Just got a question asking about how hormones work regarding the sex of cells. So I will just do a quick simplified explanation.

Okay, so cells in humans do not actually know their own sex. It isn't hard coded in, and the cell carries the instructions to make both expressions where there is any variation at all.

The cell doesn't know which way we are going to go. It just is, and can go either way. The deciding factor is when a hormone comes along and binds to the receptor the cell has for it.
Think of it as a lock and key, or perhaps a post box with a specific address on it.

So of your body makes androgens (like testosterone, dihydrotestosterone), these bind to the androgen receptors. Clickty, clack, the receptor heads into the nucleus of the cell, carrying the instruction to switch things up.

As I said, we have both instructions in our code (DNA). By default the "female" associated stuff is on. When the receptor hits the nucleus, it turns off the "female" instructions and turns on the "male" instructions.

Like commenting out code, or dip switches on your motherboard

Now, that cell then behaves using the new instructions. And voila.

Now that is just one cell. A whole bunch of cells grouped together is called tissue. If you have enough hormones, all the cells switch over. Or none. Or some. It's like voting, really.

So hormones change the function of the tissue. Zoom out a little and now we are looking at fatty tissue, muscle tissue, glands, hair follicles etc etc. They behave differently using the two sets of instructions.

Puberty is when you get hormones really kicking in, and so your tissues start doing stuff like growing boobs, hair, your voice dropping, muscles growing, fat deposits shifting etc etc.

These are called 'secondary sex characteristics' and its the stuff we key off for attraction

So here is an important thing to understand. If you change the hormone levels, new cells begin to switch instructions. Again, it is like voting.

Hormone replacement therapy (HRT) does precisely that, it replaces the current hormone levels in your body with the levels you need to cast your vote over which way your cells go.

That's why trans men taking androgens get hairy, muscular and get deeper voices.

Likewise, trans women taking androgen blockers, estrogen and sometimes progesterone get boobs, soft skin, softer hair, cheek apples and all their cake goes to their hips all of a sudden.

Why? Because genetically speaking, they ARE the sex they are setting their hormones to.

Hormones in, cells change, different bits of DNA express themselves.

So, okay, why is it that taking hormones doesn't change... you know... certain bits of the body.

Well, actually it does. A lot. And I can talk about that from a science point of view in a later thread, however what you need to understand is there are windows of opportunity.

Our first hormone bath happens in utero. Actually we get two, but for now just imagine the baby blasts itself with hormones at a critical moment in development.

That vote seals the deal for certain ducts in the body. A duct is like a tube of cells, from which more complex...

...stuff grows, like fallopian tubes, vagina, wombs etc.

They react to hormones too, either hanging around or destroying them.

Once a duct is destroyed, it aint coming back.

So, that window of opportunity has closed.

So how does shifting hormone levels effect us and why is it important to understand? Well, here is the gotcha... our tissue develops at certain times in the pregnancy. The gonads early, then genitals, then the brain, months later.

So what happens if the hormone levels change?

What happens if you get a blast of androgens early on, but not when your brain develops? What happens if the womb ruptures and mother's hormones get in? What happens when our medicines cross the placental barrier?

Trouble, That's what.

And what happens if some of your cells have receptors that do not bind to the hormones that they should?

Or your body is missing an enzyme that means it starts to produce androgens instead of adrenaline?

Trouble.

And that 'trouble' I speak of is that the person develops in a way that doesn't fit the simplistic "boys and girls" model.

Humans, unfortunately, are far more complex than that.

We do not come in 100 male and 100 female flavors. Our genetics doesn't contain one code set.

And as hormones shift, so do we.

Ever wonder why old ladies often get hairy chins?

Ever wonder why trans people who use HRT start looking completely different?

Ever wonder what intersex is? Or why you can't do a single blood test to find out the sex of an athlete?

Science.

Nature is about variety. Variation is a driving force of evolution. Variety is everywhere in the world around us.

It is in our nature to have variety.

Humans do NOT come in two neat biological categories with hard lines between us. We simply don't.

We are way more complex.

Most of us are either men, or women. Some of us are somewhere between ( intersex). Some of us are wired up in different ways, falling between or outside the average in a million different ways. And that's okay. That's nature.

I hope that helps.

If you like my science break downs, how about you shout me a coffee? It's not like I am paid for my time or anything :) at least I can be jittery on java. http://Www.ko-fi.com/dellak 

Now, the next question I usually get is about "but what about your chromosomes?"

Okay, so again in super simple terms, a chromosome is a packet of DNA. A bag of instructions. In the Y chromosome is a set of instructions called the SRY region (its a bit more complex than this) but for now, just imagine the SRY is the "hey, lets make a boy" form.

If you have a Y chromosome, you usually have the SRY region. So XY usually get the "lets make a boy" form, and XX usually do not.

I say "usually" because, like any good beauroceacy, forms can get misplaced.

The "lets make a boy" form acts on your developing gonads. They pull the fuck up from developing the gonads into ovaries, and switch over to making them testes.

Ovaries and testicles are homologous. Same tissue, different set of instructiona being expressed. Got it?

The testes are the cheeky buggers that give you that androgen bath I told you about. So in theory, you get a Y, you get SRY, so you get testes, so you get androgens and they then tell your body to switch instructions to male.

It's a chain reaction

So what do the chromosomes have to do with picking your sex? Kicking off that chain reaction.

After that?

FUCK ALL

After that, you are hormone bound, baby. It's your hormones that determine which way you go. So the gonads set your hormones.

And that's assuming the chain reaction went off like domino alley. If not... well, you get a variation.

People who jump up and down and say that "there are two sexes only, and anyone else is one of those sexes with a condition" don't get the whole variation thing essential in evolution. They would be horrified to know they themselves may be a variant.

There isn't really "pure" or "correct", but rather comfortably functional in environmental conditions. Intersex people are not 'wrong' or 'broken' they are people just fine, thank-you very much.

In mosaic Klinefelters, a person has XXY in some tissues, XX or XY in other, in splotches of tissue all over their body. Are they male or female? Does it matter? Should they be able to go topless on a hot day, or not? Which bathroom should they use?

See? Humans are complex.

Anyway, it is midnight and I am about to turn into a pumpkin.

Good night. Science loves you even when idiots don't.

X

Trans men are men.
Trans women are women.
Intersex people make up over 1.6 percent of the population.
Non binary people are valid.
Humans are complex.
Eat healthy, be kind to yourself. BLACK LIVES MATTER.

And sorting hats do not exist