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. Author manuscript; available in PMC: 2015 Dec 1.
Published in final edited form as: Semin Cell Dev Biol. 2014 Sep 28;0:204–212. doi: 10.1016/j.semcdb.2014.09.022

Figure 3. Paracellular flux routes vary along the crypt-villus.

Figure 3

Fluorescence microscopy showing F-actin (red), claudin-2 (green), and nuclei (blue) in mouse jejunum. Note the increased claudin-2 expression in the crypt region. Tight junctions in the upper villus are permeable to small molecules (<6 Å), such as glucose, while channels with radii estimated to be 10-15 Å have been described in the lower part of the villus. Crypt tight junctions are permeable to macromolecules with radii up to 60 Å. Along with enhanced expression of claudin-2, which mediates paracellular Na+ and, possibly, water flux, this may promote net water secretion into the crypt space.