What you really need to know for this dotpoint is the structure and function of veins, arteries and capillaries. Remember that the Structure always related to the function.
So what you need to know about veins is that:
It transports deoxygenated blood from the bodycells to the heart and thus is under low pressure as it is far away from the heart. Thus, the vein diameter is about the same as the artery but it does not have as thick muscle tissue (thus the vein walls are thin) as it does not need to withstand the pressure of the heart pumping. They also have valves to prevent backflow as the lack of pressure from the heart means that without the valves, the blood will flow backwards (and we don't want that!)
