In these experiments, FITC-dextrans between 4 and 150 kDa were introduced into non-evert stomach or gut sacs from 2 week old (black), 4 week old (white) and 12 week old (blue) mice. Apparent permeability (Papp) in the intestine decreased with age, the size of the dextran, and the tissue’s distance from the stomach. Papp values represent the mean ± SEM (n = 5). One-way ANOVA with Dunnett’s multiple comparison test; * P < 0.05, ** P < 0.01, *** P < 0.001, compared to respective size marker in 12 week old mice.