Sex Hormones: how do they work?
The hormones that interests us for trans HRT are sex hormones. Those are an informal subgroup of steroid hormones. We’ll discuss here how hormones have effects on our bodies, and learn about the importance of “receptors”.
And first, what are they? As we said before, sex hormones is a group that covers 3 subgroups of steroid hormones: androgens (among which the famous testosterone), estrogens (estradiol will be our main friend for feminizing HRT), and progestogens (progesterone is the main naturally occuring one). That’s why they are sometimes called sex steroids, but also gonadal steroids, since they are mostly produced in our gonads: testes and ovaries.
It is common to picture the mode of actions of hormones as the key and keyhole image. The hormones are keys that circulate in the body until they reach a cell with the right keyhole. We call those keyholes receptors. Estrogens are all the keys that can only open estrogenic keyholes (receptors) - be it synthetic or natural estrogens, and the same goes for androgens.
We all have those different receptors: it is not because you were assigned male at birth and produce mostly testosterone that your cells won’t have estrogen receptors. If it were the case, HRT for trans people would not work at all. There can be, however, differences between people, moments of life, and hormone balance exposure, in terms of the repartition and sensitivity of those receptors in the body cells.
If the binding happens (the key gets into the hole), then the cell is given the order to express a certain aspect of itself coded in DNA. For example, when an estrogen hits and opens the receptor of skin cells, those cells get the message to produce less sebum, which leads to less greasy skin - in the limits given by the DNA. In other words, sex hormones will only “unlock” and express what is already coded in DNA, which cannot be changed by any medication. This explains the differences in development observed between people with the same profile and the same hormone levels.
In short, we call estrogens all hormones that fit in the estrogen receptors, androgens all those that fit in the androgens receptors, and the same goes for progestogens. And this means that there is not just one estrogen, androgen, and progestogen. Let’s have a look now at these different kinds of each sex hormone, and why it matters to know about them.