the discharge of a secondary
oocyte from the
graafian follicle; in an adult woman this normally occurs at intervals of about 28 days and alternates between the two ovaries. As a rule, only one secondary oocyte is produced, but occasionally ovulation produces two or more; if more than one subsequently become fertilized, the result may be multiple births, such as twins or triplets. adj.,
adj ov´ulatory.
Ovulation takes place approximately at the midpoint of the
menstrual cycle, 14 days after the onset of menstruation. During the preceding weeks, a
graafian follicle (cell cluster in the ovary containing the oocyte) grows from the size of a pinhead to that of a pea. At the moment of ovulation, the follicle bursts open and the ovum is discharged.
The discharged ovum enters the
fallopian tube adjoining the ovary and moves toward the uterus; if it encounters a spermatozoon while it is still alive (about 48 hours), the two merge and
fertilization takes place, usually in the fallopian tube. The fertilized ovum then makes its way to the uterus, where it becomes embedded in the prepared wall as the first stage of growth of the fetus (see illustration, and see also
reproduction). If fertilization does not take place the ovum loses its vitality and the blood and tissue lining the uterus are shed in the menstrual flow.

Ovulation.