The ileum is the terminal portion of the small intestine. The ileum connects with the large intestine (colon) at a region known as the cecum. The actual point of connection is therefore termed the ileocecal_valve.

The ileum resembles the duodenum because villi (sing: villus) are present in the mucosal layer. The structure of the villi, however, is much less pronounced in the ileum because most nutrient absorption is completed before the materials arrive at the ileum, therefore not as much surface area is required. Also notice that the intestinal_crypts (crypts_of_Lieberkuhn) are present, as is the lamina_propria. The outstanding feature of the ileum is the regular presence of lymphatic nodules (Peyers_patches) in the submucosa. These lymphatic nodules can be found elsewhere in the small intestine, but the greatest aggregation of Peyer's patches is in the ileum.