Life is Hot and Cold (Part I)

Why do we sometimes feel too hot or too cold and have to do something about it to feel better?

We live in a world made up of matter.  Matter consists of atoms and molecules that must follow physical and chemical laws.  All life is made up of atoms and molecules that are organized into cells.  Our body has trillions of them.  So, our body must contend with the laws of nature which include physical phenomena like heat and temperature which, although related to each other, are not the same. 

Heat is the transfer of energy from one object to another.  The laws of nature state that heat must be released when work is done.  Experience shows that when a machine uses energy to do work it naturally gives off heat.  Just put your hand close to any working machine and you’ll literally feel this truth.  This law applies to the body as well.  When our cells (by cellular respiration) release energy from glucose, so they can do work, they naturally give off heat.  So, the more work your body does the more heat it produces.  The laws of nature also state that heat must transfer from a warmer to a cooler object when they come in contact with each other.  Touch a hot stove and the transfer of heat from it to your fingers will cause them to burn.  Grab some ice cubes and the transfer of heat from your fingers to them will make them melt.  Since your body is always surrounded by air (and sometimes water), it’s always losing, or gaining, heat from it. 

Temperature is a measure of an object’s internal energy and random molecular motion.  This energy often comes from heat, but can also come from other sources like electrical and nuclear energy.  The higher an object’s temperature the more random motion of its molecules and the lower an object’s temperature the less random motion of its molecules.  Common experience shows that for a molecule like H2O, its degree of random molecular motion affects its physical state.  Under 32oF (0oC), it’s a solid called ice, between 32oF-212oF (0oC-100oC), it’s a liquid called water and over 212oF (100oC) it’s a gas called water vapor.       

Your body’s surface temperature, on its skin, is usually lower than its core temperature within its blood and organs.  This can be demonstrated by blowing air from your warmer lungs onto your hands to feel heat being transferred to the cooler surface of your skin.  Your body’s core temperature is a reflection of the degree of random motion within the molecules that make up your cells.  It’s mainly affected by two processes: how much heat it produces from the energy its cells use to do work (metabolism) and how much heat the body loses to, or gains from, its surroundings. 

Just as a machine can malfunction if it’s too hot or too cold, so too, the cells that make up the organs of your body can malfunction if its core temperature is too high or too low.   Most of the enzymes the body uses for its metabolic processes work best within an ideal temperature range which is usually 97o-99oF (36o-37oC).  If the core temperature rises too high, or drops too low, it will not only impair the function of the enzymes but also the integrity of the proteins and the plasma membrane of the cell as well.  A core temperature over 107oF (42oC) usually causes structural and enzymatic protein breakdown resulting in impairment of cellular respiration and destabilization of the plasma membrane.  This causes brain malfunction, loss of temperature control, muscle breakdown and multi-organ failure resulting in death.  A core temperature below 91oF (33oC) usually causes a significant reduction in enzyme activity and metabolic function resulting in a marked decrease in energy production.  This leads to brain malfunction, loss of temperature control, impaired muscle function and multi-organ failure resulting in death.  So, you can see that it’s important for your body to control its core temperature. 

The body has two different sets of temperature sensors called thermoreceptors.  The peripheral thermoreceptors are in the skin and detect either hot or cold.  Their main function is to warn the body when it’s being exposed to extremes in temperature that may result in tissue damage (thermal burn or frostbite).  The central thermoreceptors detect the core temperature and are located within the chest, abdomen and hypothalamus.  The hypothalamus controls the body’s core temperature.  How it knows what the proper core temperature should be for survival is at present poorly understood.  It’s thought that the hypothalamus acts like a thermostat to keep the body's core temperature around a set-point which, as noted above, for most healthy people is 97oF-99oF (36o-37oC).   

Experience shows that when the hypothalamus makes us feel too hot or too cold, in other words, warns us that our core temperature is too high or too low, we can do things to try to correct the situation.  If you’re too hot you can reduce the amount of heat your body is producing by stopping your present activity.  If you’re too hot you can remove some of your warm clothing to allow heat to leave your body easier.  If you’re too hot you can get out of direct sunlight to prevent its heat from warming you too much or you can turn on a fan or pour cold water on your body to help it lose more heat.  If you’re too cold you can go indoors away from the outside freezing weather.  If you’re too cold you can increase the amount of heat your body produces by increasing your level of activity (like rubbing your hands together, stamping your feet, or moving around more).  If you’re too cold you can put on heavier clothing to prevent your body from losing too much heat or stand near something hot, like a fire so your body can get more heat.      

If your body’s core temperature goes too far out of range, it can malfunction and die.  By your hypothalamus telling you that you are too hot or too cold, it’s warning you (like the temperature gauge on the dashboard of a car) that you may become ill soon unless you do something about it.

Three Questions for Mr. Darwin

    1. How did my body anticipate its need to be protected from outside temperature extremes and where did the information come from to tell it how to make peripheral thermoreceptors, place them exactly where they were needed, and how do they work?

    2. How did my body anticipate its need to control its core temperature (to allow its molecular structures and metabolic processes to work properly) and where did the information come from to make central thermoreceptors, place them exactly where they were needed, and how do they work?

    3. How does my hypothalamus know what my body’s ideal core temperature should be so it can tell me to do something about it when it’s not right?

 


Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"


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.

Comments and questions are welcome.

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