It is there, we are sorry, but it seems that all you can do is warm up. Or drink something hot. It is cold, yes. We are homeothermal animals. We are able to keep the body temperature constant when the cold comes. For that, we need to replenish the heat that is lost, through metabolism. Today we will talk about the relationship between humans and the cold.
Mammals have two ways of responding to the winter temperature drop. The insulation with the outside can be increased. Or raise metabolic activity to produce more heat that compensates for the greatest loss. That is, raise the body's metabolism by moving it.
Regarding the former, there are several ways in which a mammal can modify its isolation:
- Change body posture to expose a smaller surface to the outside.
- Limit blood circulation at the periphery of the limbs, even if they cool, retaining heat in vital organs.
- Act on the coat to increase the thickness of the air layer that insulates the surface of the body from the outside.
Below certain temperatures these responses are not enough and you have to spend more energy by increasing the metabolism. That is why it is important to have abundant food when the cold arrives. Or failing that, with reservation deposits.
From Africa with love
Human beings are special. We are homeotherms, yes, but our species emerged in Africa. Our hominid lineage is African. We evolve in the savannah and many of our characteristics are a clear reflection of our origin.
During that evolution we were practically naked. We develop a great ability to sweat and cool in a very efficient way by evaporating sweat on the body surface. So much so that the displacement to cold areas forced us to certain changes. How to wear clothes with an adequate insulation capacity at the temperature of each zone.
In spite of that, life in truly cold places has demanded considerable additional efforts. Heating is required, wearing warm clothes and getting the necessary food to eat more. When the temperature sensors that we have distributed in different places of the body detect the thermal descent, they inform the hypothalamus, a nervous structure inside the brain.
He responds by giving the orders due, both to the endocrine and nervous systems. Certain orders cause changes in peripheral blood circulation and the disposition of the coat. This increases the degree of isolation. Others raise metabolic activity. In these settings hormones such as adrenaline, norepinephrine and thyroid are involved. They cause an increase in metabolism.
The humans and the cold
Those who have brown fat, present in different amounts in almost all mammals including humans, have an advantage. This fabric has the sole function of producing heat. If necessary, we also shiver.
Mammals in cold areas are logically well adapted to life in icy environments. A young polar bear keeps its metabolism constant up to 0⁰ C, and it is estimated that it would only multiply it by three to 60 bajoC below zero. Arctic foxes, huskies and other large Arctic mammals practically do not need to raise their metabolism except at truly extreme temperatures, such as 25 or 30 bajoC below zero.
We humans have not stopped being savannah primates, so all this is very expensive. Humans and cold do not get along. A naked individual begins to raise his metabolism by lowering the temperature of approximately 26 ⁰C, and to 8 ⁰C triples it.