© 2020 Katie Musicco
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I’m assuming by now you understand the general function of your reproductive system. And I’m sure for most of your adult like you’ve been trying to avoid pregnancy, scared that you could get pregnant if you sit beside the wrong guy. The fact is you can only get pregnant a few days out of each cycle. There is so much power in understanding how your body works.
Phase 1: Menstruation
In the hours before you get your period, blood vessels in the endometrium lining (lining of your uterus) tighten up, cutting off blood flow to the lining. This causes it to start to die. Then the blood vessels relax again, which triggers the gradual shedding of the endometrium: aka you get your period. This continues for around four to seven days on average. The heaviest of the shedding is typically happens within the first 24 hours. Therefore the first two days are typically your heaviest.
The endometrium wastes no time regenerating itself to hold a fresh new layer to accommodate a future embryo later in the cycle. This regrowth begins within two days of when you start to bleed. By day 3 of your cycle, estrogen and progesterone receptors form in the endometrium, and your hormones take control of the endometrium building. Around day 6, the endometrium is about 1 to 2 mm thick.
While the lining is doing its thing, your ovaries are waking up as well. The follicles on your ovaries that house your eggs, one egg to a follicle, beginning on about day 4. The follicles are less than 4 mm across at this point, but they will quintuple in size, to about 20 mm.
This whole shebang – endometrium shedding, endometrium regenerating, follicles glowing is orchestrated by the interplay of hormones. Estrogen and progesterone kick it off. Their levels fall which signal the release of gonadotropin-releasing hormone (GnRH), which triggers menstrual bleeding, GnRH in turn signals the release of follicle-stimulating hormone (FSH), which appropriately enough, stimulates the growth of follicles.
Phase 2: Pre-Ovulation
During your period, your pituitary gland signals for FSH levels to rise. This rise stimulates the ovaries to begin ripening between fifteen and twenty follicles in preparation for the release of the egg each one holds. During this phase your FSH levels continue to rise still signalling to the follicles. Each one of the follicles produces estrogen, which determines when you will ovulate. So estrogen rises gradually during this phase.
Full follicle development can take up to fourteen days, therefore around day 4 or so of your period up to ovulation. For some a normal follicular phase may last anywhere from ten to twenty days. Typically, by day 6 or 7 of your cycle, one follicle has become the lead follicle, and the rest simply shrink away.
Rising estrogen tells your body to reduce FSH, so no more follicles are produced. Estrogen levels peak on about day 12 or 13, signalling the pituitary gland for the release of luteinizing hormone (LH), which in turn triggers the release of an egg.
As estrogen continues to rise this influences changes in cervical mucus (CM). You may notice that you feel more moist and your cervical mucus change from sticky or rubbery to being opaque, whitish, and creamy, like hand lotion (this is not yet fertile CM). As estrogen rises even higher, it will thin out and become transparent and stretchy, like egg whites, this is fertile cervical mucus which makes it easier for sperm to navigate through.
During all of this the endometrium has been regenerating. It thickens further as estrogen rises, and by ovulation a healthy endometrium will be about 7 to 10 mm thick.
Phase 3: Ovulation
Typically ovulation takes place on or around day 14 of a regular cycle. But it can be as early as day 10 or as late as day 20 and long s the cycle is regular, it’s nothing to worry about. It typically happens within twenty-four hours of the surge of LH. Occasionally, a cycle produces no egg, which is normal. For time to time, two eggs are releases, always within twenty-four hours of each other. This is how we get fraternal twins. Twenty-four hours after ovulation, progesterone levels rise to the point at which any further release of eggs is impossible. Contrary to popular belief, ovulation doesn’t necessarily alternate from one ovary to the other from month to month.
Whichever side it comes from, the egg is about the size of the period at the end of this sentence. Upon it’s release from the lead follicle, the egg is quickly drawn into the Fallopian tube, a process that takes only about twenty seconds.
The egg remains alive for twelve to twenty-four hours, traveling toward the uterus. When it’s time is up, if the egg has not been fertilized by the sperm, it disintegrates and is eventually reabsorbed into the body. If an egg is going to be fertilized, it happens within a matter of hours of ovulation, probably by a sperm that’s been waiting there for it. Sperm need fertile cervical mucus to swim through to reach the egg – mucus in which they can survive for up to three to four days – and that mucus is produced thanks to increasing estrogen levels in the lather days of the follicular phase.
