Since the temperature of the organism is essentially maintained while breathing, is the work done by the organism considered isothermal?


2 Answers 2


The process is not isothermal, the air heats up when incoming and outgoing. Nor it is adiabatic. I would say in a pV diagram it occurs at (almost) constant pressure (when the diaphragm moves, almost concomitant air enters the lungs, filling it, so maintaining a certain equillibrium between internal and external pressure).

The temperature of the body is maintained the same by the liberation of internal energy of the ingested carbon chain molecules in the inner celular structure, what compensates this and other heat changes with the environment (such as radiation).

But it takes care also to assure that 'the temperature of the body is always the same', as long as, there is no single temperature for it. For example the skin tends to be a few degrees lower then the viscera. All in all, there are models that consider the body a kind of 'onion-like' structure, in relation to its temperature, going from inside shells (in which temperature is higher) to outside.


Since our body temperature is fixed at 37degree celcius and breathing is done inside the body so under normal conditions, breathing is isothermal.

  • $\begingroup$ The air is certainly not at a constant temperature. $\endgroup$
    – Chris
    Commented Jan 31, 2018 at 6:08
  • $\begingroup$ But when air will enter in our body it will gain equilibrium temperature with our body. $\endgroup$ Commented Jan 31, 2018 at 6:12
  • $\begingroup$ That makes it not isothermal, I would think? Since the temperature of the air is changing. $\endgroup$
    – Chris
    Commented Jan 31, 2018 at 6:14
  • 1
    $\begingroup$ Yes, that is correct. It is not an isothermal process. $\endgroup$ Commented Jan 31, 2018 at 6:17

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