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Menopause and HRT


Hormones And The Menstrual Cycle

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 many others.

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:
bulletFollicle Stimulating Hormone (FSH)
bulletLuteinizing 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.

Menstrual Cycle


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:
bulletThe estrogen stimulates the endometrial lining of the uterus. It become thicker and enriched so that it can receive the fertilized egg if necessary.
bulletThe estrogen suppresses the further secretion of FSH.
bulletAt 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.
bulletThe 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 Fall.

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 LH. As estrogen rises, FSH falls. As estrogen falls, FSH rises.

During perimenopause, the hormone balance starts to go slightly out of balance.

bulletEstrogen and/or progesterone are at lower than usual levels, and
bulletFSH and/or LH are somewhat higher than before, while still cycling.

After menopause, the typical pattern of the hormones is:

bulletContinually high levels of FSH and
bulletContinually 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 perimenopause, 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



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