Other epithelial cells in the crypts correspond largely to those in the epithelium of the intestinal villi. One exception are Paneth cells which are located at the bottom of the crypts. They release a number of antibacterial substances, among them lysozyme, and are thought to be involved in the control of infections. In addition to enterocytes, the epithelium is composed of mucus-secreting goblet cells and endocrine cells. The lamina propria is, similar to the lamina propria of the stomach, unusually cell rich.
Lymphocytes often invade the epithelium or form solitary lymphoid nodules in the lamina propria.
Lymph nodules may form longitudinal aggregations of 30-50 nodules in the lamina propria of the ileum. These large aggregations are called Peyer's patches . The muscularis mucosae has two layers and extends into the intestinal villi, where the smooth muscle cells form a longitudinal bundle in the centre of the villi. The submucosa contains glands only in the duodenum . Submucosal glands of the duodenum are also called Brunner's glands .