ABSTRACT
Acknowledgments..................................................................................................343 References..............................................................................................................344
In the mammalian gastrointestinal tract, a primary function of the tight junction (TJ) is to form the barrier that restricts the flux of molecules between the lumen and the interstitium along the paracellular pathway. In the small intestine, both transcellular and paracellular absorption of nutrients and water contribute to transport across the epithelial barrier (see Chapter 4 by Reuss). Although transcellular transport across cell membranes is accomplished by specific transporters, paracellular absorption occurs across the TJ. However, the small intestine is also charged with maintaining
a protective barrier separating the lumen, a potentially toxic milieu, from the interstitium. Thus, TJ permeability must be precisely tuned to permit water and nutrient absorption while preventing passage of toxic substances.
