Hi. Hans Selye is often referred to as the father of stress, most of his work was focused on the maintenance of homeostasis, the conditions within our bodies have to be maintained within very quite narrow margins for optimum health and in fact he became interested in the way our bodies respond to the various demands made upon it. He coined the term stress to describe the broad, non specific, physiological responses to demands that required adaptation. He didn't really think of stress as the same as anxiety or fear, though these could be a source of stress, it was about demands, these could be good or bad, activity demands, excessive heat or cold, infections etc, he thought the physiological response was the same. This was of course in 1936 and based on the technology of the time, in fact there are often differences in the responses and his work has been built upon, particularly in relation to psychological effects. Stress isn't a defect or a problem, its highly adaptive and may underpin most motivated behaviour, the only reason people get up in the morning is because life is a series of expectations and demands. Its only when we are faced with major stressors we are unable to control for extended periods that it becomes a problem, in fact dealing with stressors effectively can be a major source of pleasure and feelings of achievement.
Many of the systems we use to maintain our internal state are based in the brain, and this uses two integrated messenger systems to control things, the nervous system which is fast and specific and through the hypothalamus, the endocrine system which is slower, more persistent and has much more generalized effects. I've never really been comfortable with describing cortisol as the stress hormone, its misleading, we produce cortisol all the time, following a particular pattern over the day, if we didn't we would sicken and die. If we have to deal with significant stress, we produce more, along with a number of other hormones. Their main function in this case is making more energy resources available for rapid use, it induces a catabolic state. Its release isn't always in response to stress, its actually in anticipation of increased energy needs, we produce most at the start of the day.
Testosterone on the other hand is largely produced at night and has an anabolic action, promoting tissue building, physiologically the effects can be thought of as almost the opposite of cortisone, there is also evidence that high levels of cortisone suppress T. production.
If you think about it the study of emotions is the clearest example of how our mind and body operates as an integrated system, we are usually aware of the effects in our bodies, that's why we call them feelings. Its pretty easy to find info on the effects of the different hormones. The effects on production are less well established but this might be interesting.
https://www.ncbi.nlm.nih.gov/pubmed/7983641