Back to Basics: The Menstrual Cycle
Whether you are a cycle expert or just starting to learn about all of this, I am SO glad you are here. As women, we have a very unique physiology and it can be argued that our hormonal cycle is at the center of our health. Dysfunction in our cycle is definitely a major marker for disease and dysfunction in our bodies and can be used as great feedback to know that something is going on. My hope is that women are all well educated on their cycles and are able to discern when symptoms are a normal part of the hormonal cycle and when symptoms might be telling us something is off.
So, let’s get Back to the Basics!
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Before we dive into deeper topics in Women’s Health this month, let’s make sure we have a basic awareness and understanding of a woman’s Menstrual Cycle and hormones.
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In general, a menstrual cycle is around 28-29 days long but can vary from female to female and from cycle to cycle (we are all unique). The length of your menstrual cycle is calculated from the first day of your period to the day before your next period starts. Girls get their first period (menarche) on average between the ages 11 and 14. Physiologically, the Menstrual cycle is a biofeedback system, meaning each structure and gland involved is affected by the activity of the others. This system starts in our brain in the Hypothalamus which stimulates the pituitary gland to produce/release certain hormones which act on the ovaries to produce sex hormones estrogen and progesterone which then regulate our cycle. When there is dysfunction in any part of this loop - it affects the other parts and this is where we see disease and health issues arise. Now let’s look at each phase in more detail. ↓
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Phases:
Menstruation - this is the shedding/elimination of the thickened lining of the uterine walls (endometrium) through the vagina if a fertilized egg is not implanted. Menstrual fluid contains blood, cells from lining of uterus, and mucus. Average length of menstruation for most is between 3-7days.
The Follicular phase - starts on first day of menstruation and ends with ovulation. Prompted by the hypothalamus, the pituitary gland releases Follicle Stimulating Hormone (FSH). This hormone stimulates the ovary to produce around five to 20 follicles which each house an immature egg. Usually, only one follicle will mature into an egg, while the others die. This can occur around days 10-16 of a 28 day cycle. The growth of the follicles stimulates the lining of the uterus to thicken in preparation of implantation of a fertilized egg (possible pregnancy).
Ovulation - release of a mature egg from the surface of the ovary. Usually occurs mid-cycle, around two weeks or so before menstruation starts. During follicular phase, the developing follicle causes a rise in the level of estrogen. The hypothalamus recognizes these rising levels and releases gonadotrophin-releasing hormone (GnRH). This hormone prompts the pituitary gland to produce a raised level of luteinizing hormone (LH) and FSH. Within two days, ovulation is triggered by high levels of LH. The egg is funneled into the Fallopian tube and toward the uterus by waves of small, hair-like projections. The life span of an egg is about 24 hrs and unless it is fertilized by a sperm during this time, it will die.
The luteal phase - During ovulation, the egg bursts from its follicle, but the ruptured follicle stays on the surface of the ovary. For the next two weeks or so, the follicle transforms into a structure known as the corpus luteum. This structure starts releasing progesterone, along with small amounts of estrogen. This combination of hormones maintains the thickened lining of the uterus, waiting for a fertilized egg to implant. If a fertilized egg implants, it produces the hormones that are necessary to maintain the corpus luteum. This includes human chorionic gonadotrophin (HCG), the hormone that is detected in a urine test for pregnancy. The corpus luteum keeps producing the raised levels of progesterone that are needed to maintain the thickened lining of the uterus. If pregnancy does not occur, the corpus luteum withers and dies, usually around day 22 in a 28 day cycle. The drop in progesterone levels causes the lining of the uterus to fall away. This is known as menstruation. The cycle then repeats.
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Now as a disclaimer - if you’re numbers don’t match up with the phases above, that does NOT mean you are abnormal. Each woman and each cycle is completely unique from the next and that is why it is so critical to know YOUR cycle. YOU are the expert on your body and your cycle and that’s why we are going to dive into more topics later this month that go over what types of things you should look for and what you should track while you are learning your cycle.
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Now that we know our cycle a little better, I’m going to talk about non-hormonal birth control options next week, so keep an eye out for that!
