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Across
  1. 2. The outermost layer of the heart wall.
  2. 3. The largest vein in the body.
  3. 6. The type of cells that fight infections and support the immune system.
  4. 7. The circulation loop carrying blood between heart and lungs.
  5. 8. The smallest blood vessels where gas exchange occurs.
  6. 10. The valve that prevents backflow into the left atrium.
  7. 12. The chemical messengers transported by the blood to regulate body functions.
  8. 15. The largest artery in the body.
  9. 16. The valve that prevents backflow into the right ventricle.
  10. 18. The blood vessel carrying oxygenated blood from lungs to heart.
Down
  1. 1. The circulation loop carrying blood between heart and body.
  2. 4. The waste product removed by the blood and expelled through the lungs.
  3. 5. The substances the heart transports to provide energy and sustain cells.
  4. 9. The chamber that receives deoxygenated blood from the body.
  5. 11. The chamber that pumps oxygenated blood to the body.
  6. 13. The thickest, muscular middle layer of the heart wall.
  7. 14. The iron-containing protein in red blood cells that carries oxygen.
  8. 17. The fibrous sac surrounding the heart.