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CaffeineSippingMan t1_iui4u3h wrote

Reply to comment by CharlesOSmith in What is the actual mechanism by which the body generates a fever? by Pheophyting

If we are allowing less heat loss, why do we feel warm on the forehead?

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Kraz_I t1_iuio4x6 wrote

Your body can’t stop dry heat from conducting out. If the blood in the vessels of your brain and head are hotter than normal, then you will feel warmer to the touch. There’s no way for your body to become more insulating except by wearing more layers or a blanket. The amount of heat lost via dry conduction is much less than what would be lost due to sweat. Water carries much more heat than air, and when it evaporates, it also removes more heat by conduction. That’s why if you get sweat on your shirt and then move to a place at room temperature, your shirt will feel uncomfortably cold.

Also when you feel someone’s forehead, your hand is a better heat conductor than air, and your hands and extremities also tend to run colder than your core body temperature, so foreheads feel warm to the touch even at normal temperatures.

I don’t have a background in physiology, but in materials science, so I understand heat conduction. If I made a mistake, someone who knows could chime in

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PatrickKieliszek t1_iujc2s4 wrote

Although evaporation dominates as a method of heat loss, there are two biological mechanisms that I am aware of that can additionally decrease dry conduction.

Capillary constriction in the skin reduces blood flow and makes the skin a more efficient insulator.

Piloerection of hair follicles helps trap air against the skin and improve insulation (works better on hirsute people and is mostly redundant in people that wear clothing).

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an711098 t1_iujoqqg wrote

Do you happen to know how capillary constriction transmits across other organs? Would it be fair to assume that if the capillaries in our skin constrict, capillaries in other parts of the body are constructing too? E.g. I recently read a summary (layperson here) of a paper suggesting Covid 19 triggers capillary constriction in the brain and am wondering if that triggers manifestations in other organs? Or if the circulatory system is big enough that capillaries in one part of the body don’t have to experience the same fluctuations as another (provided no mechanical separation like a tourniquet or tumour or whatever)?

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JCoco17 t1_iuk7b8s wrote

Different systems respond to different messages. Brain and muscles increase blood flow, while digestion decreases blood flow under stress.

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