We are all familiar with thermostats — devices we use to regulate temperature, typically in central heating and air conditioning systems, as well as ovens, refrigerators, and water heaters. The thermostat monitors the temperature of the system and activates or deactivates the heating or cooling equipment to maintain a desired temperature setting. Modern thermostatic control was invented by my fellow Scotsman Andrew Ure (1778-1857) in the 1830s (though the concept goes back at least as early as 1620 when Cornelis Drebbel, a Dutch innovator, developed a mercury thermostat that controlled the temperature of a chicken incubator). Andrew Ure invented a bimetallic thermostat, which would be caused to bend in response to heat (as one of the metals would expand), thereby severing the supply of energy.

The Body’s Thermostat

But did you know that our bodies also contain their own thermostat, which is responsible for maintaining our body temperature at the optimal level? It is found in the region of the brain called the hypothalamus, a structure that is responsible for maintaining the proper body temperature setting by balancing heat loss with heat production.

To accomplish its task, the hypothalamus has to take readings of both the internal and external temperature. The internal temperature readings are taken by specialized neurons of the hypothalamus that detect alterations in the temperature of the blood passing through the brain. There are also temperature receptors in the skin that relay information concerning the external temperature. This sensory information is integrated by the hypothalamus, which promotes the effector responses to bring the body back to its set temperature. For example, if the body temperature rises above the set point, the neurons of the hypothalamus initiate mechanisms to dissipate heat, such as vasodilation (expansion of blood vessels near the skin surface) and sweating. Conversely, if the body temperature falls below the set point, the neurons trigger mechanisms to conserve heat, such as vasoconstriction (narrowing of blood vessels near the skin surface) and shivering.

How the Body Loses Heat

Vasodilation results in greater loss of heat to the environment (and thereby accomplishes cooling), as warm blood is brought close to the surface of the body. Of course, this process is ineffective if the external environmental temperature is above the temperature of the body. In such cases, heat loss may be accomplished through sweating. The sweat is evaporated from the body surface by the excess body heat. The production of heat can also be reduced by decreasing muscle tone (i.e., the slightly contracted state of our muscles that maintains our posture, discussed here).

How the Body Conserves Heat

There are also mechanisms for conserving heat in a cold environment. Vasoconstriction is the process by which blood is shunted away from the surface of the body. There is also a reduction in sweat, which may even stop entirely if the hypothalamus’s temperature drops beneath 37 degrees centigrade. An increase in muscle tone can also generate additional heat. When core body temperature approaches 36 degrees centigrade, the increased muscle tone is recognizable as shivering, which results in five-fold greater heat production than usual.

Fever

During a fever, the body temperature is raised to an abnormally high level. A fever can be caused by substances called pyrogens, which include bacteria, chemicals released during inflammation (called endogenous pyrogens), and foreign proteins. Pyrogens, it is thought, chemically affect the hypothalamus, raising the thermostat’s temperature setting. Bodily responses are thus stimulated to increase the temperature to this new setting. For example, suppose you have strep throat. The hypothalamic thermostat’s temperature setting is reset to 38 or 39 degrees centigrade. Since the body temperature is now lower than the thermostat setting, the mechanisms of heat production and conservation are switched on. This causes you to shiver (i.e., chills). When enough heat has been generated to raise the body temperature to the new setting, you will feel neither too cold, nor too warm, since your temperature is now at the appropriate level set by the hypothalamic thermostat. Eventually, the pyrogens are no longer effective, and the temperature setting of the thermostat is reduced back to normal again, approximately 37 degrees centigrade. Now you begin to feel warm, and this leads to the activation of the body’s mechanisms for losing heat (i.e., sweating and vasodilation). The sweating is evidence that your normal temperature is being re-established.

What does a fever mean for the body’s ability to fight off an infection? At higher temperatures, the activity of white blood cells is significantly enhanced, and also the metabolism of some pathogens is hindered. Fevers thus play an important role in eliminating the pathogen from the body. There is more of a danger when the fever reaches too high a level. The metabolic rate is increased in response to a fever. This increases the generation of heat, which results in an even greater increased temperature. Unless it is stopped by an external event (such as the death of the pathogen or the use of aspirin), this positive feedback loop will continue. After passing through approximately 41 degrees centigrade, the hypothalamus is no longer able to properly control temperature. A consequence can be the denaturation of enzymes, which distorts their shape and renders them unable to perform catalysis. This results in cellular death. The death of neurons (which cannot be readily replaced) can even result in brain damage after a prolonged high fever. There are medications (e.g., aspirin) that may be used to reduce a fever by affecting the hypothalamus.

Intelligent Design

It is uncanny that research into the hypothalamus should reveal it to so strikingly resemble our own technology. The existence of thermostatic control of our body temperature is not at all surprising supposing life to be the product of a purposeful engineer. But how likely is it that such a well-controlled system for regulating temperature should have arisen by accidental processes of chance and physical necessity? In my estimation, it is exceedingly unlikely. Thus, the existence of the hypothalamic thermostat supports the thesis of intelligent design.