Body temperature regulation (thermoregulation)

Body temperature regulation, also known as thermoregulation, is how an organism keeps its body temperature within certain limits.

For humans, the normal body temperature ranges between 36.1°C, or 97 °F, and 37°C, or 98.6°F.

When body temperature increases above 38.5° C, or 101.3°F, that’s called hyperthermia.

The opposite condition, when body temperature decreases below 35 °C, or 95 °F, is known as hypothermia.

Thermoregulation is needed in response to internal and external temperature variations.

Internal temperature variations are sensed by specialized nerve cells, called thermoreceptors, located in the anterior hypothalamus.

Now, the hypothalamus works as a thermostat.

The front part or the anterior hypothalamus responds to increased environmental temperatures and it also controls the core temperature of the body.

The back part or the posterior hypothalamus, on the other hand, responds to decreased environmental temperatures.

Changes in the external temperature are sensed by the skin thermoreceptors, which are specialized nerve cells located in the skin.

For example, during winter, when the environmental temperature is less than the body temperature, the skin receptors sense these variations and send the information to the anterior hypothalamus which will then inform the posterior hypothalamus that the body has to generate heat.

Now, besides the behavioral habits, such as putting more clothes on or drinking hot tea, there are several other physiologic mechanisms through which heat production is increased.

First, thyroid hormone action is stimulated.

Thyroid hormones are thyroxine or T4 and triiodothyronine or T3, which is the active form.

One of their roles is to increase heat production and they do that by stimulating conversion of T4 to T3.

T3 then increases the production of the energy molecule adenosine triphosphate or ATP in the body.

ATP is basically the energy currency in the cell and the more we have, the more of it can be used to generate heat.

Because these hormones are thermogenic hormones, any excess or deficit of these hormones will disturb the thermoregulation.