Small intestine villi. Fluorescence light micrograph of a cross-section through a normal human small intestine 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. 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 shown in blue, and cell nuclei are stained in red.