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Across
  1. 5. Arteries usually carry _____ blood.
  2. 6. A structure in the vein that prevents blood from flowing backwards.
  3. 8. Red blood cells contain a protein called _____ that helps to transport oxygen.
  4. 10. A white blood cell that produces antibodies that can trap pathogens.
  5. 13. Veins usually carry _____ blood.
  6. 14. A white blood cell that can kill pathogens.
Down
  1. 1. A foreign cell that can cause diseases.
  2. 2. Phagocytes kill pathogens using this process.
  3. 3. Blood vessel with the smallest lumen.
  4. 4. Blood vessel that carries blood away from the heart.
  5. 7. Blood vessel with the largest lumen.
  6. 9. Blood vessel with elastic walls.
  7. 11. Red blood cells carry _____ through the blood.
  8. 12. Blood vessel that carries blood into the heart.
  9. 15. Capillaries have thin walls that are one _____ thick.