Small intestine mucosa

Cryosection of human small intestinal mucosa, showing the crypts (of Lieberkuhn). These 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.