Science

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Across
  1. 2. Natural pacemaker of the heart
  2. 5. Tiny blood vessels in lungs and tissues
  3. 6. System that circulates blood
  4. 7. Arteries supplying heart muscle
  5. 9. Muscle that controls breathing
  6. 11. Blood vessel that returns blood to the heart
  7. 12. Tiny sacs where gas exchange occurs
  8. 14. Heartbeat sound caused by closing valves
  9. 18. Smallest blood vessels
  10. 20. Flap that keeps food out of airway
  11. 21. Passageway for food and air
  12. 22. Gas we exhale
  13. 23. Thin tissue lining lungs
  14. 26. Liquid part of blood
  15. 28. Gas inhaled for respiration
  16. 29. Circulation to and from lungs
  17. 31. Number of chambers in the heart
  18. 33. Organ that filters blood
  19. 34. Main vein bringing blood from body to heart
  20. 35. Blood cells carrying oxygen
  21. 38. Blood cells that fight infection
  22. 39. Blood vessel that carries blood away from the heart
Down
  1. 1. Network of vessels returning fluid to blood
  2. 3. Dome-shaped breathing muscle
  3. 4. Main air tubes branching to lungs
  4. 8. Transport of blood through the body
  5. 10. Exchange of gases in alveoli
  6. 13. Main vein from head and arms
  7. 15. Windpipe
  8. 16. Protein that carries oxygen
  9. 17. Upper chamber of the heart
  10. 19. Largest artery in the body
  11. 24. Blood pressure measure when heart contracts
  12. 25. Blood pressure when heart relaxes
  13. 27. Main organ of breathing
  14. 30. Voice box
  15. 32. Organ that pumps blood
  16. 34. Flap preventing backflow of blood
  17. 36. Structure covering the trachea when swallowing
  18. 37. Lower chamber of the heart