Hormones And The
In order to understand what happens during perimenopause and menopause, and how hormone
replacement works, it is important to understand how the normal menstrual cycle operates.
The story of menstruation and menopause is really the story of the ovaries, the uterus and
the pituitary gland.
Within each ovary are thousands of tiny sacs called follicles. At the time a woman has
her first period, she may have as many as 500,000 follicles, each of which is filled with
eggs. Usually, early in each menstrual cycle, just one of these eggs begins to
"ripen." Around mid-cycle, the follicle bursts open, and the ripened egg passes
into the fallopian tube, which leads to the uterus. This process is called ovulation. If
it meets sperm along the way, the egg may be fertilized, and the resulting fertilized egg
soon begins to divide and differentiate into multiple cells while continuing its journey
to the uterus.
In the meantime, the uterus has been preparing to welcome and nurture the newly
fertilized egg since the end of the last menstrual period. The lining of the uterus (the
endometrium) has become thicker and enriched with blood and nutrients, so when the
fertilized egg reaches its destination, it can easily implant itself into the uterine wall
and begin to grow into an embryo, a fetus, and eventually, an infant.
If the egg is not fertilized, it still continues its journey into the uterus. In the
absence of a hormonal message that fertilization has occurred the uterus ends its
preparations for pregnancy and discards the endometrial lining it has built up, as well as
the extra blood and nutrients it has amassed. This familiar event is known by a number of
names: menstruation, menstrual bleeding, "my period," "the curse," and
Regular menopause signals to the woman that she is healthy and not pregnant, and that
conception is still possible in the future. Once menstruation starts to lose its
regularity (usually every 26-28 days), it probably means menopause is approaching, and the
remaining fertile days are numbered. When periods stop altogether, menopause has arrived.
The regularity of the menstrual cycle is controlled by the balance of four hormones:
|Follicle Stimulating Hormone (FSH)|
|Luteinizing Hormone (LH)|
What Happens During The Menstrual Cycle?
Refer to the diagram.
Days 1-5: Estrogen Falls, FSH Rises.
Menstrual bleeding begins on Day 1 of the cycle and lasts approximately 5 days. During
the last few days prior to Day 1, a sharp fall in the levels of estrogen and progesterone
signals the uterus that pregnancy has not occurred during this cycle. This signal results
in a shedding of the endometrial lining of the uterus.
Since high levels of estrogen suppress the secretion of FSH, the drop in estrogen now
permits the level of FSH to rise. FSH (follicle stimulating hormone) stimulates follicle
development. By Day 5 to 7 of the cycle, one of these follicles responds to FSH
stimulation more than the others and becomes dominant. As it does so, it begins secreting
large amounts of estrogen.
Days 6-14: Estrogen Is Secreted, FSH Falls.
A large amount of estrogen is secreted by the follicle during this phase of the
menstrual cycle. This estrogen does several things:
|The estrogen stimulates the endometrial lining of the uterus. It become thicker and
enriched so that it can receive the fertilized egg if necessary.|
|The estrogen suppresses the further secretion of FSH.|
|At about mid-cycle (Day 14), the estrogen helps stimulate a large and sudden release of
luteinizing hormone (LH). This LH surge, which is accompanied by a transient rise in body
temperature, is a sign that ovulation is about to happen.|
|The LH surge causes the follicle to rupture and expel the egg into the Fallopian tube.|
Days 14-28: Estrogen And Progesterone Secretion First Rise, Then
After the follicle is ruptured, its walls collapse. It is now known as the corpus
luteum. Immediately after ovulation, the corpus luteum begins secreting large amounts of
progesterone, which helps prepare the endometrial lining for implantation of the
fertilized egg. If the egg is fertilized, a small amount of the hormone called human
chorionic gonadotrophin (HCG) is released. (HCG, which can be detected as early as seven
days after fertilization, is the basis for the early pregnancy tests.)
HCG keeps the corpus luteum viable, so it can continue pumping out estrogen and
progesterone, which, in turn, keep the endometrial lining intact. By about Week 6 to 8 of
gestation, the newly formed placenta takes over the secretion of progesterone.
If the egg is not fertilized, the corpus luteum starts to "crumble", causing
the levels of estrogen and progesterone to drop. Without these hormones to support it, the
uterus soon sheds its lining, and menstruation begins. In addition, with no estrogen to
suppress it, FSH levels again start to rise. Thus, one cycle ends and another begins.
What Happens During Perimenopause and Menopause?
As we have seen, the key to the flawless rotation of menstrual cycle during the child
bearing age in women is the hormonal balance among estrogen, progesterone, FSH, and
estrogen rises, FSH falls. As estrogen falls, FSH rises.
During perimenopause, the hormone balance starts to go slightly out of balance.
|Estrogen and/or progesterone are at lower than usual levels, and|
|FSH and/or LH are somewhat higher than before, while still cycling.|
After menopause, the typical pattern of the hormones is:
|Continually high levels of FSH and|
|Continually low levels of estrogen and progesterone.|
The follicles remaining in the ovaries of a perimenopausal woman are generally less
sensitive to stimulation by FSH than the ones that are present during the child bearing
age. There will be occasionally a cycle in which the follicle do not develop fully. We
will call these cycles abnormal cycles. The number of such abnormal cycles without a
mature follicle increases as we approach menopause and finally there will be cycles in
which no follicle develops at all. For most of the perimenopause, normal and abnormal
cycles tend to be intermixed. One month a follicle will develop normally, and other
months, with increasing frequency, it will not.
When a follicle fails to develop properly, it secretes less estrogen. The low level of
estrogen cannot fully suppress the secretion of FSH by the pituitary gland. So, as
estrogen levels fall, FSH levels rise. If estrogen levels are sufficiently low, they may
fail to trigger the LH surge that's supposed to rupture the follicle, and the egg isn't
released. This is termed an anovulatory cycle (a cycle without ovulation).
If the follicle doesn't rupture, the corpus luteum cannot form, and consequently,
progesterone cannot be released at the appropriate time. The lack of normal amounts of
estrogen gives rise to all the familiar discomforts of estrogen deficiency, from hot
flushes and insomnia to depression and palpitations. In the long run, heart disease and
osteoporosis may follow.
The decline of estrogen and progesterone, which may happen before the
signals the uterus to shed its endometrial lining prematurely. This results in a general
shortening of the length of the cycles, and often, the timing of estrogen and progesterone
decline varies from month to month, resulting in irregular cycles. Shorter cycles,
irregular cycles, or both are often the first signs that the perimenopause has started.
Androgens, like testosterone, also decline during this period, but at a much slower
rate than estrogen and progesterone in many women. The ovaries continue to secrete
testosterone even after menopause.
(Source: Jonathan V. Wright, M.D. and John Morgenthaler, "Natural Hormone
Replacement," Smart Publications.)
See Also: Estrogen
Next Topic: Symptoms of
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