Fig. 1.

Schematic drawing of the principle of measuring mucus thickness ex vivo. A: colon. B: ileum. The distance between the epithelial surface and the surface of the mucus layer (d) is measured by a micropipette connected to a micromanipulator and a digimatic indicator. To obtain the vertical thickness of the mucus layer (t), the distance (d) is multiplied with the cosine of the angle of the micropipette, which in this case is 45° (t = d × cos45). In colon, which lacks villi, the epithelial surface is easily identified. In ileum, we used a two-step procedure to measure mucus thickness: first we measured the distance from the mucus surface to the tip of the villi and next we measured the height of the villi. Mucus thickness was then calculated as the sum of the two values.