Villi from the small intestine

Cryosections of human small intestinal mucosa showing the villi and crypts (of Lieberkuhn). The villi are finger-like projections which increase the surface area of the intestine, improving the efficiency of food absorption. The crypts are tubular invaginations of the epithelium around the villi. They are lined largely with younger epithelial cells which are involved primarily in secretion. Integrin which can be found on the basolateral membrane of epithelial cells, and also shows up on scattered stromal cells, is stained in green. Cytokeratin, which stains epithelial cells, is in blue, and cell nuclei are stained in red.