Hormones work together in our body to keep it in balance. Especially our menstrual cycles hormones.

This is how: 

• the brain produces a hormone that signals to a specific organ or gland in our body
• that organ / gland responds and produces its own unique hormone
• that hormone is then recognized by the brain – yay! My signal worked!
• The brain then continues that same level of signaling because it’s working! 

An oversimplified example of our thyroid hormones because thyroid hormone is involved in all sorts of functions of our body – mental development, body heat / cold, energy levels. It can affect almost every organ system – our reproductive systems included!

• The pituitary gland in the brain secretes thyroid-stimulating hormone (TSH)
• This hormone does what it says it does – stimulates the thyroid! The thyroid gland then secretes thyroid hormones called T3 (triiodothyronine) and T4 (thyroxine)
• T3 and T4 then signal back to the brain that their levels are great
• And the brain continues to secrete that same level of TSH because it’s the right level

But … 

If the thyroid gland dysfunctions and accidentally produces too much T3 / T4, the brain notices that high level and decreases its production of TSH because it wants the thyroid gland to calm down. If the thyroid gland dysfunctions and secretes too little T3 / T4, the brain notices and increases TSH to try to stimulate the thyroid more. 

This is called a feedback loop, and it happens in every hormone system in our body. 

Now, let’s look at the menstrual cycle hormones – what they are, what they do, and their feedback loops! 

First, a high level overview of menstrual cycle: 

When I use the term “menstrual cycle”, I mean the entire “monthly” cycle – everything that happens from one period all the way through to the next period. The period (also called menses) is the bleeding part of that cycle. But hormonal changes happen in a cyclic rhythm the rest of the time too!

The menstrual cycle is usually separated into 2 phases – the follicular phase and the luteal phase:

1. Follicular phase: 
   • Starts with a period. Hormones are low. The uterine lining is shedding in response to a decrease in estrogen and progesterone that just happened. This is the beginning of a new cycle. 
   • Follicle stimulating hormone (FSH) starts to increase. FSH stimulates the follicles in the ovaries to produce estrogen
   • Estrogen increases gradually during this phase of the menstrual cycle and peaks about 1 day before ovulation. 
2. Luteal phase: 
   • Luteinizing hormone (LH) surges. LH levels are what Ovulation Prediction Kits are looking for – it peaks about 36 before ovulation (it can take several hours to reach the urine). 
   • An egg pops out of the mature follicle  – this is OVULATION! – and is gently swept up by the fallopian tubes ends called the fimbria. It then starts moving its way down the fallopian tube to the uterus
   • The mature follicle turns into a cyst called the corpus luteal cyst. This cyst secretes progesterone. Progesterone is Pro-gestation, or Pro-Pregnancy. If a pregnancy occurs, it helps sustain it. If a pregnancy does not occur, the corpus luteal cyst starts dissolving and progesterone drops dramatically
   • At the same time progesterone drops, estrogen drops too. The drops in these 2 hormones signal to the uterine lining that it’s not needed this month and a period occurs. Now we’re back to Day #1

So lots of stuff going on, right? 

If you want to know even more details, read on! 

SUPER DUPER DETAILED FOLLICULAR PHASE: 

In the early part of the menstrual cycle (the last few days or just after your period), GnRH (gonadotropin releasing hormone) is released by the hypothalamus. It tells the pituitary gland to produce Follicle stimulating hormone (FSH). FSH was a favorite of mine in medical school because … no memorization required – it does exactly what it says it does: it stimulates follicles!!

FSH stimulates this month’s group of follicles in the ovary to start becoming active. 

There are specific cells within these follicles called granulosa cells. These cells produce estrogen. So when FSH starts stimulating these cells, estrogen is produced. 

That estrogen then travels back to the brain and tells GnRH to slow down, which then slows down FSH. See – there’s that feedback loop!

However, estrogen is still being produced from the follicles in the ovary. 

And a few days later, an unusual thing happens – with continued exposure to estrogen, GnRH starts responding in the opposite way and starts INCREASING. This increase tells FSH to increase again too. This increasing amount of FSH helps one of the follicles mature so much that it becomes the dominant follicle, secreting even more estrogen through that maturation. The dominant follicle is the one that goes on to release the egg that month during ovulation. 

This peak of FSH right before ovulation is all FSH is needed for. It’s done its job and won’t be stimulated again until the next cycle. 

Side note about estrogen: 

As you can see, estrogen plays a dominant role in female physiology and if you’ve heard anything about female hormones, you’ve probably heard about it! It can affect all organ systems in our bodies – obviously the reproductive system, but also our brain, heart, musculoskeletal, you name it, systems too. Put in stress response, confidence, and better at sports too. 

As just outlined, estrogen is at its highest level in the follicular part of the menstrual cycle – the week or so right before ovulation. That’s also when females tend to feel their most confident and sexy. It’s probably from estrogen! 

From an evolutionary perspective this makes sense. Feeling more sexy makes you more likely to have sex! And this is the time of the cycle to have sex to get pregnant and therefore more likely to reproduce. See how that all goes together? 

SUPER DUPER DETAILS ABOUT THE LUTEAL PHASE: 

Luteinizing hormone (LH) surges right before ovulation and causes the egg from that dominant follicle to ovulate. It then causes luteinization (hence the name!) of the estrogen secreting, follicle surrounding granulosa cells. 

What does luteinization mean? It means it turns those granulosa cells in the corpus luteum. The corpus luteum is the cyst that is formed after ovulation. 

Now that LH surged, caused ovulation, and signaled for the granulosa cells to become the corpus luteum, it’s done. It now stays low again until the next cycle too. 

After ovulation, those estrogen producing granulosa cells have changed. Now they produce estrogen AND progesterone. Initially estrogen drops low, then slightly builds up again over the 7-8 days after ovulation. 

Progesterone is the real star of the show now. Estrogen takes the back seat because its levels stay relatively low. 

Progesterone is pro-gestation, or pro-pregnancy. If a pregnancy does occur, the corpus luteum persists to continue to supply progesterone that’s needed for a healthy pregnancy until the pregnancy itself can secrete enough progesterone. If a pregnancy does not occur, the corpus luteum dissolves, causing a dramatic and sudden decrease in estrogen and progesterone, which in turn causes a period. 

(And now we’re back to Day#1 of the cycle because first day of period = Day 1)

Side note about progesterone: 

Progesterone can cause some of those early pregnancy and PMS symptoms – bloating, slowing of the intestine, skin changes, moodiness. But, the acute drop in progesterone and estrogen that causes a period to occur is also linked to PMS symptoms too. 

Understanding this part of your cycle and why you might feel like crap can be super helpful  – it’s not in your head, knowledge is power, hormones are powerful, understanding them helps you understand you.