Organization of the intestinal mucosa and barriers to oral drug delivery

Abstract The gastrointestinal tract is the most important site for oral drug absorption, where the drug molecules penetrate the intestinal mucosal barrier from the lumen into the systemic circulation. The small intestine is the most important site for drug absorption. The intestinal mucosa epithelium acts as a selective barrier for the oral absorption of nutrients and drug molecules. The drug oral bioavailability is influenced by the physicochemical properties of the drug, the cellular structure and the biochemical components of the small intestine. To design successful oral delivery methods, it is necessary to evaluate the cellular structure and biochemical compositions of the intestinal mucosal barrier. Thus, the cellular structure and organization of the villi on the intestinal mucosal barrier are described, including absorptive epithelial, goblet, microfold, and crypt cells. The physical properties of the absorptive epithelial cells including the presence of tight junctions, adherens junctions, and desmosomes are elucidated. The roles of biochemical components such as transporters and metabolic enzymes that are important during drug transport are discussed. Finally, the physicochemical properties of drug molecules that are essential for crossing the intestinal mucosal barrier are defined in this section.