Menstruation refers to a monthly natural process of the woman's body in which the lining of the uterus is shed and removed through the vagina. Prior to this ovulation occurs in which an egg is released from the ovaries by the action of hormones. Following this the uterine lining develops in preparation for conception and pregnancy. When pregnancy fails to occur, the action of the hormones stimulates uterine contractions which aid in the removal of the lining. This process is a highly complex one that is entirely dependent on the hormones. As such the hormonal levels must be adequate and must function properly in order for this cycle to take place every month. Hormonal imbalances and abnormalities in functioning of the hormones disrupt the process of ovulation, thereby hampering the monthly cycle.
In the menstrual cycle, the brain produces hormones that signal the ovaries to produce an egg and to secrete estrogen which assists in creating the uterine lining. When ovulation occurs, the ovary that has released the egg produces progesterone, a hormone which prepares the uterus for conception. When pregnancy does not take place, the production of progesterone decreases and the menstrual flow begins. Menstrual bleeding can only occur after ovulation takes place as progesterone is only produced during this time. It is however possible for menstrual bleeding to occur without ovulation. This type of bleeding is irregular and is known as dysfunctional uterine bleeding, also called anovulatory bleeding. Here, the menstrual flow differs in its amount, schedule and duration and is mostly taken to mean a menstrual period.
The hormone progesterone is not produced when ovulation does not take place, but the uterine lining still develops due to estrogen and continues to take place, since there is no progesterone to balance out the estrogen effects. As such the uterine lining begins to shed in an irregular manner and occurs only when it cannot hold itself any longer. This is called estrogen breakthrough bleeding and leads to very heavy and irregular periods. Estrogen withdrawal bleeding can also take place and occurs mostly in peri-menopausal women. Here the uterine lining does not develop adequately resulting in very light and short periods and there may also be spotting between menstrual cycles. Menstruation without the occurrence of ovulation or anovulatory bleeding can occur at any point during the reproductive years of a woman. It usually takes place a year or a couple of years after a girl's first period, and can also occur in women that are approaching menopause. This condition is generally diagnosed by the gynecologist after all other causes of irregular bleeding have been tested and eliminated by way of diagnostic tests.
answered by G M