I would think that there would so many chemical reactions going inside our body,friction produced by blood in veins, subcutaneous and visceral fat acting as heat insulators.

I was wondering to what extent different factors play a role in protecting our body against cold.for example say blood circulation might be responsible for creating 70% of the body heat and also a person with high blood pressure may produce more heat in his body.

also, perhaps fever or any other disease would be an exception to the normal heat creating process in our body.just like the gonads or testes which are cooler than the rest of the body.

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    $\begingroup$ Pretty much Mitochondria. $\endgroup$ – AMR Oct 24 '15 at 0:36
  • $\begingroup$ I cannot vouch for this source, but it has a basic overview of mitochondrial heating. education.seattlepi.com/… $\endgroup$ – AMR Oct 24 '15 at 0:44
  • $\begingroup$ Specifically, we are burning the carbon-carbon bonds in the sugar molecules we ingest. You could call this oxidation; oxygen is the terminal electron acceptor in the electron transfer chain (as in loss of electrons is oxidation, and gain of electrons is reduction). The process is not 100 % efficient, so while some of the energy is captured as ATP, or reducing power, the portion that is not captured is given off as heat. Phillip Morrison has a great video of cyclists in the Tour de France where he burns a pile of donuts on a barbecue to show how much energy they burn every day. $\endgroup$ – mdperry Oct 24 '15 at 1:26

In summary, cellular respiration and thermogenin.

Most of the energy in our body comes from cellular respiration. Cellular respiration is how ATP, the major source of cellular energy, is made from glucose. Cellular respiration generates heat mo matter what because not all of the energy from glucose is converted to ATP.

In certain cells, a protein known as thermogenin allows the protons in the cellular respiration to flow from the inner membrane to the matrix (the protons are in the inner membrane of the mitochondria as the electrons from glucose were used to pump them). This generates heat. In regular cellular respiration, the proton gradient is used to make ATP, but now, it juet generates heat.

Also, ATP can be hydrolyzed directly in brown fat cells and muscle cells to produce heat along with inorganic phosphate and ADP.

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    $\begingroup$ Not only respiration generates heat; pretty much all cellular processes generate heat, including the usage of ATP to drive various things. Muscle contraction is a large contribution. $\endgroup$ – Roland Oct 24 '15 at 8:00
  • $\begingroup$ @Roland yes, but isn't cellular respiration the process in which most of the heat is generated? $\endgroup$ – TanMath Oct 24 '15 at 23:47
  • $\begingroup$ Respiration is certainly a large component, but I'm not sure it's the largest. Basically it amounts to how large the free energy of a reaction is and what fraction of that energy is released as heat. I don't have the numbers, but certainly muscle contraction is a large component too. $\endgroup$ – Roland Oct 25 '15 at 16:43

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