A brief overview of the menstrual cycle is essential to understanding what happens to the body during menopause. Taking a close look at how your body functions will help increase your sense of comfort and familiarity, and place the sometimes puzzling symptoms of menopause into perspective.
Monthly Ovarian Cycle
While men manufacture sperm each day, often into advanced age, women are born with a single lifetime supply of egg cells that are released from the ovaries gradually throughout the menstrual years. The entire structure of an egg, with its surrounding flat sheet of cells, is called a follicle. The ovarian cycle begins when the follicular cells swell, absorbing a cholesterol-rich fluid that is then converted into steroid hormonespredominantly estrogen, a woman's most important sex hormone. These hormones act as chemical messengers that orchestrate the menstrual cycle, which lasts an average of 28 days. Some of these hormones escape the follicle into the bloodstream and travel throughout the body. Not only do the sex organs need estrogen to function, but almost every part of your body is affected by the hormones produced by the ovaries.
The ovary raises many follicles each month but usually only one follicle matures to reach ovulation. Ovulation occurs when the egg is released from its follicleleaving the ovary, entering the fallopian tube, and journeying toward the uterus. If the egg is fertilized by a sperm, pregnancy occurs.
The cycle continues after ovulation with the reconnection and multiplication of the cells of the ruptured follicle in the ovary. The former follicle grows and takes on a yellow color, thus its name, corpus luteum ("yellow body"). As the corpus luteum grows, it secretes increasing amounts of estrogen and progesterone, raising the levels of these hormones in the blood. If the egg is not fertilized by the fourteenth day after ovulation, the cells of the corpus luteum begin to die and, simultaneously, hormone levels in the blood decline sharply.
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What's Missing in Menopause
Menopause occurs when the ovaries shut down and menstruation ends. But, as the diagram at left shows, more than menstruation is at stake. During the regular monthly cycle, the egg-bearing follicles within the ovaries produce first a burst of estrogen, then a follow-up surge of both estrogen and progesterone. When ovulation stops, so does virtually all production of these hormones. Because estrogen plays many roles in the female body including maintenance of bone density, stimulation of breast tissue, and nurture of the vaginal membranesits loss has numerous ramifications, collectively known as the "Change." |
Monthly Uterine Cycle
Along with ovarian changes, the uterus goes through a cycle of its own. When stimulated by the estrogen secreted during the ovarian cycle, the lining of the uterus (the endometrium) develops to serve as a bed for the fertilized egg. As hormone levels in the blood rise, the endometrial cells multiply, and blood vessels grow to provide nourishing oxygen, causing an increase in the thickness of the endometrial tissue.
When hormone levels drop at the end of the ovarian cycle, the blood vessels in the endometrium begin to deteriorate and deprive the cells of nourishment. The elimination of blood, mucus and the dead cells from the endometrial tissue, in the form of menstrual blood flow, generally occurs for three to five days. This signals the start of a new cycle.
The Control Center
The entire monthly cycle is controlled by certain centers in the brain. The hypothalamus, located in the base of the brain, releases several hormones directly into the bloodstream.
One of these, gonadotropin releasing hormone (GnRH), prompts the pituitary gland to secrete two hormones called the gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH). These hormones control the ovaries. FSH stimulates the development of follicles in the ovaries. LH causes ovulation and changes the ruptured follicle into the corpus luteum. In turn, the progesterone produced by the corpus luteum prevents the pituitary from releasing additional FSH and LH, thus preventing the growth of new follicles until the next cycle. The ovaries' declining production of estrogen and progesterone at the end of the cycle signals the hypothalamus to produce GnRH, which begins the cycle anew.
