What are hormones?
Endocrinology, or the study of the endocrine system, is a complex branch of physiology. The key players of the endocrine system are hormones. Although many are aware that hormones play an important role in the human body, fewer people actually know why. Moreover, knowing what a hormone truly is can help one to understand the way all hormones function in the body. Thus, a hormone, by definition, is a “chemical messenger” transported by the blood stream. This chemical messenger targets specific receptor sites on a particular cell, causing within it a physiological response. Interestingly, a hormone has no direct way of reaching its “target cell.” Instead, it must travel throughout the entire blood stream until it locates, and binds to, its specific receptor sites. That being said, each hormone effects different organs and cells in completely different and unique ways.
Although the body performs many daily functions, the metabolism, in particular, always seems to be of popular interest. Of course, hormones are responsible for regulating one’s body functions, including cellular metabolism (the cell’s level of efficiency). Considering our cells constitute our entire being, it is important to understand how efficiently they operate. Fortunately, this can all be understood through the analysis of hormones.
How the metabolism works
Cellular metabolism is monitored by, not one, but multiple hormones. Interestingly, each hormone involved with metabolic function is secreted at different locations in the body. Nonetheless, the relationship between these hormones provides critical understanding of the metabolism, and all must function properly in order for it to operate.
Starting with the brain, the hormone Thyrotropin Releasing Hormone, or TRH, is secreted by the hypothalamus. This portion of the brain is responsible for primitive functions of the body, ranging from thermoregulation and water balance, to sex drive and childbirth. Once the hypothalamus releases TRH, the hormone locates TRH receptor sites, which are found on the (anterior) pituitary gland. This results in the stimulation of the pituitary gland, which in turn, causes it to secrete a different hormone called Thyroid Stimulating Hormone, or TSH. After TSH is released, it circulates throughout the entire blood stream until it reaches TSH receptor sites, which are found on the thyroid gland. Once the thyroid is stimulated, Thyroid Hormone, or TH, is released, causing a direct increase effect on cellular metabolism.
Note: About 90% of Thyroid hormone is in a form called Thyroxine, or T4. Meanwhile, the other 10% of Thyroid Hormone is called Triiodothyronine, or T3. The difference between these forms of Thyroid Hormone lies within their structures. Thyroid Hormone refers to T3 and T4 collectively.
Although a “fast metabolism” seems desirable, an excess of any hormone is not necessarily a good thing. Hyperthyroidism (overactive Thyroid) can result in many negative side effects, including uncontrolled weight loss and a rapid or irregular heartbeat. For those suffering with cardiac problems, the side effects of an overactive thyroid can be of great concern. On the other hand, hypothyroidism (under-active Thyroid), can result in uncontrolled weight gain, fatigue, and lethargy. Of course, such side effects are undesirable, to say the least. Despite all of this, TRH, TSH, and TH are typically in regulation with each other. Although significant hormonal imbalances can have great side effects, slight imbalances are not as severe, and typically go unnoticed.
Flow chart of metabolic hormones:
(1) The hypothalamus secretes Thyrotropin Releasing Hormone.
(2) TRH stimulates the (anterior) pituitary gland to secrete Thyroid Stimulating Hormone.
(3) TSH stimulates the thyroid gland to secrete Thyroid Hormone.
(4) TH stimulates the metabolism of most cells throughout the body
(TH also inhibits the release of TSH by the pituitary in order to prevent an over-secretion of TH).