Microdissection by ultrasonication: scanning electron microscopy of the epithelial basal lamina of the alimentary canal in the rat.

The epithelial basal lamina of the various parts of the alimentary canal of the rat was exposed by removal of the overlying epithelium. This was achieved by prolonged fixation in OsO4 or immersion in aqueous boric acid or both, followed by dehydration in acetone and exposure to ultrasonic vibration. The surface of the esophageal basal lamina is undulating with smooth hills and valleys, the smallest of which model the basal surfaces of the germinal cells of the epithelium. The stomach presents a perforated appearance because of ostia formed by evaginations of the basal lamina to enclose glands. In the small intestine, clavate rather than cylindrical villous cores are separated by ostia of intestinal crypts. In the large intestine, ostia are separated by broad areas of basal lamina in the cecum but are close together in the colon. The complex contours of the basal lamina are largely determined by the basal surface of the overlying epithelium but may be affected by structures in the underlying interstitium. Subepithelial lymph nodes, for example, are covered by a conspicuously porous basal lamina. Each nodule may be surrounded by ostia of as many as 20 crypts of Lieberkühn. The basal lamina of the ileocecal valve displays gradual transition from ileum to cecum.