Within eighteen to twenty-four hours of ovulation, progesterone thickens the mucus, and it once again becomes opaque and no longer conducive to sperm survival or movement. Once an egg is fertilized, it continues on it’s way toward the uterus, a journey of about six days.
Phase 4: Potential Implantation
Progesterone is the dominant hormone in the second, post-ovulation half of your cycle, known as the luteal phase. Progesterone switches off production of FSH and LH, thereby preventing the release of any more eggs. It thickens the endometrium and helps it secrete nutrients so that it will be ready to nourish an embryo if called upon to do so. And it causes your basal body temperature (BBT) to rise (which is favourable to implantation), closes the cervix, and thickens CM, forming a plug that is meant to prevent more sperm from entering the cervix after fertilization. All tis progesterone is released by the corpus lute, which is formed from the collapse of the empty follicle that released the egg.
The length of the luteal phase is determined by how long the corpus luteum lasts, generally between 12-16 days. The luteal phase needs last at least eleven to twelve days, or there won’t be enough time for an embryo to implant, and even if an egg has been fertilized, no pregnancy will result or an early miscarriage may take place.
The embryo arrives in the uterus by the fifth or sixth day of the journey, cells busily dividing all the way. Generally it implants – attaches to the endometrium – within a day after that. The uterus itself assists with implantation by actually pressing its from and back walls together, holding the embryo in place. To achieve this, the body removes fluid from the endometrium in a process called pinocytosis.
Once the fertilized egg has nestled into the endometrium, it gives off the pregnancy hormone human chorionic gonadotropin (HCG), the signal your standard pregnancy test “pee stick” is looking for. That HCG also tells the corpus lute back in the ovarian wall to continue releasing progesterone to sustain the endometrium, instead of shutting the uterine lining down after the usual 12 to 16 days. (Five to six weeks later, the placenta will take over the task of producing progesterone and maintaining the endometrium). At this point, the menstrual cycle is effectively finished (for the next nine months, anyway), and pregnancy has begun. After eight weeks of pregnancy, the little ball of cells has developed and differentiated enough to officially be known as a fetus.
If there is no fertilization or no implantation, the corpus luteum begins to degenerate, ultimately stopping the flow of progesterone, and the blood vessels leading to the endometrium begin closing down, in preparation for endometrial shedding. Estrogen levels begin to fall as well, and the drop in estrogen and progesterone trigger the release of GnRH and FSH, bringing the process full circle: the next period begins. The drop in progesterone is what may cause the symptoms we know as premenstrual syndrome (PMS).
Chinese Medicine considers menstruation to be essentially yin. Yin is the body’s functions related to nourishment, moistening, and cooling; the complementary opposite of yang.
The period, when you shed the lining of your uterus, requires the movement of blood. Follicle building also requires yin and building your endometrium requires blood and yin.
Nourishing yin governs phase 2 as well. The estrogen predominating is considered to be a yin hormone. Yin promotes growth (of follicles) and building (of the endometrium). The production of fertile cervical mucus also requires yin. Developing follicles require good blood flow as well as yin. The quality of yin affects the quality of the egg itself, as well as the growth of the follicle around it. Preparing the uterine lining also requires blood and yin, as well as Jing.
At mid-cycle, yin cedes it’s dominance to the yang energy required by the hormonal transformation necessary for ovulation. This shift is reflected in the changing of the dominant hormone from estrogen to progesterone. This hormonal changing of the guard requires an even flow of qi and blood to occur smoothly and in a timely fashion. Qi also guides the release of the e.g. and it’s progress down the fallopian tube.
In Chinese medicine, the luteal phase (our phase 4) is dominated by yang energy, which is warming and energizing. The body needs yang energy to sustain progesterone levels. If you are deficient in yang (or progesterone), your BBT may climb too slowly in the luteal phase, or drop too soon, making implantation less likely. Generally, women’s bodies are warmer in the luteal phase, and for thousands of years doctors of Chinese medicine have stressed the importance of a warm uterus for implantation. Implantation also relies on a good flow of blood to the uterus to create a strong endometrium.
If you are not pregnant, your progesterone levels drops in the phase. To negotiate this transformation smoothly, your body needs qi and blood to flow smoothly. When they don’t, the result in PMS symptoms, including mood swings, breast tenderness, bloating, food cravings, fatigue, and headaches.
Yang energy flows once again into yin on the first day of your period, a significant transformation in Chinese medicine view of things.