Take this as a very oversimplified explanation, along the lines of "plants absorb carbon dioxide and relese oxygen and this is called phoysynthesis".
So, a form of testosterone is produced by both men and women. Women have the ability to convert testosterone to oestrogen and progesterone. This ability is concentrated in the ovaries - hence women with PCOS having high T counts. This also means upon high T introduction, the ovaries try madly to convert the new excess of T and in the process goes literally crazy and cancerous - a complete hysterectomy is inevitable for FtM.
Both men and women also produce sex hormone receptors that accept testosterone, oestrogen or progesterone. The count/ratio of these receptors is determined pretty much at the same time as chromosomal sex. Both sexes generally produce a decently large-ish amount of T receptors.
This means every human being has a built in lower and upper limit for sex hormones. It also means that for MtF specifically, once their upper limit for oestrogen and progesterone is reached, everything is treated as testosterone as T-receptors vastly outnumber the others in men. In other words, if oestrogen is introduced on its own, all it does is boost the T receptor count. Here is a version with more jargon:
Testosterone or
androgen receptors have also been identified in VSM cells. The expression of androgen receptors in VSM appears to vary depending on the sex and the status of the gonads. The androgen receptor protein, as detected by
Western blot in rat aortic smooth muscle cells, is less in the cells of females than those of males. In uterine smooth muscle of monkey, androgen receptor mRNA levels are up-regulated by combined
estradiol plus testosterone treatment while estradiol treatment alone had little or no effect, suggesting that a collaborative action of estradiol and testosterone enhances androgen receptor expression [14].
Source
Antiandrogens work by targeting and binding the T- specific receptors to bring the ratio closer to a woman's.
Incidentally, feminization through phyto-oestrogen (aka soy tits) is also a
myth. Or in other words, we do not have an epidemic of babies raised on soy formula growing tits or menstruating early or trooning out.
Going by anecdata of grown ass men developing limp wrists and tiddies, the culprit is far more likely to be the BPAs from the plastic cups and sippy lids coffees and cheap alcohol tend to be served in, which are - you guessed it, antiandrogens.
