Menstruation
A fertilization is possible only within the first 24 hours after ovulation. If the ovum does not encounter any sperm cells during this time, it simply dies and disintegrates. Obviously, in this case there is no implantation either. As a result, the thick special lining of the uterus is not needed, but soon begins to break down and slough off. The waste material, consisting mainly of mucus, lining tissue, and variable amounts of blood, is discharged through the vagina. This discharge is known as the monthly bleeding or menstruation (from lat. mensis, month). It usually lasts between 3 and 5 days. In popular language, these days are also sometimes referred to simply as the "period." The first day of menstruation is usually considered the first day of the entire menstrual cycle.