And what this basically means is molecules and ions cannot actually get around cells. They must actually pass through that cell to get from one side, the lumen side, to the other side, our extracellular fluid side. So basically, this means that in order for things like water to actually get past one side of the cell, the lumen cavity, to the other side of the cell, the extracellular fluid, something actually must pass through the cell membrane on the lumen side and to the cell membrane on the extracellular side. Now, the apical side is the lumen side of the cell, and this side is the Basil lateral side. It's the side found on our extracellular side. Now, type junctions are composed primarily of a network of proteins known as claudine.