I am doing a crossword puzzle for the Circulatory and Respiratory Systems review.

3. Pumps blood to heart
6. What returns fluid that leaks from capillaries back to the circulatory system
7. Branching system of tubes which sends air to the alveoli
9. Contains blood with little oxygen and a lot of carbon dioxide
15. A dangerous tumor in the respiratory system
16. Muscle that relaxes when you exhale
19. Moves substances through the body

Down:
5. Separates the atria from the ventricle; keeps blood flowing one way
8. Thin-walled blood vessel that allows for gas exchange
11. Hair-like structures that line the trachea and nose
12. Receives blood from the lungs
17. Movement of air in and out of lungs
18. Location of gas exchange in the lungs
20. Oxygen transport blood component