vaginal bleeding resulting from the process of periodic shedding of the endometrium. The first day of menstrual flow marks the beginning of a new menstrual cycle.
In theory, most of us probably know that a woman*’s body releases hormones in varying intensities and amounts in a cyclical manner in something like a 28-day-rhytm (that is, as long as you are not using hormonal contraceptives).
What *exactly* goes on within one menstrual cycle is a question, that even most people who menstruate do not seem to be able to answer easily. Moreover, while I was doing some research on the lastest scientific data pertaining to the menstrual cycle, I was shocked how generic most of the information was that I was able to access easily. It took quite a number of hours and effort in putting together the little bits and pieces of information I was offered, to satisfy my scientific curiosity going beyond:
I believe that knowledge is power. I offer this knowledge to you, so that you may empower yourselves. And I encourage you to seek out more information on any topic you are interested to know more deeply!
The Menstrual Cycle
Menstrual cycles vary in length, ‘usually’ lasting between 21 and 35 days. The length of your cycle is influenced by numerous factors, such as age, stress, diet, quality and length of sleep, use of contraceptives as well as physical disorders such as endometriosis or polycycstic ovarian syndrome (PCOS). The menstrual cycle is measured from the first day of menstrual bleeding, Day 1, up to Day 1 of your next menstrual bleeding.
The menstrual cycle is governed by fluctuations in hormones produced by the hypothalamus (Gonadotropin releasing hormone, GnRH) the pituitary gland (follicle stimulating hormone [FSH] and luteinizing hormone [LH]), and the ovaries (estrogens, testosterone) as well as the corpus luteum (progesterone). The phases of your menstrual cycle are triggered by hormonal changes.
Menstrual Phase (2 ~ 6 days)
Day 1 of your cycle is initiated by a dramatic drop in both estrogen and progesterone, causing the thickened lining of the uterus (endometrium) to shed. Blood loss of 10-80ml is considered ‘normal’ menstrual flow. Most of your menstrual blood loss happens during the first 3 days.
Follicular Phase (Pre-ovulatory Phase; ~ 18 days)
Technically, the follicular phase starts with Day 1 of your menstrual cycle. Upon stimulation from the hypothalamus via GnRH, the pituitary gland (another hormon gland in your brain) releases the hormone FSH (follicle stimulating hormone), which stimulates an egg-cell in the ovaries to grow. Typically, one egg begins to mature within a small sacklike-structure called follicle. This process can vary in length and plays the biggest role in how long your cycle is. At the same time, the ovaries begin to produce more estrogen, causing the lining of the uterus to thicken.
The last 5 days of the follicular phase, plus ovulation day, are your fertile window.
Rising levels in estragiol produced by the ovaries trigger, via a positive-feedback loop, a surge in LH released by the pituitary gland. This is what induces the release of the matured egg into its fellopian tube, the event known as ‘ovulation’.
Luteal Phase (Pre-Menstrual Phase; ~ 10 Days)
The luteal phase starts on ovulation day, when the egg is released from the egg follicle on the ovary. The empty follicle sack (‘corpus luteum’) then begins to produce progesterone. Together with estradiol, the most important estrogen in the menstrual cycle, progesterone prepares the endometrium for implantation. At the same time, progesterone inhibits the production of lutenizing hormone and estrogen (by acting on the hypothalamus). During the late luteal phase, as both estrogen and progesterone levels fall, the shedding of the uterine lining along with the unfertilized egg is triggered. This is what is refered to as menstrual flow.
And there you have it, folks! Now you know the major physiological and endocrinological players involved in the menstrual cycle. For those of you who prefer visual over lexical information, I refer you to the graphs below (with a tip ‘o the hat to Mikael Häggström).
If you have any questions or requests for more in-depth research, feel free to leave a comment below or drop me a line. Lots of love!