Hormones and Fertility
What is menstruation?
Menstruation is the technical term for getting your period. About once a month, females who have gone through puberty will experience menstrual bleeding. This happens because the lining of the uterus has prepared itself for a possible pregnancy by becoming thicker and richer in blood vessels. If pregnancy does not occur, this thickened lining is shed, accompanied by bleeding. Bleeding usually lasts for 3-8 days. For most women, menstruation happens in a fairly regular, predictable pattern. The length of time from the first day of one period to the first day of the next period normally ranges from 21-35 days.
How does the menstrual cycle work?
The menstrual cycle is controlled by a complex orchestra of hormones, produced by two structures in the brain, the pituitary gland and the hypothalamus along with the ovaries.
If you just want a quick, general overview of the menstrual cycle, read this description.
For a more detailed review of the physical and hormonal changes that happen over the menstrual cycle, click here.
General overview of the menstrual cycle:
The menstrual cycle includes several phases. The exact timing of the phases of the cycle is a little bit different for every woman and can change over time.
Cycle days (approximate)Events of the menstrual cycle
The first day of menstrual bleeding is considered Day 1 of the cycle.
Your period can last anywhere from 3 to 8 days, but 5 days is average.
Bleeding is usually heaviest on the first 2 days.
Once the bleeding stops, the uterine lining (also called the endometrium) begins to prepare for the possibility of a pregnancy.
The uterine lining becomes thicker and enriched in blood and nutrients.
Somewhere around day 14, an egg is released from one of the ovaries and begins its journey down the fallopian tubes to the uterus.
If sperm are present in the fallopian tube at this time, fertilization can occur.
In this case the fertilized egg will travel to the uterus and attempt to implant in the uterine wall.
If the egg was not fertilized or implantation does not occur, hormonal changes signal the uterus to prepare to shed its lining, and the egg breaks down and is shed along with lining.
The cycle begins again on Day 1 menstrual bleeding.
Comprehensive explanation of the menstrual cycle:
The menstrual cycle has three phases:
1. Follicular Phase (Days 1-14)
This phase of the menstrual cycle occurs from approximately day 1-14. Day 1 is the first day of bright red bleeding, and the end of this phase is marked by ovulation. While menstrual bleeding does happen in the early part of this phase, the ovaries are simultaneously preparing to ovulate again. The pituitary gland (located at the base of the brain) releases a hormone called FSH – follicle stimulating hormone. This hormone causes several ‘follicles’ to rise on the surface of the ovary. These fluid filled “bumps” each contain an egg. Eventually, one of these follicle becomes dominant and within it develops a single mature egg; the other follicles shrink back. If more than one follicle reaches maturity, this can lead to twins or more. The maturing follicle produces the hormone estrogen, which increases over the follicular phase and peaks in the day or two prior to ovulation. The lining of the uterus (endometrium) becomes thicker and more enriched with blood in the second part of this phase (after menstruation is over), in response to increasing levels of estrogen. High levels of estrogen stimulate the production of gonadotropin-releasing hormone (GnRH), which in turn stimulates the pituitary gland to secrete luteinizing hormone (LH). On about day 12, surges in LH and FSH cause the egg to be released from the follicle. The surge in LH also causes a brief surge in testosterone, which increases sex drive, right at the most fertile time of the cycle.
2. Ovulatory Phase (Day 14)
The release of the mature egg happens on about day 14 as a result of a surge in LH and FSH over the previous day. After release, the egg enters the fallopian tube where fertilization may take place, if sperm are present. If the egg is not fertilized, it disintegrates after about 24 hours. Once the egg is released, the follicle seals over and this is called the corpus luteum.
3. Luteal Phase (Days 14-28)
After the release of the egg, levels of FSH and LH decrease. The corpus luteum produces progesterone. If fertilization has occurred, the corpus luteum continues to produce progesterone which prevents the endometrial lining from being shed. If fertilization has not occurred, the corpus luteum disintegrates, which causes progesterone levels to drop and signals the endometrial lining to begin shedding.
What is normal bleeding?
There is a range of normal bleeding – some women have short, light periods and others have longer, heavy periods. Your period may also change over time.
Normal menstrual bleeding has the following features:
Your period lasts for 3-8 days
Your period comes again every 21-35 days (measured from the first day of one period to the first day of the next)
The total blood loss over the course of the period is around 2-3 tablespoons but secretions of other fluids can make it seem more
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