase of the menstrual cycle may vary by up to a week between women.
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Last Updated: Apr 3, 2013