Your body, explained: the parts and hormones nobody taught you

Ten minutes. Everything after this will make sense.

Read this before anything else on HowToHealth.

Let's get on the same page about our bodies.

You should know this. Every woman should. But most of us were never taught — smart, capable women don't know where their ovaries are, and it's not because they weren't paying attention. Half of us learned the word "estrogen" from a skincare ad. Our bodies are amazing and a little chaotic at the same time, and nobody sat us down and walked us through them. Health class covered how not to get pregnant and then stopped.

So here's the version I wish someone had handed us at fifteen. No scary diagrams, no quiz at the end. Let's get into it.

The parts

Your ovaries. Two of them, one on each side, about the size of an almond, sitting low in your belly a little below your hip bones. They do two jobs: they hold your eggs, and they make most of your hormones. That second job is the one everyone forgets, and it’s why so much of how you feel — energy, mood, skin, sleep — traces back to them.

Your uterus. The muscular organ in the middle, about the size of your fist. Its inside lining thickens every month to get ready for a possible pregnancy. When there isn’t one, the lining sheds. That’s your period.

Your period is not just “blood.” It’s the lining leaving.

Your follicles. Inside each ovary, eggs sit in tiny sacs called follicles. Every month a group of them starts growing, one wins, and that one releases its egg. When you hear “cysts” in the context of PCOS, this is what they’re talking about — follicles that started and stalled. Not the scary kind.

Ovulation. The moment the winning follicle releases its egg. This is the actual main event of your cycle, not your period. Your period is what happens because ovulation happened and no pregnancy followed. If you’re not ovulating, you can still bleed — but it isn’t the same thing, and it doesn’t mean the same thing. This one distinction explains half of what confuses women about their own bodies.

The cycle, in four moves

Your cycle starts on the first day of your period. Not the last. The first day of real bleeding is day one.

Move one: the bleed. The old lining leaves. Hormones are at their lowest. This is why the first day or two can feel flat and tired — it isn’t in your head.

Move two: the build. A follicle grows and starts pumping out estrogen. Estrogen rebuilds the lining, and it’s also the hormone behind the week where you feel clear, social, and like yourself. This is usually the best-feeling stretch of the month.

Move three: ovulation. Estrogen peaks, your brain sends a signal, and the egg is released. Somewhere around the middle of the cycle, though “middle” varies a lot from woman to woman.

Move four: the wait. The empty follicle turns into a little temporary gland that makes progesterone. Progesterone holds the lining in place and turns up your body temperature slightly. If no pregnancy happens, it drops off, the lining lets go, and you’re back to move one. That drop is where PMS lives — the days before your period when mood, sleep, cravings, and bloating go sideways.

A “regular” cycle is roughly 21 to 35 days from one day one to the next day one, with a bleed of about two to seven days. Some variation month to month is normal. Consistently outside that range, or so unpredictable you can’t answer “when was your last period” — that’s information, and it’s worth bringing to someone.

The hormones

You have more than these, but these four run the show.

Estrogen. Made mostly by your ovaries. Builds the lining, keeps your bones dense, your skin elastic, your brain sharp, your mood steadier, your vagina comfortable. It rises through the first half of your cycle and peaks at ovulation. Too little and you feel dry, flat, and foggy. Too much relative to progesterone and you get heavy periods, sore breasts, and bloating.

Progesterone. Only made in meaningful amounts after ovulation. That’s the key fact. If you didn’t ovulate, you didn’t make much progesterone that month. It’s calming — it helps with sleep and steadies mood — and its drop at the end of the cycle is what triggers your period. Many of the women who tell me “my second half of the month is a disaster” are describing a progesterone problem, which is often an ovulation problem underneath.

Testosterone and the androgens. Yes, you make testosterone. Every woman does, in smaller amounts than a man — and you need it. It’s part of why you have energy, muscle, sex drive, and motivation. But when it runs high, as it does in PCOS/PMOS, it shows up as acne, hair where you don’t want it, thinning where you do, and irregular ovulation. “Androgens” is just the family name for testosterone and its relatives.

Insulin. Not a “female hormone,” but I’m including it because it’s the one that quietly runs everything else. Insulin moves sugar out of your blood and into your cells. When your body stops responding to it well — insulin resistance — the ovaries respond by making more androgens, ovulation gets erratic, and the whole cycle above starts misfiring. This is why a hormone condition can be, underneath, a blood sugar condition. It’s the single most useful thing to understand about PCOS/PMOS, and almost nobody explains it.

A hormone condition can be, underneath, a blood sugar condition.

How this differs from a man

Same hormones, different amounts and a completely different rhythm.

A man’s testosterone follows a daily pattern — highest in the morning, lower at night, roughly the same every day. His hormones run on a 24-hour clock.

Yours run on a roughly monthly clock. Estrogen and progesterone rise and fall across weeks, and how you feel, sleep, recover from workouts, crave food, and handle stress shifts along with them. That’s not weakness. It’s a different operating system, and most health advice — including a lot of fitness and nutrition research — was written for the 24-hour one.

Knowing where you are in your own cycle is the first step to stop measuring yourself against a body that doesn’t work like yours.

Why tracking is the whole game

Everything in this article becomes useful the moment you start writing down day one.

Track it in an app — most are free and take ten seconds a day. Note the first day of bleeding, how heavy, how long, and the days you felt terrible or great. Three months of that tells a provider more than anything you’ll remember to say in the room. It’s how you’ll know if a cycle is actually irregular or just felt that way. And later, when you change something — food, sleep, a medication, a supplement — your cycle is the free monthly report card on whether it’s working.

One note on apps: they estimate ovulation from your past cycles. If your cycles are irregular, that estimate is a guess, not a measurement. Use the app for the record, not for the prediction.

The cheat sheet

Screenshot this.

Ovaries — hold your eggs, make your hormones.

Ovulation — the egg is released. The real main event.

Period — the lining leaving because no pregnancy followed. Day one of bleeding = day one of your cycle.

Estrogen — builds. First half of the cycle. Your “feel like myself” hormone.

Progesterone — holds and calms. Only after ovulation. Its drop = PMS and your period.

Testosterone — you make it, you need it, too much shows up on your skin and hair.

Insulin — the one underneath all of it.

Regular cycle — 21 to 35 days, bleeding 2 to 7 days.

What to do this week

Open your phone, download a cycle tracker, and enter the first day of your last period — or the honest answer, which might be “I don’t know.” Either one is a starting point.

Then come back and read the rest of what I write, because now you have the vocabulary for it.

You’re not behind. You just weren’t taught. Now you have been.

Congratulations, you’re healthing.

In the comments: tell the women here something in this article you genuinely didn’t know. I promise you’re not the only one — and that’s the whole point of this place.

Coming next: You were handed the pill for your symptoms. Here’s what nobody explained.