Label the characteristics that are true or the different kinds of endothelial cells we have seen in the course so far. Flexible and can collapse or expand to allow for dramatic changes in blood flow amount Have tight junctions that strictly control the molecules that can pass through to the other side. Are flexible and can withstand small changes in pressure, but once collapsed and difficult to reopen. Solution !. endothelium of the capillary bed which forms the lining for the vascular system. 2Adjacent epithelial cells are sealed by tight junctions benaeath their apical surface. 3. Arteries. 4. capillaries..