Menstrual Cycle
To understand what happens hormonally during perimenopause and menopause, it helps to understand what happens hormonally during the menstrual cycle. Four hormones are primarily responsible for the menstrual cycle: estrogen, progesterone, follicle stimulating hormone (FSH), and luteinizing hormone (LH).

The development of an egg follicle in the ovary is stimulated by FSH. As the egg matures, it secretes estrogen, which stimulates the lining of the uterus (endometrium) to prepare for a fertilized egg by becoming thicker and rich with blood and nutrients. The increased estrogen then suppresses the secretion of FSH (this is referred to as negative feedback loop), which prevents any more eggs from developing during that cycle. Ovulation occurs when a surge in estrogen produces a surge in LH, which causes the follicle to rupture, releasing the egg into the fallopian tube. The ruptured follicle is now known as the corpus luteum, and it secretes progesterone, which helps prepare the endometrium for a fertilized egg. If the egg is fertilized, estrogen and progesterone continue to be released, keeping the endometrium intact. If the egg is not fertilized, the corpus luteum stops producing progesterone and estrogen and progesterone levels drop. Lower levels of these hormones cause the endometrium to shed and menstruation to begin. The cycle begins again as FSH levels rise because the low estrogen level does not suppress it.


Figure 1: Menstrual Cycle Hormones

During perimenopause, the eggs become less sensitive to FSH and may not develop. If the egg does not develop properly, less estrogen is secreted and levels may not be high enough to cause the LH surge necessary for ovulation. This is known as an anovulatory cycle (a cycle without ovulation). Because the follicle does not rupture, there is no corpus luteum to secrete progesterone. The low levels of estrogen and progesterone cause irregular and/or heavy periods. Menopause occurs due to the loss of the follicles, which leads to decreased levels of estrogen and progesterone.

Web site: http://www.alternativemedicinechannel.com/menopause/

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Menstruation and the Menstrual Cycle
What is the menstrual cycle?
The menstrual cycle is the process by which a woman’s body gets ready for the chance of a pregnancy each month. The average menstrual cycle is 28 days from the start of one to the start of the next, but it can range from 21 days to 35 days.
In the beginning of the menstrual cycle, levels of estrogen rise, causing the lining of the uterus to grow and get thicker. An egg starts to mature in one of the ovaries. Around the middle of the cycle, the egg leaves the ovary, a process called ovulation.

The egg begins to travel down the fallopian tubes to the uterus. If the egg becomes fertilized by a sperm cell and attaches to the uterus, the woman becomes pregnant. If not, the uterus does not need the extra thick lining and it begins to shed.

This shedding of the uterine lining through the vagina is menstruation.


What is menstruation?
Menstruation is the part of a woman’s monthly menstrual cycle in which blood and tissue are discharged from the vagina. It is also commonly called a period or menstrual period.
Most menstrual periods last from three to five days. In the United States, most girls start menstruating at age 12, but girls can start menstruating between the ages of 8 and 16.


What are the signs of menstruation?
Bleeding from the vagina is the primary sign of menstruation.
Some women have other symptoms around the time of menstruation, including:

Cramping, bloating, and sore breasts
Food cravings
Mood swings and irritability
Headache and fatigue
If these symptoms are severe, it might be a sign of premenstrual syndrome (PMS). PMS usually occurs one or two weeks before menstruation. PMS may affect a woman of any age who has menstrual periods. If the symptoms disrupt your lifestyle, you may want to seek medical care.


What if I have a problem with my menstrual periods?
A stop in menstrual periods (called amenorrhea), or other menstrual irregularities could be a sign that something is wrong. Menstrual irregularities can mean bleeding between your periods, skipping a period, or having very heavy menstrual periods. It is important to tell your health care provider about these symptoms.

Are there treatments for painful menstruation?
Placing a heating pad on the abdomen and over-the-counter pain relievers may help lessen the symptoms. It is important to tell your health care provider if you have severe cramping and pain or other symptoms, during menstruation.

Web site: http://www.nichd.nih.gov/health/topi...rual_cycle.cfm

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From the Menstrual Period to Ovulation (the details you may not know!)
When your menstrual cycle begins, your estrogen levels are low. Your hypothalamus (which is in charge of maintaining your hormone levels) sends out a message to your pituitary gland which then sends out the follicle stimulating hormone (FSH). This FSH triggers a few of your follicles to develop into mature eggs. One of these will develop into the dominant follicle, which will release a mature egg and the others will disintegrate. As the follicles mature they send out another hormone, estrogen. The high levels of estrogen will tell the hypothalamus and pituitary gland that there is a mature egg.

A luteinizing hormone (LH) is then released, referred to as your LH surge. The LH surge causes the egg to burst through the ovary wall within 24-36 hours and begin its journey down the fallopian tube for fertilization. The follicle from which the egg was released is called the corpus luteum, and it will release progesterone that helps thicken and prepare the uterine lining for implantation. The corpus luteum will produce progesterone for about 12-16 days (the luteal phase of your cycle.) If an egg is fertilized, the corpus luteum will continue to produce progesterone for a developing pregnancy until the placenta takes over. If fertilization does not occur the egg dissolves after 24 hours.

At this time your hormone levels will decrease and your uterine lining will begin to shed about 12-16 days from ovulation. This is menstruation (menstrual period) and brings us back to day 1 of your cycle. The journey then begins all over again.

Web site: http://www.americanpregnancy.org/get...ovulation.html

Ovulation Calendar: http://www.americanpregnancy.org/get...ncalendar.html (not sure if it's accurate)

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Key Facts of Ovulation:
An egg lives 12-24 hours after leaving the ovary
Normally only one egg is released each time of ovulation
Ovulation can be affected by stress, illness or disruption of normal routines
Some women may experience some light blood spotting during ovulation
Implantation of a fertilized egg normally takes place 6-12 days after ovulation
Each woman is born with millions of immature eggs that are awaiting ovulation to begin
A menstrual period can occur even if ovulation has not occurred
Ovulation can occur even if a menstrual period has not occurred
Some women can feel a bit of pain or aching near the ovaries during ovulation called mittelschmerz, which means "middle pain" in German
If an egg is not fertilized, it disintegrates and is absorbed into the uterine lining

Web site: http://www.americanpregnancy.org/get...ovulation.html