There are several research and clinical diagnostic tests that actually measure permeability of the gut wall.

The phosphorus is then transported across the gut wall.

The parasite infects the cells of the gut wall.

Having finally reached the small intestine, they sink their hooks into the gut wall and start to feed on blood.

The splanchnopleuric layer forms the circulatory system and future gut wall.

The gut wall there is rich with veins and arteries.

But since the gut wall undulates, it is easy to contaminate the sample with cells from just below the surface, which do.

Once inside the fly, the L1 larvae "hatch" from the egg membrane and penetrate the gut wall.

For the moment, his work was with the ragged multiple perforation in the gut wall.

This creates tiny holes in the gut wall, making it more permeable.