There is a lot of misinformation out there in the bodybuilding world. I like to call it bro-logic. It's the dumb one-liners you hear brobros telling each other in the gym; toolbags passing misinformation back and forth like a venereal disease (believe me, it's that bad). Things like "repping out is 12 reps, dude," or "yeah bro, let's do another set--you're hella strong!" after a set of all forced reps. Sigh. This is why I listen to EDM so loud at the gym--I have to in order to drown out the retardation.
Oftentimes, the most dangerous, pervasive, and completely-off-base bro-logic centers around human endocrinology--you know, hormones and stuff. Because of the ultra-obvious elephant in the gym, many do not bother educating themselves enough about managing and manipulating the body's natural hormonal responses to training, diet, and other external and internal stimuli. Welcome to remedial endocrinology!
Let's start small: what is a hormone? A hormone is an organic compound secreted by an organ or tissue with the purpose of modifying the function of a target cell. The endocrine system uses the bloodstream as its main signalling pathway, as opposed to exocrine organs which secrete hormones directly into ducts which lead to the outside world, i.e. mammary glands excreting progesterone along with breast milk (crucial for development). Paracrine hormone signalling, on the other hand, occurs with hormones whose degradation process is too accelerated for long-term survival in the bloodstream, necessitating the release of hormones local to the target cell. Paracrine signalling is commonplace during blood clotting and tissue repair (and also influences spermatogenesis in the testes). Tropic hormones are hormones whose target organ is another endocrine organ, such as the hypothalamus targetting the thyroid. Steroid hormones are the hormones typically involved in the development and maintenance of the reproductive system and secondary sex characteristics ("steroid" in current nomenclature usually refers to anabolic steroids, but here I will use it with the actual meaning in mind).
Your entire endocrine system is governed by homeostasis: a return to equilibrium. Change something about your endocrine system (start taking birth control pills for example) and your body will try a bunch of different things to try to "even things out" again. One of the predominant mechanisms for this is the negative feedback loop. This loop occurs both in the short-term and the long-term. This means that when you add something to the system, the system will produce less in order to maintain equilibrium. The negative feedback loop contributes significantly to long-term levels when additional hormones are introduced and used over long periods. In this example, using birth control pills for multiple consecutive years will result in lower estrogen production by your body.
Sex hormone production kicks off in the pituitary and hypothalamus. GnRH is released by the hypothalamus and causes secretion of FSH (follicle-stimulating hormone), and LH (luteinizing hormone) in the pituitary. In males FSH acts by aiding in the development of the testes (through Sertoli cells), while in females it stimulates follicular develop in the ovaries (granulosa cells). In males, LH causes testosterone synthesis by binding to Leydig cells (and thereby activating them). In females, LH binds to thecal cells in the ovaries, causing testosterone and adrostenedione to be produced. From here, testosterone is broken down in both males and females. In males, it is acted on by 5-alpha reductase, an enzyme responsible for creating DHT, an androgen 10 times more powerful than testosterone (an androgen is a compound responsible for "male" characteristics such as hirsutism, deep voice and ball-dropping (LOL)). In females, testosterone is acted on by aromatase, an enzyme which converts the testosterone into estrogen. This reaction occurs in both males and females (but to a lesser extent in males unless additional testosterone is introduced, in which case it would obviously occur to a greater extent) and aromatase is present in the ovaries and testes as well as "peripheral" tissues. These mechanisms directly influence the negative feedback loop for the production of steroid hormones.
It is important to note that testosterone and adrostenedione are not produced directly by males or females, but are rather synthesized from cholesterol through cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) pathways (like all steroid hormones). cAMP and PKA are both regulatory messengers responsible for many biological functions elsewhere in the body as well. Because these pathways function the same in males and females, it is easier to simply refer to "testosterone synthesis."
That's all for now, I'm headed to the gym and also feeling bored with blogging :P Comments, questions, criticisms welcome below!