These particles are seen as alien invaders by the body, and are therefore attacked.
Due to its autoimmune nature, Celiac disease also attacks the body itself, causing inflammation and damage to the inside of the small intestine.
The normal small intestine features small hair-like projections along its length known as villi. These increase the surface area and therefore assist in the absorption of the nutrients that the body needs to stay healthy. The first photo represents these healthy, upright villi.
The celiac autoimmune response causes so much damage to these villi (in some cases flattening them entirely) that they are no longer effective, as represented by the second photo. There are tests for celiac disease that will check what condition the villi are in.
However, all is not lost! Changing over to a gluten free diet will allow your body to repair itself, and your health will improve tremendously.