Fig. 6.

Schematic view of the turnover of goblet cells and mucus in the colon. The subsequent steps in this process are marked by red MUC2. Schematic explanation of how (i) goblet cells are formed in the crypt and MUC2 mucin is formed in the crypt goblet cells and during transportation to the surface (Upper Left); (ii) MUC2 is released and expanded in volume to form a sheet that forms the inner mucus layer from below (A) (Upper Right); (iii) MUC2 are transported with the inner mucus layer (B) (Lower Left); and (iv) MUC2 is converted to the outer loose mucus layer at a sharp border and then expanded in volume in the outer loose mucus layer (C) (Lower Right). Finally, MUC2 mucin is dissolved by bacterial enzymes and transported away with the fecal stream (not illustrated).