The wall of the small intestine is highly folded to form villi. Between the villi are infoldings known as crypts of Lieberkühn. Fig. 1.1 is a diagram of a section through a single villus and a crypt of Lieberkühn. [Figure 1.1] Fig. 1.1 shows that the epithelium of the villus contains mainly goblet cells and cells known as enterocytes. Both cell types have microvilli on the apical surface (surface facing the gut lumen). Goblet cells are involved in the production of mucus. Enterocytes are adapted for the absorption of the soluble products of digestion. These products enter the circulatory system.