Hormones involved in uterine cycle, pregnancy and oogenesis

For my STEAM project I further investigated and portrayed a few aspects of the female reproductive system. In particular, I examined the role of hormones during oogenesis, the menstrual (uterine) cycle, ovulation and pregnancy. The hormones in investigation were progesterone, estrogen, luteinizing hormone (LH), follicle stimulating hormone (FSH), gonadotropin releasing hormone (GnRH) and human chorionic gonadotropin (hCG).

The medium I used as a metaphor for the interaction of the uterine cycle, ovulation and pregnancy was a train that proceeded on a circular track with a single junction that led off the circle. In this metaphor, the circular portion of the track is the uterine cycle, ever progressing and repeating, provided that fertilization does not occur. The junction that joins the circular region to the departing region represents two possible routes depending on the occurrence of fertilization by sperm. The departing path represents pregnancy and leads to birth. Along the sides of all the tracks are markings of certain milestones of each biological sequence along with the hormone levels that accompany. Hormones are color-coded (fig. 3). I chose to use a train set and rail to describe the female reproductive cycle because it feels far more accessible to me. I have been fascinated by the uterine cycle, pregnancy and ovulation for some time now, but found that there was a tremendous complexity to each concept. Upon diving into what is occurring behind the scenes for each, I immediately tried to think of analogies or metaphors to help myself understand the literature and for whatever reason, the idea of a railway seemed to help the most. I figured that if I brought the metaphor in my head to life and properly labelled it, then maybe others who struggle to wrap their heads around how involved the female reproductive system is will benefit the same way I did.

Figure 1: An overview of the train metaphor.

Hormonal Regulation

Looking at the figures that are more zoomed in (figs. 2,3,4,5) one can see that various notable events or sections are labelled in black, progesterone levels are purple, estrogen is green, GnRH is lime, hCG is red, FSH is blue, and LH is orange. The labelled levels around the track indicate hormone levels at that point in the cycle which cause and regulate the accompanying events. An important representation of hormonal control occurs in fig. 2 on the top right. This section shows how the ovulation event is triggered by the GnRH->LH & FSH -> estrogen pathway leading to a critical level of estrogen and the resulting positive feedback loop that causes LH to surge and trigger ovulation. The immediately following event is the two diverging railways depending on whether or not the secondary oocyte is fertilized. Oogenesis is visualized in-depth on fig. 4.

Something I wanted to discuss, but could not represent in my piece due to my desire to keep it simple and accessible, was birth control. They prevent pregnancy by interfering with the “railway system” I created. Using hormones, they either prevent ovulation or change the consistency of cervical mucus to block sperm (Rivera, R., Yacobson, I., & Grimes, D., 1999) and I wanted to elaborate on this because so many people choose to use birth control, yet may not understand how it works. Oral contraceptives work primarily through the action of progesterone, but some contain both estrogen and progesterone. The way it works is multifactorial. Both exogenous estrogen and progesterone interfere with a negative feedback loop. Specifically: GnRH-> FSH -> follicle development + estrogen and GnRH-> LH -> (corpus luteum development -> progesterone) + ovulation. By introducing the end products of these schemes, the amount of GnRH is reduced and thus, all of it’s following products: FSH and LH. Without FSH no follicle develops and without LH, ovulation does not occur. Bringing it back to the railway system metaphor, it is as if the divergence in the railway does not even exist because ovulation was necessary to proceed it. Even if it did, like I mentioned previously, progesterone causes cervical mucus to be inhospitable to sperm (Cooper DB, Mahdy H., 2021).

Figure 2: The Uterine cycle region of the train track.

Figure 3: Color coding for each hormone.

Figure 4: An overview of Oogenesis and folliculogenesis. 

Figure 5: The hormones and notable events associated with pregnancy.

Figure 6: Diverging railways indicating the possibility of fertilization.

Bibliography:

Betts, J., et al (2013). The Reproductive System. In Anatomy & physiology. Textbook, OpenStax College, Rice University. 

Cooper DB, Mahdy H.(2021) Oral Contraceptive Pills. [Updated 2021 Jul 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430882/

“Hormones of Pregnancy and Labour.” (Mar. 2018)You and Your Hormones, You and Your Hormones, www.yourhormones.info/topical-issues/hormones-of-pregnancy-and-labour/#:~:text=High%20levels%20of%20progesterone%20are,is%20sufficient%20to%20maintain%20pregnancy. 

Kumar, P., & Magon, N. (2012). Hormones in pregnancy. Nigerian medical journal : journal of the Nigeria Medical Association, 53(4), 179–183. https://doi.org/10.4103/0300-1652.107549

SCHOFIELD B. M. (1960). Hormonal control of pregnancy by the ovary and placenta in the rabbit. The Journal of physiology, 151(3), 578–590. https://doi.org/10.1113/jphysiol.1960.sp006461

Rivera, R., Yacobson, I., & Grimes, D. (1999). The mechanism of action of hormonal contraceptives and intrauterine contraceptive devices. American journal of obstetrics and gynecology, 181(5 Pt 1), 1263–1269. https://doi.org/10.1016/s0002-9378(99)70120-1