Digested food is able to pass into the blood vessels in the wall of the small intestine through a process called diffusion. The inner wall (called mucosa) of the small intestine is covered with folds called plicae circulares that project finger-like projections of tissue called villi. Celiac disease damages these villi.
Villi are small, finger-like projections in the small intestines that help absorb the nutrients. The blunting or flattening of the villi can be caused by the damage done by the immune system due to celiac disease after ingesting gluten-containing foods.