What exactly happens in the menstrual cycle?

Have you ever felt curious to know what happens in the menstrual cycle? In this article, we’ll discover the developments that led to what we know as the period.

Periods prepare the body for fertilization and pregnancy. It starts at the beginning of a girl's puberty and ends with her menopause. Periods differ from one girl to another, but they usually occur around the age of 12. Menopause happens a year after the last menstrual cycle (normal period).

The four phases of the menstrual cycle are:

1. The menstrual phase

2. Follicular or proliferative phase

3. Ovulatory phase 

4. Luteal or secretory phase

The first phase: Menstrual phase

Commonly known as the "period." It typically lasts 3-7 days, and the first day of bleeding is considered the first day of the whole cycle. During this phase, the thickened lining of the uterus breaks down and is shed through the vagina. This shedding consists of blood and tissue that was intended to nourish the baby if pregnancy had occurred. 

The second phase: Follicular or proliferative phase

The follicular phase is the longest of the cycle, as it lasts from 14 to 21 days. During this phase, the ovaries accommodate a developing egg that will be released in ovulation, when a mature egg is released from the ovary.

Here’s a more detailed explanation:

Now, the hypothalamus sends signals to the pituitary gland, which then releases the Follicle-Stimulating Hormone (FSH), which is the key player here. It stimulates the ovaries to produce around 20 tiny, fluid-filled sacs called follicles. Each of these follicles contains an immature egg, and as these little follicles begin to grow, they start producing estrogen that steadily rises in the progress of this phase.

After the development of the follicles, only one will become the "dominant follicle." This follicle grows more rapidly and houses the egg that will eventually be released. (The other follicles will wither away and be reabsorbed by the body.)

The increasing levels of estrogen have another vital role as they stimulate the lining of the uterus, called the endometrium, to thicken and become rich in blood vessels and nutrients. This provides a soft, hospitable environment for a fertilized egg to implant.

As estrogen levels reach a critical peak towards the end of the follicular phase, it triggers a sudden surge in another hormone from the pituitary gland: Luteinizing Hormone (LH). This is the signal that kicks off ovulation, marking the end of the follicular phase and the beginning of the next exciting stage of the menstrual cycle!

The third phase: Ovulatory phase 

The dominant follicle, now fully mature, leaves the ovary under the influence of the LH surge. The follicle ruptures, releasing the egg. Once it's released, the egg will be swept into the fallopian tube (it moves by tiny finger-like projections, fimbriae). Typically, the egg can be fertilized 12 to 24 hours after its release. 

The last phase: Luteal or secretory phase

Remember the follicle that released the mature egg? Now, the remaining follicle cells transform into a new structure called the corpus luteum (it means yellow body). The yellow body's primary role is to release progesterone, which is the dominant hormone during this phase. With the influence of rising progesterone, the endometrium starts to grow, making it thick and rich in blood vessels. 

Now, to determine the end of this cycle, we have two possible paths:

• If Pregnancy Occurs: 

If the egg gets fertilized, the developing fetus begins to produce a hormone called hCG. Its main role is to signal to the yellow body to continue producing progesterone that prevents the endometrium from shedding.

• If Pregnancy Does NOT Occur: 

Without the hCG signal, the yellow body begins to degenerate and shrink around 11 days after ovulation. This leads to a rapid decline of progesterone, which means the endometrium will shed, leading to another menstrual cycle. 

Far from just a "period," the menstrual cycle is a continuous journey of preparation and renewal. Understanding it helps us to be more aware of our body's needs during these phases. 

Reference List

Nebraskamed.com. (2024). What are the phases of the menstrual cycle, and how do they affect your body? [online] Available at: https://www.nebraskamed.com/health/healthy-lifestyle/womens-health/what-are-the-phases-of-the-menstrual-cycle-and-how-do-they.

Cleveland Clinic (2022). Follicular Phase Of Menstrual Cycle: Hormone Levels & Length. [online] Cleveland Clinic. Available at: https://my.clevelandclinic.org/health/body/23953-follicular-phase.

Cleveland Clinic (2022). Luteal Phase Of The Menstrual Cycle: Symptoms & Length. [online] Cleveland Clinic. Available at: https://my.clevelandclinic.org/health/articles/24417-luteal-phase.

White, K. (2018). All About Periods (for Teens) - KidsHealth. [online] Kidshealth.org. Available at: https://kidshealth.org/en/teens/menstruation.html.

Elara Care. (2022). Luteal Phase - What it is and how it impacts you. [online] Available at: https://elara.care/hormones/luteal-phase-what-is-it-and-how-it-impacts-you/.