Understanding the menstrual cycle
The menstrual cycle encompasses all the mechanisms that prepare the female body for a possible pregnancy each month. Two types of hormones fluctuate during the menstrual cycle: estrogen and progesterone.
These hormonal variations take a toll on human psychology and physiology. Hormones influence mood, morphology, and also the [appearance of your skin](/b/hormones-and-skin). They can even be closely linked to certain pathologies like hormonal acne and menstrual migraines.
A woman's cycle starts with the first day of menstruation and ends with the start of the next cycle's period. Each cycle lasts about 28 days, but its length can vary from person to person and from month to month. The first half of the cycle involves preparations for ovulation while the second half prepares the ovaries for the implantation of an egg, or the start of a new cycle if fertilization hasn't occurred.
The menstrual cycle can be divided into 4 key phases:
1. Menstrual Week.
During this week, estrogen and progesterone levels are low. The lining of the uterus, which has thickened in the previous cycle to accommodate the fertilized egg, is removed, resulting in blood loss. But the ovaries don't waste any time and restart egg production immediately. Inside each ovary are thousands of follicles. Each follicle contains an immature egg. At each stage, a few follicles develop simultaneously.
2. The pre-ovulation week.
During this week, your body intensively prepares to ovulate. Following a competition between follicles, only the largest at this stage remains which becomes the dominant follicle. All the others regress. Estrogen production increases as this follicle grows. While your ovaries are working to produce an egg, the lining of your uterus rebuilds and grows under the effect of estrogen to accommodate the egg. At this point in your cycle, your body increases its chances to ensure that the egg is fertilized.
Just before ovulation, estrogen reaches a threshold value in your bloodstream. Signals are then picked up by your brain, giving the orders to trigger the expulsion of the ovum by one of the two ovaries: this is called ovulation. It takes place around the 14th day. The ovum then persists for about 24 hours, waiting to be fertilized.
3. The week after ovulation.
After ovulation, your body's main concern is to maintain a possible pregnancy. The follicle that expelled the egg turns into a corpus luteum, which starts to produce progesterone. This is how progesterone takes over from estrogen for the purpose of preventing a miscarriage in early pregnancy.
4. The pre-menstrual week.
In the absence of fertilization, the corpus luteum regresses, causing progesterone levels to drop at the end of the week and triggering menstruation. The cycle rebegins.
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