Measuring the entropy change in our body What is an efficient way to measure the entropy change of our body in a day? Do we measure work done by the heart or such?
Thanks for the help!
 A: Do you mean entropy change ? Or entropy flow ? The amount of entropy in the body is rather constant. Whatever is created in the body comes out. The basic metabolism is very roughly 6000 kJ. This will go into heat, that will exit the body to the ambient air. Extra intake of energy might at least in part be used to do work, and will not become heat, and thus not create entropy within the body. Skin temperature is about 37°C i.e. 310°K.
So one can very roughly estimate the entropy flux as 20 kiloJoules per Kelvin. 
Since the air is slightly colder than the skin, the increase of entropy in the air is a bit larger.
A: I have a totally different perspective on this.  The change in entropy of ones body from one day to the next depends only on the initial and final states of the body, and not on the details of the irreversible processes (including heat interchange  with the surroundings) that took the body from the initial to the final state.  This change is a function only of the initial and final cellular makeups of the body.  So it is determined by the increase in new cells and the death of old cells.  The heat exchange has nothing to do with this.  Of course, determination of the changes in the numbers of cells of various kinds would be a pretty daunting task, involving the biochemistry of the system.
If the body were experiencing only reversible changes, it might be possible to establish the entropy change by considering the entropy heat flux, and the changes in entropy between the waste products exiting and the fuel products entering (air and food).  However, the actual changes are not irreversible, so this approach can't be used.
A: A very interesting question. 
When the body transfers heat to its surroundings it loses entropy. On the other hand, the oxidation processes for metabolizing food (glucose) generates entropy in the body. The change in entropy I suppose is the difference between the two. You may want to do some research on the internet. I found the following link interesting:
https://www.ncbi.nlm.nih.gov/pubmed/2634157
Whether overall our entropy increases or decreases each day, I can't quantify. But we know that entropy is associated with irreversible changes. And we know that aging is an irreversible process. So in that respect, I would think that the overall change in entropy of our bodies is increasing. But I confess, I have no equations to back up that opinion.
Hope this helps.
