Ileocecal lip

The ileocecal lip (labrum ileocaecale), also known as the inferior lip of the ileal orifice, forms the lower boundary of the ileal orifice at the ileocecal junction. It is a semilunar mucosal fold that is attached to the line of junction between the terminal ileum and the cecum. Compared with the superior ileocolic lip, the ileocecal lip is typically longer and more concave, and projects into the lumen of the large intestine as a prominent cushion-like fold.

Structurally, the ileocecal lip is formed by a reduplication of the mucous membrane and circular smooth muscle fibers of the intestinal wall, whereas the longitudinal muscle fibers and peritoneum continue uninterrupted from the small intestine to the large intestine. The surface of the lip facing the ileum is lined by villous mucosa characteristic of the small intestine, while the surface facing the cecum is covered by large-intestinal mucosa lacking villi and containing numerous tubular glands. Together with the superior ileocolic lip, the ileocecal lip forms the valvular mechanism of the ileal orifice, regulating the passage of intestinal contents from the ileum into the cecum.