Understanding what happens in menopause helps discern between the facts and myths surrounding this process.
First, let’s take a look at what happens during menstruation, which will help us understand menopause.
Women are born with up to 100,000 oocytes, or immature cells that can mature into ovum (eggs), in her ovaries. During the reproductive phase of her life (between menarche and menopause) a woman uses about 400 of these oocytes. Menopause occurs when the remaining oocytes become non-functional or depleted, usually caused by age.
Menstruation typically occurs in fixed phases caused by various hormones spurring physiological responses that cause an egg to be released through the fallopian tubes. If the egg is fertilized, the woman is pregnant. If not, the lining of the uterus is shed to prepare for the next ovulation, causing the menstrual bleeding known as a period.
How does menstruation happen?
At the beginning of a woman’s cycle, her brain secretes follicle stimulating hormone (FSH). This stimulates the development of follicles, which contain oocytes. The developing follicles release estrogen, which stimulates the secretion of gonadotropin releasing hormone (GnRH). Luteinizing hormone (LH) is then secreted due to stimulation by GnRH. As the follicle continues to develop in what is known as the follicular phase, estrogen continues to be released.
When the follicle matures to a certain size, it releases enough estrogen to trigger a surge of LH. With the boost of LH, the primary oocyte contained in the follicle matures into a secondary oocyte, and finally an ovum.
The ovum is then released from the follicle into the ovary to be fertilized. The empty follicle that remains (corpus luteum) remains in the ovary for about a week and releases progesterone. The presence of progesterone triggers the uterus’ mucosal lining to be ready for implantation and receptive of an embryo. The corpus luteum also secretes inhibin, which prevents FSH and LH from being released.
The unfertilized ovum then passes through the fallopian tube in search of a sperm for fertilization. If the egg and sperm meet, the fertilized embryo implants in the uterus. The developing embryo releases human chorionic gonadotropin (hCG) that causes the corpus luteum to remain and continue to release progesterone. If the egg remains unfertilized, however, the corpus luteum is reabsorbed into the woman’s body and progesterone is no longer present. Without progesterone, the mucosal lining of the uterus begins to shed, causing menstrual bleeding.
With the disappearance of the corpus luteum, FSH and LH are again secreted by the woman’s brain. This causes a follicle to start developing, and the entire process starts again.
So what happens in menopause?
When a woman reaches a certain age, her oocytes become non-functional. This is completely normal. Without oocytes, a follicle cannot mature. Mature follicles are what release estrogen in a woman’s body. Therefore, without oocytes, a follicle can’t mature, and a woman’s estrogen levels remain low for an extended period of time.
Low estrogen levels prevent the LH surge, ovulation, and the release of progesterone (released after ovulation) from happening. Without these factors, mucosal lining begins to thin and periods become erratic.
Low estrogen levels are also usually the cause of other menopausal symptoms, including mood swings, hot flashes, and headaches. This is why hormone-replacement therapy (HRT) is often prescribed to help treat these symptoms.
Can menopause be induced?
Yes. Hysterectomies that remove a woman’s ovaries induce menopause. Certain types of radiation and chemotherapy can also induce menopause.
Note: Neither tubal ligation nor tubal reversal surgery have any effect on the onset of menopause.
Our next article will cover common questions about menopause.
In this 5-part series, we cover all stages of menopause and discuss symptoms, treatment, and what to expect.