Some time ago i posted a newsletter for a breast cancer grant which mentioned how critical food is, since it is our largest surface area in contact with the environment. I have seen many conflicting opinions (just now, Regulation of surfactant secretion in alveolar type II cells Alexandra V. Andreeva, Mikhail A. Kutuzov, Tatyana A. Voyno-Yasenetskaya
American Journal of Physiology – Lung Cellular and Molecular Physiology Published 31 July 2007 Vol. 293 no. 2, L259-L271) which claimed that lungs were the greatest surface area, but other sites do not concur. They give 100-120 meters sq. Other refs give the square meters of gut at closer to 300. This reference (Herbert F Helander, Lars Fändriks. Surface area of the digestive tract – revisited. Scandinavian Journal of Gastroenterology, 2014; 1 DOI: 10.3109/00365521.2014.898326) gives a smaller value…. I THINK THEY FORGOT THE TENS OF BILLIONS OF MICROVILLI that are present at the apical membrane of each of the enterocytes, especially in the small intestine.  This would be easy since they did not look with the electron microscopy, then did these calculations radiologically  (kind of like hitting it with a hammer)… I have looked at both, I am sticking with the concept that total surface area in the but is way more than lung…. exact dimensions…. well… that is yet to be decided, but as an electron microscopist… you know my guess… ha ha.