The menstrual cycle is a beautiful symphony of human anatomy. It is a mechanism by which a woman’s body develops an environment suitable for developing a fetus. The cycle gets more complicated due to its ability to shed this environment if the egg is not fertilized! How does it do that? Well let’s find out! Today we will be breaking down the menstrual cycle.
The menstrual cycle has 2 phases, the follicular phase and the luteal phase:
This phase at menses (the expulsion of blood, ie. what we think of as a “period”) and goes until ovulation (the release of an egg from the ovaries). During this time a follicle (a sort of egg sack) containing a mature egg matures inside the ovary. As the follicle matures, the anterior pituitary gland in your brain will begin to release 2 hormones, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). These hormones signal the follicle to secrete estrogen, which will signal to the anterior pituitary toproduce a large surge of LH. This surge causes the egg to finish development and the follicle to burst, initiating ovulation and concluding the follicular phase (Reed & Carr, 2018; Hawkins & Matzuk, 2008).
The egg is implanted in the wall of the uterus, while the ruptured follicle forms the corpus luteum, a structure that secretes the hormone, progesterone which acts on the anterior pituitary gland to signal it to stop releasing LH & FSH. The egg is free to exit the ovary into the fallopian tube, where the egg can be fertilized by sperm. Regardless of whether it is fertilized or not, the egg moves through the fallopian tube and into the uterus. If the egg is fertilized it can be implanted into the outer layer of the uterus called the endometrium. At this point, the egg begins to grow and part of it becomes the placenta (while the other part will continue to grow into a fetus) (“Human Placenta Project: How Does the Placenta Form?,” 2017). The placenta releases Human-Chorionic Hormone (hCG) which signals the corpus luteum to maintain high progesterone (fun fact! hCG is the hormone measured in urine and blood tests to determine if a woman is pregnant) (Betz & Fane, 2020). If the egg is not fertilized, then hCG is never released, the corpus luteum dies, and the subsequent drop in progesterone and estrogen causes the endometrium to slough off, initiating a period (Reed & Carr, 2018; Hawkins & Matzuk, 2008).
As you can see the menstrual cycle is maintained by the constant fluctuations of different hormones. Every woman’s body is unique and the menstrual cycle can look different for each individual! Societal stigmatization has led many women to feel as if they have to hide this very natural aspect of womanhood. In reality, the inner-workings of our bodies should be celebrated. We hope the knowledge you learn about the mechanism of the female body will help you to see just how advanced and coordinated our nervous and endocrine systems are in the orchestration of our natural rhythms.