Understanding your menstrual cycle
The menstrual cycle starts with the first day of the period and ends when the next period begins. Hormocyclene signals are sent back and forth between the brain and the ovaries, causing changes to the sacs in the ovaries that contain eggs (follicles) and the uterus. The first part of the prepares an egg to be released from the ovary and builds the lining of the uterus, while the second part of the cycle prepares the uterus and body to accept a fertilised egg, or to shed the thickening of the uterus lining if fertilisation did not occur.
It is important to understand that your menstrual cycle is more than just the few days you are bleeding. In fact, the period is just the first part of the first phase of the cycle. The menstrual cycle may be divided into two phases: (1) follicular or proliferative phase, and (2) the luteal or secretory phase. The brain, ovaries, and uterus work together and communicate through hormones (chemical signals that are sent through one part of the body to another) to keep the cycle going each month.
A menstrual cycle always starts with the first day of the period and ends with the start of the next period. An entire menstrual cycle usually lasts between 24 and 38 days, but the length may vary from cycle to cycle, from person to person and may also change over the years.
Below is a breakdown of each phase of the cycle:
Part One of the Cycle
Menstruation (your period) is from the time bleeding starts to the time it ends. A period is the normal shedding of blood and endometrium (the lining of the uterus) through the cervix and the vagina. The first part of the menstrual cycle include menstruation and the follicular phase.
The follicular phase occurs from the start of the period until ovulation (usually midway through the cycle). During this period, the pituitary gland (a small area at the base of the brain that makes hormones) produces a hormone called follicle stimulating hormone (FSH).
FSH tells the ovaries to prepare an egg for ovulation. About halfway through the follicular phase (just as the period is ending) one follicle in one of the ovaries will be the largest. This will become the dominant follicle and is the one that will be prepared and released during ovulation. As the dominant follicle continues to grow, it produces oestrogen which peaks just before ovulation happens.
While the ovaries are working on developing the egg, the uterus is responding to the oestrogen produced by the follicles and starts to rebuild the lining that was just shed during the last period. The endometrium (the lining of the uterus) becomes thicker in preparation for a potential fertilised egg to implant.
The dominant follicle in the ovary continues to produce more oestrogen as it grows larger. When oestrogen levels are high enough, they signal the brain, causing a dramatic increase in another hormone, luteinizing hormone (LH). This spike in LH is what causes ovulation (release of the egg from the ovary) to occur.
Ovulation occurs about midway through the cycle for most women. Ovulation divides the two phases of the ovarian cycle (the follicular phase and the luteal phase).
Part Two of the Cycle
The luteal (or secretory) phase takes place from ovulation until the start of the next period. During this phase, the endometrium prepares to either support a pregnancy or to break down for menstruation. Once ovulation occurs, the follicle that contained the egg transforms into something called a corpus luteum, and begins to produce progesterone as well as oestrogen. Progesterone levels peak about halfway through this phase and the rising levels of progesterone signals the endometrium to stop thickening and to start preparing for the potential attachment of a fertilised egg.
If an egg is fertilised, progesterone from the corpus luteum supports the early pregnancy. If no fertilisation occurs, the corpus luteum will start to break down as a result in the a drop in oestrogen and progesterone levels, which causes menstruation. The hormonal changes of the luteal phase are associated with common premenstrual symptoms that many people experience, such as mood changes, headaches, acne, bloating, and breast tenderness.
The luteal phase gets its name because the endometrium is secreting (producing and releasing) many types of chemical messengers. The most notable of these messengers are the prostaglandins, which are secreted by endometrial cells and cause changes to other cells nearby.
Two prostaglandins in particular called, “PGF2α” and “PGE2”, cause the uterine muscle to contract (cramp). The cramping caused by this prostaglandin helps trigger the period. If a pregnancy occurs, prostaglandin production is inhibited so that these contractions won’t impact an early pregnancy.
Tracking symptoms throughout your menstrual cycle can help you notice patterns and anticipate changes. It can also help you identify if something is out of the norm so that you can seek the advice of a healthcare provider, if needed.
