Module 7: Figure endothelial cell
Endothelial structure and mechanisms of transcellular and paracellular pathways.
One of the primary functions of the endothelial cell is to function as a semi-permeable barrier between the plasma and the interstitial space. Substances can cross this barrier via two separate pathways. Larger molecules such as albumin move through a transcellular pathway, where they are carried across the cell by caveolae that are pinched off from the luminal side (endocytosis) and then released to the basal side by exocytosis. Ions and small molecules with molecular radii smaller that 3 nm use a paracellular pathway by passing between the cells through the interendothelial junction (IEJ). This junctional region can be opened up in response to inflammatory mediators to increase the passage of plasma proteins and inflammatory cells to the interstitial space (Module 7: Figure regulation of paracellular permeability).