Approximately every 28 days, women menstruate (bleed) due to the
shedding of their uterus lining (called endometrium). This begins from
the time of first menstruation (menarche) and ends at menopause.
The bleeding normally lasts between 1- 8 days per cycle, with 5 days being the quoted average. This cyclical bleeding occurs secondary to a complex interaction between the brain (pituitary gland) and the ovary, which manipulates hormones to prepare for potential pregnancy. This process is outlined below.
It is important to understand how these hormones interact. The brain hormones - follicular stimulating hormone (FSH) and leutinizing hormone (LH) - are capable to stimulating in the ovary, to cause the release and development of the eggs. Ovarian hormones - progesterone and estrogen - are able to reduce the levels of FSH and LH.
On day 1 of a woman's cycle (1st day of bleeding), her estrogen and progesterone levels are low, and her brain hormone levels are high. One of these brain hormones, FSH, stimulates the ovaries to select and egg to grow and develop. This occurs throughout the first half of the cycle.
The women continues to bleed for 5 days due to shedding of the uterus lining from the previous cycle (discussed later).
During the first half of the cycle (follicular phase), slowly increasing levels of estrogen from the ovary cause the endometrium lining to thicken.
At the middle of the cycle, day 14, is ovulation, where the egg is released into the woman's tubes and into the uterus under the influence of FSH. This egg releases large amounts of progesterone, which causes the endometrium to develop fully with blood vessels, and to produce a suitable environment for a fertilised egg and fetus.
However, if the egg is not fertilised by the presence of sperm in the uterus (male's ejaculate), then the egg rapidly degenerates, progesterone levels fall and the endometrium also degenerates.
As a result, the endometrium is no longer kept thick and supplied by blood under the influence of progesterone, and is shed through the cervix and vagina.
This is what the woman experiences as menstruation. With the drop in estrogen and progesterone, FSH levels again rise and select and egg for the next cycle. And so the process continues.
If the egg does become fertilised, the egg is kept alive and continues to release progesterone. This maintains the endometrial lining and provides a suitable site for implantation in the uterus.
The bleeding normally lasts between 1- 8 days per cycle, with 5 days being the quoted average. This cyclical bleeding occurs secondary to a complex interaction between the brain (pituitary gland) and the ovary, which manipulates hormones to prepare for potential pregnancy. This process is outlined below.
It is important to understand how these hormones interact. The brain hormones - follicular stimulating hormone (FSH) and leutinizing hormone (LH) - are capable to stimulating in the ovary, to cause the release and development of the eggs. Ovarian hormones - progesterone and estrogen - are able to reduce the levels of FSH and LH.
On day 1 of a woman's cycle (1st day of bleeding), her estrogen and progesterone levels are low, and her brain hormone levels are high. One of these brain hormones, FSH, stimulates the ovaries to select and egg to grow and develop. This occurs throughout the first half of the cycle.
The women continues to bleed for 5 days due to shedding of the uterus lining from the previous cycle (discussed later).
During the first half of the cycle (follicular phase), slowly increasing levels of estrogen from the ovary cause the endometrium lining to thicken.
At the middle of the cycle, day 14, is ovulation, where the egg is released into the woman's tubes and into the uterus under the influence of FSH. This egg releases large amounts of progesterone, which causes the endometrium to develop fully with blood vessels, and to produce a suitable environment for a fertilised egg and fetus.
However, if the egg is not fertilised by the presence of sperm in the uterus (male's ejaculate), then the egg rapidly degenerates, progesterone levels fall and the endometrium also degenerates.
As a result, the endometrium is no longer kept thick and supplied by blood under the influence of progesterone, and is shed through the cervix and vagina.
This is what the woman experiences as menstruation. With the drop in estrogen and progesterone, FSH levels again rise and select and egg for the next cycle. And so the process continues.
If the egg does become fertilised, the egg is kept alive and continues to release progesterone. This maintains the endometrial lining and provides a suitable site for implantation in the uterus.
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