Figure 1.

Graphical representation of the six epithelial transport characteristics for the uptake of cytotoxic compounds from oral administration, adapted from Chan et al. [37]. 1—Paracellular absorption via the interstitial spaces between cells, this is restricted by intercellular tight junctions. 2—Transport mechanisms at either the apical or the basolateral membranes. 3—Restriction of transport into the blood flow by apical membrane efflux transporters. 4—Efflux membrane transporters enabling clearance of compounds from the blood. 5—Metabolism of compounds prior to transport to the blood. 6—Co-ordination of metabolizing enzymes and apical efflux transporters forming an intestinal absorption barrier.