TSH: Thyroid stimulating hormone. Nothing to do with MTF HRT per se. However if your TSH has an issue, your thyroid probably has one, which can leadto various problems including depression and metabolism disbalances.
Thyroxine: Another thyroid hormone. Not sure what it does exactly, but again, nothing to do with HRT per se.
FSH: Follicle stimulating hormone. It's what's telling your testicles to produce T and sperm.
SHBG: Sex hormone-binding globulin. It's a protein that links to estradiol and/or testosterone, making it unable to interact with your cells, but also keeping it "in storage" for some eventual deficiency. If you happen to have tons of SHBG, I guess it actually could affect how useful HRT is for you.
What I meant was that skin (well, it's skin - I'm guessing clogged pores and tons of other factos can make one's skin more or less absorbing of transdermal HRT than anothers') and the digestive system (because your pills go through acid and enzymes designed to destroy protein, and hormones are proteins, and also because the liver acts as a doorman, eliminating some of your hormones [my understanding of this is limited]) have varying levels of what proportion of the hormones entering the body end up in the blood stream.
As for weight, it's simple. Dissolve one cube of sugar in one small glass of water and taste it. Then dissolve it in a large glass of water. It won't be nearly as sweet. It's the same for hormones. The taller/fatter/generally larger you are, the more blood you have. So the same pills of estradiol won't have the same effects on a skinny dwarf than on a large giant.
This is why endos go by blood levels (picomole per LITRE), instead of absolute doses, to determine HRT. Because everyone is different. If they just gave X pills a day to everyone, they'd run into problems, because some would overdose and others would see no difference.
