The intestinal wall is highly folded. The first level of folding are the plica circulares. These intestinal folds are coated with villi that contain the specialized cells of the small intestine. Absorptive cells (enterocytes) have microvilli that form a brush border that further increases the surface area for absorption of nutrients.
The apical surface of an enterocyte faces the intestinal lumen. Its basolateral surface is in contact with extracellular fluids. Cell junctions between the cells form a tight barrier between the apical and basolateral surfaces. In addition to absorptive cells, goblet (mucous) cells are present in the villi. These secrete protective mucus. Inside the villus is an arteriole, venule, and lacteal (lymphatic vessel) into which absorbed nutrients enter to be distributed throughout the body.
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