Exactly what is a hormone? Most of the time we think of hormones more in terms of sex hormones such as estrogen, progesterone and testosterone. This is far from what actually is occurring on a hormonal level in the human body. It is estimated that there are currently at least 50 known different hormones in the human body. You can be sure that we will find additional ones with continued research and understanding of human physiology. So…. back to my original question, what exactly is a hormone? By definition ,a hormone is a chemical substance produced in different cells of the body that helps regulate the activity of certain cells or organs.
Hormones are each unique in their structure, function and their effects on cells/organs. Some examples of hormones are: insulin, cortisol, thyroxine, growth hormone, adrenalin/ epinephrine, melatonin, gastrin, prolactin, oxytocin, parathyroid hormone, thymulin, prostaglandins, leptin and many more.
Hormones regulate blood sugar, blood pressure, overall metabolic rate, stimulates the reproductive system, affects the immune system, affects mood, lactation, regulates minerals and water balance in the body, affects sleep/wake cycles, calcium balance and bone health, essential for nervous system and brain function, blood production, regulates digestion, influences blood clotting, affects inflammation in the body and many more functions. Essentially, hormones are the regulators of many functions in the body and we could not exist without them!
Some of the glands and organs that release hormones are, the hypothalamus, pituitary gland (also know as the master gland), pineal, thyroid, parathyroid, thymus, heart, adrenals, kidney, stomach, liver, pancreas, small intestines, ovaries, testes, fat tissue, skin and are finding more having to do with the brain.
There are four basic categories of hormones. The categories are based upon the chemical structure and what they where originally derived from chemically.
The first group are derived from singular amino acids. An example would be thyroid hormone being derived from an amino acid called tyrosine. Melatonin being derived from tryptophan.
The next category are hormones derived from strings of connected amino acids called peptides. Some examples are insulin, glucagon, angiotensin, growth hormone, parathyroid hormone and leptin.
The third category is the more familiar group when we think of hormones. These are known as steroid hormones and they are derived from cholesterol. Some examples are estradiol, aldosterone, cortisol, progesterone, and testosterone.
The last category are hormones that are found in virtually every single cell in the body. They are found primarily in the cell membrane. They are derived from fats in our diet mostly omega 3 and omega 6 fats. They are called the eicosanoids. They have an extremely important role in the inflammatory processes in the body. Some examples are, prostaglandins and leukotrienes and thromboxanes.
RELEASE OF HORMONES
Hormones are manufactured in certain cells that are found in different organs or different tissues in the body. The cells that produce the hormones are called secretory cells. The cells that receive the hormonal signals are called target cells. In order to respond to the hormone, these target cells have specialized proteins that are called receptors. Some of these receptors are located on the surface of the target cell or found within the target cell. The receptors within the cells will be found in the nucleus or cytoplasm of the cell.
There are three main modes of hormonal transport in the human body. The first is called endocrine signaling. This is where highly specialized cells are gathered together and release/ secrete hormones into the blood stream. The hormones are circulated throughout the body and are “picked up” by the target cells that quite a distance from the secretory cells. An example would be your thyroid gland. The secretory cells are known as follicular cells and release thyroxine (T4) qnd some T3 into the blood stream.
Another method is called paracrine signaling. This is where the secretory cell is close to the target cells and the hormones do not have to travel very far. Often the target cells are adjacent to the secretory cells. Some examples of paracrine signaling involves blood clotting, tissue repair, cell division and growth, scar tissue formation and allergy reactions.
The last is called autocrine signaling. This is where the secretory cell is also the target cell. Some examples would be a white blood cell called a Tlymphocyte comes in contact with a virus and causes itself to produce growth hormones to cause the cell to grow and divide and produce more T- lymphocytes. Another is where the beta cells in the pancreas produce insulin. As the insulin levels increase they will then cause the cells to slow insulin production.
Once the hormones are released they need to travel to their target cells. In the autocrine and paracrine signaling it is not necessary for the hormones to travel any significant distance. However, in the endocrine situation the hormones travel a considerable distance and usually travel in the blood stream. Most hormones released into the blood and particularly with steroid hormones like estrogens, testosterone, progesterone, and cortisol are attached to a protein in the blood that helps to transport the hormone intact until needed. These hormones are referred to as “bound hormones” and are general considered inactive. These proteins are usually called globulins or albumins and you may have seen them on a blood test. Please note that these two major proteins in the blood do many other things than transport hormones. Some examples of hormone transporters are thyroxine binding globulin (TBG) for thyroxine, sex hormone binding globulin ( SHBG) for testosterone and estrogen. These proteins are produced mostly by the liver. So proper liver function is essential for proper hormonal delivery!
BOUND AND UNBOUND HORMONES
Many hormones are attached to transport proteins while in the blood and some portions of the hormones are unattached and are considered “unbound” or more commonly known as “free” hormones. Free hormones can reflect the hormones more readily available for immediate tissue cell usage. On most blood tests, the total levels are only measured and not free levels. Therefore, running a free T3 or free testosterone can give you a lot more information about the status of hormone availability versus just measuring the total levels. This is probably much more important with steroid hormones since they often have a “stronger” bond to these transport proteins. However, this is not 100% correct as there are other factors that can come into play.
The bottom line…. We want to know the levels of hormones that have reached the cell. One of the best ways of doing this is via salivary hormone testing. The saliva does contain a myriad of hormones that have reached the cells.
As mentioned earlier, target cells must be able to detect the appropriate hormone that helps direct the target cells metabolism and function. In order to do so they often have specialized proteins on the surface membrane of the cell or within the cell itself. These receptors often form a complex between itself and the actual hormone. This complex is what initiates cell changes and also can affect the genes in the nucleus of the cells causing further changes. It is believed that steroid hormones in particular have profound effects on the genetic expression of the cells.
The receptors are also very sensitive to hormones. As a matter of fact many hormones are found in very dilute amounts even in the bloodstream. Just to give you a few examples. Testosterone in men is at concentrations of 300- 1000ng/dl that comes out to about .000000300 – .00001000 grams in about a 1/2cup of blood. Estradiol in women is 50-200 pg/ml or about .000000000050 – .000000000200 grams in 20 drops of blood. Thyroxine or T4 is 4.5-12 ug/dl or about .000004500 – .000012000 grams in about a 1/2 cup of blood. These are amazingly small amounts. So, hormones are pretty powerful and the target receptors are very sensitive to these low levels of hormones. This is one of the reasons that hormones need to be balanced carefully and not just taken casually.
The eiconosoids which are fatty hormones found in the cell membrane can also affect the function of these receptors