Ileocolic lip

The ileocolic lip (labrum ileocolicum), a.k.a. the superior lip of the ileal orifice, forms the upper boundary of the ileal orifice at the ileocecal junction. It is a semilunar fold that projects into the lumen of the large intestine and is attached by its convex border to the line of junction between the terminal ileum and the ascending colon.

The ileocolic lip forms a prominent cushion-like fold that contributes to the valvular mechanism separating the small and large intestines. Structurally, it is formed by a reduplication of the mucous membrane and circular smooth muscle fibers of the intestinal wall, while the longitudinal muscle layer and peritoneum continue uninterrupted across the junction. The surface of the lip facing the ileum is lined by villous mucosa characteristic of the small intestine, whereas the surface facing the colon is covered by large-intestinal mucosa devoid of villi and containing numerous tubular glands.

Together with the inferior ileocecal lip, the ileocolic lip helps regulate the passage of intestinal contents from the ileum into the large intestine.