I have tried to figure out how many square meters are involved in the interface of our environment in lungs and in intestines. I think it is fair given the low surface are of skin to consider it as secondary in m2 to the other two. I think i remember around 17 m2 or something close. But I have read 2 publications that have shown up in numerous lay publications as well that say the gut has less surface area than previously determined. The early estimates (that is, when looking at plicae, villi, AND micovilli – when they exist on epithelial cells in the gut) that the m2 was something on the order of about 7000. The similar number for lung was between 30 and 200 m2 . I don’t know which is right, but the numbers for lung appear now to be more around 70 m2 , and the numbers for gut are also around 200 m2 . this would make these wet surface areas equivalent…. I think that is hard to believe. I am not suggesting one can be had without the other (LOL), but the mere number of microvilli, on the epithelial cells in the gut just is staggering, and the microvilli on type II cells in the lung, just not the same (the gut microvilli are actually brush border type structures, rigid, numberous, close together) while only a few little plasmamembrane blips on the alveolar cells exists, and random floppy microvilli on alveolar type II cells.
Just for me it would be hard to think of them being any near the same, and even then with the reduced value for gut, (down from the 7000 m2 ) still is a greater surface area than lung.
THUS, gut is the greater surface area interface with the environment: so eat wisely, you are eating your environment.