Menopause is perhaps most easily understood as the opposite process to menarche, the start of the monthly periods. However, menopause in women cannot satisfactorily be defined simply as the permanent "stopping of the monthly periods", because in reality what is happening to the uterus is quite secondary to the process; it is what is happening to the ovaries that is the crucial factor.
As an illustration of the central role that the ovaries play, it is worth pointing out that when for medical reasons the uterus has to be surgically removed (hysterectomy) in a younger woman, her periods will of course cease permanently, and the woman will be incapable of pregnancy, but as long as at least one of her ''ovaries'' is still functioning, the woman will ''not'' have reached menopause. Even without the presence of the uterus, ovulation and the release of the sequence of reproductive hormones will continue to cycle on, until menopause is reached. In contrast to this, in circumstances where a woman's ovaries are removed (oophorectomy), even if the uterus were to be left intact, the woman will immediately be in "surgical menopause". Surgical menopause is a menopause which is induced both suddenly and totally, by removal of both ovaries prior to the age of natural menopause.
On average, assuming there has been no surgical intervention, the first evidence of the onset of the menopause transition time is slight variations in the length of the menstrual cycle. These variations become more pronounced over time, and eventually lead to skipped ovulations, skipped periods, and spans of time with no periods, after which menstruation may resume. The transition is considered to be over once a woman has experienced 12 months without any menstrual bleeding, even though perimenopause symptoms (more accurately called effects) may extend well beyond this point in time.
The average age of natural menopause (in Australia) is 51.7 years , although this varies considerably from one individual to another. It is not uncommon for women to notice changes in their menstrual cycle length during the years approaching their menopause. Women may also notice changes in bleeding patterns (menstrual flow may become lighter, or may become heavier). The term "perimenopause", which literally means "around the menopause", refers to the menopause transition years, a span of time both before and after the date of the last menstrual period.
The hormonal contextThe stages of the menopause transition have been classified according to a woman’s reported bleeding pattern, supported by changes in the pituitary follicle stimulating hormone FSH levels .
In younger women, during a normal menstrual cycle the ovaries produce estradiol, testosterone and progesterone in a cyclical pattern under the control of FSH and luteinising hormone (LH) which are both produced by the pituitary gland. Blood estradiol levels remain relatively unchanged, or may increase approaching the menopause, but are usually well preserved until the late perimenopause. This is presumed to be in response to elevated FSH levels. However, the menopause transition is characterized by marked, and often dramatic, variations in FSH and estradiol levels, and because of this, measurements of these hormones are not considered to be reliable guides to a woman's exact menopausal status .
Menopause is based on the natural or surgical cessation of estradiol and progesterone production by the ovaries, which are a part of the body's endocrine system of hormone production, in this case the hormones which make reproduction possible and influence sexual behavior. After menopause, estrogen continues to be produced in other tissues, notably the ovaries, but also in bone, blood vessels and even in the brain . However the dramatic fall in circulating estradiol levels at menopause impacts many tissues, from brain to skin.
In contrast to the sudden fall in estradiol during menopause, the levels of total and free testosterone, as well as dehydroepiandrosterone sulfate (DHEAS) and androstenedione appear to decline more or less steadily with age. An effect of natural menopause on circulating androgen levels has not been observed . Thus specific tissue effects of natural menopause cannot be attributed to loss of androgenic hormone production. However, women who have had their ovaries surgically removed, who have had their ovaries damaged by chemotherapy or radiotherapy, or who have ovarian gonadotropin suppression, do have loss of ovarian androgen production as a result.
Menopause can be surgically induced by bilateral oophorectomy (removal of ovaries), which is often, but not always, done in conjunction with removal of the Fallopian tubes (salpingo-oophorectomy) and uterus (hysterectomy). Cessation of menses as a result of removal of the ovaries is called "surgical menopause". The sudden and complete drop in hormone levels usually produces extreme withdrawal symptoms such as hot flashes, etc. Removal of the uterus without removal of the ovaries, a hysterectomy, does not cause menopause, although pelvic surgery can often precipitate a somewhat earlier menopause, perhaps because of a compromised blood supply to the ovaries.
Adapted from the Wikipedia article Menopause, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki