November 1, 2008

Temperature Control & Thyroid Function: How the Body Does It and Why

By Dr. Howard Glicksman

Heat and Temperature: Random Forces of Nature
Stand next to, or touch, anything that is using energy to work and you will invariably feel heat emanating from it. Heat is the transfer of energy from one object to another. In contrast, temperature is a measure of an object’s internal energy, often derived from heat, and other forms of energy such as electrical or nuclear. This internal energy is a reflection of the motion of an object’s atoms or molecules. With an increase or decrease in temperature (internal energy), a substance’s atoms have more or less disorder due to an increase or decrease in their motion which can affect its physical state. So for example, when the temperature is below 0 C, H2O tends become a solid known as ice, and when its between 0-100 C, the increased disorder makes H2O turn into a liquid we call water, and if the disorder within it further increases due to having a temperature above 100 C it becomes a gas that we call water vapor.

In general, for most things, when the temperature rises within them indicating more internal energy and therefore more atomic or molecular activity, they usually expand and when there is less energy they contract. Finally, when two objects with different amounts of internal energy (temperature) come in contact with each other the one that is higher usually releases heat energy to the one that is lower resulting in the former having less internal energy and a drop in temperature to the benefit of the other one.

This is a fact of nature and consequently also a fact of life. When energy is used to power something, whether it be a car, a computer, or the human body, the release of heat is sure to take place at the same time. This is what the random forces of nature do: release energy in the form of heat to the surrounding environment whenever work is being done, whether it’s a car racing down the road, a computer crunching numbers, or the neuromuscular system, the heart, and the lungs, working together to keep us alive.

Therefore the energy which the body derives from breaking down glucose in the presence of oxygen to drive its metabolic activity causes the release of heat energy within it and also to the environment in which it lives. In other words, the body’s core temperature is a function of how much heat energy it releases within itself from the work its cells do by its metabolism and how much heat energy it either gains from, or loses to, its environment.

In the same way that heat radiates from the sun and can warm the body, the body’s own production of heat by its metabolism working to stay alive and function radiates its own heat energy by way of infrared rays to its surroundings. This accounts for over 50% of total body heat loss. If the body comes in direct contact with something cold, like sitting on a frozen pond, it will release heat as well by way of conduction.

In addition, the body tends to warm the air surrounding it, and when cool air from a breeze blows this warmed air away by convection, this allows more cool air to take its place to be warmed causing further heat loss. The combination of conduction and convection generally accounts for about 25% of total body heat loss. Finally, when water on the surface of the body is able to absorb heat from it and be released into the air by evaporation this results in heat loss as well and this takes place in the lungs, the mouth, and from perspiration on the surface of the skin.

Heat and Temperature: A Fact of Life
One could rightly question why this should be considered important regarding life and how it might have come into being until one understands one more thing. Another fact of life is that the molecules which form the cells of the body, and especially the enzymes that drive its chemical reactions, can stop working properly, and even degrade, if the body’s core temperature is not adequately maintained. That is to say that the internal energy which results in the motion of the atoms and molecules that make up the body have definite limitations for body survival. Just as the random forces of nature in the way of internal energy can make H2O go from being solid ice, to refreshing water, to steamy water vapor, these same physical and chemical laws apply to the molecules that make up our bodies and therefore life must take these things into account in order to remain viable.

Therefore, with regard to heat and temperature, the random forces of nature cause two things to happen which directly relates to the body’s capacity to live and function. First, they cause heat to be released when work is being done. And second, they cause objects to transfer heat to each other. This means, as mentioned above, that the body’s core temperature directly relates to not only the internal heat it releases from its metabolism but also how much heat energy it gains from, or loses to, its environment. Since the proteins that make up the body and the enzymes that drive its metabolic processes are affected by temperature if the body is going to be able to survive it will have to control its core temperature. And in fact, lucky for us, it has the ability to do this by a process called thermoregulation.

The ideal core body temperature runs between about 36-37 C (97-99 F). If the core temperature rises above or drops below this range this has a direct effect on the speed of chemical reactions in the cells of the body. Most enzymes have an ideal range within which they perform their function efficiently. So if the temperature rises or drops too much this may affect their function and ultimately can cause destruction of protein and eventually death. It is a medical fact that if the body’s core temperature rises much above 42 degrees C (107 F) this usually will result in seizures, coma, and death. Similarly, a drop in core temperature below 33 C (92 F) will result in death as well since brain function and temperature control itself will have been lost.

So one can see that the body needs to keep its core temperature within a narrow range to allow it to survive and function properly and that this thermoregulation is related not only to the heat generated by the body’s own metabolism but also the heat gained, or mostly lost, from the body by radiation, conduction, convection, and evaporation. 

The body’s temperature as it relates to heat energy, and how it is controlled and is ultimately affected by thyroid function is the topic of this column. It is up to you to ask yourself if it is plausible to believe, as evolutionary biologists would have us do, that such an integrated organization of components accomplishing thermoregulation in the body to combat the effects of the random forces of nature, unlike, for example the car and the computer, could themselves have come about by the random forces of nature as well.

Heat and Temperature: Control is the Key to Life
In order to have a system that controls anything, whether a chemical level like oxygen or glucose, or in this case, a physiological parameter such as temperature, one needs to have three essential components working together. First, one must be able to detect the thing trying to be controlled. If the body had no way of being able to know its level of oxygen or glucose, or its temperature, how would it then be able to control it? The second thing needed is something to integrate this information and compare it with what is inherently known to be what that chemical level or parameter of body function should be. If the body had no way of knowing what range its oxygen or glucose level, or temperature should be then what good would it be to be able to detect these things and how could the body be able to control them? Once the body is able to sense the parameter in question, such as its oxygen or glucose level, or the temperature, and knows whether an adjustment needs to be made, as determined by the integrator, it then must be able to send a message somewhere to be able to do something about it. This “something” is the third and last component called the effector. 

Keep this in mind! The body has many different systems which control various chemical levels and parameters of body function; chemicals like oxygen, carbon dioxide, glucose, calcium, water, hydrogen ion, sodium and potassium, and parameters like blood pressure, temperature, and pulse, just to name a few. Each and every one of these items of body function must be kept within very narrow ranges for survival. And each of the systems involved in controlling each one of these parameters have at the very least, these three separate components; a sensor, an integrator, and an effector, which work together to help keep them under control. The absence or dysfunction of any one component resulting in the loss of control of any one of these parameters would result in death.

The information needed for the body to produce the components of each of these necessary systems is located in the DNA of each cell but that doesn’t explain how they come together and function. In other words, trying to figure out how life works requires much more than just looking at how it is organized into various parts. That’s only the beginning! Once you have the parts you have to consider not only how they together can perform a function, but also how that function results in the ability to control the internal environment and allow for survival.

Also remember that what modern evolutionary biologists expect you to believe is that this control of numerous chemical and functional parameters that has been taking place in the body since its first existence all came about by the random forces of nature; without a mind being at work. Imagine this. It took human ingenuity over a million years to be able to do what the body has been doing by necessity since its beginning: detect its own chemical levels such as oxygen, carbon dioxide, and glucose, and physiological parameters such as core temperature and blood pressure. Medical science and its therapeutics are based on how the body has been able to work and keep itself alive despite what the random forces of nature tend to do to it: like in the case of heat and temperature: cause destruction of protein, elimination of metabolic reactions, and ultimately death. That’s what the random forces of nature do: they cause disorder and death: not life !!

Remember, the mere presence of parts should not assume function and the mere presence of function should not assume survival capacity! So let’s see how the body keeps itself from getting too hot or cold and where the thyroid gland fits into body metabolism

Heat and Temperature: The Sensor
In order for the body to be able to control its temperature it must first be able to detect it within itself. This is provided for by what are called thermoreceptors. They exist strewn throughout the skin and are divided into ones that detect cold or heat. No one really knows how they work but it has been determined that they are nerve endings whose constant messages along nerve fibers are modulated by the change in coolness or warmness in the skin immediately surrounding them.  In addition to these sensors in the periphery, there are ones located centrally within the body and especially within the hypothalamus of the brain which provide a reading of the core temperature. The information about the temperature in the central and peripheral regions of the body are sent by nervous messages to the hypothalamus in the brain for analysis.

Heat and Temperature: The Integrator
As noted above, the hypothalamus, which receives the information from the central and peripheral thermoreceptors has the task of trying to keep the core temperature usually around 37 C (98.6 F). No one knows how it knows what the temperature should be in order to perform its function as the integrator for body thermoregulation but medical science does know what actions the hypothalamus applies when things need adjustment.

When the thermoreceptors of the body tell us that we’re too hot or too cold there are things that we can do to try to correct the situation. Just as the thirst and hunger centers tell us to drink and eat, when the hypothalamus tells us we are either too hot or too cold we either remove heavy clothing, get out of direct sunlight, and turn on a fan to cool down, or put on a coat, go near a fire, and stamp our feet and rub our hands together to warm ourselves.

Besides telling us that we’re hot or cold, when the hypothalamus detects a rise or lowering of temperature above or below what the temperature should be in the body it is able to send nervous messages to certain tissues in the body to try to correct the situation. Some people like to describe the hypothalamus as acting like the thermostat in your home. When you want your house to be a certain temperature you set the thermostat to turn on the system to either warm it up or cool it down and then when the temperature is right it turns the system off.

But this analogy fails to point out a very important difference. The thermostat in your home works as an “all or nothing” device. It either turns on your system or turns it off, there’s no in between. In contrast, the hypothalamus is always sending out nervous signals to the tissues that ultimately have an effect on body temperature. By modulating the frequency and intensity of these signals depending on what is going on in the body, it is able to take control of the body’s temperature.

Therefore I think the more appropriate analogy to be used for how the body controls its temperature through the hypothalamus is by considering the pulse wiper blades on our cars. They can be set at a basal rate and then can be adjusted up or down to increase or decrease their frequency when the need arises. Now let’s look at where the hypothalamus sends these signals and how the tissues involved affect temperature control in the body.

Heat and Temperature: The Effectors
 The skin and the tissues below it provide the body with insulating protection from its environment. Being so close to the surface of the body, the warm blood that travels in the circulation of the skin has a tendency to cause the body to lose heat. In normal situations, such as being indoors and at rest, the body is easily able to control its core temperature simply by adjusting the flow of blood in the cutaneous circulation. 

Remember that the body is always producing heat because of its metabolism and therefore its temperature can be offset by the many different ways that it gives off heat. When the temperature in the body drops or rises the hypothalamus adjusts up or down the messages it sends out along the autonomic nervous system to the muscles surrounding the blood vessels in the skin. These messages affect the release of a neurohormone called norepinephrine which attaches onto specific receptors on these muscle cells and tells them to contract thereby adjusting down the flow of blood to the skin, something called vasoconstriction. So when the body gets too cool the hypothalamus sends out stronger messages that tell the blood vessels to close more to preserve more heat. When the body warms up the hypothalamus responds by sending out less norepinephrine which causes the muscles surrounding the blood vessels to relax, allowing more blood flow to the skin surface, something called vasodilation, which allows for more heat loss.

When the body experiences extremes of temperature, such as severe heat or cold, these same cutaneous circulation adjustments become maximized and usually require other mechanisms to help in the situation. In fact, compared to the normal blood flow to the skin the body can make it increase or decrease more than 10 X in either direction when it becomes either too hot or too cold. So in effect, the cutaneous circulation is capable of making a 100 fold adjustment depending on the temperature needs of the body.

In conjunction with vasodilation of the skin’s circulation to facilitate heat loss when its temperature rises, the body is also able to recruit millions of sweat glands to release perspiration on the surface of skin so that further heat loss may take place by evaporation. Sweating is triggered by the hypothalamus also through the sympathetic nervous system just like vasoconstriction and vasodilation except instead of using norepinephrine as the messenger, acetylcholine is the neurotransmitter that is used for this task.

When the body is at rest and in a comfortable environment it loses about 50cc/hr of water by perspiration. But when the body is very active and in a humid and hot setting it can lose upwards of 1-2 liter/hr of fluid through sweating which by evaporation allows it to give off the excess heat it is producing because of its actions and its environment.

When vasoconstriction of the skin’s circulation and external efforts to limit heat loss and gain heat by putting on something warm and getting close to a fire are inadequate to raise the body’s core temperature the hypothalamus is able by two different mechanisms to generate heat from the body’s metabolism.

The first way the hypothalamus is able to have the body make more heat is to tell it to start shivering. Shivering is caused by the involuntary rhythmic contraction and relaxation of complementary muscles, such as joint flexors and extensors. This action causes the muscles to release heat energy rather than perform work. The second way the hypothalamus can try to have the body make more heat is to increase the release of various hormones, such as norepinephrine, epinephrine, and thyroid hormone, and others, which can increase the metabolic release of heat from the cells of the body.

Heat and Temperature: Recap
So in summary, the random forces of nature involves the production of heat from the metabolic processes that keeps the body alive. This heat causes the atoms in the molecules of the body to have internal energy which is measured as the body’s core temperature. However, the survival and functional capacity of these proteins, and in particular the enzymes for important chemical reactions, is dependent on the body staying within a certain temperature range. Therefore in order to survive and function properly the body must be able to control its temperature. This is determined by the internal heat released from the body’s metabolism and what it receives from its environment in conjunction with its loss of heat to the environment by radiation, conduction, convection, and evaporation.

The body is able to achieve this thermoregulation by having temperature sensitive tissue called thermoreceptors which are peripherally located in the skin and centrally located throughout the body which inform the hypothalamus of the body’s internal energy status. In response to fluctuations in temperature the hypothalamus, based on its knowledge of what core temperature is needed for body survival, is able to notify the person to make external adjustments to avoid heat or cold as the case may be, adjust the body’s heat loss through the circulation of the skin and sweating, and vary the body’s heat production through the release of specific hormones and if necessary by shivering. As the temperature moves up or down the hypothalamus continues to monitor the situation and makes the necessary adjustments through all of the abovementioned mechanisms. 

Heat and Temperature: Thyroid Anyone?
One of the most important hormones in the body regarding its metabolism is thyroid hormone, which is produced and secreted by the thyroid gland in the neck. This gland is able to take in iodine which has been absorbed by the gastrointestinal tract and combine it with other molecules to form the thyroxine (T4) which directly affects the body’s metabolic rate.

Thyroxine is transported through the body on a specific protein called thyroxine-binding globulin, which is made in the liver. It then attaches to a specific receptor in most of the cells of the body which causes an increase in protein synthesis and oxygen consumption resulting in cell growth and maturation. The final result of all of this activity in the body’s cells is to cause an increase in metabolism and the release of heat.   

One can immediately see from what was mentioned above that since the body’s temperature is directly related to the heat released by its metabolism, that with an excess of thyroxine (hyperthyroidism) the body would tend to feel too hot and with too little (hypothyroidism) the body would tend feel too cold. These and many other symptoms relating to an increase or decrease in metabolism is what happens when the thyroid gland doesn’t work properly. But how does the body control all of this in order to keep the thyroxine level, as Goldilock’s said, “just right” so we can survive and function?

Once again we must look to the question of what it takes for the body to be able to control anything. It first must have a sensor that is able to detect the thing that needs to be controlled. Then the cells that learn of this must inherently know how to respond to a specific level by sending out a message that directly affects it. Then the cells that effect the necessary change must have a receptor that acknowledges the message which results in the effector doing something to correct the situation.

In order for the body to keep its metabolism at the right rate so we can feel comfortable and go about our lives with the proper energy the hypothalamus sends a message called thyrotropin releasing hormone (TRH) to the pituitary gland which reacts to it by sending out thyroid stimulating hormone (TSH). This TSH goes to the thyroid gland where it attaches to specific receptors that tell the cells to make and release thyroxine (T4).

Both the hypothalamic and pituitary release of TRH and TSH respectively occur at a basal rate and both the hypothalamus and the pituitary gland are able to sense the level of thyroxine which keeps them informed of how much is being released by the thyroid gland. The ability for the hypothalamus and pituitary to be able to detect the level of thyroxine results in what is called a negative feedback, or feedback inhibition. If the thyroxine level rises too high the production and release of TRH and TSH from the hypothalamus and pituitary respectively, are reduced, and if the thyroxine level drops too low this causes an increase in the release of TRH and TSH. This is what is called an inverse relationship: when one goes up it causes the others to go down and vice versa. This is a very common mechanism used in the body to control its various chemicals and physiological parameters as the previous articles have demonstrated.
So, in effect, the thyroid gland produces the hormone called thyroxine which directly affects the metabolism of most of the cells of the body. The hypothalamus and the pituitary are both able to detect the thyroxine level and integrate that information in order to adjust their production and release of TRH and TSH respectively. Ultimately TRH affects TSH production and TSH itself attaches to TSH receptors on the thyroid gland cells to tell it to produce thyroxine. So with adjustments up or down of TSH release this directly affects thyroxine production: and the circle is complete.

Heat and Temperature: Control is the Key: By Macroevolution?
At first glance, on a superficial level, it may indeed appear that life could have come about by the random forces of nature without a mind being at work (intelligent design). Certainly the similarities between what constitutes various life forms makes one wonder if somehow they all just developed on their own. But the question that seems never to be asked by those who espouse this belief is how and why life ceases to be through disease, dysfunction and death. A cursory analysis of what the random of forces of nature tend to do will result in the conclusion that they tend to cause death, not life, as this article about heat energy and temperature has shown. The only way for life to exist is for it to organize itself in a way that allows it to use energy to its advantage and control the chemicals and physiological functions within it. I maintain that the public is easily misled because it does not understand these principles.   

Once you have the parts you have to consider not only how they together can perform a function, but also how that function results in the ability to control the internal environment and allow for survival. The mere presence of parts should not assume function and the mere presence of function should not assume survival capacity!

Dr. G.

Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Copyright 2008 Dr. Howard Glicksman. All rights reserved. International copyright secured.
File Date: 12.08.08