The menstrual cycle is experienced by approximately 50% of the world’s inhabitants, and is vital to sustain the human population. Yet it is a phenomenon that has been fraught with myth, taboo, confusion and misunderstanding.
Throughout history it was believed that the menstruating women could sour wine, kill insects or cause fruit to drop from trees! Menstrual blood was believed to be toxic, the female in need of purification, fuelling the belief that women were the weaker sex.[1]
Whilst today much of the myth and taboo of menstruation has been debunked, confusion remains (among women and men alike) surrounding the cyclical nature of menses and the role it plays in women’s health and fertility.
What are the facts?
It is believed that by 20 weeks of foetal development the female embryo contains somewhere between 6 and 7 million oocytes, at birth she has a million and by the time she reaches menarche she has approximately 300,000.[2] This perpetuated the idea that women are born with a certain amount of eggs, of which they will eventually run out. However, there is newer evidence to suggest that the ovaries contain stem cells that can create new oocytes, indefinitely.[3]
The average Australian woman reaches menarche around the age of 12-13 and can expect to menstruate, with relative regularity, until 45-50 years of age. That’s 30-40 years of menstruation, resulting in 360-400 periods across her lifetime!
The length of the menstrual cycle varies considerably from woman to women, and is dependent on a number of factors, the most critical being her health. A cycle of 28 days is generally considered normal, however cycles can range healthily between 21 and 35 days.
The cycle of hormones
The menstrual cycle is governed by the interplay between various reproductive hormones. The primary glands responsible for controlling the cycle include the hypothalamus, anterior pituitary gland, ovaries and uterus. Within this reproductive hormone feedback loop, the title of ‘master controller’ can be given to the hypothalamus; it is the nexus of the nervous and endocrine systems.
The menstrual cycle starts when the hypothalamus secretes gonadotrophin-releasing hormone (GnRH), which acts upon the pituitary, triggering the release of follicle stimulating hormone (FSH) and luteinising hormone (LH). FSH and LH act upon the ovaries, triggering the release of oestrogen and progesterone, feeding back to the hypothalamus. It is the varying levels of these hormones that differentiate the phases of the cycle and initiate the flow from one phase to next.
The follicular phase
Day one of the cycle is the first day of menstruation. A period lasts between 3 and 5 days (note that this does not include pre- or post-menstrual spotting). Menstrual discharge is made up of blood, endometrial transudate, and cervical and vaginal secretions. Normal loss is about 50mL over the course of the period; a loss of greater than 80mL is considered heavy.[1]
During the period, oestrogen levels are low, triggering the hypothalamus to release GnRH, which in-turn triggers the pituitary to release FSH. FSH can stimulate the growth of up to 20 follicles and, as they develop, the follicles begin releasing oestrogen, signalling the endometrium to thicken. At around day 8, one of the follicles will have become dominant, thus allowing the ovum within to fully develop. Body temperature remains normal within this phase.
Oestrogen (or more specifically oestradial) levels continue to rise. The increased levels trigger the hypothalamus to release GnRH, causing a small rise in FSH and a significant surge in LH. Oestradial is the feel good, or “yang-like” hormone, responsible for stimulating the release of serotonin and dopamine. This serves to increase mood, energy, libido and vaginal lubrication, thus gearing the body up to potentially try and make a baby.
Ovulation (or the release of the ovum from the dominant follicle) occurs, as triggered by the aforementioned surge in LH, following-on from which FSH and LH levels drop significantly. This is on or around day 14 and these hormonal changes give rise to a body temperature increase of around 0.2 of a degree.
During the follicular phase, vaginal secretions also change. The rising levels of oestrogen stimulate glands around the cervix to secrete cervical fluid. At the beginning of this phase secretions are sticky and opaque. Closer to and at ovulation, the secretions become clear and stretchy with a raw-egg like consistency. This fluid is necessary for conception to occur, providing a natural lubrication, nutrients and a means by which sperm can travel safely to the fallopian tubes.
The luteal phase
The luteal phase follows ovulation, where the corpus luteum (the now empty ovarian follicle) secretes greater and greater levels of progesterone, and reduced levels of LH. Progesterone literally means “pro-gestation” and, as such, now starts acting on the endometrium, ensuring it matures so as to allow for the successful implantation of a fertilised embryo.
As progesterone increases, oestrogen drops and levels out, causing a drying up of cervical fluid. Progesterone creates a calming, relaxing, or “yin-like”, effect as a result of its conversion to allopregnanalone, which has very similar effects to the soothing neurotransmitter gamma-aminobutyric acid (GABA).
If fertilisation were to occur, the embryo would travel through the fallopian tube and implant in the prepared endometrium. Once there, it would release human chorionic gonadotrophin (hCH), which would signal the corpus luteum to continue to secrete progesterone. The corpus luteum continues to do so for about three months, after which the placenta takes over for the remainder of the pregnancy.
As progesterone stimulates the thyroid, body temperature continues to rise. If conception does not occur, the corpus luteum degenerates over the next 14 or so days, thus the hormones that it secretes reduce. This drop in progesterone stimulates the shedding of the endometrium and menses recommences.
Body temperature then decreases and returns to normal. The lowered level of oestrogen stimulates the hypothalamus to release GnRH and the cycle starts over.
In a time where hormone imbalances are plaguing women in epidemic proportions[4] it is important that women have a thorough understanding of the symphonic rise and fall of hormones required for healthy menstruation. This is not only necessary to help decipher a woman’s state of health, but to help empower her to embrace her own cyclic nature.
References
- Trickey R. Women, hormones and the menstrual cycle. Melbourne, Australia: Melbourne Holistic Health Group, 2011.
- Hechtman L. Clinical naturopathic medicine. Chatswood: Churchill Livingstone Elsevier, 2012.
- White YA, Woods DC, Takai Y, et al. Oocyte formation by mitotically active germ cells purified from ovaries of reproductive age women. Natural Med2012;18(3): 413-421 [Full Text]
- Hyman MA. The lifecycles of women: restoring balance. Altern Ther Health Med 2007;13(3):10-16 [Full Text]
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