By Kelsey Mumford, Medical Advisor
No one ever really explains what hormone cycles are, which is crazy considering that they affect half of the population on (usually) a monthly basis. Read on to learn more about these cycles in terms that your groovy, 21st-century brain will understand.
A hormone, or menstrual, cycle is the process of shedding the uterus lining and rebuilding it again. It usually occurs every 28-29 days, but this can vary. There are two stages of this cycle, and the transition between them is controlled by hormones.
Stage 1: The Follicular Phase (Starts with Menstruation)
The first stage is called the “follicular phase”, which starts with menstruation and which you can think of as the time of the month that your uterus does some deep cleaning. Similar to you after breaking up with your s/o, she feels like she needs to remove everything from her house that reminds her of the last cycle. She throws out her whole lining (called the endometrium) like she’s listening to an early-2000s Kelly Clarkson album, which is what causes that monthly bleeding that everyone loves SO much.
This typically lasts from three days to a week (take all the time you need, uterus) and coincides with the rise of a hormone called “follicular stimulating hormone”, or FSH. This hormone tells your ovaries to produce 5-20 follicles, which each contain immature eggs. Only one egg will typically mature each month, and once the lucky follicle that gets to mature its egg is chosen, your uterus lining will grow again in case it needs to provide a home for a pregnancy coming up.
Stage 2: The Luteal Phase (Starts with Ovulation)
But then, your brain senses this rising FSH level and the estrogen that accompanies it and tells your body to produce a hormone called “luteinizing hormone”, or LH, two weeks into your cycle. This cuts off the follicular stage of your hormone cycle like it was a Tinder date giving you stalker-y vibes and kickstarts the second stage, called the “luteal phase”. LH causes your body to ~ovulate~, which means that the chosen, mature egg is released from the ovary lining. It travels down the fallopian tube towards your uterus, propelled by forward movements of small hair-like projections in the tube, similar to the hair on your legs blowing in the wind when you haven’t shaved for *cough* a month (or two).
Once the egg is released from the ovary and makes its way to the uterus, it only sticks around for 24 hours to find a new s/o (sperm) before deciding to pass away (we love the drama, egg). This 24 hours about two weeks after the first day of your last period is called the “fertile window”, meaning you are the most fertile during this time (but remember, those sperm can stick around for up to five days in the reproductive tract and you are somewhat fertile outside of your window, so always remember to take that birth control or use condoms!).
During the luteal phase, the follicle from which the chosen egg bursts from (queue Troy and Vanessa’s “Breaking Free”) sticks around on the surface of the ovary and transforms into something called the “corpus luteum” (like a shadow of its old self, or you when you are deprived of snackies at work). This structure starts making a hormone called progesterone (and some estrogen), which grows that uterine lining again in case that egg finds *the one* and it needs to house a pregnancy. If a fertilized egg implants in the lining during this time, it starts to produce a hormone called human chorionic gonadotrophin (which is what urine pregnancy tests measure!), which tells the corpus luteum to continue doing its thang and making that progesterone to maintain the thick uterus lining for the pregnancy.
Back to Stage 1: The Follicular Phase (Starts with Menstruation)
However, if no pregnancy occurs during this time, then the corpus luteum chooses violence and self-destructs. Now three weeks after the first day of the last period, it stops making progesterone, which tells your uterus that the thick lining it just spent weeks creating is no longer needed (the unfertilized egg says it’s not you, it’s me). Naturally, the uterus responds to this by getting rid of that lining (Alexa, play “Bleeding Love” by Leona Lewis) and the cycle starts all over again, beginning with menstruation.
So there you have it! The entire menstrual cycle. The below graph summarizes the above information, and is the same one that medical students learn from in school (did you just become half a doctor?!). Next time your cycle restarts with menstruation, follow along with its month-long flings like they’re your next favorite Rom-Coms (Alexa, when does “How to Lose a Guy in 10 Days” next play on PrimeTime?).