This figure shows portions of two adjacent villi at higher magnification. The epithelium consists chiefly of enterocytes. These are columnar absorptive cells that typically exhibit a striated border (SB), the light microscopic representation of the microvilli on the apical surface of each enterocyte. The dark band at the base of the striated border is due to the terminal web of the cell, a layer of actin filaments that extends across the apex of the cell to which the actin filaments of the cores of the microvilli attach. The nuclei of the enterocytes have essentially the same shape, orientation, and staining characteristics. Even if the cytoplasmic boundaries were not evident, the nuclei would be an indication of the columnar shape and orientation of the cells. The enterocytes rest on a basal lamina not evident in H&E–stained paraffin sections. The eosinophilic band (arrow) at the base of the cell layer, muscularis externa (ME ) and is not included in the plicae. (The serosa cannot be distinguished at this magnification.) Most of the villi (V ) in this specimen have been cut longitudinally, thereby revealing their full length as well as the fact that some are slightly shorter than others. The shortening is considered to be due to the contraction of smooth muscle cells in the villi. Also seen here are the lacteals (L), which in most of the villi are dilated. Lacteals are lymphatic capillaries that begin in the villi and carry certain absorbed dietary lipids and proteins from the villi to the larger lymphatic vessels of the submucosa.
of the intestine, whereas the villi are projections that extend into the lumen. The glands are surrounded by cells of the lamina propria; the villi are surrounded by space of the intestinal lumen. The lamina propria with its lacteal occupies a central position in the villus; the lumen occupies the central position of the gland. Also note that the lumen of the gland tends to be dilated at its base. Studies of enzymatically isolated preparations of mucosa show that the bases of the glands are often divided into two to three fingerlike extensions resting on the muscularis mucosae.
where one would expect a basement membrane, actually consists of flat lateral cytoplasmic processes from the enterocytes. These processes partially delimit the basal-lateral intercellular spaces (asterisks) that are dilated, as can be seen here, during active transport of absorbed substrates.
The epithelial cells with an expanded apical cytoplasm in the form of a cup are goblet cells (GC ). In this specimen, the nucleus of almost every goblet cell is just at the base of the cup, and a thin cytoplasmic strand (not always evident) extends to the level of the basement membrane. The scattered round nuclei within the epithelium belong to lymphocytes (Ly).
The lamina propria (LP ) and the lacteal (L) are located beneath the intestinal epithelium. The cells forming the lacteal are simple squamous epithelium (endothelium). Two nuclei of these cells (EC ) appear to be exposed to the lumen of the lacteal; another elongate nucleus slightly removed from the lumen belongs to a smooth muscle cell (M) accompanying the lacteals.
KEY EC, endothelial cell GC, goblet cell GI, intestinal glands (crypts) L, lacteal LP, lamina propria Ly, lymphocytes M, smooth muscle cell ME, muscularis externa MM, muscularis mucosae Muc, mucosa PC, plicae circulares S, serosa SB, striated border SubM, submucosa V, villi arrow, basal processes of enterocytes asterisks, basal-lateral intercellular spaces dashed line, boundary between villi and intestinal glands