Labels:door | earth | person | road | rock | sidewalk | sky | stairs | tribute album | windowpane OCR: INSIDE VEIN EINS are vessels that return blood to the heart largest veins are about the width of two fingers. Their walls are thinner than arteries because blood in vein lower pressure. Veins are usually only partly full and appear to be collapsed. as shown in this cross- -section. However, veins are major reserv oir, storing about 6 per cent of the body's blood at any one time. To help blood move toward the heart, veins have one-way valves prevent blood flowing back along them under the force of gravity. |Wall of vein
