So this is a small portion of our lymph vessel. Now, notice along the lymph vessel, we have these endothelial cells. So the walls of the lymph vessels consist of endothelial cells that overlap slightly. And at the portions where they overlap, these overlapping portions act as one way doors. And when there is a fluid build up inside the tissue, that fluid pressure pushes on these overlapping sections, these one way doors. And that opens these endothelial cells and allows fluid to actually flow into the endothelial cell.