Hormones are regulated in the body much like the temperature in your home. A thermostat is used to set a desired temperature and either the heating or cooling unit brings the room temperature to the desired level and this feeds back to the thermostat turning off the heating or cooling unit. This is a negative feedback loop that maintain a constant and consistent temperature level. In the body the thermostat is an area of the brain called the hypothalamus and one of its most important functions is controlling the pituitary gland, a small gland located behind the eyeballs at the base of the brain. The pituitary is responsible for much of the hormone production and control in the body especially controlling the thyroid, adrenal glands and gonads: testicles and ovaries. Whether the hormone produced is thyroxine, cortisol or testosterone, estrogen etc. when the proper level is reached as determined by the hypothalamus the pituitary gland is shut down, thus the same negative feedback loop as your thermostat at home. This consistent balance is called homeostasis in the body. When we investigate a hormone, in this case testosterone, laboratory values are aimed at distinguishing between hypothylamic pituitary issues versus gonadal issue, i.e. the thermostat vs the heating or cooling unit. This is very important to know before considering hormone treatments.
When testosterone levels are low, low normal or just inadequate for an individual first the hypothalamus-pituitary function must be assessed as well as testicular function. If the pituitary gland is the issue this is addressed, usually through an endocrinologist. If the testicles are just not producing enough testosterone and the pituitary is working overtime, testosterone replacement therapy is needed. However, if the testosterone is low or inadequate and the pituitary could be working better other methods are used alone or in combination with replacement.